Abstract:
In one embodiment, a method of fabricating a segmented electrode stimulation lead for implantation within a human patient for stimulation of tissue of the patient, the method comprises: providing a conductive ring, the conductive ring comprising an inner surface and an outer surface, the conductive ring comprising a plurality of grooves provided in the inner surface; electrically coupling a plurality of wires to the conductive ring; forming a stimulation assembly of the lead including the conductive ring and the plurality of wires; and grinding down the outer surface of the stimulation assembly of the lead at least until reaching the plurality of grooves to separate the conductive ring into a plurality of electrically isolated segmented electrodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/238,917, filed Sep. 1, 2009, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This application is generally related to stimulation leads, and in particular to stimulation leads with segmented electrodes and methods of fabrication. 
       BACKGROUND INFORMATION 
       [0003]    Deep brain stimulation (DBS) refers to the delivery of electrical pulses into one or several specific sites within the brain of a patient to treat various neurological disorders. For example, deep brain stimulation has been proposed as a clinical technique for treatment of chronic pain, essential tremor, Parkinson&#39;s disease (PD), dystonia, epilepsy, depression, obsessive-compulsive disorder, and other disorders. 
         [0004]    A deep brain stimulation procedure typically involves first obtaining preoperative images of the patient&#39;s brain (e.g., using computer tomography (CT) or magnetic resonance imaging (MRI)). Using the preoperative images, the neurosurgeon can select a target region within the brain, an entry point on the patient&#39;s skull, and a desired trajectory between the entry point and the target region. In the operating room, the patient is immobilized and the patient&#39;s actual physical position is registered with a computer-controlled navigation system. The physician marks the entry point on the patient&#39;s skull and drills a burr hole at that location. Stereotactic instrumentation and trajectory guide devices are employed to control the trajectory and positioning of a lead during the surgical procedure in coordination with the navigation system. 
         [0005]    Brain anatomy typically requires precise targeting of tissue for stimulation by deep brain stimulation systems. For example, deep brain stimulation for Parkinson&#39;s disease commonly targets tissue within or close to the subthalamic nucleus (STN). The STN is a relatively small structure with diverse functions. Stimulation of undesired portions of the STN or immediately surrounding tissue can result in undesired side effects. Mood and behavior dysregulation and other psychiatric effects have been reported from stimulation of the STN in Parkinson&#39;s patients. 
         [0006]    To avoid undesired side effects in deep brain stimulation, neurologists often attempt to identify a particular electrode for stimulation that only stimulates the neural tissue associated with the symptoms of the underlying disorder while avoiding use of electrodes that stimulate other tissue. Also, neurologists may attempt to control the pulse amplitude, pulse width, and pulse frequency to limit the stimulation field to the desired tissue while avoiding other tissue. 
         [0007]    As an improvement over conventional deep brain stimulation leads, leads with segmented electrodes have been proposed. Conventional deep brain stimulation leads include electrodes that fully circumscribe the lead body. Leads with segmented electrodes include electrodes on the lead body that only span a limited angular range of the lead body. The term “segmented electrode” is distinguishable from the term “ring electrode.” As used herein, the term “segmented electrode” refers to an electrode of a group of electrodes that are positioned at the same longitudinal location along the longitudinal axis of a lead and that are angularly positioned about the longitudinal axis so they do not overlap and are electrically isolated from one another. For example, at a given position longitudinally along the lead body, three electrodes can be provided with each electrode covering respective segments of less than 120° about the outer diameter of the lead body. By selecting between such electrodes, the electrical field generated by stimulation pulses can be more precisely controlled and, hence, stimulation of undesired tissue can be more easily avoided. 
         [0008]    Implementation of segmented electrodes are difficult due to the size of deep brain stimulation leads. Specifically, the outer diameter of deep brain stimulation leads can be approximately 0.06 inches or less. Fabricating electrodes to occupy a fraction of the outside diameter of the lead body and securing the electrodes to the lead body can be quite challenging. 
       SUMMARY 
       [0009]    In one embodiment, a method of fabricating a segmented electrode stimulation lead for implantation within a human patient for stimulation of tissue of the patient, the method comprises: providing a conductive ring, the conductive ring comprising an inner surface and an outer surface, the conductive ring comprising a plurality of grooves provided in the inner surface; electrically coupling a plurality of wires to the conductive ring; forming a stimulation assembly of the lead including the conductive ring and the plurality of wires; and grinding down the outer surface of the stimulation assembly of the lead at least until reaching the plurality of grooves to separate the conductive ring into a plurality of electrically isolated segmented electrodes. 
