Myokinetic prosthesis control oriented environmental magnetic disturb analysis

Abstract

Several medical applications involve the use of remote magnet tracking for retrieving the position of tools instrumented with one or more magnets, when a free line-of-sight between the magnets and the tracker is not available. Our group recently proposed to implant passive magnetic markers (i.e. permanent magnets) in the forearm muscles of an amputee in order to track the displacements of those muscles during contraction. The idea is to use the retrieved information to control a hand prosthesis. We called this the myokinetic control interface. However, besides the system feasibility, how much its accuracy and precision are affected by external noise sources has not been quantified yet.
Here, through an experimental setup, we investigated the influence of different magnetic/electromagnetic interferences on the localization accuracy of three permanent magnets. The magnetic field generated by the magnets was collected both in interference-free conditions and in presence of disturbances. Localization errors achieved under different conditions, and for both raw and low-pass filtered signals, were derived. Results showed that the steel bar caused the maximum average localization error, equal to 9.8 mm and 74° in terms of position and orientation, respectively. The microwave oven caused instead the maximum localization variability, with a standard deviation of 0.21 mm and 2.2°. The low-pass filtering operation (5 Hz cut-off frequency) did not lead to significant improvement in the accuracy, resulting in an error decrease always below 7% compared to the unfiltered signals.
This work is important because it gives a quantitative measure of the disturbances encountered in everyday life which could cause the failure of those systems exploiting remote tracking.