US20050075680A1 - Methods and systems for intracranial neurostimulation and/or sensing - Google Patents

Abstract

Methods and systems for intracranial neurostimulation and/or sensing are disclosed. An intracranial signal transmission system in accordance with an embodiment of the invention includes a generally electrically insulating support body having a head portion configured to be positioned at least proximate to an outer surface of a patient's skull, and a shaft portion configured to extend into an aperture in the patient's skull. The system can further include at least one electrical contact portion carried by the support body. The at least one electrical contact portion can be positioned to transfer electrical signals to, from, or both to and from the patient's brain via the aperture in the patient's skull.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application is a continuation-in-part of pending U.S. application Ser. No. 10/418,796, filed Apr. 18, 2003, and incorporated herein in its entirety by reference.
TECHNICAL FIELD
• The present invention relates to intracranial electrodes and methods for implanting and using intracranial electrodes. These electrodes and methods may be suited for neurostimulation systems and may also be used in electroencephalography and other recording systems, e.g., evoked potential recordings.
BACKGROUND
• A wide variety of mental and physical processes are known to be controlled or influenced by neural activity in the central and peripheral nervous systems. For example, the neural functions in some areas of the brain (e.g., the sensory or motor cortices) are organized according to physical or cognitive functions. Several other areas of the brain also appear to have distinct functions in most individuals. In the majority of people, for example, the areas of the occipital lobes relate to vision, the regions of the left inferior frontal lobes relate to language, and the regions of the cerebral cortex appear to be involved with conscious awareness, memory, and intellect. Because of the location-specific functional organization of the brain, in which neurons at discrete locations are statistically likely to control particular mental or physical functions in normal individuals, stimulating neurons at selected locations of the central nervous system can be used to effectuate changes in cognitive and/or motor functions throughout the body.
• In several existing applications, neural functions are treated by electrical or magnetic stimulation powered by a neural stimulator that has a plurality of therapy electrodes and a pulse system coupled to the therapy electrodes. The therapy electrodes can be implanted into the patient at a target site for stimulating the desired portions of the brain. For example, one existing technique for masking pain in a patient is to apply an electrical stimulus to a target stimulation site of the brain.
• The brain can be stimulated in several known fashions. One type of treatment is referred to as transcranial electrical stimulation (TES), which involves placing an electrode on the exterior of the patient's scalp and delivering an electrical current to the brain through the scalp and the skull. TES, however, is not widely used because the delivery of the electrical stimulation through the scalp and the skull causes patients a great amount of pain and the electrical field is difficult to direct or focus accurately.
• Another type of treatment is transcranial magnetic stimulation (TMS), which involves using a high-powered magnetic field adjacent the exterior of the scalp over an area of the cortex. TMS does not cause the painful side effects of TES. Unfortunately, TMS is not presently effective for treating many patients because the existing delivery systems are not practical for applying stimulation over an adequate period of time. TMS systems, for example, are relatively complex and require stimulation treatments to be performed by a healthcare professional in a hospital or physician's office. The efficacy of TMS in longer-term therapies may be limited because it is difficult to (a) accurately localize the region of stimulation in a reproducible manner, (b) hold the device in the correct position over the cranium for the requisite period, and (c) provide stimulation for extended periods of time.
• Another device for stimulating a region of the brain is disclosed by King in U.S. Pat. No. 5,713,922, the entirety of which is incorporated herein by reference. King discloses a device for cortical surface stimulation having electrodes mounted on a paddle that is implanted under the skull of the patient. These electrodes are placed in contact with the surface of the cortex to create “paresthesia,” which is a vibrating or buzzing sensation. Implanting the paddle typically requires removal of a relatively large (e.g., thumbnail-sized or larger) window in the skull via a full craniotomy. Craniotomies are performed under a general anesthetic and subject the patient to increased chances of infection.
• A physician may employ electroencephalography (EEG) to monitor neural functions of a patient. Sometimes this is done alone, e.g., in diagnosing epileptic conditions, though it may also be used in conjunction with neurostimulation. Most commonly, electroencephalography involves monitoring electrical activity of the brain, manifested as potential differences at the scalp surfaces, using electrodes placed on the scalp. The electrodes are typically coupled to an electroencephalograph to generate an electroencephalogram. Diagnosis of some neurological diseases and disorders, e.g., epilepsy, may best be conducted by monitoring neural function over an extended period of time. For this reason, ambulatory electroencephalography (AEEG) monitoring is becoming more popular. In AEEG applications, disc electrodes are applied to the patient's scalp. The scalp with the attached electrodes may be wrapped in gauze and the lead wires attached to the electrodes may be taped to the patient's scalp to minimize the chance of displacement.
• EEG conducted with scalp-positioned electrodes requires amplification of the signals detected by the electrodes. In some circumstances, it can be difficult to pinpoint the origin of a particular signal because of the signal dissipation attributable to the scalp and the skull. For more precise determinations, EEG may be conducted using “deep brain” electrodes. Such electrodes extend through the patient's scalp and skull to a target location within the patient's brain. Typically, these deep brain electrodes comprise lengths of relatively thin wire that are advanced through a bore through the patient's skull to the desired location. If the electrodes are to be monitored over an extended period of time, the electrodes typically are allowed to extend out of the patient's skull and scalp and are coupled to the electroencephalograph using leads clipped or otherwise attached to the electrodes outside the scalp. To avoid shifting of the electrodes over time, the electrodes typically are taped down or held in place with a biocompatible cementitious material. The patient's head typically must be wrapped in gauze to protect the exposed electrodes and the associated leads, and the patient is uncomfortable during the procedure. This may be suitable for limited testing purposes-deep brain encephalography typically is limited to tests conducted in hospital settings over a limited period of time, usually no more than a few days-but could be problematic for longer-term monitoring, particularly in nonclinical settings.
• Screws have been used to attach plates or the like to patients' skulls.FIG. 1, for example, schematically illustrates a conventional cranial reconstruction to repair afracture50 or other trauma. In this application, aplate60 is attached to theouter cortex12 of theskull10 bycortical bone screws62. Theplate60 spans thefracture50, helping fix the skull in place on opposite sides of thefracture50. As can be seen inFIG. 1, thescrews62 do not extend through the entire thickness of the skull. Instead, thescrews62 are seated in theouter cortex12 and do not extend into thecancellous18 or theinter cortex14. In some related applications, thescrews62 may be longer and extend into or even through thecancellous18. Physicians typically take significant care to ensure that thescrews62 do not extend through the entire thickness of the skull, though, because penetrating the skull can increase the likelihood of trauma to or infection in the patient's brain.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic illustration of a conventional cranial reconstruction.
• FIG. 2A is a schematic view in partial cross section of an intracranial electrode in accordance with one embodiment of the invention implanted in a patient.
• FIG. 2B is a schematic top elevation view of the implanted intracranial electrode ofFIG. 2A.
• FIG. 3A is a schematic illustration in partial cross section of an intracranial electrode in accordance with another embodiment of the invention implanted in a patient.
• FIG. 3B is a schematic top elevation view of the implanted intracranial electrode ofFIG. 3A.
• FIG. 4A is a schematic illustration in partial cross section of an intracranial electrode in accordance with yet another embodiment of the invention implanted in a patient.
• FIG. 4B is a side view of a dielectric member of the electrode ofFIG. 4A.
• FIG. 5 is a schematic illustration in partial cross section of an intracranial electrode in accordance with still another embodiment of the invention implanted in a patient.
• FIG. 6A is a schematic illustration in partial cross section of an intracranial electrode in accordance with a further embodiment of the invention implanted in a patient.
• FIG. 6B is a schematic top elevation view of the implanted intracranial electrode ofFIG. 6A.
• FIG. 7 is a schematic illustration in partial cross section of an intracranial electrode in accordance with still another embodiment of the invention implanted in a patient.
• FIG. 8 is a schematic side view of a broken-away portion of a patient's skull in which an intracranial electrode in accordance with another embodiment of the invention has been implanted.
• FIG. 9 is a schematic partial cross-sectional view taken along line9-9 ofFIG. 8.
• FIG. 10 is an isolation view of a portion of the implanted electrode ofFIG. 9.
• FIG. 11 is a perspective view of selected components of the intracranial electrode ofFIGS. 8-10.
• FIG. 12 is a schematic illustration in partial cross section of an intracranial electrode in accordance with yet another embodiment of the invention implanted in a patient.
• FIG. 13 is a schematic illustration in partial cross section of an intracranial electrode in accordance with one more embodiment of the invention implanted in a patient.
• FIG. 14 is a schematic illustration in partial cross section of an intracranial electrode in accordance with a further embodiment of the invention implanted in a patient.
• FIG. 15 is a schematic partial cross-sectional view of the intracranial electrode ofFIG. 13 with a retaining collar of the electrode in a radially compressed state.
• FIG. 16 is a schematic partial cross-sectional view of the intracranial electrode ofFIG. 14 with the retaining collar in a radially expanded state.
• FIG. 17 is a schematic illustration in partial cross section of a deep brain intracranial electrode in accordance with an alternative embodiment of the invention implanted in a patient.
• FIG. 18 is a schematic illustration in partial cross section of a deep brain intracranial electrode in accordance with still another embodiment of the invention implanted in a patient.
• FIG. 19 is a schematic overview of a neurostimulation system in accordance with a further embodiment of the invention.
• FIG. 20 is a schematic overview of a neurostimulation system in accordance with another embodiment of the invention.
• FIG. 21 is a schematic illustration of one pulse system suitable for use in the neurostimulation system ofFIG. 17 orFIG. 18.
• FIG. 22 is a schematic top view of the array of electrodes inFIG. 17.
• FIGS. 23-26 are schematic top views of alternative electrode arrays in accordance with other embodiments of the invention.
• FIG. 27 is a schematic view in partial cross section of an intracranial electrode implanted in a patient in accordance with another embodiment of the invention.
• FIG. 28 is a schematic view in partial cross section of an intracranial electrode implanted in a patient in accordance with another embodiment of the invention.
• FIG. 29 is a schematic view in partial cross section of an intracranial electrode implanted in a patient in accordance with another embodiment of the invention.
• FIG. 30 is a schematic view in partial cross section of an intracranial electrode having an adjunct depth-penetrating electrode implanted in a patient in accordance with another embodiment of the invention.
• FIG. 31 is a schematic view in partial cross section of another intracranial electrode having an adjunct depth-penetrating electrode implanted in a patient in accordance with another embodiment of the invention.
• FIG. 32 is a schematic view in partial cross section of a neural stimulation system implanted in a patient in accordance with an alternative embodiment of the invention.
• FIG. 33 is a schematic view in partial cross section of a neural stimulation system implanted in a patient in accordance with yet another embodiment of the invention.
• FIG. 34A is a schematic view in partial cross section of an intracranial electrode system implanted in a patient in accordance with another embodiment of the invention.
• FIG. 34B is a schematic illustration of an electrical energy transfer mechanism in accordance with an embodiment of the invention.
• FIG. 35 is a schematic view in partial cross section of portions of intracranial electrode system implanted in a patient in accordance with an embodiment of the invention.
• FIG. 36 is a schematic overview of an intracranial electrode system implanted in a patient in accordance with an embodiment of the invention.
• FIG. 37 is a schematic view in partial cross section of a set of intracranial electrodes implanted in a patient in accordance with a further embodiment of the invention.
• FIG. 38 is a schematic view in partial cross section of an intracranial electrode in accordance with a further embodiment of the invention.
• FIG. 39 is a schematic view in partial cross section of an intracranial electrode in accordance with an embodiment of the invention.
• FIG. 40 is a schematic overview of an intracranial electrode system having RFID capabilities in accordance with a further embodiment of the invention.
• FIG. 41 illustrates a depth measurement procedure employing a depth acquisition stick according to an embodiment of the present invention.
• FIG. 42 is a flowchart illustrating depth measurement procedures in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
• A. Overview
• Various embodiments of the present invention provide intracranial electrodes and methods for implanting and using intracranial electrodes. It will be appreciated that several of the details set forth below are provided to describe the following embodiments in a manner sufficient to enable a person skilled in the art to make and use the disclosed embodiments. Several of the details and advantages described below, however, may not be necessary to practice certain embodiments of the invention. Additionally, the invention can also include additional embodiments that are not described in detail with respect toFIGS. 1-42.
• One aspect of the invention is directed to an intracranial signal transmission system that includes a generally electrically insulating support body having a head portion configured to be positioned at least proximate to an outer surface of a patient's skull. The support body can further have a shaft portion configured to extend into an aperture in the patient's skull. At least one electrical contact portion is carried by the support body and can be positioned to transfer electrical signals to, from, or both to and from the patient's brain via the aperture in the patient's skull.
• An intracranial signal transmission system in accordance with another aspect of the invention includes an electrical contact portion configured to be positioned in an aperture of a patient's skull, and an electrical energy transfer device configured to be releasably positioned external to the patient's scalp. The energy transfer device can be coupleable to a signal transmitter to transmit signals to the electrical contact portion while the electrical contact portion is positioned beneath the patient's scalp, and while the energy transfer device is positioned external to the patient's scalp. In particular embodiments, the electrical energy transfer device can include a flexible outer layer, an adhesive gel layer positioned to contact the patient's scalp, a conductive layer positioned between the outer layer and the adhesive gel layer, and a conductive lead connected to the conductive layer.
