Variability in the cardiac EIT image as a function of electrode position, lung volume and body position

A study was conducted using the Sheffield electrical impedance tomography ( EIT) portable system DAS-01 P to determine the change in the cardiac image with electrode position, lung volume and body position. Sixteen electrodes were positioned in three transverse planes around the thorax at the level o f the second intercostal space, at the level of the xiphisternal joint, and midway between upper and lower locations. Data were collected at each elec trode level with the breath held at end expiration and after inspiring 0.5, 1 and 1.5 1 of air with the subject in both the supine and sitting positio n. These data were analysed using a Matlab developed program that calculate s the average resistivity change in the cardiac region from automatically d etermined borders. Results show significant individual variability with ele ctrode position and air volume. The middle electrode most consistently show s an increase in impedance in the region of the heart during systole. In so me subjects the change in the ventricular-volume-like curve showed a greate r than 50% change as a function of lung volume. The pattern of variability with electrode position was not consistent among subjects. In one subject M RI images were obtained to compare actual structures with those seen in the EIT image. The results suggest that using these electrode locations reliab le and consistent data, which could be used in clinical applications, canno t be obtained.