Termination of a shield within an implantable medical lead

A shield located within an implantable medical lead may be terminated in various ways at a metal connector. The shield may be terminated by various joints including butt, scarf, lap, or other joints between insulation layers surrounding the lead and an insulation extension. The shield may terminate with a physical and electrical connection to a single metal connector. The shield may terminate with a physical and electrical connection by passing between an overlapping pair of inner and outer metal connectors. The metal connectors may include features such as teeth or threads that penetrate the insulation layers of the lead. The shield may terminate with a physical and electrical connection by exiting a jacket of a lead adjacent to a metal connector and lapping onto the metal connector.

TECHNICAL FIELD

Embodiments relate to implantable medical leads that include shields. More particularly, embodiments relate to the termination of the shield within implantable medical leads.

BACKGROUND

Implantable medical systems including implantable medical devices (IMD) and associated implantable medical leads provide functions such as stimulation of muscle or neurological tissue and/or sensing of physiological occurrences within the body of a patient. Typically, the IMD is installed in a subcutaneous location that is accommodating and relatively accessible for implantation. For instance, to provide stimulation near the spine or pelvis, the IMD may be installed in a pocket located on the abdomen or upper buttocks region of the patient. The implantable medical lead is installed, either through a percutaneous procedure or a surgical procedure, depending upon the type of lead that is necessary.

Once installed, the lead extends from the stimulation site to the location of the IMD. The separation of the stimulation site to the location of the IMD varies, but may typically range from about 20 cm to about 100 cm. For relatively lengthy separation, if a lead of adequate length is unavailable then a lead extension may be implanted to span from the IMD to a proximal end of the implantable lead.

The implantable medical lead includes connector rings on a proximal end and electrodes on a distal end, and conductive filars interconnecting the electrodes at the proximal end connector rings to the electrodes at a distal end. The lead includes a jacket, often made of a flexible but biocompatible polymer, and the filars are insulated from the body tissue by the jacket. However, the filars are not insulated by the jacket from the presence of electromagnetic radiation. Electromagnetic radiation in the radio frequency (RF) spectrum induces currents into the filars and thus presents current at the electrode that is unintended. In the patient's normal daily experience, the level of RF radiation that is encountered is at a negligible level, and there is no danger of heating of tissue by the unintended current that may result.

RF radiation poses a risk to tissue in contact with the electrodes when the intensity is significantly higher than the background levels. The surface area of each electrode is relatively small so that a small amount of tissue must dissipate a potentially large amount of induced current. In particular, if the patient is exposed to the RF radiation from a magnetic resonance imaging (MRI) scan, there is a high probability that tissue damage at the stimulation site(s) can occur. This tissue damage may be very dangerous, particularly so for neurological tissue. Therefore, patients with IMDs are typically not permitted to have a body coil MRI scan for at least these reasons.

SUMMARY

Embodiments address issues such as these and others by providing an implantable lead that includes a shield within the jacket that may reduce the amount of current induced on the filars within the lead. The shield may be terminated at an electrical connector in various ways to prevent wires of the shield from losing electrical contact, fraying, and otherwise migrating within the lead.

Embodiments provide a method of terminating a shield within a jacket of an implantable medical lead. The method involves providing an inner insulation layer and providing an inner metal ring located near an end of the inner insulation layer. The method further involves providing the shield between the inner insulation layer of the jacket and an outer insulation layer of the jacket, a portion of the shield lapping onto the inner metal ring and providing an outer metal ring about the inner metal ring with the portion of the shield being positioned between the inner metal ring and the outer metal ring.

Embodiments provide a method of terminating a shield within a jacket of an implantable medical lead. The method involves providing an inner insulation layer having a proximal end and providing an outer metal ring about the inner insulation layer in proximity to the proximal end. The method further involves providing an outer insulation layer that surrounds the inner insulation layer and that terminates prior to the proximal end of the inner insulation layer and providing the shield between the inner insulation layer of the jacket and the outer insulation layer of the jacket, the shield extending beyond the termination of the outer insulation layer with a portion of the shield lapping onto the metal ring.

Embodiments provide a method of terminating a shield within a jacket of an implantable medical lead. The method involves providing the shield between an inner insulation layer of the jacket and an outer insulation layer of the jacket, the shield terminating by the end of the inner insulation layer, the outer insulation layer terminating prior to an end of the shield and the inner insulation layer. The method further involves bonding an insulation extension layer onto the end of the inner insulation layer and positioning a metal ring over the shield and inner insulation layer where the outer insulation layer is not present.

Embodiments provide an implantable medical lead that includes an inner insulation layer, an inner metal ring located near a proximal end of the inner insulation layer, and an outer insulation layer that surrounds the inner insulation layer. The implantable medical lead further includes a shield between the inner insulation layer and the outer insulation layer, a portion of the shield lapping onto the metal ring and an outer metal ring about the inner metal ring with the portion of the shield being positioned between the inner metal ring and the outer metal ring.

Embodiments provide an implantable medical lead that includes an inner insulation layer having a proximal end and an outer metal ring about the inner insulation layer in proximity to the proximal end. An outer insulation layer surrounds the inner insulation layer and that terminates prior to the proximal end of the inner insulation layer. A shield is located between the inner insulation layer of the jacket and the outer insulation layer of the jacket, the shield extending beyond the termination of the outer insulation layer with a portion of the shield lapping onto the metal ring.

Embodiments provide an implantable medical lead that includes a jacket comprising an inner insulation layer and an outer insulation layer. A shield is located between the inner insulation layer and the outer insulation layer, the shield terminating by the end of the inner insulation layer, the outer insulation layer terminating prior to an end of the shield and the inner insulation layer. An insulation extension layer is bonded onto the end of the inner insulation layer, and a metal ring positioned over the shield and inner insulation layer where the outer insulation layer is not present.

DETAILED DESCRIPTION

Embodiments of implantable medical leads that include shields are disclosed herein. Ten primary subject matter topics are presented, where each new topic begins with reference toFIGS. 1,3,11,16,18,30,49,59,73, and77. However, this detailed description should be read as a whole whereby subject matter of embodiments corresponding to one particular topic is applicable to embodiments corresponding to other topics.

For instance, shield details disclosed in relation toFIGS. 1-2Hare also applicable to the shields of all embodiments disclosed inFIGS. 3-80Cwhere such shield details may be desired. The examples of grounding a shield within a lead as disclosed in relation toFIGS. 3-15Eare applicable to all embodiments disclosed herein where a grounded shield may be desired. The examples of shielding the extension and interconnecting the shielding of the lead to the extension as disclosed in relation toFIGS. 16-17Gare applicable to all embodiments disclosed herein where inclusion of a shielded extension may be desired. The examples of terminating the shield as disclosed in relation toFIGS. 18-48are applicable to all embodiments disclosed herein where terminating the shield within the lead body may be desired. The examples of rotationally coupling the lead body to a stylet as disclosed in relation toFIGS. 49-58are applicable to all embodiments disclosed herein where such rotational coupling may be desired. The examples of markers for the lead as disclosed in relation toFIGS. 59-72are applicable to all embodiments disclosed herein where such a marker may be desired. The examples of breaking the circumferential mechanical continuity of the shield as disclosed inFIGS. 73-76Dare applicable to all embodiments disclosed herein where such a lack of continuity may be desired. The examples of guarding the termination of the shield as disclosed inFIGS. 77-80Care applicable to all embodiments disclosed herein where a guarded shield termination may be desired.

Embodiments disclosed in relation toFIGS. 1-2Hprovide for radio frequency (RF) shielding of an implantable lead that may be connected to an implantable medical device (IMD). A shield is present within the jacket of the implantable lead. The shield is designed to provide RF shielding while also providing various mechanical properties suitable for implantation.

FIG. 1shows an example of an implantable medical system1100that includes an IMD1102coupled to a lead1108. The IMD1102includes a metal can1104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD1102includes a header1106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can1104. The header1106is shown transparently for purposes of illustration. The header1106provides a structure for securing the lead1108to the IMD1102and for establishing electrical connectivity between circuitry of the IMD1102and electrodes of the lead1108.

The lead1108includes electrodes1116on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings1110on a proximal end that is positioned within the header1106. The connector rings1110make physical contact with electrical connections1111within the header. The electrical connections1111may include a metal contact that the connector ring1110rests against upon being inserted into the header1106where a wire extends from the metal contact into the can1104where the circuitry is housed. Signals applied by the IMD1102to the connector rings1110are conducted through the lead1108to the electrodes1116to provide the stimulation therapy to the patient.

The lead1108is secured in the header1106such as by a set screw block1112within the header1106that allows at least one set screw1114to be tightened against at least one of the connector rings1110. A shield1118such as the one discussed below with reference toFIGS. 2A and 2Bis located within the lead1108. The shield1118may or may not be grounded to the metal can1104at the IMD1102ofFIG. 1or at various points along the length of the lead. The shield1118may or may not be grounded through other mechanisms as well. For instance, the shield1118may be located within the lead1108at a small distance from the surface so that the shield1118will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.

FIGS. 2A and 2Bshow an example of the lead1108, where a shield1118is present. An outer jacket layer1120is shown transparently inFIG. 2Afor purposes of illustrating the shield1118. The shield1118blocks at least some RF energy from directly coupling to conductive filars1124that are present within the lead1108. The conductive filars1124extend the length of the lead and interconnect the proximal connector rings1110to the distal electrodes1116so that stimulation signals are conducted from the proximal end to the distal end of the lead1108.

As shown inFIG. 2A, the shield1118of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. The metal braid wire may be a biocompatible metal, particularly for embodiments where a portion of the shield1118may be exposed for purposes of grounding. Biocompatible metals ensure that if the shield1118is exposed to tissue, either by design or due to wear on the lead1108, the shield1118does not become a toxin to the patient.

As shown inFIG. 2B, the shield1118may be embedded within the jacket of the lead1108. One manner of constructing the lead1108with the shield1118is to provide a jacket that includes an inner layer of insulation1122that isolates an inner region1121where the filars1124and any additional insulation layer1126, such as polytetrafluoro-ethylene (PTFE) that may surround each filar1124are located. According to some embodiments, this inner layer1122may have a post-assembly thickness1130of at least 2 mils and may be significantly larger such as 5 or 6 mils depending upon size constraints for the lead1108and/or the size of the outer layer1120. The shield1118may then reside on the outer portion of the inner layer1122, and the jacket's outer layer of insulation1120may then enclose the shield1118. The outer layer1120provides an overall lead diameter1134. The outer jacket1120maybe added over the braid1118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield1118to RF couple to tissue, typically as capacitive coupling, either as an alternative to grounding at the can of the IMD or specific points along the length or in addition to grounding at the can or along the length, the entire outer jacket layer1120may be relatively thin, particularly for the portion passing over the braid wires of the shield1118. According to the various embodiments a post-assembly thickness1132for the portion of the outer layer1120passing over a single braid wire may be on the order of 0.5 to 5 mils. The thickness of the outer layer1120over the shield1118is reduced by a braid wire diameter at points where braid wires intersect. Accordingly, the post-assembly thickness1132over the single wire may vary depending upon a chosen braid wire diameter so that adequate coverage also exists at the intersection points. Furthermore the thickness may be less than 0.5 mils, particularly where tissue in-growth is not of concern and in that case the outer layer1120could be omitted.

This thickness of the outer layer1120over the braid wires may also vary depending upon the type of metal used for the braid wires. For instance, it has been found that the thickness of the outer layer1120has less of an impact on the heating at the electrode when using a titanium braid wire than when using a tantalum wire with all else being equal. However, with an outer layer1120whose post-assembled thickness1132is on the lower side of the range, such as 2 mils or less, tantalum braid wires may allow for less heating at the electrodes than if titanium braid wires are used.

Where the shield1118grounds at the can1104and/or at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield1118may be located further from the outer surface of the lead1108. This increased depth of the shield1118within the jacket may provide for a more durable lead1108in terms of protecting the braid wires in areas of high flexure and motion, such as in the lumbar spine.

The inner and outer jackets1122,1120may be constructed of the same or similar materials such as various flexible polymers, examples of which are polyurethanes and silicones. Biocompatible materials may be used, especially for the outer layer1120when the outer layer1120has direct contact with body tissue. A lumen1128may be included in an inner region1121, particularly for percutaneous leads1108, to allow a stylet to be inserted for purposes of pushing and steering the lead into the desired position within the patient. For leads where an inner region1121is filled to define the lumen1128, such as where filars1124are cables rather than the coils as shown, this inner region1121may be constructed of materials such as polyurethanes, silicones, polyetheretherketone (PEEK), nylon or other biocompatible polymer material.

FIG. 2Cshows a view of the implantable lead1108where various parameters related to the braid wires can be seen. The inner layer of insulation1122, as well as the outer layer1120, defines an axial dimension1136that runs along the length of the lead1108. Braid wires such as braid wires1140,1142are braided around the inner layer1122. A first set of braid wires including braid wire1140is wound around the inner layer1122in a first direction while a second set of braid wires including braid wire1142is wound around the inner layer1122in a second direction that is opposite the first. The braid wires of the first set and the braid wires of the second set weave together during the braiding with a braid wire of the first set passing over some wires and under others of the second set in a repeating pattern.

The weaving may use a particular pattern, such as passing over one, passing under one, passing over one, and so on or such as passing over two, passing under two, passing over two, and so on. With wires of larger diameter, or where wires are used in pairs, then a pattern of two-over-two-under helps reduce the stress on the wire as it weaves back and forth. If the wires are small and single, with a relatively large aperture between braid wires, then one-over-one-under works well. The wire stress is a factor to consider because implant leads flex continually with body motion and typically are expected to last many years.

The braiding has various parameters of interest. A first parameter is the braid angle1144. Here, the braid angle1144is defined as the angle of the braid wire as measured transversely from the axial dimension1136; however, others sometimes define it relative to the axis of the lead. So, as shown inFIG. 2C, the braid angle1144is measured between the braid wire and the transverse dimension1138. According to various embodiments, the braid angle measured in this way is less than 60 degrees.

This braid angle1144has several implications. The braid angle1144is one factor in setting the maximum dimension of the braid aperture1141shown inFIG. 2C, and hence the degree of coverage formed by the braid wires. This braid angle1144is also a factor in relation to the degree of stiffness of the lead in flexure and the tendency of the braid wires to break during flexure. The braid angle is also a factor in the cohesion of the outer layer of insulation1120to the inner layer of insulation1122, because when the aperture is of adequate size, cohesion occurs between the two layers1120,1122through the aperture.

Another parameter of interest as shown inFIG. 2Cis the axial spacing1146between adjacent wires of a set. According to various embodiments, the axial spacing1146has an upper limit equal to the lead diameter1134. The axial spacing1146is also a factor in the aperture size, the axial stiffness, the bending stiffness, and the kink resistance.

Another parameter of interest, which is related to the braid angle1144and the axial spacing1146, is the number of wires in each set. According to various embodiments, the first set of braid wires which are wound in the first direction includes at least three braid wires. Likewise, the second set of braid wires which are wound in the second direction includes at least three braid wires. These two sets of at least three braid wires each ensures that for the various ranges of parameters disclosed herein, the aperture1141has a transverse dimension that is sufficiently small to effectively shield the RF energy in the MRI spectrum, which typically spans from 43 MHz to 128 MHz.

The total number of braid wires is limited by the allowable axial and bend stiffness for the braid angle and braid wire size. In some examples, there may be as many as 16 braid wires in each set for a total of 32 braid wires. However, as shown in the example ofFIG. 2C, each set includes six braid wires, where braid wire1140reappears on a given side of the lead1108after five other braid wires are wound. Likewise, braid wire1142reappears on the side of the lead1108after five other braid wires are wound.

FIG. 2Dshows another lead embodiment1150that demonstrates another braid wire parameter of interest. In this example, the braid wires are paired so that two braid wires that are in contact wind around the inner layer1122instead of a single wire. For instance, dual braid wires1152and1154of a first set wound in a first direction are in contact as each winds around the inner layer1122. Dual braid wires1156and1158of a second set wound in a second direction are in contact as each winds around the inner layer1122.

The braid wires bundled together in this manner affect the stiffness of the lead1108as well as the aperture size. Bundling braid wires in this manner may provide coverage like that of wider dimensioned braid wires, such as rectangular braid wires, but without the increased bending stresses associated with the corners present on the rectangular braid wire.

FIG. 2Eis an enlarged view of a portion of a lead1108to illustrate the cross-section of the braid wires. The view is a cross-section where the cut through the lead1108is taken at an angle perpendicular to the direction of travel of the topmost braid wire1142so as to provide a true cross-section of the topmost braid wire1142. Here the topmost braid wire1142has a round cross-section and provides a braid wire diameter1148. According to various embodiments, the braid wire diameter ranges from about 0.5 mils to about 2.5 mils. The braid wire diameter is measured as the dimension that faces outward from the inner layer1122as shown inFIG. 2E. The round cross-section lacks corners that may otherwise affect the bend stiffness of the lead1108, but the round cross-section provides less coverage than other cross-sectional shapes that have a same height extending into the outer layer1120from the inner layer1122.

FIG. 2Fis an enlarged view of a portion of a lead1160to illustrate the cross-section of the braid wires. As inFIG. 2E, the view is a cross-section where the cut through the lead1160is taken at an angle perpendicular to the direction of travel of the topmost braid wire1162so as to provide a true cross-section of the topmost braid wire1162. Here the braid wire1162has a rectangular cross-section and provides a braid wire width1168. According to various embodiments, the braid wire width ranges from about 2 mils to about 5 mils. The braid wire width is measured as the dimension that faces outward from the inner layer1164as shown inFIG. 2F. The rectangular cross-section has corners that may affect the bend stiffness of the lead1108but provides more coverage than a round cross-sectional shape that has a same height extending into an outer layer1166from the inner layer1164.

FIG. 2Gis an enlarged view of a portion of a lead1170to illustrate the cross-section of the braid wires. As inFIG. 2E, the view is a cross-section where the cut through the lead1170is taken at an angle perpendicular to the direction of travel of the topmost braid wire1172so as to provide a true cross-section of the topmost braid wire1172. Here the topmost braid wire1172has an oval cross-section and provides a braid wire major axis diameter1178. According to various embodiments, the braid wire major axis diameter ranges from about 0.5 mils to about 4 mils. The braid wire major axis diameter is measured as the dimension that faces outward from the inner layer1176as shown inFIG. 2G. The oval cross-section lacks corners that may affect the bend stiffness of the lead1108but provides coverage similar to a rectangular cross-section that has a same height extending into an outer layer1174from the inner layer1176.

In each of the examples ofFIGS. 2E-2G, regardless of the cross-sectional shape and the material used, the braid wires have an ultimate tensile strength satisfactory for implantation. According to the various embodiments, this ultimate tensile strength is at least 150,000 pounds per square inch (150 ksi).

FIG. 2Hshows the lead1108from end to end with the shield1118in view to illustrate the termination of the shield1118at the proximal end1105and the distal end1107. The shield1118terminates prior to reaching the most distal connector1109of the proximal end1105and prior to reaching the most proximal electrode1116of the distal end1107. Terminating the shield1118at a distance1117from the connector1109and at a distance1119from the electrode1116reduces the likelihood of RF energy that radiates from the end of the shield, leaking from the shield onto the conductor filars and then to the connector1109and/or electrode1116. However, the shield termination distances1117,1119are not too large so that adequate coverage over the filars1124is maintained.

