Abstract:
An apparatus for monitoring an electrophysiological signal within a magnetically sensitive apparatus comprises a stretchable elastic cap having a plurality of electrode holders designed to be filled with a conductive electrolyte. Electrodes are disposed within the electrode holders and leads extend from the electrodes. The electrodes and the leads are made of a non-ferromagnetic conductive material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional U.S. patent application Ser. No. 60/107,918, filed Nov. 10, 1998 by Don DuRousseau, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to medical devices and more specifically to techniques for acquiring uncontaminated electrical signals from the brain and body, without the use of pre-amplification electronics, especially while located within the harsh operating environment produced by a functional magnetic resonance imaging (fMRI) system. 
     BACKGROUND OF THE RELATED ART 
     Conventional EEG, EOG, ECG, EMG, and other physiological signals are typically recorded using individually placed electrodes that are fixed on the scalp and body with adhesives or by the use of a cap type system. Examples of these techniques are those developed by Sams et al (U.S. Pat. No. 4,085,739) or Gevins et al (U.S. Pat. Nos. 4,967,038 and 5,038,782). In these placement methods, the electrodes are attached to amplifiers used to acquire and record the related electrical and physiological activity. These amplifier systems require a very low impedance contact with the skin and are very susceptible to emissions from other electrical equipment, such as an MRI device. In such an environment, the input stage of a conventional EEG, ECG or EMG amplifier is susceptible to the very large induced electrical and magnetic fields generated by a magnetic resonance imager to the point where the amplifier cannot function properly. In addition, these amplifier systems are almost always powered from an AC Voltage source and, therefore, radiate electromagnetic interference (EMI), which causes contamination of the anatomical and functional data acquired by the fMRI system and compromises the integrity of these data. 
     A prior attempt to collect EEG signals within the fMRI environment, by Ives et al (U.S. Pat. No. 5,445,162) is based on a battery powered analog pre-amplifier system in which individual electrodes are glued to the scalp and the electrical activity is amplified within the bore of the imaging device. The signals are then converted to light energy by additional analog circuits placed nearby the patient. While still within the harsh fMRI environment, these signals are communicated along fiber-optic cables outside the shielded room, which protects the imaging equipment from unwanted interference, to a secondary amplifier system that is located outside the shielded room and attached to a PC for collecting and processing the data. However, this optically coupled pre-amplification system is expensive, bulky, and cumbersome to operate. In addition, due to size restrictions within the head coil (located inside the imager) and the inability to use digital circuits in the design, due to broadcast interference from internal clock circuits, the AC-coupled nature of this devices makes it susceptible to large artifacts caused by transient signals produced during normal operation of the imaging system. 
     SUMMARY OF THE INVENTION 
     The problems of the prior art, described above, are solved, in accordance with the present invention, by providing an EEG Electrode Positioning System using an elastic head cap (hereinafter Quik-Cap), to position electrodes on the head and face to acquire electrical signals and communicate them to external amplifier equipment. The Quik-Cap provides a stretchable elastic cap and chinstrap portion capable of comfortably fitting a wide range of head size and shape variability. The Quik-Cap provides a plurality of electrode holders designed to be filled with a conductive electrolyte. In addition, the Quik-Cap provides a wire harness assembly that can be configured with either carbon or metal lead wires and is capable of interfacing with any type of commercially available amplifier system. 
     Some specific features and objectives of the invention include the following. 
     The present invention provides a low cost system for rapidly applying large numbers of electrodes on the head and body that is capable of acquiring signals inside an fMRI system and communicating them outside the shielded environment without the use of any electronic amplification. 
     It is another objective of the present invention to use carbon lead wires attached to the electrodes positioned on the head and body to limit the susceptibility of the system to contamination from an MRI system and to communicate signals outside a shielded fMRI environment to amplifiers attached to a PC for collecting and processing electrophysiological and other physiologically correlated data. 
     Another object of the present invention to use metal electrodes composed of Tin, Gold, Silver-Chlorided Silver, or a combination or amalgam of Silver-Chloride powders, each carried in soft rubber electrode mounts and connected to carbon lead wires to limit the susceptibility of the system to physiological and electronically induced contamination. 
