Abstract:
A cortical sensing device is provided that includes a sensing element and at least one pad attached adjacent to a support member. The pad is substantially thin and made from flexibly-conformable material to accurately and safely place the sensing device upon the brain surface. Contact between the lower surface of the pad and the brain surface anchors the sensing element at a desired position against unintentional movement. The sensing device preferably has three circular pads equidistant from one another. A method to position a cortical sensing device upon a brain surface is also disclosed comprising the steps of providing a cortical sensing device having a sensing element and three dielectric pads attached to a support dielectric member where the member and the pads are thin and flexibly-conformable, placing the sensing device upon the brain surface at a desired position for sensing brain activity, and allowing the pads to conform to the brain surface so that interaction therebetween prevents movement of the sensing element along the brain surface.

Description:
FIELD OF THE INVENTION 
     This invention is related generally to intracranial sensing devices and, more particularly, to cortical sensing devices. 
     BACKGROUND OF THE INVENTION 
     Surgical removal of epileptogenic brain is indicated for the treatment of many medically refractory focal seizure disorders. Such surgery demands a high degree of accuracy in identifying the epileptogenic foci. Various methods have been used in attempting to determine the location of these foci, and all involve sensing cortical electrical activity using electrical contacts applied in various ways. 
     While scalp contacts were customarily used for many years to identify epileptogenic foci, accurate localization of the loci was usually very difficult with the recordings obtained from such contacts. Therefore, many medical centers in recent years have progressed to using intracranial recording techniques to better define regions of cortical epileptogenicity whereby the safety and effectiveness of epileptogenic brain removal is enhanced. 
     Intracranial recording techniques have typically involved one of two different types of sensing devices—intracortical depth electrodes or cortical strip electrodes. While depth electrodes are necessary in certain circumstances, techniques using cortical strip electrodes have been shown to be relatively safe and serve as valuable alternatives. 
     The relative safety of cortical strip electrodes lies in the fact that, unlike depth electrodes, they are not invasive of brain tissue. Depth electrodes are narrow, typically cylindrical dielectric structures with contact bands spaced along their lengths. Such electrodes are inserted into the brain in order to establish good electrical contact with different portions within the brain. Cortical strip electrodes, on the other hand, are flat strips that support contacts spaced along their lengths. Such strip electrodes are inserted between the dura and the brain, along the surface of and in contact with the brain, but not within the brain. 
     A cortical strip electrode has a flexible dielectric strip within which a plurality of spaced aligned flat contacts and their lead wires are enclosed and supported in place between front and back layers of the material forming the dielectric strip. Each flat contact has a face or main contact surface which is exposed by an opening in the front layer of the dielectric strip. Insulated lead wires, one for each contact, are secured within the strip and exit the strip from a proximal end. The dielectric material used in such cortical strip electrodes is typically a flexible, bio-compatible material such as silicone. 
     While the typical cortical strip electrode works fine in many situations, there are applications for which its structure is not well suited. For instance, monitoring may be desired at a variety of positions around the surface of the brain. The placement of a number of strip electrodes, with their associated multiple contacts, may be more than is necessary. Cortical sensing devices that allow sensing elements such as electrical contacts to be individually positioned at various positions around the brain surface in an easy and safe manner would be an improvement over the current state of the art. 
     One can appreciate that when a sensing element of a cortical sensing device is placed in contact with the cortex, it is critical that the sensing element remain in that same fixed position relative to the cortex since knowledge of its exact position is necessary to properly interpret the device&#39;s readings. The typical cortical electrode is, however, not well anchored or held in place at its desired position upon the brain without being sandwiched between the dura and the cerebral cortex. With these electrodes, it is hoped then that they will not be moved and, for this reason, precautions are often made so as not to disturb the externally positioned lead wires. Nevertheless, movement of the electrode can occur and this movement may even cause inadvertent penetration of the brain. Thus, there is a need for an improved cortical sensing device which can be anchored at a desired position such that it is much less likely to penetrate brain tissue inadvertently and better able to remain at its selected position upon the brain. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide an improved cortical sensing device that prevents injury to the patient. 