• An intracranial signal transmission system in accordance with still another aspect of the invention includes a shaft configured to extend through an aperture in a patient's skull, and a head connected to the shaft. The head can be configured to be positioned adjacent to an external surface of the patient's skull and can be eccentrically positioned relative to the shaft. Accordingly, the head can have a first portion extending outwardly from the shaft by a first distance, and a second portion extending outwardly from the shaft by a second distance different from the first distance. The system can further include an electrical contact portion carried by at least one of the shaft and the head.
• Other aspects of the invention are directed to methods for installing electrodes and/or transmitting intracranial electrical signals. A method in accordance with one aspect of the invention includes drilling a hole in a patient's skull, and determining a distance from an outer surface of the patient's skull to a feature beneath the outer surface of the patient's skull by inserting an elongated member having graduation markings into the pilot hole. The method can further include selecting a size of an intracranial electrode based on the distance determined with the elongated member, and inserting the intracranial electrode into the hole. The method can still further include securing the intracranial electrode to the patient's skull.
• A method in accordance with another aspect of the invention includes forming an aperture in a patient's skull, with the aperture having a first generally conical portion with a first diameter at an external surface of the patient's skull, and a second portion having a second diameter smaller than the first diameter, located beneath the external surface. The method can further include disposing proximate to the aperture an electrical contact portion carried by a support body having a shaft and a head depending from the shaft. The head can have a generally conical shape, with an angle between an external surface of the shaft and an external surface of the head being obtuse. The method can still further include inserting the support body into the aperture so that the shaft extends through the second portion of the aperture and the head engages a wall of the aperture at the first portion of the aperture.
• A method in accordance with yet another aspect of the invention includes forming an aperture in the patient's skull, disposing proximate to the aperture an electrical contact portion carried by a support body having a shaft and a head depending from the shaft, with the shaft having an external surface and a plurality of surface features. The method can still further include inserting the support body into the aperture so that the shaft extends into the aperture, and then allowing the patient's bone tissue to grow into interengagement with the surface features.
• For ease of understanding, the following discussion is subdivided into three areas of emphasis. The first section discusses certain intracranial electrodes; the second section relates to select embodiments of neurostimulation systems; and the third section outlines methods in accordance with other embodiments of the invention.
• B. Intracranial Electrodes
• FIGS. 2-15 illustrate intracranial electrodes in accordance with various embodiments of the invention. Like reference numbers are used throughout these figures to designate like or analogous elements.
• FIGS.2A-B illustrate anintracranial electrode100 in accordance with one embodiment of the invention. Thiselectrode100 includes ahead102 attached to a threadedshaft110. Thehead102 andshaft110 may be integrally formed of an electrically conductive material, e.g., titanium or another biocompatible, electrical conductive metal. Thehead102 may include one ormore slots104, an allen head recess (not shown), or other structure (e.g., a square drive or TORX™ drive recess) adapted to facilitate turning theelectrode100. As theelectrode100 is turned, thethreads112 of the threadedshaft110 will advance a generally distally positionedcontact surface115 of theelectrode100 toward thedura mater20. The length of theshaft110 may be selected so that thecontact surface115 of theelectrode100 electrically engages the surface of thedura mater20 without causing undue harm to thedura mater20 or the underlying cerebral cortex. Thecontact surface115 may comprise a relatively blunt end to reduce trauma to the dura mater and theunderlying brain tissue25.
• In one embodiment, theintracranial electrode100 is adapted to be electrically connected to a pulse system (1050 inFIG. 18, for example), as described below. Theelectrode100 may be connected to the pulse system in any desired fashion. In the illustrated embodiment, theelectrode100 is coupled to such a pulse system by means of anelectrical lead120. Theelectrical lead120 shown inFIGS. 2A and 2B comprises an elongated, subcutaneouslyimplantable body124, which may have an insulative sheath. An electrically conductive ring orwasher122 may be attached to an end of thebody124. In one embodiment, an opposite end of thebody124 is physically attached to a component of the pulse system. In other embodiments, the leads may be operatively connected to one or more components of the pulse system without being physically attached thereto, e.g., using a transmitter and antenna or a magnetic coupling. Embodiments of pulse systems incorporating such wireless links are disclosed in U.S. Patent Application Publication No. US 2002/0087201, the entirety of which is incorporated herein by reference.
• Thehead102 of theelectrode100 is adapted to be implanted subcutaneously beneath the patient's scalp30 (shown schematically inFIG. 2A). As explained below, theelectrode100 may be used to deliver an electrical signal to thebrain tissue25 adjacent thecontact surface115. At higher stimulus levels, electrical contact between the patient'sscalp30 and thehead102 of theelectrode100 may be uncomfortable for the patient. If so desired, thescalp30 may be electrically insulated from thehead102. This may be accomplished by applying on the head102 a quantity of a dielectric, biocompatible, cementitious material (not shown), which may be cured or dried in place. In another embodiment, thehead102 may be covered with a separate cap130 (shown in dashed lines inFIG. 2A) formed of a dielectric material, e.g., a dielectric, biocompatible plastic, that may be glued, press-fit, or otherwise attached to thehead102 and/or thelead120.
• The dimensions of theelectrode100 can be varied to meet various design objectives. In one embodiment, however, theelectrode100 is longer than the thickness of the patient's skull. More specifically, thehead102 is adapted to be seated at an extracranial subcutaneous site while the threadedshaft110 is only slightly longer than the skull thickness at the intended treatment site. Lengths on the order of 4-50 mm, for example, may be appropriate in certain applications. The diameter of thehead102 and the threadedshaft110 may also be varied. For most applications,shafts110 having diameters (typically excluding the width of the threads112) of no greater than 4 mm will suffice. Shaft diameters of about 1-4 mm are likely, with diameters of 1.5-2.5 mm being well suited for most applications. FIGS.2A-B illustrate anelectrode100 having aconstant diameter shaft110, but it should be understood that the shaft diameter may vary. For example, theshaft110 may taper distally to improve the ability of theshaft110 to be self-tapping. Thehead102 typically will have a larger diameter than an adjoining portion of theshaft110. (It should be recognized thatFIGS. 2-15 are not drawn to scale. In particular, the aspect ratio of the electrodes is significantly reduced to better illustrate certain functional aspects of the designs.)
• FIG. 3A illustrates anintracranial electrode150 in accordance with another embodiment of the invention. Thisintracranial electrode150 is similar in many respects to theintracranial electrode100 of FIGS.2A-B. For example, theelectrode150 includes an electrically conductive threadedshaft110 defining a blunt,atraumatic contact surface115 adjacent a distal end.
• The connection of theelectrode150 to thelead160 in FIGS.3A-B differs somewhat from the connection of theelectrode100 and lead120 in FIGS.2A-B, however. In FIGS.2A-B, theelectrode100 is electrically coupled to thelead120 by compressively engaging the electricallyconductive ring122 of thelead120 between theelectrode head102 and theskull10. In FIGS.3A-B, theelectrode150 includes ahead152 includingslots154 or other structure for engaging a screwdriver, wrench, or the like. Thehead152 is adapted to engage acap162 carried by thelead160 that electrically couples thebody164 of thelead160 to thehead152 of theelectrode150. In the illustrated embodiment, thecap162 comprises a dielectric body (e.g., a dielectric plastic material with some resilience) having an electrically conductiveinner surface163, which may be provided by coating an interior surface of thecap162 with a metal. In one embodiment, thecap162 is adapted to resiliently deform to be press-fitted on thehead152. Thebody164 of thelead160 may be coupled to the electrically conductiveinner surface163 of thecap162, thereby providing an electrical pathway between theelectrode150 and a pulse system (not shown) operatively coupled to thelead160.
• In one embodiment, thecap162 is sized to be subcutaneously implanted beneath the patient'sscalp30. In the illustrated embodiment, thehead152 and thecap162 both extend outwardly beyond theouter cortex12 of the patient'sskull10. In another embodiment (discussed in more detail below with respect toFIGS. 38 and 39) some or all of the length of thehead152 and/or thecap162 may be countersunk into a recess formed through theouter cortex12 and/or an outer portion of the cancellous18. This can improve patient comfort, which can be useful if theintracranial electrode150 is intended to be implanted permanently or for an extended period of time.
• FIGS.4A-B schematically illustrate aspects of anintracranial electrode200 in accordance with another embodiment. Theelectrode200 may comprise an electrically conductiveinner portion205 and an electrically insulativeouter portion206. In the illustrated embodiment, the electricallyconductive portion205 of theelectrode200 includes ahead202 and a threadedshaft210 defining acontact surface215 for electrically contacting the patient'sdura mater20. These elements of theelectrode200 and their electrical connection to thelead120 are directly analogous to theelectrode100 shown in FIGS.2A-B. The electrically insulativeouter portion206 of theelectrode200 shown inFIG. 4A comprises adielectric member240 that is disposed between the threadedshaft210 and the patient'sskull10. As shown inFIG. 4B, thisdielectric member240 may take the form of a tapered sleeve. Thesleeve240 may have an upper ring-like portion242 and a plurality ofdeformable flanges244 extending distally therefrom. Theflanges244 may be adapted to be urged outwardly into compressive contact with a bore formed in the patient'sskull10 when the threadedshaft210 is advanced into the interior of thesleeve240. Although not shown inFIG. 4B, ribs or teeth may be provided on the exterior surfaces of theflanges244 to further anchor thesleeve240 in the cancellous18. In one embodiment, thesleeve240 is formed of a dielectric plastic and the threads of the threadedmember210 may be self-tapping in the inner wall of thesleeve240.
• When implanted in askull10 as shown inFIG. 4A, thedielectric sleeve240 will electrically insulate theskull10 from the electricallyconductive shaft210 of theelectrode200. (Thesleeve240 need not completely electrically isolate the skull andshaft210; it merely serves to reduce electrical conduction to theskull10.) As explained below, some embodiments of the invention employ an array comprising a plurality of intracranial electrodes implanted at various locations in a patient'sskull10. The use of a dielectric member such as thedielectric sleeve240 can help electrically isolate each of theelectrodes200 fromother electrodes200 in the array (not shown). If so desired, theelectrode200 may be provided with adielectric cap230 sized and shaped to be implanted subcutaneously beneath the patient's scalp30 (not shown inFIG. 4A). Much like thecap130 ofFIG. 2A, thiscap230 may electrically insulate the patient's scalp from the electricallyconductive head202. This may further improve electrical isolation of theelectrodes200 in an array.
• FIG. 5 illustrates anintracranial electrode250 in accordance with yet another embodiment of the invention. Thiselectrode250 includes an electricallyconductive shaft260 electrically coupled to a subcutaneouslyimplantable head262 and a distally positionedcontact surface265. Theshaft260 is received in the interior of an externally threaded dielectric layer280. Theshaft260 may be operatively coupled to the dielectric layer280 for rotation therewith as the electrode is threadedly advanced through the patient'sskull10. In one embodiment, this may be accomplished by a spline connection between theshaft260 and the dielectric layer280. In other embodiments, the dielectric layer280 may be molded or otherwise formed about theshaft260.
• In one particular embodiment, the dielectric layer280 comprises an electrically insulative ceramic material. In another embodiment, the dielectric layer280 comprises an electrically insulative plastic or other biocompatible polymer that has sufficient structural integrity to adequately anchor theelectrode250 to theskull10 for the duration of its intended use. If so desired, the dielectric layer280 may be porous or textured to promote osseointegration of long-term implants. For shorter-term applications, the dielectric layer280 may be formed of or covered with a material that will limit osseointegration.
• In at least some of the preceding embodiments, theintracranial electrode100,150,200, or250 has a fixed length. In the embodiment shown in FIGS.2A-B, for example, the distance between the base of thehead102 and thecontact surface115 remains fixed. When the threadedshaft110 is sunk into theskull10 to a depth sufficient to compress theconductive ring122 of thelead120 between thehead102 and theskull10, this will also fix the distance from the exterior surface of theouter cortex12 of theskull10 to thecontact surface115. The thickness of theskull10 can vary from patient to patient and from site to site on a given patient's skull. Hence, the pressure exerted by thecontact surface115 against thedura mater20 will vary depending on the thickness of the skull. If theelectrode100 is selected to be long enough to make adequate electrical contact with the dura mater adjacent the thickest site on a skull, the pressure exerted by thecontact surface115 against thedura mater20 may cause undue damage at sites where the skull is thinner. Consequently, it can be advantageous to provide a selection of electrode sizes from which the physician can choose in selecting anelectrode100 for a particular site of a specific patient's skull.
• FIGS. 6-12 illustrate embodiments of electrodes with adjustable lengths. FIGS.6A-B, for example, illustrate anintracranial electrode300 that is adapted to adjust a distance between the outer surface of theskull10 and acontact surface315 of theelectrode300. This, in turn, enables the contact force between thecontact surface315 and the surface of thedura mater20 to be varied without requiring multiple electrode lengths.
• Theintracranial electrode300 ofFIGS. 6A and 6B includes a probe orshaft310 that has a blunt distal surface defining thecontact surface315 of theelectrode300. Theshaft310 has aproximal end312 that may include atorque drive recess314 or the like to facilitate rotation of theshaft310 relative to ahead320 of theelectrode300. At least a portion of the length of theshaft310 is externally threaded. In the illustrated embodiment, the shaft has an externally threaded proximal length and an unthreaded surface along a distal length.