         [0010]    The foregoing has outlined rather broadly certain features and/or technical advantages in order that the detailed description that follows may be better understood. Additional features and/or advantages will be described hereinafter which form the subject of the claims. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the appended claims. The novel features, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  depicts a cross-sectional view of a conductive ring for fabrication of a segmented electrode stimulation lead according to one representative embodiment. 
           [0012]      FIG. 2  depicts a detailed cross-sectional view of a conductive ring for fabrication of a segmented electrode stimulation lead according to one representative embodiment. 
           [0013]      FIG. 3  depicts a side view of a conductive ring for fabrication of a segmented electrode stimulation lead according to one representative embodiment. 
           [0014]      FIGS. 4A-4E  depict processing of one or more conductive rings to form a stimulation tip assembly according to one representative embodiment. 
           [0015]      FIG. 5  depicts a stimulation tip according to one representative embodiment. 
           [0016]      FIGS. 6A and 6B  depict a splicing tube for splicing of wires of a stimulation lead according to one representative embodiment. 
           [0017]      FIG. 7A  depicts a stimulation system including a segmented stimulation lead according to one representative embodiment. 
           [0018]      FIG. 7B  depicts a segmented electrode stimulation lead for use in the system of  FIG. 7A  that may be fabricated according to embodiments disclosed herein. 
           [0019]      FIG. 8  depicts a lead body assembly for attachment to a stimulation tip according to some representative embodiments. 
           [0020]      FIG. 9A  depicts a ring structure for fabricating segmented electrodes that includes an alignment structure according to one representative embodiment. 
           [0021]      FIG. 9B  depicts a ring structure and an insulative spacer that include complementary mating structures for fabricating segmented electrodes according to one representative embodiment. 
           [0022]      FIG. 9C  depicts a ring structure that is inserted molded with a resin material according to one representative embodiment. 
           [0023]      FIG. 9D  depicts the ring structure of  FIG. 9C  after machining to include a central aperture according to one representative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The present application is generally related to a process for fabricating a stimulation lead comprising multiple segmented electrodes. In one preferred embodiment, the lead is adapted for deep brain stimulation (DBS). In other embodiments, the lead may be employed for any suitable therapy including spinal cord stimulation (SCS), peripheral nerve stimulation, peripheral nerve field stimulation, cortical stimulation, cardiac therapies, ablation therapies, etc. 
         [0025]    In one embodiment, a ring of conductive material is machined to facilitate the fabrication of segmented electrode lead. As shown in  FIGS. 1 and 3 , ring  100  is preferably implemented as a continuous or substantially continuous annular tube or cylinder of conductive material. In one embodiment, ring  100  is fabricated from platinum iridium material although any suitable biocompatible, conductive material may be employed. 
         [0026]      FIG. 1  depicts a cross-sectional view of ring  100  according to one representative embodiment. Ring  100  comprises an outer surface  101  and an inner surface  102 . In one embodiment, ring  100  comprises an inner diameter of 0.041 inches and an outer diameter of approximately 0.061 inches. Using these dimensions, ring  100  comprises a thickness of approximately 0.02 inches. Any suitable dimensions may be provided for ring  100  depending upon the desired stimulation therapy for the fabricated stimulation lead. Also, the dimensions may vary along the length of ring  100  (see discussion of  FIG. 3  below) and/or about the circumference of ring  100 . 
         [0027]    Additionally, ring  100  comprises a plurality of grooves (shown as  103   a - 103   c  in  FIG. 1 ) on the inner surface  102  of ring  100 . The machined grooves  103  are preferably disposed at equal angular distances from each other along inner surface  102  of ring  100 . For example, the center point of each groove may be separated by 120° when ring  100  is intended to be separated into three segmented electrodes. 
         [0028]    Grooves  103  are machined into the inner surface  102  of ring  100  to provide a reduction in the thickness of ring  100  at a respective angular portion of ring  100 . Machined groove  103   c  is individually shown in  FIG. 2 . In one preferred embodiment, groove  103   c  (and grooves  103   a  and  103   b ) reduces the thickness from outer surface  101  to inner surface  102  to approximately 0.005 inches (shown as distance  201  in  FIG. 2 ). 
