Fully Duplex Implantable Pulse Generator (IPG) System and Electro-Optical Percutaneous Leads

Abstract

The present invention provides an IPG and lead configuration with both a novel optical folding assembly and optical processor assembly that provides the advantages of low heat generation and compact package size. The surgical lead provided provides additional advantages over the prior art, such as integral formation of optical and electrical components in a compact size. The present invention further provides a processing advantage to measure and compensate for degradation of the optical system over time.

Description

[Technical field]

[0001] The present invention relates to an improved implantable pulse generator ("IPG") and header combination using optical reflectometry for spinal cord stimulation ("SCS"). [Background technology]

[0002] Chronic pain can result from a variety of pathologies, including nerve injury, as in neuropathic pain, and chronic stimulation of mechanical nociceptors, as in spinal pain. Functional ability is severely affected by pain and is often refractory to pharmacological and surgical treatments. In these cases, SCS can be an effective treatment for pain by modulating the physiological transmission of pain signals from the periphery to the brain. This is achieved by applying electrical impulses to the spinal cord via an electrode array implanted adjacent to the spinal canal.

[0003] A typical IPG system of the prior art is described with reference to Figures 1, 2 and 3. A spinal column 1 is shown having a number of vertebrae grouped into four sections or types: lumbar 2, thoracic 3, cervical 4, and sacral 5. The cervical vertebrae 4 include the first cervical vertebra (C1) through the seventh cervical vertebra (C7). Just below the seventh cervical vertebra are the first of twelve thoracic vertebrae 3, including the first thoracic vertebra (T1) through the twelfth thoracic vertebra (T12). Just below the twelfth thoracic vertebra 3 are five lumbar vertebrae 2, including the first lumbar vertebra (L1) through the fifth lumbar vertebra (L5), which are attached to the sacral vertebrae 5 (S1 through S5), which are naturally fused in adults.

[0004] A representative thoracic vertebra 10 has been shown to have many notable features in common with the lumbar vertebra 2 and cervical vertebra 4. The thick oval bone segment that forms the anterior surface of the vertebra 10 is the vertebral body 12. The vertebral body 12 is attached to a bony vertebral arch 13 through which the spinal nerves 11 pass. The vertebral arch 13 forms the posterior surface of the vertebra 10 and is composed of two pedicles 14, which are short raised processes that extend from the sides of the vertebral body 12, and bilateral lamina 15. The broad plates projecting from the pedicles 14 join in a triangle to form a hollow, arched spinal canal 16. Spinous processes 17 project from the junction of the bilateral lamina 15. Transverse processes 18 project from the junction of the pedicles 14 and the bilateral lamina 15. The structure of the vertebral arch protects the spinal cord 20 and spinal nerves 11 that pass through the spinal canal.

[0005] Surrounding the spinal cord 20 is the dura mater 21, which contains cerebrospinal fluid (CSF) 22. The epidural space 24 is the space within the spinal canal that lies outside the dura mater.

[0006] One or more electrodes 30 are placed in the epidural space 24 between the dura 21 and the wall of the spinal canal 16 toward the posterior side of the spinal canal nearest the bilateral lamina 15 and the spinous processes 17. The electrodes 30 have electrode leads 31 that are connected to an IPG 32 and a control unit 33.

[0007] The IPG 32 delivers electrical stimulation in the form of current pulses to the spinal cord through leads 31 to electrodes 30. The pulses generate an electric field that impinges on target neurons in the spinal cord and disrupts the perception of pain. The amplitude of the electric field is critical to successful spinal cord stimulation. Insufficient electric field will not depolarize the target neurons, rendering the treatment ineffective. Excessive electric field will stimulate neighboring cell populations, resulting in harmful stimulation.

[0008] Establishing a consistent, therapeutic, and non-toxic level of stimulation is predicated on establishing an ideal current density in the target neurons of the spinal cord. In principle, this should be a simple matter of establishing an optimal electrode current taking into account the local bulk conductivity of the surrounding tissue. In reality, however, because the spinal cord is suspended in cerebrospinal fluid within the spinal canal, spinal cord motion causes the optimal electrode current to change as a function of the patient's position and activity. Significant changes in the distance between the epidural electrode array and the targeted spinal neurons have been shown to occur. As a result, optimal stimulation requires dynamic adjustment of the electrode stimulation current as a function of the distance between the electrode array and the spinal cord.

[0009] Dynamically adjusting spinal cord stimulation electrode current as a function of the distance between the electrode array and the spinal cord has several advantages: excessive stimulation currents can be avoided, thereby reducing the possibility of harmful stimulation and potentially reducing device power consumption, and inappropriate stimulation currents can be avoided, thereby eliminating periods of reduced therapeutic efficacy.

[0010] Dynamic modulation of electrode current can be controlled by using optical reflectance measurements to determine the thickness of the dorsal cerebrospinal fluid (dCSF) column between the spinal cord and the electrode array. Optical signals are sent to the surrounding tissue and collected by a sensor to calculate the approximate distance between the electrode and the spinal cord. The magnitude of stimulation is altered accordingly to deliver the optimal current for pain relief. Examples of this technology are shown in U.S. Patents 10,035,019 and 9,656,097 to Wolf II, both of which are incorporated herein by reference.

[0011] One challenge in the implantation and use of IPGs is the package size. For the IPG to survive long-term in the in vivo environment, the package size must be as small as possible to reduce rejection rates and shorten scar formation times. Small package size also reduces the chance of migration of the package or the surgical leads exiting it.

[0012] Another challenge with IPG systems is properly interpreting the reflected optical signals. Prior art half-duplex systems require multiple surgical leads to be precisely positioned near the target neurons. Such placement during surgery is difficult. This problem is further exacerbated by lead movement, which can lead to misalignment of the fibers and degradation of the optical feedback that controls the modulation of the stimulation signal.

[0013] Another challenge for IPG systems is power constraints and heat generation. To ensure long-term battery life in the IPG package, the power usage of the IPG must be minimized. Furthermore, to prevent rejection, heat generation in the in vivo environment must be minimized. Therefore, both power consumption and heat generation must be kept as low as possible.

