Patent Publication Number: US-2020289002-A1

Title: CONTOUR ELECTROCORTICOGRAPHY (ECoG) ARRAY

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application 62/819,042, which was filed on Mar. 15, 2019 and is entitled Contour Electrocorticography (ECoG) Array. The &#39;042 application is incorporated, in its entirety, by reference into this application. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with government support under 1734806 awarded by the National Science Foundation. The government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     This application relates to systems, devices, and methods involving monitoring brain activity or responses. More specifically, systems, devices, and methods, employing active electrodes or other sensors positioned adjacent to brain matter in order to discern neural signals of the cerebral cortex or other neural sources, are provided herein. 
     TECHNICAL BACKGROUND 
     ElectroCorticoGraphy (ECoG) is a neurophysiological technique that allows direct intraoperative cortical electrical activity recording from the cerebral cortex. This technique was developed by Penfield and Jasper in the 1940s. ECoG has been used to help define the epileptogenic cortical region intraoperatively and provide surgeons with the same type of the cerebral potential recording as the ElectroEncephaloGram (EEG), but without the scalp and skin interference of an EEG. Intraoperative localization of electrical neuronal patterns using ECoG may assist with intervention techniques in patients with epilepsy, and brain tumor-related epilepsy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate embodiments and serve to explain principles of operation of possible embodiments, whether or not explicitly provided herein. 
         FIG. 1  shows a perspective front view of a human brain with a trident ECoG array and wireless transceiver as may be employed in some embodiments. 
         FIG. 2  shows a side view of a brain with an ECoG array as may be employed in some embodiments. 
         FIG. 3  shows frontside and backside plan views of a 3×3 ECoG array as may be employed in some embodiments. 
         FIG. 4  shows frontside and backside views of electronics that may be employed in ECoG testing devices or systems of some embodiments. 
         FIG. 5  shows a 3×3 ECoG array connected to a PCB with wireless electronics as may be employed in some embodiments. 
         FIG. 6  shows a schematic of a trident ECoG array as may be employed in some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments may include devices, systems, and methods comprising adaptable substrates and sensors with circuit topology or other configurations or designs for performing ECoG testing of a patient. The testing may be performed alone or concurrently with various medical procedures. These substrates may support sensors positioned as an array, and may be employed while accessing specific portions of the cortex or other brain surface by an external stimulator. In embodiments, the sensors may serve to collect neural signals, may stimulate neural signals, and may do both. In embodiments, a suitable number of active electrodes or other sensors positioned as an array may be employed and may serve to provide contour coverage of the brain surface being tested. In some embodiments, wireless transceivers or transmitters may be employed to broadcast the sensed neural signals or information derived using the sensed neural signals to a remote system monitor that may be configured to report real-time brain surface responses from imposed stimulation. The imposed stimulation may come from a hand held stimulator, a robotically manipulated stimulator, and from electrodes or other sensors on the substrate as well. 
     Substrates of embodiments may be flexible and may be configured such that electrodes or other sensors supported by the substrate may contour a target testing area of a brain of a patient and may receive and report detectable responsive brain signals during the testing. The substrate and sensors may also be configured to allow a surgeon or other medical professional access close to the substrate and sensors during a procedure. This access may be provided by openings in the substrate, by spacings between adjacent substrates, by spacings in the substrate, and by other configurations as well. The substrates may be contoured as well as flexible in order to closely mimic the contours of the cortex, or other brain area, to be tested using ECoG. Because of the flexibility, contours, and/or locations of the sensors, in embodiments little or no need of further manipulation or added pressure to ensure contact may be needed to obtain viable ECoG signals. Also, a practitioner may have access to portions of the cortex or other brain location nearby the sensors and substrate because of the open configuration of the substrate. This proximal access to the cortex or other brain surface area may allow a surgeon or other practitioner to pinpoint specific sensor areas and specific brain surface areas for ECoG testing. In other words, embodiments may provide a practitioner with discrete access in and around sensors located on the cortex for testing of specific brain tissue. Moreover, embodiments may provide individual addressing of sensors such that a practitioner may receive tailored feedback during ECoG testing identifying specific locations of the brain tissue or specific sensor locations of an array or both. Through this tailored ECoG array of sensors, a practitioner may not need to apply any pressure or large amounts of pressure on the sensor or sensors during procedures. Thus, embodiments can provide a practitioner with access to ECoG tests of brain tissue responses using stimulus locations between sensors supported by a substrate. 
