MAGNETIZATION-TRANSFER IMAGING OF RAT-BRAIN UNDER NON-STEADY-STATE CONDITIONS - CONTRAST PREDICTION USING A BINARY SPIN-BATH MODEL AND A SUPER-LORENTZIAN LINESHAPE

Magnetization transfer contrast imaging using turbo spin echo and cont inuous wave off-resonance irradiation was carried out on rat brain in vivo at 4.7 T. By systematically varying the off-resonance irradiation power and the offset-frequency, the signal intensities obtained under steady-state for both transverse and longitudinal magnetization were successfully analyzed with a simple binary spin-bath model taking into account a free water compartment and a pool of protons with restricte d motions bearing a super-lorentzian lineshape. Due to important RF po wer deposition, such experimental conditions are not practical for rou tine imaging on humans. An extension of the model was derived to descr ibe the system for shorter off-resonance pulse duration, i.e., when th e longitudinal magnetization of the free protons has not reached a ste ady-state. Data sets obtained for three regions of interest, namely th e corpus callosum, the basal ganglia, and the temporal lobe, were corr ectly interpreted for off-resonance pulse durations varying from 0.3 t o 3 s. The parameter sets obtained from the calculations made it possi ble to predict the contrast between the different regions as a functio n of the pulse power, the offset frequency, and pulse duration. Such a n approach could be extended to contrast prediction for human brain at 1.5 T. (C) 1998 Academic Press.