Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
MR Clinical Science, Philips, Best, The Netherlands.
NMR Biomed. 2023 Jun;36(6):e4808. doi: 10.1002/nbm.4808. Epub 2022 Aug 29.
Off-resonance radio frequency irradiation can induce the ordering of proton spins in the dipolar fields of their neighbors, in molecules with restricted mobility. This dipolar order decays with a characteristic relaxation time, T , that is very different from the T and T relaxation of the nuclear alignment with the main magnetic field. Inhomogeneous magnetization transfer (ihMT) imaging is a refinement of magnetization transfer (MT) imaging that isolates the MT signal dependence on dipolar order relaxation times within motion-constrained molecules. Because T relaxation is a unique contrast mechanism, ihMT may enable improved characterization of tissue. Initial work has stressed the high correlation between ihMT signal and myelin density. Dipolar order relaxation appears to be much longer in membrane lipids than other molecules. Recent work has shown, however, that ihMT acquisitions may also be adjusted to emphasize different ranges of T . These newer approaches may be sensitive to other microstructural components of tissue. Here, we review the concepts and history of ihMT and outline the requirements for further development to realize its full potential.
离频射频辐射可以诱导具有受限流动性的分子中质子自旋在其邻近的偶极场中排序。这种偶极序以特征弛豫时间 T 衰减，与核与主磁场的对准的 T 和 T 弛豫非常不同。不均匀磁化转移（ihMT）成像是磁化转移（MT）成像的一种改进，它可以在运动受限的分子内分离出 MT 信号对偶极序弛豫时间的依赖性。由于 T 弛豫是一种独特的对比机制，ihMT 可能能够改善组织的特征描述。最初的工作强调了 ihMT 信号与髓鞘密度之间的高度相关性。然而，偶极序弛豫似乎比其他分子在膜脂质中长得多。最近的工作表明，ihMT 采集也可以进行调整，以强调 T 的不同范围。这些较新的方法可能对组织的其他微观结构成分敏感。在这里，我们回顾了 ihMT 的概念和历史，并概述了进一步发展以实现其全部潜力的要求。
