WO2008080073A2

WO2008080073A2 - Implantable neuromodulation system including wirelessly connected pulse generator and electrode array assembly

Info

Publication number: WO2008080073A2
Application number: PCT/US2007/088580
Authority: WO
Inventors: Jerry S. Culp; John L Janik; Don Malackowski; Douglas A. Staunton
Original assignee: Stryker Corporation
Priority date: 2006-12-22
Filing date: 2007-12-21
Publication date: 2008-07-03
Also published as: WO2008080073A3

Abstract

An implantable neuromodulation system (30) including an electrode array assembly (32) and an implantable pulse generator (34). Signals are wirelessly translated from the implantable pulse generator to the electrode array assembly. A power extractor and supply circuit integral with the electrode array assembly extracts the power from the signals. Instructions contained in the signals are executed by a switch circuit (156) also part of the electrode array assembly for selectively flowing current between selected ones of the electrodes (124) that are part of the assembly.

Description

IMPLANTABLE NEUROMODULATION SYSTEM

INCLUDING WIRELESSLY CONNECTED PULSE GENERATOR

AND ELECTRODE ARRAY ASSEMBLY

Field of the Invention

[0001] The present invention relates to an implantable system for stimulating neural tissue, especially nerve tissue within the spine. More particularly this invention is related to an implantable system for stimulating tissue that includes an electrode array assembly that is wirelessly connected to an implantable pulse generator.

Background of the Invention

[0002] Implantable tissue stimulation systems are used for a wide variety of applications, such as the treatment and suppression of pain in humans by neuromodulation of spinal cord nerve signals. These systems may also be used for other applications of neuromodulation, such as cardiac pacing, treatment of depression, bladder control, and muscle movement. These stimulation systems typically include an implantable battery-powered electronic stimulator unit (also known as an implantable pulse generator (IPG)), which provides sequenced electrical impulses to a stimulating electrode or electrode array. An electrode array can be a thin, elongated member, or a paddle-shaped unit. Some electrode arrays are shaped to be inserted in the epidural space of the spinal column. The implantable stimulator unit is often placed in a subcutaneous pocket either in the upper portion of the gluteus or in the lateral portions of the mid-abdomen. The electrodes of the electrode array are connected to the stimulator unit by wire leads implanted in the body.

[0003] When the system is actuated, the stimulation unit causes one or more of the electrodes forming the array to emit an electrical signal. This signal is applied to the neural network. One use of such a signal is to override a signal that has been emitted from some other location within the body. Such a signal may for example be signal generated by a damaged nerve indicating that a particular tissue or body location is in pain. Thus, by using a neuromodulation unit, the pain signal can be modulated before it enters the brain. The modulation of this signal with the stimulating system thus eliminates or reduces the need to use drugs, with their attendant disadvantages in order to minimize the effects of the pain signal on the patient. [0004] A disadvantage of known tissue stimulators is associated with the wire used to connect the stimulator unit and the electrode array. These wires are subjected to stress as a result of the inevitable movement of the surrounding tissue. This stress in turn, leads to wire breakage and/or separation from either the stimulator unit or electrode array. The wires can fail at any point, particularly connection points and the point at which the wires exit the spinal column. This can make it necessary to remove the neuromodulation system and surgically implant a replacement system. In addition, failure of the connection points may result in contamination from biological material seeping into the stimulator unit.

[0005] Moreover, if the wires do not fail, they can pull on the electrode array as the body moves. This movement can cause electrode array migration which leads to inaccurate tissue stimulation. Such inaccurate tissue stimulation can lead to an ineffective treatment. The wires can also be damaged by regular body movement such as repetitive movements of the spinal column.

[0006] Further, the need to provide the wires adds to the surgical implantation of a tissue stimulation system as the wires must be tunneled through the patient from the electrode lead connection points of the electrode array to the implanted stimulator unit. This can involve extensive tunneling as the electrode array is typically located in the epidural space of the spinal column, and the implantable stimulator unit is often placed in a subcutaneous pocket either in the upper portion of the gluteus or in the lateral portions of the mid-abdomen. The need to implant the stimulator unit and the wiring significantly increases the surgery time and the discomfort of the patient due to the need to implant the stimulator unit in an additional location in the body, and further increases the risk of infection. Then, additional time must be spent in the surgical procedure connecting the wires to the implantable pulse generator.

[0007] Heretofore, stimulation systems for treatment of humans have been unable to both effectively engage and stimulate targeted neuro-tissues without a complex system of lead wires implanted throughout the body connecting the pulse-emitting electrodes to the stimulation device providing the necessary power and command information to the electrodes .

[0008] Another disadvantage of many known neurological tissue stimulators is associated with the power supplies used to energize these stimulators. Many previous stimulation systems include batteries. Such batteries are typically located within the IPG. Reliance on battery power limits to the lifetime of the implants. Other known stimulators include an external transceiver coil. This coil serves as an inductive power coupler. Often this coil is placed near the skin. Hybrid systems with both coils and rechargeable batteries are also known. Rechargeable batteries have a longer lifetime, but must typically be recharged every one to two weeks. Recharging may be performed by inductive coupling of an external recharger and the stimulator unit.

