Active electrode, bio-impedance based, tissue discrimination system and methods of use

• US 20060085049A1
• Filed: 10/19/2005
• Published: 04/20/2006
• Est. Priority Date: 10/20/2004
• Status: Active Grant

• Current Assignee: Nervonix, Inc.
• Original Assignee: Nervonix, Inc.
• Inventors: Cory, Phillip C., Cory, Joan M., Schulz, Waldean A., Ray, Paul L., Kramer, Daniel A.
• Granted Patent: US 7,865,236 B2
• Time in Patent Office: Days
• US Class Current: 607/48
• CPC Class Codes: A61B 2562/0215 Silver or silver chloride containing
• CPC Class Codes: A61B 2562/0217 Electrolyte containing
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/4041 Evaluating nerves condition
• CPC Class Codes: A61B 5/4519 Muscles A61B5/389, A61B5/224 take precedence
• CPC Class Codes: A61B 5/4893 Nerves

Abstract

Systems and methods for discriminating and locating tissues within a body involve applying a waveform signal to tissue between two electrodes and measuring the electrical characteristics of the signal transmitted through the tissue. At least one of the electrodes is constrained in area so that localized electrical characteristics of the tissue are measured. Such localized electrical characteristics are determined over a portion of a body of the subject by using an array of electrodes or electrodes that can be moved over the body. A controller may implement the process and perform calculations on the measured data to identify tissue types and locations within the measured area, and to present results in graphical form. Results may be combined with other tissue imaging technologies and with image-guided systems.

Claims

1. A tissue discrimination system, comprising:

a sensor circuit selected from the group of a voltage sensor, a current sensor and a combination of a voltage and a current sensor;

a waveform electrode having an area no more than approximately 10 mm², the waveform electrode electrically coupled to the sensor circuit;

a return electrode electronically coupled to the sensor circuit; and

a controller electronically coupled to the sensor circuit and configured to;

cause an electrical signal to be applied to the waveform electrode and the return electrode, the electrical signal having a frequency between approximately 500 Hz and approximately 2500 Hz;

receive a signal from the sensor circuit; and

using the signal received from the sensor circuit, calculate a result useful for discriminating tissue.

2. The tissue discrimination system of claim 1, further comprising:

a signal generator electronically coupled to the controller and electrically coupled to the waveform electrode and the return electrode, the signal generator being configured to receive a control signal from the controller and, in response to the control signal, generate the electrical signal applied to the waveform electrode and the return electrode.

3. The tissue discrimination system of claim 1, further comprising a display electronically coupled to the controller, wherein the controller is further configured to send control signals to the display to cause the calculated result to be presented on the display.

4. The tissue discrimination system of claim 1, further comprising a memory coupled to the controller, wherein the controller is further configured to store the calculated result in the memory.

5. The tissue discrimination system of claim 4, wherein the controller is further configured to store the calculated result in the memory in a data format useable by an image guided medical system.

6. The tissue discrimination system of claim 1, further comprising:

an array assembly containing a plurality of waveform electrodes; and

a first switch assembly electronically coupled to the plurality of waveform electrodes, to the sensor circuit and to the controller, the first switch assembly being configured to electrically connect a selected waveform electrode to the sensor circuit in response to a control signal received from the controller.

7. The tissue discrimination system of claim 1, further comprising:

an array assembly containing a plurality of return electrodes; and

a second switch assembly electronically coupled to the plurality of return electrodes, to the sensor circuit and to the controller, the second switch assembly being configured to electrically connect a selected return electrode to the sensor circuit in response to a control signal received from the controller.

8. The tissue discrimination system of claim 1, further comprising:

a first wireless data transceiver coupled to the sensor circuit; and

a second wireless data transceiver coupled to the controller,

wherein the first and second wireless data transceivers are configured to communicate control signals and data signals between the controller and the sensor circuit.

9. The tissue discrimination system of claim 1, further comprising:

a first wireless data transceiver coupled to the display; and

a second wireless data transceiver coupled to the controller,

wherein the first and second wireless data transceivers are configured to communicate control signals and display signals between the controller and the display.

