SACT template

We establsihed the SACT template by using a large sample of diffusion data of school-age children (380 participants). We provided two types of diffusion tensor (DT) templates. One is for the entire age range (6-12 years old), another one is for each specific age.Under the downloaded data, four folders are corresponding to different kinds of templates. Specifically, SACT includes the tensor template of the entire age range (‘SACT_06_12_DT.nii.gz’) which is in the same space as the CHN-PD template (https://helab.bnu.edu.cn/chn-pd/). The corresponding fractional anisotropy (FA) and trace map (3*Mean diffusivity, MD) are also available (‘SACT_06_12_DT_fa.nii.gz’, ‘SACT_06_12_DT_tr.nii.gz’). The ‘SACT_06_12_mask.nii.gz’ is the brain mask. Similarly, age-specific templates can be found in the age-specific folders, e.g., ‘/Age_Specific_SACT/Age_06_07’. Here, ‘06_07’ stands for the age range between 6 years old and 7 years old. To conveniently use the SACT template with tensor-based registration methods (DTI-TK), we also provided the corresponding templates which are padded with zeros to ensure the matrix size of the template as 256*256*256, which are available under the folders ended with ‘DTI_TK’.Moreover, the tensor templates are organized as six tensor components stored in the lower triangular order, i.e., Dxx, Dyx, Dyy, Dzx, Dzy, and Dzz. It is in the same order as the one specified by the NIfTI standard. The unit of diffusivity is 10-3mm2.s-1.Finally, to conveniently and accurately use the SACT template for the TBSS (ref. 1) analysis, we provided the ‘SACT_LowerCingulum_1mm.nii.gz’ under the ