Optimizing Electrode Configuration for Electrical Impedance Measurements of Muscle via the Finite Element Method
Mina Jafarpoor, Jia Li, Jacob K. White, and Seward B. Rutkove
Volume: 60, Issue: 5, Page: 1446-1452
Electrical impedance myography (EIM) is a 4-electrode impedance-based technique for the evaluation of neuromuscular diseases, including amyotrophic lateral sclerosis and muscular dystrophy. In this study, we evaluated how alterations in the size and conductivity of muscle and thickness of subcutaneous fat impact on multifrequency EIM data, with the aim of identifying an optimized electrode configuration for EIM measurements. Finite element models were developed for the human upper arm based on anatomic data; material property data (conductivity and relative permittivity) of the tissues was obtained from the rat and published sources. Of the three major EIM parameters, resistance, reactance, and phase, the reactance was least susceptible to alterations in the subcutaneous fat thickness, regardless of electrode arrangement. For example, a quadrupling of fat thickness resulted in a 375% increase in resistance at 35 kHz but only a 29% reduction in reactance. By further optimizing the electrode configuration, the change in reactance could be reduced to just 0.25%. These analyses describe a basic approach for further electrode configuration optimization for EIM. The figure shows the basic finite element models using two different electrode configurations and the associated differences in resistance and reactance values for varying subcutaneous fat thicknesses.