         [0029]    To facilitate the attachment of conductive wires during the lead fabrication process, ring  100  comprises a plurality of channels (shown as  104   a - 104   c  in  FIG. 1 ) for receiving a respective wire. The reduction in the wall thickness of ring  100  caused by channels  104  is preferably significantly less than the reduction in wall thickness caused by grooves  103 . 
         [0030]      FIG. 3  depicts a side view of ring  100  according to one representative embodiment. As shown in  FIG. 3 , ring comprises distal portion  301 , medial portion  302 , and distal portion  303 . Distal portions  301  and  303  are preferably raised relative to medial portion  302 . That is, the outer diameter of ring  100  is greater at distal portions  301  and  303  relative to the outer diameter of ring  100  at medial portion  302 . 
         [0031]      FIGS. 4A-4C  depict attachment of conductor wires  401  to ring  100  according to one representative embodiment. During a first step of the wire attachment process, conductor wires  401  and ring  100  are placed onto a welding mandrel as shown in  FIG. 4A . Preferably, wires  401  are placed within the interior of ring  100  along channels  104  (shown previously in  FIG. 1 ) and bent over the outer surface  101  of ring  100 . Conductor wires  401  are held in a secured position using band  402  as shown in  FIG. 4B . Laser energy is then applied to each of conductors  401  to laser weld wires  401  to ring  100 . The laser welding mechanically and electrically couples the conductors  401  to ring at the respective channels  104 .  FIG. 4C  depicts ring assembly  400  including attached conductors  401  after the welding process is performed according to one representative embodiment. By attaching wires  401  in this manner according to one embodiment, the wire attachment process may provide several advantageous. For example, a direct line of sight is provided for application of the laser energy. Also, a smaller laser spot size than typically used for electrode laser welding processes may be employed. This process also permits visual inspection to identify any potential wire fraying. Further, this process may provide superior weld consistency.  FIG. 4D  depicts ring assembly  400  after removal from the welding mandrel. 
         [0032]    In some embodiments, multiple ring assemblies  400  are placed in sequence to form a stimulation lead.  FIG. 4E  depicts stimulation tip assembly  450  according to one representative embodiment. Tip assembly  450  comprises two assemblies  400  placed in sequence and separated by spacer  451 . Although only two assemblies  400  are shown in  FIG. 4E , any suitable number of assemblies  400  could be employed in any suitable configuration or pattern. Spacers  451  are preferably fabricated using a polymer capable of reflow and, most preferably, is the same polymer as used for a lead body of the stimulation lead. Also, as shown in the embodiment of  FIG. 4E , conventional ring electrode  452  is separated from one of the assemblies  400  by another spacer  451 . A respective wire  401  is electrically and mechanically coupled to ring electrode  452 . 
         [0033]    Wires  401  are threaded through the interiors of each preceding structure in tip assembly  450 . An additional wire may be threaded through the interiors of the structures to accommodate a tip electrode (not shown in  FIG. 4E ). In some embodiments, assemblies  400 , ring electrode  452 , spacers  451  are placed about a segment of tubing (not shown). Outer tubing may be placed about the portion of wires  401  extending away from conventional ring electrode  452 . 
         [0034]    Tip assembly  450  is preferably subjected to injection molding. A tip electrode may also be attached at the distal end of assembly  450 . Grinding (e.g., centerless grinding) or any other suitable material removal technique is performed to reduce the outer diameter of the molded assembly. 
         [0035]    When the grinding is performed, material along the outer surface of each ring  100  of ring assemblies  450  is removed. The outer diameter of each ring  100  is gradually reduced until the grinding process exposes grooves  103 . When grooves  103  are exposed in a respective ring  100 , the ring  100  is separated into multiple electrically isolated segments to function as segmented electrodes due to their respective electrical connection to their respective wires  401 . As shown, ring  100  is adapted to separate into three segmented electrodes, although similar designs could be employed to contain fewer or more segmented electrodes. 
         [0036]    In some representative embodiments, selected structures within assembly  450  may be adapted to ensure that each ring  100  is aligned in substantially the same manner. That is, upon grinding, each segmented electrode will be aligned in a relatively precise angular manner relative to segmented electrodes at other longitudinal locations of the stimulation lead. For example, as shown in  FIG. 9A , each ring  900  may comprise ridge  910  for alignment purposes. The ridges  910  may permit visual inspection to determine the alignment. Alternatively, ridges  910  may be attached to a suitable fixture (not shown) to ensure the proper alignment. In another embodiment, each ring  100  and spacer  451  may include complementary mating structures (see, e.g., structure  951  in  FIG. 9B ) to attach each structure in a predetermined manner. In another embodiment, a rigid resin may be insert molded (shown as material  975  in  FIG. 9C ) within the inner surface of ring structure  970  for fabrication of segmented electrodes. A center aperture may be then be machined to facilitate provision of conductor wires. The remaining molded material may be left within grooves (as shown in  FIG. 9D ) to reduce the probability of segment peeling during the grinding process. 
