Magnetic Resonance Methodology, Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland.
Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
Magn Reson Med. 2022 Nov;88(5):1962-1977. doi: 10.1002/mrm.29367. Epub 2022 Jul 8.
Definition of a macromolecular MR spectrum based on diffusion properties rather than relaxation time differences and characterization of non-Gaussian diffusion of brain metabolites with strongly diffusion-weighted MR spectroscopy.
Short echo time MRS with strong diffusion-weighting with b-values up to 25 ms/μm at two diffusion times was implemented on a Connectom system and applied in combination with simultaneous spectral and diffusion decay modeling. Motion-compensation was performed with a combined method based on the simultaneously acquired water and a macromolecular signal.
The motion compensation scheme prevented spurious signal decay reflected in very small apparent diffusion constants for macromolecular signal. Macromolecular background signal patterns were determined using multiple fit strategies. Signal decay corresponding to non-Gaussian metabolite diffusion was represented by biexponential fit models yielding parameter estimates for human gray matter that are in line with published rodent data. The optimal fit strategies used constraints for the signal decay of metabolites with limited signal contributions to the overall spectrum.
The determined macromolecular spectrum based on diffusion properties deviates from the conventional one derived from longitudinal relaxation time differences calling for further investigation before use as experimental basis spectrum when fitting clinical MR spectra. The biexponential characterization of metabolite signal decay is the basis for investigations into pathologic alterations of microstructure.
基于扩散特性而非弛豫时间差异定义大分子磁共振波谱，并采用强扩散加权磁共振波谱对脑代谢物的非高斯扩散进行特征描述。
在 Connectom 系统上实施短回波时间 MRS，并在两个扩散时间内进行高达 25 ms/μm 的强扩散加权，同时结合进行光谱和扩散衰减建模。采用基于同时采集的水和大分子信号的联合方法进行运动补偿。
运动补偿方案防止了大分子信号中虚假的信号衰减，反映出非常小的表观扩散常数。使用多种拟合策略确定大分子背景信号模式。用双指数拟合模型表示对应于非高斯代谢物扩散的信号衰减，得出的人类灰质参数估计与已发表的啮齿动物数据一致。使用对整体光谱信号贡献有限的代谢物信号衰减的约束条件的最佳拟合策略。
基于扩散特性确定的大分子谱与基于纵向弛豫时间差异的常规谱不同，在将其用作拟合临床磁共振谱的实验基础谱之前，需要进一步研究。代谢物信号衰减的双指数特征描述是研究微观结构病理改变的基础。
