Adaptive multilevel thresholding for SVD-based clutter filtering in ultrafast transthoracic coronary flow imaging

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Biomedical Engineering

Background:

• Conventional Doppler techniques face challenges in transthoracic coronary flow imaging due to unfocused waves, resolution limits, and tissue motion.
• Existing ultrafast Doppler and singular value decomposition methods struggle with optimal tissue-blood and blood-noise thresholding, limiting image contrast.
• This hinders accurate coronary flow measurement in complex ultrasound scenarios.

Purpose of the Study:

• To develop a novel local blood subspace detection method for improved transthoracic coronary flow imaging.
• To overcome limitations in thresholding for ultrafast Doppler and singular value decomposition in challenging ultrasound environments.
• To enhance contrast and reduce artifacts in coronary blood flow visualization.

Main Methods:

• Introduced a local blood subspace detection method using multilevel thresholding by the valley-emphasized Otsu's method for pixel-level tissue-blood (TB) and blood-noise (BN) threshold estimation.
• Developed a weighted mask (WM) to assess blood content based on local TB and BN thresholds.
• Implemented a tree-structure k-means clustering approach with noise rejection (NR) for computational efficiency, applying local thresholding (LT) on a cluster-based (CB) level (CBLT+NR+WM).

Main Results:

• Evaluated the proposed CBLT+NR+WM method using an ex-vivo swine heart model.
• Demonstrated significant improvements compared to conventional global thresholding methods.
• Achieved average increases of 10.8-dB (Contrast-to-Noise Ratio) and 11.2-dB (Contrast) in suppressing tissue signals.
• Showed average increases of 5-dB (CNR) and 9-dB (Contrast) in suppressing noise signals.

Conclusions:

• The proposed method effectively attenuates residual tissue and noise signals.
• Outperforms conventional global thresholding in enhancing Doppler image quality.
• Shows significant promise for accurate coronary flow measurement in challenging transthoracic ultrasound settings.