[0009] The difficulty with the limited lifetime (5-10 years) of the surgically implanted battery is that a patient using such a system will require another surgical procedure to replace the battery either just prior to or after battery failure. Such a procedure serves to drive up the overall cost of the system by requiring more hospital and operating room time and causes considerable patient discomfort. Accordingly, much effort has been made to increase the energy capacity of the battery and therefore increase the battery lifetime. Given limitations on energy density of batteries, it has often been necessary to increase the size of the battery to increase its capacity. This leads to the undesirable requirement of the need to likewise increase the size of the implanted stimulator unit.

[00010] To reduce the difficulty inherent in limited battery lifetime, the prior art has offered a solutions such as the use of external radio frequency power transmitters. These systems eliminate the need to occasionally replace the implanted battery. However, these systems require a transceiver coil to be worn by the patient in close proximity to the skin for effective transmittance in order to operate the implanted neurostimulator unit. This close fitting of the external transceiver coil has been reported as uncomfortable and irritating.

[00011] Other representative patents that show tissue, and specifically neuro-stimulation, systems or electrodes include U.S. Pat. Nos. 3,646,940; 3,724,467; 3,822,708; 6,516,227; 6,980,864; 7,043,304; 6,757,970; 6,553,263; 6,909,917; 6,973,342; 4,379,462; 5,938,690; 6,027,456; 6,748,276; 6,754,539; 6,038,480; 5,417,719; 6,654,642; 4,044,774; 6,453,198; and 4 , 690 , 144. SUMMARY OF THE INVENTION

[00012] This invention is directed to a new and useful implantable neurological tissue stimulator. The stimulator of this invention includes an implantable pulse generator and an implantable electrode array assembly separate from the implantable pulse generator. Also part of this invention is a power supply module. The power supply module is worn or carried by the individual in whom the power converter and electrode array assembly are implanted.

[00013] Once the system is implanted, the power supply module transfers by radiant energy to the implantable pulse generator. The pulse generator, in turn converts the received power to a signal that will be less attenuated by internal body tissue. The converter transmits this signal, wirelessly, to the electrode array assembly. Embedded in the power signal are instructional data. A front end receiver integral with the electrode array extracts the energy from the power signal. The receiver extracts the instructions and forwards them to a drive circuit, also part of the electrode array assembly. Based on the received instructions, the drive circuit selectively applies energy to the electrodes.

[00014] The system of this invention therefore does not include a physical, wired connection between the power converter and the electrode array assembly. Therefore, the disadvantages associated by the presence of such a wire are eliminated.

[00015] These and other features and advantages of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification and appended drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[00016] FIG. 1 is a symbolic view of a human body;

[00017] FIG. 2 is a cross sectional view of a human body embodying the present invention as taken along line II-II in FIG. 1;

[00018] FIG 3 is a block diagram of the components internal to a power supply module of this invention

[00019] FIG 4 is a plan view of one face, the outer directed face, of a pulse generator of this invention;

[00020] FIG. 5 is a cross sectional view of the pulse generator depicting the primary components internal to the module;

[00021] FIG 6 is a block diagram of the components internal to the pulse generator;

[00022] FIG 7 is a side view of an electrode array assembly of this invention;

[00023] FIG 8 is a block diagram of the components internal to the electrode array assembly;

[00024] FIG 9 is a schematic diagram of the power switch assembly connected to a single one of the electrodes of the electrode array assembly;

[00025] FIG 10 illustrates how a flexible electrode array is held in intimate contact against the spinal cord dura by a spring biasing member.

DETAILED DESCRIPTION

[00026] With reference to the figures, FIG. 1 and FIG. 2 show an example of an implantable wireless neuromodulation

(tissue stimulation) system 30 of this invention includes an electrode array assembly 32, an implantable pulse generator 34. Both the electrode array assembly 32 and pulse generator 34 are implanted in the patient. Also part of system 30 of this invention and worn or otherwise externally carried by the patient is a power supply module 36. The implantable components communicate and are powered via at least one wireless communication link. Power supply module 36 may include software to control the operation of the neurostimulation system and a power delivery system. As explained further below with reference to FIG. 3, implantable pulse generator 34 includes a power harvester and an energy converter. Also internal to the implantable pulse generator 34 is control circuitry and a radio frequency power delivery system for delivering power and control signals to the leadless electrode array assembly 32. As described in more detail below, implantable leadless electrode array assembly 32 includes an array of electrodes 124 (Figure 7) .

[00027] FIG. 2 shows an axial cross section of the human body to demonstrate the system configuration in the body and the relative location of the system components to one another. In one embodiment of the present invention, the power supply module 36 is located outside of the body. Implantable pulse generator 34 is located immediately below the skin and subcutaneous fat layers 38 and above the muscle tissue 40 of the body. Electrode array assembly 32 is located in the epidural space 40 of the spinal column 42. More particularly, the electrode array assembly is disposed against a section of the spinal cord 44 to which the stimulating signal is applied. In one embodiment of the present invention, the implantable pulse generator 34 is advantageously implanted in the back of the patient to reduce the over all distance between the relay station and the leadless electrode array.

