Paul M Record

Multifrequency electrical impedance tomography

Multifrequency tomography may be conveniently achieved by sequentially sweeping the probing drive current and measuring the resultant voltages at each frequency. If events change during measurement comparisons between frequencies cannot be made. Mixing several frequency components may decrease acquisition time but increase the complexity of the instrumentation. A third method is described using Fourier transformation that enables simultaneous multifrequency measurements without an increase in instrumentation. A signal is constructed from a number of sinusoidal components of known amplitude and phase. This group of components is transformed into a time series by the inverse Fourier transform and applied to the object via a voltage or current source. Transforming the detected voltage back into Fourier components will provide the frequency response of the object. Data are collected in this way for all projections and tomograms reconstructed for each frequency. This has the advantage that no special detector is required; both in-phase and quadrature components are available and systematic errors may be easily corrected by software. This technique is demonstrated using a resistor phantom with known frequency-dependent perturbations.

Finite Element Modelling For Electrical Impedance Tomography

Sensitivity coefficients for changes in resistivity of individual voxels within the object are dependant upon the change in resistivity within other voxels. This is demonstrated using finite element models for both on and off-plane perturbations. It is proposed that more appropriate finite element models of body sections will elicit more information for practical electrical impedance tomography reconstruction algorithms.

Active Electrodes For Electrical Impedance Tomography The Limitation Of Active Stray Capacitance Compensation

Active electrodes for impedance imaging have been developed in Toulouse and in Stoke-on-Trent. In order to increase the accuracy of measurement, an active approach for limiting the buffer input stray capacitance by positive feedback has been tried. Limitations of this technique are exposed.

Modelling of the adult head for electrical impedance tomography

A 2-d finite element model is used to simulate the adult head. The effect of gross variations of skull thickness on the sensitivity of measurement pairs to areas within the model are obtained. The implications of these measurements for electrical impedance tomography of the adult brain are discussed. Inter-patient variability of the adult skull may be a key factor in electrical impedance tomography of the adult head.

Raw data interchange format for electrical impedance tomography

A data interchange format is described to allow groups working on electrical impedance tomography (EIT) with disparate algorithms and instruments to compare results. The procedure has been tested by exchanging data by e-mail. The format is defined in the appendix.

Impedance Imaging Electrodes - A New Measurement Technique

A new technique is described which exploits capacitively coupled non-electrolyte electrodes to allow two electrodes measurement of tissue section impedance. By inductively cancelling the electrode capacitance the exciting voltage is applied directly across this section. The series impedance thus measured is then only of the tissue.