Multiple‐ <scp>TE</scp> Based Blood–Brain‐Barrier Water Exchange Time Measurement Using a <scp>TE</scp> ‐Resolved <scp>3D TSE</scp> Stack‐Of‐Spirals Readout

ABSTRACT 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 &lt; 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.