         [0037]      FIG. 5  depicts stimulation tip  500  after the removal of material of rings  100  according to one representative embodiment. As shown in  FIG. 5 , stimulation tip comprises tip electrode  501 , segmented electrodes  502 , and proximal ring electrode  503 . Wires  401 , which are electrically coupled to respective ones of tip electrode  501 , segmented electrodes  502 , and ring electrode  503 , are contained with body  504  of insulative material from the tubing and molding. The insulative material may include BIONATE® (thermoplastic polycarbonate urethane), a silicon based material, or any other suitable biocompatible material. As shown in  FIG. 5 , stimulation tip  500  is then ready to be integrated with other components to form a stimulation lead according to some representative embodiments. 
         [0038]      FIG. 8  depicts intermediate lead body assembly  850  adapted for connection to a stimulation tip according to one representative embodiment. Lead body assembly  850  comprises lead body  800  with a suitable number of conductors (shown individually as conductors  801   a - 801   h ) embedded or otherwise enclosed within insulative material. Conductors  801  are provided to conduct electrical pulses from the proximal end of lead assembly  850  to the distal end of lead assembly  850 . Lead body  800  may be fabricated using any known or later developed processes. Examples of various lead body fabrication processes are disclosed in U.S. Pat. No. 6,216,045, U.S. Pat. No. 7,287,366, U.S. Patent Application Publication No. 20050027340A1, and U.S. Patent Application Publication No. 20070282411A1, which are incorporated herein by reference. 
         [0039]    As is known in the art, each individual conductor  801  is commonly provided with a thin coating of a higher durometer insulator such as perfluoroalkoxyethylene (PFA). The purpose of the higher durometer coating is to ensure that the wire within the conductor  801  remains insulated in the event that the softer polymer material of the lead body  800  is breached or otherwise fails while the lead body  800  is implanted within a patient. The conductors  801  are commonly helically wound and insulative material (e.g., a polyurethane, PURSIL®, CARBOSIL®, etc.) is applied over the conductors to hold conductors  801  in place and to support conductors  801 . Other common types of lead bodies provide individually coiled conductors within separate lumens of a lead body. Such lead bodies may also be utilized according to some embodiments. 
         [0040]    As shown in  FIG. 8 , the outer insulative material of the lead body  800  is removed at the distal end of lead body  800  to permit access to a length of each conductor  801 . For example, a suitable laser (e.g., a UV laser) can be used to remove the insulative material over a controlled portion of the pre-formed lead body  800  to release a length of each conductor  801  from lead body  800 . Alternatively, manual stripping may be performed to release each conductor  801 . Depending upon the type of harder insulative material applied to each individual conductor  801 , a separate process may be used to further expose a conductive portion of the wire of each conductor. Lead body assembly  850  may then be electrically coupled to stimulation tip  500 . 
         [0041]      FIGS. 6A and 6B  depict splicing tube  600  for facilitating splicing of conductors wires during fabrication of a stimulation lead.  FIG. 6A  depicts a full view of tube  600  and  FIG. 6B  depicts a detailed view of tube  600  to show conductor detail. 
         [0042]    Initially, a lead body is processed to release individual conductors from a distal end of the lead body (see  FIG. 8 ). The released ends of respective conductors from the lead body are placed within grooves of splicing tube  600  (e.g., conductor  612  is shown placed within groove  601  as shown in  FIGS. 6A and 6B ). The proximal ends of the wires from stimulation tip  500  are also placed within the grooves of splicing tube  600  (e.g., conductor  611  is shown placed over conductor  612  in  FIG. 6B ). 
         [0043]    Conductive filler material  602  is preferably provided for each pair of conductors in the grooves of splicing tube  600 . In one embodiment, material  602  is provided in ribbon form about each pair of conductors. Material  602  and the pair of conductors are subjected to laser welding. The welding preferably causes material  602  to flow into the strands of the conductor wires making both a mechanical and electrical connection. 
