Mathews V P, Elster A D, King J C, Ulmer J L, Hamilton C A, Strottmann J M
Department of Radiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-1088.
AJR Am J Roentgenol. 1995 Jan;164(1):169-72. doi: 10.2214/ajr.164.1.7998532.
Magnetization transfer (MT) imaging is an MR technique in which image contrast is altered by applying RF pulses that saturate a restricted pool of hydrogen protons associated with cell membranes, proteins, and other macromolecules. Protons in this restricted pool, unlike those in tissue-free water, are not visible on MR due to their short T2 relaxation times. However, these restricted protons modulate the observed signal from free water by dipolar and chemical exchange interactions. In MT imaging, specifically tailored RF pulses are applied to saturate selectively the restricted macromolecular pool. This saturation is "transferred" to the free protons, causing their signal amplitude to decrease [1]. Increased signal intensity due to T1 shortening caused by gadolinium administration does not depend upon macromolecular interactions and is not appreciably suppressed by MT pulses (Fig. 1). Consequently, MT pulses act synergistically with gadolinium to increase the visibility of enhancing lesions by preferentially suppressing nonenhancing background tissue [2]. The purpose of this paper is to demonstrate the principles underlying the synergistic effects of MT saturation and paramagnetic contrast agents and to illustrate these effects in clinical MR imaging and MR angiography.
磁化传递（MT）成像是一种磁共振技术，通过施加射频脉冲来改变图像对比度，这些射频脉冲会使与细胞膜、蛋白质及其他大分子相关的有限氢质子池饱和。与无组织水（自由水）中的质子不同，这个有限质子池中的质子由于其短T2弛豫时间，在磁共振成像上不可见。然而，这些受限质子通过偶极和化学交换相互作用调节来自自由水的观测信号。在MT成像中，会施加专门定制的射频脉冲来选择性地饱和受限的大分子池。这种饱和会“传递”到自由质子上，导致其信号幅度降低[1]。钆剂给药引起的T1缩短导致的信号强度增加并不依赖于大分子相互作用，且不会被MT脉冲明显抑制（图1）。因此，MT脉冲与钆剂协同作用，通过优先抑制未强化的背景组织来增加强化病变的可见性[2]。本文的目的是阐述MT饱和与顺磁性造影剂协同效应的基本原理，并在临床磁共振成像和磁共振血管造影中说明这些效应。
