Magnetization transfer in magnetic resonance fingerprinting

Purpose To study the effects of magnetization transfer (MT, in which a semi-solid spin pool interacts with the free pool), in the context of magnetic resonance fingerprinting (MRF). Methods Simulations and phantom experiments were performed to study the impact of MT on the MRF signal and its potential influence on T-1 and T-2 estimation. Subsequently, an MRF sequence implementing off-resonance MT pulses and a dictionary with an MT dimension, generated by incorporating a two-pool model, were used to estimate the fractional pool size in addition to the B1+, T-1, and T-2 values. The proposed method was evaluated in the human brain. Results Simulations and phantom experiments showed that an MRF signal obtained from a cross-linked bovine serum sample is influenced by MT. Using a dictionary based on an MT model, a better match between simulations and acquired MR signals can be obtained (NRMSE 1.3% vs. 4.7%). Adding off-resonance MT pulses can improve the differentiation of MT from T-1 and T-2. In vivo results showed that MT affects the MRF signals from white matter (fractional pool-size similar to 16%) and gray matter (fractional pool-size similar to 10%). Furthermore, longer T-1 (similar to 1060 ms vs. similar to 860 ms) and T-2 values (similar to 47 ms vs. similar to 35 ms) can be observed in white matter if MT is accounted for. Conclusion Our experiments demonstrated a potential influence of MT on the quantification of T-1 and T-2 with MRF. A model that encompasses MT effects can improve the accuracy of estimated relaxation parameters and allows quantification of the fractional pool size.