Abstract
Objective. Electrical impedance tomography has the potential to image fast neural activity associated with physiological or epileptic activity throughout the brain. These applications pose a particular challenge as expected voltage changes on the electrodes are less than 1% and geometrical constraints of the body under investigation mean that electrodes can not be evenly distributed around its boundary. Unlike other applications, however, information regarding the location of expected activity is typically available. An informative method for choosing current paths that maximise sensitivity to specific regions is desirable. Approach. Two electrode addressing protocol generation methods based on current density vectors concentrated in a region of interest have been proposed. One focuses solely on maximising its magnitude while the other considers its distribution. The quality of reconstructed images using these protocols was assessed in a simulation study conducted in a human and rat mesh and compared to the protocol that maximises distance between injecting electrodes. Main results. When implementing the protocol that focused on maximising magnitude, the current density concentrated in a region of interest increased by up to a factor of 3. When the distribution of the current was maximised, the spread of current density vectors increased by up to fivefold. For the small conductivity changes expected in the applications explored, image quality was best when implementing the protocol that maximised current density. The average image error when using this protocol was 7% better than when employing other protocols. Significance. We conclude that for fast neural EIT applications, the protocol that maximises current density is the best protocol to implement.
Highlights
For all positions the max A protocol resulted in the protocol where the current density was most evenly spread across the surface of a hemisphere, tables 4 and 5. This method aimed to maximise the magnitude of the current density in the regions of interest (ROI); for seven out of eight positions in the human and in all positions in the rat, it resulted in the lowest current density magnitude
Two protocol generation methods based on the magnitude and distribution of current density concentrated in a ROI have been developed
The results from the simulations suggest that, when the signal is small, increased current density magnitude attributed to implementing the max J protocol improves image quality
Summary
The current injection protocol describes the set of electrodes through which current is sequentially injected, the choice of which greatly influences the sensitivity to perturbations in different locations. Approaches to optimise the current injection protocol have included those based on distinguishability (Isaacson 1986, Adler et al 2011) as well as more application specific methods. These include breast (Dehghani et al 2005), head (Fabrizi et al 2009) and cardiac (Tehrani et al 2012) EIT. For 3D domains, Malone et al (2014b) have proposed using a protocol that maximises the distance between injecting electrodes to enhance sensitivity to perturbations throughout the volume
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