Myelin water imaging using a short-TR adiabatic inversion-recovery (STAIR) sequence
Ya-Jun Ma, Hyungseok Jang, Alecio F. Lombardi, Jody Corey-Bloom, Graeme M. Bydder
Abstract
Purpose
To develop a new myelin water imaging (MWI) technique using a short-TR adiabatic inversion-recovery (STAIR) sequence on a clinical 3T MR scanner.
Methods
Myelin water (MW) in the brain has both a much shorter T1 and a much shorter T2* than intracellular/extracellular water. A STAIR sequence with a short TR was designed to efficiently suppress long T1 signals from intracellular/extracellular water, and therefore allow selective imaging of MW, which has a much shorter T1. Numerical simulation and phantom studies were performed to investigate the effectiveness of long T1 signal suppression. TheT2* in white matter (WM) was measured with STAIR and compared with T2* measured with a conventional gradient recall echo in in vivo study. Four healthy volunteers and 4 patients with multiple sclerosis were recruited for qualitative and quantitative MWI. Apparent MW fraction was generated to compare MW in normal WM in volunteers to MW in lesions in patients with multiple sclerosis.
Results
Both simulation and phantom studies showed that when TR was sufficiently short (eg, 250 ms), the STAIR sequence effectively suppressed long T1 signals from tissues with a broad range of T1s using a single TR/TI combination. The volunteer study showed a short T2* of 9.5 ± 1.7 ms in WM, which is similar to reported values for MW. Lesions in patients with multiple sclerosis showed a significantly lower apparent MW fraction (4.5% ± 1.0%) compared with that of normal WM (9.2% ± 1.5%) in healthy volunteers (p < 0.05).
Conclusions
The STAIR sequence provides selective MWI in brain and can quantify reductions in MW content in patients with multiple sclerosis.