     As examples, embodiments can provide for an array of electrodes positioned and/or configured to: i) simultaneously record neural signals while providing stimulation on specific portions of the cortex using a user-guided stimulator; ii) stimulate multiple sites concurrently and/or independently using multiple electrodes, iii) acquire neural signals over a large cortex area; and/or iv) acquire neural signals at a setting remote from the neural source using wireless or other communication techniques. Other procedures and processes may also be provided by embodiments. 
     Embodiments may provide ECoG arrays that allow recording of the cortical and subcortical electrical activity while simultaneously enabling the performance of a surgical resection or other procedure by a surgeon. In these and other embodiments, during an awake or other brain procedure, the sensors may be placed on the cortical surface for recording the electrical activities and the identification of epileptiform patterns. These patterns may occur after direct cortical electrical stimulation and may serve as a surrogate for a forthcoming seizure or micro-seizures. 
     ECoG arrays of embodiments may have several geometries and sizes, which can vary from single strip (one-dimension array) electrodes (1×4 cm or 1×6 cm) or other sensors with a support substrate, to grid electrodes or other sensors (two-dimensional array) on a substrate. In embodiments, the strip electrode (one-dimensional array) or other sensor may only support monitoring in one direction (e.g., superior) unless multiple strips are placed, and the grid electrodes or other sensors (two-dimensional array) may allow procedures to be performed over a large desired area because of the larger access area these embodiments may provide. 
     As noted above, embodiments, may include flexible substrate materials that provide appropriate electrode or other sensor contact with the brain. Embodiments may also include transmission systems to allow sensor signals to be transmitted with wires or wirelessly from a testing location to a system monitor for observance or other use during or after a medical procedure. Thus, embodiments may employ a system monitor or another device to record neural signals in-situ during brain surgery. This recording of neural signals may be collected by the system monitor or elsewhere while stimulating specific portions of the cortex using a hand-held stimulator or other stimulator. Embodiments may be configured to perform recording through configurations that allow access within and around the ECoG arrays while recording neural signals. 
     Embodiments may provide access during a medical procedure by: selectively placed material layers of the substrate, which can provide direct access as well as indirect access; through connection access points in a substrate or between substrates; through wireless communications between sensors and a system monitor or other component; through spaced electrodes in two-dimensional arrays; and through other techniques and system topologies. For example, in some embodiments, one or more perforations or openings on the array substrate may be provided to allow for in-situ recording and simultaneous stimulation by a surgeon or other practitioner. 
     Embodiments may be configured to be placed at or around the contour of the cortex. In so doing, access to suitable signals and/or more signals from the cortex may be acquired. Embodiments may be configured with a thin elastomer layer as a substrate and robust electrodes supported by the substrate. These electrodes or other sensors may be configured to provide monitoring and/or stimulation of active brain tissue. The electrodes or other sensors may be sized such that their weight is sufficient to hold them nearby or up against the surface of the brain being analyzed. This weight, in combination with the configuration of the substrate, e.g., its thickness, shape, and material flexibility, can serve to have an ECoG array lay in direct or near direct contact with the brain surface during testing. This close proximity can provide for sensing low level brain surface responses to stimulation as well as for reduced signal noise in the responses received by a sensor. 
