Source: http://www.google.com/patents/US20040263174?dq=6263352
Timestamp: 2014-07-13 01:32:27
Document Index: 519283301

Matched Legal Cases: ['art 106', 'art 106', 'art 106', 'art 106', 'art 112', 'art 106', 'art 106']

Patent US20040263174 - Magnetic resonance imaging interference immune device - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA voltage compensation unit reduces the effects of induced voltages upon a device having a single wire line. The single wire line has balanced characteristic impedance. The voltage compensation unit includes a tunable compensation circuit connected to the wire line. The tunable compensation circuit applies...http://www.google.com/patents/US20040263174?utm_source=gb-gplus-sharePatent US20040263174 - Magnetic resonance imaging interference immune deviceAdvanced Patent SearchPublication numberUS20040263174 A1Publication typeApplicationApplication numberUS 10/887,533Publication dateDec 30, 2004Filing dateJul 8, 2004Priority dateJun 24, 2003Also published asCA2517771A1, EP1636612A2, EP1636612A4, US6949929, US7123013, US7729777, US7742825, US20040263172, US20040263173, US20080058913, WO2005003790A2, WO2005003790A3Publication number10887533, 887533, US 2004/0263174 A1, US 2004/263174 A1, US 20040263174 A1, US 20040263174A1, US 2004263174 A1, US 2004263174A1, US-A1-20040263174, US-A1-2004263174, US2004/0263174A1, US2004/263174A1, US20040263174 A1, US20040263174A1, US2004263174 A1, US2004263174A1InventorsRobert Gray, Stuart MacDonaldOriginal AssigneeBiophan Technologies, Inc.Export CitationBiBTeX, EndNote, RefManReferenced by (36), Classifications (17), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetMagnetic resonance imaging interference immune deviceUS 20040263174 A1Abstract A voltage compensation unit reduces the effects of induced voltages upon a device having a single wire line. The single wire line has balanced characteristic impedance. The voltage compensation unit includes a tunable compensation circuit connected to the wire line. The tunable compensation circuit applies supplemental impedance to the wire line. The supplemental impedance causes the characteristic impedance of the wire line to become unbalanced, thereby reducing the effects of induced voltages caused by changing magnetic fields. Images(12) Claims(70)
BRIEF DESCRIPTION OF THE DRAWINGS [0055] The present invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the present invention, wherein: [0056]FIG. 1 is a schematic of an implanted pacemaker arrangement in a body; [0057]FIG. 2 is a schematic of a pacemaker lead comprising three conductive strands; [0058]FIG. 3 is a schematic of a sensing system used with a pacemaker; [0059]FIG. 4 illustrates an embodiment of a pacemaker canister according to the concepts of the present invention; [0060]FIG. 5 illustrates another embodiment of a pacemaker canister according to the concepts of the present invention; [0061]FIG. 6 illustrates a further embodiment of a pacemaker canister according to the concepts of the present invention; [0062]FIG. 7 is an illustration of inductive currents in conductor loops; [0063]FIG. 8 is an illustration of canceling inductive currents in conductor loops according to the concepts of the present invention; [0064]FIG. 9 is a schematic of an embodiment of a pacemaker lead utilizing inductive loops according to the concepts of the present invention; [0065]FIG. 10 is a schematic of an embodiment of inductive loops in a pacemaker canister according to the concepts of the present invention; [0066]FIG. 11 is a schematic of an embodiment of inductive loops around a pacemaker canister according to the concepts of the present invention; [0067]FIG. 12 illustrates of an embodiment of a medical device with an external voltage cancellation unit according to the concepts of the present invention; [0068]FIG. 13 illustrates of another embodiment of a medical device with an external voltage cancellation unit according to the concepts of the present invention; [0069]FIG. 14 illustrates a portion of coiled leads used in a medial device according to the concepts of the present invention; [0070]FIG. 15 illustrates another embodiment of a portion of coiled leads used in a medial device according to the concepts of the present invention; [0071]FIG. 16 illustrates a further embodiment of a portion of coiled leads used in a medial device according to the concepts of the present invention; [0072]FIG. 17 illustrates another embodiment of a portion of coiled leads used in a medial device according to the concepts of the present invention; [0073]FIG. 18 illustrates a circuit diagram representing a guide wire with an unbalancing impedance circuit according to the concepts of the present invention; [0074]FIG. 19 illustrates another embodiment of a circuit diagram representing a guide wire with an unbalancing impedance circuit according to the concepts of the present invention; [0075]FIG. 20 illustrates a balun used in conjunction with a guide wire according to the concepts of the present invention; and [0076]FIG. 21 is a circuit diagram representing a capacitance unbalanced balun unit according to the concepts of the present invention. DETAILED DESCRIPTION OF THE PRESENT INVENTION [0077] The present invention will be described in connection with preferred embodiments; however, it will be understood that there is no intent to limit the present invention to the embodiments described herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the present invention as defined by the appended claims. [0078] For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference have been used throughout to designate identical or equivalent elements. It is also noted that the various drawings illustrating the present invention are not drawn to scale and that certain regions have been purposely drawn disproportionately so that the features and concepts of the present invention could be properly illustrated. [0079]FIG. 1 is a schematic showing a