[0014] Another challenge for optical IPG systems is Fresnel reflection. Fresnel reflection occurs at all optical interfaces throughout the leads and fibers and can be assumed to account for approximately 4% signal loss per optical interface. Interface losses are constant over time. Fiber degradation due to bending also introduces Fresnel loss. However, fiber degradation losses are not constant and vary over time. Optical losses affect the accuracy of the optical feedback that controls the stimulation signal.

[0015] Another challenge with optical IPG systems is that the laser output changes due to power fluctuations and component aging, and the characteristics of the optical system change over time, reducing the effectiveness of the stimulation signal control and therefore the effectiveness of the stimulation signal.

[0016] The prior art has attempted to address these challenges in a number of ways, all of which have fallen short.

[0017] For example, U.S. Patent No. 9,656,097 to Wolf II describes a full duplex IPG lead in which both transmit and receive light beams can travel down the same fiber. However, Wolf discloses the use of a circulator to separate the two beams, which is impractical due to the package size of the circulator and the optical losses incurred.

[0018] As another example, U.S. Patent No. 7,7342,817 to Malinowski et al. describes an IPG with connectors for electrical leads and an epoxy coating for biocompatibility, but Malinowski does not disclose the use of optical feedback to achieve appropriate stimulation signal strength.

[0019] As another example, U.S. Publication No. 2021 / 0001114 to Wolf II discloses coupling optical leads to an IPG header adjacent to a ruby ​​passthrough window that is vertically aligned with a photodetector, but Wolf does not disclose how to recognize or compensate for degradation of the optical system over time.

[0020] U.S. Publication No. 2018 / 0154152 to Chabrol discloses a system for deep brain stimulation using a probe with stimulating electrodes and a light emitting optical fiber. However, Chabrol does not address the use of optical signals to control the stimulation signal to the spinal cord, nor does it address how to test for degradation of the optical signal over time or any resulting loss.

[0021] Deficiencies exist in the prior art with respect to power usage constraints, heat generation, and maintaining accurate optical feedback over time. Thus, there is a need in the art for an improved IPG, including header orientation, connectors, leads, and electrodes, that tracks optical signal degradation due to Fresnel reflections and provides a stable optical signal while reducing power consumption and heat generation. [Brief description of the drawings]

[0022] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings. [Figure 1] FIG. 1 is a lateral view of the human spine showing the approximate location of percutaneous leads and IPGs for spinal cord stimulation. [Diagram 2] FIG. 2 is an axial view of the thoracic spine showing the spinal cord and the location of percutaneous lead pairs. [Diagram 3] FIG. 3 is a sagittal cross-sectional view of the human spine showing the approximate location of the percutaneous leads. [Figure 4] FIG. 4 is a schematic diagram of a preferred embodiment IPG system. [Diagram 5] FIG. 5 is an isometric view of a preferred IPG device. [Figure 6] FIG. 6 is an exploded isometric view of a preferred IPG device. [Figure 7] FIG. 7 is an exploded isometric view of a preferred IPG case. [Figure 8] FIG. 8 is an exploded isometric view of a preferred IPG header. [Figure 9] FIG. 9 is an exploded isometric view of a preferred die stack. [Figure 10] FIG. 10 is a partial cross-sectional view of a preferred header assembly. [Figure 11] FIG. 11 is an isometric view of the lead assembly of the preferred embodiment. [Figure 12] FIG. 12 is a cross-sectional view of a lead assembly of a preferred embodiment. [Figure 13] FIG. 13 is a flow chart of a preferred control program for operation of the IPG. [Figure 14] FIG. 14 is a flow chart of a preferred method of Fresnel compensation. [Figure 15] FIG. 15 is a flow chart of a preferred method for normalizing source radiation. [Figure 16] FIG. 16 is a flow chart of a preferred method for correcting source power variations.

[0023] In the following description, like parts are designated by the same numerals in the specification and figures. The figures are not necessarily drawn to scale and may be shown in exaggerated or generalized form for clarity and conciseness. Unless otherwise noted, all tolerances and use of the term "about" indicate plus or minus 5%.

[0024] 4, a preferred embodiment of the stimulation system 400 will be further described. The stimulation system 400 further comprises an IPG 401 in operative communication with a controller 450.

[0025] IPG 401 is housed in a sealed composite case 402, as will be further described. Composite case 402 houses the IPG's working components and serves to secure leads 422A, 422B, 424A and 424B, as will be further described.

[0026] The operative components of the system include an optical fold assembly 406 in optical alignment with leads 422A and 422B. Similarly, the operative components include an optical fold assembly 404 in optical alignment with leads 422A and 422B. The optical fold assembly 406 transmits and receives optical signals from leads 422A and 422B to be interpreted by an optical signal processor 405. Similarly, the optical fold assembly 404 transmits and receives optical signals from leads 422A and 422B to be interpreted by an optical signal processor 403. The optical signal processor 405 and the optical signal processor 403 are operatively connected to a main processor 407 that controls the function of the IPG, as will be further described. The main processor 407 is operatively connected to a signal generator 409 that generates electrical stimulation signals to target neural populations that are delivered to the spinal cord via leads 422A, 422B, 424A, and 424B, as will be further described. Communications circuitry 411 is also operatively connected to main processor 407. Main processor 407 receives programming instructions and control signals from said communications circuitry, as will be further described.

[0027] The IPG 401 includes a battery 415. The battery 415 is operatively connected to all electrical components of the system. The battery 415 receives a recharging current from an induction coil 413, as will be further described.

[0028] The IPG 401 is surgically implanted beneath the dermis 430.

[0029] The controller 450 resides outside the dermis 430. The controller 450 includes a main processor 454 that controls the functions of said controller. The main processor 454 is connected to an I / O keyboard and display unit 458 that is fixed to the outer casing. The main processor 454 is operatively connected to a communication circuit 456. The communication circuit 456 is wirelessly connected to the communication circuit 411. The main processor 454 includes sufficient memory to receive instructions from the I / O keyboard and display unit 458 and transfer them to the main processor 407 via the communication circuit 456 and the communication circuit 411 to control the operation of the IPG 401. The main processor 454 is further operatively connected to an induction coil 452. The induction coil 452 is inductively coupled to the induction coil 413 to transfer power for charging the battery.

[0030] Referring now to FIG. 5, the IPG 401 will be further described.

