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Currently, methods such as conventional ultrasound B-mode scanning (US), computerized X-ray tomography (CT), magnetic resonance imaging (MRI), standard X-ray diagnostics, radioisotope imaging and thermography are used to visualize the internal structure of tissue in vivo and to diagnose the patient. Doppler tomography (DT) is an innovative method of reconstructing the image of the tissue section using ultrasonic waves and Doppler effect. In contrast to the currently applied solutions (US), this method uses a continuous wave, which, in theory, allows one to operate with higher energy and to detect smaller inclusions within the examined tissue. This study focuses on the analysis of DT simulation in circular geometry, where a two-transducer ultrasonic probe circulating around the tested object is used to measure the useful signal. In this paper, the influence on the tested object’s cross-section imaging quality of both the simulated Doppler signal’s registration parameters, and the calculation algorithm’s parameters, were analyzed.
Doppler signals collected on the abdomen of the pregnant woman were submitted to the discrete wavelet transform using the db 10 wavelet. The wavelet reconstruction products were submitted to the autocorrelation analysis. The processing, supported with the ultrasonographic scanning enabled identification of the fetal periodic activities. The fetal pseudo-breathing movement velocity always falls in the range of 5-10 mm/s (Doppler frequency range 12.5-25 Hz), velocities of cardiac structures - in the range of 20-75 mm/s (Doppler frequency 50-200 Hz). The signals resulting from fetal displacements provoked by maternal breathing and cardiac action or fetal hiccup are expected not to adversely affect estimation of the fetal rhythms. These findings are important for the development of fetal monitoring systems.
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