This application relates to deep brain stimulation (DBS), and more particularly, to methods and systems for using sensed neural responses for facilitating aspects of DBS.
Implantable neurostimulator devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within Deep Brain Stimulation (DBS). DBS has been applied therapeutically for the treatment of neurological disorders, including Parkinson's Disease, essential tremor, dystonia, and epilepsy, to name but a few. Further details discussing the treatment of diseases using DBS are disclosed in U.S. Pat. Nos. 6,845,267, 6,845,267, and 6,950,707. However, the present invention may find applicability with any implantable neurostimulator device system.
Each of these neurostimulation systems, whether implantable or external, typically includes one or more electrode carrying stimulation leads, which are implanted at the desired stimulation site, and a neurostimulator, used externally or implanted remotely from the stimulation site, but coupled either directly to the neurostimulation lead(s) or indirectly to the neurostimulation lead(s) via a lead extension. The neurostimulation system may further comprise a handheld external control device to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. Typically, the stimulation parameters programmed into the neurostimulator can be adjusted by manipulating controls on the external control device to modify the electrical stimulation provided by the neurostimulator system to the patient.
Thus, in accordance with the stimulation parameters programmed by the external control device, electrical pulses can be delivered from the neurostimulator to the stimulation electrode(s) to stimulate or activate a volume of tissue in accordance with a set of stimulation parameters and provide the desired efficacious therapy to the patient. The best stimulus parameter set will typically be one that delivers stimulation energy to the volume of tissue or neural pathways that must be stimulated in order to provide the therapeutic benefit (e.g., treatment of movement disorders), while minimizing the volume of non-target tissue or neural pathways that are stimulated. A typical stimulation parameter set may include the electrodes that are acting as anodes or cathodes, as well as the amplitude, duration, and rate of the stimulation pulses.
Non-optimal electrode placement and stimulation parameter selections may result in excessive energy consumption due to stimulation that is set at too high an amplitude, too wide a pulse duration, or too fast a frequency; inadequate or marginalized treatment due to stimulation that is set at too low an amplitude, too narrow a pulse duration, or too slow a frequency; or stimulation of neighboring neural populations or other areas remote to the stimulation site via connecting neural pathways that may result in undesirable side effects. For example, bilateral DBS of the subthalamic nucleus (STN) has been shown to provide effective therapy for improving the major motor signs of advanced Parkinson's disease, and although the bilateral stimulation of the subthalamic nucleus is considered safe, an emerging concern is the potential negative consequences that it may have on cognitive functioning and overall quality of life (see A. M. M. Frankemolle, et al., Reversing Cognitive-Motor Impairments in Parkinson's Disease Patients Using a Computational Modelling Approach to Deep Brain Stimulation Programming, Brain 2010; pp. 1-16). In large part, this phenomenon is due to the small size of the STN. Even with the electrodes are located predominately within the sensorimotor territory, the electrical field generated by DBS is non-discriminately applied to all neural elements surrounding the electrodes, thereby resulting in the spread of current to neural elements affecting cognition. As a result, diminished cognitive function during stimulation of the STN may occur do to non-selective activation of non-motor pathways within or around the STN.
The large number of electrodes available, combined with the ability to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician or patient. In the context of DBS, neurostimulation leads with a complex arrangement of electrodes that not only are distributed axially along the leads, but are also distributed circumferentially around the neurostimulation leads as segmented electrodes, can be used.
To facilitate such selection, the clinician generally programs the external control device, and if applicable the neurostimulator, through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC) or mobile platform. The PC or custom hardware may actively control the characteristics of the electrical stimulation generated by the neurostimulator to allow the optimum stimulation parameters to be determined based on patient feedback, including both, but not limited to, behavioral and clinical response, anatomical and neurophysiological information and to subsequently program the external control device with the optimum stimulation parameters.
When electrical leads are implanted within the patient, the computerized programming system may be used to instruct the neurostimulator to apply electrical stimulation to test placement of the leads and/or electrodes, thereby assuring that the leads and/or electrodes are implanted in effective locations within the patient. The system may also instruct the user how to improve the positioning of the leads, or confirm when a lead is well-positioned. Once the leads are correctly positioned, a fitting procedure, which may be referred to as a navigation session, may be performed using the computerized programming system to program the external control device, and if applicable the neurostimulator, with a set of stimulation parameters that best addresses the neurological disorder(s).
An aspect of programming the patient's stimulation parameters involves determining which electrodes to use to make electric fields that are best configured to treat the patient's symptoms and to avoid unwanted side effects. In the context of DBS, the leads are typically implanted into a particular region of the brain, such as the STN, as described below. Stimulation of that region may be effective at modulating the patient's symptoms. However, if intensity or amplitude of the stimulation becomes too great it may also stimulate nearby and/or remote non-target areas of the brain and cause side effects. Ideally, the clinician would like to determine a position within the target area of the patient's brain and determine an electrode configuration that provides a large range of stimulation intensities (i.e., a large therapeutic window) without stimulating non-target areas. Thus, there is a need for methods and systems that assist a clinician in doing so.
