Harmonization of cerebral blood flow measurements by multi-delay 3D gradient and spin echo, and single-delay 2D echo planar imaging.

Purpose: Cerebral blood flow (CBF) is commonly measured by pseudo-continuous arterial spin labeling (PCASL) in human research, but recent advancements in methodology have limited data reuse. The object of this work is to harmonize two distinct PCASL techniques within a cohort with a wide range of CBF values.

Methods: Participants had two PCASL sequences collected within a single session: a single post-label delay sequence with a 2D echo-planar imaging (EPI) readout, " ${\text{CBF}}_{2\text{D},1\text{PLD}}$ ", and a five post-label delay sequence with gradient and spin echo (GRASE) 3D readout, " ${\text{CBF}}_{3\text{D},5\text{PLD}}$ ". Linear regression modeling to impute ${\text{CBF}}_{3\text{D},5\text{PLD}}$ from ${\text{CBF}}_{2\text{D},1\text{PLD}}$ , hemoglobin, and age were assessed within gray matter (GM) and white matter (WM) using leave-one-out cross-validation for prediction errors and confidence intervals. Within-subject coefficient of variation (wsCV) and inter-class correlation coefficient (ICC) were calculated using ${\text{CBF}}_{3\text{D},5\text{PLD}}$ imputed vs. measured as pseudo test-retest pairs.

Results: Fifty participants, ages 8-45 (median 25) years, had usable ${\text{CBF}}_{3\text{D},5\text{PLD}}$ and ${\text{CBF}}_{2\text{D},1\text{PLD}}$ , including 17 participants with sickle cell disease (SCD), who were matched by age ( $p=0.90$ ) and sex ( $p=0.16$ ) to those without SCD. A multiple linear regression model including hemoglobin and age fit GM CBF ( ${{\text{R}}^2}_{\text{adj.}}=0.82$ ; for WM CBF ${{\text{R}}^2}_{\text{adj.}}=0.78$ ). The wsCV for ${\text{CBF}}_{3\text{D},5\text{PLD}}$ was 9.1% for GM, 11.3% for WM. ICC was 0.89 for GM and 0.87 for WM. Models without age or hemoglobin fit slightly worse.

Conclusion: Our study demonstrates feasibility to impute 3D-GRASE multi-PLD CBF from a 2D-EPI single-PLD technique, which promotes data sharing and harmonization.