Contrast-based transient flow vector distribution in arterial stenosis based on plane wave bubble wavelet imaging and modified optical flow method

The objective of this study was to accurately obtain the transient flow vector distribution (FVD) of microbubbles in arterial stenosis by modified optical flow method based on ultrasound contrast plane wave imaging (UCPI). First, a bolus injection experiment was performed in an arterial stenosis flow phantom using inverted plane waves at 400Hz frame rate controlled by Sonix-Touch. The contrast-to-tissue ratio (CTR) of UCPI images and detection sensitivity of microbubbles was then improved by pulse inversion bubble wavelet imaging (PIWI) technique based on a pair of inverted bubble wavelet constructed according to the modified Herring equation. Next, transient displacement and FVD of microbubbles among a set of UCPI images with high CTR and sensitivity were obtained by a modified optical flow method, which added a discontinuity preserving spatio-temporal smoothness constraint, to accurately mark and evaluate the hemodynamic feature in the stenosis. Finally, FVD of microbubbles in the arterial stenosis was depicted clearly by PIWI-based UCPI. Compared to those obtained using pulse inversion harmonic imaging, CTR of UCPI in the stenosis and detection sensitivity of microbubbles near arterial wall were improved by up to 10.09 ± 2.96 dB and 12.52 ± 2.10 dB, respectively. Axial microbubble velocity in the stenosis was 28.45 ± 3.05 mm/s; it was in accordance with the set value. Moreover, compared with results obtained by the conventional optical flow method, an anticlockwise vortex of microbubbles in the distal was described more accurately by the transient FVD obtained using the modified optical flow method. It indicated that contrast-based transient FVD in the arterial stenosis can be acquired accurately by PIWI-based UCPI combined with modified optical flow method.