The shield termination distance from the distal electrodes and proximal connectors may vary. According to the various embodiments, the distance may range from about 0.5 millimeters to about 10 centimeters depending upon the location of the lead1108. For instance, if the distal tip is located in the brain or spinal column where intensities of RF energy are lower, then distance from the end of the shield1118to the nearest edge of the distal electrode may be from 0.5 mm up to about 10 cm, or from about 2 mm to 2 cm to further reduce electrode coupling and filar exposure. However, in other locations where the entire lead1108is just under the skin as for peripheral nerve stimulation, the distance from the end of the shield1118to the nearest edge of the distal electrode may be less than about 2 cm to prevent overexposure of the filars1124. In these cases, the distance may be on the order of 2 mm or more to ensure that excessive RF coupling from the shield1118to the electrodes is avoided.

In one particular example, the lead1108is provided with a shield1118where the total lead diameter is 53.6 mils. The inner insulation layer1122has an as assembled inside diameter of 35 mils and an as assembled outside diameter of 50.19 mils for a total thickness of 5.89 mils or 5.39 mils to the inner edge of the braid wire. The outside insulation layer1120has an as assembled outside diameter of 53.6 mils and a total thickness of 3.41 mils, with 1.41 mils of thickness existing over braid wire intersection points and while the thickness over a single braid wire approaches 2.66 mils as the single braid wires approaches an intersection point where the single braid wire will pass under an intersecting braid wire. The braid wire is round in cross-section with a diameter of 1.25 mils and being embedded by about 0.5 mils into the inner layer1122. Two sets of eight braid wires are provided for a total of sixteen braid wires, with the braid wires establishing a braid angle of 22 degrees with an axial spacing between adjacent braid wires of 7.5 mils. The shield1118terminates about 2 mm from the nearest edge of the distal electrode and proximal connector.

In another particular example, the lead108is provided with the specifications described in the preceding paragraph except that the shield gaps and depth the shield sinks into the inner insulation layer1122are different. Here, the shield1118terminates about 1 mm from the nearest edge of the distal electrode and proximal connector and the shield sinks 0.25 mil. As a result, the inner insulation thickness to the inner edge of the braid wire is 5.6 mils.

In another particular example, the lead108is provided with the specifications described in the preceding paragraph except insulation thicknesses, braid angle, and proximal shield gaps differ. In this example, the braid depth from the outer surface of the outer layer1120to the outer edge of a braid wire is about 2 mils at braid wire intersection points while the thickness over the braid wire approaches 3.25 mils as the single braid wire approaches an intersection point where the braid wire passes under an intersecting braid wire. The inner insulation layer122has an average thickness of 4.5 mils to the inner edge of the braid wire while the braid wire sinks into the inner insulation layer1122by about 0.25 mil. The shield1118terminates about 1.27 mm from the nearest edge of the distal electrode and terminates about 10 mm from the nearest edge of the proximal connector. The braid angle is about 23 degrees.

Embodiments disclosed in relation toFIGS. 3-10Cprovide for radio frequency (RF) grounding of a shield present within an implantable lead. The shield may be grounded in various ways such as to a can of an implantable medical device (IMD) or to a ground plate on a header of the IMD. The pathway for grounding may be a direct current pathway or be capacitively coupled. The pathway for grounding the shield may couple to the shield at a point along the lead that is external to the header of the IMD or may couple to the shield at a point within the header.

FIG. 3shows an example of an implantable medical system2100that includes an IMD2102coupled to a lead2108. The IMD2102includes a metal can2104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD2102includes a header2106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can2104. The header2106is shown transparently for purposes of illustration. The header2106provides a structure for securing the lead2108to the IMD2102and for establishing electrical connectivity between circuitry of the IMD2102and electrodes of the lead2108.

The lead2108includes electrodes2116on a proximal end that are positioned at a stimulation site within a patient. The lead also includes connector rings2110on a proximal end that is positioned within the header2106. The connectors2110make physical contact with electrical connections2111within the header. The electrical connections2111may include a metal contact that the electrode2110rests against upon being inserted into the header2106where a wire extends from the metal contact into the can2104where the circuitry is housed. Signals applied by the IMD2102to the electrodes2110are conducted through the lead2108to the electrodes2116to provide the stimulation therapy to the patient.

The lead2108is secured in the header2106such as by a set screw block2112within the header2106that allows at least one set screw2114to be tightened against at least one of the connectors2110. The shield2118may be grounded by metal contacts provided along the lead to establish a ground pathway from the shield2118to the tissue. As another option, the shield2118may be located within the lead2108at a small distance from the surface so that the shield2118will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.

FIGS. 4A and 4Bshow an example of the lead2108, where a shield2118is present. An outer jacket layer2120is shown transparently inFIG. 4Afor purposes of illustrating the shield2118. The shield2118blocks at least some RF energy from directly coupling to conductive filars2124that are present within the lead2108. The conductive filars2124extend the length of the lead and interconnect the proximal connectors2110to the distal electrodes2116so that stimulation signals are conducted from the proximal end to the distal end of the lead2108.

As shown inFIG. 4A, the shield2118of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield2118, particularly for embodiments where a portion of the shield2118may be exposed for purposes of grounding. While the shield2118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead2108in an overlapping manner or an outer layer2120that is heavily doped with conductive particles.

As shown inFIG. 4B, the shield2118may be embedded within the jacket of the lead2108. One manner of constructing the lead2108with the shield2118is to provide an inner jacket2122that encloses the filars2124and any additional insulation layer2126, such as polytetrafluoroethylene (PTFE) that may surround each filar2124. The shield2118may then reside on the outer portion of the inner jacket2122, and the outer jacket2120may then enclose the shield2118. The outer jacket2120maybe added over the braid2118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield2118to RF couple to tissue, typically as a capacitive coupling, either as an alternative to grounding at the can of the IMD or in addition to grounding at the can, the amount of the outer jacket layer2120covering the shield2118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield2118grounds at the can of the IMD and grounding via a capacitive coupling from the shield through the outer jacket2120directly to the tissue is of less significance, then the shield2118may be located further from the outer surface of the lead2108.

The inner and outer jackets2122,2120may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. A lumen2128may be present inside of the inner jacket2122around which the insulated filars2124are coiled or otherwise positioned. The lumen2128may be useful, particularly for percutaneous leads2108, to allow a stylet to be inserted for purposes of pushing and steering the lead2108into the desired position within the patient.

FIG. 4Cshows one example of exposing the shield2118for purposes of grounding the shield2118. In this example, the outer layer2120of the jacket has been removed at first point along the lead2108near the proximal end to expose the shield2118and the inner jacket2122. For example, an excimer laser may be used to ablate the outer layer2120. Physical contact may then be established between the shield2118and an electrode attached to the lead, a spring loaded connector or a connector block, a wire, or other direct current or capacitive coupling. For instance, a ground wire could be adhesively bonded with glue or tape in contact with the exposed shield2118. Depending upon the embodiment, this first point along the lead where the shield2118is exposed may be located either inside or outside of the header of the IMD. Furthermore, depending upon the embodiment the coupling to the exposed shield2118may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground.

FIG. 4Dshows another example of providing a pathway to ground the shield2118. Here, an electrode2130is attached at the first point along the lead2108near the proximal end to provide a robust physical connection to a spring loaded connector, a connector block, a wire, or other direct current or capacitive coupling. Depending upon the embodiment, this first point along the lead where the electrode2130is positioned may be located either inside or outside of the header of the IMD. Furthermore, depending upon the embodiment a coupling to the electrode2130may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground.

FIGS. 5A-5Cshow embodiments of grounding the shield to the can of the IMD by using a connector block mounted on the IMD and coupling a grounding path to the shield outside of a header of the IMD. The implantable medical system2150includes an IMD2152having a metal can2154and a header2156. One or more leads2164extend from the header and pass through a connector block2158that is mounted to the can2154.

The connector block2158includes features to ground the shield of the lead2164to the can2154, such as a connector2160and a can attachment2162. For instance, the connector block2158may be constructed of a biocompatible plastic or other non-conductor while the connector2160provides conduction to the can attachment2162. The can attachment2162may be of various forms. For example, a wire that extends from the connector2160to the can2154where the can attachment2162is welded or otherwise affixed to the can2154. As another example, the connector block2158may include a metal plate that contacts the metal can2154via a weld or other attachment.

FIG. 5Bis a side view showing a pair of pass-through features of the connector block2158and a pair of leads2164having shields to be grounded. The connector block2158is shown in a cross-section so that a set screw2168is visible. The electrode or other contact for the shield of the lead2164is positioned within the pass-through2166such that the set screw2168and the electrode or other contact for the shield are aligned. The set screw2168is tightened against the electrode or other contact to establish the ground to the can2154. The pass-through2166may be a slot through the connector block2158so that the lead2164can be lowered into the slot. As another option, the pass-through2166may be a bore through the connector block2158and the lead2164is fed through the bore.

FIG. 5Cis a side view showing a pair of pass-through features of another embodiment of the connector block2158and a pair of leads2164having shields to be grounded. The connector block2158includes spring loaded connectors2172. The electrode or other contact for the shield of the lead2164is positioned within the pass-through2170such that the spring loaded connector2172and the electrode or other contact for the shield are aligned. The electrode or other contact to the shield is forced within the spring loaded connector2172to establish the ground to the can2154. As with the embodiment ofFIG. 5B, the pass-through2170of this embodiment may be a slot through the connector block2158so that the lead2164can be lowered into the slot or may be a bore through the connector block2158where the lead2164is fed through the bore.

FIG. 6shows one example of a spring loaded connector2174. The spring loaded connector2174can open slightly when forced by insertion of the lead2164and then is biased back against the electrode or other contact of the lead2164once the lead is seated within the spring loaded connector2174. Other spring loaded connector designs are also applicable.

FIG. 7Ashows an implantable medical system2180where the shield of a lead2188is being grounded to a metal can2184of an IMD2182externally of the header2186. Here, a direct current pathway is being provided between the shield and the metal can2184. A spring loaded connector2192contacts an electrode2190on the lead2188where the electrode2190is in contact with the shield. A wire2194may be made from materials such as titanium, tantalum, platinum, stainless steel, nickel chromium, and alloys, and serves as a ground conductor. This wire2194is attached to the spring loaded connector2192by a weld or other bond. The wire2194extends from the spring loaded connector2192to the metal can2184where a weld2196or other bond such as with glue or tape attaches the wire2194to the metal can2184.

FIG. 7Bshows an implantable medical system2200where the shield of a lead2208is being grounded to a metal can2204of an IMD2202externally of the header2206. Here, a direct current pathway is also being provided between the shield and the metal can2204. A metal connector block2210having a set screw2212contacts an electrode on the lead2208where the electrode is in contact with the shield. A wire2214serving as a ground conductor is attached to the connector block2210by a weld or other bond. The wire2214extends from the connector block2212to the metal can2204where glue2216, such as a conductive epoxy or carbon filled polymer adhesive, or other bond such as a weld or tape attaches the wire2214to the metal can2204.

FIG. 7Cshows an implantable medical system2220where the shield of a lead2228is being grounded to a metal can2224of an IMD2222externally of the header2226. Here, a direct current pathway is also being provided between the shield and the metal can2224. A coupling2230such as a ring electrode is in contact with the shield. A wire2232serving as a ground conductor is attached to the coupling2230by a weld or other bond. The wire2232extends from the coupling2230to the metal can2224where a crimp connector2234or other bond such as a weld or tape attaches the wire2232to the metal can2224.

For the examples ofFIGS. 7A-7C, various examples of connecting the grounding wire to the lead and to the can are disclosed. It will be appreciated that any combination of these and other examples of connections of the ground wire may be used to provide the direct current pathway that ultimately provides an RF ground from the shield to the metal can.

FIG. 8Ashows an implantable medical system2240where the shield of a lead2248is being grounded to a metal can2244of an IMD2242externally of the header2246. Here, a capacitively coupled pathway is being provided between the shield and the metal can2244. A coupling2250such as a spring loaded connector or a ring electrode contacts the lead2248and is in contact with the shield. A wire2252serving as a ground conductor is attached to the coupling2250by a weld or other bond. The wire2252extends from the coupling2250to nearby the metal can2244where a piece of tape2254or other tab affixed to the can2244attaches to the wire2252. The tape2254, such as double-sided tapes, epoxies, or polymer based adhesive, or other tab holds the wire in proximity to the metal can2244to establish a capacitive coupling between the wire2252and the can2244.

FIG. 8Bshows an implantable medical system2260where the shield of a lead2268is being grounded to a metal can2264of an IMD2262externally of the header2266. Here, a capacitively coupled pathway is being provided between the shield and the metal can2264. A piece of tape2270or other tab contacts the lead2268at a point where the shield is present. A wire2272serving as a ground conductor is attached to the tab2270and is held nearby the lead2268and shield to establish a capacitive coupling between the wire2272and the shield. The wire2272extends from the tab2270to the metal can2264and is affixed to the metal can2264with a weld2274or other bond.

FIG. 8Cshows an implantable medical system2280where the shield of a lead2288is being grounded to a metal can2284of an IMD2282externally of the header2286. Here, a capacitively coupled pathway is being provided between the shield and the metal can2284. A coupling2290such as a spring loaded connector or a ring electrode contacts the lead2288and is in contact with the shield. A wire2292serving as a ground conductor is attached to the coupling2290by a weld or other bond and extends from the coupling2290to nearby the metal can2284. Non-conductive glue or another non-conductive bond2294to the can2284is present to adhere to the wire2292and hold the wire in proximity to the metal can2284to establish a capacitive coupling between the wire2292and the can2284.

For the examples ofFIGS. 8A-8C, various examples of connecting the grounding wire to the lead and to the can are disclosed, using combinations of direct current couplings and capacitive couplings. It will be appreciated that any combination of these and other examples of direct current coupling and capacitive coupling connections of the ground wire may be used to provide the capacitively coupled pathway that ultimately provides an RF ground from the shield to the metal can.

FIG. 9Ashows an implantable medical system2300where the shield of a lead2308is being grounded to a metal can2304of an IMD2302within the header2306. Proximal electrodes2310of the lead2308are electrically connected via wires2312to the IMD2302. Here, a direct current coupled pathway is being provided between the shield and the metal can2304. A coupling2314such as a spring loaded connector or a ring electrode contacts the lead2308and is in contact with the shield. A set screw2316may be present to further hold the proximal end of the lead2308in place within the header2306. A wire2318serving as a ground conductor is attached to the coupling2314by a weld or other bond and extends from the coupling2314to the metal can2304where a weld2320or other bond holds the wire2318to the can2304.

FIG. 9Bshows an implantable medical system2330where the shield of a lead2338is being grounded to a metal can2334of an IMD2332within the header2336. Proximal electrodes2340of the lead2338are electrically connected via wires2342to the IMD2302. Here, a direct current coupled pathway is being provided between the shield and the metal can2334. A coupling2344such as a spring loaded connector or a ring electrode contacts the lead2338and is in contact with the shield. A wire2346serving as a ground conductor is attached to the coupling2344by a weld or other bond and extends from the coupling2344to the metal can2334where a weld2348or other bond holds the wire2346to the can2334.

FIG. 9Cshows an implantable medical system2350where the shield of a lead2358is being grounded to a metal can2354of an IMD2352within the header2356. Proximal electrodes2360of the lead2358are electrically connected via wires2362to the IMD2352. Here, a capacitively coupled pathway is being provided between the shield and the metal can2354. A coupling2364such as a spring loaded connector or a ring electrode contacts the lead2358and is in contact with the shield. A wire2366serving as a ground conductor is capacitively coupled to the coupling2364within the header2356by the header structure holding the wire in proximity to the coupling2364. The wire2366extends from the capacitive coupling to the metal can2354where a weld2368or other bond holds the wire2366to the can2354.

FIG. 9Dshows an implantable medical system2370where the shield of a lead2378is being grounded to a metal can2374of an IMD2372within the header2376. Proximal electrodes2380of the lead2378are electrically connected via wires2382to the IMD2372. Here, a capacitively coupled pathway is being provided between the shield and the metal can2374. A coupling2384such as a spring loaded connector or a ring electrode contacts the lead2378and is in contact with the shield. A wire2386serving as a ground conductor is capacitively coupled to the coupling2384within the header2376by the header structure holding the wire in proximity to the coupling2384. The wire2386extends from the capacitive coupling toward the metal can2374and is capacitively coupled to the can2374within the header2376by the header structure holding the wire in proximity to the can2374.

FIG. 9Eshows an implantable medical system2390where the shield of a lead2398is being grounded to a metal can2394of an IMD2392within the header2396. Proximal electrodes2402of the lead2398are electrically connected via wires2404to the IMD2392. Here, a capacitively coupled pathway is being provided between the shield and the metal can2394. A coupling2406such as a spring loaded connector or a ring electrode contacts the lead2398and is in contact with the shield. A shunt plate such as a tab2408or similar structure serving as a ground conductor extends from the coupling2406toward the can2394and is capacitively coupled to the can2394within the header2396by the header structure holding the tab2408in proximity to the can2394.

FIG. 9Fshows an implantable medical system2410where the shield of a lead2418is being grounded to a metal can2414of an IMD2412within the header2416. Proximal electrodes2420of the lead2418are electrically connected via wires2422to the IMD2412. Within the can2414, filter feed through (FFT) circuits2424are present to capacitively couple the wires2422to the metal can2414while allowing connection of the wires2422to stimulation circuits. The FFT circuits2424for the electrodes2420protects the IMD2412from electromagnetic background noise picked up by the filars, albeit potentially less noise due to the presence of the shield.

Here, a capacitively coupled pathway is being provided between the shield and the metal can2414also via an FFT circuit2430. A coupling2426such as a spring loaded connector or a ring electrode contacts the lead2418and is in contact with the shield. A wire2428serving as a ground conductor extends from the coupling2426toward the can2414and terminates at the FFT circuit2430to provide the capacitive coupling between the shield and the can2414.

As shown, the coupling2426to the shield may be an existing electrode of the lead2418that provides stimulation signals to a filar within the lead2418. In that case, the FFT circuit2430may provide capacitive coupling to the can for both the filar and the shield. In such a case, it may be desirable to capacitively couple the shield to the coupling2426so that relatively low frequency stimulation signals are not present on the shield but induced RF current on the shield has a pathway to the FFT circuit2430. For example, the outer jacket may separate the shield from the electrode by a separation on the order of 0.5-5 mils to allow an RF coupling to occur. As an alternative to using the same coupling and FFT circuit for both the shield and the filar, the shield may be provided a dedicated coupling2426and a dedicated FFT circuit2430that are independent of any electrodes and filars within the lead2418.

For the examples ofFIGS. 9A-9F, various examples of connecting the grounding conductor to the lead and to the can within the header are disclosed, using combinations of direct current couplings and capacitive couplings. It will be appreciated that any combination of these and other examples of direct current coupling and capacitive coupling connections of the ground conductor may be used to provide the capacitively coupled pathway that ultimately provides an RF ground from the shield within the header to the metal can. For instance, a capacitive coupling may be provided in any of the various embodiments at the coupling to the shield as discussed above in relation toFIG. 9F.

FIG. 10Ashows an implantable medical system2440where the shield of a lead2448is being grounded to a metal can2444of an IMD2442outside of the header2446. Here, a ground pathway is being provided between the shield and a ground plate2454installed on the header2446. The ground plate provides a relatively large surface area in comparison to an individual electrode and allows for safe dissipation of induced RF current on the shield in the same manner as grounding to the can2444. A coupling2450such as a spring loaded connector or a ring electrode contacts the lead2448and is in contact with the shield. A wire2452that serves as a ground conductor is attached to the coupling2450by a weld or other bond and extends from the coupling2450to the ground plate2454where a weld or other bond holds the wire2452to the ground plate2454.

