Alternate Ascending/Descending Directional Navigation Approach for Imaging Magnetization Transfer Asymmetry

摘要

A new method for imaging magnetization transfer (MT) asymmetry with no separate saturation pulse is proposed in this article. MT effects were generated from sequential two-dimensional balanced steady-state free precession imaging, where interslice MT asymmetry was separated from interslice blood flow and magnetic field inhomogeneity with alternate ascending/descending directional navigation (ALADDIN). Alternate ascending/descending directional navigation provided high-resolution multislice MT asymmetry images within a reasonable imaging time of ~3 min. MT asymmetry signals measured with alternate ascending/descending directional navigation were 1–2% of baseline signals (N = 6) in agreement with those from the conventional methods. About 70% of MT asymmetry signals were determined by the first prior slice. The frequency offset ranges in this study were >8 ppm from the water resonance frequency, implying that the MT effects were mostly associated with solid-like macromolecules. Potential methods to make alternate ascending/ descending directional navigation feasible for imaging amide proton transfer (~3.5 ppm offset from the water resonance frequency) were discussed.