Disclosed herein is a method of optimizing a location on an electrode lead implanted in a patient's brain for providing electrical stimulation to the patient, wherein the electrode lead comprises a plurality electrodes, the method comprising: using one or more of the plurality of electrodes to sequentially provide electrical stimulation at different locations on the electrode lead, for each stimulation location: using one or more of the plurality of electrodes to record first signals, wherein the first signals are indicative of electric potentials evoked in the patient's brain by the stimulation, and recording second signals, wherein the second signals are indicative of motor activity evoked by the stimulation, and selecting an optimized location on the electrode lead for providing therapeutic electrical stimulation based on the first and second signals. According to some embodiments, the recorded first signals are indicative of evoked resonant neural responses evoked by the stimulation. According to some embodiments, the second signals are generated using electromyography (EMG), one or more mechanical sensors, speech sensors, and/or electrochemical sensors. According to some embodiments, the second signals are generated using a cortical array. According to some embodiments, the electric potentials evoked in the patient's brain are correlated with therapeutic efficacy of the stimulation. According to some embodiments, the motor activity evoked by the stimulation is correlated with an undesirable side effect of the stimulation. According to some embodiments, selecting an optimized location on the electrode lead based on the first and second signals comprises using the first and second signals to determine a therapeutic window for each of the stimulation locations. According to some embodiments, the first signals are indicative of potentials evoked in the patient's subthalamic nucleus (STN). According to some embodiments, the second signals are indicative of recruitment of neural elements in the patient's corticospinal tract by the stimulation. According to some embodiments, selecting an optimized location on the electrode lead based on the first and second signals comprises: for each stimulation location determining a value for a feature of the first signal and a value for a feature of the second signal, selecting a plurality of stimulation locations where the value for the feature of the second signals is less than a threshold value, and selecting a stimulation location from the plurality of stimulation locations where the value for the feature of the first signal is the greatest. According to some embodiments, selecting an optimized location on the electrode lead based on the first and second signals comprises: for each stimulation location determining a ratio comprising a value for a feature of the first signal and a value for a feature of the second signal and comparing the ratio to a threshold value.
Also disclosed herein is a system for providing stimulation to a patient's brain using an electrode lead that is implantable in the patient's brain and comprises a plurality of electrodes, the system comprising: control circuitry configured to: use one or more of the plurality of electrodes to sequentially provide electrical stimulation at different locations on the electrode lead, for each stimulation location: use one or more of the plurality of electrodes to record first signals, wherein the first signals are indicative of electric potentials evoked in the patient's brain by the stimulation, and receive one or more second signals that are indicative of motor activity evoked by the stimulation, and select an optimized location on the electrode lead for providing therapeutic electrical stimulation based on the first and second signals. According to some embodiments, the recorded first signals are indicative of evoked resonant neural responses evoked by the stimulation. According to some embodiments, the second signals are generated using electromyography (EMG), one or more mechanical sensors, speech sensors, and/or electrochemical sensors. According to some embodiments, the second signals are generated using a cortical array. According to some embodiments, the electric potentials evoked in the patient's brain are correlated with therapeutic efficacy of the stimulation. According to some embodiments, the motor activity evoked by the stimulation is correlated with an undesirable side effect of the stimulation. According to some embodiments, selecting an optimized location on the electrode lead for based on the first and second signals comprises using the first and second signals to determine a therapeutic window for each of the stimulation locations. According to some embodiments, the first signals are indicative of potentials evoked in the patient's subthalamic nucleus (STN). According to some embodiments, the second signals are indicative of recruitment of neural elements in the patient's corticospinal tract by the stimulation. According to some embodiments, selecting an optimized location on the electrode lead based on the first and second signals comprises: for each stimulation location determining a value for a feature of the first signal and a value for a feature of the second signal, selecting a plurality of stimulation locations where the value for the feature of the second signals is less than a threshold value, and selecting a stimulation location from the plurality of stimulation locations where the value for the feature of the first signal is the greatest. According to some embodiments, selecting an optimized location on the electrode lead based on the first and second signals comprises: for each stimulation location determining a ratio comprising a value for a feature of the first signal and a value for a feature of the second signal and comparing the ratio to a threshold value.