FIG. 10Bshows an implantable medical system2460where the shield of a lead2468is being grounded to a metal can2464of an IMD2462within the header2466. Here, a ground pathway is also being provided between the shield and a ground plate2474installed on the header2466. A coupling2470such as a spring loaded connector or a ring electrode contacts the lead2468and is in contact with the shield. A wire2472that serves as a ground conductor is attached to the coupling2470by a weld or other bond and extends from the coupling2470to the ground plate2474where a weld or other bond holds the wire2472to the ground plate2474.

FIG. 10Cshows an implantable medical system2480where the shield of a lead2488is being grounded to a metal can2484of an IMD2482within the header2486. Here, a ground pathway is being provided between the shield and a connector block2492with a relatively large surface area that also acts as a ground plate installed on the header2486. In this example, the connector block2492is a set screw block that uses a set screw2494to tighten against a coupling2490on the lead2488. The coupling2490such as a ring electrode contacts the lead2448and is in contact with the shield. A set screw2494extends from the coupling2490and through the connector block2492and acts as a ground conductor to provide the ground pathway from the shield to the connector block2492. Other conductive features may also be present within the connector block2492to contact the coupling2490and provide the RF ground pathway.

For the examples ofFIGS. 10A-10C, various examples of connecting the grounding conductor to the lead and to the ground plate are disclosed. It will be appreciated that any combination of direct current coupling and capacitive coupling connections may be used to provide the pathway that ultimately provides an RF ground from the shield to the ground plate. For instance, a capacitive coupling may be provided in any of the various embodiments at the coupling to the shield as shown inFIGS. 10A-10Cand as discussed above in relation toFIG. 9F. Likewise, a capacitive coupling may be present between a ground conductor extending from the coupling to the shield and the ground plate.

Embodiments disclosed in relation toFIGS. 11-15Ealso provide for radio frequency (RF) grounding of a shield present within an implantable lead. The shield may be grounded in various ways such as directly to tissue at one or more points along the lead body. The pathway for grounding may be a direct current pathway or be capacitively coupled. The pathway for grounding may utilize an exposed or nearly exposed shield at one or more points along the lead body, metal conductors attached to the lead at one or more points, a jacket with a conductive doping at one more points, and so forth.

FIG. 11shows an example of an implantable medical system3100that includes an IMD3102coupled to a lead3108. The IMD3102includes a metal can3104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD3102includes a header3106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can3104. The header3106is shown transparently for purposes of illustration. The header3106provides a structure for securing the lead3108to the IMD3102and for establishing electrical connectivity between circuitry of the IMD3102and electrodes of the lead3108.

The lead3108includes electrodes3116on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings3110on a proximal end that is positioned within the header3106. The connector rings3110make physical contact with electrical connections3111within the header. The electrical connections3111may include a metal contact that the connector ring3110rests against upon being inserted into the header3106where a wire extends from the metal contact into the can3104where the circuitry is housed. Signals applied by the IMD3102to the connector rings3110are conducted through the lead3108to the electrodes3116to provide the stimulation therapy to the patient.

The lead3108is secured in the header3106such as by a set screw block3112within the header3106that allows at least one set screw3114to be tightened against at least one of the electrodes3110. With the lead3108in place, the shield3118of the lead3108may then become grounded to the body along one or more points down the length of the lead from the IMD3102.

FIGS. 12A and 12Bshow an example of the lead3108, where a shield3118is present. An outer jacket layer3120is shown transparently inFIG. 12Afor purposes of illustrating the shield3118. The shield3118blocks at least some RF energy from directly coupling to conductive filars3124that are present within the lead3108. The conductive filars3124extend the length of the lead and interconnect the proximal electrodes3110to the distal electrodes3116so that stimulation signals are conducted from the proximal end to the distal end of the lead3108.

As shown inFIG. 12A, the shield3118of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield3118, particularly for embodiments where a portion of the shield3118may be exposed for purposes of grounding. While the shield3118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead3108in an overlapping manner or an outer layer3120that is heavily doped with conductive particles.

As shown inFIG. 12B, the shield3118may be embedded within the jacket of the lead3108. One manner of constructing the lead3108with the shield3118is to provide an inner jacket3122that encloses the filars3124and any additional insulation layer3126, such as polytetrafluoroethylene (PTFE) that may surround each filar3124. The shield3118may then reside on the outer portion of the inner jacket3122, and the outer jacket3120may then enclose the shield3118. The outer jacket3120maybe added over the braid3118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield3118to RF couple to tissue, typically as capacitive coupling, either as an alternative to grounding at the can of the IMD or in addition to grounding at the can, the amount of the outer jacket layer3120covering the shield3118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield3118grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield may be located further from the outer surface of the lead3108with additional features of the lead providing the coupling at the one or more specific locations as discussed below.

The inner and outer jackets3122,3120may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. A lumen3128may be included inside of the inner jacket3122around which the insulated filars3124are coiled or otherwise positioned. The lumen3128may be useful, particularly for percutaneous leads3108, to allow a stylet to be inserted for purposes of pushing and steering the lead3108into the desired position within the patient.

FIG. 12Cshows one example of exposing the shield3118at a particular point along the lead3108for purposes of grounding the shield3118. In this example, the outer layer3120of the jacket has been removed at a first point along the lead3108distant from the distal end to expose the shield3118and the inner jacket3122. For example, an excimer laser may be used to ablate the outer layer3120. Physical contact may then be established between the shield3118and the tissue or between the shield3118and an electrode attached to the lead.

FIG. 12Dshows another example of providing a pathway to ground the shield3118. Here, a metal conductor, specifically a ring electrode3130, is attached at the first point along the lead3108distant from the distal end to provide a robust physical connection to the tissue while avoiding tissue in-growth that may occur if the shield3118is exposed directly. Depending upon the embodiment, a coupling of the shield3118to the electrode3130may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground. The ring electrode3130may be attached by methods such as crimping, clamping, welding, and the like.

FIG. 12Eshows an example of nearly exposing the shield3118at a particular point along the lead3108for purposes of grounding the shield3118. In this example, the outer layer3120of the jacket has been almost entirely removed at a first point along the lead3108distant from the distal end to nearly expose the shield3118and the inner jacket3122. Only a very thin layer3120′, on the order of about 0.5-5 mils, of the outer layer3120is remaining Physical contact between the shield3118and the tissue is avoided so that tissue in-growth does not occur, and the shield3118capacitively couples to the tissue to provide the RF pathway to ground.

FIG. 12Fshows an example of exposing, or nearly exposing, the shield3118at a plurality of points3202along the lead. At these points3202, the outer layer3120has been at least partially ablated or otherwise removed to place the shield3118in closer proximity to the body tissue so that an RF pathway to ground is established. Where the shield3118is exposed, the RF pathway is a direct current coupling to the tissue. Where the shield3118is nearly exposed, the RF pathway is a capacitive coupling to the tissue.

Where multiple points of the RF pathway to ground are present, a particular separation of the multiple points is provided. A nearest edge-to-nearest edge distance between one point and an adjacent one is shown by the distance from edge3204to edge3206. Where the outer layer is removed, the flexibility and strength of the lead is altered for the region including those points and this distance from edge3204to edge3206can be used to control the flexibility and strength.

Where multiple points of the RF pathway to ground are direct current couplings, another concern is current induced by the gradient magnetic fields present in a magnetic resonance (MR) scan. If the most proximal and most distal points of the direct current coupling are spaced too far apart, then the magnetic gradient may induce a dangerous current through the shield and produce a significant stimulation of tissue at those ground points along the lead. Therefore, choosing the nearest edge-to-nearest edge separation to fall within an illustrative range of 2 millimeters (mm) or more with a most proximal to most distal separation, such as edge3204to edge3208, of about 40 centimeters (cm) or less may allow for flexibility of the lead in the region while maintaining small loops that prevent large magnetic gradient induced currents should the shield be exposed at the points3202.

FIG. 12Gshows an example of coupling the shield3118to ground with a plurality of metal conductors such as rings3130at a plurality of points3210along the lead. At these points3202, the outer layer3120has been at least partially ablated or otherwise removed to place the shield3118in close proximity with the metal conductors3130so that an RF pathway to ground is established through the metal conductors3130. Where the shield3118is exposed to the metal conductors3130, the RF pathway is a direct current coupling to the tissue. Where the shield3118is nearly exposed to the metal conductors3130, the RF pathway is a capacitive coupling to the tissue.

As with the example ofFIG. 12F, where multiple points of the RF pathway to ground are present, a particular separation of the multiple points is provided. A nearest edge-to-nearest edge distance between one point and an adjacent one is shown by the distance from edge3212to edge3214. The flexibility and strength of the lead is altered for the region including those points, with the metal conductors3130limiting the bending in this region to essentially those sections of lead between the metal conductors3130. Thus, in one example, a nearest edge-to-nearest edge distance may be maintained at or above 2 mm or 50% of the grounding ring length so that flexibility of the lead is maintained.

Also, where the shield3118is direct current coupled to the metal conductors3130, a magnetic gradient induced current is of concern because the metal conductors3130have a direct current coupling to the tissue. In that case, the separation of the most proximal to the most distal may be kept within a range that prevents a large loop and avoids a large magnetic induced gradient current. In this particular example, the most proximal to the most distal distance, such as from edge3212to edge3216, may be maintained at or below approximately 40 cm so that magnetic gradient induced currents are insignificant.

FIG. 12Hshows a cross-section of the lead3108at a particular point where the outer jacket3120has been ablated or otherwise removed. In this example, the lead3108at this particular point includes a metal conductor3130with a direct current coupling to the shield3118. The outer layer3120of the jacket has been removed to allow the metal conductor3130, a ground ring as shown, to wrap around the lead and contact the shield3118. The filars may be present within the inner jacket3122or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3122or any other inner layer as shown inFIG. 12B.

FIG. 12Ishows a cross-section of the lead3108at a particular point where the outer jacket3120has been ablated or otherwise removed. In this example, the lead3108at this particular point has the shield3118exposed to tissue for a direct current coupling by entirely removing the outer layer3120. The filars may be present within the inner jacket3122or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3122or any other inner layer as shown inFIG. 12B.

FIG. 12Jshows a cross-section of the lead3108at a particular point where a portion of the outer jacket3120has been ablated or otherwise removed. In this example, the lead3108at this particular point includes a metal conductor3130with a capacitive coupling to the shield3118. The outer layer3120of the jacket has been partially removed, with a remaining thickness of about 0.5 mils to 5 mils, to nearly expose the shield3118. This allows the metal conductor3130, a ground ring as shown, to wrap around the lead and capacitively couple with the shield3118at RF frequencies. The filars may be present within the inner jacket3122or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3122or any other inner layer as shown inFIG. 12B.

FIG. 12Kshows a cross-section of the lead3108at a particular point where a portion of the outer jacket3120has been ablated or otherwise removed. The outer layer3120of the jacket has been partially removed, with a remaining thickness of about 0.5 mils to 5 mils, to nearly expose the shield3118. The shield3118capacitively couples to the tissue at RF frequencies. The filars may be present within the inner jacket3122or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3122or any other inner layer as shown inFIG. 12B.

FIG. 13Ashows an example of a ring electrode3220that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode may be constructed of platinum, platinum-iridium, titanium, tantalum, stainless steel, and other similar biocompatible metals. The ring electrode3220may have a gap3222. The ring electrode3220may be sprung open to fit around the lead at the particular point where the jacket has been ablated, and the ring electrode3220is crimped back into a tightly fitting configuration. As another example, the ring electrode3220may be flat and then rolled into the ring shape about the lead. In some examples, the gap3222may close upon crimping while in other embodiments the gap3222may remain to some degree.

FIG. 13Bshows an example of another ring electrode3224that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode3224includes a tab3226that extends away from the lead to provide an additional surface area and extension into the tissue for adding grounding of the shield3118. The ring electrode3220may be sprung open to fit around the lead at the particular point where the jacket has been ablated and the ring electrode3220is crimped back into a tightly fitting configuration. As in the previous example, the ring electrode3224may be flat and then rolled into the ring shape about the lead while maintaining a flat portion as the tab3226.

FIG. 13Cshows an example of another ring electrode3228that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode3228forms a helix. The ring electrode3228may be sprung open to fit around the lead at the particular point where the jacket has been ablated and the ring electrode3228is crimped back into a tightly fitting helical configuration. As in the previous examples, the ring electrode3228may be flat and then rolled into the helical ring shape about the lead

FIG. 13Dshows an example of a ring electrode3230that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode3230has an outer side3234that faces away from the shield3118and an inner side3236that faces toward the shield3118and may directly contact the shield3118. In this example, the outer side3234has a non-conductive coating3232applied so that the outer side3234does not have a direct coupling to the tissue. The non-conductive coating may be of various types such as polyurethane, silicone or other biocompatible polymers.

The inner side3236may either have a direct current coupling or a capacitive coupling to the shield. With multiple ring electrodes3230in place on a lead, magnetic gradient induced current which is at a relatively low frequency is not a concern because the non-conductive coating3232prevents the relatively low frequency induced current from flowing to the tissue. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground to the tissue through the capacitive coupling provided by the non-conductive coating3232.

FIG. 13Eshows an example of a ring electrode3240that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode3240has an outer side3242that faces away from the shield3118and an inner side3244that faces toward the shield3118and may directly contact the shield3118. In this example, the inner side3244has a non-conductive coating3246applied so that the inner side3244does not have a direct coupling to the shield3118even if the shield3118is entirely exposed to the ring electrode3240. The non-conductive coating3246may be of the various types discussed above in the previous example.

The outer side3242may have a direct current coupling to the tissue. With multiple ring electrodes3240in place on a lead, magnetic gradient induced current is not a concern because the non-conductive coating prevents the relatively low frequency induced current from flowing from the shield3118to the ring electrode3240. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground through the ring electrode3240to the tissue through the capacitive coupling provided by the non-conductive coating3246.

FIG. 13Fshows an example of a ring electrode3250that may be attached to a lead3108to form the RF pathway to ground from the shield3118. The ring electrode3250has an outer side3252that faces away from the shield3118and may directly contact the tissue and an inner side3254that faces toward the shield3118and may directly contact the shield3118. In this example, both the inner side3254and the outer side3252have a non-conductive coating3256applied. The inner side3254does not have a direct current coupling to the shield3118even if the shield is entirely exposed to the ring electrode3250. The outer side3252does not have a direct current coupling to the tissue even if in physical contact with the tissue. The non-conductive coating3256may be of the various types discussed above in the previous examples.

With multiple ring electrodes3250in place on a lead, magnetic gradient induced current is not a concern because the non-conductive coating prevents the relatively low frequency induced current from flowing from the shield3118to the ring electrode3250. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground through the ring electrode3250to the tissue through the capacitive couplings on each side of the ring electrode3250provided by the non-conductive coating3256.

While the examples ofFIGS. 13A-13Fshow various shapes of ring electrodes, it will be appreciated that various other shapes are also applicable for metal conductors being attached to the lead to provide the RF ground pathway. Furthermore, whileFIGS. 13D-13Fshow a particular ring electrode shape with a non-conductive coating, it will be appreciated that the non-conductive coating is applicable to either or both sides of any of the metal conductor configurations including those ofFIGS. 13A-13C.

FIG. 14Ashows a cross-section of a lead3260that includes an outer jacket layer3266that surrounds a shield3262and an inner jacket layer3264. The outer jacket layer3266is doped with conductive particles3268at a particular point along the length of the lead. These conductive particles3268provide RF conductive qualities for the outer jacket layer3266. Thus, the RF energy couples from the shield3262to the tissue through the doped outer jacket layer3266. Examples of the conductive particles include carbon, tantalum, titanium, platinum, platinum-iridium, and other biocompatible conductive substances. The filars may be present within the inner jacket3264or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3264or any other inner layer like that shown inFIG. 12B.

FIG. 14Bshows the lead3260with a plurality of points3272along the lead where the conductive particles3268are present within the outer layer3266. The doped outer layer3266is exposed to create the RF pathway to ground from the outer layer3266to the tissue.

FIG. 14Cshows a cross-section of a lead3260where the outer jacket layer3266that surrounds a shield3262has been removed via ablation or other technique to expose the shield3262and the inner jacket layer3264. Here, the inner jacket layer3264is doped with conductive particles3268at least at the particular point(s) along the length of the lead where the outer layer3266has been removed. These conductive particles3268provide RF conductive qualities for the outer portion of the inner jacket layer3264where the shield3262is present. Thus, the RF energy couples from the shield3262to the tissue through the doped jacket layer3264. The filars may be present within the inner jacket3264or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket3264or any other inner layer like that shown inFIG. 12B.

FIG. 14Dshows the lead3260with a plurality of points3274along the lead where the conductive particles3268are present within the inner layer3264. The outer layer3266is removed at these points3274to expose the doped inner layer3264and to create the RF pathway to ground from the inner layer3264to the tissue.

FIGS. 15A and 15Bshow an example of an implantable medical lead3108where a lead anchor3280is attached. In this example, the lead anchor3280is an RF conductor to the tissue to provide the ground pathway for the shield3118. In this particular example, the lead3108includes a ring electrode3130that is coupled to the shield3118, either via a direct current coupling or a capacitive coupling. The lead anchor3280is constructed of metal or other conductor, or at least has a portion that is or conductive and directly contacts or nearly contacts the ring electrode3130and the tissue to ground the shield3118at RF frequencies. This ground pathway is secured in place via the conventional mounting of the lead anchor3280to the lead body and by the wings3282being sutured in place to the tissue. The filars may be present within the inner jacket or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket or any other inner layer like that shown inFIG. 12B.

FIGS. 15C and 15Dshow another example of an implantable medical lead3108where a lead anchor3280is attached. In this example, the lead anchor3280is an RF conductor to the tissue to provide the ground pathway for the shield3118. In this particular example, the lead3108does not have a ring electrode3130coupled to the shield3118. However, as seen inFIG. 15D, the lead anchor has gripping teeth3284that sink into the outer layer of the jacket and either directly contact or nearly contact the shield3118. The filars may be present within the inner jacket or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket or any other inner layer like that shown inFIG. 12B.

Directly contacting the shield3118creates a direct current coupled RF pathway while nearly contacting the shield3118creates a capacitively coupled RF pathway. As with the previous example, the lead anchor3280is constructed of metal or other conductor, or at least has a portion that is conductive and contacts or nearly contacts the tissue to ground the shield3118at RF frequencies. This ground pathway is secured in place via the conventional mounting of the lead anchor to the lead body and by the wings3282being sutured in place to the tissue.

In these embodiments, the anchor may capacitively couple to the shield3118without teeth or rings being present, particularly where the depth of the shield within the outer layer3120is relatively small. For example, for depth of the shield3118of about 5 mils or less, the anchor may reside on the outer layer3120and capacitively couple to the shield3118to provide the RF pathway to ground.

FIG. 15Eshows an example of an implantable medical lead3108where a lead anchor3290is attached. In this example, the lead anchor3290is an RF conductor to the tissue to provide the ground pathway for the shield3118. However, in this particular example, lead anchor3290provides a capacitive coupling to ground by utilizing a non-conductive outer material or coating3292to contact the tissue. The lead anchor3290may have either a direct current coupling or capacitive coupling to the shield3118, or ring electrode3130if any. The capacitive coupling to the tissue prevents the lead anchor3290from becoming a magnetic gradient induced current electrode, such as where other shield electrodes are present at other points along the lead3108.

