Multi-Echo versus T2-Prepared pCASL: what to use for measuring water transport across the Blood Brain Barrier

Motivation: To resolve which of two commonly-used T2-based ASL approaches is preferable for quantifying water transport across the BBB. Goal(s): This research compares T2-values and SNR between multi-echo and T2-prepared ASL sequences. Approach: In-vivo scans and simulations were performed. The approaches were combined into a single sequence and also tested separately. T2-values, and temporal and spatial SNR were compared. Results: Both sequences measured similar T2, although multi-echo underestimated T2 at early PLDs possibly due to the signal-crushing effect of imaging gradients on flowing spins. Nevertheless, multi-echo is preferred because of superior tSNR/sSNR, more echoes, and less T2-blurring by virtue of its short readout time. Impact: This work informs the community about which multi-TE ASL sequence should be used for BBB water transport measurements. Moreover, it highlights potential pitfalls and inaccuracies associated with the sequences, which will help to provide more reliable interpretation of future results.