         [0044]    The lead body, the splicing tube, and the electrode array are subjected to overmolding. In one preferred embodiment, the splicing tube is formed of thermoplastic material that flows and fuses with the overmolding material, the material of the lead body, the material of the stimulation tip, etc. Accordingly, upon overmolding, an integrated stimulation lead is formed that is substantially free of gaps and free of weakened transitions between separate non-fused layers of insulative material. Suitable grinding techniques are applied to provide a uniform diameter along the lead. 
         [0045]    Terminals, electrical contacts for receiving electrical pulses, (not shown) are then provided on the proximal end where the terminals are electrically coupled to the conductive wires internal to the lead body. The terminals may be provided using any known or later developed fabrication process. An example of the suitable fabrication process is shown in U.S. Pat. No. 6,216,045. 
         [0046]    During the foregoing discussion, certain fabrication steps have been discussed in a particular sequence. The sequence discussed herein has been presented for the convenience of the reader. It shall be appreciated that the discussed sequence is not required and any suitable order of fabrication may be performed without departing from the scope of the application. Moreover, certain steps may be performed concurrently or separately. For example, grinding may be applied to certain segments of the lead separately or grinding may be applied simultaneously to multiple segments. 
         [0047]      FIG. 7A  depicts stimulation system  700  according to one representative embodiment. Neurostimulation system  700  includes pulse generator  720  and one or more stimulation leads  701 . Examples of commercially available pulse generator include the EON®, EON MINI®, and the LIBRA® pulse generators available from St. Jude Medical Neuromodulation Division. Pulse generator  720  is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses for application to neural tissue of the patient. Control circuitry, communication circuitry, and a rechargeable battery (not shown) are also typically included within pulse generator  720 . Pulse generator  720  is usually implanted within a subcutaneous pocket created under the skin by a physician. 
         [0048]    Lead  701  is electrically coupled to the circuitry within pulse generator  720  using header  710 . Lead  701  includes terminals (not shown) that are adapted to electrically connect with electrical connectors (e.g., “Bal-Seal” connectors which are commercially available and widely known) disposed within header  710 . The terminals are electrically coupled to conductors (not shown) within the lead body of lead  701 . The conductors conduct pulses from the proximal end to the distal end of lead  701 . The conductors are also electrically coupled to electrodes  705  to apply the pulses to tissue of the patient. Lead  701  can be utilized for any suitable stimulation therapy. For example, the distal end of lead  701  may be implanted within a deep brain location or a cortical location for stimulation of brain tissue. The distal end of lead  701  may be implanted in a subcutaneous location for stimulation of a peripheral nerve or peripheral nerve fibers. Alternatively, the distal end of lead  701  positioned within the epidural space of a patient. Although some embodiments are adapted for stimulation of neural tissue of the patient, other embodiments may stimulate any suitable tissue of a patient (such as cardiac tissue). An “extension” lead (not shown) may be utilized as an intermediate connector if deemed appropriate by the physician. 
         [0049]    Electrodes  705  include multiple segmented electrodes as shown in  FIG. 7B . The use of segmented electrodes permits the clinician to more precisely control the electrical field generated by the stimulation pulses and, hence, to more precisely control the stimulation effect in surrounding tissue. Electrodes  705  may also include one or more ring electrodes or a tip electrode (not shown in  FIG. 7B ). Any of the electrode assemblies and segmented electrodes discussed herein can be used for the fabrication of electrodes  705 . Electrodes  705  may be utilized to electrically stimulate any suitable tissue within the body including, but not limited to, brain tissue, tissue of the spinal cord, peripheral nerves or peripheral nerve fibers, digestive tissue, cardiac tissue, etc. Electrodes  705  may also be additionally or alternatively utilized to sense electrical potentials in any suitable tissue within a patient&#39;s body. 
         [0050]    Pulse generator  720  preferably wirelessly communicates with programmer device  750 . Programmer device  750  enables a clinician to control the pulse generating operations of pulse generator  720 . The clinician can select electrode combinations, pulse amplitude, pulse width, frequency parameters, and/or the like using the user interface of programmer device  750 . The parameters can be defined in terms of “stim sets,” “stimulation programs,” (which are known in the art) or any other suitable format. Programmer device  750  responds by communicating the parameters to pulse generator  720  and pulse generator  720  modifies its operations to generate stimulation pulses according to the communicated parameters. 
         [0051]    Although certain representative embodiments and advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate when reading the present application, other processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the described embodiments may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.