Utilizing an anchor to provide an RF pathway to ground, as shown inFIGS. 15A-15E, may also be useful considering that the typical mounting location of an anchor is at a point where the intensities of the RF fields change. For instance, an anchor may be positioned near the entry hole of the cranium where the lead3108is used for brain stimulation. The intensities of the field may change from one side of the entry hole to the other and providing the RF pathway to ground via an anchor near the entry hole may assist in dissipating energy received by the shield3118externally of the entry hole to prevent such energy from traveling through the shield3118and through the entry hole toward the shield termination which is closer to the stimulation electrodes.

Embodiments disclosed in relation toFIGS. 16-17Gprovide for shielding of both an implantable medical lead and an implantable lead extension. The two shields are interconnected with a radio frequency (RF) conductive path to maintain a continuity of the shielding along the length between the implantable medical device (IMD) and the stimulation site.

FIG. 16shows an example of an implantable medical system4100that includes an IMD4102coupled to a lead4108. The IMD4102includes a metal can4104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD4102includes a header4106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can4104. The header4106is shown transparently for purposes of illustration. The header4106provides a structure for securing the lead extension4142to the IMD4102and for establishing electrical connectivity between circuitry of the IMD4102and distal connectors of the lead extension4142that are located in a distal housing4140.

The extension4142also includes ring connectors4110on a proximal end that is positioned within the header4106. The ring connectors4110make physical contact with electrical connections within the header. The electrical connections may include a metal contact that the ring connector4110rests against upon being inserted into the header4106where a wire extends from the metal contact into the can4104where the circuitry is housed. Signals applied by the IMD4102to the ring connectors4110are conducted through the extension4142to the connectors within the housing4140to provide the stimulation signals to the lead4108. The extension4142is secured in the header4106such as by a set screw block4112within the header4106that allows at least one set screw4114to be tightened against at least one of the ring connectors4110.

The lead4108includes electrodes4116on a distal end that are positioned at a stimulation site within a patient. The lead4108also includes ring connectors on a proximal end that is positioned within the housing4140. The ring connectors make physical contact with electrical connections within the housing4140. The electrical connections may include a metal contact such as a Bal Seal® connector of the Bal Seal Engineering, Inc. of Foothill Ranch, Calif., another spring loaded connector, or a set screw block that the electrode rests against upon being inserted into the housing4140. A wire extends from the metal contact of the housing4140into the extension4142to connect with the filars of the extension4142. Signals applied by the IMD4102to the ring connectors4110are conducted through the extension4142and lead4108to the electrodes4116to provide the stimulation therapy to the patient.

The lead4108is secured in the housing4140such as by a set screw block within the housing4140that allows at least one set screw to be tightened against at least one of the electrodes. A shield4144of the extension and a shield4118of the lead4108that are discussed below with reference toFIGS. 17A-17Gare present to prevent the induced RF current on the filars. The shields4118,4144may be grounded at the IMD4102ofFIG. 16or at various grounding points established along the extension4142and/or lead4108. As another option, the shield4144of the extension4142and/or the shield4118of the lead4108may be located within the extension4142or lead4108at a small distance from the surface so that the shields4118,4144will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length. In any of these cases, continuity may be maintained between the shields4118and4144as discussed herein

FIGS. 17A-17Gshow examples of the extension4142and lead4108where shields4118,4144are present. The lead4108is inserted through an opening4146in the housing4140on the distal end of the extension4142. Outer jacket layers4120,4141for the lead4108and extension4142are shown transparently inFIG. 17Afor purposes of illustrating the shields4118,4144. The shields4118,4144block at least some RF energy from directly coupling to conductive filars that are present within the lead4108and extension4142. The conductive filars extend the length of the extension4142and lead4108and interconnect the proximal connector rings4110of the extension4142to the distal electrodes4116of the lead4108so that stimulation signals are conducted to the stimulation site.

As shown inFIG. 17A, the shields4118,4144of this example are braided metal wires. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desirable to utilize a biocompatible metal for the shields4118,4144, particularly for embodiments where a portion of the shields4118,4144may be exposed for purposes of grounding. While the shield4118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead4108in an overlapping manner or an outer layer4120that is heavily doped with conductive particles.

FIG. 17Aalso shows a set screw block4143present on the housing4140. The set screw block4143may be used to fix the proximal end of the lead4108in place within the opening4146of the housing4140where a set screw is tightened against a connector ring on the lead4108. Other manners of fixing the lead4108within housing4140may also be used.

FIG. 17Bshows a coupling of the lead4108to the housing4140as a cross-section taken through the coupling of a shield connector4132to a shield electrode4130. The shield4118of the lead4108may be embedded within the jacket of the lead4108. One manner of constructing the lead4108with the shield4118is to provide an inner jacket4122that encloses the filars4124and any additional insulation layer4126, such as polytetrafluoroethylene (PTFE) that may surround each filar4124. The shield4118may then reside on the outer portion of the inner jacket4122, and the outer jacket4120may then enclose the shield4118. The outer jacket4120maybe added over the braid4118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield4118to RF couple to tissue, typically as a capacitive coupling, either as an alternative to or in addition to grounding at the can of the IMD or elsewhere, the amount of the outer jacket layer4120covering the shield4118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield4118grounds at the can of the IMD and grounding via a capacitive coupling from the shield through the outer jacket4120directly to the tissue is of less significance, then the shield4118may be located further from the outer surface of the lead4108.

The inner and outer jackets4122,4120may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. A lumen4128may be included inside of the inner jacket4122around which the insulated filars4124are coiled or otherwise positioned. The lumen4128may be useful, particularly for percutaneous leads4108, to allow a stylet to be inserted for purposes of pushing and steering the lead4108into the desired position within the patient.

To provide a robust connection for the shield4118, the shield electrode4130such as an electrode ring may be wrapped around the outer layer4120to contact the shield4118and provide a direct current coupling to the shield4118. A direct current coupling between the shields avoids large variations in the characteristic impedance for the shielding from the extension4142to the lead4108. Avoiding variations in the characteristic impedances may reduce the degree of RF reflection that occurs within the shield4118, which in turn reduces the amount of RF heating that may occur via the stimulation electrodes.

The housing4140includes the shield connector4132, such as a set screw block, a Bal Seal® connector, or another spring loaded connector. The shield connector4132of this embodiment is enclosed within a housing layer4134and contacts the shield electrode4130of the lead4108. The housing layer4134may be constructed of various non-conductive materials such as polyurethane, polysulfone, nylon, silicone and polyetheretherketone (PEEK) and provides a relatively rigid structure similar to that provided by the header4106of the IMD4102.

A shield jumper wire4136is included in this embodiment within the housing layer4134. The shield jumper wire4136contacts the shield connector4132and extends from the shield connector4132into the housing layer4134and extends proximally to the shield4144within the extension4142. The shield jumper wire4136may be welded, crimped, or otherwise affixed to the shield conductor4132and the shield4144.

FIG. 17Cshows an example similar to the example ofFIG. 17B. The lead4108is constructed in the same manner. However, the housing4140utilizes a different construction. In the housing4140, a housing shield4138is present and extends to the shield conductor4132where the housing shield4138contacts the shield connector4132. No jumper wire is needed because the housing shield4138establishes continuity of the shielding from the shield connector4132to the shield4144present within the extension4142.

The housing shield4138may be affixed to the shield connector4132in various ways. For instance, the housing shield4138may be welded or crimped to the shield connector4132to provide a direct current coupling. In some embodiments, the shield connector4132is distal relative to stimulation connectors of the housing4140. In those cases, extending the housing shield4138through the housing4140to the shield connector4132provides additional shielding protection from RF induced currents.

FIG. 17Dshows the lead4108coupled to the housing4140with a cross-section through a stimulation electrode coupling for embodiments of the housing4140that include a shield jumper wire4136. The lead4108includes a stimulation connector4150and a stimulation jumper wire4156that interconnects the filar4124to the stimulation connector4150. The housing4140includes a stimulation connector4152that contacts the stimulation connector4150to form a direct current coupling. A stimulation jumper wire4154of the housing4140contacts the stimulation connector4152and extends through the housing layer4134in the proximal direction to a corresponding filar within the extension4142.

As shown inFIG. 17D, both the shield jumper wire4136and the stimulation jumper wire4154are present within the housing layer4134. Separation between them is provided to avoid transferring significant RF energy being captured by the shields4118,4144from the shield jumper wire4136to the stimulation jumper wire4154. For instance, the separation may be in the range of 0.1 millimeters (mm) to 2.0 mm where the housing layer4134is constructed of polyurethane, polysulfone, nylon, and PEEK or has a dielectric property of between about 2 and 10.

FIG. 17Eshows the lead4108coupled to the housing4140with a cross-section through a stimulation connector coupling for embodiments of the housing4140that include the housing shield4138extending through the housing4140. The lead4108includes the stimulation connector4150and the stimulation jumper wire4156that interconnects the filar4124to the stimulation connector4150. The housing4140includes the stimulation connector4152that contacts the stimulation connector4150to form a direct current coupling. The stimulation jumper wire4154of the housing4140contacts the stimulation connector4152and extends in the proximal direction to a corresponding filar within the extension4142.

As shown inFIG. 17E, the housing shield4138and the stimulation jumper wire4154are present within different layers of housing material. The stimulation jumper wire4154is present within a housing inner layer4162while the housing shield4138is present about the housing inner layer4162. A housing outer layer4160surrounds the housing shield4138and the housing inner layer4162. The housing inner layer4162and the housing outer layer4160may be constructed of various non-conductive materials such as those discussed above for the housing layers4134, and these layers4160,4162may be the same or different non-conductive materials. Separation like that discussed above between the stimulation jumper wire4154and the housing shield4138is provided to avoid transferring significant RF energy being captured by the shields4118,4144from the housing shield4138to the stimulation jumper wire4154.

FIG. 17Fshows an embodiment of the housing4140where the shield jumper wire4136is present. The shield jumper wire4136has an attachment point4172such as a weld or crimp to the shield connector4132where the shield electrode4130is seated. The shield jumper wire4136has another attachment point4184such as a weld or crimp to the shield4144of the extension4142.

The stimulation jumper wires4154,4182have attachment points4174,4178such as a weld or crimp to the stimulation connectors4152where the stimulation electrodes4150,4176are seated. Only two stimulation jumper wires4154,4182are shown for purposes of clarity, and it will be appreciated that any number of stimulation connectors and corresponding stimulation jumper wires may be present within the housing4140. As shown, separation is provided between the shield jumper wire4136and the stimulation jumper wires4154,4182to avoid transferring RF energy to the stimulation jumper wires4154,4182.

FIG. 17Gshows an embodiment of the housing4140where the housing shield4138is present. The housing shield4138has attachment points4186such as welds or crimps to the shield connector4132where the shield electrode4130is seated. The housing shield4138continues through the housing out layer4160while surrounding the housing inner layer4162. The housing shield4138transitions to the extension shield4144upon reaching the junction of the housing4140to the body of the extension4142. In other embodiments, the housing shield4138may be attached to the shield4144via welds or crimps rather than transitioning into the body of the extension4142as the shield4144.

The stimulation jumper wires4154,4182have attachment points4174,4178to the stimulation connectors4152where the stimulation electrodes4150,4176are seated. As shown, separation is provided between the housing shield4138and the stimulation jumper wires4154,4182to avoid transferring RF energy to the stimulation jumper wires4154,4182.

Embodiments as disclosed in relation toFIGS. 18-29provide for termination of a radio frequency (RF) shield present within an implantable medical lead for use with an implantable medical device (IMD). The shield may be terminated in various ways such as by terminating at an edge of a butt, scarf, or lap joint to an insulation extension. Furthermore, the shield termination may include features such as a ring attached at the shield termination point within the insulation, shield wires with folded over ends, or barbs between the insulation layers.

FIG. 18shows an example of an implantable medical system5100that includes an IMD5102coupled to a lead5108. The IMD5102includes a metal can5104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD5102includes a header5106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can5104. The header5106is shown transparently for purposes of illustration. The header5106provides a structure for securing the lead5108to the IMD5102and for establishing electrical connectivity between circuitry of the IMD5102and electrodes of the lead5108.

The lead5108includes electrodes5116on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings5110on a proximal end that is positioned within the header5106. The connector rings5110make physical contact with electrical connections5111within the header. The electrical connections5111may include a metal contact that the connector ring5110rests against upon being inserted into the header5106where a wire extends from the metal contact into the can5104where the circuitry is housed. Signals applied by the IMD5102to the connector rings5110are conducted through the lead5108to the electrodes5116to provide the stimulation therapy to the patient.

The lead5108is secured in the header5106such as by a set screw block5112within the header5106that allows at least one set screw5114to be tightened against at least one of the connector rings5110. A shield5118as shown inFIGS. 19A and 19Bmay be grounded to the body along one or more points down the length of the lead from the IMD5102via ground rings and/or the shield5118may be grounded at the can5104of the IMD5102ofFIG. 18. As another option, the shield5118may be located within the lead5108at a small distance from the surface so that the shield5118will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.

Regardless of the manner of grounding, the shield5118terminates on one end near the proximal end and on the opposite end near the distal end of the lead5108. At the termination point, shields having multiple metal wires such as braided shields are subject to fraying and shield wire migration. Preventing the shield wire from fraying and/or migrating to the tissue or to stimulation conductors within the lead5108may be desirable to prevent RF energy captured by the shield5118from being directed onto a small area of tissue via an electrode or exposed shield wire.

FIGS. 19A and 19Bshow an example of the lead5108, where a shield5118is present. An outer insulation layer5120of a lead jacket is shown transparently inFIG. 19Afor purposes of illustrating the shield5118. The shield5118blocks at least some RF energy from directly coupling to conductive filars5124that are present within the lead5108. The conductive filars5124extend the length of the lead and interconnect the proximal electrodes5110to the distal electrodes5116so that stimulation signals are conducted from the proximal end to the distal end of the lead5108.

As shown inFIG. 19A, the shield5118of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield5118, particularly for embodiments where a portion of the shield5118may be exposed for purposes of grounding. While the shield5118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead5108in an overlapping manner or an outer layer5120that is heavily doped with conductive particles.

As shown inFIG. 19B, the shield5118may be embedded within the jacket of the lead5108. One manner of constructing the lead5108with the shield5118is to provide an inner insulation layer5122of the jacket that encloses the filars5124and any additional insulation layer5126, such as polytetrafluoroethylene (PTFE) that may surround each filar5124. The shield5118may then reside on the outer portion of the inner insulation layer5122, and the outer insulation layer5120may then enclose the shield5118. The outer jacket5120maybe added over the braid5118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield5118to RF couple to tissue, typically as a capacitive coupling, either as an alternative to grounding at the can5104of the IMD5102or at specific points along the lead5108or in addition to such grounds, the amount of the outer jacket layer5120covering the shield5118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield5118grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield5118may be located further from the outer surface of the lead5108with additional features of the lead providing the coupling at the one or more specific locations as discussed below.

The inner and outer insulation layers5122,5120of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethane, and silicones. A lumen5128may be included inside of the inner jacket5122around which the insulated filars5124are coiled or otherwise positioned. The lumen5128may be useful, particularly for percutaneous leads5108, to allow a stylet to be inserted for purposes of pushing and steering the lead5108into the desired position within the patient.

FIG. 20shows an embodiment of an implantable medical lead5108in cross-section with a cut taken down an axial centerline. The lead5108terminates at a butt joint5130where the inner insulation layer5122, shield5118, and outer insulation layer5120terminate. At this butt joint5130, an insulation extension5132abuts and is bonded via RF heating, thermal, reflow, or similar processes to the blunt ends of the inner insulation layer5122, outer insulation layer5120, and shield5118.

As shown in this example, the shield5118terminates at the butt joint5130rather than farther back within the jacket formed by the inner and outer insulation layers5122,5120. The insulation extension5132in this example extends the remainder of the lead5108where ring electrodes5134are located. The filars5124jumper to their respective ring electrodes via a filar jumper5136. The lumen may be present with the filars5124being located about the lumen.

The material for the insulation extension5132may be selected to provide more or less stiffness than the inner and outer insulation layers5122,5120, depending upon which end of the lead the butt joint5130is located. For instance, where the electrode5134is on the proximal end of the lead5108and is being positioned within the header5106of the IMD5102, the insulation extension5132may be constructed of a stiffer material. Where the electrode5134is on the distal end of the lead5108and is being steered to the stimulation site within the body, the insulation extension5132may be constructed of a more flexible material.

Using a stiffer material as the insulation extension5132on the proximal end aids in the insertion of the proximal end into the header5106. As a particular example, the outer insulation5120may be constructed of polyurethane having a durometer 55 D or similar rating while the insulation extension5132may be constructed of a polyurethane having a durometer 75 D or similar rating.

Using a less stiff material as the insulation extension5132on the distal end aids in the positioning of the distal end at the stimulation site. As a particular example, the outer insulation5120may be constructed of polyurethane having a durometer 55 D or similar rating while the insulation extension5132may be constructed of polyurethane having a durometer 80 A or similar rating.

The gap between the termination of the shield5118at the butt joint5130and the nearest edge of the electrode5134is selected to avoid RF problems. In particular, the distance is selected so that RF coupling is avoided while the unshielded region of the filars5124is not overly exposed to RF. For MRI frequencies that typically range from 43 MHz to 128 MHz, a spacing of from 0.5 mm to 10 cm may be acceptable for these embodiments.

FIG. 21shows another embodiment of an implantable medical lead5108in cross-section with a cut taken down an axial centerline. The lead5108terminates at a scarf joint5140where the inner insulation layer5122, shield5118, and outer insulation layer5120terminate at a wedged cut. At this scarf joint5140, an insulation extension5132that has a complementary wedged cut abuts and is bonded to the wedged end of the inner insulation layer5122, outer insulation layer5120, and shield5118via RF heating, thermal, reflow or similar processes.

The scarf joint5140may be used rather than the butt joint5130ofFIG. 20because the scarf joint5140increases the bonding area. As shown in this example, the shield5118terminates at the scarf joint5140rather than farther back within the jacket formed by the inner and outer insulation layers5122,5120. The insulation extension5132in this example extends the remainder of the lead5108where ring electrodes5134are located. The filars5124jumper to their respective ring electrodes via a filar jumper5136.

Similar to the previous embodiment ofFIG. 20, the material for the insulation extension5132in this embodiment ofFIG. 4may be selected to provide more or less stiffness than the inner and outer insulation layers5122,5120, depending upon which end of the lead the scarf joint5140is located. For instance, where the electrode5134is on the proximal end of the lead5108and is being positioned within the header5106of the IMD5102, the insulation extension5132may be constructed of a stiffer material such as polyurethane with a durometer 75 D. Where the electrode5134is on the distal end of the lead5108and is being steered to the stimulation site within the body, the insulation extension5132may be constructed of a more flexible material such as polyurethane with a durometer 80 A.

The gap between the termination of the shield5118at the butt joint5130and the nearest electrode5134is selected to avoid RF problems. In particular, the distance is selected so that RF coupling is avoided while the unshielded region of the filars5124is not overly exposed to RF. For MRI frequencies that typically range from 43 MHz to 128MHz, spacing between the edge of the electrode5134nearest the scarf joint5140and the termination of the shield5118at the scarf joint5140may range from 0.5 mm to 10 cm for these embodiments. With the scarf joint5140ofFIG. 21, the spacing between the termination of the shield5118and the electrode5134varies for different locations around the circumference of the scarf joint5140, but the shortest spacing is maintained at 0.5 mm or above and the longest spacing is maintained at 10 cm or below.

FIG. 22shows a set of steps to create the embodiments ofFIGS. 20 and 21. Initially, a structure including the inner insulation layer5122, outer insulation layer5120, and shield5118may be provided. The shield5118has been braided over the inner insulation layer5122and then the outer insulation layer5120has been positioned and reflowed or otherwise bonded over the inner insulation layer5122and the shield5118. To begin construction of the lead5108and the butt joint5130or scarf joint5140, the structure is cut to size by making a cut through the insulation layers5120,5122and the shield5118at a cutting step5142. For a butt joint5130, the cut is perpendicular to the axial dimension to create the blunt end. For a scarf joint5140, the cut is at angle other than 90 degrees to the axial dimension to create the wedged end.

The insulation extension5132is also provided with a complementary end to bond to the lead5108to form the butt joint5130or scarf joint5140. For the butt joint5130, the insulation extension5132is cut perpendicular to the axial dimension to create the blunt end. For the scarf joint5140, the insulation extension5132is cut at an angle other than 90 degrees to the axial dimension to create the wedged end. The two blunt ends for the butt joint5130are brought together and bonded at a bonding step5144. Likewise, the two wedged ends for the scarf joint5140are brought together and bonded at the bonding step5144.

FIG. 23shows another embodiment of an implantable medical lead5108in cross-section with a cut taken down an axial centerline. The lead5108terminates at a lap joint5150. The lap joint5150involves removing an end portion of the outer insulation layer5120and applying a replacement outer insulation layer5152onto the area of the shield5118and inner insulation layer5122where the outer insulation layer5120is missing. The replacement outer insulation layer5152also laps over a section of the insulation extension5132and may extend to the nearest electrode5134.

As shown, the shield5118has been crimped down into the inner insulation layer5122at the region where the outer insulation layer5120has been removed. Doing so prevents the shield5118from bunching together during installation of the outer replacement insulation layer5152. This may be especially the case where the replacement outer insulation layer5152is in the form of tubing that slides into place over the shield5118and inner insulation layer5122prior to attaching the insulation extension5132. Where the replacement outer insulation layer5152is tubing, once being slid into place, it is reflowed or otherwise bonded to the inner insulation layer5122. As an alternative, the replacement outer insulation layer5152may be injection molded into place.

As shown in this example, the shield5118terminates at the lap joint5150rather than farther back within the jacket formed by the inner and outer insulation layers5122,5120. The insulation extension5132in this example extends the remainder of the lead5108where ring electrodes5134are located. The filars5124jumper to their respective ring electrodes via a filar jumper5136. The lumen may be present in some embodiments with the filars5124being located about the lumen.

In this embodiment the replacement outer insulation layer5152may be constructed of a material that differs in stiffness from the outer insulation layer5120depending upon which end of the lead5108the lap joint5150is located. For instance, where the electrode5134is on the proximal end of the lead5108and is being positioned within the header5106of the IMD5102, the replacement outer insulation layer5152may be constructed of a stiffer material such as durometer 75 D polyurethane. Where the electrode5134is on the distal end of the lead5108and is being steered to the stimulation site within the body, the replacement outer insulation layer5152may be constructed of a more flexible material such as 80 A polyurethane.

In this embodiment, like that of the previous ones, the material for the insulation extension5132may also be selected to provide more or less stiffness than the inner and outer insulation layers5122,5120, depending upon which end of the lead the lap joint5150is located. For instance, where the electrode5134is on the proximal end of the lead5108and is being positioned within the header5106of the IMD5102, the insulation extension5132may be constructed of a stiffer material such as durometer 75 D polyurethane. Where the electrode5134is on the distal end of the lead5108and is being steered to the stimulation site within the body, the insulation extension5132may be constructed of a more flexible material such as 80 A polyurethane.

The gap between the termination of the shield5118at the lap joint5150and the nearest electrode5134is also selected to avoid RF problems. For MRI frequencies, a spacing of from 0.5 mm to 10 cm may be acceptable for these embodiments.

FIG. 24shows one example of a set of steps that create the lap joint5150ofFIG. 23. Initially, a structure including the inner insulation layer5122, outer insulation layer5120, and shield5118may be provided. The shield5118has been braided over the inner insulation layer5122and then the outer insulation layer5120has been positioned and reflowed or otherwise bonded over the inner insulation layer5122and the shield5118. To begin construction of the lead5108and the lap joint5150, the structure is cut to size by making a cut through the insulation layers5120,5122and the shield5118at a cutting step5154. For a lap joint5150, this first cut is perpendicular to the axial dimension to create a blunt end.

Once cut to size, the outer insulation layer5120is then ablated by some distance to expose the shield5118and the inner insulation layer5122at an ablating step5156. Ablation may be done using tools such as an excimer laser which can very precisely ablate to expose the shield5118. The length of the outer insulation layer5120to be ablated may vary, but an illustrative range is from 0.25 centimeters (cm) to 5 cm.

Once ablation is complete, the next step may vary. The replacement outer insulation layer5152may be installed in various manners such as by reflowing tubing or by injection molding. If by injection molding, then the next step may be either a crimping step5158or an injecting step5162. If by reflowing tubing, then it may be helpful to proceed to the crimping step5158after ablating.

At the crimping step5158, the shield5118is crimped so as to sink down into the inner insulation layer5122at the area where the outer insulation layer5120has been removed. If a ring or other tool is used to crimp the shield5118into the inner insulation layer5122, the ring or other tool may then be removed. Where the replacement outer insulation layer5152is being installed as tubing that is reflowed, then the next step is tubing step5160. Where the replacement outer insulation layer5152is being installed by injection molding, then the next step is injecting step5162.

At the tubing step5160, the tubing is slid onto the inner insulation layer5122and over the shield5118at the area where the outer insulation layer5120has been removed and where the shield5118has been crimped down. The tubing extends beyond the end of the inner insulation layer5122so that it may eventually be bonded to the insulation extension5132. The tubing is reflowed, RF heated, etc. to bond to the inner insulation layer5122and to the end of the outer insulation layer5120where the ablating stopped to form the replacement outer insulation layer5152. Contemporaneously or sequentially, the insulation extension5132is bonded in place at the blunt end of the inner insulation layer5122and to the tubing of the replacement outer insulation layer5152that extends beyond the inner insulation layer5122at a bonding step5164. This tubing may be reflowed, RF heated, etc. onto the insulation extension5132.

Returning to the injecting step5162, in the scenario where the replacement outer insulation layer5152is to be injection molded, then the injecting step5126takes place either after the ablating step5156or after the crimping step5158. Material such as the desired polyurethane is injected onto the inner insulation layer5122and the shield5118to form the replacement outer insulation layer5152. Contemporaneously, the insulation extension5132is bonded to the inner insulation layer5122and to the replacement outer insulation layer5152at the bonding step5164.

Alternative manners of creating the lap joint5150may also be used. For instance, the structure of the outer insulation layer5120, inner insulation layer5122, and shield5118may be bonded to the insulation extension5132via a butt joint. Then, the area where the replacement outer insulation layer5152will be positioned that is currently occupied by the outer insulation layer5120is ablated. The insulation extension5132is also ablated at the same or similar depth as the outer insulation layer5120. The replacement outer insulation layer5152may then be injection molded or shrunk into position at the ablation site.

FIG. 25shows an embodiment with an additional feature that may be included for the lap joint5150. To further protect the termination of the shield5118from fraying or migrating, the wire ends of the shield5118may be capped with a ring5166. The ring5166may be metal, plastic, or similar materials. In this example, a region5168of the inner insulation layer5122has been ablated to allow the ring to be positioned over the ends of the wires of the shield5118.

FIG. 26shows an embodiment with an additional feature that may be included for the butt or scarf joints5130,5140. To further protect the termination of the shield5118from fraying or migrating, the wire ends of the shield5118may be capped with a ring5170. Similar to the lap joint scenario, the ring5170may be metal, plastic, or similar materials. In this example, a region5172of the outer insulation layer5120has been ablated to allow the ring5170to be positioned over the ends of the wires of the shield5118, and then this region5172may be filled using a reflow or injection molding of the polyurethane or other polymer.

FIG. 27shows an embodiment with an additional feature that may be included for a joint5176, which may be of various types such as the butt, scarf, or lap joints5130,5140, and5150. At the joint5176, the outer insulation layer5120of the lead5108encounters another layer5178. This layer5178may be the insulation extension5132and/or the replacement outer insulation layer5152. In either case, wires of the shield5118may partially extend into the layer5178. However, prior to bonding the layer5178to the layers5120or5122, the ends of the wires of the shield5118may be individually folded over as shown inFIG. 27. In this manner, the folded over ends are less likely to fray and migrate.

FIG. 28shows an embodiment with another feature that may be included for a joint at the termination of the shield5118to assist in holding the bond between the inner insulation layer5122and the insulation extension5132in place. In this example, a lap joint5150is shown, but it will be appreciated that this feature may be applicable to other joints as well including butt and scarf joints5130,5140. Here, the replacement outer insulation layer5152may be tubing that is provided with barbs5151that extend toward the inner insulation layer5122and the shield5118.

During reflow, the barbs may sink into the inner insulation layer5122as the inner insulation layer5122softens more so than the barbs5151, and the replacement outer insulation layer5152descends into position. The barbs5151may also sink into the insulation extension5132once reflow or other bonding is attempted after the insulation extension5132has been inserted to provide extra grip between the replacement outer insulation layer5152and the insulation extension5132. The barbs5151then provide extra grip between the inner insulation layer5122and the insulation extension5132particularly during axial tension. Rather than incorporating the barbs into the replacement outer tubing5152of the lap joint example, a separate barbed ring may be positioned on the inner insulation layer5122and then the replacement outer insulation layer5152is reflowed or otherwise bonded into place.

FIG. 29shows an embodiment with another feature that may be included for a joint at the termination of the shield5118to assist in holding the bond between the inner insulation layer5122and the insulation extension5132in place. In this example, a lap joint5150is shown, but it will be appreciated that this feature may be applicable other joints as well including butt and scarf joints5130,5140. Here, a barbed ring5153is positioned inside of the inner insulation layer5122and is forced to expand radially until the barbs of the barbed ring5153sink into the inner insulation layer5122. The barbs of the barbed ring5153may also sink into the inside of the insulation extension5132. The barbed ring5153provides extra grip between the inner insulation layer5122and the insulation extension5132especially during axial tension. This barbed ring5153feature may also be used in conjunction with the barbs5151shown inFIG. 28.

Embodiments as disclosed in relation toFIGS. 30-48also provide for termination of a radio frequency (RF) shield present within an implantable medical lead for use with an implantable medical device (IMD). The shield may be terminated in various ways such as by terminating at a joint to an insulation extension where one or more metal connectors are present in various configurations to provide a ground path for the shield. Furthermore, the shield termination may include features such as a shield wires with folded over ends, or barbs between the insulation layers.

FIG. 30shows an example of an implantable medical system6100that includes an IMD6102coupled to a lead6108. The IMD6102includes a metal can6104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD6102includes a header6106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can6104. The header6106is shown transparently for purposes of illustration. The header6106provides a structure for securing the lead6108to the IMD6102and for establishing electrical connectivity between circuitry of the IMD6102and electrodes of the lead6108.

The lead6108includes electrodes6116on a distal end that are positioned at a stimulation site within a patient. The lead also includes ring connectors6110on a proximal end that is positioned within the header6106. The ring connectors6110make physical contact with electrical connections6111within the header. The electrical connections6111may include a metal contact that the ring connector6110rests against upon being inserted into the header6106where a wire extends from the metal contact into the can6104where the circuitry is housed. Signals applied by the IMD6102to the ring connectors6110are conducted through the lead6108to the electrodes6116to provide the stimulation therapy to the patient.

The lead6108is secured in the header6106such as by a set screw block6112within the header6106that allows at least one set screw6114to be tightened against at least one of the ring connectors6110. A shield6118as shown inFIGS. 31A and 31Bmay be grounded to the body along one or more points down the length of the lead from the IMD6102via ground rings and/or the shield6118may be grounded at the can6104of the IMD6102ofFIG. 30.

Regardless of the manner of grounding, the shield6118terminates on one end near the proximal end and on the opposite end near the distal end of the lead6108. At the termination point, shields having multiple metal wires such as braided shields are subject to fraying and shield wire migration. Preventing the shield wire from fraying and/or migrating to the tissue or to stimulation conductors within the lead6108may be desirable to prevent RF energy captured by the shield6118from being directed onto a small area of tissue via an electrode or exposed shield wire.

FIGS. 31A and 31Bshow an example of the lead6108, where a shield6118is present. An outer insulation layer6120of a lead jacket is shown transparently inFIG. 31Afor purposes of illustrating the shield6118. The shield6118blocks at least some RF energy from directly coupling to conductive filars6124that are present within the lead6108. The conductive filars6124extend the length of the lead and interconnect the proximal ring connectors6110to the distal electrodes6116so that stimulation signals are conducted from the proximal end to the distal end of the lead6108.

As shown inFIG. 31A, the shield6118of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield6118, particularly for embodiments where a portion of the shield6118may be exposed for purposes of grounding. While the shield6118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead6108in an overlapping manner or an outer layer6120that is heavily doped with conductive particles.

As shown inFIG. 31B, the shield6118may be embedded within the jacket of the lead6108. One manner of constructing the lead6108with the shield6118is to provide an inner insulation layer6122of the jacket that encloses the filars6124and any additional insulation layer6126, such as polytetrafluoroethylene (PTFE) that may surround each filar6124. The shield6118may then reside on the outer portion of the inner insulation layer6122, and the outer insulation layer6120may then enclose the shield6118. The outer insulation layer6120may be added over the shield6118and shrunk in place or may be extruded over the shield6118. The outer jacket6120maybe added over the braid6118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield6118to RF couple to tissue, typically as a capacitive coupling, in addition to grounding at the can or along the lead, the amount of the outer jacket layer6120covering the shield6118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield6118grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield6118may be located further from the outer surface of the lead6108.

The inner and outer insulation layers6122,6120of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. A lumen6128may be included inside of the inner jacket6122around which the insulated filars6124are coiled or otherwise positioned. The lumen6128may be useful, particularly for percutaneous leads6108, to allow a stylet to be inserted for purposes of pushing and steering the lead6108into the desired position within the patient.

FIG. 32shows an embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108includes a butt joint6130where the inner insulation layer6122and shield6118terminate. The outer insulation6120terminates prior to the butt joint6130to expose the shield6118and inner insulation layer6122. A metal connector6131is positioned over the shield6118and inner insulation layer6122and abuts the end of the outer insulation layer6120. At the butt joint6130, an insulation extension6132abuts and is bonded to the blunt end of the inner insulation layer6122, shield6118, and metal connector6131such as via reflow or injection molding.

As shown in this example, the shield6118terminates at the butt joint6130rather than farther back within the jacket formed by the inner and outer insulation layers6122,6120. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located on the proximal end at a separate from the nearest connector ring ranging from about 0.5 millimeters to about 10 centimeters. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The material for the insulation extension6132may be selected to provide a different amount of stiffness than the inner and outer insulation layers6122,6120. For instance, the insulation extension6132may be constructed of a stiffer material to aid in the insertion of the proximal end into the header6106. As a particular example, the outer insulation6120may be constructed of polyurethane having a durometer 55 D or similar rating while the insulation extension6132may be constructed of a polyurethane having a durometer 75 D or similar rating.

The shield6118may be terminated with an exposed metal connector6131at a butt joint on the distal end so long as no terminating ground ring is present at the proximal end to thereby avoid stimulation induced by magnetic gradients. In such a case, the insulation extension may have a durometer rating similar to the outer layer6120but may instead be constructed of polyurethane having a durometer 80 A or similar rating.

The metal connector6131is separated from the distal electrode by at least 0.5 mm up to 10 cm for some body locations, to avoid excessive RF coupling to the distal electrode, with 2 mm being one example of spacing that provides adequate filar coverage with insignificant coupling to the distal electrode. Where the distal end is located in a high RF intensity area such as just under the skin for peripheral nerve stimulation, then the distance may be kept smaller, such as less than 2 cm to avoid overexposure of the filars6124.

FIG. 33shows another embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108terminates at a scarf joint6140where the inner insulation layer6122and shield6118terminate at a wedged cut. The outer insulation6120terminates prior to the scarf joint6140to expose the shield6118and inner insulation layer6122. A metal connector6131is positioned over the shield6118and inner insulation layer6122and abuts the end of the outer insulation layer6120. At this scarf joint6140, an insulation extension6132that has a complementary wedged cut abuts and is bonded to the wedged end of the inner insulation layer6122, shield6118, and metal connector6131such as via reflow or injection molding.

The scarf joint6140may be used rather than the butt joint6130ofFIG. 32because the scarf joint6140has an increased bond area. As shown in this example, the shield6118terminates at the scarf joint6140rather than farther back within the jacket formed by the inner and outer insulation layers6122,6120. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located on the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136.

Similar to the previous embodiment ofFIG. 32, the material for the insulation extension6132in this embodiment ofFIG. 33may be selected to provide a different stiffness than the inner and outer insulation layers6122,6120. For instance, the insulation extension6132may be constructed of a stiffer material such as polyurethane with a durometer 75 D.

The metal connector6131may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connector6131to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 34shows a set of steps to create the embodiments ofFIGS. 32 and 33. Initially, a structure including the inner insulation layer6122, outer insulation layer6120, and shield6118may be provided. The shield6118has been braided over the inner insulation layer6122and then the outer insulation layer6120has been positioned and reflowed or otherwise bonded over the inner insulation layer6122and the shield6118. To begin construction of the lead6108and the butt joint6130or scarf joint6140, the structure is cut to size by making a cut through the insulation layers6120,6122and the shield6118at a cutting step6142. For a butt joint6130, the cut is perpendicular to the axial dimension to create the blunt end. For a scarf joint6140, the cut is at angle other than 90 degrees to the axial dimension to create the wedged end.

The end portion of the outer insulation layer6120is ablated to reveal the shield6118at ablating step6144. The metal connector6131, such as a ring connector, may then be crimped or welded onto the shield6118at crimping step6146.

The insulation extension6132is bonded to the lead6108to form the butt joint6130or scarf joint6140at a bonding step6148. For the butt joint6130, the insulation extension6132is cut perpendicular to the axial dimension to create the blunt end. For the scarf joint6140, the insulation extension6132is cut at an angle other than 90 degrees to the axial dimension to create the wedged end. The two blunt ends for the butt joint6130are brought together and bonded at a bonding step6148. Likewise, the two wedged ends for the scarf joint6140are brought together and bonded at the bonding step6148.

FIG. 35shows another embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108includes a lap joint6150where the inner insulation layer6122and the shield6118terminate. The lap joint6150involves removing an end portion of the outer insulation layer6120sufficient to allow space for the metal connector6131and a replacement outer insulation layer6152to lap over the area of the shield6118and inner insulation layer6122where the outer insulation layer6120is missing. The metal connector6131abuts the end of the outer insulation layer6120. The replacement outer insulation layer6152abuts the metal connector6131, laps over a section of the insulation extension6132, and may extend to the nearest electrode6134.

