Evaluation of myelination by means of the T2 value on magnetic resonance imaging.

The progress of myelination in the cerebrum was evaluated by visual inspection, and magnetic resonance (MR) imaging and the transverse relaxation time (T2) was calculated from double echo images. Twenty-three pediatric cases, who did not show intracranial organic changes on MR examination, were included. The T2 values in the corpus callosum (CC), frontal deep white matter (FWM), occipital deep white matter (OWM) and centrum semiovale (CS) were calculated, and the changes in these values with age were followed. During the first year of life, a rapid decrease in the T2 value was seen, followed by a more gradual decrease. The T2 value seemed to reach the adult level between 2 and 3 years of life in all areas examined. The T2 values between 2 and 16 years in CC, FWM, OWM and CS were 59.7 +/- 3.6, 64.5 +/- 5.2, 69.8 +/- 4.8 and 66.3 +/- 3.3 ms (mean +/- S.D.), respectively. The T2 values in patients with clinically diagnosed Pelizaeus-Merzbacher disease (PMD) and late onset Krabbe disease were also calculated. In PMD, non-progressive prolongation of the T2 value was observed in all areas. In late onset Krabbe disease, on the other hand, progressive prolongation of the T2 values was mainly demonstrated in OWM and the posterior part of CS. These results suggest that the T2 value in the cerebral white matter allows more objective judgement than visual inspection, and makes it possible to clarify the mechanism underlying abnormal myelination, i.e. progressive or not.