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

磁共振成像（MRI）是一种独特的无创观察人体内部结构的方法。由于这不是一种通过放大图像来观察每个组织内部精细结构的方法，因此很难将这种方法应用于小鼠和大鼠等小型实验动物。有一种利用计算机技术放大CRT上图像的方法，但这种方法要求原始图像清晰，信噪比高。核磁共振理论告诉我们，磁场越高，得到的核磁共振信号越强。通常用于200或300 MHz核磁共振光谱的超导磁体产生强而均匀的磁场。我们计划使用常规的200 MHz核磁共振光谱仪（Brucker MSL200）对实验动物的内部进行成像。为此，我们设计了适合于该机器的MRI成像探头。作为初步实验，我们制作了一个共振频率为300 MHz的Dadok型亥姆霍兹线圈（直径50 mm）作为成像探头，并将其应用于磁孔尺寸较大（183 mm）的超导磁体（Oxford）上，产生7T的磁场。一台SIS 300/183成像系统在东芝工作站上操作。用该系统对幼龄（5周龄）和老龄（24月龄）Wistar大鼠的大脑矢状面和冠状面进行成像时，可以清楚地显示大脑皮层的组织学改变、第三脑室的增大和与衰老有关的脑变性的颅顶骨肥大。MR图像分辨率为0.8 mm。在这些结果的基础上，我们随后设计了一种适合布鲁克MSL200的成像探头，直径为25毫米。该探针现在用于积累成像数据并作为核磁共振显微镜进行测试。

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.