typical pacemaker arrangement 100. The pacemaker comprises a pulse generator canister 102 housing a power supply (not shown) and electronic components (not shown) for sensing and producing electrical pacing pulses. The pulse generator canister 102 has connected to it insulated conductive leads 104 that pass through the body (not shown) and into the heart 106. Conventional bipolar pacemaker leads have two conductive strands, one for pacing and sensing, and the other for ground. The path of the leads 104 is generally not straight. The leads 104 have one or more electrodes 112 in contact with the heart 106. The direct line 108 from the heart 106, where the electrodes 112 are placed, to the generator canister 102 represents a conductive path comprising body tissue (not shown) and fluids (not shown). The completed loop from the pacemaker canister 102, through the leads 104, and back to the pacemaker canister 102 along the path 108 is subject to Lenz's law. That is, a changing magnetic field 110 through the area enclosed by the completed loop (from the pacemaker canister 102, through the leads 104, and back to the pacemaker canister 102 along the path 108) can induce unwanted voltages in the leads 104 and across the heart 106. [0080] In one embodiment of the present invention, and referring to FIG. 1, the pacemaker canister 102 is made out of a non-conductive material. In another embodiment, the canister 102 is coated or covered with various non-conductive insulating materials. This increases the overall resistance of the conductive path loop and thus reduces the voltage across the tissue between electrodes 112 and the canister 102. [0081] Using a three-strand lead design allows for the separation of the pacing signals from the sensing signals and allows for different filtering techniques to be utilized on each separate conductive strand: one strand for the pacing signal for stimulating the heart, one conductive strand for the sensing of the heart's electrical state, pre-pulse, ecg, etc., and one strand for the ground path. Current bi-polar designs use only two conductive strands. This means that the pacing and the sensing signals are carried on the same strand. [0082] For example, in conventional bipolar pacemaker leads, the pacing signal goes �down� (from generator canister to heart) the pacing lead (conductive strand) while the sensing signal travels �up� (from heart to generator canister) the pacing lead. This is the �standard� bipolar pacing setup. If a filter is added to the pacing/sensing strand to block the switch gradient induced signal caused by a MRI system, the pacing pulse/signal must travel through the filter, thereby distorting the pacing pulse. [0083] According to the concepts of the present invention, by adding a third conductive strand, a diode, for example, can be put on the pacing strand and one or more filters can be put on the sensing strand. The filters on the sensing lead may be at the distal end of the pacemaker lead or in the generator canister. Thus, by using separate strands, the present invention is able to utilize different kinds of filters (RF filters, high/low pass filters, notch filters, etc.) or other electronics in conjunction with each strand depending on the different signal characteristics and/or signal direction along the conductive strand. [0084]FIG. 2 shows a schematic of a pacemaker arrangement 120 including a generator canister 122 containing a pacing pulse generator (not shown), sensing electronics (not shown) and other electronic components (not shown). Attached to the generator canister 122 is a lead assembly 140 having three conductive strands 124, 126, and 128 through lumen 138. Each of the conductive strands 124, 126, and 128 pass through the distal tip 142 of the lead assembly 140 to exposed electrodes 132, 134, and 136, respectively. The exposed electrodes 132, 134, and 136 are placed in contact with or next to the heart. [0085] Conductive strand 124 and electrode 132 are used to deliver pulses to the heart from a pacing generator within the canister 122. Conductive strand 126 and electrode 134 are used as a ground. Conductive strand 128 and electrode 136 are utilized for sensing the electrical signals generated by the heart. In this way, the sensing functionality of pacemakers can be separated from the delivery of pacing pulses. [0086] To block any induced voltage signals from the MRI system's changing magnetic fields (the RF or the gradient fields) from propagating along the conductive pulse delivery strand 124, a diode 130 is inserted into the conductive strand 124 near the distal tip of the lead assembly 142. It is noted that the diode 130 can also be is placed in the generator canister 122. [0087] With respect to FIG. 2, other electronic components (i.e. RF Chocks, notch filters, etc.) may be placed into the other conductive strands 126 and 128 shown as by components 146 and 144, respectively. It is noted that these optional electronic components 146 and 144 can be placed in the generator canister 122. [0088] Optional electronic components 146 and 144 are used to block or significantly reduce any unwanted induced signals caused by the MRI system from passing along conductive strands 126 and 128 respectively while allowing the desired sensing signals from the heart to pass along conductive strand 126 to electronics in the generator canister 122. [0089]FIG. 3 is a schematic of an embodiment of the present invention. As illustrated in FIG. 3, a patient 162 is located within an MRI system 168, wherein the patient 162 has an implanted heart pacemaker pulse generator canister 164. A surface sensor/transceiver 166 is placed on the exterior of the patient's body 162 over or near the location of the implanted pacemaker generator 164. The sensor/transceiver 166 is in communication with the MRI system 168 via communication line 170, which may be an MRI safe cable such as a fiber optical cable. Additionally, the sensor/transceiver 166 is in