Abstract Purpose This study sought to determine the intrasession repeatability of the diffusion‐weighted (DW) arterial spin labeling (ASL) sequence at different postlabel delays (PLDs). Methods We first performed numerical simulations to study the accuracy of the two‐compartment water exchange rate (Kw) fitting model with added Gaussian noise for DW PLDs at 1500, 1800, and 2100 ms. Ten young, healthy participants then underwent a structural T 1 scan and two intrasession in vivo DW ASL scans at each PLD on a 3T MRI. The Kw, arterial transit time (ATT), and cerebral blood flow maps were linearly registered to the structural images, which were then segmented using FreeSurfer into masks with 35 bilateral gray‐matter regions. Results Simulation results showed that the Kw fitting model performed at an error rate less than 10% at physiological ATTs and Kw values, but that error and bias increased at a PLD of 2100 ms and at ATT ranges where the overall blood signal fraction (A 1 ) is low. In vivo analysis showed a significant positive correlation between intrasession measurements of regional Kw at a DW PLD of 1800 ms ( β = 0.33, p < 0.001) only. Furthermore, a significant positive relationship between Kw and cerebral blood flow was seen at a DW PLD of 1500 ms ( β = 0.26, p = 0.005) and DW PLD of 2100 ms ( β = 0.39, p = 0.006). Conclusion Overall, DW ASL provides the strongest intrasession repeatability at a PLD of 1800 ms in young, healthy subjects, and a simulation study shows accurate Kw fits at physiologic range of ATTs and Kw values.
Zhu et al. (Wed,) studied this question.