10. The tissue discrimination system of claim 1, further comprising:

an array containing a plurality of waveform electrodes; and

a first switch assembly electronically coupled to the plurality of waveform electrodes and to the controller, the first switch assembly being configured to electrically connect a selected waveform electrode to the sensor circuit in response to a control signal received from the controller.

11. The tissue discrimination system of claim 10, wherein the array containing a plurality of waveform electrodes comprises:

an under layer;

an insulating over layer having a plurality of holes therethrough;

a plurality of electrical conductors positioned on the under layer such that each of the plurality of electrical conductors is located within a corresponding one of the plurality of holes in the insulating layer, each of the plurality of electrical conductors being electrically coupled to the control circuitry by a corresponding one of a plurality of electrical leads; and

electrolyte substantially filling the volume of each of the plurality of holes in the insulating over layer, the electrolyte being electrically coupled with one of the plurality of electrical conductors within the corresponding one of the plurality of holes in the insulating layer.

12. The tissue discrimination system of claim 1, further comprising:

an array containing a plurality of return electrodes; and

a second switch assembly electronically coupled to the plurality of return electrodes and to the controller, the second switch assembly being configured to electrically connect a selected return electrode to the sensor circuit in response to a control signal received from the controller.

13. The tissue discrimination system of claim 1, further comprising:

an ultrasound imaging system; and

a processor configured to receive data from the controller and the ultrasound imaging system and combine the calculated result with image data from the ultrasound imaging system.

14. The tissue discrimination system of claim 1, further comprising:

a data storage device comprising a database configured to receive and store the calculated result; and

a server coupled to the data storage device and configured to provide access to the database via a network.

15. The tissue discrimination system of claim 14 wherein the server is coupled to the Internet and configured to provide access to the database via the Internet.

16. The tissue discrimination system of claim 1, wherein the calculated result is impedance.

17. The tissue discrimination system of claim 1, wherein the calculated result is resistance.

18. The tissue discrimination system of claim 1, wherein the calculated result is reactance.

19. The tissue discrimination system of claim 1, further comprising a data storage device having stored thereon a database of information useful for assisting an operator to interpret the calculated result.

20. The tissue discrimination system of claim 1, further comprising:

an array of a plurality of waveform electrodes positioned about a cylinder, each of the plurality of waveform electrodes electrically respectively coupled to a plurality of electrical leads;

a handle rotatably coupled to the cylinder;

a cable coupled to the handle; and

a rotatable connector assembly electrically coupled to the electrical leads and to the cable.

21. The tissue discrimination system of claim 1, further comprising:

a sheet comprising a plurality of holes at least some of which are of an area equal to or less than approximately 10 mm²,

wherein the waveform electrode is configured to be positioned in one or more of the plurality of holes.

22. The tissue discrimination system of claim 1, further comprising:

a fiducial reference marker coupled to the waveform electrode; and

a position sensing system, comprising a processor, and a position sensor configured to sense the fiducial reference marker and provide a signal to the processor, wherein the processor is configured to determine a position of the waveform electrode based upon the signal provided by the position sensor.

23. The tissue discrimination system of claim 1, wherein the waveform electrode comprises:

a body configured to be held by an operator;

an electrical contactor having a distal and proximal end, where the electrical contactor is coupled to the body at the proximal end, and the distal end comprises an energized portion having an area equal to or less than approximately 10 mm² when placed in contact with skin of a subject.

24. The tissue discrimination system of claim 23, wherein the waveform electrode further comprises a reservoir containing coupling interface material, and a dispenser configured to dispense coupling interface material in the vicinity of the distal end of the electrical contactor.

25. The tissue discrimination system of claim 23, wherein the energized portion comprises a planar surface.

26. The tissue discrimination system of claim 23, wherein the energized portion comprises a walled member defining a volume bounded by walls of an insulator material and a conducting material, the volume having an open area equal to or less than approximately 10 mm², and a coupling interface material contained within the volume.

27. The tissue discrimination system of claim 23, wherein the waveform electrode further comprises a pivot coupled between the distal end of the electrical contactor and the energized portion, the pivot configured to permit the energized portion to contact the skin of the subject so that the area of contact is equal to or less than approximately 10 mm² regardless of the angle at which the waveform electrode body is positioned with respect to the skin'"'"'s surface.