• Thehead320 of theelectrode300 comprises abody322 and atubular length324 that extends from thebody322. Thebody322 may be adapted to be rotated by hand or by an installation tool. In one embodiment thebody322 is generally hexagonal to facilitate rotation with an appropriately sized wrench. In the particular embodiment shown in FIGS.6A-B, thebody322 has a pair ofrecesses323 in its outer face sized and shaped to interface with a dedicated installation tool (not shown) having projections adapted to fit in therecesses323. If so desired, the installation tool may be a torque wrench or other tool adapted to limit the amount of torque an operator may apply to thehead320 of theelectrode300 during installation. Thetubular length324 may be externally threaded so thehead320 may be anchored to theskull10 by screwing thetubular length324 into theskull10.
• Thehead320 includes an internally threaded bore326 that extends through the thickness of thebody322 and thetubular length324. Thebore326 has threads sized to mate with the external threads on theshaft310. If so desired, a biocompatible sealant (e.g., a length of polytetrafluoroethylene tape) may be provided between the threads of thebore326 and the threads of theshaft310 to limit passage of fluids or infectious agents through thebore326.
• Rotation of theshaft310 with respect to thehead320 will, therefore, selectively advance or retract theshaft310 with respect to thehead320. This will, in turn, increase or decrease, respectively, the distance between thelower face323 of thehead body322 and thecontact surface315 of theshaft310. As suggested inFIG. 6A, this may be accomplished by inserting atip344 of atorque driver340 into thetorque drive recess314 in theshaft310 and rotating thetorque driver340. Thetip344 of thetorque driver340 may be specifically designed to fit thetorque drive recess314. In the embodiment shown in FIGS.6A-B, thetorque drive recess314 is generally triangular in shape and is adapted to receive atriangular tip344 of thetorque driver340. If so desired, thetorque driver340 may comprise a torque wrench or the like that will limit the maximum torque and operator can apply to theshaft310 of theelectrode300.
• If so desired, thetorque driver340 may includegraduations342 to inform the physician how far theshaft310 has been advanced with respect to thehead320. As noted below, in certain methods of the invention, the thickness of the skull at the particular treatment site may be gauged before theelectrode300 is implanted. Using this information and thegraduations342 on thetorque driver340, the physician can fairly reliably select an appropriate length for theelectrode300 to meet the conditions present at that particular site.
• In the embodiment shown in FIGS.6A-B, thehead320 and theshaft310 are both formed of an electrically conductive material. Theconductive ring122 of thelead120 may be received in a slot formed in thelower face323 of thebody322. Alternatively, thering122 may be internally threaded, permitting it to be threaded over the external threads of thetubular length324 before thehead320 is implanted. If so desired, thering122 can instead be compressively engaged by thelower face323 of thehead320 in a manner analogous to the engagement of thehead102 with thering122 inFIG. 2A, for example.
• In another embodiment, thehead320 is formed of a dielectric material, such as a dielectric ceramic or plastic. This may necessitate a different connection between the lead120 and theshaft310, such as by electrically contacting thelead120 to theproximal end312 of theshaft310. Employing adielectric head320 can help electrically insulate theskull10 from theelectrodes300, improving signal quality and reducing interference between thevarious electrodes300 in an array, as noted above.
• FIG. 7 schematically illustrates anintracranial electrode350 in accordance with a further embodiment of the invention. Theelectrode350 includes a shaft or probe360 having aproximal end362 and a distally locatedcontact surface365. Theshaft360 may include a first threadedportion360aand a second threadedportion360c. In the embodiment shown inFIG. 7, the first and second threadedportions360aand360care separated by an unthreadedintermediate portion360b. In an alternative embodiment, the two threadedportions360aand360cdirectly abut one another.
• Theintracranial electrode350 of this embodiment also includes ahead370 having an internally threadedbore376 extending through its thickness. The threads of thebore376 are adapted to mate with the threads of the first threadedportion360a. By rotating theshaft360 with respect to the head370 (e.g., with a screwdriver340), the distance between thehead370 and thecontact surface365 can be adjusted in much the same manner described above in connection with FIGS.6A-B.
• Thehead320 of theelectrode300 in FIGS.6A-B has an externally threadedtubular length324 that extends into theskull10 and helps anchor theelectrode300 to theskull10. Theshaft310 may then move with respect to the skull by rotating theshaft310 with respect to thehead320. In the embodiment shown inFIG. 7, thehead370 is not directly anchored to theskull10. Instead, the threads of the second threadedportion360care adapted to threadedly engage theskull10 to anchor theelectrode350 with respect to theskull10 and thehead370 is attached to the first threadedportion360aof theshaft360. In one embodiment, theshaft360 may be threaded into a pilot hole in theskull10. Once theshaft360 is positioned at the desired depth, thehead370 may be screwed onto the first threadedportion360aof theshaft360 to help fix theshaft360 with respect to the skull and provide a less traumatic surface to engage the patient's scalp (not shown) when the scalp is closed over theelectrode350. In another embodiment, the length of theelectrode350 may first be adjusted by rotating theshaft360 with respect to thehead370. Once theelectrode350 has the desired length, theshaft360 may be advanced into theskull10. Theshaft360 may be graduated to facilitate adjustment to the appropriate length. If so desired, the first threadedportion360amay be threaded in a direction opposite the second threadedportion360cand/or the pitch of the threads in the first threadedportion360amay be different from the pitch of the threads in the second threadedportion360c.
• In the embodiment ofFIG. 7, theshaft360 of theelectrode350 extends through thedura mater20 and thecontact surface365 of theelectrode350 is in direct contact with the cerebral cortex of the patient's brain. This is simply intended to illustrate one alternative application. In other embodiments, the length of theelectrode350 may be selected so that thecontact surface365 electrically contacts thedura mater20 without extending therethrough, much as illustrated inFIG. 6A, for example.
• FIGS. 8-11 illustrate anintracranial electrode400 in accordance with another embodiment of the invention. Theintracranial electrode400 includes a shaft or probe410 that is slidably received by ahead420. Theshaft410 comprises an electrically conductive material and defines anelectrical contact surface415, e.g., on its distal end.
• In the preceding embodiments, some or a majority of the head of the electrode extends outwardly beyond the outer surface of theskull10. In the particular implementation shown inFIGS. 8-10, thehead420 is received entirely within the thickness of theskull10. It should be understood, though, that this is not necessary for operation of the device, and this is shown simply to highlight that the position of thehead420 with respect to theskull10 can be varied. In another embodiment, at least a portion of thehead420 extends outwardly beyond the outer surface of theskull10.
• Thehead420 includes abase430 and anactuator422. Thebase430 includes an externally threadedbody432 and atubular length434 that extends from thebody432. A portion of thetubular length434 carriesexternal threads436. Thetubular length434 may also include one ormore locking tabs440, each of which includes anactuating surface442.
• Theactuator422 has an internally threaded bore424 that is adapted to matingly engage thethreads436 on thebase430. Rotating theactuator422 with respect to the base430 in a first direction will advance theactuator422 toward theactuating surface442 of each of thetabs440. Theactuator422 may urge against the actuating surfaces442, pushing thetabs440 inwardly into engagement with theshaft410. This will help lock theshaft410 in place with respect to thebase430. Rotating theactuator422 in the opposite direction will allow thetabs440 to resiliently return toward a rest position wherein they do not brake movement of theshaft410. The force with which theshaft410 engages the dura mater20 (not shown) then can be adjusted to a desired level by moving theshaft410 with respect to thebase430. When theshaft410 is in the desired position, theactuator422 may be moved into engagement with thetabs440 to hold theshaft410 in the desired position.
• FIG. 12 illustrates an adjustable-lengthintracranial electrode450 in accordance with another embodiment. Theintracranial electrode450 includes an axially slidable probe orshaft452 and ahead460. Thehead460 includes abody462 and an externally threadedtubular length464. Thetubular length464 includes an axially extendingrecess466 sized to slidably receive a portion of theshaft452. An O-ring465 or the like may provide a sliding seal between thehead460 and theshaft452.
• Thecontact surface455 of theshaft452 is pushed against the surface of thedura mater20 with a predictable force by means of aspring454 received in therecess466. InFIG. 12, thespring454 is typified as a compressed coil spring formed of a helically wound wire or the like. In this embodiment, anelectrical contact469 of the lead468 may be electrically coupled to the wire of thespring454. Electrical potential may then be conducted to theshaft452 by the wire of thespring454.
• In another embodiment (not shown), thespring454 comprises a compressed elastomer, which may take the form of a column that fills some or all of the diameter of therecess466. The elastomer may comprise a biocompatible polymeric material, for example. In such an embodiment, the elastomer may be electrically conductive, e.g., by filling a polymeric material with a suitable quantity of a conductive metal powder or the like. In another embodiment, one or more wires may be embedded in the elastomeric material to conduct an electrical signal across the elastomer to theshaft452.
• In the illustrated embodiment and the alternative embodiment wherein thespring454 comprises an elastomer, thehead460 may be formed of a dielectric material, helping electrically insulate theskull10 from theshaft452. In an alternative embodiment, thehead460 may be formed of an electrically conductive material. Even though the other structural elements of theelectrode450 may remain largely the same, this would avoid the necessity of having the lead468 extend through thehead460; an electricallyconducive ring122 or the like instead may be employed in a manner analogous to that shown inFIG. 6A, for example.
• FIG. 13 depicts and adjustable-lengthintracranial electrode475 in accordance with a different embodiment. Some aspects of theintracranial electrode475 are similar to theintracranial electrode450 shown inFIG. 12. In particular, theintracranial electrode475 includes an axially slidable probe orshaft480 that is slidably received in an axially extendingrecess488 in atubular length492 of ahead490. A proximal face of thebody490 may include a pair of tool-receivingrecesses494, which may be analogous to the tool-receivingrecesses323 noted above in connection withFIG. 6A, to aid in the installation of thebody490. If so desired, one or more seals may be provided between theshaft480 and thebody490. In the embodiment shown inFIG. 13, thebody490 carries a first O-ring493 and theshaft480 and carries a second O-ring484 sealed against the interior of therecess488. These O-rings may also serve as abutments to limit axial travel of theshaft480 in therecess488.
• Thecontact surface481 of theshaft480 is pushed against the surface of thedura mater20 with a predictable force by means of aspring486. Thespring486 may be substantially the same as thespring454 shown inFIG. 12, and the various materials suggested above for thespring454 may also be employed in thespring486 ofFIG. 13.
• InFIG. 12, thespring454 provides the electrical connection between the lead468 and theshaft452. In the embodiment ofFIG. 13, however, thelead496 may be connected directly to theshaft480 through alumen495 in thebody490. Thislumen495 is sized to slidably receive a reduced-diameter neck482 of theshaft480. As thebody490 is screwed into theskull10 and moves toward thebrain25, contact between theshaft480 and thedura mater20 will urge theshaft480 upwardly, moving theneck482 upwardly within thelumen495.
• Theelectrode475 ofFIG. 13 may facilitate delivering a highly reproducible contact force of thecontact surface481 of theshaft480 against thedura mater20. The position of the reduced-diameter neck482 of theshaft480 within thelumen495 will vary in a fixed relationship with the force exerted on thespring486 by theshaft480. Since the force of theshaft480 against thespring486 is essentially the same as the force of theshaft480 against thedura mater20, knowing the position of theneck482 within thelumen495 can give the operator an indication of the force exerted against thedura mater20. In one particular embodiment, the interior of thelumen495 may be graduated to mark off the depth of theneck482 in thelumen495. In another embodiment, thebody490 may be driven into theskull10 until the height of theneck482 in thelumen495 reaches a predetermined point, e.g., when the top of theneck482 is flush with the top of thebody490.
• FIG. 14 illustrates anintracranial electrode500 in accordance with still another embodiment of the invention. Thiselectrode500 includes an electrically conductive probe orshaft510 having ahead512 and acontact surface515. A radiallycompressible retaining collar540 extends along a portion of the length of theshaft510. As shown inFIG. 15, the retainingcollar540 may be adapted to assume a radially reduced configuration in response to a compressive force, indicated schematically by the arrows F. This compressive force F may be generated by collapsing the retainingcollar540 and restraining it in the lumen of an introducing sheath (not shown) sized to be received in a bore through theskull10. When this force F is removed (e.g., by retracting the introducing sheath), the retainingcollar540 may expand radially outwardly away from theshaft510, as illustrated inFIG. 16.
• To implant theelectrode500 in theskull10, theshaft510 may be advanced into a bore in the skull until thecontact surface515 exerts the desired contact force against thedura mater20. Once theshaft510 is in the desired position, the compressive force F on thecollar540 may be released, allowing thecollar540 to expand outwardly into compressive engagement with the lumen of the bore in theskull10. This will help hold theelectrode500 in place with respect to the skull without requiring permanent anchoring of theshaft510 to theskull10.
• Theshaft510 may be electrically coupled to a pulse system (not shown) by alead520. Thelead520 may include acap522 having an electrically conductiveinner surface524 coupled to abody526 of the lead. Thelead520 may be analogous to thelead160 shown in FIGS.3A-B. Any other suitable electrical connection between theshaft510 and the pulse system may be employed.
• In one embodiment, thecollar540 comprises a dielectric material. This will help electrically insulate theskull10 from theshaft510. In another embodiment, thecollar540 is electrically conductive and thelead520 may be electrically coupled to theshaft510 via thecollar540.
• In the embodiment shown inFIG. 14, theshaft510 may have a length only a little longer than the thickness of the patient'sskull10 and thecontact surface515 may be relatively blunt. Such a design is useful for relatively atraumatic contact with thedura mater20. In another embodiment suggested in dashed lines inFIGS. 15 and 16, theelectrode500 may instead have a substantiallylonger shaft510aand a relativelysharp contact surface515a. Such an embodiment may be useful for directly stimulating a particular location within the cerebral cortex or some other location within the deeper tissues of the brain.
• FIG. 17 schematically illustrates how certain principles of the invention can be embodied in a subcortical or deep brainintracranial electrode550. Theelectrode550 generally includes a threadedshaft560 having ahead562. Thehead562 may be coupled to a pulse system or a sensing unit (as described below) via alead160 in the same manner lead160 is attached to thehead152 ofelectrode150 in FIGS.3A-B. (Like reference numbers are used in these figures to indicate like elements.) Theelectrode550 also includes an elongateconductive member570 that extends inwardly from theskull10 to a selectedtarget site28. Theconductive member570, which may comprise a length of a conductive wire, may be electrically shielded by a dielectric sheath along much of its length and have an exposed, electricallyconductive tip574.
