Cohen Yoram, Assaf Yaniv
School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel.
NMR Biomed. 2002 Nov-Dec;15(7-8):516-42. doi: 10.1002/nbm.778.
This review deals with high b-value q-space diffusion-weighted MRI (DW-MRI) of neuronal tissues. It is well documented that at sufficiently high b-values (and high q-values) neuronal water signal decay in diffusion experiments is not mono-exponential. This implies the existence of more than one apparent diffusing component or evidence for restriction. The assignment of the different apparent diffusing components to real physical entities is not straightforward. However, the apparent slow diffusing component that was found to be restricted to a compartment of a few microns, if originating mainly from a specific pool and if assigned correctly, may potentially be used to obtain more specific MR images with regard to specific pathologies of the CNS. This review examines the utility of analyzing high b-value diffusion MRS and MRI data using the q-space approach introduced by Callaghan and by Cory and Garroway. This approach provides displacement probability maps that emphasize, at long diffusion times, the characteristics of the apparent slow diffusing component. Examples from excised spinal cord, where the experimental conditions for which the q-space analysis of MR diffusion data was developed can be met or approached will be presented. Then examples from human MS patients, where q-space requirement for the short gradient pulse is clearly violated, are presented. In the excised spinal cord studies, this approach was used to study spinal cord maturation and trauma, and was found to be more sensitive than other conventional methods in following spinal cord degeneration in an experimental model of vascular dementia (VaD). High b-value q-space DWI was also recently used to study healthy and MS diseased human brains. This approach was found to be very sensitive to the disease load in MS, compared with other conventional MRI methods, especially in the normal appearing white matter (NAWM) of MS brains. Finally, the potential diagnostic capacity embedded in high b-value q-space analyzed diffusion MR images is discussed. The potentials and caveats of this approach are outlined and experimental data are presented that show the effect of violating the short gradient pulse (SGP) approximation on the extracted parameters from the q-space analysis.
本综述探讨了神经元组织的高b值q空间扩散加权磁共振成像（DW-MRI）。有充分文献记载，在足够高的b值（和高q值）下，扩散实验中神经元水信号衰减并非单指数形式。这意味着存在不止一种表观扩散成分或限制证据。将不同的表观扩散成分与实际物理实体对应并非易事。然而，若发现表观慢扩散成分局限于几微米的隔室，且主要源自特定池并被正确归类，那么它可能被用于获取关于中枢神经系统特定病理的更具特异性的磁共振图像。本综述研究了使用Callaghan以及Cory和Garroway提出的q空间方法分析高b值扩散磁共振波谱（MRS）和磁共振成像（MRI）数据的效用。这种方法提供了位移概率图，在长扩散时间时突出了表观慢扩散成分的特征。将展示来自切除脊髓的例子，在那里可以满足或接近开发磁共振扩散数据q空间分析的实验条件。然后展示来自人类多发性硬化症（MS）患者的例子，在那里明显违反了短梯度脉冲的q空间要求。在切除脊髓的研究中，该方法用于研究脊髓成熟和创伤，并且发现在血管性痴呆（VaD）实验模型中跟踪脊髓退化时比其他传统方法更敏感。高b值q空间扩散加权成像（DWI）最近也被用于研究健康和患有MS的人类大脑。与其他传统MRI方法相比，该方法被发现对MS中的疾病负荷非常敏感，尤其是在MS大脑的正常外观白质（NAWM）中。最后，讨论了高b值q空间分析的扩散磁共振图像中潜在的诊断能力。概述了这种方法的潜力和注意事项，并展示了实验数据，这些数据显示了违反短梯度脉冲（SGP）近似对从q空间分析中提取的参数的影响。