communication with the implanted pacemaker pulse generator canister 164. The means of communication between the sensor/transceiver 166 and the implanted pacemaker generator 164 may be acoustic, optical, or other means that do not interfere with the imaging capabilities or image quality of the MRI system. The signals may be digital or analog. [0090] Moreover, with respect to this embodiment of the present invention, a transmitter/receiver is placed in the pacemaker canister 164 so that the MRI system 168 can be in operative communication with the pacemaker system and vice versa. Thus, the pacing system can transmit signals to the MRI system 168 indicating when the pacemaker is about to deliver a pacing pulse to the heart. The transmitted signals may be digital or analog. In response to this transmitted signal, the MRI system 168 stops or pauses the MRI switched gradient field (imaging scanning sequence) to allow the pacing pulse to occur. After the pacing pulse has been delivered to the heart, the MRI system 168 resumes or begins a new imaging scanning sequence. [0091] In another mode of operation, the MRI system 168 sends signals to the implanted heart pacemaker pulse generator canister 164 through the sensor/transceiver 166 indicating the application of switched gradient fields. The pacemaker may use this information to switch filters or other electronics in and out of the circuit to reduce or eliminate voltages induced in the pacemaker leads by the gradient fields. For example, the pacemaker may switch in additional resistance or inductance or impedance into the pacing/sensing and/or ground strands based on the signal from the MRI system 168 signifying the application of the gradient fields. [0092] In another configuration, there is no surface sensor/transceiver or communication line to the MRI system 168. Instead, there is a special sensor in the implanted heart pacemaker pulse generator canister 164 that can sense the application of the gradient fields. In response thereof, the pacemaker switches into the electrical circuit of the pacing/sense and/or ground leads a charging source which is used to charge the implanted heart pacemaker pulse generator canister 164, leads, and/or electrodes to an electrical potential opposite to that which would be induced by the gradient fields. In this way, the induced voltages caused by the gradient fields are cancelled out or reduced to a safe level, by the application of this voltage source. [0093] In a preferred embodiment of the present invention, the charging/voltage source receives its power from inductively coupling to the MRI system's RF field. The oscillating RF field supplies power to charge special capacitors in the implanted heart pacemaker pulse generator canister 164. It is noted that other external power sources can be used to power the charging/voltage source in the implanted heart pacemaker pulse generator canister 164. [0094]FIG. 4 is a diagram of an assembly 170 for the pacemaker generator components comprising the canister housing 172, a programmable logic unit (PLU) 184, a power source 174, and a pulse generator 176. Additionally, means for communicating with an external sensor/transceiver is provided by transceiver 180. Other electronic components 178; e.g., signal filters, signal processors, lead connectors, etc. are also located in the canister 172. The pacing leads 182 pass through the canister 172 and connect to the internal electronics 178. During an MRI examination, the signals transmitted and received by the transceiver 180 may be used to synchronize the MRI system's scanning sequences with the delivery of the pacing signals. [0095] In another embodiment, as depicted in FIG. 5, the pacing generator assembly 190 further includes a second power module 186 which may be an inductive coil and/or capacitor bank, suitable for capturing and storing power from the MRI system's transmitted RF signal. [0096] In one embodiment, the power stored in the power module 186 is used to develop an electrical potential in the leads 182 that is opposed to that which is induced by the application of the MRI system's gradient fields. [0097] In another embodiment, the power stored in the power module 186 is used to operate various switches in the electronics module 178 which may switch in or out various power serge protection circuits in-line and/or signal filters to the leads 182. [0098] In a further embodiment, and referring to FIG. 5, the module 186 may be used to electrically charge the pacemaker canister 172, which is made of a conductive material, in synchronization with the application of the MRI system's gradient fields so that the electrical potential difference between the pacing electrodes and the pacemaker canister 172 is reduced. That is, the sum of the induced voltage difference due to the application of the gradient fields plus the voltage difference due to the application of the electrical charge stored in the power module 186 results is a net voltage significantly below any threshold level, above which a problem may develop. [0099]FIG. 6 depicts another assembly 200, which includes the basic components of FIG. 5 less the transceiver 180, a gradient field detector 204, and a by-pass switch component 202. By detecting the gradient signal in the pacemaker canister 172 with gradient field detector 204, the pacemaker can switch filters and/or other electronics 178 in or out of the circuit. [0100] In one embodiment, when no gradient fields are detected, the switch 202 is closed to by-pass the electronics component 178, which may be a combination of low-pass, high-pass, notch filters, diodes, and/or other electronics. In this mode (switched closed), the pacing pulse (and sensing signals) by-pass the filters components 178. When gradient field detector 204 detects the gradient signals, the switch 202 is opened and any gradient fields induced signals in the leads 182 are blocked or significantly reduced by the filters components 