     Embodiments may also include wireless communication modules to collect and/or transmit neural signals to an external reader, system manager, or other recipient. Embodiments may comprise wireless perforated ECoG arrays such that specific portions of the cortex may be accessed by an external stimulator while concurrently collecting neural signals by the ECoG array. These and other embodiments may employ sensors of various array sizes and configurations. The array configurations may include one-dimensional arrays as well as two-dimensional and three-dimensional arrays. The number of sensors on each array may be consistent and may differ. In some embodiments individual arrays may be addressable, and in some embodiments individual sensors may be addressable. 
     In some embodiments a procedure may be performed first using a first array and then a larger or smaller array may be subsequently used. This switch in array size may provide improved contour coverage of the brain surface during a procedure. Likewise, selecting a particular array size for a procedure, may also be tailored for specific contour coverage during the procedure. In other words, a small 1×2 or 1×4 or 2×2 or 3×3 or 2×3, etc. array may be selected for a small area of the cortex to be tested while a larger 12×12 or 10×10 or 15×8, etc. array may be selected for a larger subsequent testing area. These testing areas may have the same center or may overlap or may not overlap at all. Also, different size arrays may be selected in order to obtain adequate coverage during a procedure. In other words, a 3×3 or other smaller array may be used along with, i.e., concurrently with, a larger, e.g., 12×12 or large array, when the area of tissue to be tested may be better mimicked by the differing sizes. 
     Also, embodiments may employ substrates of different sizes and configurations. These configurations can include different shapes and different arcs of curvature. Both the selected shapes and arcs of curvature may be selected to closely mimic the curvature of the brain surface to be tested. As noted above, the more closely the sensors lay on the tissue the better the received test results may be. 
     Various features, steps, processes, components, and subcomponents, as may be employed in embodiments, are provided above and below. These features, steps, processes, components, subcomponents, partial steps, systems, devices, etc. may be adjusted, combined and modified in various fashions and various ways among and between the teachings and figures provided herein, as well as in other ways not specifically described herein. 
     Embodiments, therefore, may provide, a tailored design/implementation of ECoG arrays for use by neuro-surgeons or others in some embodiments, this tailored design may be adopted by manufacturers for large scale production while also providing tailored ECoG array features accessible for use by neuro-surgeons or other users. Embodiments may also provide ECoG arrays that allow recording cortical and subcortical electrical activity while simultaneously performing a surgical resection or other procedure. 
     Embodiments may be configured to be placed at or around the contour of the cortex and may be flexible enough, through the use of flexible and thin materials, to contour or mimic the cortex area beneath the placed sensor. In so doing, access to more suitable signals and/or more signals from the cortex may be acquired. Likewise, individual and/or concurrent electrode stimulus may also be provided. Thus, embodiments may be configured with a thin elastomer substrate layer and robust electrodes, to provide monitoring and/or stimulation of a cortex area. 
     Still further, as noted above, embodiments may also include wireless communication modules to collect and/or transmit neural signals to an external reader, system monitor, or other recipient. The electrodes, in embodiments, may provide forces serving to hold the thin elastomer layer to the cortex or other source of signals being monitored or stimulated. These forces may be primarily generated by the actual weight/mass of the electrodes or other sensors. In some embodiments, the weight/mass of the electrodes or other sensors may be sized to deflect or deform or otherwise contour the flexible material of a sensor to closely or exactly mimic and be adjacent to or close to the cortex or other neural signal source. 
