MR evidence of long T2 water in pathological white matter

Purpose: 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). Materials and Methods: The 48-echo T-2 relaxation data (maximum TE = 1.12 see) were acquired from 15 PKU subjects, 20 MS subjects, and 15 healthy volunteers. Regions of interest were drawn in diffuse white matter hyper-intensities (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. Results: A new water reservoir with a markedly prolonged T2 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 T2 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. Conclusion: 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.