     Another object of the invention is to provide a cortical sensing device that is easy to place at a desired position on the brain surface. 
     Another object of the invention is to provide a cortical sensing device that anchors itself to the brain surface so as to prevent unintentional movement of the sensing device with respect to the brain surface. 
     Another object of the invention is to provide a cortical sensing device that provides a large surface area contacting the brain. 
     Another object of the invention to provide a method of accurately positioning a cortical sensing device upon the brain surface. 
     These and other objects of the invention will be apparent from the following descriptions and from the drawings. 
     SUMMARY OF THE INVENTION 
     The invention is for an improved cortical sensing device facilitating the positioning of and maintenance of a sensing element at a desired position on a brain surface. The sensing device includes a support member with a sensing element and at least one pad attached to it. The pad is substantially thin and made from material that is flexibly-conformable. Flexibly-conformable refers to the ability of the pad to easily conform to the contours of the brain surface where the sensing device is placed while being able to recover its original shape and size when removed. The pad is positioned adjacent to the support member. Interaction between the brain surface and the lower surface of the pad contacting the brain surface permits the sensing device to be anchored at the location where it is placed. 
     In certain preferred embodiments, the pad comprises a single layer of material. More preferred is where the support member is also comprised of a single layer of material. Most desirable is where both the support member and the pad are formed from a unitary layer of material. 
     A highly preferred embodiment finds abutment between the lower surface of the pad and the brain surface to be substantially complete, i.e., there is little area on the lower surface of the pad not making direct contact with the brain. More desirable is where the support member and the pad are formed from a dielectric, bio-compatible material, most preferably silicone. 
     Also desirable are embodiments where the sensing device has a plurality of pads and the centers of the support member and each of the pads are not collinear. Highly preferred embodiments find each of these pads attached to the support member along an arc that has a length less than the pad&#39;s diameter and less than the diameter of the support member. This allows each pad to be easily folded along this arc in a manner independent of any of the other pads in a direction generally orthogonal to the surface of the support member. 
     In another embodiment found preferred, the sensing device has only three pads. In this embodiment, it is highly desirable to have the support member and the pads substantially circular and where each of the pads are attached along the circumference of the support member such that the centers of the pads are equidistant to one another. In this manner, the sensing device is substantially clover-shaped. 
     Most desirable is where the pad and the support member are each comprised of a single layer of material having a thickness ranging from 0.003 in. to 0.020 in. More preferred is where the thickness is less than 0.010 in. A highly preferred embodiment finds the thickness to be 0.006 in. Certain embodiments have the diameter of the support member and each pad ranging from 0.25 in. to 0.35 in. Most desirable is where the diameter is 0.30 in. 
     In other embodiments that are preferred, the sensing device has at most one sensing element. In these embodiments, the sensing device desirably also has a lead extending from the sensing element. More preferred is where the sensing element is an electrical contact capable of sensing cortical electrical activity and the lead is a lead wire. Where the sensing element is an optical sensor, the lead is oftentimes a fiber optic bundle. Most desirable embodiments find the lead wire communicating this cortical electrical activity to an external monitor. 
     A highly desired embodiment is one where the lead wire has a distal socket and this socket is sized to engage a connecting pin on a connector in a frictionally snug manner. The connector has an electrical conduit extending from it to the external monitor and is secured to a support apparatus that preferably includes an adjustable clamp adapted to clamp to the skull during surgery. 