[00028] The present invention provides a controlled amount of stimuli to specific tissues in the body consistently and according to a stimulation program stored in the memory of the system. The positive or negative polarity stimulation energy is transferred from the electrical medium to a tissue medium via the electrodes of the electrode array assembly 32. Various configurations of electrodes and stimulus parameters on the electrodes will allow for electric field focusing or steering enhancing a controller's ability to target specific tissues. In many applications, it is anticipated the current flow between the electrodes of assembly 32 will modulate the flow of neural signals to or from the brain. The below-described application, the attenuation of pain signals to the brain, is just one application of system 30 of this invention. [00029] As depicted in Figure 3, power supply module 36 includes a signal generator 52. Signal generator 52 is configured to generate a signal in the high frequency to microwave frequency ranges. In some version of the invention, this signal as at a frequency somewhere between 30 MHz and 3 GHz. The signal generator 52 is powered by a battery 53, also contained within the power supply module 36. While the connections are not shown for simplicity, the battery 53 powers the other active components internal to the power supply module. Battery 53 is rechargeable and/or disposable.

[00030] Also internal to power supply module 36 is a processor 54. Processor 54 may be any suitable microcontroller. A memory 56 shown externally from the processor 54 contains the instruction set executed by the processor for operation of system 30. Also shown connected to processor 54is an I/O unit 58. The I/O unit 58 may comprise a small display and a keypad, or a touch screen display. The I/O unit 58 is the component of system 30 through which commands for controlling the electrodes are entered. Based on the data entered through the I/O unit 58 and the instructions stored in memory 56, the processor 54 generates the instructions for actuating specific electrodes 124 integral with electrode array assembly 32. The I/O unit 58 also serves as the system component over which data regarding the operation of system 30 and data based on neurological signals measured by the system are presented to the patient or clinician.

[00031] In Figure 3 a resistor 57 is shown connected across battery 53. The voltage across resistor 57 is applied to processor 54. The fall of this voltage below a certain threshold is interpreted by processor 54 as an indication battery 53 is losing its charge. When this event occurs, processor 54 directs I/O unit 58 to generate an appropriate warning message to the user. Also, the processor 54 outputs instructions that cause the electrodes to be actuated in a power saving mode. This ensures that system 30 remains able to function, though perhaps at a reduced level of effectiveness, for an extended period when it would otherwise shut down due to battery discharge. [00032] The command signals output by the processor 54 are forwarded to a modulator/demodulator 60. Also forwarded to the modulator/demodulator 60 is the signal produced by the signal generator 52. This latter signal functions as carrier signal. Modulator/demodulator 60 thus modulates the carrier signal based on the command signals received from processor 54. In some versions of the invention, the carrier signal is subjected to pulse width modulation, frequency shift keying, amplitude shift keying phase shift keying, frequency modulation or amplitude modulation. Modulator/demodulator 60 outputs the modulated signal to an antenna 62. From the antenna 62, the signal is broadcast to the patient. In some versions of the invention, the signal broadcast by power supply module 36 is at least 100 μWatts. It should be appreciated that the maximum power will be dictated by the maximum specific absorption rates allowed by the appropriate regulatory agencies. In the United States, these agencies are the Food and Drug Administration and the Federal Communications Commission.

[00033] Antenna 62 also receives signals emitted by implantable pulse generator 34. Data signals integral with these signals are extracted by modulator/demodulator 60 and forwarded to processor 54. These data signals may include data describing the electrical energy delivered to the patient, the impedance to the delivery of this energy or sensed signals relating to the patient's nerve functions. These data may then be used by processor 54 as an input variable for regulating the actuation of the system electrodes .

[00034] Not shown is the means by which power supply module 36 is worn by the patient. Generally, power supply module 36 has a size of 130 cm³ or less and, preferably, 100 cm³ or less. This allows the module 36 to be worn on a belt, attached to an article of clothing or carried in purse, pack or pocket. The specific means by which the power supply module 36 is carried by the patient is not relevant to this invention. What is significant is that the means by which the power supply module 36 is carried is such that it allows the module to be positioned so that it can exchange signals with implantable pulse generator 34 with loss of signal strength of 75% or less and more preferably, a loss of signal strength of 50% or less.

[00035] Implantable pulse generator 34, described initially with reference to Figures 4 and 5, receives and harvests the HF/MW signal produced by the power supply module 36. The pulse generator 34 includes a housing 72 designed so that it can be implanted immediately below the skin and below or in subcutaneous fat layers so to cause minimal discomfort. In the illustrated version of the invention housing 72 is generally rectangular in shape and further formed to have rounded corners. In some versions of the invention housing 72 occupies a surface area of 15 cm² or less and has an overall thickness of 1 cm or less. In one version of the invention, housing 72 has a rectangular frame 74 formed of biocompatible material. Such materials include: metals, such as tantalum; ceramics, such as alumina ceramics; and plastics, such as polyethylene plastics. Frame 74 supports two parallel, spaced apart face plates, outer plate 76 and inner plate 78. Embedded within or adhered to the inner surface of outer face plate 76 is a high frequency antenna 80. Embedded within or adhered to the inner surface of inner face plate 78 is a low frequency antenna 108.

