  Purpose: Magnetization transfer saturation (MTsat) mapping is commonly used
to examine the macromolecular content of brain tissue. This study compared
variable flip angle (VFA) T1 mapping against compressed sensing (cs)MP2RAGE T1
mapping for accelerating MTsat imaging. Methods: VFA, MP2RAGE and csMP2RAGE
were compared against inversion recovery (IR) T1 in a phantom at 3 Tesla. The
same 1 mm VFA, MP2RAGE and csMP2RAGE protocols were acquired in four healthy
subjects to compare the resulting T1 and MTsat. Bloch-McConnell simulations
were used to investigate differences between the phantom and in vivo T1
results. Finally, ten healthy controls were imaged twice with the csMP2RAGE
MTsat protocol to quantify repeatability. Results: The MP2RAGE and csMP2RAGE
protocols were 13.7% and 32.4% faster than the VFA protocol, respectively. All
approaches provided accurate T1 values (<5% difference) in the phantom, but the
accuracy of the T1 times was more impacted by differences in T2 for VFA than
for MP2RAGE. In vivo, VFA generated longer T1 times than MP2RAGE and csMP2RAGE.
Simulations suggest that the bias in the T1 values between VFA and IR-based
approaches (MP2RAGE and IR) could be explained by the MT-effects from the
inversion pulse. In the test-retest experiment, we found that the csMP2RAGE has
a minimum detectable change of 3% for T1 mapping and 7.9% for MTsat imaging.
Conclusions: We demonstrated that csMP2RAGE can be used in place of VFA T1
mapping in an MTsat protocol. Furthermore, a shorter scan time and high
repeatability can be achieved using the csMP2RAGE sequence.
