Massaad Cynthia A, Pautler Robia G
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
Methods Mol Biol. 2011;711:145-74. doi: 10.1007/978-1-61737-992-5_7.
The use of manganese ions (Mn(2+)) as an MRI contrast agent was introduced over 20 years ago in studies of Mn(2+) toxicity in anesthetized rats (1). Manganese-enhanced MRI (MEMRI) evolved in the late nineties when Koretsky and associates pioneered the use of MEMRI for brain activity measurements (2) as well as neuronal tract tracing (3). Currently, MEMRI has three primary applications in biological systems: (1) contrast enhancement for anatomical detail, (2) activity-dependent assessment and (3) tracing of neuronal connections or tract tracing. MEMRI relies upon the following three main properties of Mn(2+): (1) it is a paramagnetic ion that shortens the spin lattice relaxation time constant (T(1)) of tissues, where it accumulates and hence functions as an excellent T(1) contrast agent; (2) it is a calcium (Ca(2+)) analog that can enter excitable cells, such as neurons and cardiac cells via voltage-gated Ca(2+) channels; and (3) once in the cells Mn(2+) can be transported along axons by microtubule-dependent axonal transport and can also cross synapses trans-synaptically to neighboring neurons. This chapter will emphasize the methodological approaches towards the use of MEMRI in biological systems.
20多年前，在对麻醉大鼠进行锰离子（Mn(2+)）毒性研究时，就已引入将Mn(2+)用作磁共振成像（MRI）造影剂（1）。锰增强磁共振成像（MEMRI）在九十年代后期得到发展，当时科雷茨基及其同事率先将MEMRI用于脑活动测量（2）以及神经元通路追踪（3）。目前，MEMRI在生物系统中有三个主要应用：（1）增强解剖细节的对比度；（2）基于活动的评估；（3）追踪神经元连接或通路追踪。MEMRI依赖于Mn(2+)的以下三个主要特性：（1）它是一种顺磁性离子，可缩短其在其中积累的组织的自旋晶格弛豫时间常数（T(1)），因此可作为一种出色的T(1)造影剂；（2）它是钙（Ca(2+)）的类似物，可通过电压门控Ca(2+)通道进入可兴奋细胞，如神经元和心肌细胞；（3）一旦进入细胞，Mn(2+)可通过微管依赖性轴突运输沿轴突运输，也可通过突触跨突触运输到相邻神经元。本章将重点介绍在生物系统中使用MEMRI的方法。
