Assessment of 1-lead and 2-lead electrode patterns in electrical impedance endotomography.

Electrical impedance endotomography (EIE) is a modality of impedance imaging where the electrodes are located on an insulating core placed at the centre of the region of interest. The absence of a physical limit to the medium surrounding the probe enables the use of remote electrodes. The present study compares the features of 2-lead measurements, where the two pairs of electrodes are located on the probe, to 1-lead measurements, where one of the two injection electrodes and one of the two sensing electrodes are located at a distance far away from the probe. The methodology was the characterization of the sensitivity matrix under the influence of electrode pattern, reconstruction radius and mesh construction. Three mesh constructions, three values of the reconstruction radius and five electrode patterns were compared. The study was carried out in 2D using calculated data. Measurement noise was simulated by an addition of 5% Gaussian white noise. The images were reconstructed using the Tikhonov method and L-curve technique. The results show that the reconstruction mesh and the radius of the reconstruction domain have less influence on the conditioning of the sensitivity matrix than the electrode pattern. Both 1-lead and 2-lead configurations enabled the reconstruction of images of relatively similar quality. Additional selection criteria are expected from hardware considerations.

Electrical impedance endotomography: sensitivity distribution against bipolar current patterns.

Electrical impedance endotomography (EIE) is a modality where the electrodes are located around an insulating core placed inside the region of interest. This approach results in significant differences with respect to conventional EIT. The paper examines the sensitivity distribution of bipolar current patterns and the influence of the spacing between the drive electrodes using a two-dimensional (2D) mathematical model. The number of pixels of sensitivity above a given sensitivity threshold decreases faster with the distance to the probe for diametric and adjacent drive than for other bipolar drive patterns. The reconstruction of images from datasets collected in vitro using a 16-electrode probe confirmed the feasibility of the method at least within a range extending to three times the radius of the probe, under the described experimental conditions. Reduction of system noise, multiple-current patterns and the use of remote current and voltage electrodes are potential methods to increase the sensitivity range. Further work includes the improvement of the model to account for finite length electrodes and the miniaturization of the probe.