     Most preferred is where the support apparatus has a post with a mount secured at the distal end and a clamp at the proximal end. The connector in this embodiment is attached to the mount. The clamp has upper and lower clamping portions where the lower clamping portion extends from the proximal end of the post and the upper clamping portion is slidably mounted to the post in registry with the lower clamping portion. The support apparatus also includes an adjustment member that is threadably mounted upon the post between the mount and the upper clamping portion. Adjusting the position of the adjustment member along the post allows it to limit the extent to which the upper clamping portion may slide axially away from the lower clamping portion. Such adjustments also can serve to urge the upper clamping portion in the direction of the lower clamping portion. 
     Another aspect of this invention finds a method for positioning a cortical sensing device on the surface of the brain. The method has the steps of (1) providing an sensing device having a sensing element supported by a dielectric member and three dielectric pads attached to this support dielectric member where the support member and the pads are each substantially thin and flexibly-conformable; (2) placing this sensing device upon the brain surface at a desired position for sensing brain activity; and (3) allowing the pads to conform to the brain surface whereby interaction between the pads and the brain surface prevents movement of the sensing device along the brain surface. 
     In a preferred embodiment, the method also includes the step of bathing the sensing device in a solution of saline or sterile water. Highly preferred is where the sensing device includes a lead extending from the sensing element for communicating brain activity sensed by the sensing element to an external monitor. Most desirable is where the sensing element is an electrical contact capable of sensing cortical electrical activity and the lead is a lead wire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a preferred cortical sensing device in accordance with this invention. 
         FIG. 2  is a cross-sectional view of the cortical sensing device taken substantially along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a perspective view of several of the cortical sensing devices in  FIG. 1  shown in contact with the brain surface and attached to a connector and support apparatus in accordance with this invention. 
         FIG. 4  is a schematic view illustrating the connection of the cortical sensing devices of  FIG. 3  to external devices through the connector and electrical conduit in accordance with this invention and with an enlarged view of an input jack on the electrical conduit. 
         FIG. 5  is an exploded view of the support apparatus in  FIG. 3  with the connector disengaged from the mount. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a top view of a cortical sensing device  10  having a preferred embodiment in accordance with this invention. Cortical sensing device  10  includes a sensing element, preferably an electrical contact  12  as shown, secured to circular support member  14 . Support member  14  is provided with a circular opening  16  surrounded by a rim  18 . Contact  12  has a central disk  20  with support-flange  22  extending along the circumference of disk  20 . Opening  16  is sized to receive disk  20  in a manner where lower surface  24  of disk  20  can protrude downward from and not be covered by support member  14 . Disk  20  protrudes no more than 0.025 in. through opening  16  and, in certain preferred embodiments, lower surface  24  is flush with support member  14 . Support-flange  22  is preferably adhesively sealed along its length to rim  18 . 
     Cortical sensing device  10  is also provided with three substantially similar circular pads  26  extending outward from support member  14 . Support member  14  and pads  26  are formed from a single thin and substantially planar layer  28  of a dielectric material that is both flexible and bio-compatible. A silicone material such as a medical grade of SILASTIC® is preferred although an equivalent dielectric elastomer can also be used. The material is also preferably transparent to enable the underlying features of the cortical surface to be visualized when sensing device  10  is placed upon the brain. 
     As illustrated in  FIGS. 1-2 , layer  28  has a thickness T and each pad  26  has a diameter D. The thickness of layer  28  is substantially uniform throughout the strip, preferably about 0.006 in. The diameter of each pad  26  ranges from 0.25 in. to 0.35 in. The center  30  of each pad  26  is equidistant from the centers of the other two pads, thereby forming a clover-like shape. Each pad  26  is attached to support member  14  along an arc  32 . 
     A proximal end  34  of a single lead wire  36  is electrically secured to contact  12  by solder or by being crimped within lip  38  of support-flange  22 . As seen in  FIG. 2 , upper cover  40  is placed over contact  12  and adhesively sealed to support member  14 . Cover  40  is formed from a transparent, bio-compatible, dielectric material similar to that comprising layer  28 . Cover  40  has a diameter slightly less than that of support member  14 . A portion of wire  36  is embedded between cover  40  and support member  14  to further firmly secure wire  36  to sensing device  10 . Distal end  42  of wire  36  is electronically attached to socket  44 . 