[0031] Composite case 402 provides mechanical support to header assembly 502 and header assembly 504, which are both positioned on opposite sides of the IPG parallel to a single transverse axis 550. Positioning the header assemblies on opposite sides of the case is important for improved distribution of heat generated by a laser, as will be further described. Each header assembly is preferably fabricated from a clear epoxy resin and serves to secure the optical and electrical components in place.

[0032] Header assembly 502 includes optical fold assembly 404. Optical fold assembly 404 is optically aligned with lead retention holes 523A and 523B. Leads 422A and 422B are disposed within and optically aligned with lead retention holes 523A and 523B. Leads 422A and 422B are removably secured within the header by set screws 506A and 506B, respectively. The leads contact optical fold assembly 404 as will be further described.

[0033] The header assembly 502 further includes a fixation portal 512 that is used to anchor the IPG to the fascia during surgery.

[0034] The header assembly 504 includes an optical fold assembly 406. The optical fold assembly 406 is optically aligned with the lead retention holes 525A and 525B. The leads 424A and 424B are disposed within and optically aligned by the lead retention holes 525A and 525B. The leads 424A and 424B are removably secured within the header by set screws 508A and 508B, respectively. The leads contact the optical fold assembly 406, as will be further described.

[0035] The header assembly 504 further includes a fixation portal 510 that is used to anchor the IPG to the fascia during surgery.

[0036] Referring now to FIG. 6, the IPG 401 will be further described.

[0037] Composite case 402 further includes a header divider portion 604 and a header divider portion 606. Each header divider portion is an angular recess in the composite case. The header dividers are generally parallel and diametrically opposed. Header divider portion 604 houses header assembly 502. Similarly, header divider portion 606 houses header assembly 504.

[0038] Header partition 604 includes a rectangular receiving window 618 and electrical pass-through holes 614. The receiving window and electrical pass-through holes allow connection between header assembly 502 and the internal components of the IPG.

[0039] Similarly, header bulkhead portion 606 includes rectangular receiving windows 620 and electrical pass-through holes 616 for connecting components of header assembly 504 with the internal components of the IPG.

[0040] Header assembly 502 includes an integrally formed positioning block 610 that fits within a receiving window 618 to optically align the header divider portion with the optical components in the case. Header assembly 504 includes an integrally molded positioning block 612 that fits within a receiving window 620 to optically align the header divider portion with the optical components in the case.

[0041] The composite case 402 including both headers forms an elliptical surface of revolution, as described in U.S. Publication No. 2021 / 0001114 to Wolf, which is incorporated herein by reference.

[0042] The composite case 402 will now be further described with reference to FIG.

[0043] Composite case 402 includes a top 702 bonded to a bottom 704. Top 702 is preferably a hollow shell fabricated from a titanium alloy, which is relatively easy to machine and can hold sufficient tolerances to allow proper alignment of the header and optics, as will be further described. Bottom 704 is preferably a hollow shell constructed from a ceramic material, which facilitates wireless communication between communication circuits and inductive coupling between inductive coils. The combination of ceramic material with the metal material of the case is also important, since heat generated from the IPG is directed toward the metal portion of the case. The metal portion of the case may be positioned toward the dermis during surgery, thereby positioning the IPG for superior heat dissipation during use.

[0044] Optical window 710 is adjacent to top portion 702 and centrally disposed below receiving window 618. Similarly, optical window 712 is adjacent to top portion 702 and centrally disposed below receiving window 620. Both optical windows are preferably welded and hermetically sealed to the underside of the top portion.

[0045] Dice stack 718 is operatively disposed below optical window 710 and adjacent to optical signal processor 405, as will be further described. Dice stack 720 is operatively disposed below optical window 712 and adjacent to optical signal processor 403, as will be further described.

[0046] Connector card 714 is disposed adjacent top portion 702 and directly below electrical pass-through hole 614. Connector card 716 is disposed adjacent top portion 702 and directly below electrical pass-through hole 616. Connector cards 714 and 716 are electrically connected to contacts of the header and main processor 407 and allow for delivery of stimulation currents to the leads, as further described.

[0047] Composite case 402 houses processor card 722. Processor card 722 structurally and electrically connects main processor 407 to optical signal processors 405 and 403, signal generator 409 and communication circuitry 411. In a preferred embodiment, main processor 407 is part number MSP430 available from Texas Instruments, Dallas, Texas, USA. Signal generator 409 is available under the trade name Saturn from Cactus Semiconductor. Communication circuitry 411 is preferably part number ZL70103 available from Microsemi, Aliso Viejo, California, USA. Optical signal processors 403 and 405 are both preferably part number ADPD4100 available from Analog Devices, Wilmington, Massachusetts, USA.

[0048] Composite case 402 further houses a battery 415 that is electrically connected to a processor card 722. The IPG's working components are preferably located adjacent to top surface 702 and held in place by an epoxy seal. After sealing, bottom 704 is hermetically sealed to top 702 by welds 706.

[0049] 8, header assembly 504 will be further described. It should be understood that header assembly 502 is structurally and functionally identical to header assembly 504, except that the locations of the aforementioned components are reversed. Only header assembly 504 will be described in detail herein, by way of example.

[0050] The header assembly 504 includes a header body 800. The header body 800 is preferably manufactured from a clear epoxy or acrylic plastic and is cast and machined to tolerances. The header body 800 is formed with a semi-ellipsoid shape sufficient to fit seamlessly within the header bay 606 and to match the plane of revolution formed by the top 702 and bottom 704.

[0051] Header body 800 includes lead retention holes 525A and 525B. Lead retention hole 525A includes a central optical axis 804, and lead retention hole 525B includes a central optical axis 802. Optical axis 802 and optical axis 804 are preferably generally parallel.

[0052] Lead retention holes 525A contain metallic toroidal contacts 814. In a preferred embodiment, eight toroidal contacts are included, each individually addressable by the main processor. Each toroidal contact 814 is connected to a lead 818. Leads 818 are positioned to intersect electrical pass-through holes 616 and are further connected to the connector card which connects to the main processor. Lead retention holes 525A terminate in a cavity 808 adjacent positioning block 612, as will be further described.

