Magnetization transfer of water T-2 relaxation components in human brain: implications for T-2-based segmentation of spectroscopic volumes

Biexponential T-2 relaxation of the localized water signal can be used for segmentation of spectroscopic volumes. To assess the specificity of the com ponents an iterative relaxation measurement of the localized water signal ( STEAM, 12 echo times, geometric spacing from 30 ms to 2000 ms) was combined with magnetization transfer (MT) saturation (40 single lobe pulses, 12 ms duration, 1440 degrees nominal flip angle, 1 kHz offset, repeated every 30 ms). Voxels including CSF were examined in parietal cortex and periventricu lar parietal white matter (10 each), as well as 13 voxels in central white matter and 16 T-1-hypointense non-enhancing multiple sclerosis lesions with out CSF inclusion, Biexponential models (excluding myelin water) were fitte d to the relaxation data. In periventricular VOIs the component of long T-2 (1736 +/- 168 ms) that is attributed to CSF was not affected by MT. In cor tical VOIs this component had markedly shorter T(2)s (961 +/- 239 ms) and s howed both attenuation and prolongation with MT, indicating contributions f rom tissue. MS lesions and central WM showed a second tissue component of i ntermediate T-2 (160-410 ms). In white matter similar NIT attenuation indic ated strong exchange between the two tissue components, prohibiting segment ation. In MS lesions, however, markedly less MT of the intermediate compone nt was found, which is consistent with decreased cellularity and exchange i n a region that is large compared to diffusion motion. (C) 2001 Elsevier Sc ience Inc. All rights reserved.