Abstracts Category : Other

Clinical Applications of Electrical ImpedanceTomography

by Tanviha Quraishi

INTRODUCTION Electrical Impedance Tomography (EIT)is an emerging clinical imaging technique. Functional EIT by EvokedResponse (fEITER) was developed at the University of Manchester asa high-speed, functional brain imaging device for use at thebedside. This 32-electrode EIT system applies an injectionfrequency of 10kHz and captures data using a 10ms temporalresolution. This thesis reports on the first volunteer and patienttrials undertaken using fEITER for the following conditions: (a)flashing visual sequence - 14 awake volunteers; (b) a voluntaryValsalva manoeuvre (VM) - 15 awake volunteers and (c) during theinduction of anaesthesia - 16 elective surgical patients.AIMS Theresearch presented in this thesis was undertaken to differentiatebetween noise and physiological changes in raw fEITER datasignals.METHODS SNR was determined for fEITER. Raw fEITER signalswere pre-processed to reduce noise and dominant trends beforemultiple comparisons between reference and stimulus data wereundertaken. Histograms and ROC curves were produced to illustratethe difference between reference and stimulus fEITER data. AUCvalues for single-subject and pooled ROC curves were calculated todetermine whether fEITER data can be reliably differentiatedbetween reference and stimulus conditions. Approximate Entropy(ApEn) was applied to evaluate the regularity of high frequencycomponents within fEITER data for each trial condition.RESULTSAverage SNR values for fEITER acquired using mesh and physicalphantoms ranged from 62.94dB to 63.58dB, and 28.29dB to 31.45dBrespectively. The following AUC values were acquired: Visualstimulus-frontal electrode pairs and electrode pairs overlying thevisual cortex 0.520 and 0.505 respectively; VM: 0.658; andinduction of anaesthesia: 0.547. The VM induced the greatestdifference between pooled reference and stimulus data. Visualstimulation and induction of anaesthesia data showed poordistinction between pooled reference and stimulus data, althoughsome single subject data did show a significant response. Nosignificant differences were acquired for the comparison ofApEn-reference and ApEn-stimulus data for all trial conditionsusing a Wilcoxons signed ranks test (visual stimulus-frontalelectrode pairs: upper p = 0.998, visual stimulus-electrodeoverlying the visual cortex: upper p = 0.980; the VM: upper p =0.976, and induction of anaesthesia: p = 0.912).DISCUSSION Althoughsingle-subject and pooled fEITER data recorded during the VMproduced the greatest differences between reference and stimulusmeasurements, stimuli such as visual flashes and induction ofanaesthesia may not be large enough to induce quantifiable changesbetween reference and stimulus data recorded from single electrodepairs.Collectively, these results provide little evidence to showthat pre-processing of raw fEITER data amplifies features in fEITERwaveforms which may be representative of physiological changesinduced by an applied stimulus.Advisors/Committee Members: POLLARD, BRIAN BJ, MARCHANT, THOMAS T, Pollard, Brian, Bryan, Angella, Marchant, Thomas.