     Embodiments may comprise real-time neural electrocorticography (ECoG) measurement systems that may comprise a flexible substrate, the substrate comprising a plurality of tines with each tine comprising a plurality of sensor electrodes. In this and other embodiments, each tine may have an arc of curvature, the arc of curvature having a diameter that serves to define the arc of curvature along a single curve or a complex curve. In embodiments, the arc of curvature may have diameters of 7.5 cm, 9 cm, 12.5 cm. 19 cm, and infinity. Other diameters in this range, as well as smaller dimeters and in different increments, may also be employed in embodiments. The biocompatible material may be a silicone or flexible polyethylene, polypropylene or other flexible polymer. In some embodiments, the substrate may be a silicone substrate. In this and other embodiments, an open spacing, i.e., a gap or void in the substrate, may exist between adjacent tines of the plurality of tines and a wired connector may be connected to an output of the plurality of sensors. Still further, a wireless transceiver may be in communication with the wired connector and each sensor electrode of the plurality of sensor electrodes may have a mass of 3 mg to 98 mg in increments between as small as 0.1 grams or even smaller. Still further, the transceiver may employ circuit topology configured to send neural signals received from the sensor electrodes to a system monitor. In embodiments, the circuit topology of the transceiver may be configured to provide contemporaneous reporting of neural signals received from the sensor electrodes when external stimulation is provided between sensor electrodes of the plurality of sensor electrodes. In embodiments, the system monitor may be configured to receive the contemporaneous neural signals from the transceiver and to record the received contemporaneous neural signals. In embodiments, a substrate may be coated with no more than 0.8 mm of medical grade silicone. In embodiments, a substrate may comprise no more than 0.8 mm of medical grade silicone. In embodiments, a flexible two-dimensional substrate may be in the shape of a trident. In embodiments, the sensors may be equidistantly spaced along tines of the substrate. 
     Embodiments, may comprise a neural sensor comprising a first one-dimensional array of sensors, wherein at least one sensor in the first array may have a mass of 98 mg and a second one-dimensional array of sensors, wherein at least sensor in the second array may have a mass of 98 mg. A silicone substrate may also be employed to support the first array and the second array, and the silicone substrate may have a thickness of no greater than 0.8 mm. A communication circuit may also be employed. This communication circuit, which may include a local transceiver such as local receiver  180  and antenna  185  of  FIG. 1 , may be tethered to a node, the node electrically connected to the first array or the second array or both. In embodiments, the sensors of the first array may be circular and may be spaced apart from each other at least by their average circumference. In embodiments, the first array and the second array may be positioned on tines of a triton and the spacing between the first array and the second array may at least be 2.0 mm, other spacings may also be used. In embodiments, the node may be coupled to a transceiver, the transceiver configured to provide contemporaneous reporting of neural signals received from the sensors when external stimulation is provided between sensors of the first one-dimensional array and the second one-dimensional array. In embodiments, the first one-dimensional array and the second one-dimensional array may be parallel to each other. In embodiments, the transceiver may be configured with an antenna and the transceiver may be configured to wirelessly communicate with a system monitor. 
     Embodiments may include a real-time neural electrocorticography (ECoG) measurement system comprising a flexible two-dimensional substrate, the substrate comprising a plurality of arrays with each array comprising a plurality of sensors. In embodiments, each array may have an arc of curvature that may be at least nineteen centimeters in length; the substrate may comprise a biocompatible material; and an open spacing may exist between adjacent arrays of the plurality of arrays. In embodiments, a wired connector may be connected to an output of the plurality of sensors and a wireless transceiver may be in communication with the wired connector. In embodiments each sensor of the plurality of sensors may have a mass of 3.0 mg to 98 mg and the transceiver may have a circuit topology configured to send neural signals received from the sensors to a system monitor. In embodiments, the arrays may be one-dimensional arrays and the circuit topology of the transceiver may be configured to provide contemporaneous reporting of neural signals received from the sensors when external stimulation is provided between sensors of the plurality of sensors. In embodiments, the system monitor may be configured to receive the contemporaneous neural signals from the transceiver and to record the received contemporaneous neural signals. In embodiments, the substrate may comprise no more than 0.8 mm of medical grade silicone and the flexible two-dimensional substrate may be in the shape of a polygon. In embodiments, the sensors may be equidistantly spaced along one-dimensional arrays of the substrate. 
