Coherent Nonlinear Ultrasound Imaging: From Microvasculature to Capillaries.

It is not straightforward for ultrasound imaging from microvasculature to capillaries. The main challenge stems from the detection of low-velocity or quasistatic signal components in the capillaries. To address this, we propose a coherent nonlinear ultrasound imaging method, where a nonlinear coherence operator acted on point spread function (PSF) is leveraged to improve detection sensitivity of microbubbles (MBs). Low-velocity MBs can thus be extracted without clutter filtering. Through visualizations of low-velocity microvasculature in rat brain/kidney/testis and early-stage glioma, coherent nonlinear ultrasound imaging paves the way toward capillary-level microangiography.