Impact of Postlabeling Delay on Arterial Spin-Labeling MRI-Based Measures of Cerebral Blood Flow in a Simultaneous PET/MRI Study of Aging

BACKGROUND AND PURPOSE: O]water PET acquired using PET/MRI imaging in a study of aging and Alzheimer disease (AD). MATERIALS AND METHODS: O]water PET using Spearman correlation across cortical regions and vascular territories. RESULTS: O]water PET were strongest for 1800 msec single-PLD and generally decreased with longer PLDs, except the occipital lobe, where all PLDs showed poor agreement. Multiple-PLD ASL showed similar correlation strengths as 2000 msec single-PLD. CONCLUSIONS: O]water PET, suggesting it may be an effective choice for studying CBF in aging and AD populations. While multiple-PLD ASL offered comparable performance, it did not confer notable benefits compared with the best-performing single-PLD under similar acquisition time constraints. These findings underscore the importance of PLD selection in ASL protocols in older or cognitively impaired cohorts and highlight the value of assessing intermediate-term reliability in longitudinal studies.