       FIG. 3  shows a number of sensing devices  10  positioned upon the surface  46  of the cerebral cortex following a craniotomy. Sockets  44  of each wire  36  have a tapered interior to snugly receive a connector pin  52  on a connector  48  in frictional engagement. Connector  48  is mounted upon a support apparatus  50 , each being illustrated in  FIGS. 3-5  in a preferred embodiment in accordance with this invention. 
     Pads  26  interact with brain surface  46  so that sensing device  10  clings to the cortex. Lateral movement of sensing device  10  is avoided once each sensing device  10  has been individually positioned at a desired specific location that is selected by the physician for that sensing device  10  to perform a certain procedure such as sensing brain activity. Bathing each sensing device  10  in saline or sterile water before placing it upon brain surface  46  helps in preparing sensing device  10  for secure placement. 
     Disk surface  24  of contact  12  makes direct contact with brain surface  46 . Contact  12  is preferably platinum or stainless steel and can be utilized to measure brain electrical activity or to provide electrical stimulation to a select tissue region. Other sensing elements such as chemical sensors and optical sensors can be used in place of or in connection with an electrical contact or electrode to monitor chemical activity, temperature and blood flow within the cortex. Pulling upward upon sensing device  10  in a direction away from brain surface  46  allows sensing device  10  to be disengaged from brain surface  46  for relocation to another site on brain surface  46  where sensing device  10  can initiate similar treatment. 
     As can be seen in  FIG. 3 , pads  26  do not need to be sandwiched between the dura and the cortex to remain in place. Moreover, given the size and shape of sensing device  10 , one can clearly see that the weight of sensing device  10  is less of a factor in its ability to stay in one spot than is the case for the heavier strip sensing devices in the prior art. 
     The thinness of pads  26 , the length of arcs  32 , and the nature of the material selected for layer  28  each contribute to the ability of pads  26  to retain their shape but still be sufficiently flexible to conform to an area of brain surface  46  of comparable size. Each arc  32  has a length less than the diameter of support member  14  and less than the diameter of pad  26 . Each pad  26  is capable of swinging about its adjacent arc  32  independently of any other pad  26  such that each pad  26  is free to drape over the portion of brain surface  46  directly beneath it. In this manner, sensing device  10  provides as much as 300% more area in direct contact with brain surface  46  than is touched by contact  12  and its surrounding support member  14  alone. 
     As illustrated in  FIGS. 3-5 , connector  48  is provided with a plurality of connecting pins  52 . Each pin  52  is in electrical communication with an electrical conduit  54 , each wire conduit  54  having an input jack  56  attached at the end opposite from the corresponding connecting pin  52 . 
     Input jack  56  enables the electrical conduit  54  and thereby the associated sensing device  10  to be connected to an external device  58 . Where sensing device  10  is intended to monitor electrical brain activity, external device  58  will preferably consist of a conventional monitoring device with output display and a suitable power source to record or display information communicated by sensing device  10 . Electrical conduits  54  preferably combine to form a conduit ribbon  60  upon exiting connector  48  so that individual loose wires can be avoided. As seen in  FIG. 4 , conduit ribbon  60  separates into the individual electrical conduits  54  at a distance from connector  48  to enable one or more input jacks  56  to be electronically attached to the necessary external devices  58 . 
     Connector  48  is mounted to support apparatus  50  to provide better access to connector  48  during treatment of a patient. As illustrated in  FIGS. 3 and 4 , support apparatus  50  includes a clamp  62  for attaching support apparatus  50  to the skull  64 . Clamp  62  comprises a lower clamping portion  66  forming the proximal end  67  of a post  68  and an upper clamping portion  70  slidably disposed upon post  68 .  FIG. 5  shows that lower clamping portion  66  has a smooth lower clamping surface  72  extending outward from axis  74  of post  68 . Upper clamping portion  70  is provide with a serrated upper clamping surface  76  that is in registry with lower clamping surface  72 . 
