Label-Free Hemodynamic Mapping via Ultrafast Power Doppler-Enhanced Photoacoustic Imaging reveals early therapy-induced functional changes in the tumor

Real-time, non-invasive imaging of tumor vascular function is critical for assessing treatment response and informing therapeutic decisions. In this study, we present a dual-modality imaging approach that integrates Ultrafast power Doppler ultrasound (UPD) with multispectral photoacoustic (PA) imaging to quantify spatiotemporal changes in tumor oxygenation and perfusion following photodynamic therapy (PDT). Our results demonstrate that PDT induces dose- and time-dependent spatial heterogenic alterations in both oxygenation and perfusion. To better interpret the spatial interplay between tumor oxygenation and vascular perfusion, we developed a Vascular Function Index (VFI), which classifies tumor subregions into four functional quadrants based on perfusion and oxygenation status at every voxel within the 3D tumor region. This framework revealed dynamic, time-dependent changes in tumor hypoxia and perfusion, with high-dose treatment groups showing a progressive increase in hypoxic and non-perfused regions, underscoring the spatiotemporal nature of PDT-induced vascular response.