Also disclosed herein is a method of implanting a stimulation lead in the brain of a patient, wherein the stimulation lead comprises a plurality of electrodes, the method comprising: positioning the lead at a first position in the patient's brain, using one or more of the electrodes to apply stimulation to the patient's brain, using one or more of the plurality of electrodes to record first signals, wherein the first signals are indicative of electric potentials evoked in the patient's brain by the stimulation, recording second signals, wherein the second signals are indicative of motor activity evoked by the stimulation, and using the first and second signals to determine one or more of (i) whether to move the lead to a new position or (ii) to adjust stimulation parameters based on the evoked responses. According to some embodiments, the recorded first signals are indicative of evoked resonant neural responses evoked by the stimulation. According to some embodiments, the second signals are generated using electromyography (EMG), one or more mechanical sensors, speech sensors, and/or electrochemical sensors. According to some embodiments, the second signals are generated using a cortical array. According to some embodiments, the electric potentials evoked in the patient's brain are correlated with therapeutic efficacy of the stimulation. According to some embodiments, the motor activity evoked by the stimulation is correlated with an undesirable side effect of the stimulation. According to some embodiments, selecting an optimized location on the electrode lead for based on the first and second signals comprises using the first and second signals to determine a therapeutic window for each of the stimulation locations. According to some embodiments, the first signals are indicative of potentials evoked in the patient's subthalamic nucleus (STN). According to some embodiments, the second signals are indicative of recruitment of neural elements in the patient's corticospinal tract by the stimulation.
Also disclosed herein is a method of optimizing one or more stimulation parameters for providing electrical stimulation to a patient's brain using an electrode lead implanted in the patient's brain, wherein the electrode lead comprises a plurality of electrodes, the method comprising: using one or more of the plurality of electrodes to provide stimulation to the patient's brain, using one or more of the plurality of electrodes to record first signals, wherein the first signals are indicative of electric potentials evoked in the patient's brain by the stimulation, recording second signals, wherein the second signals are indicative of motor activity evoked by the stimulation, and adjusting one or more parameters of the stimulation based on the first and second signals. According to some embodiments, the one or more parameters are one or more of an electrode configuration, an amplitude, a pulse width, and a frequency.
The invention may also reside in the form of a programed external device (via its control circuitry) for carrying out the above methods, a programmed IPG or ETS (via its control circuitry) for carrying out the above methods, a system including a programmed external device and IPG or ETS for carrying out the above methods, or as a computer readable media for carrying out the above methods stored in an external device or IPG or ETS. The invention may also reside in one or more non-transitory computer-readable media comprising instructions, which when executed by a processor of a machine configure the machine to perform any of the above methods.
An implantable neurostimulator system, such as a DBS system, typically includes an Implantable Pulse Generator (IPG) 10 shown in
In yet another example shown in
Lead wires 20 within the leads are coupled to the electrodes 16 and to proximal contacts 21 insertable into lead connectors 22 fixed in a header 23 on the IPG 10, which header can comprise an epoxy for example. Once inserted, the proximal contacts 21 connect to header contacts 24 within the lead connectors 22, which are in turn coupled by feedthrough pins 25 through a case feedthrough 26 to stimulation circuitry 28 within the case 12, which stimulation circuitry 28 is described below.
In the IPG 10 illustrated in
In a DBS application, as is useful in the treatment of movement symptoms in Parkinson's disease for example, the IPG 10 is typically implanted under the patient's clavicle (collarbone). Lead wires 20 are tunneled through the neck and the scalp and the electrode leads 15 (or 33) are implanted through holes drilled in the skull and positioned for example in the subthalamic nucleus (STN) and the Globus pallidus internus (GPi) in each brain hemisphere.
IPG 10 can include an antenna 27a allowing it to communicate bi-directionally with a number of external devices discussed subsequently. Antenna 27a as shown comprises a conductive coil within the case 12, although the coil antenna 27a can also appear in the header 23. When antenna 27a is configured as a coil, communication with external devices preferably occurs using near-field magnetic induction. IPG 10 may also include a Radio-Frequency (RF) antenna 27b. In
Stimulation in IPG 10 is typically provided by electrical pulses each of which may include a number of phases such as 30a and 30b, as shown in the example of
In the example of
IPG 10 as mentioned includes stimulation circuitry 28 to form prescribed stimulation at a patient's tissue.
Proper control of the PDACs 40i and NDACs 42i allows any of the electrodes 16 and the case electrode Ec 12 to act as anodes or cathodes to create a current through a patient's tissue, R, hopefully with good therapeutic effect. In the example shown, and consistent with the first pulse phase 30a of
Other stimulation circuitries 28 can also be used in the IPG 10. In an example not shown, a switching matrix can intervene between the one or more PDACs 40i and the electrode nodes ei 39, and between the one or more NDACs 42i and the electrode nodes. Switching matrices allows one or more of the PDACs or one or more of the NDACs to be connected to one or more electrode nodes at a given time. Various examples of stimulation circuitries can be found in U.S. Pat. No. 6,181,969, 8,606,362, 8,620,436, U.S. Patent Application Publications 2018/0071520 and 2019/0083796. The stimulation circuitries described herein provide multiple independent current control (MICC) (or multiple independent voltage control) to guide the estimate of current fractionalization among multiple electrodes and estimate a total amplitude that provides a desired strength. In other words, the total anodic current can be split among two or more electrodes and/or the total cathodic current can be split among two or more electrodes, allowing the stimulation location and resulting field shapes to be adjusted. For example, a “virtual electrode” may be created at a position between two physical electrodes by fractionating current between the two electrodes. In other words, the virtual electrode is not co-located with any of the physical electrodes. Appreciate, that in the context of split ring electrodes, such as electrodes E2-E4 (
Much of the stimulation circuitry 28 of
Also shown in
Referring again to
To recover all charge by the end of the second pulse phase 30b of each pulse (Vc1=Vcc=0V), the first and second phases 30a and 30b are charged balanced at each electrode, with the first pulse phase 30a providing a charge of −Q (−I*PW) and the second pulse phase 30b providing a charge of +Q (+I*PW) at electrode E1, and with the first pulse phase 30a providing a charge of +Q and the second pulse phase 30b providing a charge of −Q at the case electrode Ec. In the example shown, such charge balancing is achieved by using the same pulse width (PW) and the same amplitude (|I|) for each of the opposite-polarity pulse phases 30a and 30b. However, the pulse phases 30a and 30b may also be charged balance at each electrode if the product of the amplitude and pulse widths of the two phases 30a and 30b are equal, or if the area under each of the phases is equal, as is known.
