Motivation: Magnetization Transfer (MT) is an important contrast in neuroimaging that is typically limited by specific absorption rate (SAR) safety limits. Goal(s): Improve contrast-to-noise ratio (CNR) efficiency of MT ratio (MTR) mapping in the brain at 0.55T where SAR constraints are less restrictive and longer, more efficient readouts are feasible. Approach: Sequence parameters were fully constrained by hardware limits and optimized for maximum CNR efficiency of MTR between white and gray matter. A range of repetition times (TR) were explored. Results: In-vivo 3D MTR maps showed improved CNR efficiency with longer TR, with optimized sequence parameters operating at the limits of the system. Impact: Efficient acquisitions at lower field resolves the two greatest difficulties of deploying Magnetization Transfer Ratio images in the clinic, namely scan time and SAR concerns.
Leitão et al. (Tue,) studied this question.