178. In the open mode, the pacing and sensing signals pass through the filters component 178 as well. [0101] The gradient detector 204 may communicate the sensing of the gradient field to other components in the pacemaker via its connection to the PLU 184 so that the pacing signal can be modified, if necessary, to compensate for any distortion it may suffer by now going through the filters component 178. Additionally, the sensing signal, now also passing through the filter components 178 may be distorted. This may be compensated for by including signal recovery/reconstruction logic into the PLU or into a separate signal-processing component. [0102] Referring back to FIG. 1, by increasing the impedance of the leads 104, the voltage across the tissue gap from the electrodes 112 and the pacemaker canister 102 can be reduced. Inserting a resistor or using a higher resistive wire for the pacemaker leads 104 will reduce the current induced in the current loop, which includes the virtual loop portion across the (heart 112) tissue to the pacemaker generator canister 102. [0103] By using various inductors in-line with the various leads 104, it is possible to make the leads 104 have a high impedance for the low frequency MRI gradient fields frequency and a low impedance for the MRI system's RF frequency. Alternatively, different impedances (inductors/resistors/capacitors) may be switched in-line or out of the leads' circuitry depending on the timing and application of the gradient and/or RF fields. [0104] In another embodiment, not shown, the pacemakers' electronics can be augmented to include one or more digital signal processors. By converting the sensing signal into a digital signal, the digital signal processor (DSP) can reconstruct the sensing signal after it has passed through filters and has been distorted by the filtering or other elements that may have been added to the lead circuit. The DSP may also be used to reject any signals that do not have a correct cardiac signature, thus rejecting any signals caused by the switched gradient fields, which is a non-cardiac signal. [0105] In another embodiment of the present invention, a pacemaker lead or other medical device, having a long conductive lead and functioning in an MRI environment, may be configured, according to the concepts of the present invention, to include additional loops to cancel the induced voltage effects in the leads of the original current loop formed by the leads. [0106] In a further modification of the present invention (not shown), an electrical lead component for a medical device includes an electrical lead that provides an electrical path to a desired tissue region. The electrical lead component further includes a voltage source, such as a battery or capacitor and a sensor to sense voltages induced by the changing MRI electromagnetic field. A switching device, connected to the sensor and voltage source, connects the voltage source to the electrical lead in response to the sensed voltage induced by the changing MRI electromagnetic field such that the voltage source provides a voltage that is opposite to the voltage which would be induced by the changing MRI electromagnetic field in the medical device electrical lead so as to reduce voltages induced by the changing MRI electromagnetic field. The electrical lead component further includes a variable resistor connected to the voltage source to regulate an amount of voltage being provided. The changing MRI electromagnetic field is a MRI switched gradient field or a MRI switched gradient field. [0107] Additionally, the present invention may be modified (not shown) so that a medical device that is capable of providing medical treatment to a desired tissue region is associated with a voltage source and a sensor to sense voltages induced by the changing MRI electromagnetic field. A switching device, connected to the sensor and voltage source, connects the voltage source to the medical device in response to the sensed voltage induced by the changing MRI electromagnetic field such that the voltage source provides a voltage that is opposite to the voltage which would be induced by the changing MRI electromagnetic field in the medical device so as to reduce voltages induced by the changing MRI electromagnetic field. The medical device is further associated with a variable resistor connected to the voltage source to regulate an amount of voltage being provided. The changing MRI electromagnetic field is a MRI switched gradient field or a MRI switched gradient field. [0108] In FIG. 7, two conductive loops 260 and 270 having the same amount of area and in the same plane, positioned in a changing magnetic field 262 and 272, develop currents 264 and 274. In FIG. 7, both induced currents I1 and I2 travel in the same direction (clockwise direction shown) at all times as the magnetic field 262 and 272 oscillate. [0109]FIG. 8 shows that by connecting the two conductive loops 260 and 270 of FIG. 7 to form a single conductor 280, the currents induced in each lobe can be made to cancel each other out. The two loops are connected so that a single conductor is formed which crosses over itself at 284. In this case, as shown in FIG. 8, the two currents 286 and 288 cancel each other out resulting in net current of zero magnitude around the conductor 280. This type of configuration of conductors in a changing magnetic field may be used to cancel induced currents in the conductors. [0110]FIG. 9 depicts an implanted pacemaker system 220 comprising a pacing generator canister 102, conductive leads 104, and electrodes 112 positioned in the heart 106. Additional loops 222 are added to the overall configuration of the lead 104 in the body with one or more crossings 224. In accordance with the concepts of the present invention, the plane of the loop 222 is in the same plane as defined by the rest of the lead geometry. [0111] The same oscillating magnetic field 110 passes through loop 222 and the loop