Temporal evolution acquisition based arterial spin labeling (TEA-ASL) for accurate estimation of apparent T2 of perfusion signal in brain

Abstract

Accurate quantification of apparent transverse relaxation (T2) in brain can be useful for non-invasive assessment of blood oxygenation and blood-brain barrier (BBB) function. While arterial spin labeling (ASL) combined with multi-echo readouts offers a contrast-agent-free approach to map apparent T2, in vivo applications remain challenging due to rapid signal decay and low signal-to-noise ratio (SNR) at longer echo times (TEs), likely leading to overestimation of T2 values. We propose a novel temporal evolution acquisition based ASL (TEA-ASL) sequence incorporating an optimized variable refocusing flip angle (RFA) train to preserve signal across all TEs. Data were acquired on a 5T MRI system combining a pseudo-continuous ASL (pCASL) with the proposed TEA readout with 12 echo times (32-384 ms). The variable RFA scheme significantly improved signal stability across the echo train compared to conventional acquisition with constant RFAs. Accuracy and clinical feasibility of the proposed method was validated by simulations, phantom scans, in-vivo test/retest experiments and in a patient with middle cerebral artery stenosis. The proposed TEA-ASL technique provides robust apparent T2 mapping in brain at ultra-high field, offering a promising tool for probing oxygenation-related hemodynamics and BBB-associated pathophysiology.