Developpement d'un systeme de tomographie d'impedance electrique multifrequence pour la detection de l'oedeme pulmonaire

Multifrequency electrical impedance tomography (MF-EIT) is a non-invasive medical technique for imaging the conductivity distribution of a human body section.; The main goal of this research project is to apply MF-EIT to the detection of pulmonary oedema. Currently, the standard diagnostic technique for pulmonary oedema is radiography. However; this technique has a low sensitivity and is considered invasive since it exposes the patient to x-rays. To circumvent these problems, many studies have been carried out to determine whether conventional (single frequency) EIT could be used to detect pulmonary oedema. These studies show that conventional EIT is more useful for monitoring the evolution of the disease than for its detection. Since MF-EIT has the potential to identify tissues, including biological liquids, it is believed that it could become an alternative, or, at least, a complement to radiography for diagnosis of pulmonary oedema.; This Ph.D. project thus aims at providing the foundation of a research program in MF-EIT applied to the detection of pulmonary oedema. The specific goals are (1) to build an MF-EIT system, constituting a development platform for future projects at the Institut de genie biomedical, and (2) to develop image reconstruction methods adapted to this technology.; The system that we developed, called TIE-5-MF, consists of two units: the active electrodes module (AEM) and the synthesis and demodulation module (SDM). These modules were designed and built respectively during a master's project and within this Ph.D. project. The AEM contains the analog circuits for impedance measurements. It is connected to the patient using disposable electrodes. The SDM comprises (1) a synthesis unit to generate the multifrequency carriers used by the AEM to apply current, (2) a demodulation unit to demo-dulate the voltage measurements returned by the AEM, (3) a control module to configure all programmable components of the system and to synchronize the data acquisition sequence, and (4) a USB port to interface the system with a computer.; The TIE-5-MF system provides impedance measurements at 1 to 8 frequencies simultaneously within the 70 to 950 kHz range. In this project, we restricted the choice to single frequency mode and multifrequency mode with eight frequencies. For safety reasons, the amplitude of the carriers spectral components in multifrequency mode was set to one eighth the amplitude in single frequency mode. Moreover, because of the considerable amount of data generated in multifrequency mode, the maximum acquisition rate for this mode was limited to 5 frames/s, where a frame represents the measurement set necessary to reconstruct an image. In single frequency mode, a rate of 20 frames/s is possible.; We developed six image reconstruction methods classified in two modes: dynamic and quasi-static. In dynamic mode, the images show conductivity variations between two instants while in quasi-static mode, the images show conductivity variations between two frequencies. The dynamic mode is thus well adapted to monitoring applications whereas the quasi-static mode could be used for diagnosis.; We carried out simulations with a torso model to validate the reconstruction methods. We showed that they could follow the increase in percentage of simulated oedema. However, detection remains difficult. We think that intra-individual comparison of the affected pulmonary tissue with a tissue whose conductivity does not vary with oedema would facilitate the detection of this pathology.; We also carried out various experiments by combining the TIE-5-MF system with the reconstruction methods. For the in vitro experiments and those carried out on a resistive phantom, images obtained with the quasi-static reconstruction mode showed only test, objects whose conductivity varied with frequency. In dynamic mode, all test objects were visible since the images represent the conductivity variations caused by the addition of the object...