Translational Imaging Group, CMIC, UCL, UK.
Department of Radiology, Boston Childrens Hospital and Harvard Medical School, 300 Longwood Avenue, Boston, MA, USA.
Neuroimage. 2017 Nov 15;162:65-72. doi: 10.1016/j.neuroimage.2017.08.013. Epub 2017 Aug 8.
Preterm birth disrupts and alters the complex developmental processes in the cerebral cortex. This disruption may be a contributing factor to widespread delay and cognitive difficulties in the preterm population. Diffusion-weighted magnetic resonance imaging (DW MRI) is a noninvasive imaging technique that makes inferences about cellular structures, at scales smaller than the imaging resolution. One established finding is that DW MRI shows a transient radial alignment in the preterm cortex. In this study, we quantify this maturational process with the "radiality index", a parameter that measures directional coherence, which we expect to change rapidly in the perinatal period. To measure this index, we used structural T-weighted MRI to segment the cortex and generate cortical meshes. We obtained normal vectors for each face of the mesh and compared them to the principal diffusion direction, calculated by both the DTI and DIAMOND models, to generate the radiality index. The subjects included in this study were 89 infants born at fewer than 34 weeks completed gestation, each imaged at up to four timepoints between 27 and 42 weeks gestational age. In this manuscript, we quantify the longitudinal trajectory of radiality, fractional anisotropy and mean diffusivity from the DTI and DIAMOND models. For the radiality index and fractional anisotropy, the DIAMOND model offers improved sensitivity over the DTI model. The radiality index has a consistent progression across time, with the rate of change depending on the cortical lobe. The occipital lobe changes most rapidly, and the frontal and temporal least: this is commensurate with known developmental anatomy. Analysing the radiality index offers information complementary to other diffusion parameters.
早产会破坏和改变大脑皮层的复杂发育过程。这种破坏可能是导致早产儿广泛延迟和认知困难的一个因素。弥散加权磁共振成像（DW MRI）是一种非侵入性的成像技术，可以在比成像分辨率更小的尺度上推断细胞结构。一个已确立的发现是，DW MRI 显示早产儿皮层有短暂的放射状排列。在这项研究中，我们使用“放射指数”来量化这个成熟过程，该指数是一个衡量方向一致性的参数，我们预计它会在围产期迅速变化。为了测量这个指数，我们使用结构 T 加权 MRI 来分割皮层并生成皮层网格。我们为网格的每个面获取法向量，并将它们与通过 DTI 和 DIAMOND 模型计算出的主扩散方向进行比较，以生成放射指数。本研究纳入了 89 名胎龄少于 34 周的婴儿，他们在 27 至 42 周胎龄之间最多接受了 4 次成像。在本手稿中，我们从 DTI 和 DIAMOND 模型量化了放射指数、各向异性分数和平均扩散率的纵向轨迹。对于放射指数和各向异性分数，DIAMOND 模型比 DTI 模型具有更高的灵敏度。放射指数在整个时间内呈一致的进展，其变化率取决于皮质叶。枕叶变化最快，额叶和颞叶最慢：这与已知的发育解剖学相一致。分析放射指数提供了与其他扩散参数互补的信息。