       FIG. 1  shows a perspective front view of a human brain with a trident ECoG array as may be employed in some embodiments. The brain  100  is shown with a trident shaped ECoG array  130 . Also shown are the system monitor  110  and the hand-held stimulator  120  as well as antennas  185  and  115  and node  175 . The node  175  is shown as a connection junction between connections  160 , and the connection  170 . During a procedure, the handheld stimulator  120  may be placed at various testing points  150  and provide a stimulating voltage to the particular testing point of brain tissue. The sensors  140 , which may be electrodes, nearest the testing point  150  being stimulated, may sense brain signals and report these sensed signals back through connections  160  and  170 . These connections  160  and  170  may comprise a wire or other electrical pathway supported by a flexible substrate. The flexible substrate may have an inherent curve or bow. Connection  170  may be coupled to a wireless transmitter that may itself be communicating with system monitor  110 . The system monitor  110  may take the received data and determine which one or more sensors  140  are receiving response signals from the brain tissue and the magnitude of each received signal at the particular sensor. This received and determined information may then be reported to the practitioner performing the procedure and may also be stored for later analysis. As can be seen in  FIG. 1 , the connections  160  may be spaced apart from one another and may have multiple sensors laying along their lengths. As can also be seen, the substrate connections  160  may be tines, and may be oriented as tines of a fork, as shown in  FIG. 1 . The array  130 , which is trident shaped, may also have various other shapes in embodiments. These may include connection loops with sensors, one or more spars with one or more sensors, elliptical, circular, triangular, polygonal, and other configurations as well. The connection  170  serves as a common bus for the connections  160  between them and a local receiver  180 . This local receiver  180  may be a transceiver communicating back and forth with the system monitor  110 . In embodiments, the connection  170  may be hardwired directly with the system monitor  110  and may not have an intervening local receiver. An advantage of the local receiver may be additional access being provided in and around the target tissue testing site because of the absence of a wired lead connection between the array  130  and the system monitor. 
     The substrate in  FIG. 1 , which is positioned around the connections  160 , as well as in other embodiments, may comprise 0.25 mm-0.7 mm thick medical grade emulated silicone as well as other materials including those with similar properties to silicone. Embodiments may employ silicone between 0.5 mm and 0.7 mm and less than 0.75 mm. Other FDA materials approved for cortex applications may be considered, provided they have a flexure under the weight of the electrodes to contour or mimic the surface arc of the cortex in which will be monitored by the sensor. 
     Embodiments may be made through various manufacturing techniques including 3D printing, extrusion, and injection molding. The electrodes or other sensors of embodiments may have various thicknesses including 0.125 mm, 0.25 mm. 0.3 mm. 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, and 0.8 mm as well as being thinner or thicker in embodiments. Conductive Ag epoxy may be used to connect wires from a sensor array/stimulator array to a 10-pin cable for communication to and from the sensor. Other connection techniques, such as micro-welding, may also be employed to connect the sensor/stimulator to the support circuit. Embodiments may be enclosed by 0.5 mm-thick medical-grade emulated silicone. Thus, arrays, connecting wires, local receivers, etc., may each be coated. This coating material or other coating materials may be selected to allow arrays to easily cover the contour surface of the cortex. 
     The electrodes or other sensors of embodiments may be circular, cubical, and other shapes. Cylindrical sizes can range from 1.0 mm to 5.0 mm in diameter as well as other sizes. Likewise, polygonal sizes can include these same size ranges. The electrodes or other sensors may be 0.125 mm-thick, which may serve to increase the conformal coverage of electrodes on the contour surface of the cortex or other test location. The electrodes or other sensors may have a mass of 6.80 mg as well as have a range of mass of 3.0 mg-98 mg in increments of 0.1 mg or larger or smaller. In embodiments, the electrodes or other sensors may have enough mass in order to serve to hold the sensor down and to the cortex and to maintain an adjacent or near adjacent juxtaposition between the sensors electrodes and the cortex or other neural system being stimulated and/or monitored. The electrodes or other sensors may also be controlled to provide individual stimulus as well as groupings of stimulus to the cortex or other area being monitored. 
