User interface for identifying midlines of spinal cord

Techniques for delivery of electrical neurostimulation therapy to a patient are disclosed. In one example, a processor controls delivery of electrical neurostimulation therapy to a patient by an electrical neurostimulation therapy device and via a plurality of combinations of a plurality of electrodes disposed along a lead inserted across an anatomical midline of a spinal cord of the patient and angled relative to the anatomical midline, the lead connected to the electrical neurostimulation therapy device. The processor determines, based on the electrical neurostimulation therapy, a location of a physiological midline of the spinal cord. The processor selects, based on the location of the physiological midline, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient. Further, the processor displays a representation of the physiological midline and the anatomical midline relative to the spinal cord.

TECHNICAL FIELD

This disclosure generally relates to systems for electrical neurostimulation of a patient.

BACKGROUND

Electrical neurostimulation therapy, e.g., for pain relief, may be delivered by one or more electrodes positioned along one or more leads inserted into a patient. Positioning of the leads is important to effectively deliver therapy to target site of the patient. Ideally, in the case of spinal cord stimulation (SCS) for pain relief, the leads should be placed on either side of a physiological midline of a spinal cord of the patient (e.g., a conceptual midline wherein electrical neurostimulation delivered to the left of the physiological midline provides pain relief to only a left side of the body of the patient, while electrical neurostimulation delivered to the right of the physiological midline provides pain relief to only a right side of the body of the patient). Typically, a physician uses a fluoroscope to place a first lead parallel and left of an anatomical midline of the spinal cord (e.g., a line bisecting the spinal cord into two lateral sections) and a second lead parallel and right of the anatomical midline of the spinal cord. However, the physiological midline only roughly correlates to the anatomical midline of the spinal cord, and may differ by several millimeters. After implanting the leads, the clinician, while still in the operating room, tests various electrodes combinations among the two leads and the patient provides feedback as to where the patient feels paresthesia or reduction of pain. This process is time consuming and may be inaccurate as the patient suffers disorientation from anesthesia.

SUMMARY

In general, the disclosure describes techniques for more accurately delivering electrical neurostimulation to a spinal cord of a patient. In one example, a clinician implants at least one lead at an angle relative to and across an anatomical midline of a spinal cord of the patient. In some examples, the at least one lead is implanted at an angle of 5-20 degrees relative to the anatomical midline of the spinal cord. In some examples of the techniques disclosed herein, the clinician implants a first and second lead angled 5-20 degrees relative to and across the anatomical midline of the spinal cord. In alternate examples, the first lead is implanted parallel to and offset from the anatomical midline of the spinal cord, while the second lead is implanted at an angle of 5-20 degrees relative to and across the anatomical midline of the spinal cord. Such an implantation procedure as described herein may ensure that at least several electrodes are implanted on either side of the physiological midline of the spinal cord of the patient.

After surgery, and outside of the operating room, the clinician may test various combinations of electrodes to determine the combination that provides the greatest pain relief to the patient. The clinician may use feedback from the patient regarding the different combinations of electrodes to identify a position of the physiological midline of the spinal cord of the patient. The clinician may use a user interface to mark, in reference to the first and second leads, the location of the anatomical midline of the spinal cord via a fluoroscope, and to further mark the location of the physiological midline of the spinal cord via the patient feedback. Accordingly, such an implantation procedure may eliminate the need to perform testing of the implanted electrodes within the operation room, which may reduce the cost of the procedure, increase the reliability of the feedback received from the patient, and eliminate the need to wake the patient up from anesthesia to provide feedback on the electrical neurostimulation therapy, paresthesia, and pain sensations.

In one example, this disclosure describes a method including: controlling, by one or more processors, delivery of electrical neurostimulation therapy to a patient by an electrical neurostimulation therapy device and via a plurality of combinations of a plurality of electrodes, wherein the plurality of electrodes are disposed along a lead inserted across an anatomical midline of a spinal cord of the patient and angled relative to the anatomical midline of the spinal cord, the lead connected to the electrical neurostimulation therapy device; determining, based on the delivery of the electrical neurostimulation therapy, a location of a physiological midline of the spinal cord of the patient; selecting, based on the location of the physiological midline of the spinal cord, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient; and controlling, by the one or more processors, delivery of electrical neurostimulation therapy to the patient by the electrical neurostimulation therapy device and via the selected at least one electrode of the plurality of electrodes.

In another example, this disclosure describes an electrical neurostimulation therapy system including: a plurality of electrodes disposed along a lead inserted across an anatomical midline of a spinal cord of a patient and angled relative to the anatomical midline of the spinal cord, the lead connected to an electrical neurostimulation therapy device; a therapy delivery circuit of the electrical neurostimulation therapy device configured to deliver electrical neurostimulation therapy to the patient via a plurality of combinations of the plurality of electrodes; and one or more processors configured to: control delivery of the electrical neurostimulation therapy to the patient; determine, based on the delivery of the electrical neurostimulation therapy, a location of a physiological midline of the spinal cord of the patient; based on the location of the physiological midline of the spinal cord of the patient, select at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient; and control delivery of electrical neurostimulation therapy to the patient by the electrical neurostimulation therapy device and via the selected at least one electrode of the plurality of electrodes

In another example, this disclosure describes an electrical neurostimulation therapy system including: a plurality of electrodes disposed along a lead inserted across an anatomical midline of a spinal cord of a patient and angled relative to the anatomical midline of the spinal cord, the lead connected to an electrical neurostimulation therapy device; a therapy delivery circuit of the electrical neurostimulation therapy device configured to deliver electrical neurostimulation therapy to the patient via a plurality of combinations of the plurality of electrodes; and one or more processors configured to: control delivery of the electrical neurostimulation therapy to the patient; determine, based on the delivery of the electrical neurostimulation therapy, a location of a physiological midline of the spinal cord of the patient; and present, for display to a user, a representation of the spinal cord, the location of the physiological midline of the spinal cord relative to the spinal cord, and a location of an anatomical midline of the spinal cord relative to the spinal cord.

