Abstract:
In one embodiment, an implantable pulse generator for electrically stimulating a patient comprises: a metallic housing enclosing pulse generating circuitry; a header mechanically coupled to the metallic housing, the header adapted to seal terminals of one or more stimulation leads within the header and to provide electrical connections for the terminals; the header comprising an inner compliant component for holding a plurality of electrical connectors, the plurality of electrical connectors electrically coupled to the pulse generating circuitry through feedthrough conductors, wherein the plurality of electrical connectors are held in place in recesses within the compliant inner component, the header further comprising an outer shield component adapted to resist punctures, the outer shield component fitting over at least a portion of the inner compliant component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/479,058, filed May 23, 2012 (issued as U.S. Pat. No. 8,433,411) which is a continuation of U.S. patent application Ser. No. 12/100,814, filed Apr. 10, 2008 (issued as U.S. Pat. No. 8,190,259) which, in turn, claims the benefit of U.S. Provisional Application No. 60/910,941, filed Apr. 10, 2007, the disclosure of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application is generally related to a header design for an implantable pulse generator for accepting one or more stimulation leads. 
       BACKGROUND 
       [0003]    Neurostimulation systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders. Spinal cord stimulation (SCS) is an example of neurostimulation in which electrical pulses are delivered to nerve tissue in the spine for the purpose of chronic pain control. Other examples include deep brain stimulation, cortical stimulation, cochlear nerve stimulation, peripheral nerve stimulation, vagal nerve stimulation, sacral nerve stimulation, etc. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated nerve tissue. Specifically, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Thereby, paresthesia can effectively mask the transmission of non-acute pain sensations to the brain. 
         [0004]    Neurostimulation systems generally include a pulse generator and one or more leads. The pulse generator is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses, control circuitry, communication circuitry, a rechargeable battery, etc. The pulse generation circuitry is coupled to one or more stimulation leads through electrical connections provided in a “header” of the pulse generator. Specifically, feedthrough wires typically exit the metallic housing and into a header structure of a moldable material. Within the header structure, the feedthrough wires are electrically coupled to annular electrical connectors. The header structure holds the annular connectors in a fixed arrangement that corresponds to the arrangement of terminals on a stimulation lead. When a stimulation lead is properly inserted within a port of the header, each terminal of the lead contacts one of the annular electrical connectors and, thereby, is electrically coupled to the pulse generating circuitry through the feedthrough wires. 
         [0005]    A number of fabrication issues are associated with the selection of the material for the header. If a non-compliant high durometer material is selected for the header, additional complexity is typically provided to the header design to hold the electrical connectors in place. Also, the placement of the electrical connectors in such a header can be unduly difficult. Alternatively, if a compliant material is selected for the header, the header can be easily punctured or otherwise damaged by surgical tools during an implantation procedure. 
       SUMMARY 
       [0006]    In one embodiment, an implantable pulse generator for electrically stimulating a patient comprises: a metallic housing enclosing pulse generating circuitry; a header mechanically coupled to the metallic housing, the header adapted to seal terminals of one or more stimulation leads within the header and to provide electrical connections for the terminals; the header comprising an inner compliant component for holding a plurality of electrical connectors, the plurality of electrical connectors electrically coupled to the pulse generating circuitry through feedthrough wires, wherein the plurality of electrical connectors are held in place in recesses within the compliant inner component, the header further comprising an outer shield component adapted to resist punctures, the outer shield component fitting over at least a portion of the inner compliant component. 
         [0007]    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 
         [0008]      FIG. 1  depicts an implantable pulse generator that includes a header according to one representative embodiment. 
           [0009]      FIGS. 2A and 2B  depict known electrical connectors that can be utilized within a header according to representative embodiments. 
           [0010]      FIG. 3  depicts a compliant inner component of a header according to one representative embodiment. 
           [0011]      FIG. 4  depicts a shield component of a header according to one representative embodiment. 
           [0012]      FIG. 5  depicts a structure for holding an antenna in a helical manner according to one representative embodiment. 
           [0013]      FIG. 6  depicts a schematic of an equivalent circuit for an antenna according to one representative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Some representative embodiments are directed to a header design for a neurostimulation system. The header design preferably comprises a compliant silicone component and a shield component of a non-compliant material. The silicone component and the shield component cooperate to provide seals between the lead electrodes and to provide a barrier to protect against damage or punctures from surgical tools used during implantation. The header design also preferably comprises an antenna component that defines a helical antenna path to support RF communications. Also, the antenna component is preferably adapted to facilitate coupling of the antenna with tissue of the patient to achieve a greater communication range for the implantable pulse generator. 