[00036] Suspended by frame 74 and located between the outer and inner face plates 76 and 78, respectively, is a substrate 82. Substrate 82 supports the remaining below- described signal processing and power storing components of the pulse generator 34.

[00037] Implantable pulse generator high frequency antenna 80 is designed to maximize the exchange of signals with the power supply antenna 62. The signals received by converter antenna 80 are applied to two processing circuits, seen in Figure 6. A first one of the processing circuits to which the signal out from antenna 80 is applied is a power extraction and storage circuit. In Figure 6 this circuit is represented by a capacitor 84 tied between antenna 80 and ground an inductor 86 and a diode 87. One end of the inductor 86 is connected to the junction between antenna 80 and capacitor 84. The opposed end of inductor 86 is connected to a forward biased diode. The opposed end of diode 87 is tied to a rechargeable battery 88, also part of the power extraction and storage circuit. Collectively, capacitor 84, inductor 86, diode 87 and battery 88 represent that the pulse generator power extraction and storage circuit converts the AC signal developed across antenna 80 into a storable charge and stores the charge for use by other components internal to the implantable pulse generator 34. For purposes of simplicity, the connection of the power signal supplied by battery 88 to most of the other components internal to the pulse generator 34 are not shown. [00038] High frequency antenna 80 of pulse generator 34 is also connected to a high frequency (HF) modulator/ demodulator 92. Modulator/demodulator 92 extracts the data signals from the signals received by antenna 80. The signals extracted by modulator/demodulator 92 are forwarded a relay processor 94.

[00039] Also internal to implantable pulse generator 34 is a low frequency signal generator 98. The low frequency signal generator 98 which, like other components of module 34, is powered by battery 88, generates a signal at frequency that will, with a minimum of attenuation, pass through the tissue internal to the patient. Generally, the signal output between 100 kHz and 20 MHz. [00040] The signal produced by low frequency signal generator 98 is employed by a low frequency (LF) modulator/demodulator 104 as a carrier signal. The signal produced by relay processor 94 is the modulating signal. Thus, the function of relay processor is to convert the data stream received from modulator/demodulator 92 into a format wherein the signals containing the data can be used to modulate the low frequency signal. In some versions of the invention, no such conversion is required. In these versions of the invention, the data signal extracted from HF modulator/demodulator 92 is applied directly to LF modulator/demodulator .

[00041] The modulated low frequency signal is applied to and broadcast by low frequency antenna 108. [00042] Pulse generator 34 also includes a high frequency signal generator 110. The high frequency signal generator 110 produces a carrier signal at the same frequency as the carrier signal produced by power supply module signal generator 52. The signal produced by high frequency signal generator 110 is applied to modulator/demodulator 104. The modulator/ demodulator 104 uses the signal from generator 110 as a carrier signal. Specifically, this signal is used as a carrier signal when relay processor 94 instructs the modulator/demodulator 104 to transmit data back to the power supply module 36.

[00043] It should be understood that both low frequency signal generator 98 and high frequency signal generator 110 are selectively actuated. Specifically, in order to conserve power, both signal generators are normally off. Relay processor 94 turns on the low frequency signal generator 98 whenever there is a need to transmit data or power the electrode array assembly 32. The relay processor 94 turns on the high frequency signal generator whenever there are data to transmit to the power supply module 36.

[00044] Figure 7 illustrated one electrode array assembly 32 of system 30 of this invention. Electrode array assembly 30 includes a flexible substrate 122 formed from biocompatible material. Disposed on one side of the substrate 122 is an array of electrodes 124. The assembly of Figure 7 is shown as having only five (5) electrodes 124. This is understood to be only for purposes of illustration. In practice, in many versions of the invention fewer or more electrodes 124 may be integral with the electrode array assembly. Each electrode 124 will occupy a surface area of between 0.25 mm² and 6 mm². Disposed on the opposed side of substrate 122 is a low frequency antenna 126. Disposed on the same side of substrate 122 as antenna 126 are below described components that apply current to the electrodes 124. In Figure 7, these components are diagrammatically represented as rectangles 127 and 145. Not shown are the vias that extend through substrate 124. The vias are the conductive paths over which current is applied to the electrodes 124.

[00045] Antenna 126 is designed to maximize signal exchanges with the low frequency signal broadcast by pulse generator antenna 108. The signal from antenna 126 is applied to a power extractor and supply circuit. In Figure 8, the electrode array assembly power extractor and supply circuit is represented by a capacitor 128, an inductor 130, a diode 131 and a rechargeable cell 132. The capacitor 128 is shown connected between antenna 126 and ground. One end of inductor 130 is connected to the junction between the antenna 126 and the capacitor 128. The opposed end of inductor 130 is connected to the forward biased diode 131. The second of diode 131 is tied to the positive terminal of rechargeable cell 132.

[00046] The charge stored in cell 132 is applied to two power supplies 136 and 138. Power supply 136 generates a regulated positive DC signal. The signal produced by power supply 136 is applied to plural variable gain amplifiers 140, plural amplifiers 140a and 140b seen in Figure 9. For simplicity, only a single amplifier is illustrated. Power supply 138 generates a regulated negative DC signal. The signal produced by power supply 138 is applied to plural variable gain amplifiers 142; plural amplifiers 142a and 142b seen in Figure 9. [00047] The power harvested by the electrode array assembly 32 is also applied to a low frequency signal generator 144. The low frequency generator 144 produces a carrier signal at the same frequency at which the carrier produced by pulse generator low frequency generator signal generator 98 is produced. While not illustrated, it should be understood that cell 132 also powers the other components integral with the electrode array assembly 32. [00048] The signal that develops across antenna 126 is also applied to a modulator/demodulator 146. Modulator/ demodulator 146 extracts the data signals from the signals received from antenna 126. These data signals are applied to a stimulation sequence generator 148. In some versions of the invention, stimulation sequence generator 148 is a programmable gate array. [00049] The signals extracted by modulator/demodulator 146 are the instructions that indicate what currents should be applied to the individual electrodes 124 and the combination of electrodes and/or sequence in which these currents should be applied. (For ease of illustration, in Figure 8, only four (4) electrodes 124 are shown.) In an alternative version of the invention, each set of instructions includes a code indicating in which electrode combination and/or sequence current should be applied to the electrodes. Each set of instructions also includes data indicating the strength of the current to be applied.

[00050] Based on the above instructions, stimulation sequence generator 148 retrieves from an associated memory 150 a sequence listing. The sequence listing is the actual instructions for regulating how the below described components apply currents to the individual electrodes. Additional data in the instructions received by the stimulation sequence generator 148 can include the strengths of the currents to be applied to the individual electrodes. Based on these data, stimulation sequence generator 148 sets the gains of amplifiers 140 and 142.

[00051] Stimulation sequence generator 148 clocks out the instructions causing the appropriate actuation of the electrodes 124. The clocking out of these signals is based on a constant frequency clock signal. In Figure 8 this clock signal is supplied by a clock 152 shown as a separate component and connected to the stimulation sequence generator 148.

[00052] A power supply switch circuit 156 is the actual circuit that applies the currents to the individual electrodes 124. Switch circuit 156 includes, for each electrode 124 a number of switches that can selectively tie the electrode to each of the amplifiers 140 and 142. In Figure 9, the switches that control the application of current to a single one of the electrodes are shown as a series of FETs. Thus, the output signal from a first one of the positive voltage amplifiers, amplifier 140a, is shown as being applied to the electrode 124 through a FET 162 and a FET 166. The output signal from a second one of the positive voltage amplifiers, amplifier 140b, is shown as being applied to the electrode 124 through a FET 164 and FET 166. The output signal from a first one of the negative voltage amplifiers, amplifier 142a, is shown as being applied to the electrodes through a FET 168 and a FET 172. Alternatively, the output signal from the second negative voltage amplifier, amplifier 142b, is shown as being applied to the electrode 124 through a FET 170 and FET 172. Thus, power supply switching circuit 156 can be considered a multiplexer .

[00053] During operation of system 30, the stimulation sequence generator 148 asserts the gate signals to FETs 162-172 to ensure the appropriate signal is applied to each electrode. It should be understood that, during some stimulation processes a signal may not be applied to a particular electrode 124. In this instance one or more of the FETs 162-172 tied to a particular electrode may be turned off. The turning off of the appropriate FETs essentially disconnects the particular electrode from the rest of the electrode array assembly 32.

[00054] The voltage present at the electrode 124 is also measured by the electrode array assembly 32. This is shown by the tap off between electrode 124 and the junctions of electrodes 166 and 172. The signal present at this point is applied to an analog to digital converter. 176. In Figure 8 a single ADC connected to a single electrode 124 is shown. While not shown, it should be appreciated that a high impedance buffer circuit may be connected to this tap off. This circuit minimizes the loss of current in the signal applied to the ADC 176.

[00055] The digitized representation of electrode voltage produced by ADC 176 is applied to the stimulation sequence generator 148. In some versions of the invention, based on preprogrammed instructions that are always, executed, the stimulation sequence generator periodically forwards the digitized representations of electrode voltage to the modulator/demodulator 146. Modulator/demodulator then periodically broadcasts these signals back to pulse generator 34 over antenna 126. The signal produced by low frequency signal generator 144 is used as the carrier signal. In alternative versions of the invention, the signals carrying the electrode voltage level data are only broadcast by the electrode array assembly 32 in response to a specific write request. In both versions of the invention it should be appreciated that, the implantable pulse generator 34, upon receipt of these signals, forwards these signals to the power supply module 36.

[00056] As seen in Figure 7, the electrode array assembly is positioned in the spinal column 42 so that the individual electrodes 124, 124a-e in Figure 7, are disposed against the spinal cord. When the system is actuated, processor 54 generates instructions indicating to which specific electrodes 124 the voltages should be applied. These data are broadcast by antenna power supply 36 over antenna 62. Implantable pulse generator 34 receives these signals over high frequency antenna 80. The power contained in these signals is stored in rechargeable battery 88. Modulator/demodulator 92 extracts the instruction signal transmitted by the power supply module. The relay processor 94, if necessary, forwards the extracted signals to the low frequency modulator/demodulator 104. The instruction signals or just the carrier signal, are broadcast by low frequency antenna 108 to the electrode array assembly 32.

[00057] The power contained in the signals received by the electrode array assembly 32 is stored in cell 132. The instructions extracted from the signals by the modulator/demodulator 146 are forwarded to the stimulation sequence generator 148. Based on these data and the sequence pattern data retrieved from memory 150, stimulation sequence generator 148 clocks out instructions to the power switches 156 indicating which electrodes 124 are to be tied to which voltage source (which amplifier 140a, 140b, 142a or 142c) . Based on both the received instructions and sequence data, the stimulation sequence generator 148 also establishes the gain of amplifiers 140a, 140b, 142a and 142b.

[00058] More particularly, when voltages are applied to the electrodes 124 they are applied so that there is balanced current flow between the electrodes. Thus if a positive voltage X is applied to a first set of one or more electrodes, than a negative voltage X is applied to a second set of one or more electrodes different from those in the first set . The goal of this process is to ensure a balanced charge between electrodes; the current emitted by the first set of electrodes equals the current drawn by the second set of electrodes. This serves to minimize, if not eliminate the extent direct current is passed through tissue. The minimization/elimination of this current flow serves to avoid the interference with neuromodulation or tissue necrosis such current flow could otherwise cause. [00059] This current flows through the nerves forming the spinal cord 44. In Figure 7 this current flow is represented by dashed lines from electrode 124b to adjacent electrodes 124d and 124e. When the assembly 30 of this invention is used to attenuate the sense of pain, this energy stimulates the dorsal columns of the spinal cord. This stimulation causes the nerves in this section of the spinal cord to emit action potentials. It is believed that the action potentials produced by these nerves in this section of the spinal cord along with chemical and hemodynamic factors influence the inputs to the brain' s percept of pain at a given dermatomal level due to the input of pain signals from pain sensing nerves.

[00060] It should be appreciated that, in system 30 of this invention, energy is thus passed from the power supply module to the pulse generator at a relatively high frequency. This signal is not as easily attenuated by epidermal tissue and subcutaneous fat as are lower frequency signals. However, higher frequency signals are significantly attenuated by the muscle tissue between the subcutaneous fat. Therefore, the signal transfer between the pulse generator 34 and the electrode array assembly 32 is at lower frequency. This reduces the absorption of this signal into the surrounding tissue.

[00061] It should be appreciated that electrodes 124 can be arranged on a substrate in a pattern other than a pure linear pattern. Thus, the electrodes 124 could be arranged in a matrix wherein there are plural rows some of which contain two or more electrodes. In this and other versions of the invention, the electrodes can be selected for actuation so that there is not necessarily a 1:1 ratio to which positive and negative voltages are, respectively, applied. This makes it possible to focus the current on specific sections of tissue in order to accomplish the desired therapeutic effect. When providing assemblies with a significant number of electrodes, typically between 8 to 500 electrodes and often between 20 and 200 electrodes, one can also by patient feedback determine optimal electrode selection, polarity and charge sequencing in order to accomplish the desired therapeutic effect. [00062] The surface spinal cord dura is curved. Therefore, it may be desirable to provide the electrode array assembly with members to ensure that the electrodes remain in contact with the spinal cord 44. One such assembly is seen in Figure 10. Here a curved biasing member 182 is shown to extend upwardly from the outer surface of the substrate 122a. The outer surface of the biasing member abuts the epidural-defining surface of the adjacent vertebra. The biasing member thus pushes the substrate 122a and by extension, the electrodes 124 towards the dura of the spinal cord 44. This intimate contact provides stability for the electrodes and reduces the impedance to electrical current.

[00063] In an alternative version of the invention, the substrate of the electrode array assembly 32 is provided with a C-shaped cuff formed of flexible material (cuff not illustrated) . This cuff urges the substrate around, and the electrodes against the spinal cord dura. The backing or cuff can be formed of flexible material that, when compacted and released from a delivery cannula, expands to approximately its original shape. Either the cuff or the backing allows the electrode array assembly to be inserted percutanously . [00064] Alternative versions of this invention are possible. For example, in one alternative version of the invention, the electrodes may be disposed on plural substrates. Typically, but not always, in this version of the invention, each electrode-carrying substrate includes its own array of plural electrodes. In some embodiments of this version of the invention, each substrate contains its own components for both receiving power from the pulse generator and regulating the application of this power to the individual electrodes. In alternative embodiments of this version of the invention, there is a single assembly with a common antenna 126 and drive circuitry for powering and the individual electrodes. In these versions of the invention, flexible strips may connect the individual substrates together. An advantage of these versions of the invention is that it allows the electrodes to be placed relatively large distances apart from each other along or around the spinal column.

[00065] Further, in some versions of the invention wherein the array of plural electrodes is supported by a single substrate, there may still be a second and/or a third substrate. These additional substrates support the antenna 126 and and/or the associated energy storage, control and drive circuits. Again, flex circuits extend between the individual substrates. An advantage of this construction of the invention is that substrate supporting the antenna 126 can be positioned within the spinal column at a position best suited to facilitate signal exchange with the implantable pulse generator 34 while the substrate upon which the electrode array is supported can be positioned over the portion of the spinal cord wherein the currents flowed through the individual electrodes will offer the most beneficial therapeutic effect. Further, in this version of the invention, it is possible to position the antenna 126- supporting substrate outside of the spinal column. This could further improve the exchange of signals and power with the implantable pulse generator. Since this substrate is free, tied only at one end, movement of adjacent hard and soft body tissue that would cause like movement of the substrate would result in only nominal stressing of the conductive structure connecting the one or more additional substrates disposed within the spinal column. [00066] In some versions of the invention, antenna 108 may extend out of the implantable pulse generator 34. [00067] Similarly, in some versions of the invention, the implantable pulse generator housing may be formed from material that has some flexibility. Thus, the materials from which the various components of the system 30 of this invention may be formed can be different from what has been described. Thus, the electrode array could be constructed as a multi-layer MEMS structure. In one embodiment of this version of this invention, antenna 126 is formed on one face of the structure. The electrodes 124 are formed on the opposed face. One or more of the power extraction, power storage and control and drive components are formed on intermediate layers of the MEMS structure. In other embodiments of this version of the invention, some of these components of the electrode array assembly 32 are formed on a first MEMS structure, other ones of the components are formed on a second, or even a third MEMS structure/structures .

[00068] In some alternative versions of the invention, the electrode array assembly 32 may even include a circuit that includes the sensed electrode voltage readings and the known excitation currents into impedance measurements. Data describing these impedance measurements are what are transmitted by the electrode array assembly 32 and then relayed by the implantable pulse generator 34 to the power supply module 36. Also, in some versions of the invention, it may not be necessary to provide power supply circuits. In these versions of the invention the storage device, (the capacitor or cell) that holds the charge extracted from the signal from the implantable pulse generator may be selectively connected to the electrodes by power switches 156. Amplifiers 140 and 142 may similarly not be present in all versions of the invention.

[00069] Capacitors could replace the implantable batteries. Also, the described processors may not truly be processors that operate based on loaded instructions. A processor may for example by a programmable gate array or an application specific integrated circuit (or circuits) that generate the requisite output in response to the received input signals or instructions.

[00070] In another embodiment of the present invention, an alternative to the radio frequency transmission of energy to the wireless stimulation system is to use the conductive pathways naturally occurring in the body. Nerves and blood vessels are conductive pathways through the body that the central nervous system uses to transmit information to and from specific locations. Therefore, in one embodiment of the present invention, an energy transfer system using electricity could utilize the vessel pathways as conductive paths to the implanted device. In yet another embodiment of the present invention, ultrasound transduction, vibration transduction, or magnetic induction can be used as a means to wirelessly send energy to the implanted stimulator. In still another embodiment of the present invention, power can be generated by harnessing the energy of movements of the body due to body movements, involuntary mechanisms, temperature gradients, etc. In this embodiment, the external device would be limited to signal/control transmission rather than power and signal transmission. Some versions of the invention may include a hardwired connection between the implantable pulse generator and the electrode array assembly.

[00071] Therefore, it is an object of the appended claims to cover all such modifications and variations that come within the true spirit and scope of this invention.

Claims

What is claimed is:

1. A neuromodulation stimulation system, the system comprising: an electrode array assembly (32) including: a flexible substrate (122) formed of material that can be positioned in the vicinity of neurological tissue and a plurality of spaced apart electrodes (124) disposed on the substrate for applying a current through the neurological tissue; and an implantable pulse generator (36) formed from components that allows the implantable generator to be disposed within the body, the implantable pulse generator including: a device (94) for generating instruction signals indicating between which electrodes the current should flow; and a signal generator (98), characterized in that: the implantable pulse generator further includes: a modulator (104) for receiving the instruction signals and that is connected to the signal generator, said modulator configured to modulate the output of the signal generator based on the instruction signals; and a first antenna (108) for receiving the modulated signals from said modulator and wirelessly broadcasting the signals to the electrode array assembly; and the electrode array assembly includes: an antenna (126) receiving the signals transmitted wirelessly from said implantable pulse generator first antenna; a power extractor and supply circuit (128, 130, 131, 132) connected to said electrode array antenna for extracting and storing power from the received signals; a demodulator (140) connected to the electrode array antenna for extracting the instruction signals from the received signals; and a switch circuit (156) disposed between said at power extractor and supply circuit for selectively apply current to selected ones the electrodes based on the instruction signals extracted by said demodulator and said antenna, said power extractor and supply circuit and said switch circuit are all connected to the substrate (122) .