DETAILED DESCRIPTION

FIG. 1is a conceptual diagram illustrating system30that delivers stimulation therapy to spinal cord38of patient36in accordance with the techniques of the disclosure. System30delivers electrical neurostimulation therapy from implantable stimulator34to spinal cord38via one or more electrodes (not shown) carried by, i.e., located on, implantable medical leads32A and32B (collectively “leads32”) as well as the housing of implantable stimulator34, e.g., housing electrode37. System30and, more particularly, implantable stimulator34, may operate in in a current-based or voltage-based configuration. That is, in a current-based example, implantable stimulator34delivers controlled current stimulation pulses or waveforms to patient36via one or more regulated, stimulation electrodes. Alternatively, in a voltage-based example, implantable stimulator34may be configured to deliver constant voltage pulses. Various parameters of the pulses or waveforms may be defined by one or more stimulation programs. The pulses or waveforms may be delivered substantially continuously or in bursts, segments, or patterns, and may be delivered alone or in combination with pulses or waveforms defined by one or more other stimulation programs. In some example, implantable stimulator34delivers spinal cord stimulation (SCS) therapy to patient36via the electrodes carried by, i.e., located on, leads32to provide pain relief therapy to patient36.

Stimulator34may be implanted in patient36at a location minimally noticeable to the patient. For SCS, stimulator34may be located in the lower abdomen, lower back, or other location to secure the stimulator. Leads32may be tunneled from stimulator34through tissue to reach the target tissue adjacent to spinal cord38for stimulation delivery. At the distal ends of leads32are one or more electrodes (not shown) that transfer the stimulation pulses from the lead to the tissue substantially simultaneously with stimulation pulses.

In the example ofFIG. 1, the distal ends of leads32are placed adjacent to the target tissue of spinal cord38. The proximal ends of leads32may be both electrically and mechanically coupled to implantable stimulator34either directly or indirectly via a lead extension and header. Alternatively, in some examples, leads32may be implanted and coupled to an external stimulator, e.g., through a percutaneous port. In additional example implementations, stimulator34may be a leadless stimulator with one or more arrays of electrodes arranged on a housing of the stimulator rather than leads that extend from the housing.

Application of certain techniques will be described in this disclosure with respect to implantable stimulator34and implantable leads32having ring electrodes for purposes of illustration. Ring electrodes are commonly used in electrical neurostimulation applications because they are simple to program and are capable of delivering an electrical field to any tissue adjacent to leads32. However, other types of electrodes may be used. For example, the electrodes of leads32may have a complex electrode array geometry that is capable of producing shaped electrical fields. The complex electrode array geometry may include multiple electrodes (e.g., partial ring or segmented electrodes) around the perimeter of each lead32, rather than one ring electrode. In this manner, electrical stimulation may be directed in a specific direction from leads32to enhance therapy efficacy and reduce possible adverse side effects from stimulating a large volume of tissue. In alternative examples, leads32may have shapes other than elongated cylinders as shown inFIG. 1. For example, leads32may be electrode pads on a paddle lead, circular (i.e., ring) electrodes surrounding the body of leads32, spherical leads, bendable leads, conformable electrodes, cuff electrodes, segmented electrodes, or any other type of electrodes capable of forming unipolar, bipolar or multi-polar electrode configurations and effective in treating patient36. In some examples, one or more of the electrodes may be unregulated. In some examples, the housing of implantable stimulator34, e.g., housing electrode37, functions as an anode and/or return path for the electrical stimulation.

The stimulation pulses may be delivered using various electrode arrangements such as unipolar arrangements, bipolar arrangements or multipolar arrangements. A unipolar stimulation arrangement generally refers to the use of an anode on the housing that sources current and one or more cathodes on one or more leads that sink current. A bipolar stimulation arrangement generally refers to the use of an anode on a lead that sources current and a cathode on the same lead and/or another lead that sink current. A multipolar stimulation arrangement generally refers to the use of more than one anode on a lead that each source current and one or more cathodes on the same lead or another lead that sink current, or the use of one anode on a lead that sources current and multiple cathodes on the same lead or another lead that sink current. A hybrid stimulation arrangement that combines both unipolar and bipolar electrode relationships may be referred to as an omnipolar arrangement. In an omnipolar arrangement, an anode on the housing may be used to deliver stimulation pulses substantially simultaneously with at least one anode on a lead and at least one cathode on a lead. In this case, for an omnipolar arrangement, at least one anode on a lead and at least one anode on the housing can be used simultaneously in combination with at least one cathode on a lead. In other omnipolar arrangements, a cathode on the housing may be used to deliver stimulation pulses substantially simultaneously with at least one cathode on a lead and at least one anode on a lead. In this alternative case, for an omnipolar arrangement, at least one cathode on a lead and at least one cathode on the housing can be used simultaneously in combination with at least one anode on a lead. Any of the above electrode arrangements, or other electrode arrangements, may be used to deliver electrical stimulation in accordance with techniques described in this disclosure.

Implantable stimulator34delivers stimulation to spinal cord38to reduce the amount of pain perceived by patient36. The stimulation delivered by implantable stimulator34may take the form of stimulation pulses or continuous stimulation waveforms, and may be characterized by controlled current or voltage levels, as well as programmed pulse widths and pulse rates in the case of stimulation current pulses. Stimulation may be delivered via selected combinations of electrodes located on one or both of leads32and on the housing. Stimulation of spinal cord38may, for example, prevent pain signals from traveling through the spinal cord and to the brain of the patient. Patient34perceives the interruption of pain signals as a reduction in pain and, therefore, efficacious therapy.

In some examples, therapy system30further includes external programmer40. External programmer40may be used to define stimulation therapy parameters for use by implantable stimulator34. In some examples, programmer40is a clinician programmer, which is a handheld computing device that permits a clinician to program stimulation therapy for patient36via a user interface, e.g., using input keys and a display. For example, using the clinician programmer, the clinician may specify stimulation parameters, i.e., create programs, for use in delivery of stimulation therapy. The clinician programmer may support telemetry (e.g., radio frequency (RF) telemetry) with implantable stimulator34to download programs and, optionally, upload operational or physiological data stored by implantable stimulator34. In this manner, the clinician may periodically interrogate implantable stimulator34to evaluate efficacy and, if necessary, modify the programs or create new programs. In some examples, the clinician programmer transmits programs to a patient programmer (not depicted) in addition to or instead of implantable stimulator34. In some examples, the patient programmer may serve as the clinician programmer.

In other examples, external programmer40is a patient programmer. Like the clinician programmer, the patient programmer may be a handheld computing device. The patient programmer may also include a display and input keys to allow patient36to interact with the patient programmer and implantable stimulator34. In this manner, the patient programmer provides patient36with a user interface for control of the stimulation therapy delivered by implantable stimulator34. For example, patient36may use the patient programmer to start, stop or adjust electrical stimulation therapy. In particular, the patient programmer may permit patient36to adjust stimulation parameters of a program such as duration, current or voltage amplitude, pulse width and pulse rate. Patient36may also select a program, e.g., from among a plurality of stored programs, as the present program to control delivery of stimulation by implantable stimulator34.

