Zhang Hui, Dyrby Tim B, Alexander Daniel C
Microstructure Imaging Group, Department of Computer Science, University College London, London WC1E 6BT, United Kingdom.
Med Image Comput Comput Assist Interv. 2011;14(Pt 2):82-9. doi: 10.1007/978-3-642-23629-7_11.
This paper proposes a technique for a previously unaddressed problem, namely, mapping axon diameter in crossing fiber regions, using diffusion MRI. Direct measurement of tissue microstructure of this kind using diffusion MRI offers a new class of biomarkers that give more specific information about tissue than measures derived from diffusion tensor imaging. Most existing techniques for axon diameter mapping assume a single axon orientation in the tissue model, which limits their application to only the most coherently oriented brain white matter, such as the corpus callosum, where the single orientation assumption is a reasonable one. However, fiber crossings and other complex configurations are widespread in the brain. In such areas, the existing techniques will fail to provide useful axon diameter indices for any of the individual fiber populations. We propose a novel crossing fiber tissue model to enable axon diameter mapping in voxels with crossing fibers. We show in simulation that the technique can provide robust axon diameter estimates in a two-fiber crossing with the crossing angle as small as 45 degrees. Using ex vivo imaging data, we further demonstrate the feasibility of the technique by establishing reasonable axon diameter indices in the crossing region at the interface of the cingulum and the corpus callosum.
本文提出了一种针对此前未解决问题的技术，即利用扩散磁共振成像（diffusion MRI）在交叉纤维区域绘制轴突直径。使用扩散磁共振成像对这类组织微观结构进行直接测量，提供了一类新的生物标志物，与从扩散张量成像得出的测量结果相比，能给出关于组织更具体的信息。大多数现有的轴突直径映射技术在组织模型中假设单一的轴突方向，这限制了它们仅适用于最具一致性取向的脑白质，比如胼胝体，在那里单一取向假设是合理的。然而，纤维交叉和其他复杂结构在大脑中广泛存在。在这些区域，现有技术无法为任何单个纤维群体提供有用的轴突直径指标。我们提出一种新颖的交叉纤维组织模型，以实现对具有交叉纤维的体素进行轴突直径映射。我们在模拟中表明，该技术能够在交叉角度小至45度的双纤维交叉中提供可靠的轴突直径估计。利用离体成像数据，我们通过在扣带与胼胝体界面的交叉区域建立合理的轴突直径指标，进一步证明了该技术的可行性。