As shown, the shield6118has been crimped down into the inner insulation layer6122at the region where the outer insulation layer6120has been removed. Doing so prevents the shield6118from bunching together during installation of the outer replacement insulation layer6152. This may be especially the case where the replacement outer insulation layer6152is in the form of tubing that slides into place over the shield6118and inner insulation layer6122prior to attaching the insulation extension6132. Where the replacement outer insulation layer6152is tubing, once being slid into place, it is reflowed or otherwise bonded to the inner insulation layer6122. As an alternative, the replacement outer insulation layer6152may be injection molded into place.

As shown in this example, the shield6118terminates at the lap joint6150rather than farther back within the jacket formed by the inner and outer insulation layers6122,6120. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

In this embodiment the replacement outer insulation layer6152may be constructed of a material that differs in stiffness from the outer insulation layer6120. For instance, the replacement outer insulation layer6152may be constructed of a stiffer material such as durometer 75 D polyurethane. In this embodiment, like that of the previous ones, the material for the insulation extension6132may also be selected to provide a different stiffness than the inner and outer insulation layers6122,6120. For instance, the insulation extension6132may also be constructed of a stiffer material such as durometer 75 D polyurethane.

The metal connector6131may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connector6131to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 36shows one example of a set of steps that create the lap joint6150ofFIG. 35. Initially, a structure including the inner insulation layer6122, outer insulation layer6120, and shield6118may be provided. The shield6118has been braided over the inner insulation layer6122and then the outer insulation layer6120has been positioned and reflowed or otherwise bonded over the inner insulation layer6122and the shield6118. To begin construction of the lead6108and the lap joint6150, the structure is cut to size by making a cut through the insulation layers6120,6122and the shield6118at a cutting step6154. For a lap joint6130, this first cut is perpendicular to the axial dimension to create a blunt end.

Once cut to size, the outer insulation layer6120is then ablated by some distance to expose the shield6118and the inner insulation layer6122at an ablating step6156. Ablation may be done using tools such as an excimer laser which can very precisely ablate to expose the shield6118. The length of the outer insulation layer6120to be ablated is sufficient to allow for the metal connector6131as well as the amount of the replacement outer insulation layer6152that laps onto the inner insulation layer6122. This length of ablation of the outer insulation layer6120may vary but an illustrative range is from 0.25 centimeters (cm) to 5 cm.

Once ablation is complete, the metal connector6131may then be put in position over the inner insulation layer6122and shield6118. The metal connector6131is crimped or welded to the shield6118while abutting the end of the outer insulation layer6120at a crimping step6158.

Once the metal connector6131is installed, the next step may vary. The replacement outer insulation layer6152may be installed in various manners such as by reflowing tubing or by injection molding. If by injection molding, then the next step may be either a crimping step6160or an injecting step6164. If by reflowing tubing, then it may be helpful to proceed to the crimping step6160after ablating.

At the crimping step6160, the portion of the shield6118that is exposed beyond the metal connector6131is crimped so as to sink down into the inner insulation layer6122. If a ring or other tool is used to crimp the shield6118into the inner insulation layer6122, the ring or other tool may then be removed. Where the replacement outer insulation layer6152is being installed as tubing that is reflowed, then the next step is tubing step6162. Where the replacement outer insulation layer6152is being installed by injection molding, then the next step is injecting step6164.

At the tubing step6162, the tubing is slid onto the inner insulation layer6122and over the shield6118at the area where the outer insulation layer6120has been removed and where the shield6118has been crimped down. The tubing extends beyond the end of the inner insulation layer6122so that it may eventually be bonded to the insulation extension6132. The tubing is reflowed or otherwise bonded to the inner insulation layer6122and to abut the end of the metal connector6131. Contemporaneously, the insulation extension6132is bonded in place at the blunt end of the inner insulation layer6122and to the tubing of the replacement outer insulation layer6152that extends beyond the inner insulation layer6122at a bonding step6166. This tubing may be reflowed or otherwise bonded onto the insulation extension6132.

Returning to the injecting step6164, in the scenario where the replacement outer insulation layer6152is to be injection molded, then the injecting step6164takes place either after the crimping step6158or after the crimping step6160. Material such as the desired polyurethane is injected onto the inner insulation layer6122and the shield6118to form the replacement outer insulation layer6152. Contemporaneously, the insulation extension6132is bonded to the inner insulation layer6122and to the replacement outer insulation layer6152at the bonding step6166.

Alternative manners of creating the lap joint6150may also be used. For instance, the structure of the outer insulation layer6120, inner insulation layer6122, and shield6118may be bonded to the insulation extension6130via a butt joint. Then, the area where the metal connector6131and replacement outer insulation layer6152will be positioned that is currently occupied by the outer insulation layer6120is ablated. The insulation extension6132is also ablated at the same or similar depth as the outer insulation layer6120. The metal connector6131may then be positioned, and the replacement outer insulation layer6152may then be injection molded or shrunk into position at the ablation site.

FIG. 37shows another embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108includes a joint between the inner insulation layer6122and the insulation extension6132where the inner insulation layer6122and the shield6118terminate. An inner metal connector6172is positioned around the inner insulation layer and an outer metal connector6174is positioned around the inner metal connector6172. A portion of the shield6118is located between the inner metal connector6172and the outer metal connector6174such that a robust physical and electrical connection is established to the shield6118.

In this example, the shield6118is braided after the inner metal connector6172has been positioned so that the braid of the shield6118laps over the inner metal connector6172. The outer insulation layer6120terminates short of the end of the shield6118and inner insulation layer6122. This may be achieved by ablating the outer insulation layer6120where it has been previously extruded over the shield and inner metal connector6172.

As shown in this example, the shield6118terminates between the metal connectors6172,6174rather than farther back within the jacket formed by the inner and outer insulation layers6122,6120. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connectors6172,6174may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connectors6172,6174to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above for connector ring6131.

FIG. 38shows an alternative manner of attaching the outer metal connector. Rather than ablate the outer insulation layer6120at the area where the shield6118and inner metal connector6172are located, an outer metal connector6176having features such as teeth that can penetrate through the outer insulation layer6120is used. The outer metal connector6176is crimped in place so that the features penetrate through the outer insulation layer6120to reach the shield6118and the inner metal connector6172and establish the physical and electrical connection.

FIG. 39shows a similar embodiment to that ofFIG. 37where the lead includes the inner metal connector6172and the outer metal connector6174. However, in this example, the shield6118does not terminate between the metal connectors6172,6174but a portion6119of the shield6118continues beyond those connectors6172,6174to extend over the remaining portion of the inner insulation layer6122. This portion6119of the shield6118may be crimped into a sunken position within the inner insulation layer6122.

A replacement outer insulation layer6152may be bonded over the portion6119of the shield6118to form a lap joint. The insulation extension6132may then be bonded to the inner insulation layer6122and the replacement outer insulation layer6152. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connectors6172,6174may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connectors6172,6174as well as any portion of the shield6118extending beyond the metal connectors6172,6174to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 40shows a similar embodiment to that ofFIG. 37where the lead includes the inner metal connector6172and the outer metal connector6174. However, in this example, the inner metal connector6172does not wrap around the outside of the inner insulation layer6122but instead is embedded within the inner insulation layer6122so as to provide a flush surface for the shield6118to be braided upon. The shield6118is located between this inner metal connector6172and the outer metal connector6174. In this example, the metal connectors6172,6174together with the inner insulation layer6122form a butt joint with the insulation extension6132.

The insulation extension6132is bonded to the inner insulation layer6122and abuts the metal connectors6172,6174. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connectors6172,6174may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connectors6172,6174to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 41shows one example of a set of steps that create the shield termination ofFIGS. 37-40. The inner metal connector6172is positioned on the inner insulation layer6122or embedded at the end at a connector step6182. The shield6118is braided onto the inner insulation layer6122and over the inner metal connector6172at a braiding step6184. The outer insulation layer6120is bonded by reflow or another process onto the inner insulation layer6122over the shield6118and over the inner metal connector6172such as by a reflowing step6186.

At this point, preparation is made for the outer metal connector6174. In one example, the outer insulation layer is ablated at an ablating step6188and then the outer metal connector is crimped or welded onto the exposed shield6118at the overlap to the inner metal connector6172at a crimping step6190. Alternatively, the inner metal connector6176having the sharp features is crimped onto the outer insulation layer6120with the sharp features penetrating to the shield6118and the inner metal connector6172at a crimping step6192. The insulation extension6132is then bonded to the inner insulation layer6122at a bonding step6194.

FIG. 42shows a similar embodiment to that ofFIG. 37where the lead includes the inner metal connector6172and the outer metal connector6174. However, in this example, the inner metal connector6172does not wrap around the outside of the inner insulation layer6122prior to the shield6118being braided. Instead, the shield6118is braided over the inner insulation layer6122and the inner metal connector6172is then crimped or welded onto the shield6118. The shield6118may be sunken into the inner insulation layer6122in the area where the inner metal connector6172is positioned.

The shield6118inverts as a whole at an inversion6123so that a portion6121of the shield6118laps over the inner metal connector6172. The outer metal connector6174may then be crimped or welded in placed about the portion6121and the inner metal connector6172. A robust electrical and physical termination of the shield6118occurs between the metal connectors6172,6174. The inversion6123may provide additional benefits for the shield6118, such as reducing any RF energy leakage that might otherwise occur at a blunt end of the shield6118.

The insulation extension6132is bonded to the inner insulation layer6122and abuts the metal connectors6172,6174. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connectors6172,6174may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connectors6172,6174to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 43shows one example of a set of steps that create the shield termination ofFIG. 42. The outer insulation layer6120, inner insulation layer6122, and shield6118are cut to form a blunt end at a cutting step6202. A portion of the outer insulation layer6120is then ablated to reveal the shield6118and inner insulation layer6122at an ablating step6204. The inner metal connector6172is positioned on the shield6118and around the inner insulation layer6122with a portion of the shield6118and the inner insulation layer6122extending beyond the metal connector6172at a connector step6206. The shield6118is inverted as a whole and lapped onto the inner metal connector at a folding step6208.

At this point, the outer metal connector is crimped or welded onto the exposed shield6118at the overlap to the inner metal connector6172at a crimping step6210. Alternatively, the outer metal connector6176having the sharp features is crimped onto the outer insulation layer6120with the sharp features penetrating to the shield6118and the inner metal connector6172. The insulation extension6132is then bonded to the inner insulation layer6122at a bonding step6212.

FIG. 44shows another embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108includes a joint between the inner insulation layer6122and the insulation extension6132where the inner insulation layer6122terminates. In this example, the shield6118does not remain braided upon the inner insulation layer6122. Instead, a metal connector6131is positioned on the inner insulation layer6122and a portion6125of the shield6118is braided onto the metal connector6131. The outer insulation layer6120is positioned over the braid6118up to the metal connector6131where the braid6118exits the outer insulation layer6120when lapping onto the metal connector6131.

The portion6125may be exposed outside of the lead6108as a result of lapping onto the metal connector6131. However, for embodiments where the metal connector6131is for insertion into the header6106of the IMD6102, the exposure may occur immediately at the exit to the header6106or nearby the header seal. To the extent tissue in-growth is to be avoided in that area, an insulation ring6216of material the same as or similar to the outer insulation layer6120may be reflowed or otherwise bonded over the portion6125.

As shown in this example, a replacement outer insulation layer6152may be present to form a lap joint between the inner insulation layer6122and the insulation extension6132. The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connector6131may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connector6131to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 45shows one example of a set of steps that create the shield termination ofFIG. 44. The metal connector6131is positioned on the inner insulation layer6122at a connector step6220. The shield6118is braided onto the inner insulation layer6122and over the metal connector6131at a braiding step6222. The outer insulation layer6120is bonded by reflow or another process onto the inner insulation layer6122over the shield6118up to the metal connector6131such as by a reflowing step6224. The insulation ring6216may then be reflowed or injection molded over the braid portion6125on the metal connector6131at a bonding step6226.

FIG. 46shows another embodiment of an implantable medical lead6108in cross-section with a cut taken down an axial centerline. The lead6108includes a joint between the inner insulation layer6122and the insulation extension6132where the inner insulation layer6122terminates. In this example, the shield6118does not remain braided upon the inner insulation layer6122. Instead, a tapered ablation is created through the outer insulation layer6120and inner insulation layer6122and the shield6118exits the outer insulation layer6120and separates from the inner insulation layer6122at the taper.

A metal connector6232with a threaded taper6234is threaded onto the taper of the inner and outer insulation layers6122,6120. The threaded taper6234bites into the inner and outer insulation layers6122,6120to provide a sturdy physical connection. The shield6118passes through the metal connector6232to an opposite side where an opposite taper is present. There, the shield6118terminates while being positioned firmly between the taper of the metal connector6232and a taper of an inner metal connector6236that is positioned about the insulation extension6132.

The insulation extension6132in this example extends the remainder of the lead6108where ring connectors6134are located at the proximal end. The filars6124jumper to their respective ring connectors via a filar jumper6136. The lumen may be present in some embodiments with the filars6124being located about the lumen.

The metal connectors6232,6236may be included on either the proximal or distal end to terminate the shield6118as discussed above. The separation of the metal connectors6232,6236to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.

FIG. 47shows one example of a set of steps that create the shield termination ofFIG. 46. The inner metal connector6236is positioned at the end of the inner insulation layer6122at a connector step6242. The shield6118is braided onto the inner insulation layer6122and over the inner metal connector6236at a braiding step6244. The outer insulation layer6120is bonded by reflow or another process onto the inner insulation layer6122over the shield6118such as by a reflowing step6246.

The inner and outer insulation layers6122,6120are ablated to form the taper and expose the shield6118at an ablating step6248. The outer metal connector6232is then placed into position over the inner metal connector6236and the taper of the inner and outer insulation layers6122,6120at a connector step6250. Here, the outer metal connector6232may be turned relative to the inner and outer insulation layers6122,6120to sink the threaded taper6234into the inner and outer insulation layers6122,6120while the outer metal connector6232firmly contacts the shield6118positioned against the inner metal connector6236. The outer metal connector6232may be crimped or welded into place over the shield6118and the inner metal connector6236.

FIG. 48shows an embodiment with an additional feature that may be included for a joint6276, which may be of various types such as the butt, scarf, or lap joints6130,6140, and6150. At the joint6276, the outer metal connector6131,6174of the lead6108encounters another layer6278. This layer6278may be the insulation extension6132and/or the replacement outer insulation layer6152. In either case, wires of the shield6118may partially extend into the layer6278. However, prior to bonding the layer6278to the layer6122, the ends of the wires of the shield6118may be individually folded over at areas6274as shown inFIG. 48. In this manner, the folded over ends are less likely to fray and migrate.

Embodiments as disclosed in relation toFIGS. 49-58provide for rotation of a stylet within a lumen of an implantable medical lead by applying rotation directly to the implantable medical lead. The implantable medical lead has torsional stiffness and is rotationally coupled to the stylet. The torsional stiffness may be provided by features within the jacket of the lead body, such as a shield. The rotational coupling of the implantable medical lead to the stylet may be provided via features of the lead and/or stylet.

FIG. 49shows a scenario where an implantable medical lead7108is being implanted within a patient. The lead7108enters the patient at an introduction site7112where an introduction needle provides a passageway into the body. The lead7108is shown transparently for purposes of illustration to reveal a stylet7132present within a lumen of the lead7108. The stylet7132, and specifically the bent tip7134of the stylet7132, is used to steer the lead7108as the lead7108is being inserted in order to direct the distal end of the lead7108to the stimulation site which may be a significant distance from the introduction site7112.

The bent tip7134is rotated in position by the stylet7132being rotated. The stylet7132may include a stylet hub7130on the proximal end. This stylet hub7130may engage the lead7108as discussed below. To rotate the stylet7132and the bent tip7134, the doctor may apply rotation7136directly to the lead7108at the introduction site7112rather than reaching back to grasp the stylet hub7130. The lead7108is torsionally stiff such that the rotation7136causes rotation along the length of the lead7108including rotation7138near the proximal end, rotation7142of the hub, and rotation7140near the distal end.

The stylet7132is rotationally coupled to the lead7108at one or more points. The rotational coupling may be near the proximal end or the distal end of the lead7108, and this rotational coupling may be done in various ways as described below. Thus, the rotation7136being applied to the lead7108at the introduction site7112causes the stylet7132to rotate along the length to the bent tip7134.

The stylet7132and stylet hub7130may be constructed of various materials. For example, the stylet may be constructed of steel, stainless steel, tungsten, beryllium, and their alloys which provides torsional rigidity. The stylet hub may be constructed of various materials such as nylon, polycarbonate, or other rigid engineering plastics.

FIG. 50shows an implantable medical system in place once the lead7108has been directed to the stimulation site. The implantable medical system includes an IMD7102having a biocompatible case and a header7106. The lead7108includes distal electrodes7116at the stimulation site that are used to provide the stimulation. The lead also includes proximal connectors7110that are fixed by a set screw or other mechanism within the header7106and are connected to electrical circuitry of the IMD7102. The IMD7102produces stimulation signals that are provided to the connectors7110. Filars within the lead7108carry the stimulation signals from the connectors7110to the electrodes7116.

FIGS. 51 and 52show an embodiment of the implantable medical lead7108where a shield7118is present that provides the torsional rigidity. An outer jacket layer7120is shown transparently inFIG. 51for purposes of illustrating the shield7118. The shield7118may be included for various reasons in addition to creating the torsional rigidity. For example, the shield7118may provide protection from unwanted RF energy. For instance, the lead7108may be a magnetic resonance imaging (MRI) safe lead that allows the patient to have an MRI scan without risking tissue damage due to induced RF currents in the filars of the lead7108. The conductive filars7124extend the length of the lead7108and interconnect the proximal connectors7110to the distal electrodes7116so that stimulation signals are conducted from the proximal end to the distal end of the lead7108.

As shown inFIG. 51, the shield7118of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, platinum, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield7118, particularly for embodiments where a portion of the shield7118may be exposed for purposes of grounding. While the shield7118is shown as a braid, other shield configurations may be chosen such as a metal foil that is wrapped in an overlapping fashion. If shielding is not desired, then the foil may be more loosely wrapped and still provide torsional rigidity.

As shown inFIG. 52, the shield7118may be embedded within the jacket of the lead7108. One manner of constructing the lead7108with the shield7118is to provide an inner jacket7122that encloses the filars7124and any additional insulation layer7126that may surround each filar7124. The shield7118may then reside on the outer portion of the inner jacket7122, and the outer jacket7120may then enclose the shield7118.

The shield7118may ground to tissue via an RF coupling through the outer layer7120and/or via grounding to the can7104and/or to the tissue via ground rings. For embodiments where it is desirable for the shield7118to RF couple to tissue, the outer jacket layer7120may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield7118grounds at the can of the IMD and grounding via a RF coupling from the shield7118through the outer jacket7120directly to the tissue is of less significance, then the shield7118may be located further from the outer surface of the lead7108. The outer jacket7120may be added over the shield7118by shrinking in place or by being extruded over the shield7118.

The inner and outer jackets7122,7120may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. The lumen7128is included in the inner jacket7122, particularly for percutaneous leads7108, to allow the stylet7132to be inserted for purposes of pushing and steering the lead into the desired position within the patient.

As shown in the cross-section ofFIG. 52, at this particular point along the lead the stylet7132is free within the lumen7128. The stylet7132has clearance relative to the lumen7128. This clearance may aid in the insertion of the stylet7132into the lumen7128.

