Centre for Integrative Neuroscience, University of Tuebingen, Tuebingen, Germany; Department of Psychology, University of Tübingen, Tübingen, Germany; Max Planck Institute for Biological Cybernetics, Tübingen, Germany; Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA; Computer Science and AI Lab (CSAIL), Massachusetts Institute of Technology, Cambridge, MA, USA.
Neuroimage. 2018 Jan 15;165:11-26. doi: 10.1016/j.neuroimage.2017.09.060. Epub 2017 Sep 29.
Recent advances in MR technology have enabled increased spatial resolution for routine functional and anatomical imaging, which has created demand for software tools that are able to process these data. The availability of high-resolution data also raises the question of whether higher resolution leads to substantial gains in accuracy of quantitative morphometric neuroimaging procedures, in particular the cortical surface reconstruction and cortical thickness estimation. In this study we adapted the FreeSurfer cortical surface reconstruction pipeline to process structural data at native submillimeter resolution. We then quantified the differences in surface placement between meshes generated from (0.75 mm) isotropic resolution data acquired in 39 volunteers and the same data downsampled to the conventional 1 mm voxel size. We find that when processed at native resolution, cortex is estimated to be thinner in most areas, but thicker around the Cingulate and the Calcarine sulci as well as in the posterior bank of the Central sulcus. Thickness differences are driven by two kinds of effects. First, the gray-white surface is found closer to the white matter, especially in cortical areas with high myelin content, and thus low contrast, such as the Calcarine and the Central sulci, causing local increases in thickness estimates. Second, the gray-CSF surface is placed more interiorly, especially in the deep sulci, contributing to local decreases in thickness estimates. We suggest that both effects are due to reduced partial volume effects at higher spatial resolution. Submillimeter voxel sizes can therefore provide improved accuracy for measuring cortical thickness.
最近磁共振（MR）技术的进展使得常规功能和解剖成像的空间分辨率提高，这就需要能够处理这些数据的软件工具。高分辨率数据的出现也提出了一个问题，即更高的分辨率是否会实质性地提高定量形态磁共振成像（neuroimaging）程序的准确性，特别是皮质表面重建和皮质厚度估计。在这项研究中，我们调整了 FreeSurfer 皮质表面重建流水线，以处理原生亚毫米分辨率的结构数据。然后，我们量化了从 39 名志愿者采集的各向同性分辨率为 0.75mm 的结构数据和下采样到传统的 1mm 体素大小的相同数据生成的网格之间表面位置的差异。我们发现，在原生分辨率下处理时，皮质在大多数区域的厚度估计值较小，但在扣带回和舌回以及中央沟后缘较厚。厚度差异由两种效应驱动。首先，灰-白质表面更接近白质，尤其是在富含髓鞘、对比度低的区域，如舌回和中央沟，导致厚度估计值局部增加。其次，灰质-脑脊液（CSF）表面更接近内部，尤其是在深沟中，导致厚度估计值局部减少。我们认为这两种效应都归因于更高空间分辨率下部分容积效应的减少。因此，亚毫米体素大小可以为测量皮质厚度提供更高的准确性。