[0053] Lead retention holes 525B contain metallic toroidal contacts 812. In a preferred embodiment, eight toroidal contacts are included, each individually addressable by the main processor. Each toroidal contact 812 is connected to a lead 816. Leads 816 are positioned to intersect electrical pass-through holes 616 and are further connected to the connector card which connects to the main processor. Lead retention holes 525B terminate in a cavity 806 adjacent positioning block 612, as will be further described.

[0054] Lead retention hole 525A includes a threaded vertical bore 840. Once lead 424A is placed in lead retention hole 525A, set screw 508A is placed in threaded vertical bore 840 directly adjacent anchor ring 832 to secure lead 424A within lead retention hole 525A.

[0055] Similarly, lead retention hole 525B includes a threaded vertical bore 838. Set screw 508B is positioned within threaded vertical bore 838 directly adjacent lead anchor ring 830. Set screw 508B is advanced into contact with lead anchor ring 830, retaining lead 424B in lead retention hole 525B.

[0056] The optical fold assembly 406 further includes a parabolic redirector 820 and a parabolic redirector 822. The parabolic redirector 820 includes an integral lens 824. The parabolic redirector 822 includes an integral lens 826. The parabolic redirector 820 and the parabolic redirector 822 are rigidly secured to the cavities 806 and 808, respectively, in contact with and adjacent to the optical window 712, as will be further described. In a preferred embodiment, the parabolic redirectors are molded in place on the header. The integral lens 824 is optically aligned with the optical axis 802.

[0057] Dice stack 720 is disposed beneath and in contact with optical window 712. Dice stack 720 includes vertical cavity surface emitting lasers ("VCSELs") 850 and VCSELs 852, as will be further described. In each case, the VCSELs can emit light in a unique wavelength range, but preferably in the range of about 400 to 810 nanometers, or from blue (about 400 nanometers to about 500 nanometers) to green (about 520 nanometers to about 532 nanometers) to near infrared (about 700 nanometers to about 810 nanometers). In a preferred embodiment, each VCSEL is part number V00146 available from Vixar, Inc., Plymouth, Minnesota, USA. Each laser generates about 10 milliwatts in the near infrared and about 5 milliwatts in the blue range. Other lasers in the wavelength range of approximately 400-580 nanometers (blue, cyan, green, yellow) or other visible ranges may be utilized. VCSEL 850 is positioned to emit light perpendicular to the central vertical optical axis of parabolic redirector 820. Similarly, VCSEL 852 is positioned to emit light perpendicular to the central vertical optical axis of parabolic redirector 822.

[0058] Toroidal contact 812 is designed to engage and make electrical contact with ring 860 of lead 424B, as will be further described. Toroidal contact 814 is designed to engage and make electrical contact with ring 862 of lead 424A, as will be further described.

[0059] Lead 424B is positioned by lead retaining hole 525B for alignment with optical axis 802. Lead plug 424A is positioned by lead retaining hole 525A for alignment with optical axis 804.

[0060] Lead 424B terminates in a collet 880, as will be further described. Lead 424A terminates in a collet 882, as will be further described. When assembled, lead 424B and collet 880 are held adjacent to integral lens 824 by set screws 508B. Lead 424A and collet 882 are held adjacent to integral lens 826 by set screws 508A. An index matching gel is provided to minimize Fresnel reflections between the lens and the leads.

[0061] Dice stack 720 will be further described with reference to Figure 9. It should be understood that dice stack 718 and dice stack 720 are functionally and structurally identical. Only dice stack 720 will be described in detail.

[0062] The die stack 720 includes a photodiode package 914. In a preferred embodiment, the photodiode package 914 is part number S5980-09 (ESI) available from Hamamatsu Photonics K.K. of Shizuoka, Japan.

[0063] A preferred photodiode package has four photodiodes. In one embodiment, all four photodiodes are used as receivers. In another embodiment, two photodiodes 906A and 906B are used as receivers, one for each lead, and two photodiodes 906C and 906D are used as monitor photodiodes, one for each laser. The two monitor photodiodes function as output monitors that normalize the laser emission and compensate for power source variations over time, as will be further described.

[0064] The photodiodes 906A, 906B, 906C, 906D are recessed and secured in a housing 916, which is preferably a ceramic composite. The housing 916 is held in place within the case by an epoxy seal, rigidly fixing the position of the photodiodes. Each photodiode typically provides a sensitivity of approximately 0.72 A / W. The photodiodes 906A, 906B, 906C, and 906D are surrounded by electrical contacts 908 and 910. These contacts are operatively connected to a suitable optical signal processor by a flexible cable (not shown). A cover plate 912 is disposed adjacent to and in contact with the four photodiodes. In a preferred embodiment, the cover plate 912 is formed of polished crystal glass having opposing optically parallel faces. The cover plate 912 includes gold traces 902 and 904. The gold traces are preferably deposited on the glass surface opposite the photodiode using photolithography or evaporation. VCSEL 850 is rigidly secured to cover plate 912 adjacent to and in electrical contact with gold trace 902. VCSEL 852 is rigidly secured to optical window 712 adjacent to and in electrical contact with gold trace 904. The gold traces provide power to the VCSEL and allow the main processor to select which wavelength laser to activate, as will be further described. Gold trace 902, gold trace 904, and contacts 908 and 910 are electrically connected by flex cables (not shown) to the appropriate optical signal processor and main processor 407.

[0065] 10, a partial cross-sectional view of the IPG 401 in use is further described. It should be understood that each parabolic redirector, die stack, and mating components of the headers and leads are structurally and functionally identical.

[0066] The parabolic redirector 822 further comprises a parabolic body 1001 and an integral lens 826. The parabolic body 1001 and the integral lens 826 are preferably integrally formed from crystal glass having a refractive index of about 1.46 to 1.68, similar to silicone resin.

[0067] Parabolic body 1001 includes a parabolic surface 1022. Parabolic surface 1022 is preferably a parabolic surface with a curvature designed to produce one focal point at the front-VCSEL and another focal point at a plane aligned with the optical axis of the fiber.

[0068] The paraboloid 1022 includes an exterior reflective coating, preferably evaporated silver. In another embodiment, the paraboloid 1022 is coated with a titanium dioxide compound. Preferably, the paraboloid 1022 is also polished.

[0069] The paraboloid 1001 further includes an interface surface portion 1020 adjacent the optical window 712. The interface surface portion 1020 is flat within acceptable optical tolerances. Preferably, an index matching material, such as epoxy, resides adjacent the surface and the optical window to provide low reflection losses and stability of the component. In another preferred embodiment, the interface surface portion 1020 may be positioned adjacent the optical window 712 with an index matching gel and secured with a suitable epoxy adhesive.

[0070] The parabolic redirector 822 is further comprised of an integral lens 826, which is a collimating lens and includes a convex lens surface 1014 directed inwardly of the parabolic surface 1022. In a preferred embodiment, the convex lens surface 1014 is secured to the parabolic body 10011 by a suitable index-matching epoxy. In another preferred embodiment, the parabolic body and the integral lens are integrally formed. In this case, the convex lens surface is formed by a suitable density transition between the integral lens 826 and the parabolic body 1001. The integral lens 826 includes an interface surface 1024 adjacent to the fiber 1002. The interface surface 1024 is preferably polished flat within suitable optical tolerances.

[0071] The header body 800 includes a conical light receiving surface 1050 at the proximal end of the lead retaining hole 525A. The interface surface portion 1024 is oriented parallel to the fibers 1002 of the lead 424A at the optical interface 1012 and is held in place by interference between the collet 882 and the conical light receiving surface 1050 of the lead retaining hole 525A.

[0072] A positioning block 612 forms an extension of the header body and serves to position the parabolic redirector. The positioning block is located within a receiving window 620 in the top 702. The interface between the receiving window 620 and the positioning block 612 fixes the vertical optical axis of the parabolic redirector above the VCSEL 852 and in position to reflect light from the parabolic surface 1022 back to the optical axis 804 of the fiber 1002 in lead 424A.

[0073] In use, the VCSEL 852 generates a laser light pulse 1004 that travels vertically upwards towards the parabolic surface 1022. The parabolic surface reflects the light approximately 90 degrees from vertical upwards to horizontally aligning it along the optical axis 804 through the integral lens into the fiber 1002 and out the distal end of the fiber towards the spinal cord. In all cases, the pulse from the VCSEL is specularly reflected from the spinal cord, giving it its high multispectral albedo. However, the blue, light blue, green and yellow pulses are preferentially absorbed by surrounding tissue and hemoglobin if present, and in the case of infrared light, are preferentially reflected from these tissues. Upon reflection from the spinal cord, the received light rays 1006 are collected and redirected back through the fiber 1002 to the parabolic redirector. Because the received light rays 1006 are not well aligned along the fiber, they strike the integrating lens 826 at a variety of angles. Received light beam 1006 is expanded by convex lens surface 1014 and enters parabolic surface 1002 where it is collected and directed approximately 90 degrees vertically downward from horizontal towards optical window 712. Received light beam 1006 passes through optical window 712 and enters cover plate 912 where it is directed towards photodiodes 906B and 906D.

[0074] When the VCSEL 852 is operating, a small portion of the light pulses 1004 are reflected back from the optical window 712. These back-reflected pulses 1075 immediately enter the cover plate 912 where they are transmitted to a photodiode 906D. The back-reflected pulses are converted into a signal by the photodiode and used by the main processor to normalize the power output of the VCSEL and compensate for power source fluctuations, as will be further described.

[0075] Photodiodes 906B and 906D convert the received light beam 1006 into an electrical signal that is communicated to optical signal processor 405 for further processing, as further described.

[0076] Lead 424A will now be further described with reference to Figures 11 and 12. Lead 424A, lead 424B, lead 422A and lead 422B are identical in structure and function. Only one will be described here as an example.

[0077] Lead 424A further includes a lead body 1101. Lead body 1101 is a generally flexible cylindrical extrusion distally terminated by a delivery tip 1109 and proximally terminated by a collet 882. In a preferred embodiment, the lead body is constructed of a flexible polymer such as Pellethan 55D or a similar biocompatible material. The lead body is preferably a multi-lumen extrusion with embedded and integrally formed components as will be further described.

[0078] Transmission tip 1109 is an optically transparent cylinder fused to the distal end of the lead body. In a preferred embodiment, the transmission tip is a suitable optically transparent material such as thermoplastic polyurethane. Transmission tip 1109 terminates in a hemispherical cap 1111. In a preferred embodiment, hemispherical cap 1111 and transmission tip 1109 are integrally formed. Transmission tip 1109 further includes an embedded radiopaque marker 1152. Radiopaque marker 1152 is preferably a titanium cylinder axially embedded adjacent hemispherical cap 1111.

[0079] A fiber 1002 is disposed along the central optical axis of lead 424A and extends from collet 9882 to a concave lexicon 1150. A transmission tip is fused to the fiber 1002. The fiber 1002 includes a concave lexicon 1150 at its distal end. In a preferred embodiment, the concave lexicon 1150 includes an internally reflective coating, such as titanium dioxide. The transmission tip 1109 further includes a stylet channel terminus 1151. In a preferred embodiment, the stylet channel terminus 1151 is a cylindrical opening. A stylet stop 1154 is disposed at the distal end of the terminus 1151 of the stylet channel 1151. The stylet stop 1154 is preferably a titanium cylinder.

[0080] A stylet channel 1105 extends coaxially from a stylet channel terminus 1151 in collet 882 to a stylet channel opening 1153. The stylet channel is a cylindrical cavity that runs parallel to the optical fiber and serves the purpose of housing a guide stylet for use in positioning the lead during surgery. In a preferred embodiment, stylet channel 1105 is lined with a polytetrafluoroethylene (PTFE) lining 1107 that extends the length of the lead body. The lining reduces surface friction, facilitating insertion of the stylet during surgery.

[0081] Lead body 1101 further supports a metallic anchor 1110 disposed at its proximal end. The metallic anchor is generally cylindrical in shape and is permanently secured to the exterior of the lead body.

[0082] Adjacent to metal anchor 1110, eight cylindrical proximal metal contacts 1108A, 1108B, 1108C, 1108D, 1108E, 1108F, 1108G, 1108H are fixed to the outside of the lead body at equal axial intervals and positioned to make electrical contact with the toroidal contacts of the header assembly.

[0083] Similarly, eight cylindrical metal electrodes 1106A, 1106B, 1106C, 1106D, 1106E, 1106F, 1106G, 1106H are secured to the distal end of the lead body, each of the metal electrodes being equally spaced apart in the axial direction on the outer surface of the lead body.

[0084] The lead body further includes eight radially oriented lumens 1131A, 1131B, 1131C, 1131D, 1131E, 1131F, 1131G, 1131H. Conductors 1120A, 1120B, 1120C, 1120D, 1120E, 1120F, 1120G, and 1120H are integrally formed in the lumens and extend from their respective proximal contacts to their respective distal electrodes. In a preferred embodiment, the conductors are constructed of MP35N or other similarly corrosion resistant conductive material. Each of the conductors connects exactly one proximal contact with exactly one paired metal electrode.

[0085] In a preferred embodiment, fiber 1002 and the conductor are integrally formed into the lead body during manufacture.

[0086] In a preferred embodiment, collet 882 is formed from a suitable ceramic or crystal sapphire material. Collet 882 includes a frustoconical surface 1170 at its proximal end that mates with an identical frustoconical light receiving surface 1050 of header body 800 to aid in positioning fiber 1002 relative to optical interface 1012 and to radially compress the fiber to aid in optical alignment with the parabolic redirector.

[0087] The method of IPG operation 1300 is further described with reference to Figure 13. In a preferred embodiment, the method is performed by programming instructions resident in the main processor 407's on-board memory.

[0088] In step 1302, the method begins.

[0089] In step 1304, the main processor sets an initial channel for operation. In a preferred embodiment, the initial channel includes one of the groups of four leads 422A, 422B, 422A and 422B. In other preferred embodiments, the initial channel includes one of the groups of only two or three of the leads.

[0090] In step 1306, main processor 407 activates the VCSEL in the specified channel. Preferably, the VCSEL generates a light pulse in the infrared wavelength range. A small portion of the light pulse is immediately reflected off the optical window. A large portion of the light pulse is sent to the base of the parabolic redirector and passes through the parabolic surface. The parabolic surface rotates the light approximately 90 degrees from vertical to horizontal and focuses it along the optical axis of the optical fiber for the selected lead. The transmitted light beam enters the spinal cord, hemoglobin, and other surrounding tissue, where it is reflected and received by the fiber at a concave lexicon. The received light beam travels back down the fiber to the parabolic redirector where it is rotated approximately 90 degrees from horizontal to vertical downward and focused onto the die stack.

[0091] In step 1307, the main processor 407 normalizes the source emission using the back-reflected pulse, as will be further described.

[0092] In step 1308, the main processor uses the back reflected pulses to correct for power fluctuations over time.

[0093] In step 1309, the main processor polls the photodiode to obtain a feedback signal.

[0094] At step 1310, the main processor calculates a stimulus signal based on the signal from the photodiode. The stimulus signal is preferably generated according to a table precisely as disclosed in U.S. Patent No. 9,550,063 to Wolf II I, which is incorporated herein by reference. Of course, other stimulus routines may be used.

[0095] In step 1312, the main processor modifies the stimulus signal to compensate for reduced optical feedback according to a reflection compensation value, as further described.

[0096] In step 1313, the main processor activates the signal generator to transmit the compensated stimulation signal to the toroidal contact for the lead of the selected channel. The compensated stimulation signal is transmitted to the electrode to create an electric field adjacent to a target neuron in the spinal cord.

[0097] In step 1314, the main processor polls the communication circuitry for a shutdown signal.

[0098] In step 1316, the main processor determines whether a shutdown signal is present. If not, the main processor proceeds to step 1320. If present, the main processor proceeds to step 1318.

[0099] In step 1320 , the main processor proceeds to the next lead channel in the lead group and returns to step 1306 .

[0100] In step 13188, the main processor shuts down the routine and returns to a holding state.

[0101] 14, a preferred method for deriving the compensation stimulation current values ​​of step 1312 will be further described.

[0102] In step 1402, the method begins.

[0103] In step 1404, the main processor activates the VCSEL to generate a second light pulse. Preferably, the VCSEL generates a light pulse in the blue wavelength range. However, other wavelengths may be used as long as they are different from the first pulse. The blue laser signal enters the fiber through the parabolic redirector and is transmitted to the concave lexicon of the transmitting tip. However, the blue light is preferentially absorbed by surrounding tissue and hemoglobin. Most or all of the blue signal is absorbed by these tissues. As a result, the reflected blue signal is primarily due to Fresnel reflections within the optical system. The reflected blue signal is therefore representative of the optical system signal loss between the time the blue signal is generated at the VCSEL and the time the blue signal is received at the receiver. Periodically monitoring the reflection of the blue signal allows recognition of the optical system signal loss and the increase in system noise over time.

[0104] The system loss and noise of the optical signal are similar regardless of wavelength. Thus, the system loss of the optical signal for the infrared signal pulse will be the same as the system loss of the optical signal for the blue signal pulse. A preferred electro-optical control device will generally increase the stimulation current as the strength of the optical signal decreases, based on the assumption that the spinal cord is far away from the electrodes. Thus, as the optical loss of the system increases, the control device will gradually increase the stimulation current. By decreasing the stimulation current at the same rate as the optical loss increases, optical degradation and Fresnel losses in the system can be compensated for, thereby providing a correct stimulation signal.

[0105] In step 1406, the returning blue laser signal is measured by the photodiode which returns a current value to the main processor.

[0106] In step 1408, the main processor preferably calculates the percentage of signal loss in the blue optical signal, known as the reflectance compensation value, according to the following formula:

[0107]

number

[0108] Where: RCV=Optical signal loss rate I t = Transmitted optical signal current to the VCSEL I r = Received optical signal current from the photodiode

[0109] In step 1410, the stimulation current value "I stim " is searched. stim is a current value calculated by a processor according to a correlation table between the return optical signal and the stimulation current, as described above.

[0110] In step 1412, a stimulation current correction value "I new " is preferably calculated according to the following formula:

[0111]

number

[0112] Where: I stim = Calculated stimulation current RCV=optical signal loss rate I new = Corrected stimulation current value

[0113] In step 1414, the main processor new Return a value.

[0114] At step 1416, the method ends.

[0115] 15, the preferred method of normalizing the source emissions of step 1307 is further described. The method is the same for each dice stack.

[0116] In step 1502, the method begins.

[0117] In step 1504, main processor 407 retrieves from memory the output of monitor photodiode 1. In this example, photodiode 1 is photodiode 906C adjacent to VCSEL 850.

