Photoacoustic-Strain (PAS) Imaging for Tissue Microcirculation Assessment.

Microcirculation facilitates the exchange of gases, nutrients, and waste products between blood and tissues and is critical for maintaining systemic tissue health. In this study, we introduce photoacoustic-strain (PAS) imaging, a non-invasive method for assessing tissue microcirculation. By combining externally applied deformation while performing ultrasound/photoacoustic imaging, PAS enables real-time monitoring of blood volume changes as blood is displaced from the tissue under pressure and subsequently refilled upon pressure release. Through a series of post-processing steps, spatially resolved maps of blood displacement and reperfusion rates are reconstructed, providing insights into microcirculatory dynamics. Using both in silico and in vivo experiments, PAS imaging was developed and validated, demonstrating its capability to detect and differentiate changes in microcirculation under various conditions, including vascular occlusion and tissue at different temperatures, with high sensitivity and strong robustness. These findings underscore the potential of PAS imaging as a non-invasive tool for understanding and diagnosing diseases associated with microcirculatory function.