A Minimally Invasive Framework Reveals Region-Specific Cerebrovascular Remodeling in Aging Using Intravital Functional Ultrasound Imaging and Ultrasound Localization Microscopy (fUS-ULM).

Aging impairs cerebrovascular structure and function, contributing to cognitive decline and dementia. Here, a novel, high-resolution, intravital imaging platform is presented that combines functional ultrasound (fUS) and ultrasound localization microscopy (ULM) through a chronically implanted, polymethylpentene (TPX) cranial window, a transparent implant that enables ultrasound imaging through the skull. This approach enables intravital, longitudinal, minimally invasive assessment of cerebrovascular structure and function across cortical and deep brain regions. Leveraging this platform, a new method is developed to estimate resting cerebral blood flow (CBF) by integrating microbubble (MB) velocity data from fUS with microvascular geometry derived from ULM. Notably, a significant age-related decline in the cortical arteriole-to-venule ratio (AVR) is discovered, introducing a novel biomarker of structural cerebrovascular remodeling. It is also validated that fUS can reliably assess neurovascular coupling (NVC) responses in aged mice. This study establishes a powerful, non-invasive, and repeatable investigative tool for future preclinical studies aimed at evaluating the efficacy of therapeutic interventions targeting vascular contributions to cognitive impairment and neurodegeneration.