Real-time whole-brain imaging of hemodynamics and oxygenation at micro-vessel resolution with ultrafast wide-field photoacoustic microscopy

Abstract

High-speed high-resolution imaging of the whole-brain hemodynamics is urgently needed to facilitate the next level of neurovascular research. Image acquisition speed and image quality are crucial to visualizing real-time hemodynamics in complex brain vascular networks, and displaying fast pathophysiological dynamics on a micro and macro-level, enabling advances in current queries in neurovascular and brain metabolism research, including stroke, dementia and acute brain injury. Further, real-time oxygen saturation of hemoglobin (sO2) imaging to differentiate arteries from veins and capture fast-paced oxygen delivery dynamics is needed to solve pertinent questions in these fields and beyond. Here, we present a novel ultrafast functional photoacoustic microscopy (UFF-PAM) to image the whole-brain hemodynamics and oxygen delivery. UFF-PAM takes advantage of several key engineering innovations, including Raman-shifter-based dual-wavelength laser excitation, water-immersible 12-facet-polygon scanner, high-sensitivity ultrasound transducer, and deep-learning-based image upsampling. A volumetric imaging rate of 2 Hz has been achieved over a field of view (FOV) of 11× 7.5 × 1.5 mm3 with a high spatial resolution of ~10 µm. Using the UFF-PAM system, we have demonstrated proof-of-concept functional studies on the mouse brains in response to systemic hypoxia, sodium nitroprusside, and stroke. We observed the mouse brain’s fast morphological and functional changes over the entire cortex, including vasoconstriction, vasodilation, and deoxygenation. More interestingly, for the first time, under the whole-brain FOV and micro-vessel resolution, we captured the vasoconstriction and oxygenation change simultaneously in the spreading depolarization (SD) wave. Our work provides a great potential for fundamental brain research under various pathological and physiological conditions.