Fast magnetization transfer and apparent T1 imaging using a short saturation pulse with and without inversion preparation.

PURPOSE: Measurements of magnetization transfer (MT) metrics, such as the steady-state (SS) MT ratio and apparent longitudinal relaxation rate require multiple MT irradiation durations and a long experimental time. To overcome these problems, we propose a novel method using a short MT off-resonance pulse with and without on-resonance inversion preparation pulse. THEORY AND METHODS: Computer simulations were performed to examine the accuracy of the proposed method and to find the optimal off-resonance irradiation pulse duration (Tirad) and power level (ω1). Our approach, with echo planar imaging data acquisition, was applied to animals at 9.4 T and humans at 3 T with ω1/2π = 100 Hz and 177 Hz, respectively. Steady-state MT ratio and relaxation rate were obtained from a pair of MT images at a Tirad, with and without inversion.
RESULTS: For Tirad ≥ 0.4 s, steady-state MT ratio, and relaxation rate measured at any single Tirad agreed well with those of the conventional fitting method that uses multiple Tirad. Our simulation indicates that a higher ω1 can use a shorter Tirad.
CONCLUSION: Steady-state MT ratio and relaxation rate can be determined from MT data with only one, short Tirad by incorporation of an inversion prepulse. This MT imaging approach is simple, fast, and easily implementable.