28. The tissue discrimination system of claim 1, wherein the waveform electrode comprises:

a frame;

a plurality of waveform electrodes coupled to the frame; and

a handle coupled to the frame.

29. The tissue discrimination system of claim 1, wherein the waveform electrode further comprises a coupling interface material including an electrically activated dye.

30. The tissue discrimination system of claim 6, further comprising a grid assembly comprising a plurality of openings approximately matching in shape the array assembly containing a plurality of waveform electrodes.

31. The tissue discrimination system of claim 6, wherein the system is assembled as a unitary package further comprising:

a power supply coupled to the controller;

a display coupled to the controller; and

a cable coupled between the return electrode and the sensor circuit and configure to permit the return electrode to be separate from but electrically connected to the unitary package;

wherein;

the controller is further configured to send control signals to the display to cause the calculated result to be presented on the display;

the array assembly containing a plurality of waveform electrodes are positioned on a first side of the unitary package; and

the display is positioned on a second side of the unitary package opposite the first side.

32. The tissue discrimination system of claim 31, wherein the unitary package further comprises a wireless datalink coupled to the controller.

33. A wireless electrode array system suitable for tissue discrimination applications, comprising:

a controller;

a sensor circuit electronically coupled to the controller, the sensor circuit being selected from the group of a voltage sensor, a current sensor and a combination of a voltage and a current sensor;

an electrode array assembly containing a plurality of waveform electrodes, each of the plurality of waveform electrodes having an area no more than approximately 10 mm²;

a switch assembly electronically coupled to the plurality of waveform electrodes, to the sensor circuit and to the controller;

a return electrode electrically coupled to the sensor circuit;

a signal generator electronically coupled to the controller and electrically coupled to the switch assembly and the return electrode, the signal generator being configured to receive a control signal from the controller and, in response to the control signal, generate an electrical signal applied to the waveform electrode and the return electrode; and

a wireless datalink coupled to the controller, the wireless datalink being configured to receive data from the controller and transmit the data via datalink communications, and to receive commands via datalink communications and provide the commands to the controller,

wherein

the switch assembly is configured to electrically connect a selected waveform electrode to the sensor circuit and to the signal generator in response to a control signal received from the controller, and

the controller is configured to send control signals to the signal generator and the switch assembly, receive data signals from the sensor circuit, receive commands provided by the wireless datalink, and send data signals to the wireless datalink for transmission.

34. The wireless electrode array assembly of claim 33, further comprising:

a housing enclosing the controller, signal generator and wireless datalink; and

a cable electrically coupling the switch assembly to each of the plurality of waveform electrodes in the array assembly,

wherein the return electrode is positioned on an external surface of the housing.

35. The wireless electrode array assembly of claim 34, further comprising:

a first electrical connector electrically coupled to the switch assembly; and

a second electrical connector electrically coupled to the cable,

wherein the first and second electrical connectors are complementary and the cable electrically couples the switch assembly to the plurality of waveform electrodes in the array assembly when the first and second electrical connectors are connected one to the other.

36. The wireless electrode array assembly of claim 34, further comprising a power supply positioned within the housing and electrically coupled to one or more of the signal generator, wireless datalink transceiver and controller.

37. The wireless electrode array assembly of claim 33, further comprising:

a return electrode array assembly containing a plurality of return electrodes; and

a second switch assembly electronically coupled to the plurality of return electrodes in the return electrode array assembly, to the sensor circuit and to the controller, wherein the second switch assembly is configured to electrically connect a selected return electrode to the sensor circuit and to the signal generator in response to a control signal received from the controller.

38. The wireless electrode array assembly of claim 33, wherein the controller is further configured to calculate a result from data signals received from the sensor circuit and to send the calculated result to the wireless datalink transceiver for transmission.