With reference toFIG. 1, a user, such as a clinician or patient36, may interact with a user interface of external programmer40to program stimulator34. Programming of stimulator34may refer generally to the generation and transfer of commands, programs, or other information to control the operation of the stimulator. For example, programmer40may transmit programs, parameter adjustments, program selections, group selections, or other information to control the operation of stimulator34, e.g., by wireless telemetry. In accordance with this disclosure, programmer40may transmit to the stimulator34information regarding the patient and regarding therapy the patient received during previous sessions including, for example, images that show placement of leads32.

Whether programmer40is configured for clinician or patient use, programmer40may communicate to implantable stimulator34or any other computing device via wireless communication. Programmer40, for example, may communicate via wireless communication with implantable stimulator34using radio frequency (RF) telemetry techniques known in the art or other communication standards such as, for example, Bluetooth®. Programmer40may also communicate with another programmer or computing device via a wired or wireless connection using any of a variety of local wireless communication techniques, such as RF communication according to the 802.11 or Bluetooth® specification sets, infrared communication according to the IRDA specification set, or other standard or proprietary telemetry protocols. Programmer40may also communicate with another programming or computing device via exchange of removable media, such as magnetic or optical disks, or memory cards or sticks. Further, programmer40may communicate with implantable stimulator34and other programming devices via remote telemetry techniques known in the art, communicating via a local area network (LAN), wide area network (WAN), public switched telephone network (PSTN), or cellular telephone network, for example.

Implantable stimulator34, and external programmer40may communicate via cables or a wireless communication, as shown inFIG. 1. External programmer40may, for example, communicate via wireless communication with implantable stimulator34using RF telemetry techniques known in the art or other standard communication protocols such as, for example, Bluetooth®. External programmer40also may communicate with each other using any of a variety of wireless communication techniques, such as RF communication according to the 802.11 or Bluetooth® specification sets, infrared communication, e.g., according to the IrDA standard, or other standard or proprietary telemetry protocols. External programmer40may include a transceiver to permit bi-directional communication with implantable stimulator34.

According to the techniques of the disclosure, a clinician implants at least one lead32at an angle relative to and across an anatomical midline of spinal cord38of patient36. In some examples, the at least one lead32is implanted at an angle of 5-20 degrees relative to the anatomical midline of spinal cord38of patient36. In some examples of the techniques disclosed herein, the clinician implants a first lead32A and second lead32B angled 5-20 degrees relative to and across the anatomical midline of spinal cord38. In alternate examples, the first lead32A is implanted parallel to and offset from the anatomical midline of spinal cord38, while the second lead32B is implanted at an angle of 5-20 degrees relative to and across the anatomical midline of spinal cord38. Such an implantation procedure as described herein may ensure that at least several electrodes are implanted on either side of the physiological midline of spinal cord38.

After surgical implantation of stimulator34, and outside of the operating room, the clinician may test various combinations of electrodes to determine the combination that provides the greatest pain relief to the patient. The clinician may use feedback from the patient regarding the different combinations of electrodes to identify a position of the physiological midline of spinal cord38. The clinician may use a user interface to mark, in reference to the first and second leads, the location of the anatomical midline of spinal cord38via a fluoroscope, and to further mark the location of the physiological midline of spinal cord38via the patient feedback. Accordingly, such an implantation procedure may eliminate the need to perform testing of the implanted electrodes within the operation room, which may reduce the cost of the procedure, increase the reliability of the feedback received from the patient, and eliminate the need to wake the patient up from anesthesia to provide feedback on the electrical neurostimulation therapy, paresthesia, and pain sensations.

FIG. 2is a block diagram illustrating various components of an example implantable stimulator34of system30in accordance with the techniques of the disclosure. In the example ofFIG. 2, implantable stimulator34includes processor50, memory52, power source54, telemetry circuitry56, antenna57, and a stimulation generator60. Implantable stimulator34is also shown inFIG. 2coupled to electrodes48A-Q (collectively “electrodes48”). Electrodes48A-48P are implantable and may be deployed on one or more implantable leads32. With respect toFIG. 1, lead32A and32B may carry electrodes48A-H and electrodes48I-P, respectively. In some cases, one or more additional electrodes may be located on or within the housing of implantable stimulator34, e.g., to provide a common or ground electrode or a housing anode. With respect toFIG. 2, leads32A and32B may carry electrodes48A-H and electrodes48I-P, respectively. In the examples ofFIGS. 1 and 2, a lead or lead segment carries eight electrodes to provide a 2x8 electrode configuration (two leads with 8 electrodes each), providing a total of sixteen different electrodes. The leads may be detachable from a housing associated with implantable stimulator34, or be fixed to such a housing.

In other examples, different electrode configurations comprising a single lead, two leads, three leads, or more may be provided. In addition, electrode counts on leads may vary and may be the same or different from a lead to lead. Examples of other configurations include one lead with eight electrodes (1×8), one lead with 12 electrodes (1×12), one lead with 16 electrodes (1×16), two leads with four electrodes each (2×4), three leads with four electrodes each (3×4), three leads with eight electrodes each (3×8), three leads with four, eight, and four electrodes, respectively (4-8-4), two leads with 12 or 16 electrodes (2×12, 2×16), two or more leads with 11 or 13 electrodes, or other configurations. Different electrodes are selected to form electrode combinations. Polarities are assigned to the selected electrodes to designate the electrodes as anodes or cathodes and form electrode configurations.

Electrode48Q represents one or more electrodes that may be carried on a housing, i.e., can, of implantable stimulator34, e.g., housing electrode37ofFIG. 1. Electrode48Q may also be a dedicated short lead extending from the housing, or a proximal portion of one of the leads carrying electrodes48A-48P. The proximal portion may be closely adjacent to the housing, e.g., at or near a point at which a lead is coupled to the housing, such as adjacent to a lead connection header8of the housing. Electrode48Q may be configured as a regulated or unregulated electrode for use in an electrode configuration with selected regulated and/or unregulated electrodes among electrodes48A-48P, which may be located on a lead body of one or more leads, as described above. Electrode48Q may be formed together on a housing that carries the electrode and houses the components of implantable stimulator34, such as stimulation generator60, processor50, memory52, telemetry circuitry56, and power source54.