     In mounting support apparatus  50  to the skull  64 , the spacing between both clamping surfaces  72 , 76  is increased by sliding upper clamping portion  70  in the direction of the distal end  77  of post  68 . Lower clamping portion  66  is inserted into an opening  79  in skull  64  so that lower clamping surface  72  can be placed up against the interior surface of skull  64 . Upper clamping portion  70  is then lowered to bring upper clamping surface  76  in contact with the exterior surface of skull  64 . 
     Support apparatus  50  includes adjustment member  78  to stop upper clamping portion  70  from sliding upward and to maintain upper and lower clamping portions  66 , 70  firmly in contact with skull  64 . Adjustment member  78  has a threaded bore  81  that is threadably mounted upon post  68  along a threaded portion  80  adjacent to lower clamping portion  66 . Adjustment member  78  can then be rotated in a conventional manner so that adjustment member  78  is forcefully urged against upper clamping portion  70  to reduce the spacing between clamping portions  66 , 70  and thereby firmly tighten clamp  62  upon skull  64 . 
     Support apparatus  50  also includes mount  82 . As seen in  FIG. 5 , mount  82  is provided with three apertures  84 , 86 , 88 . First aperture  84  is at one end of mount  82  and has a top portion  90  opening onto top surface  92  and a bottom portion  94  opening onto bottom surface  96 . Portions  90 , 94  are coaxial but have different diameters. Top portion  90  is sized to receive the bottom end  98  of connector  48  so that connector  48  can then be secured to mount  82  by having a fastener  100 , preferably a screw, threadably engage bottom end  98  through bottom portion  94 . 
     Second aperture  86  is at the other end of mount  82  and extends from top surface  92  to bottom surface  96 . Second aperture is adapted to receive the distal end  77  of post  68 . Third aperture  88  is orthogonal to and in communication with second aperture  86 . Third aperture  88  is sized to threadably receive a grip screw  102 . Post  68  is firmly secured within mount  82  by threadably advancing grip screw  102  within third aperture  88  until grip screw  102  is urged into contact with and frictionally engages post  68 . One can readily see that mount  82  can be raised or lowered along post  68  or pivoted about post  68  before grip screw  102  is tightened so that a desirable position for mount  82  in relation to skull  64  and thereby the adjacent surgical field can be achieved. 
     As shown in  FIG. 4 , each input jack  56  is numbered, preferably with a collar  106  embedded with numerical indicia. Likewise, a numerical decal  108  is fastened on the connector  48  adjacent to each connecting pin  52 . The number on the collar  106  of each input jack  56  is the same number found on the decal  108  corresponding to the connecting pin  52  that is connected via electrical conduit  54  to that specific input jack  56 . One can appreciate that in this manner the physician or technician can immediately identify which sensing device  10  is being monitored by a specific external device  58  by matching the number on the collar  106  of the input jack  56  connected to that device with the corresponding number on the connector  48  to see which sensing device  10  is engaged to the connecting pin  52  associated with that number. In a similar fashion, the connecting pin  52  associated with a certain desired external device  58  can be easily identified when attaching sensing devices  10  to connector  48  or when replacing one sensing device  10  with another such as when a lead breaks or contact  12  becomes inoperative. 
     Sensing devices  10  are also provided with numerical indicia  104  to use to distinguish one sensing device from the others. Although the physician or technician remains free to attach the socket  44  for a given sensing device  10  to any empty or unattached connecting pin  52  on the connector  48 , connecting the socket  44  to the connecting pin  52  having a number on the adjacent decal  108  that matches the number on the sensing device  10  itself will permit that individual to more quickly, easily and with greater assurance associate each sensing device  10  with a corresponding external device  58 . 
     Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.