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

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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.