Housing electrode48Q may be configured for use as an anode to source current substantially simultaneously with one or more electrodes48A-48P configured for use as cathodes sinking current in a unipolar arrangement. Housing electrode48Q may be configured for use as an anode to source current substantially simultaneously with current sourced by another electrode48A-48P configured for use as an anode in an omnipolar arrangement. By way of specific example, electrodes48A,48B, and housing electrode48Q each could be configured for use as anodes. Electrodes48A,48B could deliver electrical stimulation current substantially simultaneously with the electrical stimulation current delivered via housing electrode48Q. In this illustration, one or more cathodes could be formed with other electrodes (e.g., any of electrodes48C-48P) on the leads to sink current sourced by anodes48A,48B and48Q.

Memory52may store instructions for execution by processor50, stimulation therapy data, sensor data, and/or other information regarding therapy for patient36. Processor50may control stimulation generator60to deliver stimulation according to a selected one or more of a plurality of programs or program groups stored in memory52. Memory52may include any electronic data storage media, such as random access memory (RAM), read-only memory (ROM), electronically-erasable programmable ROM (EEPROM), flash memory, or the like. Memory52may store program instructions that, when executed by processor50, cause the processor to perform various functions ascribed to processor50and implantable stimulator34in this disclosure.

Processor50may include one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other digital logic circuitry. Processor50controls operation of implantable stimulator34, e.g., controls stimulation generator60to deliver stimulation therapy according to a selected program or group of programs retrieved from memory52. For example, processor50may control stimulation generator60to deliver electrical signals, e.g., as stimulation pulses or continuous waveforms, with current amplitudes, pulse widths (if applicable), and rates specified by one or more stimulation programs. Processor50may also control stimulation generator60to selectively deliver the stimulation via subsets of electrodes48, also referred to as electrode combinations, and with polarities specified by one or more programs.

Upon selection of a particular program group, processor50may control stimulation generator60to deliver stimulation according to the programs in the groups, e.g., simultaneously or on a time-interleaved basis. A group may include a single program or multiple programs. As mentioned previously, each program may specify a set of stimulation parameters, such as amplitude, pulse width and pulse rate, if applicable. For a continuous waveform, parameters may include amplitude and frequency. In addition, each program may specify a particular electrode combination for delivery of stimulation, and an electrode configuration in terms of the polarities and regulated/unregulated status of the electrodes. The electrode combination may specify particular electrodes in a single array or multiple arrays, and on a single lead or among multiple leads. The electrode combination may include at least one anode on the housing of the IMD, e.g., electrode48Q, at least one anode on a lead, electrode48A, and at least one cathode on a lead. The lead-borne anode and cathode may be on the same lead or different leads, if more than one lead is provided. A program may be defined directly, by selecting parameters and electrodes, or by zone-based programming, in which parameters and electrodes are automatically determined by the programmer in response to manipulation or positioning of stimulation zones.

Stimulation generator60is electrically coupled to electrodes48A-P via conductors of the respective lead, such as lead12inFIG. 1or leads32inFIG. 2, in implementations in which electrodes48A-P are carried by, located on, leads. Stimulation generator60may be electrically coupled to one or more housing (“can”) electrodes48Q via an electrical conductor disposed within the housing of implantable stimulator34ofFIG. 1orFIG. 2. Housing electrode48Q may be configured as a regulated or unregulated electrode to form an electrode configuration in conjunction with one or more of electrodes48A-48P located on leads of the IMD. Housing electrode48Q may be configured for use as an anode to source current substantially simultaneously with one or more electrodes, e.g., any of electrodes48A-48P, on one or more leads configured for use as anodes.

Stimulation generator60may include stimulation generation circuitry to generate stimulation pulses or waveforms and circuitry for switching stimulation across different electrode combinations, e.g., in response to control by processor50. Stimulation generator60produces an electrical stimulation signal in accordance with a program based on control signals from processor50.

For example, stimulation generator60may include a charging circuit that selectively applies energy from power source54to a capacitor module for generation and delivery of a supply voltage for generation of stimulation signal. In addition to capacitors, the capacitor module may include switches. In this manner, the capacitor module may be configurable, e.g., based on signals from processor50, to store a desired voltage for delivery of stimulation at a voltage or current amplitude specified by a program. For delivery of stimulation pulses, switches within the capacitor module may control the widths of the pulses based on signals from processor50.

In one example implementation, e.g., an omnipolar arrangement, stimulation generator60may be configured to deliver stimulation using one or more of electrodes48A-P as stimulation electrodes, e.g., anodes, while substantially simultaneously delivering stimulation using housing electrode48Q as a stimulation electrode, e.g., anode. The anodes on the lead(s) and the housing may be used to deliver stimulation in conjunction with one or more cathodes on the lead(s). As one illustration, an electrode combination selected for delivery of stimulation current may comprise an anode on the IMD housing, and anode on a lead, and a cathode on the same lead or a different lead. In other examples, the electrode combination may include multiple anodes and/or multiple cathodes on one or more leads in conjunction with at least one anode on the IMD housing. In some examples, the electrode combination may include one or more anodes on one or more leads, and one or more cathodes on the same lead or a different lead, e.g., a bipolar/multipolar arrangement. In other examples, the electrode combination may include an anode on the housing, and one or more cathodes on one or more leads, e.g., omnipolar arrangement. In yet another example, the electrode combination may include a cathode on the housing, and one or more additional cathodes on one or more leads, along with one or more anodes also on the leads, e.g., a variation of an omnipolar arrangement.

Telemetry circuitry56may include a radio frequency (RF) transceiver to permit bi-directional communication between implantable stimulator34and each of clinician programmer20and patient programmer22. Telemetry circuitry56may include an antenna57that may take on a variety of forms. For example, antenna57may be formed by a conductive coil or wire embedded in a housing associated with implantable stimulator34. Alternatively, antenna57may be mounted on a circuit board carrying other components of implantable stimulator34or take the form of a circuit trace on the circuit board. In this way, telemetry circuitry56may permit communication with clinician programmer40and patient programmer22inFIG. 1or external programmer40inFIG. 2, to receive, for example, new programs or program groups, or adjustments to programs or program groups.

Power source54may be a non-rechargeable primary cell battery or a rechargeable battery and may be coupled to power circuitry. However, the disclosure is not limited to implementations in which the power source is a battery. In another example, as an example, power source54may comprise a supercapacitor. In some examples, power source54may be rechargeable via induction or ultrasonic energy transmission, and include an appropriate circuit for recovering transcutaneously received energy. For example, power source54may be coupled to a secondary coil and a rectifier circuit for inductive energy transfer. In additional embodiments, power source54may include a small rechargeable circuit and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within stimulator34. In some embodiments, power requirements may be small enough to allow stimulator34to utilize patient motion at least in part and implement a kinetic energy-scavenging device to trickle charge a rechargeable battery. A voltage regulator may generate one or more regulated voltages using the battery power.

