Electrical impedance measurements for pulmonary disease diagnosis.

An investigation of the physical state of the human thorax and the associated thoracic electrical impedance is presented. From an experimental study with 60 subjects (23 without pulmonary disease and 37 with obstruction or restriction) it is concluded that the percentage change in the measured input impedance from the predicted value is a good index to estimate the size of oedema and the physical state of the lungs. These results are in good agreement with the theoretical analysis of the problem and the patient's physical state.

Performance of a differential synchronous demodulator for electrical impedance tomography.

The performance of a differential synchronous demodulator is presented. This demodulator is part of an electrical impedance tomography system developed by our group. In addition a technique for common-mode correction instead of common-mode feedback is proposed. A series of measurements as a function of the common-mode signal is given.

Reconstruction of impedance images using a modified perturbation method.

A modified perturbation method (MPM) arising from the replacement of the sensitivity matrix by the Jacobian matrix is presented. Our results have been made using an array processor board with four T-800 INMOS transputers. The numerical algorithm has been matched to the new system and the procedure reached a minimum 50 times faster than for a single PC/AT with mathematical co-processor. Several phantoms have been reconstructed. From the results one can see the applicability of the MPM algorithm to complicated models.