Electrode position and size in electrical impedance myography.
OBJECTIVE
Linear-electrical impedance myography (EIM) is a non-invasive technique for the evaluation of muscle, in which high-frequency alternating current is injected into the body via two surface electrodes, and the resulting voltage pattern over a selected muscle is measured using a second, larger set of electrodes. The precise location and size of the electrodes can be critical to the data obtained, and in this study the effects of variation in these factors were evaluated.


METHODS
Linear-EIM was performed in 5 subjects while varying the location of the current injecting electrodes and in an additional 8 subjects while varying the position of the voltage electrodes.


RESULTS
The major outcome variable, the 'spatially averaged phase' (theta(avg)), decreased as the ipsilateral current injecting electrode was moved farther from the voltage electrodes, reaching a plateau 15-20 cm distant. As for the voltage electrode array, distal-proximal shifts resulted in the greatest changes, with variation in theta(avg) being as high as 14% per cm; circumferential shifts around the limb had more modest effects.


CONCLUSIONS
Linear-EIM results depend systematically on current and voltage electrode positions, but with reasonable care variation can be minimized.


CONCLUSIONS
With proper attention to electrode placement, linear-EIM has sufficient reproducibility to become an important clinical tool in neuromuscular disease evaluation.
Rutkove
Seward B
SB
The Department of Neurology, Division of Neuromuscular Diseases, Harvard Medical School, Beth Israel Deaconess Medical Center and the Department of Physics, Northeastern University, Boston, MA 02215, USA. srutkove@bidmc.harvard.edu
Partida
Ramon A
RA
Esper
Gregory J
GJ
Aaron
Ronald
R
Shiffman
Carl A
CA
D000328:Adult; D017097:Electric Impedance; D004566:Electrodes; D004576:Electromyography / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D005260:Female; D005542:Forearm; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D015203:Reproducibility of Results