Modelling of an Oesophageal Electrode for Cardiac Function Tomography

Abstract

There is a need in critical care units for continuous cardiopulmonary monitoring techniques. ECG gated electrical impedance tomography is able to localize the impedance variations occurring during the cardiac cycle. This method is a safe, inexpensive and potentially fast technique for cardiac output imaging but the spatial resolution is presently low, particularly for central locations such as the heart. Many parameters including noise deteriorate the reconstruction result. One of the main obstacles in cardiac imaging at the heart location is the high impedance of lungs and muscles on the dorsal and posterior side of body. In this study we are investigating improvements of the measurement and initial conductivity estimation of the internal electrode by modelling an internal electrode inside the esophagus. We consider 16 electrodes connected around a cylindrical mesh. With the random noise level set near 0.05% of the signal we evaluated the Graz consensus reconstruction algorithm for electrical impedance tomography. The modelling and simulation results showed that the quality of the target in reconstructed images was improved by up to 5 times for amplitude response, position error, resolution, shape deformation and ringing effects with perturbations located in cardiac related positions when using an internal electrode.

Addition of internal electrodes is beneficial for focused bioimpedance measurements in the lung

“…It has been shown before that internal electrodes can improve the cardiac signal in cardiac impedance tomography (Tehrani et al 2012a(Tehrani et al , 2012b. During bronchoscopy, they can help to characterize lung tissue (Sanchez et al 2012).…”

A shape-based quality evaluation and reconstruction method for electrical impedance tomography

“…Especially in pulmonary monitoring applications, the use of electrode belts with 16 electrodes has found widespread application and enables this technology to be used for bedside monitoring. Additionally, other scenarios that use, for example, minimally invasive electrode configurations, are currently under investigation (Nasehi Tehrani et al 2012, Czaplik et al 2013. Recent experimental hardware is reported to operate with up to 100 frames per second (Oh et al 2011), but even commercially available, medical approved devices allow a temporal resolution of up to 50 frames per second.…”

A Local Region of Interest Imaging Method for Electrical Impedance Tomography with Internal Electrodes

“…Unfortunately, these measurements are insensitive to local impedance changes away from the measuring positions, whereas they are very sensitive to the boundary geometry and impedance changes near the electrodes. To improve the sensitivity and distinguishability in some local internal regions, the use of internal electrodes has been suggested by several researchers [1, 2]. These previous works were concentrated in cardiac applications of EIT as catheters are routinely introduced into various locations during cardiac monitoring, electrophysiology (EP mapping), or cardiac radiofrequency ablation (RFA).…”