Johnson G A, Benveniste H, Black R D, Hedlund L W, Maronpot R R, Smith B R
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
Magn Reson Q. 1993 Mar;9(1):1-30.
Magnetic resonance microscopy (MRM) has advanced from a technical challenge to a practical tool in a wide range of basic sciences. This article focuses on the use of MRM as a tool for histological studies. The technical challenges of limited signal to noise have been overcome by improved radio-frequency (rf) coil design and 3DFT encoding with large arrays. Resolution limits imposed by motion in in vivo studies have been overcome by improved physiologic monitoring and control and projection encoding. Integration of technologies now permits routine studies in vivo down to 50 microns. MRM has also been applied to in vitro studies of fixed tissues where absence of motion allows studies down to 10 microns. The nondestructive nature of the technique allows repeated studies of the same sample, retrospective studies through any arbitrary plane, registered studies using different contrast mechanisms, and examination of valuable specimens. The many and unique proton contrasts provided by MRM, i.e., T1, T2, and diffusion weighting, permit direct examination of the state of water in tissues, something not possible with other microscopic techniques. Finally, the inherent three-dimensional nature of MRM allows acquisition of perfectly registered isotropic 3D arrays that, when displayed with appropriate visualization tools, provide new perspectives to histologic examination. The technology of MRM continues to develop rapidly. New pulse sequences are reducing acquisition times. New computer architectures allow larger arrays. A new class of superconducting rf probe has increased the signal to noise ratio by 10 times. These developments promise routine use of MRM in histology studies with resolution to 1 micron in the near future.
磁共振显微镜（MRM）已从一项技术挑战发展成为广泛基础科学领域中的实用工具。本文重点关注MRM作为组织学研究工具的应用。通过改进射频（rf）线圈设计和采用大阵列的3DFT编码，克服了信噪比有限这一技术难题。通过改进生理监测与控制以及投影编码，克服了体内研究中因运动导致的分辨率限制。技术的整合现已允许在体内进行低至50微米的常规研究。MRM也已应用于固定组织的体外研究，在这种情况下，由于不存在运动，研究可低至10微米。该技术的非破坏性特性允许对同一样本进行重复研究、通过任意平面进行回顾性研究、使用不同对比机制进行配准研究以及检查珍贵标本。MRM提供的众多独特质子对比，即T1、T2和扩散加权，使得能够直接检查组织中的水状态，这是其他显微镜技术无法做到的。最后，MRM固有的三维特性允许获取完美配准的各向同性3D阵列，当使用适当的可视化工具显示时，可为组织学检查提供新的视角。MRM技术继续快速发展。新的脉冲序列正在缩短采集时间。新的计算机架构允许使用更大的阵列。一类新型超导rf探头已将信噪比提高了10倍。这些进展有望在不久的将来使MRM在组织学研究中得到常规应用，分辨率可达1微米。