defined by generator canister 102, conductive leads 104, electrodes 112, and conductive path 108 through the body from the heart 106 to the generator canister 102. It is noted that the total area enclosed by the loops can be adjusted by adding or removing loops 222 or by changing the area enclosed by the loops (singly or collectively). [0112] In one embodiment, the total area of the loop 222 is the same as the loop area 226. In another embodiment, the total area of the loop 222 is different from loop area 226. In another embodiment, the plane of loop 222 is different from the plane of loop area 226. In yet another embodiment, loop 222 and/or loop area 226 do not define a single plane but are curved in three different spatial directions. In yet another embodiment, loop 222 consists of at least three loops in three orthogonal planes. [0113] In a further embodiment, as illustrated in FIG. 11 and will be discussed in more detail below, the new additional loops 222 can be positioned in such a way as to encircle the pacemaker's generator canister 102. In another embodiment, as illustrated in FIG. 10 and will be discussed in more detail below, the additional loops 222 may be positioned inside the pacemaker's generator canister 102. [0114] Referring back to FIG. 9, a fastener (not shown) can be used at the loop cross over point 224 to allow for adjustment of the loop's enclosed area and/or orientation and, once adjusted, to lock in the loop's adjustments. This same fastener can also be used to adjust a plurality of loops. [0115] In another aspect of the present invention, a selection mechanism can be included in the pacemaker system. This selection mechanism is used to adjust the number of loops to include in the circuit. [0116] For example, if the loops are located within the pacemaker canister, the selection mechanism can be used to manually select how many loops to include in the lead circuit depending on where the pacemaker can is placed in the body and the length of the lead. Alternatively, the selection mechanism may be used to automatically select how many loops to include in the lead circuit depending on where the pacemaker can is placed in the body and the length of the lead. In this alternative embodiment, the present invention monitors the voltages on the pacemaker's lead(s) and selects a different number of loops to connect to the lead(s) to cancel any induced voltages. Lastly, the selection mechanism may be externally programmed and transmitted to the pacemaker's PLU that then monitors and adjusts the number of loops in the lead circuit. [0117]FIG. 10 is a schematic of a pacemaker system 300 that includes a pacemaker canister 302 and the pacemaker's leads 304. The pacemaker's canister 302 contains a programmable logic unit (PLU) 306, and other electronics 310, e.g. a pulse generator, power supply, etc. The system 300 further includes conductive loops 308 positioned within the pacemaker canister 302. [0118] The conductive loops are connected to a loop selection component 312 that provides means for selectively adjusting the number of loops to be included in the leads' circuit 304. The leads 304 are also connected to the loop selection component 312 so that the leads 304 can be electrically connected to the loops 308. [0119] The loop selection component 312 connects the loops 308 to the leads' circuit 304 in such a way that any induced voltages in the loops 308 caused by changing magnetic fields in the environment, e.g. an MRI environment, will cancel out or significantly reduce in magnitude any induced voltage along the leads 304 that have also been caused by the environment's changing magnetic fields. [0120] In one embodiment, the loop selection component 312 is adjusted manually by screws, connection pins, and/or other means. [0121] In another embodiment, the loop selection component 312 is controlled by the PLU 306. The PLU 306 may include means for receiving loop selection instructions from an external transmitter or may include sensors that measure environmental variables, e.g. changing magnetic fields in an MRI environment. From this information, the PLU 306 dynamically adjusts the loop selection component's 312 adjustable parameters so as to change which loops are included in the leads' circuitry 304. [0122] It is noted that the loops 308 need not be all in the same plane. [0123]FIG. 11 is a schematic of another pacemaker system 320. Pacemaker system 320 includes conductive loops 322 positioned externally to a pacemaker canister 302. In this embodiment, the loops 332 are connected to an input port connection 330 and to an output port connection 334 which are electrically connected to the loop selection component 324 located inside the pacemaker canister 302. Additionally, the pacemaker leads 304 are connected to an electrical connector 332 that is electrically connected to the loop selection component 324. It is noted that the conductive loops 322 need not be all in the same plane. [0124]FIG. 12 depicts a medical procedure in which a catheter 406 or other medical device, e.g. a guidewire, which is comprised of conductive leads or other conductive components, may be partially inserted into a body 402 and partially external to the body. In an MRI environment, such conductive medical devices 406 can develop problems like heating, induced voltages, etc. caused by the changing magnetic fields of the MRI system. To compensate for induced currents and/or induced voltages in such devices 406, a voltage compensation unit (VCU) 410 is electrically connected to the medical device 406 via conductive leads 412 and electrical connectors 414, externally to the patient's body 402. [0125] The medical device 406 is constructed with additional electrical connectors 414 to allow for easy attachment of the VCU device 410. The VCU device 410 is connected to a power supply or may have a built in power supply, e.g. batteries. The VCU device 410 has sensors built into it, which monitor the