Reducing Inhomogeneous MT (ihMT) Acquisition Time Using Frequency Alternation at Low Duty Cycle for Single Offset...

To evaluate Frequency Alternation at Low duty cycle for Single Offset (FALSO) as a novel Magnetization Transfer (MT) preparation scheme to increase speed and/or spatial resolution of inhomogeneous MT (ihMT) MRI by reducing the number of volumes required.

We compared FALSO MT to standard single frequency MT preparations using signal simulations and ihMT data acquired in a rat brain at 9.4 T and human brains at 3 T. Using FALSO MT preparations, combined with optimized Variable Flip Angle (VFA) MPRAGE readouts, we also acquired ihMT data at high resolution (down to 1.4 mm isotropic) to demonstrate the reduction in acquisitions required for ihMT images of sufficient SNR.

We found no statistically significant difference between ihMT ratios from data acquired using FALSO MT preparations versus averaging data following separate positive and negative frequency offset MT acquisitions (as in regular ihMT to account for MT asymmetry). Use of VFA (relative to constant flip angle) readouts allowed high-resolution ihMT images with a minimal number of volumes to be acquired and reduced variance in ihMT ratios within ROIs.

FALSO MT preparations allow for a reduction in the number of acquisitions required for ihMT while still controlling for MT asymmetry. IhMT data acquired with VFA readouts allow for higher resolution acquisitions in the same scan time. The combination of FALSO MT and VFA readouts can be used to increase the spatial and/or temporal resolution of ihMT experiments, allowing for easier clinical translation and improving the utility of ihMT in neurological studies of myelin.