Development of spectroscopic diffusion weighted imaging of metabolites in the brain

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We have designed to develop the diffusion weighted imaging (DWI) of various metabolites in the brain tissue using magnetic resonance (MR) method, by which dynamic property of substrates in metabolism of brain tissue could be investigated. This will be called spectroscopic DWI (SP-DWI) because of the combination of two techniques of water DWI and the Magnetic Resonance spectroscopy (MRS). As the first step, we have developed the MR hardware for SP-DWI.The most important factors in the hardware are the requirement of strong magnetic field and the strong gradient coil without eddy current problems. With the 4.7 Tesla system (CSI-II) in our laboratory, the observed signal is not strong enough for SP-DWI, while with the 7.0 Tesla system in the University of California San Francisco, the strong signal intensity was obtained for SP-DWI.The strong gradient with eddy current free is the other indispensable bevice. The amplifier for gradient coil (8606 TECROW) has good quality for supplying enou … More gh power. However, we had the trouble that we must made the gradient coil by ourselves because of the cut of our offered grant, and we could eliminate the the problem of eddy current. In order to resolve this problem, it is indispensable to introduce the shielded gradient coil which have no eddy current.Under those circumstances, we had designed the development of pulse sequence for the the experimental study. We concentrated on ^1H nuclei other than water proton. We have introduced the motion probing gradient (MPG) pulse necessary for DWI to the pulse sequence of localized MRS obtained by double spin echo method. In the experiment using standard solution of lactate and N-acetylalanine, the SP-DWI could be obtained from the solution of high concentration with 200-300 mM on the 4.7 Tesla system. In the experiment using rats, enough signal could not be obtained practically. It is still necessary to improve the sequence and the optimization of those technique.From those experiment, it becomes clear that SP-DWI would be extremely unique and useful for the investigation of molecular diffusion of metabolites in tissues. It is indispensable to continue to develop these important method. Although it is desirable to use ultra-high field MR device, it may be possible to obtain data using a 4.7 Tesla system in future. This method will be one of the most important methods to investigate the brain function and metabolism. Less