Compensation of the effect of sub-cutaneous tissue layers on surface EMG: a simulation study

A mathematical model of a four-layer medium (muscle+fat+skin+air) is invest igated. The system is studied in cartesian coordinates with the hypotheses of muscle anisotropy and isotropy of the fat and skin layers, assuming the fat to be less conductive than the skin. Determination of the potential dis tribution over the skin, due to sources in the muscle, is based on the solu tion of the Poisson equation in the spatial frequency domain in the differe nt media. The arbitrary constants are determined imposing the boundary cond itions. In this way the transfer function of the fat and skin layers is fou nd and can be used to compute the potential distribution of the muscle-fat interface. The physiological parameters were obtained from:literature. The results of simulation studies are proposed; it is clear that the subcutaneo us tissue layers produce an attenuation and widening of the potential distr ibution present at the muscle surface. These effects can be partially compe nsated using high-pass spatial filters as proposed in the literature. A new class of bidimensional spatial filters is proposed; the filters are define d on the basis of the information about the isotropic layers rather than be ing general filters. An approximation of the ideal inverse transfer functio n of the sub-cutaneous layers is proposed as a discrete spatial filter that can be implemented with matrices with a small number of electrodes (maximu m of 25 electrodes) and practicable interelectrode distance. A simulated ev aluation of the new filter and the limitations of the approach are presente d. (C) 1999 IPEM. Published by Elsevier Science Ltd. All rights reserved.