Comparison of arterial transit times estimated using arterial spin labeling.

OBJECTIVE: 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.
MATERIALS AND METHODS: 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.
RESULTS: 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.
CONCLUSION: 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.