Multi-frequency EIT system with radially symmetric architecture: KHU Mark1

Abstract

We describe the development of a multi-frequency electrical impedance tomography (EIT) system (KHU Mark1) with a single balanced current source and multiple voltmeters. It was primarily designed for imaging brain function with a flexible strategy for addressing electrodes and a frequency range from 10 Hz-500 kHz. The maximal number of voltmeters is 64, and all of them can simultaneously acquire and demodulate voltage signals. Each voltmeter measures a differential voltage between a pair of electrodes. All voltmeters are configured in a radially symmetric architecture in order to optimize the routing of wires and minimize cross-talk. We adopted several techniques from existing EIT systems including digital waveform generation, a Howland current generator with a generalized impedance converter (GIC), digital phase-sensitive demodulation and tri-axial cables. New features of the KHU Mark1 system include multiple GIC circuits to maximize the output impedance of the current source at multiple frequencies. The voltmeter employs contact impedance measurements, data overflow detection, spike noise rejection, automatic gain control and programmable data averaging. The KHU Mark1 system measures both in-phase and quadrature components of trans-impedances. By using a script file describing an operating mode, the system setup can be easily changed. The performance of the developed multi-frequency EIT system was evaluated in terms of a common-mode rejection ratio, signal-to-noise ratio, linearity error and reciprocity error. Time-difference and frequency-difference images of a saline phantom with a banana object are presented showing a frequency-dependent complex conductivity of the banana. Future design of a more innovative system is suggested including miniaturization and wireless techniques.

An instrumental electrode model for solving EIT forward problems

“…For EIT systems working at lower frequencies (< 500 kHz), the GIC (Oh et al 2011, Oh et al 2007b, Ross et al 2003 is widely used to alleviate the effects of capacitive loading, but it performs poorly at frequencies higher than 500 kHz.…”

Determination of Optimal Parameters and Feasibility for Imaging of Epileptic Seizures by Electrical Impedance Tomography: A Modelling Study Using a Realistic Finite Element Model of the Head

“…This would be the optimal set-up to measure seizure-related boundary voltage changes, whose detection would lead to a future application of EIT as new method for neuroimaging in epilepsy. The current EIT systems designed for brain imaging are the UCH Mk 2.5 and UCH Mk1b (Yerworth et al, 2002) serial systems and the KHU Mk1, which has parallel recording capabilities (Oh et al, 2007). However the possibility of using fully-parallel EIT systems originally designed for other applications could be considered.…”

Arquitetura de aquisição de sinais para tomografia por impedância elétrica.

“…Oh et al [10] descreve um sistema de TIE chamado KHU Mark2, caracterizado por melhorias em relaçãoà versão anterior chamada KHU Mark1 [11], desenvolvido com apoio da Kyung Hee University. Este sistema multi-frequencial opera com injeção de corrente e medição de tensão (amplitude e fase) em frequências de 10Hz até 500kHz com até 6 frequências diferentes simultâneas.…”

“…As componentes harmônicas têm grande importância por serem fruto do comportamento não linear dos circuitos eletrônicos ( [9]). 11 Utilizado para circuito que manipulam sinais diferenciais, a rejeição de modo comum, ou, em inglês, commonmode rejection rate (CMRR), refere-se a relação entre o ganho para sinais diferencias e sinais comunsàs duas (ou mais) entradas do circuito ( [9]). condição, o erro de reciprocidade 12 foi, excluindo a frequência de 10Hz, menor que 1% com média de 0.49%.…”

“…Para minimizar o processamento requerido nessa comunicação foi definida uma topologia em anel com conexões ponto-a-ponto entre os módulos e um formatoúnico de pacote. 11 Formato padrão para manipulação de valores reais em sistemas computacionais A tabela CONTROL armazena as configurações utilizadas no processo de aquisição e sua coluna dataTable indica o nome da tabela (MEASURE) onde as medições estão armazenadas.…”