Improved Background Noise Suppression and Microbubbles Localization for Ultrasound Localization Microscopy Using Acoustic Sub-Aperture Processing

Ultrasound localization microscopy (ULM) has been rapidly developed to visualize microvasculature on the micrometer scale by localizing and tracking the spatially isolated microbubbles (MBs). One of the key technologies used by ULM is ultra-high-frame-rate plane wave imaging. However, due to the unfocused transmission, the penetration is limited and the signal-to-noise ratio (SNR) is low, which makes it challenging to differentiate background noise from MBs. Acoustic sub-aperture processing (ASAP) has been proposed in power Doppler imaging to suppress background noise. In this study, we introduce ASAP beamforming method to the ULM processing chain (ASAP-ULM) by replacing conventional delay-and-sum (DAS) beamformer for better noise suppression and less false localization induced by noise. The ULM intensity results of a diabetic rat kidney show that the proposed method can effectively suppress background noise and obtain more continuous and filling microvessels than those obtained by conventional DAS-ULM.