39. The wireless electrode array assembly of claim 33, wherein the electrode array assembly comprises:

an under layer;

an insulating over layer having a plurality of holes therethrough;

a plurality of electrical conductors positioned on the under layer such that each of the plurality of electrical conductors is located within a corresponding one of the plurality of holes in the insulating layer, each of the plurality of electrical conductors being electrically coupled to the control circuitry by a corresponding one of a plurality of electrical leads; and

electrolyte substantially filling the volume of each of the plurality of holes in the insulating over layer, the electrolyte being electrically coupled with one of the plurality of electrical conductors within the corresponding one of the plurality of holes in the insulating layer.

40. A roller electrode array assembly, comprising:

a handle;

a cylinder rotatably coupled to the handle;

an array of electrodes disposed about an external surface of the cylinder, each electrode in the array of electrodes being electrically connected to an electrical lead;

a rotatable electrical connector electrically connected to each electrical lead.

41. The roller electrode assembly according to claim 40, further comprising:

return electrode coupled to the handle at a distance from the cylinder.

42. The roller electrode assembly according to claim 41, wherein the return electrode and the cylinder are separated by approximately 20 cm.

43. The roller electrode assembly according to claim 41, wherein the return electrode is configured as a roller.

44. The roller electrode assembly according to claim 40, wherein each electrode in the array of electrodes comprises:

a well formed in a surface of the cylinder;

a conducting surface positioned within the well and electrically coupled to the electrical lead; and

a coupling interface material within the well.

45. The roller electrode assembly according to claim 44, further comprising:

a reservoir containing coupling interface material, the reservoir being coupled to the handle and configured to provide coupling interface material to wells as the cylinder rotates on the handle; and

a scraper configured to remove excess coupling interface material from the surface of the cylinder as the cylinder rotates on the handle.

46. An electrode assembly, comprising:

a body configured to be held in one hand by an operator;

an electrical conductor coupled to the body at an end;

an electrical contactor having a distal and proximal end, where the electrical contactor is coupled to the body at the proximal end and electrically coupled to the electrical conductor, and the distal end comprises an energized portion having an area equal to or less than approximately 10 mm² when placed in contact with skin of a subject.

47. The electrode assembly according to claim 46, further comprising:

an indicator coupled to the body and configured to indicate when the electrical contactor is in proper electrical contact with the skin of the subject.

48. The electrode assembly according to claim 46, further comprising:

a fiducial marker coupled to the body, the fiducial marker being configured to be sensible by an external position sensing system.

49. The electrode assembly according to claim 46, further comprising:

a reservoir suitable for containing a coupling interface material; and

an actuator configured to dispense a portion of the coupling interface material from the reservoir when actuated by an operator.

50. The electrode assembly according to claim 46, wherein the energized portion comprises a planar surface.

51. The electrode assembly according to claim 46, wherein the energized portion comprises a walled member defining a volume bounded by walls of an insulator material and a conducting material, the volume with an open area equal to or less than approximately 10 mm₂, and a coupling interface material contained within the volume.

52. The tissue discrimination system of claim 51, wherein the waveform electrode further comprises a pivot coupled between the distal end of the electrical contactor and the energized portion, the pivot configured to permit the energized portion to contact the skin of the subject so that the area of contact is equal to or less than approximately 10 mm² regardless of the angle at which the waveform electrode body is positioned with respect to the skin'"'"'s surface.

53. A pad for application on skin of a subject for use with a tissue discrimination system, comprising:

a pad comprising insulator material suitable for direct application on the skin of the subject, the pad having disposed therein a means for enabling an electrical connection to be made between an electrode and the skin of the subject within an area limited to approximately 10 mm² or less.

54. The pad of claim 53, wherein the means for enabling an electrical connection comprises through holes having an area limited to approximately 10 mm² or less.

55. The pad of claim 53, wherein the means for enabling an electrical connection comprises conductors within the pad material oriented at right angles to the plane of the pad.

56. The pad of claim 55, wherein the conductors comprise carbon nanotubes.

57. The pad of claim 53, wherein the insulator material exhibits decreased electrical resistance when compressed and the means for enabling an electrical connection comprises compression of the pad beneath an electrode.

58. The pad of claim 54, wherein the insulator material comprises a plastic mesh having a mesh size of approximately 10 mm² or less.

