Zhang Hui, Alexander Daniel C
Microstructure Imaging Group, Department of Computer Science, University College London, London WC1E 6BT, United Kingdom.
Med Image Comput Comput Assist Interv. 2010;13(Pt 1):640-7. doi: 10.1007/978-3-642-15705-9_78.
Direct measurement of tissue microstructure with diffusion MRI offers a new class of biomarkers, such as axon diameters, that give more specific information about tissue than measures derived from diffusion tensors. The existing techniques of this kind assume a single axon orientation in the tissue model, which may be a reasonable approximation only for the most coherent brain white matter, such as the corpus callosum. For most other areas, orientation dispersion is not negligible and, if unaccounted for, leads to overestimation of the axon diameters, prohibiting their accurate mapping over the whole brain. Here we propose a new model that captures the effect of orientation dispersion explicitly, An efficient numerical scheme is developed to enable the axon diameter estimation by fitting the proposed model. Synthetic data experiments demonstrate that the new model provides an axon diameter index that is robust to the presence of orientation dispersion. Results on in vivo human data show reduced axon diameter index and better agreement with histology compared to previous methods suggesting improvements in the axon diameter estimate.
利用扩散磁共振成像直接测量组织微观结构提供了一类新的生物标志物，如轴突直径，与从扩散张量得出的测量结果相比，它能提供关于组织更具体的信息。这类现有技术在组织模型中假设单一的轴突方向，这可能仅对于最连贯的脑白质（如胼胝体）是合理的近似。对于大多数其他区域，方向离散不可忽略，若不加以考虑，会导致轴突直径被高估，从而无法在全脑进行准确映射。在此我们提出一种新模型，该模型明确捕捉方向离散的影响，并开发了一种高效数值方案，通过拟合所提出的模型来实现轴突直径估计。合成数据实验表明，新模型提供的轴突直径指数对方向离散的存在具有鲁棒性。体内人体数据结果显示，与先前方法相比，轴突直径指数降低，且与组织学的一致性更好，这表明轴突直径估计有所改进。
