Electrical impedance myography

Abstract

Electrical impedance myography (EIM) can be used for 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 modeling one or more impedance metrics as a function of frequency may provide impedance model parameters that can aid in the assessment and diagnosis. Devices are described that facilitate assessment and diagnosis using EIM.

What is claimed is: 
     
         1 - 14 . (canceled) 
     
     
         15 . A method for performing an impedance measurement for biological tissue having at least two cell types, the method comprising:
 positioning a first pair of electrodes on the biological tissue along a first axis;   positioning a second pair of electrodes on the biological tissue along the first axis and between the first pair of electrodes;   controlling an alternating current in the first pair of electrodes;   varying the frequency of the alternating current over a plurality of frequency values;   measuring at least one voltage from the second pair of electrodes;   determining a plurality of impedance measurements based on the alternating current over a plurality of frequency values and the at least one voltage; and   calculating a ratio of the plurality of impedance measurements.   
     
     
         16 . The method of  claim 15 , wherein the plurality of frequency values include a first frequency and a second frequency, the first frequency produces a first impedance measurement optimized for a first cell type, the second frequency produces a second impedance measurement optimized for a second cell type. 
     
     
         17 . The method of  claim 16 , wherein the first cell type is muscle and the second cell type is fat. 
     
     
         18 . The method of  claim 17 , wherein the first frequency is 50 kHz and the second frequency is 200 kHz. 
     
     
         19 . The method of  claim 15 , wherein the plurality of impedance measurements are phase values. 
     
     
         20 . The method of  15 , wherein the plurality of frequency values are 50 kHz and 200 kHz. 
     
     
         21 . A method for measuring impedance of biological tissue in an organism, the method comprising:
 contacting an electrode array to the biological tissue, the electrode array having a plurality of electrodes;   controlling an AC input signal to the electrode array; measuring an output signal from the electrode array;   determining at least one impedance measurement based on the input signal and output signal;   determining a status of the biological tissue based on the at least one impedance measurement; and   determining a status of the organism based on the at least one impedance measurement.   
     
     
         22 . The method of  claim 21 , wherein the biological tissue is a tongue of an organism. 
     
     
         23 . The method of  claim 22 , wherein the status of the biological tissue is a condition of the tongue. 
     
     
         24 . The method of  claim 21 , wherein the biological tissue is facial muscle of an organism. 
     
     
         25 . The method of  claim 21 , wherein the at least one impedance measurement is a phase value. 
     
     
         26 . The method of  claim 21 , wherein the status of the organism is a measure of disease severity. 
     
     
         27 . The method of  claim 26 , wherein the measure of disease severity is bulbar dysfunction when the organism has amyotrophic lateral sclerosis (ALS).