Magnetization transfer from inhomogeneously broadened lines (ihMT): Experimental optimization of saturation parameters for human brain imaging at 1.5 Tesla

Abstract

Purpose: Recently a new MR endogenous contrast mechanism was reported. It allows specifically imaging the magnetization transfer (MT) effect arising from inhomogeneously broadened components of the NMR spectrum, and was hence dubbed ihMT. Such unique NMR lineshape properties are presumably occurring in myelin because of its specifically ordered, multilayered sheath structure. Here, optimization of a pulsed ihMT preparation module is presented to provide guidance for future studies and improve the understanding of underlying contrast mechanisms.

Methods: This study was performed at 1.5 Tesla on healthy volunteers. A pulsed ihMT preparation was implemented in combination with a HASTE readout module. The pulse width, interpulse repetition time, total saturation duration and RF saturation power were considered for optimization of the ihMT sensitivity and contrast.

Results: An optimal configuration of the preparation module was derived, leading to 10% ihMT signal in internal capsule (relative to unsaturated data) and around 200% signal increase relative to gray matter, i.e., approximately 10-fold superior contrast compared with conventional MT ratios, measured under similar experimental conditions.

Conclusion: Overall the ihMT sequence was robust, sensitive and very specific for white matter. These findings suggest great potential for assessing brain myelination and for better characterization of myelin related disorders.

Keywords: ihMT; inhomogeneously broadened lines; magnetization transfer; myelin; specificity; white matter.