Reducing ihMT acquisition time using alternating single frequency MT preparation and variable flip angle readouts

Motivation: IhMT demonstrates unique specificity and sensitivity to myelin. However, clinical translation of ihMT is hindered by the acquisition time. Goal(s): Reduce ihMT acquisition times by: exploiting dipolar order decay for single frequency MT by frequency alternation at low duty-cycle (FALDC); and, using variable flip angles (VFA) to increase SNR. Approach: FALDC MT was compared to standard single frequency MT in simulations and brains at 3T. We compared 1.4-mm isotropic ihMT using FALDC MT and uniform versus VFA. Results: No statistically significant difference was found between FALDC MT versus averaging images from positive and negative offset MT. IhMT SNR increased significantly for VFA data. Impact: We demonstrate frequency alternating at low duty cycle MT and variable flip angle readouts significantly improve ihMT by reducing scan time and/or increasing resolution. These developments allow for easier clinical translation and will improve utility in neurological studies of myelin.