Age-related deep white matter changes in myelin and water content: A T2 relaxometry study

Abstract

Background: According to the retrogenesis hypothesis, the rate of age-related changes in white matter (WM) myelin content varies between early myelinating (parietal, occipital) and late myelinating (prefrontal, lateral-posterior temporal) areas. The multiecho spin echo (MESE), PD-to-T₂ -weighted sequence provides an index of myelin content (myelin water fraction [MWF]) derived from measurements of myelin water (via the short T₂ component [10-50 msec]) and intra- and extracellular water (via the long T₂ component [>50-200 msec]).

Purpose: To assess the shape and regional variations in the rate of age-related myelin and water content changes in deep WM regions using the MESE sequence.

Study type: Prospective, cross-sectional.

Population: In all, 90 healthy adults aged 22-81 years.

Field strength/sequence: 1.5T/ T₁ w, T₂ w, fluid attenuated inversion recovery (FLAIR), MESE sequences.

Assessment: Short T₂ , long T₂ , and MWF values were measured in prefrontal, parietal, lateral-posterior temporal, and occipital normal-appearing WM (NAWM) areas.

Statistical tests: Linear and quadratic effects of age on long T₂ and MWF were assessed through regression analyses. Regional variations in the effect of age on long T₂ and MWF values at both the individual and group level were examined, using regression and analysis of covariance (ANCOVA) analyses, respectively, controlling for total WM volume.

Results: The rate of age-related changes in long T₂ and MWF was higher for older persons and a significant increase or decline, respectively, was first noted at 60-69 years (P < 0.0033). MWF values peaked earlier (at 30 years of age) and displayed a steeper age-related reduction in prefrontal and lateral-posterior temporal NAWM as compared with the occipital lobes (P < 0.05). The opposite pattern of age-related effect was found for long T₂ values.

Data conclusion: Significant age-related reductions in myelin content were closely followed by corresponding increases in intra- and extracellular water content. These changes were more pronounced among elderly people and followed an anterior-posterior pattern.

Level of evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1393-1404.

Keywords: MRI; T2 relaxometry; age; myelin content; water content; white matter.