Effects of Arterial Transit Delay on Cerebral Blood Flow Quantification Using Arterial Spin Labeling in an Elderly Cohort

Purpose: To investigate whether measurement of arterial transit time (ATT) can improve the accuracy of arterial spin labeling (ASL) cerebral blood flow (CBF) quantification in an elderly cohort due to the potentially prolonged ATT in the cohort. Materials and Methods: We employed a 1-minute, low-resolution (12mm in-plane), sequential multidelay ATT measurement (both with and without vessel suppression) approach to characterize and correct ATT errors in CBF imaging of an elderly, clinical cohort. In all, 140 nondemented subjects greater than 70 years old were imaged at 3T with a single delay, volumetric continuous ASL sequence and also with the fast ATT measurement method. Nine healthy young subjects (286 years old) were also imaged. Results: ATTs measured without vessel suppression (superior frontal: 1.51 +/- 0.27 sec) in the elderly were significantly shorter than those with suppression (P < 0.0001). Correction of CBF for ATT significantly increased average CBF in multiple brain regions where ATT was longer than the postlabeling delay (P < 0.01) and decreased intersubject variability of CBF in frontal, parietal, and occipital regions (P < 10(-8)). Measured ATT with vessel suppression was significantly longer in the elderly subjects (eg, superior frontal: 1.76 +/- 0.25 sec) compared to the younger adults (superior frontal: 1.59 +/- 0.19 sec) in basal ganglia and frontal cortical regions (P < 0.05). Conclusion: The ATT measurement is beneficial for imaging of elderly clinical populations. If ATT mapping is not feasible or available, postlabeling delays of 2-2.3 seconds should be used for elderly populations based on longest measured regional ATTs.