T2-based segmentation of periventricular volumes for quantification of proton magnetic resonance spectra of multiple sclerosis lesions

Abstract

Partial volume averaging of signal from multiple sclerosis lesions influences biexponential fitting of the water T2 relaxation as used for tissue/CSF segmentation of spectroscopic volumes. Periventricular volumes-of-interest comprising CSF, lesion and normal-appearing white matter in varying proportion were studied. The relaxation of the localized water signal was measured at 12 echo times (STEAM, geometric spacing from 30 ms to 2000 ms, least-squares fit). Magnetization transfer (MT) was applied to identify contributions of tissue signal to the CSF component. The T2 of the long-lived component (T2_long=433–1782 ms) and its prolongation after MT were inversely correlated to the MT ratio. Hence, short T2_long is associated with overestimation of CSF partial volume, and thus metabolite concentrations. A T2-correction for the CSF partial volume was suggested and applied to the quantification of MR spectra of large MS lesions. The T2 of bulk CSF (2280±87 ms) and the influence of the TE sampling scheme were also studied.