MAGNETIZATION-TRANSFER IMAGING IN-VIVO OF THE RAT-BRAIN AT 4.7-T - INTERPRETATION USING A BINARY SPIN-BATH MODEL WITH A SUPERLORENTZIAN LINESHAPE

Proton magnetization transfer contrast (MTC) imaging, using continuous wave off-resonance irradiation, was performed on the rat brain in viv o at 4.7 Tesla. The observed MTC was studied in three different brain regions: the corpus callosum, the basal ganglia, and the temporal robe , By systematically varying the offset frequency and the amplitude of the RF irradiation, the observed signal intensities for each region of interest were modeled using a system including free water and a pool of protons with restricted motions (R. M. Henkelman, X. Huang, Q. Xian g, G. J. Stanisz, SD Swanson, M. J. Bronskill, Magn. Res. Med. 29, 759 (1993)), Most of the relaxation parameters of both proton pools remai ned fairly constant for the three regions of interest, with a T-2 valu e of about 9 mu s for the immobilized protons, whereas the rate of exc hange increased significantly from the temporal robe to the corpus cal losum, The optimal acquisition parameters for the improved MTC under s teady-state saturation were found to be 2-10 kHz offset frequency and 500-800 Hz RF irradiation amplitude, Conversely, an irradiation amplit ude of 3 kHz at an offset frequency of 12 kHz is required to minimize the direct effect of off-resonance irradiation. Such an approach could be extended to human brain imaging with the aim of characterizing tis sue-specific disease.