A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Finland.
J Magn Reson. 2010 Dec;207(2):242-50. doi: 10.1016/j.jmr.2010.09.004. Epub 2010 Sep 15.
Magnetization transfer (MT) MRI and Z-spectroscopy are tools to study both water-macromolecule interactions and pH-sensitive exchange dynamics between water and the protons of mobile chemical groups within these macromolecules. Both rely on saturation of frequencies offset from water and observation of the on-resonance water signal. In this work, an RF saturation method called Z-spectroscopy with Alternating-Phase Irradiation (ZAPI) is introduced. Based on the T(2)-selectivity of the irradiation pulse, ZAPI can be used to separate the different contributions to a Z-spectrum, as well as to study the T(2) distribution of the macromolecules contributing to the MT signal. ZAPI can be run at resonance for water and with low power, thus minimizing problems with specific absorption rate (SAR) limits in clinical applications. In this paper, physical and practical aspects of ZAPI are discussed and the sequence is applied in vitro to sample systems and in vivo to rat head to demonstrate the method.
磁化传递（MT）MRI 和 Z 谱是用于研究水-大分子相互作用以及这些大分子中可动化学基团的质子与水之间的 pH 敏感交换动力学的工具。这两种方法都依赖于从水偏移的频率饱和和观察共振水信号。在这项工作中，引入了一种称为交替相辐照 Z 谱（ZAPI）的 RF 饱和方法。基于辐照脉冲的 T2 选择性，ZAPI 可用于分离 Z 谱的不同贡献，以及研究对 MT 信号有贡献的大分子的 T2 分布。ZAPI 可以在水中进行共振操作，并且功率低，从而最大限度地减少了临床应用中特定吸收率（SAR）限制的问题。本文讨论了 ZAPI 的物理和实际方面，并将该序列应用于体外样品系统和体内大鼠头部，以证明该方法。
