Efficient Whole-Brain Quantitative Magnetization Transfer Imaging at 3T Using Segmented EPI Readout with Variable Power Magnetization Transfer Pulses (EP-vpMT)

Quantitative magnetization transfer (qMT) imaging is sensitive to myelin-related macromolecular content and brain microstructure but is limited by long scan times. We present a fast, SAR-efficient qMT technique using a segmented echo-planar imaging readout with variable power MT preparation (EP-vpMT). EP-vpMT was implemented at 3T (1.5×1.5×4.0 mm³ voxels; 9 µL) using a 3D segmented EPI readout with modulated MT RF pulses to reduce SAR while preserving contrast. Pseudo bound pool fraction (pseudo-BPF) maps were obtained from healthy participants. Consistency with pseudo-BPF derived from conventional GRE-MT and repeatability was subject to Bland-Altman analysis. Multiple sclerosis (MS) patients were examined at 3T and at 7T (2.0 mm isotropic voxels; 8 µL) to explore feasibility for assessing tissue integrity and for application at ultra-high field. EP-vpMT achieved whole-brain qMT in 6 min 25 sec, reducing scan time by 76% compared to GRE-based qMT (26 min 20 sec) while maintaining similar SAR levels. Strong agreement was observed between methods, and test-retest reliability showed minimal bias with 95% limits of agreement within a clinically negligible range. In MS patients, EP-vpMT delineated lesions at 3T and at 7T. EP-vpMT enables fast qMT imaging at 3T with strong agreement with conventional methods. Its ability to detect MS lesions and to translate to ultra-high field MRI supports future use for assessing myelin-related macromolecular content.