  Purpose: To study the effects of magnetization transfer (MT, in which a
semisolid 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 T1 and T2
estimation. Subsequently, an MRF sequence implementing off-resonance MT pulses
and a dictionary with an MT dimension by incorporating a two-pool model were
used to estimate the fractional pool size in addition to the B1+, T1, and T2
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% versus 4.7%). Adding
off-resonance MT pulses can improve the differentiation of MT from T1 and T2.
In-vivo results showed that MT affects the MRF signals from white matter
(fractional pool-size ~16%) and gray matter (fractional pool-size ~10%).
Furthermore, longer T1 (~1060 ms versus ~860 ms) and T2 values (~47 ms versus
~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 T1 and T2 with MRF. A model that encompasses MT effects can
improve the accuracy of estimated relaxation parameters and allows
quantification of the fractional pool size.
