Multiple-TE Based Blood–Brain-Barrier Water Exchange Time Measurement Using a TE-Resolved 3D TSE Stack-Of-Spirals Readout

Purpose:
To develop a slice-wise blurring-free and densely sampled TE-resolved multiple-TE (mTE) ASL sequence (TASL) for measuring blood–brain barrier (BBB) water exchange time.
Methods:
A 3D TSE spiral-readout pCASL sequence was modified to enable TE-resolved acquisition. Signals at mTEs from a single kz partition were acquired within a single shot, and the acquisition was repeated until all required kz partitions were covered. In vivo experiments were conducted on healthy volunteers using both a conventional pCASL sequence and the proposed TASL sequence. Signal intensity modulation, perfusion SNR, and quantitative parameters including cerebral blood flow (CBF), arterial transit time (ATT), intravoxel transit time (ITT), and water exchange time (T exch) were evaluated. Test–retest scans were conducted to assess reproducibility.
Results:
Compared with the conventional mTE acquisition, TASL eliminates T 2 decay-induced slice-wise intensity modulation and blurring, yielding higher whole-brain perfusion SNR across all TEs and PLDs. Estimates of CBF and ATT showed negligible differences between the two methods (both < 1%), whereas mean T exch and ITT values were 18.2% and 9.05% higher, respectively, with TASL. Bland–Altman analysis showed minimal bias, with 95% of differences within the limits of agreement (mean±1.96 SD). The inter-session ICC and wsCV of CBF, ATT, T exch, and ITT in gray matter are 0.86% and 8.38%, 0.96% and 1.98%, 0.93% and 4.04%, and 0.95% and 4.32%, respectively.
Conclusion:
TASL eliminates signal intensity modulation and blurring artifacts while providing densely sampled TE for parametric fitting. It may be a valuable tool for accurate and reliable quantification of cerebral perfusion and BBB permeability.