A portable EIT system for emergency medical care
thesisposted on 04.04.2016, 08:40 by S.B. Ayati
Electrical Impedance Tomography (EIT) is a medical imaging technique in which images of tissue conductivity within a body can be inferred from surface electrode measurements. The main goal of this study is to develop a portable EIT system incorporating an optimized electrode layout to detect intracranial haematomas for use in emergency care. A growing haematoma can cause severe and even permanent damage to the delicate tissue of the brain, morbidity, and eventual death of the patient. No capability is at present available for the diagnosis of haematomas pre-hospitalisation or by first-responders. The lack of this crucial information can lead to bad decisions on patient management, and in particular, where to send the patient. Blood has a high electrical conductivity contrast relative to other cranial tissue and can be detected and monitored using electrical impedance methods. EIT is a non-invasive, low-cost monitoring alternative to other imaging modalities, and has the potential to detect bleeding and to localize the approximate bleeding site. A device of this nature would reduce treatment delays, save on costs and waste, and most significantly, positively impact patient outcomes. The first step was a numerical simulation study on FE models. The full array and the hemi-array electrode layouts were modelled and the anomalies were simulated in different positions with different sizes. The results were obtained using TSVD and WMNM reconstruction methods by COMSOL linked with MATLAB. The simulated anomalies were detected for all the positions using both layouts; however those from the full array were in general superior to the hemi-array. In order to perform realistic experiments, a prototype EIT system was constructed in the laboratory. The constructed EIT has 16 channels and operates in the frequency range of 10 kHz to 100 kHz with a temporal resolution of 100 frames per second and high level of accuracy of 93.5 %. The minimum number of 8 electrodes was chosen in this study for emergency care. Minimizing the number of electrodes speeds up the electrode setup process and avoids the need to move the patient s head in emergency care. In the second part of this study, phantom experiments were performed to find an optimised electrode layout for emergency care. The full array and the hemi-array were investigated using phantom experiments. As expected, the full array layout had the best performance in general; however, the performance of the hemi-array layout was very poor. Thus a novel optimised electrode layout (semi-array) for emergency care was proposed and evaluated in phantom experiments. For the hemi-array and the semi-array layouts, measurement sensitivity depends strongly on the anomaly location since the electrodes are not placed all over the head. The HA layout performed very badly, with the best radial localization error of 0.8100 mm, compared to the SA layout with the worst error of 0.2486 mm. Some reconstructed anomalies located far from the electrodes in the posterior region were almost invisible or erroneous for the hemi-array layout; however, it is enhanced by using the semi-array layout. Finally, in vitro experiments were conducted on ovine models. In most of the experiments carried out by other researchers, since the location of the simulated anomalies was not known and the simulated blood was normally injected into the body or the head, localization of the anomalies was not considered and the quantity of the injected blood was investigated solely. In our new method of experiment, the position of the anomalies was known a priori and thus could be compared accurately to the EIT results. The full array and the semi-array layouts were compared in terms of detection, localisation and size estimation of haematomas. As expected, the full array layout was found to be more robust than the semi-array layout with the best mean value of the localization error of 0.0564 mm and the worst QI error of around 30%. Using a minimum number of electrodes in an optimised layout is always desirable in clinical applications. The semi-array 8-electrode layout prevents unnecessary movements and the electrode connections to the head would be very quick in emergency care. Although the semi-array 8-electrode layout reduced the sensitivity of the measurements, the findings from the experiments indicated its potential to detect and monitor haematomas and probably extend its application for emergency applications where the required accuracy is not critical.
- Mechanical, Electrical and Manufacturing Engineering