Design of the MRI probe applicable to discrimination of the fine histological changes in brauns of laboratory animals

磁共振成像（MRI）是一种无创观察体内结构的独特方法。由于这不是通过放大图像来观察每个组织内部的精细结构的方法，因此很难将该方法应用于小鼠和大鼠等小型实验室动物。用计算机技术在CRT上放大图像是一种方法，但这种方法要求原图像清晰，信噪比高。NMR理论告诉我们，磁场越高，获得的NMR信号越强。通常用于200或300 MHz NMR谱的超导磁体产生强而均匀的磁场。我们计划通过使用常规的200 MHz NMR光谱仪（Brucker MSL200）对实验室动物的内部进行成像。为此，我们设计了适合本机的MRI成像探头。作为初步实验，我们制作了Dadok型Helmholtz线圈（内径50 mm）。以300 MHz的射频谐振作为成像探头，将其应用于具有相对较大尺寸的磁体孔（183 mm）的超导磁体（Oxford），产生7T的磁场。应用该系统对青年（5周龄）和老年（24月龄）Wistar大鼠脑的矢状面和冠状面进行成像，可清楚地显示大脑皮质的组织学改变、第三脑室的扩大和颅顶骨的肥大，这些都与脑的老化性退化有关。MR图像的分辨率为0.8 mm。在这些结果的基础上，我们随后设计了一个成像探头适用于布鲁克MSL200直径为25 mm。该探头现在被用来积累成像数据和测试作为NMR显微镜。

Magnetic resonance imaging (MRI) is a unique method to noninvasively observe the structure inside body. Since this is not a method to observe the fine structures inside each tissue by magnifying its image, it is hard to apply this method to small laboratory animals as mice and rats. There is a method to magnify the image on CRT by computer technique, but this method requires the original image to be sharply taken with a high S/N ratio. The NMR theory teaches us that the higher the magnetic field the stronger are the NMR signals obtained. The superconducting magnet used for usual 200 or 300 MHz NMR spectrometry produces the strong and homogeneous magnetic field. We planned to image the inside of the laboratory animal by employing usual 200 MHz NMR spectrometer (Brucker MSL200) . For this purpose, we designed the MRI imaging probe suitable for this machine. As a preliminary experiment, we made a Dadok type Helmholtz coil (50 mm i.d.) resonating at a radiofrequency of 300 MHz as the imaging probe and apply it to the superconducting magnet (Oxford) with the relatively large size of magnet bore (183 mm) producing a magnetic field of 7T.An SIS 300/183 imaging system was operated on a Toshiba workstation. When the sagittal and coronal sections of brains of young (5 weeks old) and aged (24 months old)Wistar rats were imaged using this system, histological alterations of cerebral cortices and enlargement of the third ventricle and hypertrophy of cranical parietal bones relating to degeneration of brains with aging were clearly displayd by this system. The resolution of MR images was 0.8 mm. On the basis of these results, wa subsequently designed an imaging probe suitable for the Brucker MSL200 with a diameter of 25 mm. This probe is now utilized to accumulate imaging data and tested as an NMR microscopy.