voltages of the conductive components in the medical device 406, and delivers opposing voltages to the medical device 406 to cancel out or significantly reduce any induced voltages caused by the changing magnetic fields in an MRI (or other) environment. [0126] Additionally or alternatively, the VCU device 410 has sensors to detect the changing magnetic fields of the MRI system and can synchronize the application of the canceling voltage with the MRI System's changing fields. [0127] In another embodiment depicted in FIG. 13, the VCU device 420 is connected to the MRI system 422 via communication means 424 so that the start and end of the application of the MRI system's 422 fields may be communicated to the VCU device 420. Other information that may be required (field strengths to be applied, MRI scan sequence, etc.) may also be communicated to the VCU device 420. The communication means 424 may be electrical wires/coaxial/shielded/other, optical fiber, or an RF transmitter/receiver, or some sonic means of communication. [0128] The conductive lead of a heart pacemaker is a filer winding. The filer winding may consist of two or more conductive stands coiled together in a spring-like configuration. The current (pulses, signals) then flows over the surface and through the contact points between one loop and the adjacent loop of the winding, rather than following the windings of the individual conductive strands. This occurs because there is no significant insulating material or surface coating between the contact points of the windings. [0129] In accordance with the present invention, to reduce the alternating, induced current flowing, caused by a magnetic resonance system's changing magnetic fields, through the, for example, pacemaker's winding leads, the inductance value of the pacemaker's lead may be changed to increase the overall impedance of the pacemaker's lead. [0130] Thus in one embodiment, a suitable RF choke is inserted inline with the pacemaker's lead, preferable near the distal tip. For example, referring back to FIG. 2, and to the embodiment therein, electronic component 146 and/or 144 may comprise an RF choke. In a preferred embodiment, the RF choke has an inductance value of about 10 microHenries. In another embodiment, the inductance value is about 2 microHenries. [0131] The specific value of inductance to introduce into the, for example, pacemaker's lead depends in part on the frequency of the induced signal from the MRI system's imaging sequence that is to be blocked or significantly reduced. [0132]FIG. 14 shows a portion of a coiled multi-filer lead 450. As illustrated in FIG. 14, lead 450 includes a plurality of coil loops 452; each coil loop 452 consists of three conductive strands 454, 456, and 458. A current 460 through the lead 450 can cross contact points 464, 466, and 462 between the strands as well as the coil contact points 468 and 470. Thus, the current 460 does not follow the coiling of the lead's conductive strands 454, 456, and 458. [0133]FIG. 15 shows a portion of a coiled lead assembly 480 including a region 482 that has an insulating coating 484 applied to its surface. The coiled lead assembly 480 is depicted in an elongated position in which adjacent coil windings are not in contact with one another. It is to be understood that the normal, relaxed position of the lead assembly 480 has all adjacent coiled windings in contact. [0134] With the addition of an insulated coating 484 over the winding region 482, the current 490, 492, and 494 is now forced to substantially follow the curvature of the coiled winding 482, thus forming an inductive coil inline with the conductive lead regions 486 and 488 which do not have an insulated coating. The inductive value of the created inductor can be adjusted by adjusting the length of the region to which the insulative coating 484 is applied. [0135] It is noted that the coating 484 may be a partially resistive material. In such an example, the inductance is then adjusted by adjusting the resistive properties of the material 484. [0136]FIG. 16 is a schematic of a coiled lead assembly 500 comprised of uninsulated regions 502, 504, and 506, and coated insulated regions 508 and 510 with coatings 512, and 514, respectively. Through the application of the coating, the current is forced to substantially follow the curvature of the coiled windings, thus forming an inductive coil inline with the conductive lead regions that do not have a coating applied thereto. The inductive value of the created inductor can be adjusted by adjusting the length of the region to which the insulative coatings 512 and 514 are applied. In one embodiment, coatings 512 and 514 are the same coatings. In another embodiment, the coatings 512 and 514 are different materials. [0137] It is noted that coatings 512 and 514 may be the same coating material but having differing properties, e.g., the thickness of the coatings, or the length of the coated region 508 and 510. It is further noted that the two-coated regions 508 and 510 may have different inductive values. It is also noted that more than two different regions along the length of the lead assembly can be coated. [0138]FIG. 17 is a schematic of a portion of a coiled lead assembly 520 including at least one region 524 with a coating applied thereto. Through the application of the coating, the current is forced to substantially follow the curvature of the coiled windings, thus forming an inductive coil inline with the conductive lead regions 522 and 526 that do not have a coating applied thereto. The inductive value of the created inductor can be adjusted by adjusting the length of the region to which the insulative coating 524 is applied. Additionally, through the coated region 524 is positioned a rod 528 which also changes the inductive value of the coated region 524. It is noted that the rod 528 may be of ferrite material. It is further noted that multiple rods can be inserted into multiple coated regions along the length of the coiled lead. [0139] It is noted that multiple coatings can be applied to the same coated region of the coiled lead wherein the multiple coating layers may be comprised of different materials. It is further noted that one or more layers of the multiple layers of coatings may comprise ferrite material. [0140] In another embodiment of the present invention, the heating and/or induced voltages on catheters or guide wires is controlled or substantially eliminated by introducing or creating detuned characteristic impedance at a proximal ends (ends that are not within the body) of the catheters or guide wires. This introduction or creation of detuned characteristic impedance will be discussed in more detail with respect to FIGS. 18-21. [0141] As noted above, during MRI procedures, catheters and guide wires (wire lines), with or without grounded shielding, are used to measure physiological signals. In such instances, two-wire catheters or guide wires having a grounded shield have one conductor that carries the actual measured signal and the other wire is grounded. In terms of characteristic impedance, the two-wire catheters or guide wires having a grounded shield are unbalanced. In contrast, a single wire catheter or guide wire has characteristic impedance that is balanced. [0142] According to the concepts of the present invention, the characteristic impedance of the catheters and guide wires, used during MRI procedures, should be unbalanced at the proximal end, under all conditions, to reduce or eliminate heating and induced voltages. To realize this reduction or elimination of heating and induced voltages at the proximal end of the catheters and guide wires, used during MRI procedures, by creating an unbalanced characteristic impedance, the present invention proposes providing a Balun along the catheter and/or guide wire or at the proximal end of the catheter and/or guide wire. [0143] Using a Balun to maintain unbalanced characteristic impedance, the reactance at the distal end of the catheter and/or guide wire approaches infinity. Thus, even when there is some potential on the wire, the unbalanced characteristic impedance has approximately four times the ground loop looses of a balanced line, thereby substantially avoiding any incident of thermal injury. An example of such an arrangement is illustrated in FIG. 18. [0144] As illustrated in FIG. 18, a guide wire or catheter 650 has characteristic impedance due to its intrinsic resistance from intrinsic resistor capacitors Rp and its intrinsic inductance from intrinsic inductor L. To create the unbalanced characteristic impedance at the proximal end of the guide wire or catheter 650, a Balun 600 is placed along the guide wire or catheter 650. In other words, the Balun 600 is in vitro. [0145] The Balun 600 includes a variable capacitor C1 connected in parallel with the guide wire or catheter 650 and two variable capacitors C2 and C3 connected in series with the guide wire or catheter 650. It is noted that one end of the variable capacitor C2 is connected to the shield 625 and ground or a known voltage. The capacitance of the variable capacitors C1, C2, and C3 are adjusted to create the unbalanced characteristic impedance. [0146] More specifically, the variable capacitors C1, C2, and C3 may be used for both matching and providing a certain amount of balancing for the guide wire or catheter 650 characteristic impedance. In this example, the variable capacitors C1, C2, and C3 lift the voltage on the guide wire or catheter 650 from ground. The larger the reactance of the variable capacitors C1, C2, and C3, the more symmetric and balanced the circuit of the guide wire or catheter 650 becomes. Conversely, according to the concepts of the present invention, if the reactive capacitance of the Balun 600 is detuned (made less resonant), the circuit of the guide wire or catheter 650 becomes asymmetric and unbalanced, breaking down, to reduce the chances of thermal injury at the distal end of the guide wire or catheter 650 due to heating from induced voltages. [0147]FIG. 19 illustrates another embodiment of the present invention wherein a guide wire or catheter 6500 has characteristic impedance due to its intrinsic capacitance from intrinsic capacitors Ct and Cs and its intrinsic inductance from intrinsic inductor L. To create the unbalanced characteristic impedance at the proximal end of the guide wire or catheter 6500, a Balun 6000 is connected across the proximal end of the guide wire or catheter 6500. In other words, the Balun 6000 is outside the body at the proximal end of the guide wire or catheter 650. By having the Balun 6000 outside the body, the varying of the reactance of the guide wire or catheter 6500 can be readily and manually controlled. [0148] The Balun 6000 includes a variable capacitor C1 connected in parallel with the guide wire or catheter 6500 and a variable capacitor C2 connected in series with the guide wire or catheter 6500. It is noted that one end of the variable capacitor C1 is connected to the shield 6250 and ground or a known voltage. The capacitance of the variable capacitors C1 and C2 are adjusted to create the unbalanced characteristic impedance. [0149] More specifically, the variable capacitors C1, and C2 may be used for both matching and providing a certain amount of balancing for the guide wire or catheter 6500 characteristic impedance. In this example, the variable capacitors C1, C2, and C3 lift the voltage on the guide wire or catheter 6500 from ground. The larger the reactance of the variable capacitors C1 and C2, the more symmetric and balanced the circuit of the guide wire or catheter 6500 becomes. Conversely, according to the concepts of the present invention, if the reactive capacitance of the Balun 6000 is detuned (made less resonant), the circuit of the guide wire or catheter 6500 becomes asymmetric and unbalanced, breaking down, to reduce the chances of thermal injury at