MR evidence of long T2 water in pathological white matter

To describe what, if any, specific long T(2)-related abnormalities occur in the white matter of subjects with either phenylketonuria (PKU) or multiple sclerosis (MS).

The 48-echo T(2) relaxation data (maximum TE = 1.12 sec) were acquired from 15 PKU subjects, 20 MS subjects, and 15 healthy volunteers. Regions of interest were drawn in diffuse white matter hyperintensities (DiffWM), lesions, normal-appearing white matter (NAWM), and normal white matter. Long T(2) maps (200 msec < T(2) < 800 msec) were created for each subject.

A new water reservoir with a markedly prolonged T(2) peak was identified in DiffWM and NAWM in 12 out of 15 subjects with PKU and a long T(2) signal was also seen in 23/97 lesions in 50% of subjects with MS. Additionally, a long T(2) component was observed in the corticospinal tracts of 10 healthy volunteers. The characteristics of the long T(2) signal were unique for each subject group. Potential sources of this signal include vacuolation and increases in extracellular water.

This study supports the usefulness of increasing the data acquisition window of the multiecho T(2) relaxation sequence to better characterize the T(2) decay from pathological brain.