A model of electrical impedance tomography implemented in nerve-cuff for neural-prosthetics control

Hope, James; Vanholsbeeck, Frédérique; McDaid, Andrew

doi:10.1088/1361-6579/aab73a

Cited by 14 publications

(32 citation statements)

References 82 publications

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“…In single frequency experiments, the unobserved impedance change with transverse current may be due to the low resolution in the data acquisition module, though this limitation is offset by the dithering effect of frequencies in the same experiment cannot be compared to previous modelling in [1,12] or results in [22] as the angle between drive and measurement electrodes were different for each FDM carrier signal.…”

Section: Discussionmentioning

confidence: 99%

Extracting impedance changes from a frequency multiplexed signal during neural activity in sciatic nerve of rat: preliminary study in vitro

et al. 2019

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Objective: Establish suitable frequency spacing and demodulation steps to use when extracting impedance changes from frequency division multiplexed (FDM) carrier signals in peripheral nerve.Approach: Experiments were performed in-vitro on cadavers immediately following euthanasia. Neural activity was evoked via stimulation of nerves in the hind paw, while carrier signals were injected, and recordings obtained, with a dual ring nerve cuff implanted on the sciatic nerve. Frequency analysis of recorded compound action potentials (CAPs) and extracted impedance changes, with the latter obtained using established demodulation methods, were used to determine suitable frequency spacing of carrier signals, and bandpass filter (BPF) bandwidth and order, for a frequency multiplexed signal.Main results: CAPs and impedance changes were dominant in the frequency band 200 -500 Hz and 100 -200 Hz, respectively. A Tukey window was introduced to remove ringing from Gibbs phenomena. A +/-750 Hz BPF bandwidth was selected to encompass 99.99% of the frequency power of the impedance change. Modelling predicted a minimum BPF order of 16 for 2 kHz spacing, and 10 for 4 kHz spacing, were required to avoid ringing from the neighbouring carrier signal, while FDM experiments verified BPF orders of 12 and 8, respectively, were required. With a notch filter centred on the neighbouring signal, a BPF order of at least 6 or 4 was required for 2 and 4 kHz, respectively. Significance:The results establish drive frequency spacing and demodulation settings for use in FDM electrical impedance tomography (EIT) experiments, as well as a framework for their selection, and, for the first time, demonstrates the viability of FDM-EIT of neural activity on peripheral nerve, which will be a central aspect of future real-time neural-EIT systems and EIT-based neural prosthetics interfaces.

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Section: Discussionmentioning

confidence: 99%

Extracting impedance changes from a frequency multiplexed signal during neural activity in sciatic nerve of rat: preliminary study in vitro

et al. 2019

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“…A quasi-static approximation of Maxwell's equations was used to implement neural activity by solving the FEM models under several static conditions, where, for each condition, the electrical conductivity of fascicle sub-volumes was set to that of either the active or inactive state. This quasi-static approach is valid up to several 100s of kHz for intra-fascicle tissue [1]. Zeroth order Tikhonov regularisation was used to invert the sensitivity matrix, as was done in [17,33], with the Tikhonov regularisation parameter selected using the L-curve, or Pareto frontier curve, method [34].…”

Section: A Eit Forward Solutionmentioning

confidence: 99%

“…the medial nerve, in human. The impedance change applied to intra-fascicle tissue, Table 1, is representative of all fibres being active [1], and so provides an artificially large signal. To accommodate the large signal, the absolute noise and error value of 0.2 mV is selected to be a factor of 20 to 200 times greater than that commonly found in neural EIT systems [7,17,31].…”

Section: A Limitationsmentioning

confidence: 99%

Drive and measurement electrode patterns for electrode impedance tomography (EIT) imaging of neural activity in peripheral nerve

Hope¹,

Vanholsbeeck²,

McDaid³

2018

Biomed. Phys. Eng. Express

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Objective: To establish the performance of several drive and measurement patterns in EIT imaging of neural activity in peripheral nerve, which involves large impedance changes in the nerve's anisotropic length axis. Approach: Eight drive and measurement electrode patterns are compared using a finite element (FE) fourcylindrical 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 -0.30 in length axis and -8.8x10 -4 in the radial axis. Four of the electrode patterns generate longitudinal drive current, which runs parallel to the anisotropic axis, while the remaining four patterns generate transverse drive current, which runs perpendicular to the anisotropic axis.Main results: Transverse current patterns produce higher resolution than longitudinal current 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.

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“…A pair of second nerve cuffs with identical geometry could then be used for selective stimulation and avoidance of off-target effects. It could also have practical applications in reconstructive nerve surgery as a method for functional tractography for correct fascicular repair 32 and in human robotics 33,34 .…”

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Imaging fascicular organization of rat sciatic nerves with fast neural electrical impedance tomography

et al. 2020

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Imaging compound action potentials (CAPs) in peripheral nerves could help avoid side effects in neuromodulation by selective stimulation of identified fascicles. Existing methods have low resolution, limited imaging depth, or are invasive. Fast neural electrical impedance tomography (EIT) allows fascicular CAP imaging with a resolution of <200 µm, <1 ms using a non-penetrating flexible nerve cuff electrode array. Here, we validate EIT imaging in rat sciatic nerve by comparison to micro-computed tomography (microCT) and histology with fluorescent dextran tracers. With EIT, there are reproducible localized changes in tissue impedance in response to stimulation of individual fascicles (tibial, peroneal and sural). The reconstructed EIT images correspond to microCT scans and histology, with significant separation between the fascicles (p < 0.01). The mean fascicle position is identified with an accuracy of 6% of nerve diameter. This suggests fast neural EIT can reliably image the functional fascicular anatomy of the nerves and so aid selective neuromodulation.

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A model of electrical impedance tomography implemented in nerve-cuff for neural-prosthetics control

Cited by 14 publications

References 82 publications

Extracting impedance changes from a frequency multiplexed signal during neural activity in sciatic nerve of rat: preliminary study in vitro

Extracting impedance changes from a frequency multiplexed signal during neural activity in sciatic nerve of rat: preliminary study in vitro

Drive and measurement electrode patterns for electrode impedance tomography (EIT) imaging of neural activity in peripheral nerve

Imaging fascicular organization of rat sciatic nerves with fast neural electrical impedance tomography

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