the distal end of the guide wire or catheter 6500 due to heating from induced voltages. [0150]FIG. 20 illustrates a further embodiment of the present invention wherein a guide wire or catheter 800 is connected to a Balun 700. The Balun 700 includes a variable capacitor 710, a copper foil 720, and a non-conductive tuning bolt 730. The Balun 700 is further connected to the output of the probe 800 [0151] The Balun 700 adjusts its characteristic impedance by increasing or decreasing the number wire coils are found within the copper foil 720. The combination of the coils and the copper foil 720 forms a variable capacitor, having it impedance determined by the change in the surface area of the coils positioned opposite of the copper foil 720. As more coils are introduced into the volume created by the copper foil 720, the capacitance of this combination increases. Moreover, as fewer coils are introduced into the volume created by the copper foil 720, the capacitance of this combination decreases. Thus, the capacitance of the Balun 700 is adjusted to create the unbalanced characteristic impedance. [0152]FIG. 21 illustrates another embodiment of the present invention wherein a guide wire or catheter 900 is electronically isolated by a voltage control unit to always appear as an unbalanced line to any possible magnetic field that may be applied from a magnetic resonance imager unit (not shown). As current begins to flow due to the changing magnetic fields from the magnetic resonance imaging, a tapped voltage from a voltage-controlled oscillator in the magnetic resonance imaging unit is applied across terminals X1 and X2 of the voltage control unit. [0153] According to the concepts of the present invention, to automatically maintain an unbalanced characteristic impedance at the distal end of the guide wire or catheter 900, a capacitance unbalanced balun unit 7000, located within the voltage control unit, is connected through a variable inductor 910 to the proximal end of the guide wire or catheter 900. In other words, the voltage control unit containing the capacitance unbalanced balun unit 7000 is outside the body at the proximal end of the guide wire or catheter 900. By having the capacitance unbalanced balun unit 7000 and variable inductor 910 outside the body, the varying of the reactance (X0) of the guide wire or catheter 900 can be readily adjusted and automatically controlled by the voltage control unit circuit's reactance to the tapped voltage from the voltage-controlled oscillator in the magnetic resonance imaging unit as it is applied across X1 and X2 for any instance of time from time zero (T0) or instantiation of the magnetic resonance imaging radio-frequency pulses. [0154] The capacitance unbalanced balun unit 7000 includes two non-magnetic trimmer capacitors C1 and C2 connected in parallel with LC circuits (L1, C3) and (L2, C4), respectively, setting up a simplified dual T network that is effectively in series with the guide wire or catheter 900. It is noted that one end of the simplified dual T network is connected to neutral H1 and the other end is connected to a continuously variable voltage H2, based on inputs to the circuit from the voltage-controlled oscillator in the magnetic resonance imaging unit at X1 and X2. The reactance (X0) of the LC circuits in the T network is automatically adjusted to create the desired unbalanced characteristic impedance. [0155] More specifically, the T network L1, C1, C3 and L2, C2, C4 respectively, may be used for both matching and unmatching characteristic impedance of the guide wire or catheter 900 and to provide a certain amount of balancing or unbalancing for the guide wire or catheter 900 by varying the circuit's capacitive or inductive reactance (X0). [0156] In this example, as the voltage from the voltage-controlled oscillator in the magnetic resonance imaging unit is provided to the voltage control unit (X1 X2), the two non-magnetic trimmer capacitors C1 and C2, connected in parallel with LC circuits, (L1, C3) and (L2, C4), lift the voltage on the guide wire or catheter 900 from ground to an unbalanced state with respect to the radio-frequency pulse applied by the magnetic resonance imaging unit. The reactance of the T network and its LC circuits, (L1, C3) and (L2, C4), respectively, cause the guide wire or catheter 900 to become asymmetric and unbalanced, automatically breaking down the reactance to ensure that resonance for the guide wire or catheter 900 is never present, thus reducing the chances of thermal injury at the distal end of the guide wire or catheter 900 due to heating from induced voltages. [0157] While various examples and embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that the spirit and scope of the present invention are not limited to the specific description and drawings herein, but extend to various modifications and changes. 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A61N1/3718, A61N1/37, G01R33/285, H03H7/42, A61N1/05, G01R33/288, A61B2562/222, A61N2001/086European ClassificationG01R33/28H, G01R33/34G, A61N1/05, H03H7/42, A61N1/37Legal EventsDateCodeEventDescriptionDec 2, 2013FPAYFee paymentYear of fee payment: 4May 7, 2008ASAssignmentOwner name: MEDTRONIC, INC., MINNESOTAFree format text: RELEASE BY SECURED PARTY;ASSIGNOR:IROQOUIS MASTER FUND, LTD;REEL/FRAME:020909/0366Effective date: 20071004Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BIOPHAN TECHNOLOGIES, INC.;REEL/FRAME:020909/0169Owner name: MEDTRONIC, INC.,MINNESOTAFree format text: RELEASE BY SECURED PARTY;ASSIGNOR:IROQOUIS MASTER FUND, LTD;US-ASSIGNMENT DATABASE UPDATED:20100302;REEL/FRAME:20909/366Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BIOPHAN TECHNOLOGIES, INC.;REEL/FRAME:20909/169Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:IROQOUIS MASTER FUND, LTD;REEL/FRAME:20909/366Oct 17, 2006ASAssignmentOwner name: IROQUOIS MASTER FUND LTD., NEW YORKFree 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