Quantitative photoacoustic evaluation of graded ischemic stroke and the therapeutic efficacy of low-intensity transcranial ultrasound stimulation

Ischemic stroke represents a leading cause of global mortality and long-term disability. Consequently, rapid quantification of cerebral damage severity, coupled with timely neuromodulatory intervention, is imperative for improving clinical prognosis. In this study, we present a label-free quantitative monitoring framework utilizing optical-resolution photoacoustic microscopy (OR-PAM) to assess microvascular alterations and evaluate the therapeutic efficacy of low-intensity transcranial ultrasound stimulation (LITUS). A graded ischemic stroke model was established by modulating photothrombotic irradiation duration (3, 5, and 10 min) to validate system sensitivity. Subsequently, a Hessian filter-based segmentation pipeline was employed to extract quantitative vascular metrics. Five key morphological and functional parameters, including the photoacoustic (PA) signal intensity, vessel area fraction (VAF), average vessel diameter (AVD), branch-point number (BN), and perfused vessel density (PVD), were extracted to characterize the severity of ischemic injury. Our analysis revealed a strong negative correlation between irradiation duration and vascular perfusion-related metrics, which was further confirmed by ex vivo 2,3,5-triphenyltetrazolium chloride (TTC) staining showing duration-dependent infarct expansion. Applying this quantitative framework to the established model, we further demonstrated that acute LITUS treatment significantly alleviated microvascular hypoperfusion and promoted rapid hemodynamic recovery by restoring both functional perfusion and vascular morphology via vasodilation. These findings highlight the potential of a PAM-based quantitative framework for accurate grading of ischemic severity and evaluation of ultrasound-based neuromodulation.