Chronic Monitoring of Vascular Progression after Ischemic Stroke Using Multiexposure Speckle Imaging and Two-Photon Fluorescence Microscopy

Abstract

Monitoring the progression of the vascular structure and cerebral blood flow (CBF) after brain injury is vital to understand the neurovascular recovery process. Multiexposure speckle imaging (MESI) provides a quantitatively accurate technique for chronically measuring the postocclusion CBF perfusion of the infarct and peri-infarct regions in rodent stroke models, while multiphoton microscopy offers direct visualization of the microvascular structure. In this paper, we present imaging outcomes extending 35 days after photo-thrombotic occlusion, tracking the progression of the vasculature throughout this period. We compare MESI flow estimates within the unresolvable parenchyma with subsurface microvascular volume fractions taken with two-photon microscopy in the same regions to assess how the vascular density influences the surface-integrated MESI flow values. The MESI flow measurements and volume fractions are shown to have high correlations (r=0.90) within areas of recovering vasculature in the peri-infarct region. We also observe vascular reorientation occurring within the microvascular structure throughout the 35-day postocclusion period. With the combination of a chronic mouse model and relatively noninvasive optical imaging techniques, we present an imaging protocol for monitoring long-term vascular progression after photo-thrombotic occlusion with the potential to test the efficacy of rehabilitation and pharmacological therapies.