According to the techniques of the disclosure, a clinician implants at least one lead32at an angle relative to and across an anatomical midline of spinal cord38of patient36. In some examples, the at least one lead32is implanted at an angle of 5-20 degrees relative to the anatomical midline of spinal cord38of patient36. In some examples of the techniques disclosed herein, the clinician implants a first lead32A and second lead32B angled 5-20 degrees relative to and across the anatomical midline of spinal cord38. In alternate examples, the first lead32A is implanted parallel to and offset from the anatomical midline of spinal cord38, while the second lead32B is implanted at an angle of 5-20 degrees relative to and across the anatomical midline of spinal cord38. Such an implantation procedure as described herein may ensure that at least several electrodes are implanted on either side of the physiological midline of spinal cord38.

After surgical implantation of stimulator34, and outside of the operating room, the clinician may test various combinations of electrodes48to determine the combination that provides the greatest pain relief to the patient. For example, in response to commands from external programmer40, processor50may control stimulation generator60to deliver electrical neurostimulation to patient36via a plurality of combinations of electrodes48. The clinician may use feedback from the patient regarding the plurality of combinations of electrodes48to identify a position of the physiological midline of spinal cord38. The clinician selects, based on the location of the physiological midline of spinal cord38, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient. Processor50controls stimulation generator60to deliver electrical neurostimulation to patient36according to the selected at least one electrode of the plurality of electrodes to provide pain relief therapy to patient36.

FIG. 3is a functional block diagram illustrating various components of an external programmer40for an implantable stimulator34. External programmer40ofFIG. 3may be a clinician programmer or a patient programmer. External programmer40includes processor53, memory55, telemetry module67, user interface59, and power source61. In general, processor53controls user interface59, stores and retrieves data to and from memory55, and controls transmission of data with implantable stimulator34through telemetry module67. Processor53may take the form of one or more microprocessors, controllers, DSPs, ASICS, FPGAs, or equivalent discrete or integrated logic circuitry. The functions attributed to processor53herein may be embodied as software, firmware, hardware or any combination thereof.

Memory55may store instructions that cause processor53to provide various aspects of the functionality ascribed to external programmer40herein. Memory55may include any fixed or removable magnetic, optical, or electrical media, such as RAM, ROM, CD-ROM, magnetic disks, EEPROM, or the like. Memory55may also include a removable memory portion that may be used to provide memory updates or increases in memory capacities. A removable memory may also allow patient data to be easily transferred to another computing device, or to be removed before programmer40is used to program therapy for another patient. Memory55may also store information that controls operation of implantable stimulator34, such as therapy delivery values.

In some examples, external programmer40includes an image capturing device63. The image capturing device63may be built into the external programmer40or may be connected to the external programmer40via an interface using a wired or wireless connection. The processor53may control the image capturing device63to capture images as specified by the user of the external programmer40. In some examples, image capturing device63may be a digital camera or web camera integrated with or coupled to programmer40to capture digital photographs of images presented on hardcopy media, such as film or paper, or a digital image display screen. Alternatively, the programmer may obtain the image electronically from an imaging device, a network storage server, a removable storage medium such as Flash memory, or other devices, directly or over a network.

A clinician or patient36interacts with user interface59in order to, for example, manually select, change, or modify programs, e.g., by adjusting voltage or current amplitude, adjusting pulse rate, adjusting pulse width, or selecting different electrode combinations or configurations, and may provide efficacy feedback, or view stimulation data. User interface59may include a screen and one or more input buttons that allow external programmer40to receive input from a user. The screen may be, for example, a liquid crystal display (LCD), plasma display, organic light emitting diode (OLED), electrophoretic displays, dot matrix display, or touch screen. The input buttons may include a touch pad, increase and decrease buttons, emergency shut off button, and other input media needed to control the stimulation therapy.

Using the techniques of this disclosure, a clinician or patient36may graphically define desired stimulation regions using interface59, and may capture an image of the stimulated regions and the placement of the leads that stimulate the regions using the image capturing device63. The clinician or patient36may utilize, for example, the user interface59to control the image capturing device63to obtain an image and to manipulate the image, as will be described in more detail below. In one example, the clinician or patient may utilize the image capturing device63directly to obtain the image.

Telemetry module67allows the transfer of data to and from stimulator34. Telemetry module67may communicate automatically with stimulator34at a scheduled time or when the telemetry module detects the proximity of the stimulator. Alternatively, telemetry module67may communicate with stimulator34when signaled by a user through user interface59. To support RF communication, telemetry module44may include appropriate electronic components, such as amplifiers, filters, mixers, encoders, decoders, and the like. In other examples, telemetry module67may employ other communication standards such as, for example, Bluetooth® and telemetry module67may include the appropriate Bluetooth® components.

Programmer40may communicate wirelessly with implantable stimulator34using, for example, RF communication or proximal inductive interaction or other communication standards such as, for example, Bluetooth®. This wireless communication is possible through the use of telemetry module67which may be coupled to an internal antenna or an external antenna. Telemetry module67may be similar to telemetry module57of implantable stimulator34.

Programmer40may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired, e.g., network, connection. Examples of local wireless communication techniques that may be employed to facilitate communication between programmer40and another computing device include RF communication based on the 802.11 or Bluetooth® specification sets, infrared communication, e.g., based on the IrDA standard.

Power source61delivers operating power to the components of programmer40. Power source61may be a rechargeable battery, such as a lithium ion or nickel metal hydride battery. Other rechargeable or conventional batteries may also be used. In some cases, external programmer40may be used when coupled to an alternating current (AC) outlet, i.e., AC line power, either directly or via an AC/DC adapter. Power source61may include circuitry to monitor power remaining within a battery. In this manner, user interface59may provide a current battery level indicator or low battery level indicator when the battery needs to be replaced or recharged. In some cases, power source61may be capable of estimating the remaining time of operation using the current battery.

According to the techniques of the disclosure, a clinician may, via external programmer40, test various combinations of electrodes48of implantable stimulator34to determine the combination that provides the greatest pain relief to the patient. For example, the clinician, via user interface59of external programmer40, may control implantable stimulator34to deliver electrical neurostimulation to patient36via a plurality of combinations of electrodes48.

The clinician may use feedback from the patient regarding the plurality of combinations of electrodes48to identify a position of the physiological midline of spinal cord38. For example, upon determining that patient36experiences suppression of a pain sensation and/or paresthesia on only a right lateral side of patient36, the clinician may determine that the electrodes of the electrode combination are located to the right of the physiological midline of spinal cord38. Further, upon determining that patient36experiences suppression of a pain sensation and/or paresthesia on only a left lateral side of patient36, the clinician may determine that the electrodes of the electrode combination are located to the left of the physiological midline of spinal cord38. By determining that patient36experiences suppression of a pain sensation and/or paresthesia on both a right and a left lateral side of patient36, the clinician may determine that at some of the electrodes of the electrode combination are located to the left and right of the physiological midline of spinal cord38, e.g., the physiological midline of spinal cord38lies between the electrodes of the electrode combination. The clinician selects, based on the location of the physiological midline of spinal cord38, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient. In some examples, the clinician selects a combination of electrodes having electrodes positioned to both a left and a right lateral side of the physiological midline.

In some examples, processor53determines, based on the delivery of the electrical neurostimulation, a position of the physiological midline of spinal cord38. For example, processor53may monitor a physiological response of a tissue of patient36during delivery of a electrical neurostimulation according to a plurality of different electrode combinations. In some examples, the tissue response is an evoked compound action potential (eCAP) response of a nerve fiber of patient36. In some examples, the eCAP response arises from an external stimulation device, such as a transcutaneous electrical nerve stimulation (TENS) device, on one side of the patient's body. In some examples, the external stimulation device is attached to the patient's leg, buttocks, or one side of the lower back. While the external stimulation device delivers electrical nerve stimulation, electrodes performing eCAP monitoring detect the eCAP signal on that side of the body. In some examples, eCAP monitoring is performed in the operating room. In other examples, the tissue response is a visible muscle twitching response of patient36.

By determining that a first electrode combination evokes a response on only a right lateral side of patient36, processor50may determine that the electrodes of the first electrode combination are located to the right of the physiological midline of spinal cord38. Further, by determining that a second electrode combination evokes a response on only a left lateral side of patient36, processor53may determine that the electrodes of the second electrode combination are located to the left of the physiological midline of spinal cord38. By determining that a third electrode combination evokes a response on both a right and a left lateral side of patient36, processor53may determine that at some of the electrodes of the third electrode combination are located to the left and right of the physiological midline of spinal cord38, e.g., the physiological midline of spinal cord38lies between the electrodes of the third electrode combination. In some examples, processor50determines whether a particular electrode combination evokes a response of patient36by increasing the magnitude of the electrical stimulation and determining the motor threshold of patient36(e.g., the magnitude at which patient36experiences muscle contractions) on one side of the body or the other.

Processor53selects, based on the location of the physiological midline of spinal cord38, at least one electrode of the plurality of electrodes for subsequent delivery of electrical neurostimulation therapy to the patient. In some examples, processor53selects a combination of electrodes having electrodes positioned to both a left and a right lateral side of the physiological midline (e.g., the third electrode combination in the above example). Processor53controls delivery of the electrical neurostimulation via the selected combination of electrodes for pain relief therapy for patient36.

In some examples, user interface59includes a display screen that provides an image of spinal cord38of patient36. In such an example, the clinician provides, via user interface59, an indication of a location of an anatomical midline of spinal cord38. Processor53stores the location of the anatomical midline in memory55. Based on the indication of the location of the anatomical midline, processor53generates a representation of the anatomical midline of spinal cord38relative to the image of spinal cord38of patient36for display to the clinician via user interface59. Furthermore, as described above, processor53determines a location of the physiological midline of spinal cord38or receives, from the clinician, an indication of the location of the physiological midline from the clinician, and processor53stores the location of the physiological midline in memory55. In some examples, processor53stores the location of the physiological midline within memory52of implantable stimulator34together with fluoroscopic imagery data for patient36. Further, based on the location of the physiological midline of spinal cord38, processor53generates a representation of the physiological midline of spinal cord38relative to the image of spinal cord38of patient36for display to the clinician via user interface59.

FIGS. 4A-4Bare illustrations of example leads for delivering electrical neurostimulation in accordance with the techniques of the disclosure. The examples ofFIGS. 4A-4Bdepict implantable medical leads32implanted along T6-T7 vertebrae of spine38of patient36. Each of leads32further includes a plurality of electrodes48.

In the example ofFIG. 4A, a clinician implants leads32A and32B parallel to each other and at an angle relative to and across anatomical midline410of spinal cord38of patient36. In some examples, the clinician implants leads32A and32B at an angle of 5-20 degrees relative to anatomical midline410of spinal cord38of patient36. Such an implantation procedure as described herein may ensure that at least some of the electrodes are implanted on either side of physiological midline420of spinal cord38. For example, an electrode combination including electrodes48A of lead32A and48B of lead32B are disposed on either side of physiological midline420, and therefore may cause suppression of a pain sensation and/or paresthesia on both a left and a right lateral side of patient36. However, an electrode combination including electrodes48C of lead32A and48D of lead32B does not include electrodes to the left lateral side of physiological midline420. Thus, electrical stimulation via electrodes48C and48D may only cause suppression of a pain sensation and/or paresthesia on a right lateral side of patient36. By testing various combinations of electrodes48, the clinician may determine a combination of electrodes that lies to both a left and a right lateral side of patient36, and thereby determine the electrode combination that provides the greatest pain relief to the patient.

In the example ofFIG. 4B, a clinician implants lead32A parallel to and offset from anatomical midline410of spinal cord38and implants lead32B at an angle of 5-20 degrees relative to anatomical midline410of spinal cord38of patient36. Such an implantation procedure as described herein may ensure that at least several electrodes are implanted on either side of the physiological midline of spinal cord38.

For example, an electrode combination including electrodes48G of lead32A and48F of lead32B are disposed on either side of physiological midline420, and therefore may cause suppression of a pain sensation and/or paresthesia on both a left and a right lateral side of patient36. However, an electrode combination including electrodes48E of lead32A and48H of lead32B does not include electrodes to the left lateral side of physiological midline420. Thus, electrical stimulation via electrodes48E and48H may only cause suppression of a pain sensation and/or paresthesia on a right lateral side of patient36. By testing various combinations of electrodes48, the clinician may determine a combination of electrodes that lies to both a left and a right lateral side of patient36, and thereby determine the electrode combination that provides the greatest pain relief to the patient.

FIGS. 5A-5Dillustrate an exemplary screen shot500of a display on user interface59of programmer40, in accordance with the techniques of the disclosure. In one example, programmer40may be a clinician programmer.FIGS. 5A-5Dare discussed in the context of a patient receiving spinal cord stimulation therapy as an illustrative example. A programmer, e.g., programmer40, may receive user input via the user interface59to set up leads and parameters that define one or more stimulation programs for delivering therapy to a patient. A stimulation program may be delivered by an implantable stimulator individually or in combination with other programs, e.g., on a time-interleaved basis. A program may define an electrode combination, including a selected set of electrodes for delivery of stimulation and polarities of such electrodes, pulse current or pulse voltage amplitudes delivered by respective electrodes, pulse width and pulse rate. The user may set up a profile for the session and the patient, and proceed to configure placement of the leads.

To provide an accurate representation of implanted leads for spinal cord stimulation, the user may select which leads will be programmed with therapy. In this example, there are up to 2 leads from which a user may select. However, in other examples there may be more or less leads available to the user from which to select.FIG. 5Aillustrates a lead set up screen where the user is prompted to indicate whether all the leads, for the given number of leads implanted or being trialed, will be placed in the same region and/or programmed together by indicating “Yes” or “No.” The user may assign implanted leads to one or more regions, where the regions represent the anatomical implant location of the leads associated with the regions. A lead region may be, for example, such entity as “lumbar spine” or “epidural thoracic.” In one example, where different leads are selected for different regions, the user may view and/or program each region where only the leads associated with a selected region are viewed and/or programmed. In one example, the user may assign the case electrodes to one or more regions, either alone or in combination with the implanted leads.

Upon selecting the leads, a representation of the leads to be programmed for that region may be shown on the screen. Referring toFIG. 5A, the graphical representation of two leads32, each with 8 electrodes may be shown on the screen, because the user selected to program them all together (in this example two leads). The user may be presented with an option to import an image for the lead region being programmed. The image may be for example a fluoroscopic image of the region in which therapy is to be applied. A button611labeled “Import Fluoro Image” appears on the display as shown inFIG. 5A, which the user may select if the user opts to import a fluoroscopic image of the leads assigned to the region for which therapy is being programmed. In another example, the display may also have a “Start Camera” button (not shown), which may, upon selection by the user, display an image acquired by the camera, which the user may select to use as the background image, as an alternative for importing a previously-acquired image. Therefore, a user may have an option to either use a camera or import a previously-acquired image. One or more examples of acquiring and storing a fluoroscopic image of a therapy region in a patient may be described in U.S. Pat. No. 8,744,591 to Davis et al., titled “STORING IMAGE OF THERAPY REGION IN IMPLANTABLE MEDICAL DEVICE,” issued on Jun. 3, 2014 and in U.S. patent application Ser. No. 14/085,573 to Davis et al., titled “ASSIGNMENT AND MANIPULATION OF IMPLANTABLE LEADS IN DIFFERENT ANATOMICAL REGIONS WITH IMAGE BACKGROUND” and filed on Nov. 20, 2013, the entire content of each of which is incorporated herein by reference.

The display screen may also present options to the user to manipulate the positions or the representation of the leads32. In the example ofFIG. 5A, the user may move a lead32by tapping and holding on the lead32and dragging it, or the user may rotate or curve a lead32by tapping and holding on an anchor point and dragging as indicated by instructions provided to the user on the screen. The user may also swap the orientation of leads32by selecting the corresponding function button. The user may also manipulate the leads32further by bending, resizing, and shaping the graphical representation of the leads or portions of the leads to achieve a better match between the graphical leads and the image of the leads in the anatomical background image. In one example, the user may select starting and ending points of the leads32in the image (e.g., to match distal and proximal electrode locations in the image), and the programmer may automatically draw the graphical representation of the leads32between the two points. The display may also show the electrode configuration, showing how the leads32are inserted. In one example, an option may be displayed to “Check Lead Insertion” to check that the leads are inserted correctly. The display may also present the user with the ability to manipulate the fluoroscopic image, as shown on the left side of the screen. However, the fluoroscopic image tools may not be highlighted until a fluoroscopic image is imported.

In some examples, upon importing a fluoroscopic image of spinal cord38, the representation of the leads32may be superimposed on the fluoroscopic image of spinal cord38. While it is not shown, a similar screen may be displayed for each of the regions when multiple regions are defined, and the user may import a fluoroscopic image to one or more regions, by clicking on a tab for the region and clicking on the “Import Fluoro Image” for that region.

In one example, the user interface may display the image and graphical representation of leads in 2D. In this example, the user interface may display the same region and the corresponding graphical representation of leads implanted in the region in 2D from different perspectives corresponding to different angles or cross sections, as the implanted leads may curve in more than one direction spatially, and allow the user to manipulate the graphical representation of leads for each perspective. In another example, the user interface may display the image and graphical representation of leads in 3D. In this example, the user interface may display the region and the corresponding graphical representation of leads implanted in the region in 3D, and may allow the user to rotate and manipulate the image and the graphical representation in all directions.

After the leads and fluoroscopic image have been manipulated to match for a given region, the process may be repeated for all lead regions (if multiple regions are programmed). The fluoroscopic image may be compressed and stored in the device, by selecting the button labeled “Program” on the screen. Selecting “program” may program all the changes to the device. The display may also present the user with other options like “Tools” and “Summary” in addition to “Programming.” Subsequently, the creation of therapy may occur (per lead region) on the final lead representation of the leads with the fluoroscopic image as background.

Each process described for the example of assigning all the leads to one image, may be used with each of the different regions. When multiple regions are defined, multiple fluoroscopic images may be linked to corresponding multiple lead electrode images and locations, and attributes related to the leads and the images may be linked thereto, and the combination of the images, leads, and attributes may be programmed and stored on medical devices, such as implantable stimulator34ofFIG. 1. Each of the images may be associated with an anatomical region, or with different perspectives of the same region, for example. Additionally, a lead32may be programmed to provide therapy associated with more than one region. In one example, the user may assign and program the case electrodes for certain anatomical regions in the same manner the user assigns and programs implanted leads.

According to the techniques of the disclosure, the clinician may use user interface500to mark, in reference to the first and second leads32, the location of the anatomical midline410of spinal cord38via a fluoroscope. As depicted inFIG. 5A, the clinician selects, via cursor510, button502to set an anatomical midline of spinal cord38of patient34. In the example ofFIG. 5B, the clinician sets a position for the anatomical midline by using cursor510to drag a line410representing the anatomical midline of the spinal cord38over a fluoroscopic image of spinal cord38. In some examples, upon setting a position of the anatomical midline of the spinal cord38, the clinician may determine the location of the physiological midline of spinal cord38via patient feedback, and mark the location of the physiological midline of spinal cord38on user interface500in a similar fashion to that of the anatomical midline410.

