Comparison of arterial transit times estimated using arterial spin labeling

To compare arterial transit time estimates from two efficient transit time mapping techniques using arterial spin labeling (ASL)—flow encoded arterial spin tagging (FEAST) and Look-Locker ASL (LL-ASL). The effects of bipolar gradients and label location were investigated. Six healthy subjects were scanned with pseudo-continuous ASL (pCASL) FEAST and pulsed (PASL) and pCASL variants of LL-ASL at different labeling locations with and without bipolar gradients. Application of transit time mapping was demonstrated in a clinical case. Mean (±SD) macrovascular transit times were 363 ± 39, 676 ± 73 and 908 ± 170 ms for LL-PASL, LL-pCASL with labeling offsets of 60 and 90 mm respectively, showing linear dependence on labeling locations. Mean microvascular transit time for LL-pCASL was 1,463±135 ms, in good agreement with the FEAST estimate of 1,444 ± 128 ms. Data acquired from a patient with stroke demonstrate how transit time and CBF maps provide complementary information for clinical diagnosis. Both FEAST and LL-ASL provide transit time information in clinically acceptable scan times. Bipolar gradients can be used to tailor transit time estimates for different experimental and clinical situations.