Feasibility of using internal electrodes to improve the accuracy Cardiac Electrical Impedance Tomography

We are developing a method to monitor cardiac function in intensive care units with critically ill patients. The current gold standard is a gated heart pool scan, which provides a good assessment of global heart function, but with low resolution, long lead time, and radiation risks. Less accurate alternatives include trans-esophageal echocardiography, where the ultrasonic probe is inserted into the esophagus behind and close to the heart, and trans-thoracic echocardiography, where the probe observes the heart through the intercostal spaces. These echo modalities often do not provide satisfactory results in these patients due to lung and rib artifact, and the sizes of probe currently used for the trans-esophagus echocardiogram is large, inconvenient for patients, and unable to be left indwelling. EIT is a safe, inexpensive and potentially fast method for global cardiac output imaging but the spatial resolution is presently low. The previous methods for imaging and measurements of cardiac function were completely noninvasive[1]. Here we study internal electrode movement artefacts and report on a pilot experiment where an internal catheters based electrode were located in the superiour vena cava (SVC) and esophagus behaind heart. Reliable impedance changes were recorded over 5 ECG cycles demonstrating that internal electrode movement was low and that the electrode returns to the same position each cyle. This gives us confidence to use a static internal electrode position in our EIT mesh and to continue with EIT imaging experiements.