Assessment of Pseudo-Continuous Arterial Spin Labeling (pCASL) Inter-Session Reliability in the Quantification of Cerebral Perfusion

Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used for measuring cerebral blood flow (CBF) in a completely non-ionizing and non invasive fashion. ASL is useful in perfusion studies on healthy adult & pediatric subjects, individuals who need multiple follow-ups, and patients with varying cerebrovascular diseases where changes in CBF can be used as an indicator of tissue viability. We used a variation of the ASL technique known as pseudo-continuous ASL (pCASL). This form of ASL is the clinical standard (Alsop et al., 2015). However, it is not well documented the that pCASL is reliable between sessions spanning days to weeks. In this study, we assessed the inter-session reliability of CBF through the use of the pCASL technique. We hypothesize that the pCASL technique can be used to quantify CBF measurements across a 24-hour and 48-hour period. Subjects included 15 healthy, active duty Air Force military personnel recruited by the Wright Patterson Air Force Base from a larger experiment. Of the 15 subjects scanned on day 1 and day 2, 2 did not return for scanning on the third day. All participants were scanned in three identical evening sessions separated by 24 hours. MR imaging was conducted on a 3T MRI scanner with a 24-channel head coil. Each of the three days began with a baseline imaging scan followed by sham transcranial direct current stimulation (tDCS) and another identical imaging session. MRI acquisition included a 12-min resting-state function MRI (fMRI), three task fMRI, a T1-weighted MRI, diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS) imaging, and resting pCASL. Our work only shows the baseline imaging from each day and the resting pCASL results. Quantitative CBF maps were computed from the raw pCASL data using proton density maps and a single compartment perfusion model through the use of the clinical processing pipeline on the MRI. These CBF maps were then registered to a reference space. Changes in CBF between the three pre-sham stimulation days were analyzed on a voxel-wise basis through a one-sample t-test and permutation testing using 215 (32,768) permutations for the difference between day 1 and day 2 and 213 (8192) permutations for the difference between day 1 and day 3 and day 2 and day 3. Permutation test results were not cluster-corrected for multiple comparisons to be conservative with respect to our hypothesis but were thresholded with a t-statistic of 2.3. The experiment’s results indicated that the pCASL MRI technique can indeed be used reliably in radiological evaluation to quantitatively assess CBF within a 24-hour but not quite in a 48-hour periods