       FIG. 2  shows a side view of a brain  200  with an ECoG array  230  as may be employed in some embodiments. The ECoG array  230  in  FIG. 2  has multiple sensors  240  along its substrate  260 . The substrate  260  in  FIG. 2  is shown with openings  280  and end recesses  285 . The openings  280  are shown as rectangles but may be circular, oval, and various other shapes. The openings may be sized to allow a practitioner to insert a hand-held stimulator through the opening and onto or near brain tissue to be stimulated and/or otherwise tested or acted upon. Testing points are labelled as  250  in  FIG. 2 . The sensors  240  may be located along the various edges or other surfaces of the substrate  260  and may be used to receive brain signals responsive to the simulations. These responsive signals may be reported back through the connection  270 . 
     Like the substrate of other embodiments, the substrate in  FIG. 2  may be curved and may be flexible such that when placed on or around the brain tissue to be tested, one or more of the sensors  240  of the array  230  come in close proximity or touch the brain tissue to be tested. In some embodiments, a portion of the sensors will touch the brain tissue during testing and in some embodiments all of the sensors of an array will touch the brain tissue during testing. Upon receiving responsive signals, a system monitor may determine which sensors are best positioned relative to the test tissue and may ignore some responsive signals or the absence of responsive signals attributable to poor sensor location. 
     In embodiments, as in  FIG. 2 , the substrate may comprise biocompatible materials that are flexible enough to allow the substrate to lie along the contours of the brain area being tested. To further promote the contact between the sensors and the target rain area, the substrate may have simple curves, i.e. curves with one radius of curvature, or complex curves, i.e., curves with two or more radii of curvature, of varying degrees. The radius of curvature may be at least 19 cm in length. The radius of curvature may have diameters of 7.5 cm, 9 cm, 12.5 cm. 19 cm, and infinity. Other diameters in this range, as well as smaller dimeters, may also be employed in embodiments. The increments in the diameter change may be millimeters and centimeters. 
     During a procedure, multiple arrays of differing sizes and curves may be available for a practitioner and the practitioner may select the appropriate size as well as the appropriate simple or complex curved arrays that best mimic the curvatures of a brain area to be tested or treated during a procedure.  FIG. 2  also shows that sensors  240  need not be uniformly spaced across an entire array  230 . 
       FIG. 3  shows frontside and backside plan views of a 3×3 ECoG array  330  as may be employed in some embodiments. A ten-pin connector  370  is shown on the backside view. Also labelled in  FIG. 3  are the substrate  360  and the sensors  340  along with dimensions of the sensors and the substrate  360 . As can be seen, the substrate  360  has a rectangular shape and access openings  380 . Electrical pathways are labelled  385  in  FIG. 3  and show how sensors may be connected to each other and through the ten-pin connector  370  leaving the array  330 . As described elsewhere, this array  330  may also be flexible and may have various contours and curvatures in order to better mimic a target location of the brain. The access openings  380  may be used for stimulator placement during a procedure. 
       FIG. 4  shows frontside and backside views of electronics mounted to a PCB  410  that may be employed in ECoG testing devices or systems of some embodiments. The frontside view is labeled with controller  440 , battery socket  450 , cable adapter  460  and multiple electrical pathways  430 . The backside view is labelled with printed circuit board  410 , wireless communication module  420 , and electrical pathways  430 . The electronics of  FIG. 4  may be connected locally to an array during testing. This connection may be wired and made through the ten-pin cable shown in  FIG. 3 , as well as through other connection topologies. In embodiments, the connection between the electronics and an array may be detachable so that the electronics may be used with many arrays over time and across multiple procedures. The arrays of embodiments may be sanitized and used a single time or multiple times while the support electronics may be sterilized and reused for many procedures over the lifetime of the electronics. The circuit topology may also include amplifiers, filters, digitizers, batteries, and connecting electronics, as can be seen in  FIG. 4 . Other electronics may also be employed. As noted, embodiments may employ silicone as an encloser to protect the electronics during sterilization processes. In embodiments, components may be enclosed, except for cable adapter that may receive a 10-pin cable or other connection topology from the ECoG array. Other encapsulation configurations may also be employed. 