[0118] In step 1506, the main processor reads the output value of monitor photodiode 2. In this example, photodiode 2 is photodiode 906D adjacent to VCSEL 852.

[0119] In step 1508, the main processor compares the output of monitor photodiode 1 with the output of monitor photodiode 2. If the output of photodiode 1 is greater than the output of photodiode 2, the method proceeds to step 1512. Otherwise, the method proceeds to step 1514.

[0120] In step 1512, the difference between the output of photodiode 1 and the output of photodiode 2 is calculated by subtracting the output of photodiode 2 from the output of photodiode 1.

[0121] In step 1513, the drive current to photodiode 1 is reduced by the difference.

[0122] At step 1514, the output of photodiode 2 is compared to the output of photodiode 1. If the output of photodiode 2 is greater than the output of photodiode 1, the method proceeds to step 1515. Otherwise, the method proceeds to step 1518.

[0123] In step 1515, the difference between the output of photodiode 2 and the output of photodiode 1 is calculated by subtracting the output of photodiode 1 from the output of photodiode 2.

[0124] In step 1516, the drive current to photodiode 2 is reduced by the difference.

[0125] In step 1518, the method returns the normalized power levels of photodiode 1 and photodiode 2.

[0126] At step 1520, the method ends.

[0127] In a preferred embodiment, the difference is calculated as a percentage that can be applied directly to the photodiode current to normalize the light source.

[0128] In a preferred embodiment, method 1307 is applied between two VCSELs in a photodiode stack, such as VCSEL 850 and VCSEL 852. However, in other embodiments, normalization may be performed across all four VCSELs in the system such that each produces the same level of luminescence.

[0129] 16, the preferred method of compensating for power source variations in step 1308 will be further described.

[0130] The method begins at step 1602. Ideally, the method is performed only periodically, such as once a week, to conserve system power usage.

[0131] In step 1604, the main processor retrieves from memory an initial power level of the VCSEL. Preferably, the initial power level is measured by measuring the current from the monitor photodiode adjacent the VCSEL when the VCSEL is first activated during system start-up.

[0132] In step 1606, the main processor powers up the selected VCSEL.

[0133] In step 1612, the main processor derives the difference between the monitor photodiode power level and the initial monitor photodiode power level according to the following formula:

[0134]

number

[0135] Where: Δ=difference PL I = Initial power level PL m = Measured power level

[0136] In step 1614, the difference is stored as a percentage according to the following formula:

[0137]

number

[0138] Where: PL DIFF = Percentage power level difference PL I = Initial power level PL m = Measured power level

[0139] In step 1616, the corrected power level is calculated according to the following formula:

[0140]

number

[0141] Where: I1 = Initial current level PL DIFF = Percentage difference I2 = new power level

[0142] In step 1618, the main processor returns the new power level.

[0143] In step 1620, the method ends.

Claims

1. 1. An implantable pulse generator system comprising: Case and a lead wire retaining hole disposed in the case in a longitudinal direction and having an optical axis; a parabolic redirector having a first interface surface perpendicular to a second interface surface portion connected by a parabolic surface and focused on the optical axis; a die stack adjacent to the parabolic redirector, perpendicular to the optical axis, and parallel to the second interface surface; a laser fixed to the die stack and directed perpendicular to the second interface surface; a receiver disposed about the laser and parallel to the second interface surface; a processor operatively connected to the laser and the optical receiver, the processor having a memory; An implantable pulse generator system comprising:

2. 2. The implantable pulse generator system of claim 1, wherein the laser is a VCSEL.

3. 2. The implantable pulse generator system of claim 1, wherein the parabolic redirector includes a collimating lens centered about the optical axis.

4. 2. The implantable pulse generator system of claim 1, wherein said laser is secured to said die stack by an optical window.

5. 5. The implantable pulse generator system of claim 4, wherein the laser is electrically connected to a processor by a metal trace affixed to the optical window.

6. 2. The implantable pulse generator system of claim 1, wherein the case further comprises: a first portion made of metal forming a header partition; a header secured to the header partition portion, the header including a lead wire retaining hole; a ceramic second portion hermetically sealed to the metallic first portion; An implantable pulse generator system comprising:

7. 10. The implantable pulse generator system of claim 1 further comprising: an implantable pulse generator system having a series of toroidal electrical contacts secured in said lead retaining holes and aligned with said optical axis.

8. 8. The implantable pulse generator system of claim 7, further comprising: a flexible lead wire fixed in the lead wire holding hole; a centrally located optical fiber integrally formed with said flexible lead and coaxial with said optical axis; a series of cylindrical contacts secured to an outer surface of said flexible lead and electrically connected to said series of toroidal electrical contacts; a cylindrical electrode secured to an outer surface of said flexible lead and electrically connected to said series of cylindrical contacts; An implantable pulse generator system comprising:

9. 9. The implantable pulse generator system of claim 8, wherein the flexible lead further comprises: an implantable pulse generator system having a longitudinal stylet lumen radially disposed adjacent and parallel to said centrally disposed optical fiber.

10. 10. The implantable pulse generator system of claim 9, wherein the longitudinal stylet lumen terminates distally in a stylet stop.

11. 10. The implantable pulse generator system of claim 9, wherein the flexible lead further comprises: an implantable pulse generator system having a transparent light-transmitting tip integrally formed with said centrally located optical fiber.

12. 12. The implantable pulse generator system of claim 11, wherein the transparent light transmitting tip further comprises: An implantable pulse generator system having a centrally located radiopaque marker.

13. 9. The implantable pulse generator system of claim 8, further comprising: A set of instructions resident in the memory and which, when executed, cause the implantable pulse generator system to perform the following operations: generating a first transmitted beam from the laser at a first wavelength; directing the first transmitted beam through the parabolic redirector into the centrally located optical fiber; receiving a first received beam from the centrally located optical fiber through the parabolic redirector and incident on the optical receiver; generating a perturbation variable from the first received light beam; generating a modulated stimulus signal based on the variation variable; delivering said modulated stimulation signal to said series of cylindrical electrodes; said set of instructions.

14. 14. The implantable pulse generator system of claim 13, wherein the set of instructions further comprises: resident in the memory and, when executed, causing the implantable pulse generator system to generating a second transmitted beam from the laser at a second wavelength; directing the second transmitted beam through the parabolic redirector into the centrally located optical fiber; receiving a second received light beam from the centrally located optical fiber through the parabolic redirector and into the optical receiver; generating a compensation value from the second received light beam; modifying the modulated stimulus signal based on the compensation value; An implantable pulse generator system having:

15. 1. An implantable pulse generator system comprising: Case and a first header bay formed in the case; a second header bay formed within the case and radially disposed relative to the first header bay; a first header assembly secured to the first header bay, the first header assembly having a first lead retaining channel and a second lead retaining channel; a second header assembly secured to the second header bay, the second header assembly having a third lead retaining channel and a fourth lead retaining channel; a first electro-optical lead having a first optical axis and disposed within the first lead-retaining channel; a second electro-optical lead having a second optical axis and disposed within the second lead-retaining channel; a third electro-optical lead having a third optical axis and disposed in the third lead-retaining channel; a fourth electro-optical lead having a fourth optical axis and disposed in the fourth lead-retaining channel; a first parabolic redirector centered about the first optical axis and optically coupled to the first electro-optic lead; a second parabolic redirector centered about the second optical axis and optically coupled to the second electro-optic lead; a third parabolic redirector centered about the third optical axis and optically coupled to the third electro-optic lead; and a fourth parabolic redirector centered about the fourth optical axis and optically coupled to the fourth electro-optic lead; a first die stack having a first vertically aligned laser surrounded by a first photodiode and optically coupled to the first parabolic redirector; the first die stack having a second vertically aligned laser surrounded by a second photodiode and optically coupled to the second parabolic redirector; a second die stack having a third vertically aligned laser surrounded by a third photodiode and optically coupled to the third parabolic redirector; the second die stack having a fourth vertically aligned laser surrounded by a fourth photodiode and optically coupled to the fourth parabolic redirector; An implantable pulse generator system comprising:

16. 16. The implantable pulse generator system of claim 15, wherein the first electro-optical lead further comprises: an optical fiber arranged coaxially with a first optical axis; a series of electrical contacts secured to a proximal surface of the first electro-optical lead; a series of electrodes secured to a distal surface of the first electro-optical lead and electrically connected to the series of electrical contacts; An implantable pulse generator system comprising:

17. 17. The implantable pulse generator system of claim 16, wherein the first header bay further comprises: a series of fixed contacts rigidly disposed within said first lead-retaining channel and operably connected to an electro-optical signal generator; The electro-optical signal generator comprises: directing a first transmitted beam of light, at a first wavelength, from the first vertically aligned laser through the first parabolic redirector and into the optical fiber; receiving a first return signal from the first photodiode based on the first received light beam; and generating a stimulus signal based on the first return signal; transmitting the stimulation signal to the set of fixed contacts for transmission to the set of electrodes; 4. An implantable pulse generator system programmed to:

18. 20. The implantable pulse generator system of claim 17, wherein the electro-optical signal generator further comprises: transmitting a second transmitted beam of light at a second wavelength from said first vertically aligned laser to said first parabolic redirector and to said first electro-optical lead; receiving a second received light beam with the first photodiode; generating a compensation value from the second received light beam; modifying the stimulus signal based on the compensation value; 1. An implantable pulse generator system programmed to:

19. 20. The implantable pulse generator system of claim 17, wherein the first die stack further comprises: a second photodiode; The electro-optical signal generator further comprises: normalizing a first supply current to the first photodiode and a second supply current to the second photodiode; 1. An implantable pulse generator system programmed to:

20. 20. The implantable pulse generator system of claim 19, wherein the normalizing step further comprises: decreasing the first supply current if the first supply current is greater than the second supply current; decreasing the second supply current if the second supply current is greater than the first supply current; An implantable pulse generator system comprising:

21. 20. The implantable pulse generator system of claim 19, wherein the electro-optical signal generator further comprises: the implantable pulse generator system being programmed to compensate for time-based variations in the first supply current.

22. 22. The implantable pulse generator system of claim 21, wherein the step of correcting further comprises: deriving a difference between an initial supply current to the first photodiode and the first supply current.

23. 20. The implantable pulse generator system of claim 18, wherein the first wavelength is between about 700 nanometers and about 800 nanometers and the second wavelength is between about 400 nanometers and about 500 nanometers.

24. 20. The implantable pulse generator system of claim 18, wherein the first wavelength is between about 700 nanometers and about 800 nanometers and the second wavelength is between about 520 nanometers and about 532 nanometers.

25. 16. The implantable pulse generator system of claim 15, wherein the first parabolic redirector further comprises: a collimating lens centered on the first optical axis; a parabolic surface for reflecting a transmit light beam toward the first electro-optical lead and a receive light beam toward the first photodiode; An implantable pulse generator system comprising:

26. 26. The implantable pulse generator system of claim 25, wherein the paraboloid includes a reflective coating.

27. 16. The implantable pulse generator system of claim 15, further comprising: a transparent cover plate between the first vertically aligned laser and the first die stack and adjacent the first vertically aligned laser to the first parabolic redirector.

28. 28. The implantable pulse generator system of claim 27, further comprising: an implantable pulse generator system having a window between said first vertically aligned laser and said first parabolic redirector and sealed in said case;

29. A lead wire for a pulse generator, comprising: A flexible lead body; an optical fiber integrally formed with the flexible lead body and centrally disposed coaxially with the optical axis; a series of cylindrical contacts secured to an outer surface of said flexible lead body and electrically connected to a series of toroidal electrical contacts; a series of cylindrical electrodes secured to the exterior surface of the flexible lead body and electrically connected to the series of cylindrical contacts by a series of wires integrally formed with the flexible lead body; a longitudinal stylet lumen disposed radially adjacent and parallel to said centrally disposed optical fiber; A lead wire for a pulse generator comprising:

30. 30. The pulse generator lead of claim 29, wherein the longitudinal stylet lumen terminates distally in a stylet stop cylinder.

31. 31. The pulse generator lead of claim 30, further comprising: A pulse generator lead having a transparent light transmitting tip integrally formed with said centrally located optical fiber.

32. 32. The pulse generator lead of claim 31, wherein the transparent light transmitting tip further comprises: A pulse generator lead having a centrally located radiopaque marker.

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