High-resolution three-dimensional quantitative photoacoustic and ultrasound imaging of subcutaneous microvasculature in extremities.

Visualizing and monitoring morphological and functional information of microvasculature, including arterioles and venules, plays a crucial role in assessing vascular-related diseases. Clinical angiography methods have limitations in observing small peripheral microvessels down to 100 μm. Here, this study achieved three-dimensional (3D) non-invasive imaging of the subcutaneous microvascular network and monitored hemodynamic change by using an ultrasound (US)/photoacoustic (PA) dual-modality imaging system. Not only were the microvasculature and subcutaneous tissues in the extremities visualized with high resolution, but also the quantitative oxygen saturation (sO2) of microvessels was measured. To monitor the hemodynamic change in microvasculature, vascular occlusion was performed to simulate vascular-related disease, and successfully measured multiple parameters, such as average PA amplitude, oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and sO2, during normal perfusion, vascular occlusion, and reperfusion processes, respectively. Based on the preliminary results, the high-frequency 3D US/PA dual-modality imaging shows great potential in early diagnosis and therapeutic monitoring of microvascular-related diseases.