Therefore, and as shown in
Passive charge recovery 30c may alleviate the need to use biphasic pulses for charge recovery, especially in the DBS context when the amplitudes of currents may be lower, and therefore charge recovery less of a concern. For example, and although not shown in
External controller 60 can be as described in U.S. Patent Application Publication 2015/0080982 for example and may comprise a controller dedicated to work with the IPG 10 or ETS 50. External controller 60 may also comprise a general-purpose mobile electronics device such as a mobile phone, tablet, or other computing device that has been programmed with a Medical Device Application (MDA) allowing it to work as a wireless controller for the IPG 10 or ETS, as described in U.S. Patent Application Publication 2015/0231402. External controller 60 includes a user interface, preferably including means for entering commands (e.g., buttons or selectable graphical elements) and a display 62. The external controller 60's user interface enables a patient to adjust stimulation parameters, although it may have limited functionality when compared to the more-powerful clinician programmer 70, described shortly.
The external controller 60 can have one or more antennas capable of communicating with the IPG 10. For example, the external controller 60 can have a near-field magnetic-induction coil antenna 64a capable of wirelessly communicating with the coil antenna 27a or 56a in the IPG 10 or ETS 50. The external controller 60 can also have a far-field RF antenna 64b capable of wirelessly communicating with the RF antenna 27b or 56b in the IPG 10 or ETS 50.
Clinician programmer 70 is described further in U.S. Patent Application Publication 2015/0360038, and can comprise a computing device 72, such as a desktop, laptop, or notebook computer, a tablet, a mobile smart phone, a Personal Data Assistant (PDA)-type mobile computing device, etc. In
The antenna used in the clinician programmer 70 to communicate with the IPG 10 or ETS 50 can depend on the type of antennas included in those devices. If the patient's IPG 10 or ETS 50 includes a coil antenna 27a or 56a, wand 76 can likewise include a coil antenna 80a to establish near-field magnetic-induction communications at small distances. In this instance, the wand 76 may be affixed in close proximity to the patient, such as by placing the wand 76 in a belt or holster wearable by the patient and proximate to the patient's IPG 10 or ETS 50. If the IPG 10 or ETS 50 includes an RF antenna 27b or 56b, the wand 76, the computing device 72, or both, can likewise include an RF antenna 80b to establish communication at larger distances. The clinician programmer 70 can also communicate with other devices and networks, such as the Internet, either wirelessly or via a wired link provided at an Ethernet or network port.
To program stimulation programs or parameters for the IPG 10 or ETS 50, the clinician interfaces with a clinician programmer graphical user interface (GUI) 82 provided on the display 74 of the computing device 72. As one skilled in the art understands, the GUI 82 can be rendered by execution of clinician programmer software 84 stored in the computing device 72, which software may be stored in the device's non-volatile memory 86. Execution of the clinician programmer software 84 in the computing device 72 can be facilitated by control circuitry 88 such as one or more microprocessors, microcomputers, FPGAs, DSPs, other digital logic structures, etc., which are capable of executing programs in a computing device, and which may comprise their own memories. For example, control circuitry 88 can comprise an i5 processor manufactured by Intel Corp, as described at https://www.intel.com/content/www/us/en/products/processors/core/i5-processors.html. Such control circuitry 88, in addition to executing the clinician programmer software 84 and rendering the GUI 82, can also enable communications via antennas 80a or 80b to communicate stimulation parameters chosen through the GUI 82 to the patient's IPG 10.
The user interface of the external controller 60 may provide similar functionality because the external controller 60 can include similar hardware and software programming as the clinician programmer. For example, the external controller 60 includes control circuitry 66 similar to the control circuitry 88 in the clinician programmer 70 and may similarly be programmed with external controller software stored in device memory.
An increasingly interesting development in pulse generator systems is the addition of sensing capability to complement the stimulation that such systems provide.
