Detection of Nanoliter-Scale Cortical Perivascular Spaces Using Heavily T2-weighted MRI at 7T

BackgroundThere is increasing interest in high-contrast cerebrospinal fluid (CSF) MRI for imaging perivascular spaces (PVSs). Dilated PVSs, associated with aging, dementia, and various other conditions, are readily detected within the white matter (WM), basal ganglia, and midbrain. While 7T MRI enables detection of smaller PVSs, cortical PVS burden has received limited attention despite its potential value for understanding neurological conditions. PurposeTo investigate the detectability of cortical PVS segments in healthy participants using heavily T2-weighted MRI at 7T. Materials and MethodsA T2-weighted 3D-TSE sequence was optimized at 7T to detect CSF with high resolution and contrast-to-noise ratio (CNR) while minimizing signal from surrounding tissues. A semi-automated pipeline was developed to extract PVSs and quantify their density in the whole brain, including the cortex. ResultsSeventeen healthy volunteers (40{+/-}14 years) were scanned at 7T. Optimized TSE achieved a CSF-to-tissue CNR of [~]180:1, enabling detection of small PVSs throughout the brain and leukocortical segments. About 20% of WM PVSs contain a leukocortical segment. WM PVSs with a leukocortical segment represented 70% of the total PVS volume. PVS density in the cortex was [~]0.7% ([~]6-fold lower than WM), with highest in the insula and lowest in the auditory cortex. ConclusionHigh-resolution CSF imaging using optimized 3D-TSE MRI at 7T allows detection and quantification of leukocortical PVS segments at the gray-white matter interface in healthy individuals. This study lays the groundwork for exploring regional PVS changes related to the cortex and their potential use in diagnosis or prognosis of neurological diseases.