IMAGINE Fetal T2-weighted MRI Atlas

The fetal brain undergoes rapid changes during the second and third trimesters of gestation. In addition to overall growth, the brain dramatically changes in terms of shape, with the gyrification or folding of the cerebral cortex, and also in characteristic, as layers of neurons become myelinated. At the same time, the challenges of imaging in-vivo neonates, such as fetal and maternal motion, limited resolution, and image artifacts result in corrupted images or low-quality data. The lack of quality MR images throughout this time period and the need for improved data processing techniques for challenging datasets necessitate improved digital reference images or brain atlases. To this end we have developed a normative spatiotemporal MRI atlas of the fetal brain. The atlas includes 3D (spatio-) images of the fetal brain in isolation at a range of gestational ages (-temporal). The atlas was constructed from 81 fetuses in normative pregnancies, combined using symmetric diffeomorphoic deformable registration in space, with the influence of contributing cases weighted by age. The resulting atlas images are high-resolution representations of the average developing fetal brain at one-week intervals between 21 and 38 weeks gestational age and can be used for anatomical reference and measurement. We have segmented the atlas images facilitating the measurement and localization of individual structures (i.e. hippocampus, corpus callosum), tissue classes (i.e. white and gray matter, cerebrospinal fluid), and developmental white matter layers (i.e. subplate) in the brain. These segmentations can be used to delineate novel fetal brain images through the use of algorithmic registration and segmentation programs that use the atlas images for reference. They can also be used to provide information such as the thickness of cortical plate regions or to designate the location of neuronal tracts measured by diffusion-weighted imaging.
We have also published a fetal diffusion tensor atlas, also accessible on Harvard Dataverse.

胎儿大脑在妊娠中晚期（第二、第三孕期）会经历显著的发育变化。除整体体积增长外，其形态亦发生明显改变：不仅出现大脑皮层的脑回形成（gyrification），还会随着神经元髓鞘化进程呈现特征性变化。与此同时，活体胎儿与新生儿成像面临诸多挑战，包括胎儿与母体运动干扰、分辨率受限及图像伪影等，这些因素易导致图像损坏或数据质量低下。此阶段高质量磁共振成像（Magnetic Resonance, MR）图像的匮乏，以及针对这类高挑战性数据集优化数据处理技术的需求，都推动了对更优质数字化参考图像或大脑图谱（brain atlas）的开发。为此，我们构建了一套标准化的胎儿脑时空磁共振成像图谱（spatiotemporal MRI atlas）。该图谱涵盖了不同胎龄下的孤立胎儿大脑三维（空间-时间）图像。该图谱基于81名正常妊娠胎儿的数据构建，通过空间对称微分同胚变形配准（symmetric diffeomorphic deformable registration）进行融合，并依据胎龄对各贡献病例赋予权重。最终生成的图谱图像为21至38孕周之间、以周为间隔的平均发育中胎儿大脑的高分辨率表征，可用于解剖学参考与结构测量。我们还对图谱图像进行了分割，以支持对大脑内单个结构（如海马体、胼胝体）、组织类别（如白质、灰质、脑脊液）以及发育性白质层（如亚板）的测量与定位。这些分割结果可通过以该图谱为参考的算法配准与分割程序，用于勾画全新的胎儿脑部图像；同时还可用于提取皮层板区域厚度等信息，或标定通过弥散加权成像测得的神经束位置。
我们还发布了一套胎儿弥散张量图谱（diffusion tensor atlas），该资源同样可在哈佛数据文库（Harvard Dataverse）获取。