Influence of changing peripheral geometry on electrical impedance tomography measurements

WITH REGARD to dynamic imaging in electrical impedance tomography (EIT), theoretical deduction and practical measurements show that it is necessary to keep the peripheral geometry of the cross-section of the object under constant investigation during the reference and main measurements (a (WEBSTER 1990a, b HEIMBACK, 1990). This necessary condition, however, cannot generally be provided for in medical examination procedures. There are two reasons for this predicament; first it is almost impossible to keep the patient immobile during the measurement procedure as this is only possible with anaesthetised patients or patients with stabilised posture. Secondly, the peripheral geometry is susceptible to changes during the examination due to respiration, for example (ADLER et al., 1994). This leads to the question of the extent to which the generated image is caused by the changed resistivity distribution in the cross-section under investigation on the one hand, or by the changes of the peripheral geometry on the other hand, e.g. during respiration. corresponding radial force on the shell of the elastic tank near electrodes 5 and 13 (Fig. 1). Axis dl of the ellipse is situated in the direction of the force applied; axis d2 is perpendicular to dl. The relative changes Dx in da are