     It is a still further object of the present invention to use carbon, carbonized plastic, or conductive plastic electrodes in connection with carbon lead wires to further limit the susceptibility of the system to physiological and electronically induced contamination. 
     It is a still further object of the present invention to use needle electrodes, implantible depth electrodes, or cortical surface electrodes in connection with carbon lead wires to further limit the susceptibility of the system to physiological and electronically induced contamination while recording signals directly from the brain or spinal chord. 
     It is a still further object of the present invention that a single electrode, or group of electrodes, may also be used to acquire signals from the eyes, heart or muscles, by providing a mechanism to position electrodes in the appropriate regions of the scalp, face, chest or body. 
     Still another object of the present invention is to permit a single lead wire, or group of lead wires, to be used to connect to and communicate signals from external transducer devices used to measure signals related to oxygen uptake, respiration, heart rate, impedance, motion, acceleration, force or other such signals. 
     Yet another feature of the present invention is to provide separable elastic cap, chinstrap, and wire harness portions to position electrode holders and electrodes on the head, face and body to acquire EEG, EOG, EMG, ECG and other physiologically correlated signals from humans while inside a magnetic resonance imaging system. 
    
    
     The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the system of the present invention will be apparent from the following description in which: 
     FIG. 1 is a side view of the elastic cap and chinstrap portion of an exemplary embodiment of the present invention showing electrode holders and lead wire harness assembly in which individual lead wires are attached to electrodes (not shown) carried within the electrode holders. 
     FIG. 2A is a cross-sectional side view of the electrode holder of FIG.  1 . 
     FIG. 2B is a top plan view of the embodiment of FIG.  2 A. 
     FIG. 2C is a side plan view of the embodiment of FIG.  2 A. 
     FIG. 2D is a top-down view of a rubber O-ring used to attach the electrode holder to the elastic cap portion of FIG.  1 . 
     FIG. 3A is a cross-sectional side view along line A—A of FIG. 3B of an exemplary electrode carried within the electrode holder of FIG.  2 A. 
     FIG. 3B is a top plan view of the embodiment of FIG.  3 A. 
     FIG. 3C is a side plan view of the embodiment of FIG.  3 A. 
     FIG. 4A is a perspective top view of an alternative embodiment of a cup shaped electrode carried in an exemplary electrode holder of FIG.  2 A. 
     FIG. 4B is a perspective bottom view of an alternative embodiment using a cup shaped electrode carried in the electrode holder of FIG.  2 A. 
     FIG. 4C is a top-down view of the embodiment of the electrode of FIG.  4 A. 
     FIG. 4D is a side view of the embodiment of the electrode of FIG.  4 A. 
     FIG. 4E is a cross-sectional view of an alternative embodiment of a conductive plastic electrode embodiment carried in the electrode holder of FIG.  2 A. 
     FIG. 4F is a top plan view of the embodiment of the electrode in FIG.  4 E. 
     FIG. 5A is a top plan view of an alternative embodiment of a conductive plastic electrode embodiment carried in the electrode holder of FIG.  2 A. 
     FIG. 5B is a cross-sectional side view along line B—B of the embodiment of the conductive plastic electrode of FIG.  5 A. 
     FIG. 5C is a top plan view of an alternative embodiment of a carbon electrode embodiment carried in the electrode holder of FIG.  2 A. 
     FIG. 5D is a cross-sectional side view along line C—C of the embodiment of the carbon electrode of FIG.  5 C. 
     FIG. 6 is a top plan view of an alternative embodiment of a cortical depth electrode embodiment used with the carbon lead wire harness of the present invention. 
     FIG. 7 is a top plan view of an alternative embodiment of a cortical surface grid electrode embodiment used with the carbon lead wire harness of the present invention. 