The IPG 100 also includes stimulation circuitry 28 to produce stimulation at the electrodes 16, which may comprise the stimulation circuitry 28 shown earlier (
IPG 100 also includes sensing circuitry 115, and one or more of the electrodes 16 can be used to sense spontaneous or evoked electrical signals, e.g., biopotentials from the patient's tissue. In this regard, each electrode node 39 can further be coupled to a sense amp circuit 110. Under control by bus 114, a multiplexer 108 can select one or more electrodes to operate as sensing electrodes (S+, S−) by coupling the electrode(s) to the sense amps circuit 110 at a given time, as explained further below. Although only one multiplexer 108 and sense amp circuit 110 are shown in
So as not to bypass the safety provided by the DC-blocking capacitors 38, the inputs to the sense amp circuitry 110 are preferably taken from the electrode nodes 39. However, the DC-blocking capacitors 38 will pass AC signal components (while blocking DC components), and thus AC components within the signals being sensed will still readily be sensed by the sense amp circuitry 110. In other examples, signals may be sensed directly at the electrodes 16 without passage through intervening capacitors 38.
According to some embodiments, it may be preferred to sense signals differentially, and in this regard, the sense amp circuitry 110 comprises a differential amplifier receiving the sensed signal S+(e.g., E3) at its non-inverting input and the sensing reference S− (e.g., E1) at its inverting input. As one skilled in the art understands, the differential amplifier will subtract S− from S+ at its output, and so will cancel out any common mode voltage from both inputs. This can be useful for example when sensing various neural signals, as it may be useful to subtract the relatively large-scale stimulation artifact from the measurement (as much as possible). Examples of sense amp circuitry 110, and manner in which such circuitry can be used, can be found in U.S. Patent Application Publication 2019/0299006; and U.S. Provisional Patent Application Serial Nos. 62/825,981, filed Mar. 29, 2019; 62/825,982, filed Mar. 29, 2019; and 62/883,452, filed Aug. 6, 2019. The IPG (and/or ETS) may also be configured to determine impedances at any of the electrodes. For example, the IPG (and/or ETS) may be configured with sample and hold circuitry, controlled by the control circuitry for measuring impedances.
Particularly in the DBS context, it can be useful to provide a clinician with a visual indication of how stimulation selected for a patient will interact with the tissue in which the electrodes are implanted. This is illustrated in
GUI 100 allows a clinician (or patient) to select the stimulation program that the IPG 110 or ETS 150 will provide and provides options that control sensing of spontaneous or evoked responses, as described below. In this regard, the GUI 100 may include a stimulation parameter interface 104 where various aspects of the stimulation program can be selected or adjusted. For example, interface 104 allows a user to select the amplitude (e.g., a current I) for stimulation; the frequency (f) of stimulation pulses; and the pulse width (PW) of the stimulation pulses. Stimulation parameter interface 104 can be significantly more complicated, particularly if the IPG 100 or ETS 150 supports the provision of stimulation that is more complicated than a repeating sequence of pulses. See, e.g., U.S. Patent Application Publication 2018/0071513. Nonetheless, interface 104 is simply shown for simplicity in
Stimulation parameter interface 104 may further allow a user to select the active electrodes—i.e., the electrodes that will receive the prescribed pulses. Selection of the active electrodes can occur in conjunction with a leads interface 102, which can include an image 103 of the one or more leads that have been implanted in the patient. Although not shown, the leads interface 102 can include a selection to access a library of relevant images 103 of the types of leads that may be implanted in different patients.
In the example shown in
GUI 100 can further include a visualization interface 106 that can allow a user to view an indication of the effects of stimulation, such as electric field image 112 formed on the one or more leads given the selected stimulation parameters. The electric field image 112 is formed by field modelling in the clinician programmer 70. Only one lead is shown in the visualization interface 106 for simplicity, although again a given patient might be implanted with more than one lead. Visualization interface 106 provides an image 111 of the lead(s) which may be three-dimensional.
The visualization interface 106 preferably, but not necessarily, further includes tissue imaging information 114 taken from the patient, represented as three different tissue structures 114a, 114b and 114c in
The various images shown in the visualization interface 106 (i.e., the lead image 111, the electric field image 112, and the tissue structures 114i) can be three-dimensional in nature, and hence may be rendered in the visualization interface 106 in a manner to allow such three-dimensionality to be better appreciated by the user, such as by shading or coloring the images, etc. Additionally, a view adjustment interface 107 may allow the user to move or rotate the images, using cursor 101 for example.
GUI 100 can further include a cross-section interface 108 to allow the various images to be seen in a two-dimensional cross section. Specifically, cross-section interface 108 shows a particular cross section 109 taken perpendicularly to the lead image 111 and through split-ring electrodes E2, E3, and E4. This cross section 109 can also be shown in the visualization interface 106, and the view adjustment interface 107 can include controls to allow the user to specify the plane of the cross section 109 (e.g., in XY, XZ, or YZ planes) and to move its location in the image. Once the location and orientation of the cross section 109 is defined, the cross-section interface 108 can show additional details. For example, the electric field image 112 can show equipotential lines allowing the user to get a sense of the strength and reach of the electric field at different locations. Although GUI 100 includes stimulation definition (102, 104) and imaging (108, 106) in a single screen of the GUI, these aspects can also be separated as part of the GUI 100 and made accessible through various menu selections, etc.
