Electrical Impedance Myography

Abstract

Electrical impedance myography (EIM) can be used for the assessment and diagnosis of muscular disorders. EIM includes applying an electrical signal to a region of tissue and measuring a resulting signal. A characteristic of the region of tissue is determined based on the measurement. Performing EIM at different frequencies and/or different angular orientations with respect to a muscle can aid in the assessment and diagnosis. Devices are described that facilitate assessment and diagnosis using EIM.

1 . A method of determining at least one characteristic of a region of tissue, the method comprising acts of:
 applying a plurality of first electrical signals to the region of tissue, each of the plurality of first electrical signals being applied at a respective one of a plurality of orientations so as to propagate through at least a portion of the region of tissue in a respectively different direction with respect to a first axis of the region of tissue;   obtaining a plurality of measurements from the region of tissue, each of the plurality of measurements indicative of a respective one of a plurality of second electrical signals, each of the plurality of second electrical signals resulting from applying a respective one of the plurality of first electrical signals; and   determining the at least one characteristic based, at least in part, on the plurality of measurements.   
     
     
         2 . The method of  claim 1 , wherein the act of applying the plurality of first electrical signals to the region of tissue includes an act of applying at least one first electrical signal in a direction substantially parallel to the first axis and applying at least one first electrical signal in a direction substantially perpendicular to the first axis. 
     
     
         3 . The method of  claim 2 , wherein the act of applying the plurality of electrical signals to the region of tissue includes an act of applying at least one first electrical signal in a direction substantially parallel to the first axis and applying at least one electrical signal at least every approximately 30° rotation from the first axis over a range of approximately 180°. 
     
     
         4 . The method of  claim 2 , wherein the first axis is substantially aligned in a direction of muscle fibers of the region of tissue. 
     
     
         5 . The method of  claim 1 , wherein the plurality of first electrical signals include a plurality of current signals, and wherein the plurality of second electrical signals include a plurality of voltage signals, each resulting from a respective one of the plurality of current signals. 
     
     
         6 . The method of  claim 1 , wherein the act of determining the at least one characteristic includes an act of determining at least one property of the region of tissue at each of the plurality of orientations, based on the plurality of measurements. 
     
     
         7 . The method of  claim 6 , further comprising an act of generating a first signature of the region of tissue, the first signature comprising the at least one property as a function of orientation. 
     
     
         8 . The method of  claim 7 , wherein the at least one property includes a resistance of the region of tissue at the respective orientation. 
     
     
         9 . The method of  claim 7 , wherein the at least one property includes a reactance of the region of tissue at the respective orientation. 
     
     
         10 . The method of  claim 7 , wherein the at least one property includes a phase derived from a resistance and a reactance of the region of tissue at the respective orientation. 
     
     
         11 . The method of  claim 7 , wherein the act of determining the at least one characteristic includes an act of determining a degree of anisotropy of the first signature. 
     
     
         12 . The method of  claim 7 , wherein the act of determining the at least one characteristic includes an act of comparing the first signature with a second signature obtained from a reference region of tissue. 
     
     
         13 . The method of  claim 12 , wherein the second signature is obtained from healthy tissue. 
     
     
         14 . The method of  claim 1 , wherein the act of applying a plurality of first electrical signals includes an act of applying a plurality of first electrical signals, each at a respective one of a plurality of frequencies at each of the plurality of orientations. 
     
     
         15 . The method of  claim 14 , wherein the act of obtaining the plurality of measurements includes an act of obtaining a plurality of measurements from the region of tissue, the plurality of measurements including at least one measurement at each of the plurality of frequencies at each of the plurality of orientations. 
     
     
         16 . The method of  claim 15 , wherein the act of determining the at least one characteristic includes an act of determining at least one property of the region of tissue at each of the plurality of frequencies at each of the plurality of orientations, based on the plurality of measurements. 
     
     
         17 . The method of  claim 16 , further comprising an act of generating a first signature of the region of tissue, the first signature comprising the at least one property as a function of orientation and frequency. 
     