• In use, theconductive member570 may be slid freely through apilot hole11 formed through the skull to position thetip574 at thetarget site28 in a known manner. Thepilot hole11 may be larger than theconductive member570 or be tapped to receive the threads of theshaft560. With theconductive member570 in place, theshaft560 may be threaded into thepilot hole11, crimping theconductive member570 against an interior of thepilot hole11. This will fix theconductive member570 in place. If so desired, aproximal length572 of theconductive member570 may extend outwardly of the skull and be held in place by thehead562. The threads of the threadedshaft560 may also cut through the dielectric sheath of theconductive member570 as theshaft560 is screwed into place, making electrical contact with the conductive wire therein.
• FIG. 18 schematically illustrates a subcortical or deep brainintracranial electrode600 in accordance with an alternative embodiment of the invention. Thiselectrode600 includes ahead610 having a threadedshaft620 with an axially-extendingopening622 extending through the length of thehead610. Thehead610 may also include a gimbal fitting630 adapted to slidably receive a length of a conductive member, which may comprise the same type of elongateconductive member570 discussed above in connection withFIG. 17.
• The gimbal fitting630 is adapted to allow an operator greater control over the placement of the electricallyconductive tip574 of theconductive member570. In use, thetip574 of theconductive member570 will be threaded through an opening in thegimbal fitting630. By pivoting the gimbal fitting630 with respect to the threadedshaft620 of thehead610, the angular orientation of theconductive member570 with respect to thepilot hole11 in theskull10 can be accurately controlled. Once the operator determines that theconductive member570 is at the appropriate angle, e.g., using a surgical navigation system such as that noted below, the operator may advance theconductive member570 to position theconductive tip574 at thetarget site28. Once thetip574 is in position, thecap162 of a lead160 may be press-fitted on thebody610 of theelectrode600. This will crimp theproximal length572 of theconnective member570 between thebody610 and the conductiveinner surface163 of thecap162, providing an effective electrical connection between theconductive member570 and thebody164 of thelead160.
• FIGS. 27-29 schematically illustrate intracranial electrodes that form portions of signal transmission systems in accordance with further embodiments of the invention. InFIG. 27, an electrode700 comprises a body (e.g., a support body) that includes ahead702 coupled to ashaft710. The body of the electrode700 may be integrally formed of an electrically conductiveinner core708 clad with a biocompatible electrically insulating material712. In the illustrated embodiment, the electricallyconductive portion708 of the electrode700 extends along the length of both thehead702 and theshaft710. Anelectrical lead720 may be coupled to theelectrode core708 to facilitate electrical signal transfer, for example, for electrical stimulation and/or monitoring. In certain embodiments, thelead720 may be coupled to a pulse generator. An electrical contact orcontact portion704 transmits electrical signals to and/or from thebrain tissue25. Theelectrical contact portion704 can be integral with or connected to the conductiveinner core708. In the particular embodiments shown inFIGS. 27-29, the electrical contact portions are housed within an insulative body. Electrical contact portions in accordance with other embodiments of the invention can have other arrangements (e.g., they can form part of a larger, generally conductive element).
• FIG. 28 illustrates anotherintracranial electrode750 in accordance with an embodiment of the invention. In this embodiment, the body ofelectrode750 may comprise a biocompatibleelectrically insulating material765 containing a set of biocompatible, electricallyconductive contacts760aand760b. The electricallyconductive contacts760aand760bmay be carried by different portions of theelectrode750 to facilitate production of particular types of electric field distributions. In one embodiment, afirst contact760amay be carried by thehead762, and a second contact760bmay be carried by a distal portion of theshaft755, which may be configured to be in electrical contact with a stimulation site. A lead770 may comprise lead wires orlinks772 and774 to provide electrical signal pathways to thecontacts760aand760b.
• FIG. 29 illustrates yet another embodiment of an intracranial electrode780. In the embodiment shown, the intracranial electrode780 may compriseelectrical contacts796 and798 that are carried by a distal portion of ashaft785. Ahead782 can stabilize theshaft785 relative to theskull10. A lead790 may comprise lead wires orlinks792 and794 that are electrically coupled to one ormore contacts796 and798. Suchlead wires792 and794 may facilitate electrical stimulation and/or monitoring using one or bothcontacts796 and798.
• In an embodiment shown inFIG. 29, theshaft785 can carry twocontacts796,798, and in other embodiments, theshaft785 can carry more or fewer contacts. The diameter of theshaft785 can be selected based on factors that include the number of contacts carried by theshaft785. In particular embodiments, theshaft785 can have a diameter of from about 0.5 millimeters to about 3.0 centimeters. In other embodiments, the diameter of theshaft785 can have other values. Theshaft785 can be inserted into the skull in a manner that is consistent with the diameter of theshaft785. For example,smaller shafts785 can be inserted through a burr hole in theskull10, andlarger shafts785 can be inserted using a craniotomy procedure.
• FIGS. 30 and 31 schematically illustrate other embodiments of the invention that may be applicable to cortical, subcortical, and/or deep brain stimulation and/or monitoring situations. Such embodiments may facilitate stimulation and/or monitoring involving surface or cortical tissues and/or subcortical or deep brain tissues. InFIGS. 30 and 31, like reference numbers may correspond to identical, essentially identical, or analogous elements. One embodiment of a combinedintracranial electrode assembly800 is shown in FIG.30. The combinedintracranial electrode assembly800 comprises afirst electrode810 and asecond electrode820. The first andsecond electrodes810 and820 may be configured and dimensioned for placement relative to physically distinct locations of the brain. For example, thefirst electrode810 may be in contact with thedura20, while thesecond electrode820 may be positioned relative to a subcortical or deep brain location.
• In one embodiment, thefirst electrode810 comprises at least oneelectrical contact815 carried by a distal portion of ashaft816. Afirst lead wire830 may be coupled to the first electrode'scontact815. Thesecond electrode820 may comprise anelongate member822 that carries one or more conductive portions, sections, segments, and/orcontacts825, in a manner identical, essentially identical, or analogous to that described above. Asecond lead wire835 may be coupled to the second electrode's contact(s)825. The length of thesecond electrode820, the position of one ormore contacts825 carried by thesecond electrode820, and/or theparticular contacts825 that are electrically active at any given time may depend upon a targeted tissue type or location and/or establishment of a desired type of stimulation and/or monitoring configuration. In one embodiment, eachelectrode810,820 can provide independently controlled stimulation signals. In another embodiment, one of theelectrodes810,820 can be coupled to a transmitter to provide stimulation signals to the patient, and the other can be coupled to a sensor to receive diagnostic signals from the patient. Theelectrodes810,820 can be coupled to a common ground, or can be coupled to independent grounds.
• FIG. 31 illustrates an embodiment of anintracranial electrode assembly800 wherein afirst electrode810 comprises at least oneelectrical contact817 carried by ahead812. Although thecontact817 is shown spanning a proximal surface portion of thehead812, it is to be appreciated that thecontact817 may be located along, upon, and/or within various portions of thehead812. In one embodiment, thefirst electrode810 comprises ashaft816 that need not touch or rest against neural tissue such as thedura20. Rather, theshaft816 may be shorter than in an embodiment such as shown inFIG. 30. In another embodiment, afirst electrode810 may include a contact815 (FIG. 30) carried by theshaft816 in addition to thecontact817 carried by thehead812. Such an embodiment may include an additional lead wire (not shown).
• In a manner identical, essentially identical, or analogous to other embodiments described herein, a combinedelectrode assembly800 may be comprised of one or more electrically nonconductive portions along with one or more electrically conductive portions. In one embodiment,nonconductive portions814 and822 of the first andsecond electrodes810 and820, respectively, may be formed from one or more biocompatible materials (e.g., plastic, silicone, and/or other materials), and conductive portions such as the first and second sets ofcontacts815 and825 may be formed from one or more biocompatible conductive materials (e.g., Titanium, Platinum, and/or other materials).
• Through appropriate electrical coupling, for example, by way ofleads830 and835, to an electrical source such as a pulse generator, one ormore contacts815 may be configured as an anode or a cathode, whileother contacts825 may respectively be configured as a cathode or an anode to facilitate bipolar and/or unipolar stimulation as further described below. For example, a combinedelectrode assembly800 may be implanted into a patient such that a local contact portion, which may comprise a distal portion of ashaft816, resides at, upon, or proximate to a stimulation site; while a remote contact portion, which may comprise adistal portion826 of anelongate member822, provides a remote or distant circuit completion site.
• In general, the applicability of one or more intracranial electrode embodiments to any given neural stimulation and/or monitoring situation may depend upon the location, depth, and/or spatial boundaries of target neural structures and/or target neural populations under consideration, which may depend upon the nature of a patient's neurological condition or disorder. The extent to which an electric field reaches, penetrates, and/or travels into and/or through target neural structures and/or a target neural population may affect neural stimulation efficiency and/or efficacy. Various intracranial electrode embodiments in accordance with the invention, for example, those described above with reference toFIGS. 27-31, may have conducting portions in various positions or locations, which may facilitate establishment of particular types of electric field distributions at one or more times.
• C. Systems Employing Intracranial Electrodes
• FIG. 19 is a schematic illustration of aneurostimulation system1000 in accordance with one embodiment of the invention. Thisneurostimulation system1000 includes anarray1010 of intracranial electrodes and an internallyimplantable pulse system1050. Thearray1010 of electrodes may employ one or more electrodes in accordance with any one or more of the embodiments described above in connection withFIGS. 2-18 and/or27-31 and/or any other suitable design. In the particular implementation depicted inFIG. 19, the array1010 (shown schematically inFIG. 20) includes a first implantableintracranial electrode100aand a second implantableintracranial electrode100b, each of which may be substantially the same as theelectrode100 shown in FIGS.2A-B. Theseelectrodes100band100bextend through theskull10 into contact with thedura mater20 at two spaced-apart locations.
• Thepulse system1050 may be implanted in the body of the patient P at a location remote from thearray1010 ofelectrodes100. In the embodiment shown inFIG. 19, thepulse system1050 is adapted to be implanted subclavicularly. In the alternative embodiment shown inFIG. 20, thepulse system1050 is adapted to be implanted in a recess formed in the patient'sskull10. In either embodiment, each of theelectrodes100 in thearray1010 is electrically coupled to thepulse system1050 by means of a separate lead (120 in FIGS.2A-B) having an elongate, subcutaneouslyimplantable body124. Hence,electrode100ais coupled to thepulse system1050 by theelongate body124aof a first lead and theother electrode100bis coupled to thepulse system1050 by theelongate body124bof another lead. In one embodiment, theelongate bodies124a-bare combined into a single subcutaneously implantable cable or ribbon.
• FIG. 21 schematically illustrates onepulse system1050 suitable for use in theneurostimulation system1000 shown inFIG. 19. Thepulse system1050 generally includes apower supply1055, anintegrated controller1060, apulse generator1065, and apulse transmitter1070. Thepower supply1055 can be a primary battery, such as a rechargeable battery or other suitable device for storing electrical energy. In alternative embodiments, thepower supply1055 can be an RF transducer or a magnetic transducer that receives broadcast energy emitted from an external power source and converts the broadcast energy into power for the electrical components of thepulse system1050.
• In one embodiment, thecontroller1060 includes a processor, a memory, and a programmable computer medium. Thecontroller1060, for example, can be a computer, and the programmable computer medium can be software loaded into the memory of the computer and/or hardware that performs the requisite control functions. In an alternative embodiment suggested by dashed lines inFIG. 21, thecontroller1060 may include an integrated RF ormagnetic controller1064 that communicates with anexternal controller1062 via an RF or magnetic link. In such a circumstance, many of the functions of thecontroller1060 may be resident in theexternal controller1062 and theintegrated portion1064 of thecontroller1060 may comprise a wireless communication system.
• Thecontroller1060 is operatively coupled to and provides control signals to thepulse generator1065, which may include a plurality of channels that send appropriate electrical pulses to thepulse transmitter1070. Thepulse generator1065 may have N channels, with at least one channel associated with each ofN electrodes100 in thearray1010. Thepulse generator1065 sends appropriate electrical pulses to thepulse transmitter1070, which is coupled to a plurality ofelectrodes1080. In one embodiment, each of these electrodes is adapted to be physically connected to thebody124 of a separate lead, allowing eachelectrode1080 to electrically communicate with asingle electrode100 in thearray1010 on a dedicated channel of thepulse generator1065. Suitable components for thepower supply1055, theintegrated controller1060, thepulse generator1065, and thepulse transmitter1070 are known to persons skilled in the art of implantable medical devices.
• As shown inFIG. 20, thearray1010 ofelectrodes100 inFIG. 19 comprises a simple pair ofelectrodes100aand100bimplanted in the patient's skull at spaced-apart locations.FIGS. 23-26 illustrate alternative arrays that may be useful in other embodiments. InFIG. 23, the array1010aincludes fourelectrodes100 arranged in a rectangular array. Thearray1010bofFIG. 24 includes sixteenelectrodes100, also arranged in a rectangular array. Thearray1010cshown inFIG. 25 includes nineelectrodes100 arranged in a radial array.FIG. 26 illustrates anarray1010dthat includes fourelectrodes100×arranged in a rectangular pattern and afifth electrode100yat a location spaced from the other fourelectrodes100x. In using such an array, the fourproximate electrodes100×may be provided with the same polarity and thefifth electrode100ymay have a different polarity. In some embodiments, the housing (1052 inFIG. 19) of thepulse system1050 may serve the function of thefifth electrode100y. The precise shape, size, and location of thearray1010 and the number ofelectrodes100 in thearray110 can be optimized to meet the requirements of any particular application.