     FIG. 8 is a top plan view of an alternative embodiment of a cortical surface strip electrode embodiment used with the carbon lead wire harness of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, the fMRI-compatible electrode placement system of the present invention includes an elastic fabric cap portion  10  and chinstrap portion  11 , both composed preferably of a combined Lycra-Spandex™ material such as Style #: 96175 Black-09000, manufactured by Liberty Fabrics, 13441 Liberty Lane, Gordonsville, Va.). Attached to the elastic cap portion  10 , is a plurality of electrode holders  20   a-n . The designation “n” means that the number depends on the number of electrodes desired. In typical usage, for example, n may be in the range from 1 to 1024. Also in FIG. 1, a plurality of lead wires  13  of the present invention form a harness assembly  14 . The lead wires may be constructed of any non-ferromagnetic conductive material, but are preferably made of carbon. The lead wires may be wrapped in groups with flexible wrapping material (not shown), and extend from the electrodes (not shown) carried within the electrode holders  20   a-n  away from the head, terminating in a connector, such as a CHG-Series 40 pin connector (not shown) manufactured by 3M, Inc. The flexible wrapping (not shown) is used to ensure the wires will not be allowed to coil while inside the MRI environment in order to prevent induced heating of the lead wire material. 
     As shown in FIGS. 2A-2D, the electrode holder  20  is preferably constructed from a single piece of molded medical grade EPDM rubber, such as compound L-5099. The electrode holder  20 , provides a central hole portion  21 , which allows access to the central well portion  22 , and which passes down to the scalp surface. Electrolyte is injected through the central hole  21  to fill the central well portion  22  creating a bridge to conduct the electrical signal from the skin surface to the electrode (not shown), which rests on the ridge portion  23  located within the central well portion  22  of the electrode holder  20 . On the side of the electrode holder  20 , near the top, a hole  24  exists where a lead wire attachment portion of the electrode (not shown) extends from the electrode holder. On the outside portion of the electrode holder  20 , an indentation  25  exists in which two O-rings  26  are used to capture the elastic fabric of the cap  10  from above and below when the electrode holder is pushed through the elastic cap fabric  10 . 
     As shown in FIGS. 3A-3C, the electrode  30  of the present invention as a flat disk portion  31  with a central hole  32 . The electrode  30  also includes a lead wire attachment portion  33 , which extends outward from the flat disk portion  31  and provides a pathway  34 . Such a pathway may be created by drilling or by other mechanisms. The drilled pathway  34  provides an opening in which the lead wire  13  passes and is attached to the electrode  30  by crimping the attachment portion  33  onto the lead wire  13 . 
     In a typical assembly sequence, an O ring is slipped over the lead wire  13 . The electrode  30  is inserted into the central well portion  22  of the electrode holder  20  and rests on the ridge portion  23  to ensure correct placement. The electrode holder is inserted through a button hole or other opening in the elastic fabric cap and secured by positioning one or more O-rings over the fabric. The lead wire  13  is placed into the pathway  34  and the attachment portion  33  is crimped onto the lead wire. 
     An alternative embodiment of the preferred electrode of the present invention is shown in FIGS. 4A-4F, where typical cup shaped electrodes  40  may be composed of metal (such as those manufactured by Specialized Laboratory Equipment, 232 Selsdon Rd. South Croydon Surrey, UK, PN: BO196/02) or conductive plastic  41  (such as those manufactured by Plastics One, 6591 Merriman Rd., S.W., Roanoke, Va., PN: 36562). In a typical metal electrode, a central hole  43  exists to allow injection of electrolyte down to the skin surface. In addition, a well portion  44  is provided to hold electrolyte in contact with the electrode surface. In a typical conductive plastic electrode  41 , a central hole  45  exists to allow injection of electrolyte down to the skin surface. Again, a well portion  46  is provided to hold electrolyte in contact with the electrode surface. Both types of electrodes  40  and  41 , may be readily carried within the electrode holder  20  of the present invention. 