         [0015]      FIG. 1  depicts implantable pulse generator  100  according to one representative embodiment. Implantable pulse generator  100  comprises metallic housing  110  that encloses the pulse generating circuitry, control circuitry, communication circuitry, battery, etc. of the device. An example of pulse generating circuitry is described in U.S. Patent Publication No. 20060170486 entitled “PULSE GENERATOR HAVING AN EFFICIENT FRACTIONAL VOLTAGE CONVERTER AND METHOD OF USE,” which is incorporated herein by reference. A microprocessor and associated charge control circuitry for an implantable pulse generator is described in U.S. Patent Publication No. 20060259098, entitled “SYSTEMS AND METHODS FOR USE IN PULSE GENERATION,” which is incorporated herein by reference. Circuitry for recharging a rechargeable battery of an implantable pulse generator using inductive coupling with an external charging device is described in U.S. patent Ser. No. 11/109,114, entitled “IMPLANTABLE DEVICE AND SYSTEM FOR WIRELESS COMMUNICATION,” which is incorporated herein by reference. An example of a commercially available implantable pulse generator that may be adapted to include a header according to some representative embodiments is the EON® implantable pulse generator available from Advanced Neuromodulation Systems, Inc. 
         [0016]    As shown in  FIG. 1 , header  120  comprises compliant inner component  121 , non-compliant shield component  122 , and antenna component  123 . Compliant inner component  121  is preferably fabricated using an injection molding process and silicone based materials. Compliant inner component  121  is adapted to receive two stimulation leads (not shown) through strain relief elements  132 , although header  120  could be alternatively adapted to couple to any suitable number of stimulation leads. To minimize the profile of implantable pulse generator  100 , compliant inner component  121  is adapted to receive the stimulation leads in a side-by-side manner in one embodiment. Other embodiments may be configured to receive the stimulation leads in an above-below manner or even in an array-like manner for several stimulation leads. 
         [0017]    Compliant inner component  121  is adapted to hold a plurality of electrical connectors  131  for each stimulation lead. Specifically, compliant inner component  121  comprises a plurality of recesses defined between respective wall structures  135  in which electrical connectors  131  are disposed. The compliant material characteristic of component  121  holds electrical connectors  131  in place by applying an elastomeric force. Electrical connectors  131  are spaced apart in relation to the spacing of the terminals of the stimulation leads intended to function with implantable pulse generator  100 . Each electrical connector  131  is electrically coupled to pulse generation circuitry within metallic housing  110  through a respective feedthrough wire as is known in the art. Compliant inner component  121  is shown in isolation in  FIG. 3 . Apertures  301  within walls  135  are shown in  FIG. 3  for the respective stimulation leads. 
         [0018]    Typically, electrical connectors  131  are fabricated using an outer conductive annular or ring-like structure. Within the ring-like structure, one or more conductive members are held to engage a respective terminal of the stimulation lead. An example of known connector  200  is shown in  FIG. 2A  in which a canted spring is held within a conductive ring. Such connectors are commercially available from Bal Seal, Inc. of Foothill Ranch, Calif. Another example of known connector  250  is shown in  FIG. 2B  in which a conductive disk having arcuate connector tabs is held within a conductive ring as shown in U.S. Patent Publication No. 20050107859, entitled “SYSTEM AND METHOD OF ESTABLISHING AN ELECTRICAL CONNECTION BETWEEN AN IMPLANTED LEAD AND AN ELECTRICAL CONTACT,” which is incorporated herein by reference. It shall be appreciated that other types of electrical connectors could be employed such as “block electrical connectors” which are known in the art. Also, different types of electrical connectors could be employed within the same header in any suitable configuration. 
         [0019]    Shield component  122  (shown in isolation in  FIG. 4 ) is adapted to fit over a significant portion of and mechanically couple to inner compliant component  121 . Shield component  122  may also be adapted to fit over a portion or all of antenna component  123 . When header  120  is fully assembled and stimulation leads are placed in header  120  through strain relief elements  132 , the various conductive elements are sealed within the components of header  100 . Specifically, when implantable pulse generator  100  is implanted within a patient, the electrical components are sealed and are prevented from contacting bodily fluids. Additionally, shield component  122  is fabricated from a relatively hard material to prevent damage to or puncture of compliant inner component  121 . Specifically, if a sharp object used during the implantation procedure were to contact compliant inner component directly, compliant inner component  121  could be punctured somewhat easily. The puncture could allow entry of body fluids and cause the patient to experience electrical stimulation in the subcutaneous implantation pocket. By utilizing a suitable material for shield component  122 , compliant inner component  121  is protected from sharp surgical tools, needles, staples, and the like. An example of a suitable material for shield component  122  is a relatively high durometer Bionate® polycarbonate urethane. 