It has been observed that DBS stimulation in certain positions in the brain can evoke neural responses, i.e., electrical activity from neural elements, which may be measured either from brain itself or from other locations in the body (such as muscles). Such evoked neural responses are referred to herein generally as evoked potentials (EPs). One example of such EPs are resonant neural responses, referred to herein as evoked resonant neural responses (ERNAs). See, e.g., Sinclair, et al., “Subthalamic Nucleus Deep Brain Stimulation Evokes Resonant Neural Activity,” Ann. Neurol. 83(5), 1027-31, 2018. The ERNA responses typically have an oscillation frequency of about 200 to about 500 Hz. Stimulation of the STN, and particularly of the dorsal subregion of the STN, has been observed to evoke strong ERNA responses, whereas stimulation of the posterior subthalamic area (PSA) does not evoke such responses. Thus, ERNA may provide a biomarker for electrode location, which can indicate acceptable or optimal lead placement and/or stimulation field placement for achieving the desired therapeutic response. An example of an ERNA in isolation is illustrated in
Another example of an evoked potentials are motor evoked potentials (MEPs), which are electrical signals recorded from the descending motor pathways or from muscles following stimulation of motor pathways in the brain. An MEP is shown in isolation in
Aspects of this disclosure relate to methods and systems for using evoked potentials, such as ERNA, MEPs and other evoked potentials, as well as other recorded electrical signals, such as local field potentials and/or spontaneous activity, to inform aspects of neuromodulation therapy, such as DBS therapy. The measurements described herein can be used during the surgical implantation of the electrode leads to help the clinician implant the lead in the desired location within the patient's brain. As used herein, the terms “therapeutic evoked potentials,” “therapeutic EPs,” or “TEPs” refer to EPs that are believed to be associated stimulation and/or lead placement that is likely to provide therapeutic benefit to the patient. As described in more detail below, the clinician may obtain measurements as a function of depth as they advance the lead from the entry point of the brain along the trajectory to the desired neural target to create a spatial profile of the evoked potentials along the trajectory. Once the clinician has determined that the lead is at an optimal location with respect to the target neural tissue, the methods and systems described herein can be used to determine the optimal stimulation location, with respect to both the longitudinal position along the lead and the angular position about the lead (using directional electrodes). MICC and current fractionalization can be used to provide center points of stimulation that are between physical electrodes.
At step 903, the lead is advanced through the brain toward the target neural elements at a pre-defined step size. The step size may be on the order of 1 mm, for example. According to some embodiments, the target neural element(s) may comprise the STN, for example, the dorsolateral aspect of the STN, which is a common neural target in DBS. Other targets may include the patient's GPi. The lead may be advanced to within a certain pre-defined distance from the target neural elements. For example, the distance may be 20 mm from the target neural elements (step 904). Once the lead is within the pre-defined distance from the target neural elements sensing, as described above, may be initialized (step 905). Once sensing is initialized, it is determined whether evoked potentials can be detected (step 906). If evoked potentials are not detectable, the lead can be advanced further. Although not illustrated, a parameter sweep may be performed if evoked potentials are not detected. For example, the amplitude or other parameters of the stimulation may be adjusted in an attempt to elicit detectable EPs.
Once evoked potentials are detected, the stimulation may be swept along the longitudinal and angular (i.e., rotational) positions on the lead to determine the optimum stimulation location (step 908). For example, during the longitudinal sweep the electrode contacts at each longitudinal position can iteratively be used as the stimulating electrode and the other electrode contacts can be used as sensing/recording electrodes. According to some embodiments, directional electrodes at a given longitudinal location on the lead can be ganged together to act as a single ring electrode for stimulating and/or sensing during this step. MICC and current fractionalization can be used to provide stimulation at longitudinal locations between the electrodes. As each electrode contact from the proximal to the distal end of the lead is iteratively used as the stimulating electrode, evoked potentials are recorded at one or more of the other electrodes. This iterative process is used to create a comprehensive profile of the sensed evoked potentials relative to the locations upon the electrode lead both along and around the lead. One or more features of the evoked potentials can be extracted from the evoked potentials recorded at each of the sensing/recording electrodes. Generally, any value or metric may be used as the extracted feature(s). Examples of such features of the evoked potentials include but are not limited to:
Values for the one or more extracted features of the evoked potentials are determined as a function of the longitudinal stimulation locations along the electrode lead. The longitudinal location that yields the optimum value(s) for the one or more features can be selected as the best longitudinal location for providing stimulation. According to some embodiments, the optimum stimulation location may be the stimulation location that provides the maximum value of the evoked potential feature (such as evoked potential amplitude, peak height, etc.), indicating that stimulation at that location best activates targeted neural elements. The extracted features of the evoked potentials can be used to determine whether to advance the lead further with respect to the neural targets to obtain an optimum lead position. The decision to advance/reposition the lead may also be informed by measurements of EPs associated with side effects, such as motor EPs (MEPs), as described in more detail below. This is based on the consideration that the maximum TEP parameter may not necessarily indicate the best lead position because that lead position might be too close to neural structures that can cause side effects. So, as described in more detail below, embodiments described in this disclosure may seek to maximize TEP responses while minimizing EP responses associated with side effects. In other words, the disclosed methods and systems balance TEP response and MEP responses. At step 910, the stimulation locations, i.e., the fractionalizations determined for the longitudinal and rotational stimulation locations, can be saved and stored for later use.
