MR Spectroscopy Core Facility, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, 20892, USA.
Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, 20892, USA.
Med Phys. 2017 Aug;44(8):4169-4178. doi: 10.1002/mp.12375. Epub 2017 Jul 10.
Numerical simulations of three-dimensionally localized MRS spectra have been very time consuming for multispin systems because the current state-of-the-art method requires computation of a large ensemble of spins pixel-by-pixel in three dimensional space. This paper describes a highly accelerated technique for computing spatially localized MRS spectra using the full solution to the Liouville-von Neumann equation.
The time evolution of spatially localized multispin density matrix as the full solution to the Liouville-von Neumann equation was analyzed. A new technique based on one dimensional spatial projection of the full density matrix was proposed. This method was implemented using a computer program written in Java language.
The MRS spectra calculated using the new method were found to be identical to conventional three-dimensional simulation for the same digitization of the voxel while the new method reduced computation time by orders of magnitude and led to not only improved speed but also accuracy. Applications of the new method to phantom studies of multispin systems and quantification of in vivo MRS spectra of brain were demonstrated.
The dramatically enhanced computational efficiency makes accurate simulation of localized MRS spectra highly accessible for calculating basis sets for spectral quantification and for optimizing pulse sequences.
对于多体系统，三维局域化 MRS 谱的数值模拟非常耗时，因为当前最先进的方法需要在三维空间中逐像素计算大量的自旋体。本文描述了一种使用完整的刘维尔-冯诺依曼方程解来计算局域化 MRS 谱的高度加速技术。
分析了作为刘维尔-冯诺依曼方程完全解的局域化多体密度矩阵的时间演化。提出了一种基于全密度矩阵一维空间投影的新方法。该方法使用 Java 语言编写的计算机程序实现。
对于相同体素的数字化，使用新方法计算的 MRS 谱与传统三维模拟完全一致，而新方法将计算时间降低了几个数量级，不仅提高了速度，而且提高了准确性。该方法在多体系统的幻影研究和脑内 MRS 谱的定量中的应用得到了证明。
计算效率的显著提高使得局域化 MRS 谱的精确模拟对于计算光谱定量的基组和优化脉冲序列变得非常容易。