         [0020]    Header  120  comprises antenna component  123  to facilitate RF communication between the implantable pulse generator  100  and an exterior controller device (not shown). The exterior shell of antenna component  123  is preferably a relative high durometer polymer. In one preferred embodiment, the exterior shell of antenna component  123  is a relatively high durometer Bionate® polycarbonate urethane. Platinum ribbon  133  forms the actual far field antenna and is preferably wrapped around a helical path defined within the interior of antenna component  123 . Preferably, the antenna and communication circuitry enable wireless communications within a range of several meters. In one embodiment, platinum ribbon  133  is wrapped around molded polymer component  501  (shown in  FIG. 5 ) which is enclosed within the exterior shell of antenna component  123 . Polymer component  501  may provide any suitable number of revolutions for antenna ribbon  133 . 
         [0021]    Referring again to  FIG. 1 , platinum ribbon  133  is coupled to communication circuitry within metal housing  110  through feedthrough  134 . The upper segments of platinum ribbon  133  are disposed immediately below slots  136  of exterior shell of antenna component  123 . Slots  136  are formed by reducing the thickness of the polymer material of the exterior shell at the appropriate locations. The reduced thickness of the polymer material at these locations promotes the efficiency of the coupling of the RF signal with tissue of the patient. Such coupling facilitates a greater communication range for the RF signal. 
         [0022]    Antenna  123  is preferably fully insulated from contact with human tissue by header  120  so that no corrosion products from the conductor of the antenna enter tissue, and, there is little surface impedance variation caused by fibrosis, scar tissue, etc, after implant. Surface impedance variation on the conductor may cause the distribution of radiating current density to change, possibly in a manner which deleteriously affects the radiation pattern outside the human body. Furthermore, gross surface impedance alterations may alter the amount of total electromagnetic energy radiated from/or into the antenna by causing intended emitted/absorbed energy to be reflected back to the transmitter. 
         [0023]    The skewed cross-section shape of antenna  123  is preferably an inverted triangle with finite radius curves replacing triangle vertices. In one embodiment, the lowest, rounded, vertex is designed to be furthest from the straight top segment of each section, so that the enclosed area maximizes the storage of magnetic energy. But it is not so close to the conductive (“ground”) surface of the enclosure that coupling to the enclosure is more than a small fraction of the coupling from the top segment to tissue. In that way, RF displacement current is provided with a lower impedance path from top segments of the antenna, much lower than that between lowest rounded vertices. 
         [0024]    In some embodiments, the lowest rounded vertices may have any radius of curvature up to and including half the width of header  120 . Or, as small as the minimum bend radius of conductor  133  according to some embodiments. However, as the radius of vertex curvature decreases, the RF electric field flux density increases in proximity to that vertex. The coupling to the enclosure would increase, and so to compensate those vertices would have to be displaced closer to the top segments of antenna  123 . This would reduce the magnetic energy storage (“inductance”) of each spiral revolution, or “turn” of the antenna. The intent of some embodiments is to optimize the inductance per turn with the (“electrostatic”) coupling between turns so that the overall impedance of the antenna maximizes coupling into human tissue along the top sections of antenna  123 , while also presenting an easily-matched impedance at the antenna feed terminal. The schematic  600  ( FIG. 6 ) shows the approximate lumped element equivalent circuit. 
         [0025]    The intent of some embodiments is to enhance emission from the top of the antenna, with a return path through human tissue, such that the current density distribution maximizes radiation outside the human body. The alignment of antenna  123  is preferably adapted such that directions of maximum radiation power density tend to be located symmetrically either side of the antenna mid-plane. The optimum electric field polarization direction is transverse to the antenna mid-plane. There would be a null (minimum) of the transverse polarization radiation intensity in the antenna mid-plane, provided the surrounding medium (human tissue) was isotropic and homogeneous. 
         [0026]    Each complete path (“revolution”) of inverted triangle with curved vertices, mentioned above, connects conductively with the adjacent triangular paths at one location, so that the complete antenna consists of multiple inverted triangular spiral elements connected together. The approximate equivalent circuit is shown in  FIG. 6 , for the example of a six turn inverted triangular spiral antenna (6T ITSA). 
         [0027]    The conductor  133  of antenna  123  preferably consists of a metal strip presenting a large surface area along the top segments of the antenna, so that capacitances (C12-17, above) are maximized for a given thickness of insulation (dielectric), having a certain dielectric constant. For example, a rectangular cross section with a surface resistance per unit area much less than the surface reactances per unit area, presented by C12-17, at the radio frequency of operation. 
         [0028]    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.