PROJECT TITLE :
Effects of reverberations and clutter filtering in pulsed Doppler using sparse sequences
Duplex ultrasound is a modality in which an ultrasound system is employed for simultaneous acquisition of both B-mode images and velocity (Doppler) data. Conventional duplex sequences interleave packets of B-mode and Doppler transmissions, manufacturing undesirable gaps during B-mode interruptions. Lately, many techniques are proposed for avoiding such gaps by using sparse sequences, in which velocity spectra are generated from nonuniformly sampled Doppler information containing frequent B-mode interruptions. During this work, 2 negative effects are mentioned that may influence velocity estimation when using nonuniformly sampled sequences. Initial, it's shown that long reverberation times cause discontinuities in the signal from stationary muddle when every B-mode interruption. Second, using frequency analysis, it is shown that litter filtering of nonuniformly sampled data may introduce artifacts in the speed spectrum, and also lead to significant bias in mean velocity estimates. Methods are presented for quantification of these effects, and used to investigate 3 varieties of sparse duplex sequences for blood velocity estimation. In specific, it's argued that the use of such sequences in cardiac applications isn't suggested as a result of of long reverberation time. Additionally, it is found that the use of regression filters to filter nonuniformly sampled information might produce vital artifacts in pulsed wave Doppler spectra, however is a smaller amount important for color Doppler imaging applications. In vitro and in vivo examples are included showing the presence and magnitude of those problems in clinically relevant applications.
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