• One ormore electrodes100 ofarrays1010 such as those described herein may be provided with electrical signals in a variety of spatially and/or temporally different manners. In some circumstances, oneelectrode100 or a subset of theelectrodes100 may have one electrical potential and adifferent electrode100 or subset of the electrodes100 (or, in some embodiments, thehousing1052 of the pulse system1050) may have a different electrical potential. U.S. patent application Ser. No. 09/978,134, entitled “Systems and Methods for Automatically Optimizing Stimulus Parameters and Electrode Configurations for Neuro-Stimulators” and filed 15 Oct. 2001 (the entirety of which is incorporated herein by reference), suggests ways for optimizing the control of the electrical pulses delivered to theelectrodes100 in anarray1010. The methods and apparatus disclosed therein may be used to automatically determine the configuration of therapy electrodes and/or the parameters for the stimulus to treat or otherwise effectuate a change in neural function of a patient.
• In general, neural stimulation efficiency and/or efficacy may be influenced by an extent to and/or manner in which neural stimulation reaches and/or travels into and/or through target neural structures and/or a target neural population, which may be affected by stimulation signal polarity, electrode configuration, and/or electrical contact configuration considerations. The particular neural structures and/or neural populations targeted at any time in a neural stimulation situation, and hence such considerations, may depend upon the nature, severity, and/or spatial boundaries of a patient's neurologic dysfunction.
• Various embodiments in accordance with the present invention may be configured to provide bipolar and/or unipolar stimulation at one or more times. Neural stimulation in which both an anode and a cathode are positioned, located, or situated within, essentially across, or proximate to a stimulation site may be defined as bipolar stimulation. Neural stimulation in which one of an anode and a cathode is positioned, located, or situated within or proximate to a stimulation site while a respective corresponding cathode or anode is positioned, located, or situated remote from the stimulation site to provide electrical continuity may be defined as unipolar, monopolar, or isopolar stimulation. Unipolar stimulation may alternatively or additionally be characterized by a biasing configuration in which an anode and a cathode are positioned, located, or situated in different neurofunctional areas or functionally distinct anatomical regions. Those skilled in the art will understand that an anode and a cathode may be defined in accordance with a first phase polarity of a biphasic or polyphasic signal.
• In a unipolar configuration, apulse system1050 may apply an identical polarity signal to each electrode or electrical contact positioned upon or proximate to one or more stimulation sites. Unipolar stimulation may be defined as anodal unipolar stimulation when an anode is positioned upon or proximate to a stimulation site or a target neural population; and as cathodal unipolar stimulation when a cathode is positioned upon or proximate to a stimulation site or a target neural population.
• In various situations, neural stimulation having particular stimulation signal and/or spatial and/or temporal characteristics (e.g., bipolar stimulation, cathodal or anodal unipolar stimulation, mixed-polarity stimulation, varying duty cycle stimulation, varying frequency stimulation, varying amplitude stimulation, spatially or topographically varying stimulation, theta burst stimulation, and/or other types of stimulation applied or delivered in a predetermined, pseudo-random, and/or aperiodic manner at one or more times and/or locations), possibly in association or conjunction with one or more adjunctive or synergistic therapies, may facilitate enhanced symptomatic relief and/or at least partial recovery from neurologic dysfunction.
• An adjunctive or synergistic therapy may comprise a behavioral therapy such as a physical therapy activity, a movement and/or balance exercise, an activity of daily living (ADL), a vision exercise, a reading task, a speech task, a memory or concentration task, a visualization or imagination exercise, an auditory activity, an olfactory activity, a relaxation activity, and/or another type of behavior, task, or activity; a drug or chemical substance therapy; and/or another therapy that may be relevant to a patient's functional state, development, and/or recovery.
• Neurologic dysfunction to which various embodiments of the present invention may be directed may correspond to, for example, motor, sensory, language, visual, cognitive, neuropsychiatric, auditory, and/or other types of deficits or symptoms associated with stroke, traumatic brain injury, cerebral palsy, Multiple Sclerosis, Parkinson's Disease, essential tremor, a memory disorder, dementia, Alzheimer's disease, depression, bipolar disorder, anxiety, obsessive/compulsive disorder, Post Traumatic Stress Disorder, an eating disorder, schizophrenia, Tourette's Syndrome, Attention Deficit Disorder, a drug addiction, autism, epilepsy, a sleep disorder, a hearing disorder, and/or one or more other states, conditions, and/or disorders. Depending upon embodiment details and/or the nature of a patient's neurologic dysfunction, at least partial symptomatic relief, functional recovery, and/or functional development may occur through mechanisms corresponding or analogous to Long Term Potentiation (LTP), Long Term Depression (LTD), neuroplastic change, and/or compensatory processes.
• FIG. 32 is a schematic illustration of an exemplary implantation configuration for aneural stimulation system1000 according to an embodiment of the invention. In one embodiment, aneural stimulation system1000 may comprise a set of intracranial electrodes100cand100dcoupled bylead wires124cand124dto apulse system1050. The intracranial electrodes100cand100dmay be surgically implanted at or relative to a set of target sites, and thepulse system1050 may be implanted beneath thescalp30 and adjacent to and/or partially within theskull10. In certain configurations, a particular separation between and/or relative positioning of two or more intracranial electrodes100cand100dmay be established, such that target electrode implantation or stimulation sites may correspond to anatomically remote and/or distinct regions. This may facilitate unipolar stimulation and/or stimulation of neural populations in different neural association areas, for example, different neurofunctional areas associated with motor skills or abilities; neurofunctional areas associated with motor and language skills; and/or neurofunctional areas associated with other skills.
• FIG. 33 is a schematic illustration of another exemplary implantation configuration for aneural stimulation system1000 according to an embodiment of the invention. Relative toFIG. 32, like reference numbers may indicate like, corresponding, and/or analogous elements. As inFIG. 32, a set of intracranial electrodes100eand100fmay be implanted or positioned relative to particular neurofunctional areas. In one embodiment, the set of electrodes100eand100fmay exhibit multiple types of electrical contact configurations, orientations, and/or geometries. For example, a particular electrode100emay carry an electrical contact C_ethat is distinctly different from one or more contacts C_fcarried by another electrode100f. Depending upon embodiment details, differences in contact configuration may facilitate establishment of particular types of electric field distributions, which may influence neural stimulation efficiency and/or efficacy.
• Various portions of the discussion herein focus on use of intracranial electrodes (e.g.,electrodes100,150,200,250,300,350,400,450,475,500,550, or600) in neurostimulation systems. In certain alternative applications, intracranial electrodes may additionally or alternatively be used to monitor electrical potentials, for example, in situations involving electroencephalography or electrocorticography. A suitable electroencephalograph may incorporate a system similar to theneurostimulation system1000 shown inFIG. 19, but a sensing unit (not shown) may be used in place of thepulse system1050. Suitable components for such a sensing unit are known to those skilled in the art of electroencephalography.
• FIG. 34A illustrates anintracranial electrode system900 in accordance with an embodiment of the invention. In one embodiment, theelectrode system900 comprises an electrical energy transfer mechanism (ETM)910 externally placed adjacent to a patient'sscalp30 to couple electrical energy from apulse generator1050 to anintracranial electrode920. Alead wire915 may couple theETM910 to thepulse generator1050. Thepulse generator1050 may be of an identical, essentially identical, analogous, or different type relative to apulse generator1050 shown inFIGS. 19-21.
• In some embodiments, theETM910 may comprise a conventional adhesive patch electrode commonly used for providing an electrical coupling to a particular location on a patient. Theintracranial electrode920 may comprise a head922 coupled to ashaft924. The head922 andshaft924 may be integrally formed of an electrically conductive material forming aconductive core925 that forms an electrical energy conduit. Theconductive core925 may extend throughout a portion or along the entire length of theelectrode920. Theconductive core925 may be carried by or encased in an electrically insulating material orcladding921. Theconductive core925 may extend from an upper orproximal contact surface925ato a lower or distal contact surface925b. Contact surfaces925aand925bprovide a signal exchange interface of theconductive core925. Theconductive core925 and the insulatingmaterial921 may vary in proportionate dimensions with one another accordingly.
• FIG. 34B is a cross sectional illustration of anETM910 according to an embodiment of the invention. In one embodiment, theETM910 comprises anenergy transfer patch912 that may have several layers. In general, anETM910 may comprise an outer flexible, insulating, and/or articulatedlayer916, an electricallyconductive layer914, and agel layer912. Theconductive layer914 may be comprised of a conductive material, such as aluminum for example, for carrying or conveying an electrical signal. Theconductive layer914 may be appropriately shaped (e.g., oval or elliptical) for conforming to a portion of the skull's rounded surface, and may be coupled to thelead wire915. Theconductive layer914 forms a portion of a conductive circuit between thelead wire915 and the conductive core925 (FIG. 34A).
• Theouter layer916 may be comprised of essentially any appropriate insulating nonconductive material as is known in the art (e.g., foam). Theouter layer916 may be smooth and flexible to facilitate contouring to the patient'sskin surface30. Thegel layer912, which may be placed in contact withscalp30, may comprise one or more of an electrically conductive coupling gel912a(such as a hydrogel or wet gel), an adhesive gel912b, and/or an anesthetic gel912c. Electrical coupling gel912amay be comprised of a saline composition for enhancing electrical conductivity and decreasing losses between theconductive layer914 andscalp30. The adhesive gel912baids in keeping theETM910 in place. An anesthetic gel912cmay be incorporated to possibly reduce or retard sensations that may result from the transfer of electrical signals from theETM910 throughscalp tissues30 to theelectrode920.
• FIG. 35 illustrates yet another embodiment of portions of anintracranial electrode system900. In one embodiment, an intracranial electrode930 comprises ahead932 and a shaft934 forming a body of the electrode930. The electrode930 may contain aconductive core925 having contact surfaces935aand935bfor conducting electrical energy through thescalp30 to a stimulation site such as thedura20. The conductive core935 may be clad with an electrically insulatingmaterial931. A portion of the insulatingmaterial931 may form one or more portions of the shaft934, which may contain threads935 for tapping into the cancellous18. As in certain previous embodiments having threads, intracranial electrode930 may be tapped into theskull10 to a desired depth. A bore, notch or groove933 may be formed in a proximal portion of thehead932 to facilitate tapping the electrode930 into place.
• FIG. 36 is an illustration of anintracranial electrode system900 according to an embodiment of the invention. A set of intracranial electrodes920 (shown aselectrodes920aand920b) may be implanted relative to one or more target sites withincancellous18. For purposes of simplicity, only twoelectrodes920 are shown; however, it is to be appreciated that additional orfewer electrodes920 may be employed. In some embodiments, ETMs910 (shown as ETMs910a,910b) may be placed proximate to eachelectrode920aand920b, external to the body and adjacent thescalp30. Such a set ofETMs910 may be coupled to thepulse generator1050 vialeads915aand915b. Depending upon embodiment details and/or a type of neurologic dysfunction under consideration, theintracranial electrode system900 may be configured to provide bipolar stimulation, as afirst electrode920amay have a first polarity and a second electrode920bmay have an opposing polarity as determined by electrical signals transmitted via correspondinglead wires915aand915b, respectively. Alternatively, each of theelectrodes920 may be biased with the same polarity in a unipolar configuration. In such a situation, a return electrode (not shown) may be placed in another location upon the patient's body; or one or more portions of the pulse generator's case may serve as a return electrode. The leads915a,915bcan be generally continuous (e.g., they can extend from the corresponding ETM910a,910bto thepulse generator1050 without a break, except for an optional releasable connection at the pulse generator1050).
• FIG. 37 is an illustration of a set of implantedintracranial electrodes940aand940baccording to an embodiment of the invention. In one embodiment, theintracranial electrodes940aand940bmay compriseheads942aand942bthat are eccentrically offset relative to a center axis A1 and A2 of an electrode shaft944aand944b, respectively. A first offset may be defined for afirst electrode940aby a first radius L1 and a second radius R1, where L1>R1. Likewise, a second offset may be defined for a second electrode940bhaving a head942bwith radii L2 and R2 where R2>L2. The offset radii may facilitate the placement ofintracranial electrodes940aand940bin close or generally close proximity to one another at a distance D, while keeping D at a minimum due to the shorter radii R1 and L2. The offset radii provide maximum distancing between the ETMs910aand910b. In a situation wherein several sets of electrodes may be needed for treatment, having electrodes with off center heads942aand942bmay provide better and/or more placement options when a plurality of electrodes are to be placed in close proximity to one another. Although a set of twointracranial electrodes940aand940bare shown, it is to be understood that larger sets may be employed depending on electrode dimensions and/or a number of stimulation sites under consideration. In any of these embodiments, theelectrodes940a,940bcan be secured relative to theskull10 by inserting each of theelectrodes940a,940binto a corresponding collar, e.g., acollar540 generally similar to that described above with reference toFIG. 14. The collar can be secured to the skull with one or more securement elements (e.g., threads).
• FIG. 38 illustrates anintracranial electrode950 according to another embodiment of the invention. In one aspect of this embodiment,electrode950 comprises a body formed of a head952 andshaft954, wherein the head952 and theshaft954 are formed with an obtuse angle θ at their juncture. The obtuse angle θ provides the body of the electrode with a tapered, frustoconical shape that facilitates a more contoured, conformal implant within the cancellous18. The head952 may also be formed with a protrusion or protruded upper portion E. The protrusion E may be rounded for a more contoured abutment withscalp tissues30 to enhance patient comfort. The head952 may be contoured and/or tapered, and may be at least partially recessed within theskull10 to facilitate a more conformal positioning within the patient'sskull10. Furthermore, a recessed, contoured placement within theskull10 may provide a more aesthetically pleasing implant.