     
         18 . The method of  claim 17 , wherein the act of determining the at least one characteristic includes an act of determining a degree of anisotropy of the first signature. 
     
     
         19 . The method of  claim 18 , wherein the act of determining the muscle characteristic includes an act of comparing the first signature with a second signature obtained from a reference region of tissue. 
     
     
         20 . A method of determining at least one characteristic of a region of tissue, the method comprising acts of:
 applying a plurality of first electrical signals to the region of tissue, each of the plurality of first electrical signals being applied at a respective one of a plurality of frequencies;   obtaining a plurality of measurements from the region of tissue, each of the plurality of measurements indicative of a respective one of a plurality of second electrical signals, each of the plurality of second electrical signals resulting from applying a respective one of the plurality of first electrical signals; and   determining the at least one characteristic based, at least in part, on the plurality of measurements.   
     
     
         21 . The method of  claim 20 , wherein the plurality of first electrical signals include a plurality of current signals and the plurality of second electrical signals includes a plurality of voltage signals, each resulting from the application of a respective one of the plurality of current signals. 
     
     
         22 . The method of  claim 20 , wherein the act of determining the at least one characteristic includes an act of determining at least one property of the region of tissue at each of the plurality of frequencies, based on the plurality of measurements. 
     
     
         23 . The method of  claim 22 , further comprising an act of generating a first signature of the region of tissue, the first signature comprising the at least one property as a function of frequency. 
     
     
         24 . The method of  claim 22 , wherein the at least one property includes a resistance of the region of tissue at the respective frequency. 
     
     
         25 . The method of  claim 22 , wherein the at least one property includes a reactance of the region of tissue at the respective frequency. 
     
     
         26 . The method of  claim 22 , wherein the at least one property includes a phase derived from a resistance and a reactance of the region of tissue at the respective frequency. 
     
     
         27 . The method of  claim 23 , wherein the act of determining the at least one characteristic includes an act of determining a degree of anisotropy of the first signature. 
     
     
         28 . The method of  claim 23 , wherein the act of determining the at least one characteristic includes an act of comparing the first signature with a second signature obtained from a reference region of tissue. 
     
     
         29 . The method of  claim 28 , wherein the second signature is obtained from healthy tissue. 
     
     
         30 . The method of  claim 20 , wherein the act of applying a plurality of first electrical signals includes an act of applying the plurality of first electrical signals at the plurality of frequencies at each of a plurality of orientations. 
     
     
         31 . The method of  claim 30 , wherein the act of obtaining the plurality of measurements includes an act of obtaining a plurality of measurements from the region of tissue, the plurality of measurements including at least one measurement at each of the plurality of frequencies at each of the plurality of orientations. 
     
     
         32 . The method of  claim 31 , wherein the act of determining the at least one characteristic includes an act of determining at least one property of the region of tissue at each of the plurality of frequencies at each of the plurality of orientations, based on the plurality of measurements. 
     
     
         33 . The method of  claim 32 , further comprising an act of generating a first signature of the region of tissue, the first signature comprising the at least one property as a function of orientation and frequency. 
     
     
         34 . The method of  claim 33 , wherein the act of determining the at least one characteristic includes an act of determining a degree of anisotropy of the first signature. 
     
     
         35 . The method of  claim 34 , wherein the act of determining the muscle characteristic includes an act of comparing the first signature with a second signature obtained from a reference region of tissue. 
     
     
         36 . A device adapted for application to a surface of skin to determine at least one characteristic of a region of tissue, the device comprising:
 a first electrode adapted to apply a first electrical signal to the region of tissue;   a second electrode adapted to detect a second electrical signal at the region of tissue resulting from the application of the first electrical signal;   a rotatable base on which the first electrode and the second electrode are mounted and arranged such that, when the rotatable base is rotated, the first electrode and the second electrode are rotated with respect to the region of tissue to apply the first electrical signal to the region of tissue at a plurality of orientations so as to propagate through at least a portion of the region of tissue in a respectively different direction with respect to a first axis of the region of tissue, and to detect the second electrical signal resulting from the application of the first electrical signal at the plurality of orientations; and   a measurement component coupled to the second electrode to obtain at least one measurement indicative of the second electrical signal at each of the plurality of orientations.   
     
