MAGNETIZATION-TRANSFER FAST IMAGING OF IMPLANTED GLIOMA IN THE RAT-BRAIN AT 4.7T - INTERPRETATION USING A BINARY SPIN-BATH MODEL

C6 glioma cells were implanted in the left caudate nucleus of the rat brain. Histologic studies confirmed the presence of neoplastic tissue surrounded by a thin edematous region. Proton magnetization transfer c ontrast (MTC) fast imaging, using continuous wave off-resonance irradi ation, was performed in vivo at 4.7 T with the rapid acquisition with relaxation enhancement (RARE) sequence. The observed MTC allowed very clear distinction of the tumoral region, in which magnetization transf er (MT) ratios were lower than in healthy tissues. Contrasts were anal yzed as a function of the offset frequency and the amplitude of the ra diofrequency (RF) irradiation. The contrast was higher between the con tralateral basal ganglia and the tumor and lower between the tumor and the temporal lobe. Modeling of MT in the three brain regions was perf ormed using a system including free water and a pool of protons with r estricted motions. The rate of exchange between the two pools exhibite d a decreasing hierarchy from the basal ganglia to the tumor. T2(B) va lues for the immobile protons ranged from 9.3 mu sec in the basal gang lia to 7.5 mu sec for the glioma. The acquisition conditions leading t o the highest contrasts between the tumor and the healthy tissues corr espond to 3,000 Hz offset frequency and 300 to 700 Hz RF irradiation a mplitude.