Estimating depth and strength of point-like sources in a conductive semi-space in the presence of electrode noise....

Estimating the depth h and "strength" A of a point current source in a conductive semi-space, in the presence of spatial noise n generated by point electrodes on the surface, is a first theoretical step in estimating depth and "strength" of motor units through surface electromyography (sEMG). Two samples of the surface voltage distribution provide a system of two equations from which A and h are obtained when n = 0. When n ≠ 0, estimates A^ and h^ are obtained from Montecarlo simulations as well as their histograms, means, and variances. Two additional methods based on the width and side slope of the surface voltage distribution are introduced. This work 1) discusses how the estimates are related to the true A, h, and to the noise standard deviation σ_n and 2) addresses the issue of depth estimation of an "equivalent source" when multiple sources are distributed in specific locations. It is concluded that 1) the means of A^ and h^ have negligible bias but their coefficients of variation (CoV) may respectively reach 10% and 20% at high noise values and 2) an "equivalent source" may be the same for different source distributions.