59. The pad of claim 54, further comprising:

a fiducial marker coupled to the pad and configured to be sensed by an external position sensing system; and

indicia adjacent at least one hole in the pad identifying the at least one hole.

60. The pad of claim 59, wherein the indicia comprises a bar code symbol.

61. The pad of claim 59, wherein the indicia comprises an alphanumerical label.

62. The pad of claim 59, wherein the indicia comprises an electrical signal sensible when touched by an electrode.

63. The pad of claim 59, wherein the indicia comprises a radio-frequency oscillator configured to be sensible by a radio-frequency identification tag interrogator.

64. A grid assembly for use with a tissue discrimination system which employs an electrode array assembly;

comprising;

a frame assembly defining an array of openings each having a shape and size which permits the electrode array assembly to be positioned therein; and

a fiducial marker coupled to the frame and configured to be sensed by an external position sensing system.

65. The grid assembly according to claim 64, further comprising a return electrode electrically coupled to the frame and configured to be in electrical contact with skin of a subject when the grid is position on the subject.

66. The grid assembly according to claim 64, further comprising:

a sensor associated with at least one opening in the frame and configured to sense a presence of the electrode array assembly within the opening; and

a data output configured to provide a signal indicating the presence of the electrode array assembly within the opening.

67. An image guided medical system, comprising:

a tissue discrimination subsystem, comprising;

a sensor circuit selected from the group of a voltage sensor, a current sensor and a combination of a voltage and a current sensor;

a waveform electrode having an area no more than approximately 10 mm², the waveform electrode electrically coupled to the sensor circuit;

a return electrode electronically coupled to the sensor circuit; and

a controller electronically coupled to the sensor circuit and configured to

cause an electrical signal to be applied to the waveform electrode and the return electrode, the electrical signal having a frequency between approximately 500 Hz and approximately 2500 Hz,

receive a signal from the sensor circuit,

using the signal received from the sensor circuit, calculate a result useful for discriminating tissue, and

store the calculated result in a database; and

an image guided medical subsystem configured to guide a medical procedure using tissue discrimination data stored in the database by the tissue discrimination subsystem.

68. The image guided medical system of claim 67, wherein

the controller of the tissue discrimination subsystem is further configured to identify locations of nerves using the calculated result and to store the nerve location information within the database, and

the image guided medical subsystem is further configured to guide a medical procedure using the nerve location data.

69. The image guided medical system of claim 68, further comprising an external position sensing subsystem configured to sense a position of the waveform electrode and to correlate the sensed position with a calculated result for the waveform electrode,

wherein the image guided medical subsystem is further configured to guide the medical procedure using the nerve location data and the sensed position.

70. The image guided medical system of claim 68, wherein the image guided medical subsystem is further configured to guide the medical procedure using the nerve location data, the sensed position and at least one other image data set.

71. The image guided medical system of claim 70, wherein the at least one other image data set includes an X-ray.

72. The image guided medical system of claim 70, wherein the at least one other image data set includes computed tomography data set.

73. The image guided medical system of claim 70, wherein the at least one other image data set includes an ultrasound image data set.

74. The image guided medical system of claim 68, wherein the controller and the image guided medical subsystem are configured to send data to and received data from the database via a network.

75. A tissue imaging and discrimination sensor comprising:

a pad comprised of electrical insulating material;

a plurality of electrodes disposed within the pad; and

an ultrasound transducer disposed within the pad.

76. The tissue imaging and discrimination sensor of claim 75, wherein each of the plurality of electrodes has an area of no more than approximately 10 mm², and

the ultrasound transducer is positioned in an interstitial location with respect the plurality of electrodes.

77. The tissue imaging and discrimination sensor of claim 75, wherein the ultrasound transducer comprises a phased array ultrasound transducer array.

78. The tissue imaging and discrimination sensor of claim 75, wherein each of the plurality of electrodes comprises a well within the pad, an electrical conductor disposed within the well, and a coupling interface material disposed within the well.

79. The tissue imaging and discrimination sensor of claim 78, wherein the ultrasound transducer is coupled to the electrical conductor disposed within the well, and the coupling interface material is suitable for use as an acoustic coupling material.

