Myelin water imaging using a short‐TR adiabatic inversion‐recovery (STAIR) sequence
Yajun 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 T 1 and a much shorter T 2 * than intracellular/extracellular water. A STAIR sequence with a short TR was designed to efficiently suppress long T 1 signals from intracellular/extracellular water, and therefore allow selective imaging of MW, which has a much shorter T 1 . Numerical simulation and phantom studies were performed to investigate the effectiveness of long T 1 signal suppression. TheT 2 * in white matter (WM) was measured with STAIR and compared with T 2 * 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 T 1 signals from tissues with a broad range of T 1 s using a single TR/TI combination. The volunteer study showed a short T 2 * 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.