Suppressing tissue clutter in the presence of motion and nonlinear propagation of ultrasound

Abstract

Visualizing blood flow in small vessel with ultrasound imaging is a useful diagnosis tool for evaluating organ condition. The usage of encapsulated microbubbles that have non-linear response as contrast agents, in combination with pulsing schemes that suppress the linear tissue signal can improve the sensitivity and specificity of ultrasound flow imaging. However, the nonlinear propagation when ultrasound travels through tissue and microbubble clouds reduce contrast detection. Moreover, tissue motion causes clutter artifacts and imprecise combination of the multi-pulse transmission scheme, impairing image quality. We have previously developed an independent component analysis (ICA)-based clutter filter for high framerate imaging, which performed better than the widely used singular value decomposition (SVD) filter in presence of fast tissue motion. In this study, we examined the performance of ICA filter in combination with power modulation (PM) pulsing schemes to detect flow signal. We performed an in vitro- measurement that emulated ultrasound propagation through cloud of microbubbles and fast tissue motion. The results showed that the combination of PM and ICA filter achieved up to 6dB contrast-to-background ratio improvement compared to only PM. This improvement could be significant for myocardial perfusion imaging, where rapid tissue motion and nonlinear propagation through clouds of microbubbles are expected.