Normal-appearing white matter in multiple sclerosis has heterogeneous, diffusely prolonged T₂

T₂ relaxation in normal-appearing white matter (NAWM) of multiple sclerosis (MS) patients was reexamined using more complete sampling and analysis of decay curves, and to assess focal vs. diffuse abnormalities. Nine MS patients and 10 controls were scanned using a single-slice 32-echo pulse sequence with a 10-ms echo spacing, Decay curves from outlined white and gray matter structures were analyzed using non-negative least-squares (NNLS). Resulting T₂ distributions were each summarized by the geometric mean T₂, T₂. Different white matter structures had different mean (over the subjects in a group) T₂. Mean T₂ in NAWM was always greater than that of controls. Differences were not caused by a few voxels with extreme T₂ (i.e., focal lesions), but rather by shifts of the entire T₂ distribution (diffuse prolongation). This T₂ increase suggests diffuse myelin or axonal pathology.