Electrical Impedance Tomography (EIT) is an imaging technique used for monitoring of ventilation distribution in the lung. Small alternating currents are injected and resulting voltages are measured on the body surface with electrodes fixed around the thorax. Two-dimensional EIT (2D-EIT) is the most common technique in clinical applications but enables visualization of only one horizontal slice of the thorax. However, additional information in the cranio-caudal direction is necessary to more comprehensively assess the ventilation distribution.
3D-EIT systems address this issue, but clinically approved systems are not yet available. The aim of this study is to realize a multi-layer EIT-system with several electrode planes. An approved EIT system functions as basis for this development (PulmoVista 500, Dräger, Lübeck, Germany). Two planes were used for the technical realization of the multi-layer EIT-system. The alternation between the planes was realised using analog switches, which were controlled via a frequency generator and transfer the injected current and the measured voltages between the different electrode planes and the EIT device. The multi-layer EIT-System was applied to a phantom tank for first pilot measurements.
Results on the phantom tank with non-conductive targets at different heights reveal that the system is capable of providing information in the cranio-caudal direction. The high frame rates of EIT images combined with the high switching speed of the used analog switches enable real-time acquisition of ventilation at different thoracic planes. Thus, the modified EIT device makes it possible to comprehensively monitor the redistribution of air in the lungs during a breathing cycle, not only in a single plane, but also in the cranio-caudal direction.