Hybrid Multidelay PCASL Acquired With Time‐Encoded and Variable‐TR Schemes for the Assessment of Cerebral Perfusion in Moyamoya Disease

Multidelay arterial spin labeling (ASL) MRI requires balancing temporal information with signal-to-noise ratio (SNR). A hybrid scheme combines the high SNR of time-encoded pseudo-continuous ASL (PCASL) with the temporal flexibility of variable-TR PCASL. The purpose of the present study was to assess the SNR and quantitative performance of the hybrid scheme by comparing it to time-encoded and variable-TR schemes for evaluating cerebral perfusion in patients with moyamoya disease. Twenty patients with moyamoya disease (8 men and 12 women, 27.6 ± 22.7 years) were scanned with 3 T MRI system. Variable-TR PCASL with 12 delays (vTR12), time-encoded PCASL with seven delays (TEnc7), and hybrid PCASL with 12 (4 × 3) delays (Hyb12) were obtained. Hyb12 and vTR12 were configured with nearly identical label duration (LD) and postlabeling delay (PLD) settings. For TEnc7, it was balanced so that the maximum LD + PLD time is the same. Time-corrected SNR (SNR_t), cerebral blood flow (CBF), and arterial transit time (ATT) were measured in vascular territories within gray matter. The three parameters were compared using the Friedman's matched test, followed by the Dunn's multiple comparison test. Correlations were evaluated with Pearson's correlation, and agreement was assessed by Bland-Altman plot analysis and intraclass correlation coefficient (ICC). The SNR_t of Hyb12 (4.67 ± 1.97) was significantly higher than that of vTR12 (3.27 ± 1.37, p < 0.0001) and TEnc7 (3.52 ± 1.32, p < 0.0001). The CBF of Hyb12 (49.9 ± 13.7 mL/100 g/min) was significantly lower than that of vTR12 (54.9 ± 15.4 mL/100 g/min, p < 0.0001) and TEnc7 (57.5 ± 15.9 mL/100 g/min, p < 0.0001). The ATT of Hyb12 (1240 ± 430 ms) was significantly shorter than that of vTR12 (1474 ± 419 ms, p < 0.0001) and TEnc7 (1402 ± 333 ms, p < 0.0001). CBF and ATT measurements from Hyb12 showed strong correlations and good agreement with the other two schemes. The hybrid scheme offers higher SNR_t than both time-encoded and variable-TR schemes, which may improve the accuracy of cerebral perfusion assessment in patients with cerebral artery occlusive diseases, where delayed blood flow is a concern.