FIG. 53shows a cross-section at a point along an embodiment of the lead7108where a rotational coupling is established between the lead7108and the stylet7132. At this point, the lumen7128of the lead7108has a portion forming a passageway7144that has a square cross-sectional shape rather than being round. As one example, this passageway7144may be created in the distal tip of the lead7108, distal to the location of the distal electrodes. The stylet7132likewise has a shaft7146that has a square cross-sectional shape and that fits within the square shaped passageway7144of the lumen7128. The position of the square shaped passageway7144may be such that when the stylet7132is fully inserted in the lead7108, the square shaped shaft7146of the stylet7132mates to the square shaped passageway7144of the lumen7128. The square shape effectively keys the stylet7132to the lead7108so that a rotational coupling is achieved.

FIG. 54shows a cross-section at a point along another embodiment of the lead7108where a rotational coupling is established between the lead7108and the stylet7132. At this point, the lumen7128of the lead has a particular portion forming a passageway7148that has a star cross-sectional shape rather than being round. As one example, this passageway7148may be created in the distal tip of the lead7108, distal to the location of the distal electrodes. The stylet7132likewise has a shaft7150that has a star cross-sectional shape and that fits within the star shaped passageway7148of the lumen7128. The position of the star shaped passageway7148may be such that when the stylet7132is fully inserted in the lead7108, the star shaped shaft7150of the stylet7132mates to the star shaped passageway7148of the lumen7128. The star shape effectively keys the stylet7132to the lead7108so that a rotational coupling is achieved.

FIG. 55shows a cross-section at a point along another embodiment of the lead7108where a rotational coupling is established between the lead7108and the stylet7132. At this point, the lumen7128of the lead has a particular portion forming a passageway7152that has a hexagonal cross-sectional shape rather than being round. As one example, this passageway7152may be created in the distal tip of the lead7108, distal to the location of the distal electrodes. The stylet7132likewise has a shaft7154that has a hexagonal cross-sectional shape and that fits within the hexagonal shaped passageway7152of the lumen7128. The position of the hexagonal shaped passageway7152may be such that when the stylet7132is fully inserted in the lead7108, the hexagonal shaped shaft7154of the stylet7132mates to the hexagonal shaped passageway7152of the lumen7128. The hexagonal shape effectively keys the stylet7132to the lead7108so that a rotational coupling is achieved.

The square, star, and hexagonal shapes are shown for purposes of illustration. It will be appreciated that any number of shaped engagements may be utilized to establish a rotational coupling between the lead7108and the stylet7132. Furthermore, it will be appreciated that the coupling may occur at any point or multiple points along the lead7108where the torsional stiffness is present

FIG. 56shows a side view of a proximal end of the lead7108with the lumen7128engaging an embodiment of the stylet hub7130in order to establish a rotational coupling between the stylet7132and the lead7108. The stylet hub7130includes a tapered region7156that extends from the hub7130to the stylet7132. This tapered region7156at a large diameter end has a diameter larger than that of the lumen7128. As a result, the tapered region7156may be press fit into the lumen7128of the lead7108in order to produce a frictional fit that establishes a rotational coupling.

FIG. 57shows a side view of a proximal end of the lead7108with the lumen7128engaging another embodiment of the stylet hub7130in order to establish a rotational coupling between the stylet7132and the lead7108. The stylet hub7130includes a splined region7158that extends from the hub7130to the stylet7132. The diameter created by the splined region7158may be greater than the diameter of the lumen7128. This splined region7158may be press fit into the lumen7128of the lead7108in order to engage the splines with the lumen7128to establish a rotational coupling.

FIG. 58shows a side view of a proximal end of the lead7108with the lumen7128engaging another embodiment of the stylet hub7130in order to establish a rotational coupling between the stylet7132and the lead7108. The stylet hub7130includes a threaded region7160that extends from the hub7130to the stylet7132. The diameter created by the threaded region7160may be greater than the diameter of the lumen7128. This threaded region7160may be screwed into the lumen7128of the lead7108in order to engage the threads with the lumen7128to establish a rotational coupling.

The tapered, splined, and threaded engagements of the hub7130to the lumen7128are shown for purposes of illustration. It will be appreciated that any number of hub features may be used to engage the lumen7128to provide the rotational coupling. It will be further appreciated that similar features may be used to allow the hub7130to instead engage the outer layer7120of the lead7108at the proximal end such as by having a taper, splines, or threads that surround the outer layer7120but with a smaller diameter than the outer layer7120. These features face inward to engage the outer layer7120and establish the rotational coupling.

Embodiments as disclosed in relation toFIGS. 59-72provide radiopaque markers that are added to implantable medical leads or to implantable medical devices (IMD) connected to the leads to identify the leads as being designed for safe application of a medical procedure such as an MRI scan. The radiopaque markers are visible on an X-ray or during fluoroscopy so that administering personnel can have a visual assurance that the lead is designed for safe application of the medical procedure of interest.

FIG. 59shows an embodiment of an implantable medical system that includes an IMD8102having a can8104that houses electronics and a header8106. In this example, the IMD8102provides signals to a pair of implantable medical leads8108,8109which are physically and electrically connected to the IMD8102via the header8106.

Radiopaque markers8130,8131are provided to identify the leads8108,8109as being safe for a given procedure. In this particular example, the radiopaque markers8130,8131are tags that are fixed directly to corresponding leads8108,8109. Sutures8132of the permanent type hold the tag8130to the lead8108while sutures8133hold the tag8131to the lead8109. By individually tagging both leads8108,8109, the administering personnel can be assured that both leads are safe for the given procedure.

The tags8130,8131may be added after the leads8108,8109have been successfully implanted into the patient. For percutaneous leads, this is particularly desirable because the lead8108,8109is inserted into the body of the patient via an introducer needle that lacks clearance for the tags8130,8131. Thus, once the leads8108,8109are in position with the proximal ends of the leads being near the incision site and with the introducer needle removed, the tags8130,8131can be inserted into a pocket made for the IMD8102and sutured in place by the doctor.

The tags8130,8131may be constructed of a biocompatible material that has a density that is adequately radiopaque by being visible on an X-ray or during fluoroscopy. Examples of such materials include barium, tantalum, platinum, and platinum-iridium. The size of the tags8130,8131may vary but when sized to have a length and width in the range of 0.25 to 5 centimeters and 0.01 to 0.2 inch thickness, the tag8130,8131is adequately visible while being small enough to comfortably fit within or nearby the pocket near the IMD8102.

When administering personnel wish to perform a given medical procedure such as an MRI, the personnel may take an X-ray or conduct fluoroscopy to look for the radiopaque marker. The IMD8102itself may need to also be designed for safety during a given medical procedure and may have its own internal or external radiopaque marker. Thus, placing the tags8130,8131nearby the IMD8102may be desirable so that the tags of both the leads8108,8109and the marker of the IMD8102are in the same field of view of an X-ray or during fluoroscopy.

In this example ofFIG. 59, the tags8130,8131include an aperture8138,8139in the shape of a particular symbol. Due to the aperture8138,8139, this shape within the tag8130,8131is visibly distinguishable on the X-ray or during fluoroscopy. Thus, this aperture8138,8139may identify the safety aspects of the lead8108,8109and/or the medical procedures that are safe to conduct. The shape of the apertures8138,8139inFIG. 59is a wave that represents that the leads8108,8109are safe for an MRI scan conducted within normal operating parameters.

FIG. 60shows a similar configuration for the radiopaque tag8130. However, rather than the doctor suturing the tag8130to the lead8108, the doctor connects the proximal end of the lead8108to the IMD8102that is placed into the pocket and sutures the tag8130to the IMD8102. In the example shown, sutures8132extending from the tag8130are tied around the can8104. It will be appreciated that the sutures8132could be tied to the IMD8102in other ways or to designated features of the IMD8102.

FIG. 61shows another example of placing the tag8130in close proximity to the IMD8102and lead8108. However, in this example, the tag8130is not tied to either but is instead left loosely positioned within the pocket8136where the IMD8102is positioned. The pocket8136prevents the tag8130from migrating away from the position of the IMD8102so that the tag8130remains in the same field of view as the IMD8102and lead8108during an X-ray or fluoroscopy.

FIG. 62shows another example of placing the tag8130in close proximity to the IMD8102and the lead8108. In this example, rather than suturing the tag8130to the lead8108, the doctor may have chosen to bond the tag8130to the lead using a glue8140. Examples of a glue suitable for bonding the tag8130to the lead8108include medical adhesives.

FIG. 63shows another example of placing the tag8130in direct proximity of the IMD8102by bonding the tag8130to the IMD8102. Here, the tag8130is bonded to the IMD8102with the glue8140. Examples of a glue suitable for bonding the tag8130to the IMD8102also include medical adhesives.

FIG. 64shows another example of placing the tag8130in close proximity to the IMD8102and the lead8108. In this example, the tag8130is attached to a clamp8142, such as a U-shaped spring-loaded clamp or other clamp structures such as features that mechanically lock including detents. The clamp8142tightens against the lead8108to hold the tag8130in position relative to the lead8108.

FIG. 65shows another example of placing the tag8130in direct proximity to the IMD8102. Here, the tag8130includes the clamp8142which is tightened against the can8104of the IMD8102. The clamp8142could tighten against other portions of the IMD8102as well such as the header8106. The clamp8142ofFIG. 65may be of the same types discussed above in relation toFIG. 64.

FIG. 66shows another example of placing the tag8130in close proximity to the IMD8102and the lead8108. In this example, the tag8130has an extension8144that forms a ring shape. Initially, the extension8144may be an open ring so that it easily fits onto the lead8108. The extension8144may then be crimped to form a closed or nearly closed ring about the lead8108and to fix the tag8130relative to the lead8108.

FIG. 67Ashows an example of a radiopaque marker being installed on a lead where the radiopaque marker is not a tag. Instead, the radiopaque marker is a radiopaque coil8146′ that is in a radially expanded state produced by axially compressing the coil8146′. The radially expanded state allows the coil8146′ to be placed about the lead8108, with the lead8108traveling through the center of the coil in an axial direction. The coil8146′ is placed onto the proximal end of the lead8108, shown here with connectors8110, prior to the proximal end being inserted into the header8106.

FIG. 67Bshows the radiopaque coil8146in a radially contracted state. Here, once properly positioned along the lead8108, the coil8146has been allowed to naturally expand axially to radially contract until the coil diameter meets that of the lead8108to fix the coil8146in place on the lead8108. The lead8108is then connected to the IMD8102, with the coil8146being located in proximity to the IMD8102in this example so as to be in the same field of view. The coil8146itself is the visible shape that indicates that the lead8108is safe for a particular medical procedure such as an MRI.

The radiopaque coil8146may be constructed of materials similar to the tag8130. For instance, the coil8146may be constructed of barium, tantalum, platinum, and platinum-iridium. The size of the coil8146may vary but when sized in the range of 0.04 inch to 1.0 inch in length and from 2 mils to 0.10 inch in diameter when radially contracted, the coil8146is adequately visible while being small enough to comfortably fit within or nearby the pocket near the IMD8102.

FIGS. 68A and 68Bshow an example of a tool8150being used to place the coil8146′ in the radially expanded state onto the lead8108and to deposit the coil8146in the radially contracted state at the desired position on the lead8108. The tool8150holds the coil8146′ in the radially expanded state by providing a larger diameter than the lead8108and while providing a passageway for the lead8108.

As shown inFIG. 68B, the tool8150is positioned on the lead8108with the lead8108passing through the passageway of the tool8150. The coil8146′ is pushed off of the tool8150until the coil8146has a radially contracted end about the lead8108. The tool8150may then be pulled away from the lead8108to allow the remainder of the coil8146′ in the radially expanded state to slide off of the tool8150and onto the lead8108where the coil8146achieves the radially contracted state.

FIG. 69Ashows a polymer structure8152that may be used to place a radiopaque marker onto the lead8108.FIG. 69Bshows the polymer structure8152once positioned on the lead8108. This polymer structure8152includes a cylindrical aperture8154that allows the lead8108to pass through. The cylindrical aperture8154may stretch to a larger diameter than the lead8108such as by using a conventional anchor deployment tool to position the polymer structure onto the lead8108. The polymer structure8152may then be removed from the anchor tool to allow the polymer structure8152to contract onto the lead8108.

The polymer structure8152ofFIGS. 69A and 69Bis similar to a lead anchor. However, this polymer structure8152lacks suture wings. Because the contraction of the cylindrical aperture8154holds the polymer structure in place, no sutures are needed.

The offset of the portion8155where the radiopaque plate8156is located provides for ease of removal of the polymer structure8152from the lead8108. An axial cut can be made along the cylindrical aperture8154because the radiopaque marker does not surround the cylindrical aperture8154. However, if ease of removal is not of concern, then embodiments may provide the radiopaque plate8156centered about the cylindrical aperture8154.

FIG. 69Cshows a similar polymer structure8168. However, the polymer structure8168is in the form of a lead anchor that includes suture wings8170while also including the radiopaque plate8156. Rather than relying on the cylindrical aperture to contract onto the lead8108, the lead anchor8168may additionally or alternatively have sutures8132that tie the suture wings8170to the lead8108to hold the polymer structure8168in place in proximity to the IMD8102. The radiopaque plate8156may be centered about the lead8108within the polymer structure8160even where ease of removal is desired if the polymer structure8160is held in place by the sutures8132rather than a contracted state upon the lead8108.

FIG. 70Ashows another polymer structure8160that may be used to place a radiopaque marker onto the lead8108.FIG. 70Bshows the polymer structure8160once positioned on the lead8108. This polymer structure8160includes a cylindrical aperture8162that allows the lead8108to pass through. The cylindrical aperture8162may stretch to a larger diameter than the lead8108such as by using a conventional anchor deployment tool to position the polymer structure8160onto the lead8108. The polymer structure8160may then be removed from the anchor tool to allow the polymer structure8160to contract onto the lead8108.

The polymer structure8160includes an offset portion8164. Within this offset portion8164, a radiopaque coil8166is embedded. The radiopaque coil8166may form a symbol or other information to be conveyed to administering personnel. The radiopaque coil8166may be constructed of materials similar to the coil8146. For instance, the coil8166may be constructed of barium, tantalum, platinum, and platinum-iridium. The size of the coil8166may vary but when sized in the range of 0.04 to 1.0 inch in length and 2 mils to 0.10 inch in wire diameter with an overall diameter of 0.020 to 0.5 inch, the coil8166is adequately visible while being small enough to be contained within the polymer structure8160.

The polymer structure8160ofFIGS. 70A and 70Bis also similar to a lead anchor. However, this polymer structure8160lacks suture wings. Because the contraction of the cylindrical aperture8162holds the polymer structure8160in place, no sutures are needed.

The offset of the portion8164where the radiopaque coil8166is located provides for ease of removal of the polymer structure8160from the lead8108. An axial cut can be made along the cylindrical aperture8162because the radiopaque marker does not surround the cylindrical aperture8162. However, if ease of removal is not of concern, then embodiments may provide the radiopaque coil8166centered about the cylindrical aperture8162.

FIG. 70Cshows a similar polymer structure8172. However, the polymer structure8172is in the form of a lead anchor that includes suture wings8174while also including the radiopaque coil8166. Rather than relying on the cylindrical aperture to contract onto the lead8108, the lead anchor8172may additionally or alternatively have sutures8132that tie the suture wings8174to the lead8108to hold the polymer structure8172in place in proximity to the IMD8102. The radiopaque coil8166may be centered about the lead within the polymer structure8172even where ease of removal is desired if the polymer structure8172is held in place by the sutures8132rather than a contracted state upon the lead8108.

FIGS. 71 and 72show an embodiment of the implantable medical lead8108where a shield8118is present. This shield8118may provide protection from RF energy that allows the lead8108to be conditionally MRI safe and thus eligible to carry the radiopaque marker for an MRI. An outer jacket layer8120is shown transparently inFIG. 71for purposes of illustrating the shield8118. The shield8118may provide protection from RF energy of an MRI that might otherwise cause tissue damage due to induced RF currents in the filars of the lead8108. The conductive filars8124extend the length of the lead8108and interconnect the proximal connectors8110to the distal electrodes so that stimulation signals are conducted from the proximal end to the distal end of the lead8108.

As shown inFIG. 71, the shield8118of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield8118, particularly for embodiments where a portion of the shield8118may be exposed for purposes of grounding. While the shield8118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead8108in an overlapping manner or an outer layer8120that is heavily doped with conductive particles.

As shown inFIG. 72, the shield8118may be embedded within the jacket of the lead8108. One manner of constructing the lead8108with the shield8118is to provide an inner jacket8122that encloses the filars8124and any additional insulation layer8126that may surround each filar8124. The shield8118may then reside on the outer portion of the inner jacket8122, and the outer jacket8120may then enclose the shield8118.

The shield8118may ground to tissue via an RF coupling through the outer layer8120and/or via grounding to the can8104and/or to the tissue via ground rings. For embodiments where it is desirable for the shield8118to RF couple to tissue, the outer jacket layer8120may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield8118grounds at the can8104of the IMD8102and grounding via a RF coupling from the shield8118through the outer jacket8120directly to the tissue is of less significance, then the shield8118may be located further from the outer surface of the lead8108. The outer jacket8120may be added over the shield8118by shrinking in place or by being extruded over the shield8118.

The inner and outer jackets8122,8120may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. A lumen8128may be included inside of the inner jacket8122around which the insulated filars8124are coiled or otherwise positioned. The lumen8128may be useful, particularly for percutaneous leads8108, to allow a stylet to be inserted for purposes of pushing and steering the lead8108into the desired position within the patient.

Embodiments as disclosed in relation toFIGS. 73-76Dprovide for reduced torsional stiffness of a shield present within an implantable medical lead for use with an implantable medical device (IMD). The torsional stiffness of the shield may be reduced in various ways such as by axially cutting the shield to form a slot that breaks the circumferential mechanical continuity of the shield. The slot may then be closed to re-establish the circumferential shielding continuity of the shield and to preserve the shielding function.

FIG. 73shows an example of an implantable medical system9100that includes an IMD9102coupled to a lead9108. The IMD9102includes a metal can9104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD9102includes a header9106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can9104. The header9106is shown transparently for purposes of illustration. The header9106provides a structure for securing the lead9108to the IMD9102and for establishing electrical connectivity between circuitry of the IMD9102and electrodes of the lead9108.

The lead9108includes electrodes9116on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings9110on a proximal end that is positioned within the header9106. The connector rings9110make physical contact with electrical connections9111within the header. The electrical connections9111may include a metal contact that the connector ring9110rests against upon being inserted into the header9106where a wire extends from the metal contact into the can9104where the circuitry is housed. Signals applied by the IMD9102to the connector rings9110are conducted through the lead9108to the electrodes9116to provide the stimulation therapy to the patient.

The lead9108is secured in the header9106such as by a set screw block9112within the header9106that allows at least one set screw9114to be tightened against at least one of the connector rings9110. A shield9118as shown inFIGS. 74A and 74Bmay be grounded to the body along one or more points down the length of the lead from the IMD9102via capacitive coupling through the jacket or via ground rings. The shield9118may also be grounded at the can9104of the IMD9102ofFIG. 73.

FIGS. 74A and 75Ashow an example of the lead9108, where a shield9118is present. An outer insulation layer9120of a lead jacket is shown transparently inFIG. 74Afor purposes of illustrating the shield9118. The shield9118blocks at least some RF energy from directly coupling to conductive filars9124that are present within the lead9108. The conductive filars9124extend the length of the lead and interconnect the proximal connector rings9110to the distal electrodes9116so that stimulation signals are conducted from the proximal end to the distal end of the lead9108.

