Independent Component Analysis Filter for Small Vessel Contrast Imaging During Fast Tissue Motion

Abstract

Suppressing tissue clutter is an essential step in blood flow estimation and visualization, even when using ultrasound contrast agents. Blind source separation (BSS)-based clutter filter for high frame rate ultrasound imaging has been reported to perform better in tissue clutter suppression than the conventional frequency-based wall filter and nonlinear contrast pulsing schemes. The most notable BSS technique, singular value decomposition (SVD) has shown compelling results in cases of slow tissue motion. However, its performance degrades when the tissue motion is faster than the blood flow speed, conditions which are likely to occur when imaging the small vessels, such as in the myocardium. Independent component analysis (ICA) is another BSS technique that has been implemented as a clutter filter in the spatiotemporal domain. Instead, we propose to implement ICA in the spatial domain where motion should have less impact. In this work, we propose a clutter filter with the combination of SVD and ICA to improve the contrast-to-background ratio (CBR) in cases where tissue velocity is significantly faster than the flow speed. In an in vitro study, the range of fast tissue motion velocity was 5-25 mm/s and the range of flow speed was 1-12 mm/s. Our results show that the combination of ICA and SVD yields 7 -10 dB higher CBR than SVD alone, especially in the tissue high-velocity range. The improvement is crucial for cardiac imaging where relatively fast myocardial motions are expected.

Higher Order Singular Value Decomposition Filter for Contrast Echocardiography

“…As shown by the results of our in vitro experiment, HOSVD provides 10 dB CBR improvement over AM when the probe is moving, compared to 5 dB improvement when the probe is static (where AM is generally working well in suppressing tissue signal). In the case of SVD, it has been reported that the spatiotemporal SVD filter's capability to detect flow is deteriorated when the flow speed is slower than the tissue motion velocity [14], [17], [18]. Hence, the nearly static microbubble flow in moving probe in vitro experiment and the in vivo and the myocardial perfusion are difficult cases for spatiotemporal SVD filtering because of the high spatiotemporal correlation between the microbubble and tissue signals when they are moving along.…”

“…It has been reported that SVD suppresses tissue clutter better than conventional frequency filters and contrast pulsing schemes (AM and AMPI) [14]- [16]. However, its performance also degrades with slower flow rates and faster tissue motion since in that case the coherence between the contrast agent signal and tissue increases, thus preventing the separation into different components [14], [17], [18]. This is a crucial issue for cardiac imaging where tissue motion can reach up to 9.4 cm/s [19] and blood flow in the microcirculation is generally slower than 1 cm/s.…”