After the lead position is finalized, the clinician will seek to determine an electrode configuration that produces a best stimulation field for treating the patient's symptoms. As used herein the terms “electrode configuration,” “configuration of electrode contacts,” and the like are used to refer to how anodic and cathodic current is fractionalized among the electrode contacts to provide a particular stimulation field and/or stimulation at a particular center point of stimulation (CPS). In other words, the electrode configuration configuration/electrode contact configuration characterizes which electrodes/contacts are active, what is the polarity of each active electrode, and what is the relative strength of each active electrode.
Once it is determined that the stimulation is providing usable evoked potentials, the stimulation may be swept along the longitudinal and angular (i.e., rotational) positions on the lead to determine the optimum stimulation location/electrode configuration (step 1108). For example, for the longitudinal sweep the electrode contacts at each longitudinal position can iteratively be used as the stimulating electrode and the other electrode contacts can be used as sensing/recording electrodes. Again, directional electrodes at a given longitudinal location on the lead can be ganged together to act as a single ring electrode for stimulating and/or sensing during this step. MICC and current fractionalization can be used to provide stimulation at longitudinal locations between the electrodes. As each electrode contact from the proximal to the distal end of the lead is iteratively used as the stimulating electrode, evoked potentials are recorded at one or more of the other electrodes. This iterative process is used to create a comprehensive profile of the sensed evoked potentials relative to the locations upon the electrode lead both along and around the lead. One or more features of the evoked potentials can be extracted from the evoked potentials recorded at each of the sensing/recording electrodes. Features of the evoked potentials can be extracted from the recorded signals, as described above. Values for the one or more extracted features of the evoked potentials are determined as a function of the longitudinal stimulation locations along the electrode lead. The longitudinal location that yields the optimum value(s) for the one or more features can be selected as the best longitudinal location for providing stimulation.
Once the optimum longitudinal stimulation location is determined, the sweeping process may be repeated to optimize the rotational stimulating location by iteratively using different directional electrodes (and/or fractionalized angular locations) to provide stimulation and using the other electrodes as sensing/recording electrodes to record evoked potentials. Again, one or more features may be extracted from the evoked potentials and the rotational position that yields the optimal values for the evoked potential features may be selected as the rotational location for providing directional stimulation. As described above, MICC and current fractionalization may be used to determine optimum stimulation locations that are located between physical locations of actual electrode contacts. Again, the rotational optimization may be performed using optimization algorithms or may be performed manually. At step 1110, the stimulation locations, i.e., the fractionalizations determined for the longitudinal and rotational stimulation locations, can be saved and stored.
Notice that the algorithm 1100 detailed in
Typically, once a lead is positioned in a patient and an effective location for providing therapy is determined, the clinician will titrate the stimulation amplitude upward (i.e., slowly increase the stimulation amplitude) until side effects are seen. The range of stimulation amplitudes between the lowest amplitude at which a benefit is seen and an amplitude at which intolerable side effects occur is referred to as a therapeutic window. A clinician would typically like to provide stimulation at a location that has a large therapeutic window. However, the algorithm 1100 of
At step 1306 the sweep (longitudinal and rotational) are repeated. During this sweep the algorithm receives and records a signal indicative of side effects evoked at each of the stimulation locations. According to some embodiments, the side effects may be motor/movement related, for example if areas of the corticospinal tract are inadvertently stimulated. Indications of such side effects may be referred to herein as motor EPs (MEPs), meaning that they are evoke potentials (or other recorded signals) indicative of unintended motor activity. As used herein, the term motor EPs is contrasted to therapeutic EPs (TEPs), because TEPs are associated with beneficial or therapeutic stimulation, whereas MEPs are associated with side effects. According to some embodiments, such motor EPs may be recorded using electromyography (EMG), or the like, to measure motor activity in one or more locations in the patient's body. Alternatively (or additionally), muscle movement may be detected using one or more mechanical sensors (mechanomyography). According to some embodiments, other external sensors may be used, such as speech sensors to detect speech problems (dysarthria). According to some embodiments, motor EPs may be detected electrically near motor areas of the patient's brain, for example, using a cortical array placed in the primary motor cortex (M1) area of the brain that can detect motor activity correlated with specific side effects that manifests with movement of different body parts and that can be sensed from the signals recorded in the primary motor cortex on the pre-central gyms anterior to the central sulcus of the brain (see figure added before the claims). There is a motor map very well established in literature that can guide the placement of the cortical array to the patient specific body location where the side effects manifest. Of note, 30 to 40% of the corticospinal projection originate in M1, and the corticobulbar projections as well. Neurons in the M1 modulate their firing rate several hundred milliseconds before the actual movement starts (see, e.g., Georgopoulos, et al, “On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex,” J. Neurosci. 