Age-related changes in myelin and myelin water quantified with short-TR adiabatic inversion-recovery (STAIR) sequences

Myelin proton density fraction (MPDF) and myelin water fraction (MWF) measured with short-TR adiabatic inversion-recovery (STAIR) sequences are potential biomarkers of aging and neurodegeneration, but the effects of aging on MPDF/MWF remain unknown. This study aims to assess relationships between age and MPDF/MWF using the 3D STAIR ultrashort echo time (STAIR-UTE) and STAIR short echo time (STAIR-STE) sequences, respectively. 42 volunteers (29 young (<55y), 13 old (>55y)), were recruited for MPDF and MWF mapping for white matter (WM) and gray matter (GM) on a 3 T scanner. Excellent inter-reader reliability was demonstrated for MPDF and MWF measurements with ICC values of 0.97 and 0.98, respectively, between two readers. In the young group, WM MPDF and MWF range from 8-13 % and 6-13 %, respectively, while GM MPDF and MWF range from 5-7 % and 3-5 %, respectively. In the old group, WM MPDF and MWF range from 6-12 % and 5-13 %, and GM MPDF and MWF range from 3-6 % and 2-5 %, respectively. The young group's MPDF/MWF values were significantly higher than those of the old group. Altogether, the 42 volunteers display linear and quadratic associations of MPDF/MWF with age. MPDF demonstrated significant correlations with MWF in the majority of brain regions. This study demonstrates the capability of two myelin imaging biomarkers, STAIR-UTE measured MPDF and STAIR-STE measured MWF to map brain myelin and MW. These biomarkers hold the potential to differentiate normal aging from neuroinflammatory/neurodegenerative diseases.