     
         37 . The device of  claim 36 , wherein the first electrode and the second electrode are spaced apart in a first direction such that the first electrical signal applied to the region of tissue propagates essentially in the first direction through the region of tissue toward the second electrode. 
     
     
         38 . The device  claim 37 , wherein, when the rotatable base is rotated, the first electrical signal propagates in a different direction through the region of tissue with respect to a first axis of the region of tissue at each of the plurality of orientations. 
     
     
         39 . The device of  claim 38 , wherein the rotatable base is capable of being rotated through a range of at least 90°. 
     
     
         40 . The device of  claim 38 , wherein the rotatable base is capable of being rotated through a range of at least 180°. 
     
     
         41 . The device of  claim 38 , wherein the rotatable base is capable of being rotated through a range of at least 360°. 
     
     
         42 . The device of  claim 38 , wherein the measurement component is adapted to determine at least one property based on the at least one measurement to generate a first signature, the first signature comprising the at least one property as a function of orientation. 
     
     
         43 . The device of  claim 36 , wherein the first electrode is adapted to apply a plurality of first electrical signals to the region of tissue, each of the plurality of first electrical signals having a respective one of a plurality of frequencies, and wherein the second electrode is adapted to detect a plurality of second electrical signals, each of the plurality of second signals resulting from a respective one of the plurality of first electrical signals. 
     
     
         44 . The device of  claim 43 , wherein the measurement component is adapted to obtain a plurality of measurements, each of the plurality of measurements indicative of a respective one of the plurality of the second electrical signals. 
     
     
         45 . The device of  claim 44 , wherein the measurement component is adapted to determine at least one property based on each of the plurality of measurements to generate a first signature, the first signature comprising the at least one property as a function of orientation and frequency. 
     
     
         46 . The device of  claim 45 , wherein the at least one property includes a resistance of the region of tissue at the respective orientation and frequency. 
     
     
         47 . The device of  claim 45 , wherein the at least one property includes a reactance of the region of tissue at the respective orientation and frequency. 
     
     
         48 . The device of  claim 45 , wherein the at least one property includes a phase derived from a resistance and a reactance of the region of tissue at the respective orientation and frequency. 
     
     
         49 . The device of  claim 42 , further comprising an analysis component to determine a degree of anisotropy of the first signature. 
     
     
         50 . The device of  claim 45 , further comprising a comparison component coupled to receive the first signature, the comparison component adapted to compare the first signature with a second signature obtained from a reference region of tissue. 
     
     
         51 . The device of  claim 12 , further comprising a display coupled to the measurement component, the display adapted to present the first signature in a human perceptible format. 
     
     
         52 . A device adapted for application to a surface of skin to determine at least one characteristic of a region of tissue, the device comprising:
 a plurality of first electrodes each adapted to apply a respective one of a plurality of first electrical signals to the region of tissue;   a plurality of second electrodes respectively associated with the plurality of first electrodes to form a plurality of electrode pairs, each of the plurality of second electrodes adapted to detect a respective one of a plurality of second electrical signals at the region of tissue, each of the plurality of second electrical signals resulting from the application of a respective one of the plurality of first electrical signals;   a base on which the plurality of electrode pairs are mounted, the plurality of electrode pairs each arranged at a respective one of a plurality of orientations such that when the base is applied to the region of tissue, the plurality of first electrical signals may be selectively provided to the region of tissue at the plurality of orientations; and   a measurement component capable of being selectively coupled to each of the plurality of second electrodes, the measurement component adapted to obtain at least one measurement indicative of one of the plurality of second electrical signals corresponding to one of the plurality of second electrodes to which the measurement component is coupled.   
     
     
         53 . The device of  claim 52 , wherein the plurality of orientations are spaced apart by at least 30 degrees.