Reliability of arterial spin labeling derived cerebral blood flow in periventricular white matter

We aimed to assess the reliability of cerebral blood flow (CBF) measured using arterial spin labeled (ASL) perfusion magnetic resonance imaging (MRI) from the periventricular white matter (PVWM) by computing its repeatability and comparing to [¹⁵O]-water Positron Emission Tomography (PET) as a reference. Simultaneous PET/MRI perfusion data were acquired twice in the same session, about 15 min apart, from 16 subjects (age: 41.4 ± 12.0 years, 9 female). ASL protocols used pseudocontinuous labeling (pCASL) with background-suppressed 3-dimensional readouts, and included both single and multiple post labeling delay (PLD) acquisitions, each acquired twice, with the latter providing both CBF and arterial transit time (ATT) maps. The reliability of ASL derived PVWM CBF was evaluated using intra-session repeatability assessed by the within-subject coefficient of variation (wsCV) of the PVWM CBF values obtained from the two scans, correlation with concurrently-acquired PET CBF values, and by comparing them with that measured in other commonly used regions of interest (ROIs) such as whole brain (WB), gray matter (GM) and white matter (WM). The wsCVs for PVWM CBF with single and multi-PLD acquisitions were 5.7 (95% CI: (3.4,7.7)) % and 6.1 (95% CI: (3.8,8.3))%, which were similar to those obtained from WB, GM and WM CBF even though the PVWM region is the most weakly perfused region of brain parenchyma. Correlations between relative PVWM CBF derived from ASL and from [¹⁵O]-water PET were also comparable to the other ROIs. Finally, the ATT of the PVWM region was found to be 1.27 ± 0.27s, which was not an outlier for the arterial circulation of the brain. These findings suggest that PVWM CBF can be reliably measured with the current state-of-the-art ASL methods.