• An outer portion of theelectrode950 may be comprised of an insulatingcladding956 disposed around aconductive core955. Theconductive core955 can include a first electrical contact portion955aand a second conductive contact portion955b. It is to be appreciated by those of ordinary skill in the art that thecladding956 may be comprised of any suitable biocompatible electrically insulating material, such as, but not limited to, polymers and/or ceramic materials. Thecladding956 may contain a plurality ofpores957.Pores957 may encourage bone regeneration within and about the pores for a more friction enhanced and/or lasting placement within theskull10. In lieu ofpores957, an exterior portion of thecladding956 in contact with body tissues may also be formed with a roughened surface (not shown) that may encourage bone growth and/or regeneration. Such enhanced friction and intergrowth between thecladding956 and the cancellous18 may provide for a more secure and/or conformal placement, which may reduce or minimize positional migration of the implantedelectrodes950. Other embodiments (not shown) may include variations of thecladding957 having combinations of compatible insulative materials comprising the exterior; such as for example, an upper proximal portion of thecladding967 being comprised of a ring-like polymer insulator; and/or a distal or generally distal portion of thecladding967 being comprised of a ceramic insulator.
• FIG. 39 illustrates yet anotherintracranial electrode960 according to an embodiment of the invention. In one embodiment, theintracranial electrode960 comprises a body having ahead962 and ashaft964. One or more portions of thehead962 and/or theshaft964 may form a tapered transition region, such that a juncture of thehead962 and theshaft964 form an obtuse angle0. Theintracranial electrode960 may be surgically implanted within a patient'sskull10 such that a proximal portion (e.g., an end surface) of thehead962 is flush or substantially flush with an outer portion orlayer12 of theskull10. The entirety of theelectrode960 may be countersunk into a recess formed through theouter skull12 and cancellous18.
• Theintracranial electrode960 may also comprise acladding966 surrounding a conductive core965. Thecladding966, comprised of any suitable biocompatible material, may in some embodiments includerecesses967 which may encourage surroundingcancellous tissue18 to grow within and/or around therecesses967, thus forming an enhanced bonding between the implantedelectrode960 and theskull10. This modified bonding may discourage migration of theelectrode960.
• FIG. 40 illustrates anintracranial electrode system900 according to another embodiment of the invention. In one aspect of this embodiment, theintracranial electrode system900 comprises at least one intracranial electrode970 that includes a radio frequency identification (RFID) element, tag, or transponder971 and/or another type of proximity sensing and/or detecting device. The RFID element971 may be embedded within or carried by a portion of thehead972 and/orshaft974, for example, within an insulatingnon-conductive material973 forming a portion of thehead972. Insulatingmaterial973 may electrically insulate the RFID element971 from aconductive core975. Theconductive core975 may includecontact surface areas975aand975bthat couple to and/or comprise a portion of an electrical conduit that facilitates signal transfer or electrical communication between anETM910 and intended target tissues. TheETM910 is electrically coupled to apulse generator1050. In this embodiment, thepulse generator1050 may include an RFID unit1063 comprising an RFID reader configured to identify one or more RFID elements971 to either allow/enable or disallow/disable electrical signal transmissions to particular intracranial electrodes970 at one or more times.
• The RFID unit1063 may comprise an RFID reader that may include a transmitter and a receive module, a control unit, and a coupling element (e.g., an antenna). The reader may have three functions: energizing, demodulating, and decoding. In addition, a reader can include or be fitted with an interface that converts RF signals returned from an RFID element971 into a form that can be passed on to and/or processed by other elements (e.g., a controller1060) associated with thesystem900.
• The RFID element971 may comprise an integrated circuit that is activated when placed in a transmitting field of the RFID unit1063. The transmitting field may vary depending on specifications of the RFID element971 and/or RFID unit1063. When anETM910 is placed proximate to the intracranial electrode970, the RFID unit1063 may emit an RF signal that may used to power up the electrode's RFID element971. In one embodiment, in the event that an RFID element971 corresponds to or provides a particular code and/or other information, electrical signal transmission between thepulse generator1050 and theETM910, and hence to the electrode970, may be allowed. Such an embodiment may facilitate enhanced security neural stimulation.
• The above descriptions of embodiments of the invention are not exhaustive and it is to be appreciated that, although not detailed in every instance, certain characteristics of some embodiments may be applicable to other embodiments. Various embodiments may include characteristics that are identical, essentially identical, or analogous to those described in relation to other embodiments. For example, regarding various embodiments ofFIGS. 27-40, one or more of the following may be incorporated therewith in a manner that is identical, essentially identical, and/or analogous to that described above: an adjunct sleeve may serve as an anchor surrounding an electrode as discussed with reference toFIG. 4B; a dielectric member may be included with an insulating layer as discussed with reference toFIGS. 3A, 4A, and14; one or more mechanisms for adjusting the overall length of the electrode as discussed with reference toFIGS. 6-13 may be included; an electrode may have a compressible retaining collar as discussed with reference toFIG. 14; an electrode may have a sharper contact surface as discussed with reference toFIGS. 14 and 15; and/or thesecond electrode820 of the intracranial electrode system ofFIGS. 30 and 31 may have a gimbal type fitting, as discussed with reference toFIG. 18.
• D. Methods
• As noted above, other embodiments of the invention provide methods of implanting an intracranial electrode and/or methods of installing a neurostimulation system including an implantable intracranial electrode. In the following discussion, reference is made to the particularintracranial electrode100 illustrated in FIGS.2A-B and to theneurostimulation system1000 shown inFIG. 19. It should be understood, though, that reference to this particular embodiment is solely for purposes of illustration and that the methods outlined below are not limited to any particular apparatus shown in the drawings or discussed in detail above.
• As noted above, implanting conventional cortical electrodes typically requires a full craniotomy under general anesthesia to remove a relatively large (e.g., thumbnail-sized or larger) window in the skull. Craniotomies are performed under a general anesthetic and subject the patient to increased chances of infection.
• In accordance with one embodiment of the present invention, however, the diameter of theelectrode shaft110 is sufficiently small to permit implantation under local anesthetic without requiring a craniotomy. In this embodiment, a relatively small (e.g., 4 mm or smaller) pilot hole may be formed through at least part of the thickness of the patient's skull adjacent a selected stimulation or monitoring site of the brain. When implanting theelectrode100 of FIGS.2A-B, it may be advantageous to extend the pilot hole through the entire thickness of the skull. Care should be taken to avoid undue trauma to the brain in forming the pilot hole. In one embodiment, an initial estimate of skull thickness can be made from MRI, CT, or other imaging information. A hand-held drill may be used to form a bore shallow enough to avoid extending through the entire skull. A stylus may be inserted into the pilot hole to confirm that it strikes relatively rigid bone. The drill may then be used to deepen the pilot hole in small increments, checking with the stylus after each increment to detect when the hole passes through the thickness of theinner cortex14 of theskull10. If so desired, the stylus may be graduated to allow a physician to measure the distance to the springy dura mater and this information can be used to select anelectrode100 of appropriate length or, if an adjustable-length electrode (e.g.,electrode300 of FIGS.6A-B) is used, to adjust the electrode to an appropriate length.
• The location of the pilot hole (and, ultimately theelectrode100 received therein) can be selected in a variety of fashions. U.S. Patent Application Publication No. US 2002/0087201 and U.S. application Ser. No. 09/978,134 (both of which are incorporated hereinabove), for example, suggest approaches for selecting an appropriate stimulation site. When the desired site has been identified, the physician can bore the pilot hole to guide thecontact surface115 of theelectrode100 to that site. In one embodiment, the physician may use anatomical landmarks, e.g., cranial landmarks such as the bregma or the sagittal suture, to guide placement and orientation of the pilot hole. In another embodiment, a surgical navigation system may be employed to inform the physician during the procedure. Briefly, such systems may employ real-time imaging and/or proximity detection to guide a physician in placing the pilot hole and in placing theelectrode100 in the pilot hole. In some systems, fiducials are positioned on the patient's scalp or skull prior to imaging and those fiducials are used as reference points in subsequent implantation. In other systems, real-time MRI or the like may be employed instead of or in conjunction with such fiducials. A number of suitable navigation systems are commercially available, such as the STEALTHSTATION TREON TGS sold by Medtronic Surgical Navigation Technologies of Louisville, Colo., US.
• Once the pilot hole is formed, the threadedelectrode100 may be advanced along the pilot hole until thecontact surface115 electrically contacts a desired portion of the patient's brain. If theelectrode100 is intended to be positioned epidurally, this may comprise relatively atraumatically contacting thedura mater20; if the electrode is to contact a site on the cerebral cortex, the electrode will be advanced to extend through the dura mater. Theelectrodes100 may also be implanted to a selected depth within the cerebral cortex or at a deeper location in the brain.
• In one embodiment, the length of theelectrode100 is selected (or adjusted forelectrode300, for example) to achieve the desired level of contact and the electrode will be advanced until a known relationship with the skull is achieved, e.g., when thehead102 compresses thecontact ring122 of thelead120 against the exterior of theskull10. In another embodiment, the thickness of theskull10 need not be known to any significant accuracy before theelectrode100 is implanted. Instead, theelectrode100 may be connected, e.g., via thelead120, to an impedance monitor and the impedance may be monitored as theelectrode100 is being implanted. It is anticipated that the measured impedance will change when theelectrode100 contacts thedura mater20. Once this contact is detected, the physician may advance the electrode a small, fixed distance to ensure reliable electrical contact over time.
• As noted above, theelectrode100 may be coupled to alead120. The timing of this coupling may vary with the nature of the coupling. For a lead120 employing acontact ring122 or the like positioned below thehead102, the lead may be coupled to the electrode before the electrode is introduced into the skull. In other embodiments, the lead (e.g., lead160 of FIGS.3A-B) may be coupled to the electrode after the electrode is properly positioned with respect to the selected site of the brain. The lead, or at least a length thereof, may be implanted subcutaneously, e.g., by guiding it through a tunnel formed between the implant site and the intended site of a subclavicularly implantedpulse system1050. The patient's scalp may then be closed over thehead102 of theelectrode100 so the electrode is completely enclosed. This can materially improve patient comfort compared to more conventional systems wherein epilepsy monitoring electrodes or the like extend through the scalp to an extracorporeal connection.
• Additionally or alternatively, implant depth may be measured, estimated, or indicated through the use of a depth measurement device or apparatus.FIG. 41 is a schematic illustration of a depth measurement apparatus175 (e.g., a depth acquisition stick or DAS) and a set of intracranial electrodes I₁-I₄. In one embodiment, an appropriate electrode length may be determined by performing a depth measurement procedure using thedevice175. Thedevice175 may be inserted into a surgically formedpilot hole11. Thedevice175 may contain indicia comprising a plurality of calibrated indicators d1-d4, which provide linear measurements as to the depth of thepilot hole11. Thedevice175 may have a retainer cuff and/or sleeve176 that aids in keeping thedevice175 in an upright position for accurate depth measurements.
• Depending on the depth of thepilot hole11, intracranial electrodes11-14 may have shafts of varying lengths S₁-S₄that correspond to the demarcated indicators d₁-d₄. For example, the shaft of intracranial electrode I₁, may have a length S₁associated with a distance d, indicated on thedevice175. Likewise, intracranial electrodes I₂, I₃and I₄may be associated with distances d₂, d₃, and d₄, respectively. The depths of the pilot holes11 may vary from patient to patient depending on such variables as the age of the patient and/or an implant location in theskull10.
• FIG. 42 is a flowchart illustrating adepth acquisition procedure2000 according to an embodiment of the invention. In one embodiment, adepth acquisition procedure2000 may comprise an accessingprocedure2010 that involves surgically accessing an implantation or stimulation site. An accessing procedure may utilize a surgical navigational system and/or anatomical landmarks, as discussed above, to aid in making apilot hole11 in one or more appropriate locations. Thedepth acquisition procedure2000 may further comprise aninsertion procedure2020 that may involve insertion of a depth acquisition apparatus such as device175 (FIG. 41) into apilot hole11. As discussed above, thedevice175 may be provided with indicia corresponding to demarcations or units of length (e.g., millimeters). Thedepth acquisition procedure2000 may additionally comprise ameasurement procedure2030 that involves measuring or comparing the depth of ahole11 relative to a calibrated indicia on a measurement device, e.g., thedevice175. As discussed above, thedevice175 may have calibrations corresponding to a set of shaft lengths of a series of electrodes. Thedepth acquisition procedure2000 may also comprise amapping procedure2040 that involves mapping or correlating a measurement depth associated with apilot hole11 to a corresponding electrode, for example, one of intracranial electrodes I₁-I₄. Adepth acquisition procedure2000 may additionally comprise aselection procedure2050 that involves selecting an electrode characterized by an appropriate length or dimension for implantation.
• Once anelectrode100 is in place, an electrical stimulus may be delivered from apulse system1050 to the patient's brain via alead120 and theelectrode100. In certain embodiments of the invention discussed previously, a plurality ofelectrodes100 may be implanted in an array (e.g.,array1010,1010a,1010b, or1010c) in the patient's skull and each of theelectrodes100 may be coupled to thepulse system1050 by an electricallyseparate lead120. The precise nature of the stimulus delivered via the electrode(s)100 can be varied as desired to diagnose or treat a variety of conditions. The type, pattern, and/or frequency of stimulus may be selected in a manner identical, essentially identical, or analogous to or different from that outlined in U.S. Patent Application Publication No. US2002/0087201, for example, and/or may be optimized in a manner described in U.S. application Ser. No. 09/978,134.
• Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in a sense of “including, but not limited to.” Words using the singular or plural number also include the plural or singular number, respectively. When the claims use the word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.
• The above-detailed descriptions of embodiments of the invention are not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, whereas steps are presented in a given order, alternative embodiments may perform steps in a different order. Aspects of the invention described in the context of particular embodiments can be combined or eliminated in other embodiments.
• In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above-detailed description explicitly defines such terms. While certain aspects of the invention are presented below in certain claim forms, the inventors contemplate the various aspects of the invention in any number of claim forms. Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the invention.