80. The tissue imaging and discrimination sensor of claim 75, further comprising a fiducial marker coupled to the pad and configured to be sensed by an external position sensing system.

81. The tissue imaging and discrimination sensor of claim 78, wherein the coupling interface material includes an electrically activated dye.

82. A subcutaneous electrode array assembly suitable for use with a tissue discrimination system, comprising:

a frame;

a plurality of needle electrodes coupled to the frame;

an electrical conductor coupled to the frame, electrically coupled to each of the plurality of needle electrodes, and configured to be connect to a signal generator of a tissue discrimination system.

83. A method of discriminating tissue within a subject, comprising:

placing a waveform electrode on skin of the subject, wherein the waveform electrode has an area no more than approximately 10 mm²;

placing a return electrode on skin of the subject at a position on the skin removed from the waveform electrode;

applying a signal to the electrode array and the return electrode;

measuring a change in a characteristic of the signal resulting from transmission through tissue between the waveform and return electrodes; and

processing the measured change in the characteristics of the signal to discriminate a tissue located beneath the waveform electrode.

84. The method of discriminating tissue within a subject of claim 83, wherein

the applied signal has a frequency within the range between approximately 500 Hz and approximately 2500 Hz.

85. The method of discriminating tissue within a subject of claim 83, wherein the measured change in the characteristics of the signal comprises voltage.

86. The method of discriminating tissue within a subject of claim 83, wherein the measured change in the characteristics of the signal comprises current.

87. The method of discriminating tissue within a subject of claim 83, wherein the measured change in the characteristics of the signal comprises a phase shift.

88. The method of discriminating tissue within a subject of claim 83, wherein:

measuring a change in a characteristics of the signal comprises measuring an electrical characteristic at discrete times to generate a data series; and

processing the measured change in the characteristics of the signal comprises;

using the data series to derive coefficients of a mathematical function approximating the signal resulting from transmission through tissue between the waveform and return electrodes; and

using the derived coefficients of the mathematical function to calculate an electrical characteristic of the tissue between the waveform and return electrodes.

89. The method of discriminating tissue within a subject of claim 88, wherein the calculated electrical characteristic is impedance.

90. The method of discriminating tissue within a subject of claim 88, wherein the calculated electrical characteristic is conductance.

91. The method of discriminating tissue within a subject of claim 88, wherein the calculated electrical characteristic is susceptance.

92. The method of discriminating tissue within a subject of claim 88, wherein the calculated electrical characteristic is reactance.

93. The method of discriminating tissue within a subject of claim 88, wherein the calculated electrical characteristic is capacitance.

94. The method of discriminating tissue within a subject of claim 88, wherein

the waveform electrode comprises an array of waveform electrodes,

the method is accomplished for each waveform electrode within the array, and

the calculated electrical characteristic associated with each waveform electrode is used to image a discriminated tissue beneath the array of waveform electrodes.

95. The method of discriminating tissue within a subject of claim 94, wherein the image is presented on a display device.

96. The method of discriminating tissue within a subject of claim 94, wherein the image information is used to generate a data set representing a location of the discriminated tissue within the subject, further comprising storing the data set in a database.

97. The method of discriminating tissue within a subject of claim 83, wherein the discriminated tissue is nerve.

98. The method of discriminating tissue within a subject of claim 83, wherein

the method is repeated a number of times with the waveform electrode positioned on a different location on the skin of the subject,

the location of the waveform electrode is recorded each time,

and the calculated electrical characteristic associated with each waveform electrode location is used to image a discriminated tissue beneath the skin of the subject.

99. The method of discriminating tissue within a subject of claim 98, wherein the discriminated tissue is nerve, and the recorded locations are used to generate an image of nerve beneath the skin of the subject.

100. The method of discriminating tissue within a subject of claim 99, wherein the image information is used to generate a data set representing locations of nerve within the subject, further comprising storing the data set in a database.

101. A method of applying anesthesia to a subject, comprising:

placing an array of waveform electrodes on skin of the subject;

placing a return electrode on skin of the subject at a position on the skin removed from the array of waveform electrodes;

for each waveform electrode within the array

applying a signal to a selected one of the waveform electrodes within the array and the return electrode,

measuring a change in a characteristic of the signal resulting from transmission through tissue between the selected waveform and return electrodes, and

processing the measured change in the characteristics of the signal to determine impedance of tissue between the selected waveform and return electrodes;

using the determined impedance for each waveform electrode within the array to determine a location of a nerve beneath the array; and

applying anesthesia to the nerve using the determined location.

102. The method of applying anesthesia of claim 101, further comprising:

applying a signal to a selected one of the waveform electrodes within the array and the return electrode,

measuring a change in a characteristic of the signal resulting from transmission through tissue between the selected waveform and return electrodes, and

processing the measured change in the characteristics of the signal to determine an activity of the nerve to monitor effects of the anesthesia.

103. The method of applying anesthesia of claim 102, further comprising reapplying anesthesia to the nerve when the determined activity of the nerve indicates the anesthesia is wearing off.

104. A method of correcting electrical impedance tomography results, comprising:

placing an array of waveform electrodes on skin of the subject;

placing a return electrode on skin of the subject at a position on the skin removed from the array of waveform electrodes;

for each waveform electrode within the array

applying a signal to a selected one of the waveform electrodes within the array and the return electrode,

measuring a change in a characteristic of the signal resulting from transmission through tissue between the selected waveform and return electrodes, and

processing the measured change in the characteristics of the signal to determine impedance of tissue between the selected waveform and return electrodes;

using the determined impedance for each waveform electrode within the array to determine a location of a nerve beneath the array; and

applying a correction factor to electrical impedance tomography results to account for a preferential conductive path through the nerve.

105. A method of determining nerve density within a subject, comprising:

placing an array of waveform electrodes on skin of the subject;

placing a return electrode on skin of the subject at a position on the skin removed from the array of waveform electrodes;

for each waveform electrode within the array

applying a signal to a selected one of the waveform electrodes within the array and the return electrode,

measuring a change in a characteristic of the signal resulting from transmission through tissue between the selected waveform and return electrodes, and

processing the measured change in the characteristics of the signal to determine impedance of tissue between the selected waveform and return electrodes;

using the determined impedance for each waveform electrode within the array to determine locations of nerve beneath the array; and

calculating a density of nerve within the subject based upon the determined locations of nerve beneath the array.

106. A method of performing a medical procedure, comprising:

placing a waveform electrode on skin of the subject;

placing a return electrode on skin of the subject at a position on the skin removed from the waveform electrode;

applying a signal to the waveform electrode and the return electrode;

measuring a change in a characteristic of the signal resulting from transmission through tissue between the waveform and return electrodes;

processing the measured change in the characteristics of the signal to discriminate a tissue located beneath the waveform electrode, and

performing the medical procedure using the tissue discrimination information.

107. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises surgery, and

the surgery is conducted so as to avoid cutting the nerve.

108. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises nerve therapy, and

the nerve therapy is conducted at the location of the nerve.

109. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises a diagnostic procedure, and

the diagnostic procedure is conducted using the location of the nerve.

110. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises inserting a catheter into the subject, and

the catheter is inserted using the location of the nerve.

111. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises treating a nerve disorder, and

the location of the nerve is used to inject a pharmaceutical agent in the vicinity of the nerve.

112. The method of performing a medical procedure of claim 106, wherein:

processing the measured change in the characteristics of the signal comprises monitoring nerve activity,

the medical procedure comprises diagnosing a condition selected from the group consisting of shingles, Guillain-Barre disease and multiple sclerosis, and

the diagnosis of the condition is accomplished based upon the monitored nerve activity.

113. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises treating a nerve, and

the location of the nerve is used to position a nerve stimulator in the vicinity of the nerve prior to stimulation.

114. The method of performing a medical procedure of claim 106, wherein:

the discriminated tissue is nerve,

the medical procedure comprises performing a radiofrequency lesion on a nerve, and

the location of the nerve is used to position a radiofrequency emitter in the vicinity of the nerve prior to application.