In further examples, as illustrated inFIG. 5C, user interface500includes a button504to determine the physiological midline of spinal cord38. Upon setting a position of the anatomical midline of the spinal cord38, the clinician may select button504via cursor510. In response to the clinician selecting button504, processor53of external programmer40determines a position of the physiological midline of spinal cord38. As described above, processor50may monitor a physiological response of a tissue of patient36during delivery of electrical neurostimulation according to a plurality of different electrode combinations. In some examples, the tissue response is an evoked compound action potential (eCAP) response of a nerve fiber of patient36. In some examples, the tissue response is a visible muscle twitching response of patient36. For example, by determining that one or more electrode combinations evoke a response on only a right lateral side of patient36, processor50may determine that the one or more electrode combinations are located to the right of the physiological midline of spinal cord38. Further, by determining that one or more electrode combinations evoke a response on only a left lateral side of patient36, processor50may determine that the one or more electrode combinations are located to the left of the physiological midline of spinal cord38. By determining that one or more electrode combinations evoke a response on both a right and a left lateral side of patient36, processor50may determine that at least some of the electrodes of the one or more electrode combinations are located both to the left and right of the physiological midline of spinal cord38, e.g., the physiological midline of spinal cord38lies between the electrodes of the one or more electrode combinations. Accordingly, based on the physiological response of the tissue during delivery of electrical neurostimulation according to the plurality of different electrode combinations, processor50determines the position of the physiological midline420. As depicted inFIG. 5D, processor50marks on user display500the position of physiological midline420.

FIG. 6is a conceptual diagram illustrating a stimulation zone of electrical stimulation therapy. As described above, system30delivers electrical neurostimulation according to a plurality of different combinations of electrodes48. By monitoring a physiological response of a tissue of patient36during delivery of the electrical neurostimulation according to the plurality of different electrode combinations, system30may determine a position of a physiological midline420of spinal cord38of patient36.

As depicted inFIG. 6, once the location of the physiological midline420of spinal cord38, the clinician, via programmer40, selects a combination of electrodes that includes one or more electrodes to a left lateral side of the determined physiological midline420and a right lateral side of physiological midline420. For example, as depicted inFIG. 6, the clinician selects one or more electrodes that results in electrical field116that lies to a left lateral side of physiological midline420and a right lateral side of physiological midline420. Implantable stimulator34uses electrodes48B,49F, and48G to deliver electrical stimulation to a target tissue site118of patient36. The centroid of electrical field116is indicated by icon112.

In some examples, programmer40receives, from the clinician via user interface59, a selection of one or more electrode combinations. In other examples, processor53of programmer40automatically determines a selection of one or more electrode combinations based on the detected location of physiological midline420. In some examples, programmer40may automatically balance the anodes and cathodes of an electrode combination such that, after balancing, implantable stimulator34uses the same number of anodes and cathodes to deliver electrical stimulation to target tissue site118. In other examples, programmer40selects an electrode combination that has differing numbers of anodes and cathodes. In yet other examples, programmer40selects an electrode combination that has a single anode and multiple cathodes. In yet other examples, programmer40selects an electrode combination that has multiple anodes and a single cathode. Additional techniques for selecting combinations of electrodes are provided in U.S. Pat. No. 8,560,080 to Goetz, issued on Oct. 15, 2013, the entire content of which is incorporated herein by reference.

Thus, by determining the location of the physiological midline420, the system of the present disclosure may more accurately select an electrode combination for delivery of stimulation to patient36. For example, by determining the location of the physiological midline, the system may select an electrode combination that includes one or more electrodes to a left lateral side of the determined physiological midline420and a right lateral side of physiological midline420. By selecting such an electrode combination, the system of the present disclosure may create an electrical field116that stimulates tissue on both left lateral side and a right lateral side of patient36. Alternatively, the system may select an electrode combination that includes one or more electrodes only to a left lateral side of the determined physiological midline420or only to a right lateral side of physiological midline420. By selecting such an electrode combination, the system of the present disclosure may create an electrical field116that stimulates tissue on only a left lateral side or only a right lateral side of patient36, respectively. Such a system may allow for increased reliability and efficacy in lead placement during surgery. Accordingly, a system as described herein may eliminate the need to perform testing of the implanted electrodes within the operation room, which may reduce the cost of the procedure, increase the reliability of the feedback received from the patient, and eliminate the need to wake the patient up from anesthesia to provide feedback on the electrical neurostimulation therapy, paresthesia, and pain sensations.

FIG. 7is a flowchart depicting an example operation according to the techniques of the disclosure. For convenience,FIG. 7is described with respect toFIG. 1. According to the techniques of the disclosure, a clinician implants at least one lead32at an angle relative to and across an anatomical midline of spinal cord38of patient36(700). In some examples, the at least one lead32is implanted at an angle of 5-20 degrees relative to the anatomical midline of spinal cord38of patient36. In some examples of the techniques disclosed herein, the clinician implants a first lead32A and second lead32B angled 5-20 degrees relative to and across the anatomical midline of spinal cord38. In alternate examples, the first lead32A is implanted parallel to and offset from the physiological midline of spinal cord38, while the second lead32B is implanted at an angle of 5-20 degrees relative to and across the physiological midline of spinal cord38. Such an implantation procedure as described herein may ensure that at least several electrodes are implanted on either side of the physiological midline of spinal cord38.

After implanting the lead, the clinician, via external programmer40, controls delivery of electrical stimulation according to a plurality of combinations of electrodes48(702). The clinician determines a location of a physiological midline of the patient36based on the delivery of electrical stimulation according to a plurality of combinations of electrodes48(704). In some examples, the clinician uses feedback from the patient regarding the different combinations of electrodes to identify a position of the physiological midline of spinal cord38. In other examples, programmer40determines the location of a physiological midline based upon a tissue response of patient36to the electrical stimulation in the manner described above. The clinician may use a user interface to mark, in reference to the first and second leads, the location of the anatomical midline of spinal cord38via a fluoroscope, and to further mark the location of the physiological midline of spinal cord38via the patient feedback. Based on the location of the physiological midline of spinal cord38, the clinician selects at least one electrode for subsequent delivery of electrical stimulation (706). Implantable stimulator34delivers electrical stimulation to patient36via the selected at least one electrode to provide pain relief therapy to patient36(708).