Claims (58)

1. An intracranial signal transmission system, comprising:

a generally electrically insulating support body having a head portion configured to be positioned at least proximate to an outer surface of a patient's skull, the support body further having a shaft portion configured to extend into an aperture in the patient's skull; and

at least one electrical contact portion carried by the support body, the at least one electrical contact portion being positioned to transfer electrical signals to, from, or both to and from the patient's brain via the aperture in the patient's skull.

2. The system ofclaim 1 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, and wherein the system further comprises:

a signal transmitter operatively coupled to the first electrical contact portion to provide stimulation signals to the patient's brain; and

a sensor operatively coupled to the second electrical contact portion to receive signals from the patient's brain.

3. The system ofclaim 1 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion.

4. The system ofclaim 1, further comprising:

an electrical signal transmitter; and

a generally continuous electrical signal path connected between the electrical signal transmitter and the at least one electrical contact portion.

5. The system ofclaim 1, further comprising:

an electrical signal transmitter; and

an electrical signal path having a releasable connection at the electrical signal transmitter and being continuous between the releasable connection and the at least one electrical contact portion.

6. The system ofclaim 1 wherein the at least one electrical contact portion includes a first electrical contact portion coupleable to at least one signal transmitter to receive first electrical signals, and a second electrical contact portion coupleable to at least one signal transmitter to receive second electrical signals independent of the first electrical signals.

7. An intracranial signal transmission system, comprising:

an electrical contact portion configured to be positioned in an aperture of a patient's skull; and

an electrical energy transfer device configured to be releasably positioned external to the patient's scalp, the energy transfer device being coupleable to a signal transmitter to transmit signals to the electrical contact portion while the electrical contact portion is positioned beneath the patient's scalp and while the energy transfer device is positioned external to the patient's scalp.

8. The system ofclaim 7 wherein the electrical energy transfer device includes:

a flexible outer layer;

an adhesive gel layer positioned to contact the patient's scalp;

a conductive layer positioned between the outer layer and the adhesive gel layer; and

a conductive lead connected to the conductive layer.

9. The system ofclaim 7 wherein the electrical contact portion includes a first electrical contact portion and wherein the system further comprises:

a second electrical contact portion spaced apart from the first electrical contact portion;

a signal transmitter operatively coupled to the first electrical contact portion to provide stimulation signals to the patient's brain; and

a sensor operatively coupled to the second electrical contact portion to receive signals from the patient's brain.