As shown inFIG. 74A, the shield9118of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield9118, particularly for embodiments where a portion of the shield9118may be exposed for purposes of grounding. While the shield9118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a coiled configuration, foil strip wrapped about the lead9108in an overlapping manner or an outer layer9120that is heavily doped with conductive particles.

As shown inFIG. 75A, the shield9118may be embedded within the jacket of the lead9108. One manner of constructing the lead9108with the shield9118is to provide an inner insulation layer9122of the jacket that encloses the filars9124and any additional insulation layer9126, such as polytetrafluoroethylene (PTFE) that may surround each filar9124. The shield9118may then reside on the outer portion of the inner insulation layer9122, and the outer insulation layer9120may then enclose the shield9118. The outer insulation layer9120may be added over the shield9118and shrunk in place or may be extruded over the shield9118. The outer jacket9120maybe added over the braid9118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield9118to RF couple to tissue, typically as a capacitive coupling, in addition to grounding at the can9104or along the lead9108, the amount of the outer jacket layer9120covering the shield9118may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield9118grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield9118may be located further from the outer surface of the lead9108.

The inner and outer insulation layers9122,9120of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. A lumen9128may be included inside of the inner jacket9122around which the insulated filars9124are coiled or otherwise positioned. The lumen9128may be useful, particularly for percutaneous leads9108, to allow a stylet to be inserted for purposes of pushing and steering the lead9108into the desired position within the patient.

As shown, the shield9118has mechanical and shielding continuity about the circumference of the inner insulation layer9122. This continuity is achieved by the wires of the braided shield9118being continuous. The circumferential shielding continuity exists because there are no non-conductive openings large enough to allow RF energy to easily pass through. The mechanical continuity produces a large increase in torsional stiffness over an unshielded lead, which may be beneficial in some respects but is detrimental in other respects.

The detrimental aspects may include difficulties twisting the lead during implant procedures due to high torsional stiffness. Twisting the lead9108may be beneficial when guiding the lead9108to the stimulation site and to the IMD9102and when wrapping excess lengths of the lead9108about the IMD9102. Thus, in some instances, it may be desirable to provide a shielded implantable medical lead with reduced torsional stiffness.

FIGS. 74B and 75Bshow the lead9108once the shield9118has been cut in an axial direction to create a slot9140. A shield portion9142creates one edge of the slot9140while an opposing shield portion9144creates the opposite edge. The slot9140may be created by a single cut or by two cuts that are roughly parallel and result in a section of the shield9118being removed. The shield9118may be cut prior to applying the outer layer9120so that the outer layer9120does not need to be cut to cut the shield9118.

The shield9118ofFIG. 74Bnow lacks the circumferential mechanical continuity due to the slot9140, and the torsional stiffness is reduced considerably as a result. However, the slot9140also breaks the circumferential shielding continuity because the slot9140has an axial dimension that allows RF energy to easily pass through the slot9140. Therefore, to preserve the RF shielding function of the shield9118, the slot9140is closed in one of various ways that re-establishes the circumferential shielding continuity while allowing the circumferential mechanical continuity to remain broken.

FIGS. 74C and 75Cshow one embodiment of the lead9108where the slot9140is closed to re-establish circumferential shielding continuity by closing the slot sufficiently relative to the wavelengths of RF energy so that the RF energy cannot easily penetrate the shield9118at the location of the slot9140. In this example, the shield portion9144laps over the shield portion9142to close the slot9140from a shielding continuity standpoint. The shield portion9144may or may not contact the shield portion9142such that circumferential electrical continuity may or may not be re-established. However, either way, the shield portion9144is not bonded to the shield portion9142such that they remain mobile with respect to one another, thereby maintaining the break in the circumferential mechanical continuity.

The shield portion9144may be lapped onto the shield portion9142as a natural result of cutting the shield9118, such as where the shield9118is loosely braided over the inner insulation layer9122. The loose braiding provides an uncut shield diameter that is slightly larger than the diameter of the inner insulation layer9122such that cutting the shield9118to create the slot9140allows the shield portion9144to collapse onto the shield portion9142. This collapse of the shield9118closes the slot9140while the shield diameter is reduced down to the diameter of the inner insulation layer9122.

The outer insulation layer9120is then added over the shield9118. The outer insulation layer9120is a polymer that holds the shield9118in place against the inner insulation layer9122. However, the polymer of the outer insulation layer9120is compliant so that the shield portion9144can move relative to the shield portion9142upon application of torque to the lead9108.

FIGS. 74D and 75Dshow another embodiment of the lead9108where the slot9140is closed to re-establish circumferential shielding continuity by closing the slot9140sufficiently relative to the wavelengths of RF energy so that the RF energy cannot easily penetrate the shield9118at the location of the slot9140. In this example, the slot9140is closed by application of a shield patch9146. The shield patch9146may be constructed similarly to the braided shield9118, using the same or similar metal wire. In the example shown, the shield patch9146is a grid pattern, but it will be appreciated that other patterns may also be used such as where the grid includes U-shaped portions along the axial wires so that the U-shaped portions allow for axial extension of the lead9108. The shield patch9146overlaps onto the shield9118on both sides of the slot9140. The shield portion9144may or may not contact the shield portion9142such that circumferential electrical continuity may or may not be re-established. However, either way, the shield patch9146is not bonded to the shield9118such that the shield patch9146can move relative to the shield9118on either side of the slot9140. As a result, the circumferential mechanical continuity of the shield9118remains broken.

Because the shield patch9146is being added to the lead9108, the braided shield9118may be applied to the inner insulation layer9122in a close fitting manner as opposed to loosely braiding the shield9118. Once the cut is complete, the shield patch9146may then be placed into position directly onto the shield9118and across the slot9140.

The outer insulation layer9120is then added over the shield9118and the shield patch9146. As in the embodiment ofFIGS. 74C and 75C, the outer insulation layer9120is a polymer, and the outer insulation9120holds the shield9118in place against or close to the inner insulation layer9122and also holds the shield patch9146in place against or close to the shield9118. However, the polymer of the outer insulation layer9120is compliant so that the shield patch9146can move relative to the shield9118on either or both sides of the slot9140upon application of an axial twisting moment to the lead9108.

FIG. 76Ashows a representation of a shield9150that may be used in an implantable medical lead9108. The representation is a tube, and this tube is illustrative for multiple reasons. Where the shield9150is a braided shield, such as the shield9118, the apertures are small relative to the wavelengths of the RF energy such that the braided shield9118is effectively a tube from the perspective of the RF energy. Where the shield9150is another configuration, such as a foil strip wrapped around the inner insulation layer9122in an overlapping fashion, the foil strip forms a true tube. In either case, a linear axial cut in the shield9150reduces torsional stiffness but appears as the slot9152, which presents an opening that the RF energy may pass through.

FIG. 76Bshows a tubular representation of the shield9150that may correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, the shield9150uses the overlap technique such as that shown above inFIGS. 74C and 75Cto close the slot9152formed by the linear axial cut. As can be seen, a shield portion9156on one side of the slot9152overlaps another shield portion9154on the opposite side of the slot9152and may or may not contact the shield portion9154. Thus, the slot9152is effectively closed to establish shielding continuity across the slot9152, but the shield portions9154,9156may move relative to one another so that the mechanical continuity remains broken.

FIG. 76Cshows a tubular representation of the shield9150that may also correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, the shield9150uses a shield patch technique such as that shown above inFIGS. 74D and 75Dto close the slot9152formed by the linear axial cut. As can be seen, a shield patch9158reaches across the slot9152to overlap and may or may not physically contact the shield9150on both sides of the slot9152. Thus, the slot9152is effectively closed to establish shielding continuity across the slot9152, but the shield patch9158may move relative to the shield9150on either or both sides of the slot9152so that the mechanical continuity remains broken.

FIG. 76Dshows a tubular representation of the shield9160that may correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, the shield9160has been cut axially using a helical cut rather than a linear cut to create a helical slot9162. The slot9162breaks the circumferential mechanical continuity so as to reduce the torsional stiffness, but the slot9162also breaks the circumferential shielding continuity.

The slot9162may be closed using techniques discussed above. A shield patch may be wrapped around the helical slot9162to reach across the slot9162and achieve circumferential shielding continuity. Or, the shield9160may be given a larger diameter than the inner insulation layer upon which it is positioned so that upon creating the slot9162, the shield9160may collapse to create an overlap along the helical slot9162to establish circumferential shielding continuity. This shield patch may be another piece of foil or may be a braided patch.

Embodiments as disclosed in relation toFIGS. 77-80Cprovide for guarding a termination of a shield to reduce coupling of RF energy from the termination of the shield to filars present within an implantable medical lead for use with an implantable medical device (IMD). The guarding of the termination of the shield may be done in various ways such as by inverting the shield near the termination such that a first portion of the shield separates the termination of the shield from inner layers of the lead. Other examples may involve including separate pieces of the shield to form first and second portions, where one portion separates the termination of the other portion from the inner layers of the lead.

FIG. 77shows an example of an implantable medical system10100that includes an IMD10102coupled to a lead10108. The IMD10102includes a metal can10104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. The IMD10102includes a header10106typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can10104. The header10106is shown transparently for purposes of illustration. The header10106provides a structure for securing the lead10108to the IMD10102and for establishing electrical connectivity between circuitry of the IMD10102and electrodes of the lead10108.

The lead10108includes electrodes10116on a distal end that are positioned at a stimulation site within a patient. The lead10108also includes connector rings10110on a proximal end that is positioned within the header10106. The connector rings10110make physical contact with electrical connections10111within the header. The electrical connections10111may include a metal contact that the connector ring10110rests against upon being inserted into the header10106where a wire extends from the metal contact into the can10104where the circuitry is housed. Signals applied by the IMD10102to the connector rings10110are conducted through the lead10108to the electrodes10116to provide the stimulation therapy to the patient.

The lead10108is secured in the header10106such as by a set screw block10112within the header10106that allows at least one set screw10114to be tightened against at least one of the connector rings10110. A shield10118as shown inFIGS. 78A and 78Bmay be grounded to the body along one or more points down the length of the lead from the IMD10102via capacitive coupling through the jacket or via ground rings. The shield10118may also be grounded at the can10104of the IMD10102ofFIG. 77.

FIGS. 78A and 78Bshow an example of the lead10108, where a shield10118is present. An outer insulation layer10120of a lead jacket is shown transparently inFIG. 78Afor purposes of illustrating the shield10118. The shield10118blocks at least some RF energy from directly coupling to conductive filars10124that are present within the lead10108. The conductive filars10124extend the length of the lead and interconnect the proximal connectors10110to the distal electrodes10116so that stimulation signals are conducted from the proximal end to the distal end of the lead10108.

As shown inFIG. 78A, the shield10118of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for the shield10118, particularly for embodiments where a portion of the shield10118may be exposed for purposes of grounding. While the shield10118is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about the lead10108in an overlapping manner.

FIG. 78Bis a cross-section that shows one example of construction of the lead10108. In this embodiment, either the guard is not provided or the guard is not present at the area where the cross-section is taken. Thus,FIG. 78Bshows the general construction of the lead10108without the specifics of the guard which are discussed below in relation toFIGS. 79A-79Cand80A-80C. The shield10118may be embedded within the jacket of the lead10108. One manner of constructing the lead10108with the shield10118is to provide an inner insulation layer10122of the jacket that encloses the filars10124and any additional insulation layer10126, such as polytetrafluoroethylene (PTFE) that may surround each filar10124. The shield10118may then reside on the outer portion of the inner insulation layer10122, and the outer insulation layer10120may then enclose the shield10118. The outer insulation layer10120may be added over the shield10118and shrunk in place or may be extruded over the shield10118.

For embodiments where it is desirable for the shield10118to RF couple to tissue along, typically as a capacitive coupling, in addition to grounding at the can10104or along the lead10108, the entire outer jacket layer10120may be relatively thin, such as on the order of 0.5 to 5 mils. Where the shield10118grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield10118may be located further from the outer surface of the lead10108.

The inner and outer insulation layers10122,10120of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. A lumen10128may be included inside of the inner jacket10122around which the insulated filars10124are coiled or otherwise positioned. The lumen10128may be useful, particularly for percutaneous leads10108, to allow a stylet to be inserted for purposes of pushing and steering the lead10108into the desired position within the patient.

FIG. 79Ashows an embodiment of the implantable medical lead10108in an axial cross-section where termination of the shield10118is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80Ashows a radial cross-section of the same embodiment, with the cross section taken where the shield terminates. A single coiled filar10124is shown in this example but additional filars may be included and the filars may be of other forms such as linear cables rather than coils. In this example, the shield10118is one continuous shield of braided metal wires, but it will be appreciated that other shields may also be used such as the wrapped foil discussed above.

The shield10118of this example has an inversion10136near the distal end of the lead10108. This inversion10136creates two sections to the shield10118, a first portion10119that extends from the inversion10136back to the proximal end of the lead10108and a second portion10121that forms the distal termination of the shield10118. The inversion10136creates a guard for the shield termination.

The second portion10121is separated from the inner insulation layer10122as well as the filars10124by the first portion10119. The first portion10119is braided upon the inner insulation layer10122and then may be coated with the outer insulation layer10120with the second portion10121remaining uncoated. The inversion10136may then be created so that the second portion10121then laps onto the outer insulation layer10120so as to be separated from contact with the first portion10119. The second portion10121may extend from the inversion10136toward the proximal end by various distances, for instance ranging from about ⅛ inch to about 1 inch, such that the second portion10121may be axially shorter than the first portion10119which extends to the proximal end or the second portion10121may also extend to the proximal end. The second portion10121may then be covered by an additional outer insulation layer10117, made of the same or similar material as the outer insulation layer10120, if it is desired that the second portion10121be physically isolated from the body tissue.

The thickness of the outer insulation layer10120at the inversion10136dictates the bend radius of the inversion10136where the second portion10121laps onto the outer insulation layer10120. It may be desirable to have a bend radius that is sufficiently large, such as 0.002 inches, so that the inversion10136does not act as a shield termination from which RF might couple to the filars10124. The lead diameter that is allowable for a given application may dictate the relative thicknesses of each of the layers and thus set an upper limit for the bend radius of the inversion10136.

Prior to or contemporaneously with the addition of the outer insulation layer10117, an extension10132to the outer insulation layer10120may be created to extend further toward the distal end where electrodes such as electrode10130are located. The extension10132may be constructed of the same or similar materials as that of the outer insulation layers10117,10120. The electrode10130has a filar jumper wire10134or the filar10124itself that extends through this extension10132and between the electrode10130and the filar10124. Alternatively, the area where extension10132is shown may be created as a continuation of the outer insulation layer10117.

FIG. 79Bshows another embodiment of the implantable medical lead10108in an axial cross-section where termination of the shield10118is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80Bshows a radial cross-section of the same embodiment, with the cross section taken where the shield10118terminates. A quad coiled filar10124is shown in this example but additional or fewer filars may be included and the filars may be linear cables rather than coils. In this example, the shield10118is two separate pieces forming a first portion10123and a second portion10125of the shield10118made of braided metal wires. It will be appreciated that either or both pieces may be another form of a shield such as wrapped foil as discussed above.

The shield10118of this example has the first portion10123that is a separate piece that resides at the distal end of the lead10108and may extend toward the proximal end for a relatively short distance, for instance, in the range of about ⅛ inch to about 1 inch. The first portion10123is wrapped around the inner insulation layer10122. An intervening layer of insulation10115then surrounds the first portion10123.

The second portion10125of the shield10118is wrapped around the intervening layer of insulation10115and is therefore physically isolated from contact with the first portion10123. The second portion10125then extends on to the proximal end of the lead10108and may therefore be axially longer than the first portion10123. The outer insulation layer10120then surrounds the second portion10125. As a result of this configuration, the first portion10123is located between the termination point at the second portion10125and the inner layers including the inner insulation layer10122and filars10124.

Because there is no inversion in this embodiment ofFIGS. 79B and 80B, the thickness of the layers10115,10120may not be as large as the thickness of the outer insulation layer10120of the embodiment ofFIGS. 79A and 80Awhere that thickness established the bend radius at the inversion10136. As a result, the separation between the first portion10123and the second portion10125may be smaller than the separation between the first portion10119and the second portion10121ofFIGS. 79A and 80A. For instance, the intervening insulation layer10115may have a thickness ranging from about 0.002 inches to about 0.006 inches to control the separation between the first portion10123and second portion10125.

The outer insulation layer10120may be continued to extend on toward the distal end of the lead10108, including filling the area where the electrode10130is located. Alternatively, prior to or contemporaneously with the addition of the outer insulation layer10120, an extension layer from the outer insulation layer10120may be created to extend further toward the distal end where electrodes such as electrode10130are located. The extension may be constructed of the same or similar materials as that of the outer insulation layers10117,10120.

FIG. 79Cshows another embodiment of the implantable medical lead10108in an axial cross-section where termination of the shield10118is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80Cshows a radial cross-section of the same embodiment, with the cross section taken where the shield10118terminates. A quad coiled filar10124is shown in this example but additional filars may be included and the filars may be other forms such as linear cables rather than coils. In this example, the shield10118is two separate pieces forming a first portion10140and a second portion10142of the shield10118made of braided metal wires, but it will be appreciated that either piece may be another form of a shield such as wrapped foil as discussed above.

The shield10118of this example has the first portion10140that is a separate piece that resides at the distal end of the lead10108and that has an inversion10138to establish a first sub-portion10146and a second sub-portion10144. Both sub-portions10144,10146may extend toward the proximal end of the lead10108for a relatively short distance in the range of about ⅛ inch to about 1 inch. The first sub-portion10146is wrapped around the inner insulation layer10122. An intervening layer of insulation10113then surrounds the first sub-portion10146.

The second portion10142of the shield10118is wrapped around the intervening layer of insulation10113and is therefore physically isolated from contact with the first sub-portion10146. The second portion10142then extends on to the proximal end of the lead10108and is therefore axially longer than the first sub-portion10146and the second sub-portion10144. The outer insulation layer10120then surrounds the second portion10142. As a result of this configuration, the first sub-portion10146is located between the termination point at the second portion10142and the inner layers including the inner insulation layer10122and filars10124.

The second sub-portion10144of the first portion10140laps onto the outer insulation layer10120as a result of the inversion10138. The second sub-portion10144may then be covered by an additional outer insulation layer10127, made of the same or similar material as the outer insulation layer10120, if it is desired that the second sub-portion10144be physically isolated from the body tissue.

The thickness of both the intervening layer of insulation10113and the outer insulation layer10120at the inversion10138dictates the bend radius of the inversion10138where the second sub-portion10144laps onto the outer insulation layer10120. It may be desirable to have a bend radius that is relatively large, such as about 0.002 inches, so that the inversion10136does not act as a shield termination from which RF might couple to the filars10124. The lead diameter that is allowable for a given application may dictate the relative thicknesses of each of the layers and thus set an upper limit for the bend radius similar to the upper limit for the embodiment ofFIGS. 79A and 80A.

The outer insulation layer10127may be continued to extend on toward the distal end of the lead10108, including filling the area where the electrode10130is located. Alternatively, prior to or contemporaneously with the addition of the outer insulation layer10127, an extension layer from the outer insulation layer10120may be created to extend further toward the distal end where electrodes such as electrode10130are located. The extension layer may be constructed of the same or similar materials as that of the outer insulation layers10127,10120.

While many embodiments have been particularly shown and described, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.