       FIG. 5  shows a 3×3 ECoG array connected to a PCB with wireless electronics as may be employed in some embodiments. The array  330  is labelled along with the electronics  400  and cable adapter  460  in  FIG. 5 . As can be seen, the connection  370  may be millimeters in length. Comparatively, in other embodiments, the connection  370  may be tens or hundreds of centimeters in length, or even longer. 
     The cable adapter  460  may allow for disposable arrays to be used such that new arrays may be used for each procedure while reusing the electronics  400  for many procedures. The silicone overlay  690 , which is shown as being 20 mm in length, may also have various lengths and cover some or all of the cabling in embodiments. The silicone overlay may also have various shapes if employed. These shapes can include L configurations. Other connection techniques, designs, and topologies may also be employed in embodiments. 
       FIG. 6  shows a schematic of a trident ECoG array  130  as may be employed in some embodiments. Also labelled in  FIG. 6  are substrate tines  660 , sensors  140  located along these tines  660 , and connection pathway  670 . The connection pathway  670  shows an end with a ten-pin connection strip for connection to electronics  400  shown in earlier figures as well as for connection to other electronics in some embodiments. The lengths of the connection pathway  670  are also identified in  FIG. 6  and show how the material of the connection pathway  670  may transition from substrate material to an electrical ribbon along the length of the connection pathway  670 . 
     Curved support substrates may be employed by ECoG arrays in some embodiments. The substrates may have various curvatures. These curvatures may lie along a single diameter or be complex curves having two diameters of curvature for a single substrate. While diameters of 7.5 cm, 9 cm, 12.5 cm. 19 cm, and infinity may be used, other diameters in this range, as well as smaller dimeters, may also be employed in embodiments. These diameters of curvature may be applied to simple curves as well as complex curves. 
     Array calibration may be performed in embodiments. This calibration may serve to correlate stimulus signals with received signals by one or more sensors of an array. This calibration may be performed on a test bench using conductive gel with the array being calibrated. As voltages are applied by a stimulus the responsive signals from the sensors may be monitored and observed. Variations between input (stimulus) and output (sensor) signals may be identified and used to calibrate the electronics and/or system monitor described above. This calibration may include using root-mean square error correction as well as filtering high frequency noise and waveform distortion in the output signal. Through this calibration, output signals of the sensors may be better understood to reflect more accurate traits of the brain tissue being tested. 
     While embodiments have been illustrated herein, it is not intended to restrict or limit the scope of the appended claims to such detail. In view of the teachings in this application, additional advantages and modifications will be readily apparent to and appreciated by those having ordinary skill in the art. Accordingly, changes may be made to the above embodiments without departing from the scope of invention. 
     Various features, steps, processes, components, and subcomponents may be employed in certain embodiments. These features, steps, processes, components, subcomponents, partial steps, systems, devices, etc. may be adjusted, combined and modified in various fashions and various ways among and between the teachings and figures provided herein, as well as in other ways not specifically described herein but consistent with the teachings and discussion of this disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     The corresponding structures, material, acts, and equivalents of any means or steps plus function elements in the claims are intended to include any structure, material or act for performing the function in combination with other claimed elements. The description of certain embodiments has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill without departing from the scope and spirit of the invention. These embodiments were chosen and described in order to best explain principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for embodiments with various modifications as are suited to the particular use contemplated. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     As used herein, the terms “about” or “approximately” in reference to a recited numeric value, including for example, whole numbers, fractions, and/or percentages, generally indicates that the recited numeric value encompasses a range of numerical values (e.g., +/−5% to 10% of the recited value) that one of ordinary skill in the art would consider equivalent to the recited value (e.g., performing substantially the same function, acting in substantially the same way, and/or having substantially the same result). 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. 
     It should be noted that the terms “first”, “second”, and “third”, and the like may be used herein to modify elements performing similar and/or analogous functions. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated.