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Experimental study of electrophysiology using the fEITER system

Robinson, Rebecca Louise

[Thesis]. Manchester, UK: The University of Manchester; 2011.

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Abstract

Within neurophysiology, there is need for improvements to functional brain imaging devices. Neural processing within the brain occurs on milli-second through to second timescales. Currently there are no systems with the sufficient temporal resolution and depth sensitivity. Electrical impedance tomography (EIT) is a technique that offers milli-second imaging, depth sensitivity, portability and low cost. It is already applied routinely in other medical applications such as lung function monitoring and breast imaging. The research presented in this thesis has contributed to the design and development of a 32-electrode EIT system, known as fEITER (functional Electrical Impedance Tomography of Evoked Responses). fEITER has been designed to be a brain imaging device that has a temporal resolution of 100 fps with an overall SNR of greater than 70 dB operating at 10 kHz. In order to carry out human tests using fEITER, the system required applications to the local and national ethics (NRES) as well as safety standards regulation (MHRA). These processes were successfully completed, receiving a ‘notice of no objection’ for a clinical trial using fEITER at The University of Manchester and Manchester Royal Infirmary. A series of tank tests were analysed as a method of understanding the system performance. The data obtained from human tests showed unique results. The reference data showed a repeating ‘saw tooth’ that is time-locked to the heart beat of the volunteer, which is a novel observation in medical EIT. Furthermore, the auditory stimuli data showed topographical differences across the scalp with respect to the startle and controlled auditory stimuli. These observations are based on single-event evoked responses, which is unique within the field of evoked potential studies. From the observations reported in this thesis it is plausible that fEITER is measuring voltages changes that are due to the neural processing.