     An alternative embodiment of the preferred electrode of the present invention is shown in FIGS. 5A-5D, where conductive plastic electrodes  50  (such as those manufactured by Select Engineering Inc., 260 Lunenburg St., Fitchburg, Mass., PN: SRT-3001/LP/0.06) and carbon electrodes  51  (such as those manufactured by Select Engineering Inc., 260 Lunenburg St., Fitchburg, Mass., PN: SRT-2001/CF/40) are shown. In both cases the non-metallic nature of the electrode material makes them less susceptible to induced currents present in the MRI environment, as well as to other physiological artifacts caused by movement of the body within the MRI device. On the conductive plastic electrode  50 , a lead wire attachment means  52  exists, which provides a surface where conductive epoxy (such as EPO-TEK E2101) is used to attach the carbon lead wire  13  to the conductive plastic electrode  50 . On the carbon electrode  51 , a well portion  53  exists to hold electrolyte in contact with the electrode surface. The lead wire  13  is attached to the carbon electrode  51  by use of conductive epoxy at the electrode attachment point  54 . Both the conductive plastic electrode  50  and carbon electrode  51  may be carried within electrode holder  20  of the present invention. 
     An alternative embodiment of the preferred electrode of the present invention is shown in FIG. 6, where an implantible depth electrode assembly  60  (such as those manufactured by AD-Tech Medical Instrument Corp., 1901 William St., Racine, Wis., PN: SP-10P) is used. The depth electrode assembly  60  of the present embodiment positions  10  discreet electrodes  61   a-j  in which each acquires signals from a different region of the brain. The depth electrode assembly  60  can be placed into the cortex of a patient to collect electrical signals from multiple deep regions of the brain simultaneously. The depth electrode assembly  60  would not be carried in the electrode holder  20  of the present invention but rather the lead wire harness assembly  14  directly interfaces to the depth electrode assembly Connection System  62 . 
     An alternative embodiment of the preferred electrode of the present invention is shown in FIG. 7, where a subdural cortical surface electrode assembly  70  (such as those manufactured by AD-Tech Medical Instrument Corp., 1901 William St., Racine, Wis., PN: T-WS-20) is used. In the example given, the subdural cortical surface electrode assembly  70  of the present embodiment positions  20  discreet electrodes  71   a-t  in a grid pattern in which each acquires signals from a different region of the brain. However, other subdural cortical surface electrode assemblies exist that provide different numbers of electrodes. Grids with up to 128 discreet electrodes (not shown) are readily able commercially, but other numbers of electrodes may be used. The subdural cortical surface electrode assembly  70  can be placed on the cortex of a patient to collect electrical signals from multiple regions of the brain underlying the grid pattern formed by the electrodes of the assembly. The subdural cortical surface electrode assembly  70  would not be carried in the electrode holder  20  of the present but rather the lead wire harness assembly  14  would be directly connected to the subdural cortical surface electrode assembly Connection System  72 . 
     An alternative embodiment of the preferred electrode of the present invention is shown in FIG. 8, where a subdural cortical surface electrode assembly  80  (such as that manufactured by AD-Tech Medical Instrument Corp., 1901 William St., Racine, Wis, PN: T-WS-8) is used. The subdural cortical surface electrode assembly  80  of the present embodiment positions  8  discreet electrodes  81   a-h  in a strip pattern in which each acquires signals from a different region of the brain. However, other subdural cortical surface electrode assemblies are readily available commercially that provide from 1 up to 128 discreet electrodes (not shown). The subdural cortical surface electrode assembly  80  can be placed on the cortex of a patient to collect electrical signals from multiple regions of the brain underlying the strip pattern formed by the electrodes of the assembly. The subdural cortical surface electrode assembly  80  would not be carried in the electrode holder  20  of the present invention but would be directly connected to the lead wire harness assembly  14  through the assembly Connection System  82 . 
     In operation, the assembled Quik-Cap is placed on the patient&#39;s head and then, in appropriate embodiments, each electrode holder is filled with conductive electrolyte. Slight abrasion of the skin may be required during placement to reduce the impedance at the skin electrolyte interface to acceptable levels as determined by the input characteristics of the amplifier system to which the Quik-Cap assembly is attached. 
     In the manner described, the problems associated with collection of patient data in the environment of an MRI can be overcome. 
     In this disclosure, there is shown and described only the preferred embodiments of the invention, but as mentioned above, one should understand that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concepts as expressed herein.