2. The neuromodulation stimulation system of Claim 1, wherein said electrode array assembly further includes a curved backing formed of flexible material (182) against which at least the portion of the substrate from which the electrodes extend is mounted so that said backing shapes the substrate so that the electrodes are urged against the tissue against which the electrodes are disposed.

3. The neuromodulation stimulation system of Claims 1 or 2, wherein: a power supply module (36) that is worn external to the body is provided, said power supply module including a signal generator (52) for generating signals and an antenna (62) for broadcasting the signals into the body; and said implantable pulse generator further includes: a second antenna (80) receiving the signals broadcast by said power supply antenna; and a power extraction and storage circuit (84, 86, 87, 88) connected to said antenna for receiving the signals and storing the power contained in the signals wherein said power extraction and storage circuit is connected to said implantable pulse generator signal generator for energizing said signal generator.

4. The neuromodulation stimulation system of Claim 3, where said power supply module signal generator (52) generates signals at a first frequency; and said implantable pulse generator signal generator generates the carrier signals at a second frequency, the second frequency being lower than the first frequency.

5. The neuromodulation stimulation system of Claims 3 or 4, wherein: said power supply module further includes: a processor (54) for generating command signals indicating between which electrodes the current should flow; and a modulator for modulating the signals produced by said power supply module signal generator based on the processor-generated command signals prior to said signals being broadcast from said antenna (62); and the implantable programmable stimulator further includes a demodulator (92) connected to said second antenna (80) that demodulates the received signals to extract the command signals and wherein said switch circuit regulates the connection of said at least power supply (136, 138) based on the extracted command signals.

6. The neuromodulation stimulation system of Claims 3, 4 or 5, wherein said implantable pulse generator includes an inner face plate 78 and an opposed outer face plate 76; and said first antenna (108) is embedded in said inner face plate and said second antenna (80) is embedded in said outer face plate.

7. The neuromodulation stimulation system of Claims 1, 2, 3, 4, 5 or 6, wherein said electrode array assembly is configured to be positioned over spinal cord dura.

8. The neuromodulation stimulation system of Claims 1, 2, 3, 4, 5, 6 or 7, wherein: at least power supply (136, 138) is connected to substrate and is energized by said electrode array assembly power supply and extractor circuit; and said switch circuit is connected between said at least one power supply and said electrodes for selectively connecting signals from said at least one power supply to said electrodes (124).

9. An electrode array assembly for use with a neuromodulation stimulation system, said electrode array assembly including: a flexible substrate (122) formed of material that can be positioned in the vicinity of neurological tissue and a plurality of spaced apart electrodes (124a...e) disposed on the substrate for applying a current through the neurological tissue; and characterized in that connected to the substrate is: an antenna (126) receiving the signals wireless transmitted wirelessly from an antenna integral with an implantable pulse generator; a power extractor and supply circuit (128, 130, 131, 132) connected to said electrode array antenna for extracting and storing power from the received signals; a demodulator (140) connected to the electrode array antenna for extracting the instruction signals from the received signals; at least one power supply (136, 138) that receives power from said power extractor and supply circuit for sourcing power to said electrodes and a switch circuit (156) disposed between said power extractor and supply circuit that that selectively connects said electrodes to said power extractor and supply circuit based on the instruction signals extracted by said demodulator and said antenna.

10. The electrode array assembly of Claim 9, wherein: at least power supply (136, 138) is connected to substrate and is energized by said electrode array assembly power supply and extractor circuit; and said switch circuit is connected between said at least one power supply and said electrodes for selectively connecting signals from said at least one power supply to said electrodes (124).

11. An electrode array assembly for use with a neuromodulation stimulation system, said electrode array assembly including: a flexible substrate formed of material that can be positioned in the vicinity of neurological tissue, and a plurality of spaced apart electrodes (124a...e) disposed on the substrate for applying a current through the neurological tissue; and characterized in that: a backing formed from flexible material is disposed around the substrate for urging the substrate into a defined geometric profile.

12. The electrode array assembly of Claim 11, wherein said backing is shaped to urge the substrate into a profile that serves to conform the substrate to the outer surface of the spinal dura.

13. An implantable pulse generator for use as part of an implantable neuromodulation system, said implantable pulse generator including: a housing (74, 76, 78) formed from material that allows the housing to be implanted in a living being; and a signal generator (98) for generating signals that can be used to produce a current between two electrodes that are positioned adjacent neurological tissue characterized in that, the pulse generator further includes : a first antenna for receiving signals at a first frequency from a source external to the body (80) and a power extraction and storage circuit (84, 86, 87, 88) connected to said antenna for receiving the signals and storing the power contained in the signals for supplying the power that energizes the signal generator; a second antenna (108) for wirelessly broadcasting the signals generated by said signal generator to an electrode array assembly, wherein said signal generator generates signals at a second frequency that is lower than the first frequency.

14. The implantable pulse generator of Claim 13, wherein said first antenna is embedded in a panel of the housing.

15. The implantable pulse generator of Claims 13 or 14, wherein said second antenna is embedded in a panel.