Electrical impedance tomography based on relaxation measurements in time domain

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Electrical impedance tomography (EIT) is a real-time functional imaging technique that does not require ionizing radiation or strong magnetic fields and is suitable for bedside and potentially for mobile applications as well. Most systems on the market use single frequency measurements and are able to discriminate well between material with very different impedance (air, tissue). Current research focuses on multi-frequency systems, which also allow distinguishing between different tissues. Present approaches to multi-frequency measurement can only measure a few frequencies (multi-sine) or lead to a low frame rate (step-sine). As an elegant alternative, we consider time domain measurements to be a promising approach to deal with these limitations. To realize the existing multi-frequency EIT methods based on measurements in time domain using relaxation spectroscopy offers several advantages. When applying a broadband excitation signal, any number of time points respectively frequencies can be measured simultaneously. For multi-frequency EIT, this means that the scan rate can be further increased to better visualize fast physiological processes. It is also possible to increase the number of measured frequencies at the given scan rate in order to better differentiate the tissues. In combination with non-equidistant sampling, the amount of data can be reduced substantially in relaxation measurements. At high EIT scan rates, multiple sampling points, and a large number of electrodes, the amount of data to be transmitted and processed becomes more and more a bottleneck. Here, non-equidistant scanning can set new standards. Relaxation spectroscopy can be realized with a minimum of hardware, which also means a smaller form factor of the device. This allows to integrate the measurement instrumentation directly into active electrodes and to transmit only digital signals to a control unit. On the one hand, this would eliminate long measurement leads as an interference factor, and on the other hand, the short connection of the measurement technology would allow higher frequency ranges to be measured, which also results in more accurate tissue characterization. However, in order to make these potentials available for EIT, important basics need to be investigated. The aim of this research project is to establish a theoretical and as well practical basis for EIT measurements in time domain and thus to substantially expand the range of applications of EIT through the advantages of time domain measurement.