Electrical Impedance Tomography (EIT) is a portable, non-invasive, non-ionizing imaging technique which is being used for clinical diagnosis and monitoring and other fields of engineering. It reconstructs the spatial distribution of electrical impedance of the body from surface electrical measurements creating tomographic images. In addition to visual information, several parameters with clinical value can be extracted from EIT data to describe the function of the cardiopulmonary system, today´s most analysed organ system by EIT. However, all of the developed parameters are relative. Therefore an absolute parameter is still missing to be able to effectively compare different measurements and pathologies. Moreover, not only is there a lack of such a parameter, but also a software tool to analyse clinical and experimental EIT data. Thus, the aim of this thesis is to develop an absolute parameter and a software tool for EIT data analysis where the new and other parameters can be integrated.
In this thesis new methods for determining regional expiratory time constant based on curve fitting were developed as the first absolute EIT parameter. They were evaluated and compared with other calculation methods using artificial signals with different noise levels and later tested on real patient data. The results showed that the two main methods developed in this project were the only ones which delivered robust breath-by-breath regional expiratory time constants in real-life EIT signals and which could distinguish pathologies as well. Besides, one of the calculation methods was even fast enough for implementation in a bedside monitor for online computation.
Moreover, a software tool (ibeX) was developed which is able to determine semi-automatically several well-known lung function and haemodynamic parameters besides the above new time constant for EIT data analysis. It was designed to facilitate analysis of data obtained from clinical and experimental research. The software is based on MATLAB and has a graphical user interface with various functionalities from a revocable data selection through a reliable and powerful breath and beat detection with adaptive filtering options to the direct visual feedback. Results and data can be exported as .pdf, .xls and .mat files. For the first time in EIT history ibeX provides an efficient and reproducible breath-by-breath and beat-by-beat EIT data analysis tool for clinical users.