2, (1982) 1527-37). Using brains signals sensed from the M1 area, such as evoked potentials and local field potentials correlated with specific motor side effects episodes or activity recorded simultaneously with the dorsal STN ERNA can allow proper adjustment of the stimulation location and dosis (amplitude, pulse width and frequency) and determination of the optimal therapeutic window. Alternatively, the cortical array can be placed in the supplementary motor cortex (pre-motor cortex). According to some embodiments, motor EPs may be detected as electrical signals recorded in the patient's spinal column, i.e., an electrospinograph. According to some embodiments, motor EPs may be detected by sensing neurotransmitter levels in motor areas of the patient's brain, for example, using fast scan cyclic voltammetry (FSCV). According to some embodiments, specific MEP signals may be recorded when side effects take place. One or more detection algorithms may be configured to automatically indicate that the identified MEP is present (form example, in the M1 region) and then reduce the stimulation current to an amplitude such that the MEP disappears, but such that adequate TEPs are still present.
At step 1308, the signals indicative of side effects (i.e., the recorded motor EPs) are used to determine which stimulation locations evoke the strongest motor EPs and cause the most problematic side effects. At step 1310, the correlation between stimulation location (i.e., electrode configuration) and therapeutic EPs (from step 1304) and the correlation between stimulation location and motor EPs (from step 1308) are used to determine the optimal location on the lead to provide therapeutic stimulation. Various algorithms and/or multi-objective optimization functions may be used to determine the optimal location for providing stimulation based on balancing the stimulation location that yields the best TEP and that results in minimal, or at least acceptable MEP measurements. The details of the particular multi-objective optimization will depend on the particular implementation. For example, the algorithm may maximize the TEP parameters while minimizing the MEP (or other side effect signals). According to some embodiments the algorithm may involve keeping the side effect signals below a certain (acceptable) threshold and then searching the TEP space to find the maximum TEP value. According to some embodiments, a ratio of the TEP and MEP signals may be used and compared to a threshold, for example.
Notice that the flattened representation 1400 only correlates therapeutic and motor EPs with discreet electrode locations. But as mentioned above, MICC/current steering can be used to provide electrode configurations that provide field shapes and stimulation locations that are located between the physical electrodes. According to some embodiments, the representation of the electrode array may be configured to correlate therapeutic and motor EPs with stimulation locations that do not coincide with physical electrode locations.
Also notice that the flattened representation 1400 is “binary” with respect to presence of therapeutic and motor EPs. In other words, the representation shows that indicates either the presence or absence of therapeutic and motor EPs. However, other embodiments of such representations may be configured with gradations, such as heat maps, color coding, and the like, configured to indicate the strength of the therapeutic EPs (and/or the values of features extracted from the therapeutic EPs) and/or the motor EPs. According to some embodiments, the representation may be configured to provide a visual indication of the stimulation amplitude at which motor EPs are first observed. Such a representation may provide an indication of the therapeutic window at that stimulation location, as explained in more detail below. In other words, being able to increase the stimulation to higher amplitudes without evoking side effects contributes to a greater therapeutic window.
In the illustrated example, the TEP frequency decreases as a function of stimulation amplitude until it reaches an inflection point (1504) and plateaus at a stimulation amplitude SA2. Assume that the TEP frequency of TEPF2 is expected to correspond to the optimal therapeutic response. Notice that increasing the stimulation amplitude beyond an amplitude of SA2 does not provide any better therapeutic response (i.e., it provides no further decrease in the TEP frequency). Thus, the stimulation amplitude of SA2 is taken to the optimum stimulation amplitude.
Curve 1506 of
Curve 1508 shows the behavior of one or more recorded MEPs as a function of the stimulation amplitude. Notice that the MEP amplitude is minimal until an inflection point 1510 is reached, after which the MEP amplitude increases as a function of the stimulation amplitude. Assume that the MEP amplitude MEPA1 is the maximum acceptable MEP amplitude. In other words, if the MEP amplitude exceeds MEPA1, then the side effects of the stimulation is not tolerable for the patient, for example. That MEP amplitude arises at a stimulation amplitude of SA3.
As shown in
Although particular embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the present invention to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims.
This is a non-provisional of U.S. Provisional Patent Application Ser. No. 63/261,584, filed Sep. 24, 2021, to which priority is claimed, and which is incorporated herein by reference.
Number | Date | Country | |
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63261584 | Sep 2021 | US |