Title: Drive and measurement electrode patterns for electrode impedance tomography (EIT) imaging of neural activity in peripheral nerve,
Abstract: Objective: To establish the performance of several drive and measurement
patterns in EIT imaging of neural activity in peripheral nerve, which involves
large impedance change in the nerve's anisotropic length axis. Approach: Eight
drive and measurement electrode patterns are compared using a finite element
(FE) four cylindrical shell model of a peripheral nerve and a 32 channel
dual-ring nerve cuff. The central layer of the FE model contains impedance
changes representative of neural activity of -0.3 in the length axis and -8.8 x
10-4 in the radial axis. Four of the electrode patterns generate longitudinal
drive current, which runs perpendicular to the anisotropic axis. Main results:
Transverse current patterns produce higher resolution than longitudinal
patterns but are also more susceptible to noise and errors, and exhibit poorer
sensitivity to impedance changes in central sample locations. Three of the four
longitudinal current patterns considered can reconstruct fascicle level
impedance changes with up to 0.2 mV noise and error, which corresponds to
between -5.5 and +0.18 dB of the normalised signal standard deviation. Reducing
the spacing between the two electrode rings in all longitudinal current
patterns reduced the signal to error ratio across all depth locations of the
sample. Significance: Electrode patterns which target the large impedance
change in the anisotropic length axis can provide improved robustness against
noise and errors, which is a critical step towards real time EIT imaging of
neural activity in peripheral nerve.