Magnetic Resonance Current Density Imaging for Multi-electrode Transcranial Electric Current Stimulation

<p dir="ltr">Magnetic Resonance Current Density Imaging (MRCDI) is a non-invasive imaging modality which leverages MRI to measure the internal magnetic flux density distribution produced by an externally injected current. This current density information is used in Magnetic Resonance Electrical Impedance Tomography (MREIT) reconstructions to create detailed cross-sectional conductivity and current density distributions. The requirement of an externally injected current has necessitated the development of custom current sources, and more recently the development of switching circuits that interface with commercial MRI-compatible tDCS neurostimulators. There is an evolving trend towards multifocal neurostimulation techniques using multiple electrodes, where traditional 2-electrode montages are being superseded by EEG-like configurations employing 4, 8, and even 32 channels. As research into neurostimulation techniques continues there is a growing necessity to develop hardware that can support these complex configurations to enable multifocal MRCDI and MREIT.</p><p dir="ltr">Building upon previous research that introduced a 4-channel switching circuit, this study presents and explores the development of the first 8-channel switching circuit for use with a commercial tDCS system. A cornerstone of this research involves the use of MRI data to create a 3D head model that can be used for simulations and experimental validation. A 3D printed mould was also derived from this data and used to cast a gel head phantom for use in MRCDI and MREIT experiments. Through a series of functional tests and MRI experiments involving the gel phantom, an experiment setup comprising the 8-channel circuit is validated, demonstrating the possibility of 8-channel multifocal MRCDI.</p>