10. The system ofclaim 7 wherein the electrical contact portion includes a first electrical contact portion and wherein the system further comprises a second electrical contact portion spaced apart from the first electrical contact portion.

11. The system ofclaim 7, further comprising:

an electrical signal transmitter; and

a generally continuous electrical signal path connected between the electrical signal transmitter and the at least one electrical contact portion.

12. The system ofclaim 7 wherein the electrical contact portion includes a first electrical contact portion coupleable to at least one signal transmitter to receive first electrical signals, and wherein the system further comprises a second electrical contact portion coupleable to at least one signal transmitter to receive second electrical signals independent of the first electrical signals.

13. The system ofclaim 7 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, the first electrical contact portion having a first position relative to the support body so as to be positioned beneath the scalp by a first distance, the second electrical contact portion having a second position relative to the support body so as to be positioned beneath the scalp by a second distance greater than the first distance.

14. An intracranial signal transmission system, comprising:

a shaft configured to extend through an aperture in a patient's skull;

a head connected to the shaft, the head being configured to be positioned adjacent to an external surface of the patient's skull, the head being eccentrically positioned relative to the shaft and having a first portion extending outwardly from the shaft by a first distance and a second portion extending outwardly from the shaft by a second distance different than the first distance; and

an electrical contact portion carried by at least one of the shaft and the head.

15. The system ofclaim 14, further comprising an insert having an outer surface and aperture, the aperture being sized to receive the shaft, the outer surface having at least one securement element configured to secure the insert to the patient's skull.

16. The system ofclaim 14, further comprising an insert having an outer surface and aperture, the aperture being sized to receive the shaft, the outer surface having threads configured to secure the insert to the patient's skull.

17. An intracranial signal transmission system, comprising:

a shaft having an external surface configured to extend through an aperture in a patient's skull;

a head connected to the shaft and having a generally conical shape, with an angle between the external surface of the shaft and an external surface of the head being obtuse, and with the external surface of the head being configured to contact the walls of the aperture in the patient's skull; and

an electrical contact portion carried by at least one of the shaft and the head.

18. The system ofclaim 17 wherein the shaft has a first end surface and the head has a second end surface facing generally opposite form the first end surface, and wherein the second end surface is positioned to be flush with an outer surface of the patient's skull.

19. The system ofclaim 17 wherein the shaft has a first end surface and the head has a second end surface facing generally opposite form the first end surface, and wherein the second end surface is positioned to project outwardly from an outer surface of the patient's skull.

20. The system ofclaim 17 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, and wherein the system further comprises:

a signal transmitter operatively coupled to the first electrical contact portion to provide stimulation signals to the patient's brain; and

a sensor operatively coupled to the second electrical contact portion to receive signals from the patient's brain.

21. The system ofclaim 17 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion.

22. The system ofclaim 17, further comprising:

an electrical signal transmitter; and

a generally continuous electrical signal path connected between the electrical signal transmitter and the at least one electrical contact portion.

23. An intracranial signal transmission system, comprising:

a shaft configured to extend through an aperture in a patient's skull, the shaft having an external surface with a plurality of surface features positioned to receive growing bone tissue from the patient's skull;

a head connected to the shaft; and

an electrical contact portion carried by at least one of the shaft and the head.

24. The system ofclaim 23 wherein the surface features are recessed from the external surface of the shaft.

25. The system ofclaim 23 wherein the surface features include pores.

26. The system ofclaim 23 wherein the surface features include pores recessed from the external surface and, and wherein walls of the pores are positioned to be out of contact with walls of the aperture in the patient's skull as the shaft is positioned in the aperture.

27. The system ofclaim 23 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, the first electrical contact portion having a first position relative to the head so as to be positioned beneath the scalp by a first distance, the second electrical contact portion having a second position relative to the head so as to be positioned beneath the scalp by a second distance greater than the first distance.

28. An intracranial signal transmission system, comprising:

a shaft configured to extend through an aperture in a patient's skull;

a head connected to the shaft;

an electrical contact portion carried by at least one of the shaft and the head;

a radio frequency transponder carried by at least one of the shaft; and

at least one securement feature depending from at least one of the head and the shaft and being positioned to secure at least one of the head and the shaft to the patient's skull.

29. The system ofclaim 28, further comprising:

a signal transmitter coupled to the electrical contact portion with a signal link;

a radio frequency receiver configured to receive signals from the transponder, the radio frequency receiver being coupled to the signal transmitter to control signals transmitted to the electrical contact portion based on signals received from the transponder.

30. The system ofclaim 28 wherein the shaft and the head are formed from a generally electrically insulating material.

31. The system ofclaim 28, further comprising a radio frequency receiver configured to receive signals from the transponder.

32. A method for installing an electrical contact portion in a patient's skull, comprising:

drilling a hole in a patient's skull;

determining a distance from an outer surface of the patient's skull to a feature beneath the outer surface of the patient's skill by inserting an elongated member having graduation makings into the pilot hole;

selecting a size of an intracranial electrode based on the distance determined with the elongated member;

inserting the intracranial electrode into the hole; and

securing the intracranial electrode to the patient's skull.

33. The method ofclaim 32 wherein drilling a hole includes drilling a pilot hole, and wherein the method further comprises increasing a diameter of the hole prior to inserting the intracranial electrode into the hole.

34. A method for transmitting intracranial electrical signals, comprising:

positioning a generally electrically insulating support body proximate to a patient;

inserting a shaft portion of the support body into an aperture in the patient's skull;

positioning a head portion of the support body at least proximate to an outer surface of a patient's skull; and

transmitting electrical signals to, from or both to and from the patient's brain through the aperture in the patient's skull via at least one electrical contact portion carried by the support body.

35. The method ofclaim 34 wherein transmitting electrical signals includes transmitting electrical stimulation signals to a first electrical contact portion carried by the support body and receiving sensor signals from a second electrical contact portion carried by the support body, the second electrical contact portion being spaced apart from the first electrical contact portion.

36. The method ofclaim 34 wherein transmitting signals via at least one electrical contact portion includes transmitting signals via a first electrical contact portion carried by the support body and a second electrical contact portion carried by the support body, the second electrical contact portion being spaced apart from the first electrical contact portion.

37. The method ofclaim 34 wherein transmitting signals includes transmitting signals along a generally continuous electrical signal path connected between an electrical signal transmitter and the at least one electrical contact portion.

38. The method ofclaim 34 wherein transmitting signals via at least one electrical contact portion includes transmitting a first electrical signal via a first electrical contact portion carried by the support body and transmitting a second electrical signal via a second electrical contact portion carried by the support body, the second electrical contact portion being spaced apart from the first electrical contact portion, the first signal being independent of the second signal.

39. The method ofclaim 34 wherein the support body carries a first electrical contact portion and a second electrical contact portion, and wherein inserting a shaft portion of the support body includes positioning the first electrical contact portion a first distance beneath the scalp and positioning the second electrical contact portion a second distance beneath the scalp, the second distance being greater than the first distance.

40. A method for transmitting intracranial electrical signals, comprising:

disposing an electrode within an aperture in a patient's skull;

releasably positioning an electrical transmission device at least proximate to an external surface of the patient's scalp; and

transmitting an electrical signal through the patient's scalp between the electrode and the electrical transmission device.

41. The method ofclaim 40, further comprising drilling the aperture in the patient's skull.

42. The method ofclaim 40, further comprising adhering the electrical transmission device to the patient's scalp and wherein transmitting an electrical signal includes transmitting an electrical signal from a conductive layer positioned between an adhesive layer and a flexible outer layer of the electrical transmission device.

43. The method ofclaim 40 wherein transmitting an electrical signal includes transmitting a stimulation signal through the patient's scalp to the electrode.

44. The method ofclaim 40 wherein transmitting an electrical signal includes transmitting a sensor signal from the electrode through the patient's scalp.

45. A method for installing an intracranial signal transmission system, comprising:

positioning an electrical contact portion of the system proximate to the patient's head, the electrical contact portion being carried by a support body having a shaft portion and a head portion positioned eccentrically relative to the shaft portion;

inserting the shaft portion into an aperture in the patient's skull;

positioning at least some of the head portion external to the patient's skull;

orienting the head portion so that a first part of the head portion extends outwardly from the shaft by a first distance and a second part of the head portion extends outwardly from the shaft by a second distance different than the first distance; and

transmitting an electrical signal via the electrical contact portion.

46. The method ofclaim 45 wherein the electrical contact portion is a first electrical contact portion, the support body is a first support body, and the aperture is a first aperture, and wherein the method further comprises:

positioning a head portion of a second support body proximate to the patient's head, the second support body carrying a second electrical contact portion, the head portion of the second support body including a first part that extends outwardly from the shaft by a first distance and a second part that extends outwardly from the shaft by a second distance different than the first distance;

inserting a shaft of the second support body into a second aperture in the patient's skull, the second aperture being spaced apart from the first aperture; and

orienting a head portion of the second support body so that the first part of the head portion of the second support body is positioned toward the first part of the head portion of the second support body.

37. The method ofclaim 45, further comprising:

placing an insert into the aperture in the patient's skull;

placing the shaft of the support body in the an insert; and

securing the shaft to the insert.

48. A method for installing an intracranial signal transmission system, comprising:

forming an aperture in a patient's skull, the aperture having first generally conical portion with a first diameter at an external surface of the patient's skull, and a second portion with a second diameter smaller than the first diameter beneath the external surface;

disposing proximate to the aperture an electrical contact portion carried by a support body having a shaft and a head depending from the shaft, the head having generally conical shape, with an angle between an external surface of the shaft and an external surface of the head being obtuse; and

inserting the support body into the aperture so that the shaft extends through the second portion of the aperture and the head engages a wall of the aperture at the first portion of the aperture.

49. The method ofclaim 48 wherein the shaft has a first end surface and the head has a second end surface facing generally opposite form the first end surface, and wherein inserting the support body includes inserting the support body so that the second end surface is flush with the outer surface of the patient's skull.

50. The method ofclaim 48 wherein the shaft has a first end surface and the head has a second end surface facing generally opposite form the first end surface, and wherein inserting the support body includes inserting the support body so that the second end surface is positioned to project outwardly from the outer surface of the patient's skull.

51. The method ofclaim 48 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, and wherein the method further comprises:

transmitting a stimulation signal to the patient's brain via the first electrical contact portion; and

receiving a sensor signal from the patient's brain via the second electrical contact portion.

52. The method ofclaim 48 wherein the at least one electrical contact portion includes a first electrical contact portion and a second electrical contact portion spaced apart from the first electrical contact portion, and wherein the method further comprises:

transmitting a first stimulation signal to the patient's brain via the first electrical contact portion; and

transmitting a second stimulation signal to the patient's brain via the second electrical contact portion.

53. The system ofclaim 48, further comprising transmitting signals to, from, or both to and from the at least one electrical contact portion via a generally continuous electrical signal path.

54. A method for installing an intracranial signal transmission system, comprising:

forming an aperture in a patient's skull;

disposing proximate to the aperture an electrical contact portion carried by a support body, the support body having a shaft and a head depending from the shaft, the shaft having an external surface with a plurality of surface features;

inserting the shaft into the aperture; and

allowing the patient's bone tissue to grow into interengagement with the surface features.

55. The method ofclaim 54 wherein the surface features are recessed from the external surface of the shaft and wherein allowing the patient's bone tissue to grow includes allowing the patient's bone tissue to grow into the recesses.

56. The method ofclaim 54 wherein the surface features include pores and wherein allowing the patient's bone tissue to grow includes allowing the patient's bone tissue to grow into the pores.

57. A method for installing an intracranial signal transmission system, comprising:

forming an aperture in a patient's skull;

disposing proximate to the aperture an electrical contact portion carried by a support body having a shaft and a head depending from the shaft

inserting the shaft into the aperture;

securing the support body to the patient's skull; and

receiving signals from a radio frequency transponder carried by at least one of the shaft and the head.

58. The method ofclaim 57, further comprising controlling electrical stimulation signals transmitted to the electrical contact portion based on a signal received from the transponder.

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