Development of spectroscopic diffusion weighted imaging of metabolites in the brain

我们设计了一种利用磁共振（MR）方法对脑组织中各种代谢物进行弥散加权成像（DWI）的方法，通过该方法可以研究脑组织代谢中底物的动态特性。由于水DWI和磁共振波谱（MRS）两种技术的结合，因此将其称为光谱DWI （SP-DWI）。作为第一步，我们开发了SP-DWI的MR硬件。硬件中最重要的因素是对强磁场的要求和无涡流问题的强梯度线圈。在我们实验室的4.7特斯拉系统（CSI-II）下，观测到的信号对SP-DWI不够强，而在加州大学旧金山分校的7.0特斯拉系统下，SP-DWI获得了较强的信号强度。无涡流的强梯度是另一个不可缺少的设备。梯度线圈放大器（8606 TECROW）具有良好的质量，可以提供足够的更高的功率。但是，由于我们提供的经费削减，我们必须自己制作梯度线圈，我们可以消除涡流的问题。为了解决这一问题，必须引入无涡流的屏蔽梯度线圈。在这种情况下，我们设计了脉冲序列的发展，以进行实验研究。我们关注的是^1H原子核，而不是水质子。我们将运动探测梯度（MPG）脉冲引入到双自旋回波法获得的局部MRS脉冲序列中。在使用乳酸和n -乙酰丙氨酸标准溶液的实验中，在4.7特斯拉体系下，从200-300 mM的高浓度溶液中可以得到SP-DWI。在大鼠实验中，实际无法获得足够的信号。这些技术的顺序改进和优化仍有必要。从这些实验中可以清楚地看出，SP-DWI对于研究组织中代谢物的分子扩散是非常独特和有用的。继续发展这些重要的方法是必不可少的。虽然使用超高场MR设备是可取的，但将来可能会使用4.7特斯拉系统获得数据。该方法将成为研究脑功能和代谢的重要方法之一。少

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