Clinical application of ultra high field magnetic resonance imaging and spectroscopy

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The possibility and problems of-obtaining VRI and MRS using a high field system were examined from the basic and technical point of view. The first subject was to design the most appropriate method for localized spectra by using an experimental machine for Animal use (4.7 T and 7.0 T). As the result, the chemical shift imaging (CSI) method is best both for ^1H- and ^<31>P-MRS. According to this result, the second was decided to develop. the ^1H-CSI by resolving various problems as follows. The pulse sequence was designed to get good spectra from small voxels with good localization and with good water suppression The eddy current artifact was compensated by adjusting the dephasing and rephasing gradients. The software for data processing were designed to be that the baseline and phase distortions were corrected automatically and the metabolite mapping was carried out by using the curve-fitted data for each peak. Thus, spectra of 256 voxels with a size of 2.5x2.5x2.5 mm each were obtaine … More d within 50 minutes in the experimental system. In the spectrum of experimentally induced brain ischemia, a N-acetyl aspartate (NAA) peak decreased and a lactate peak increased. The metabolite mapping clearly visualized the changes of the distribution of metabolites in the brain. Since there is still problems in the gradient, system and RF amplifier of the clinical ultra-highs field system, the CSI method was examined by applying to the clinical system now available (1.5 T). As the result, spectra could be obtained from 256 voxels with a sue of lxlx2 cm in the normal and patient brains within 25 minutes. In conclusion, the CSI method is essential for clinical use and it is necessary to continue the research of applying and developing this method for clinical use both in the high-field and ultra-high field systems.The second suiects is to develop a diffusion weighted imaging method on a high field experimental MRI/S sytem. As an experimental brain edema models, cytotoxic and vasogenic brain edema models were examined using a 4.7 T experimental MR machine. The pulse sequence used was a spin echo method with additional motion-probing gradient (MPG) Pulses. Faster diffusion was detected in the white matter parallel to the direction of MPGS. Slower diffusion was detected perpendicular to MPGS. This indicated that the diffusion anisotropy of myelinated axonal fibers was defined in white matter. A Diffusion weighted image is useful to analyse the various brain disorders. By using the ultra-high field MRI/S system, it is supposed to be possible to obtain the spectroscopic diffusion weighted image which will clarifythe diffusion of various metabolites in the tissue. Less