| Research Abstract |
We have developed multi-modality magnetic resonance imaging (MRI) techniques for analysis of cerebral circulation, brain functions and metabolism on ultra-high magnetic field. Those are; (1) Fast ^1H chemical shift imaging (CSI) method and 2D-COSY method to detect various metabolite in the brain, (2) Diffusion-weighted imaging using ultra fast MRI (EPI-DWI), (3) Per fusion imaging using arterial spin tagging method, (4) Improvement of functional MRI (fMRI) on ultra-high field magnet and development of new fMRI method which detect nerve cell excitation. Systems used were an experimental MRI machine (7.0 T INOVA300SWB, Varian) and a whole body MRI machine for human (3.0 T, Signa Horizon, GE).
In ^1H-CSI, higher signal intensity was obtained than lower magnetic field systems and the distribution of various metabolites was visualized with high spatial resolution, such as N-acetyl aspartate (NAA), glutamine/glutamate, choline, creatine, inositol, lactate and etc. The decrease of NAA in vario
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us brain disorders were observed, indicating the loss of neurons. Increased lactate was observed in hypoxic cell fractions in malignant tumors and infarction. In 2D-COSY method, glutamine and glutamate were clearly separated and small amount of ammo acid such as taurine could be detected. In the EPI-DWI, cerebral infarction is detected at an ultra-acute stage such as 30 minutes after the onset. The diffusion tensor imaging (DTT) and fiber tracking imaging, which were calculated from the data of EPI-DWI, indicated the direction of nerve fiber clearly. The perfusion imaging using arterial spin tagging method (FAIR) is useful to detect the relative changes in cerebral blood flow, but it still requires more sensitivity even on a 3.0T system. The combination of EPI-DWI and Perfusion Imaging can possibly indicate the reversibility of damaged brain tissue. In functional MRI (fMRI), an increase of signal intensity was observed on the ultra-high magnetic field in the cortical area corresponding to each activation task such as finger movements, photic stimulation and hearing words. The fMRI was also obtained by complex tasks such as imagination. As a new fMRI method, we tried to develop topographic imaging of neuronal activity by the combination with microimaging and EPI-DWI. Theoretically it is, possible to observe the influx of water molecule in the excited nerve cell. Although we could obtain the ultra-fast diffusion weighted microimage with matrices size of 10 mirometer each, it is not enough to detect the influx of nerve cell directly so far on the experimental animal. The reason would be that the gradient strength is not enough for this experiment. More strong gradient and more strong magnetic field is necessary for this experiments. Nevertheless, the multi-modality MR methods are unique and useful methods to examine the brain metabolism and function non-invasively and to examine pathophysiology of various cerebral disorders. In this sense, further research should be continued. Less
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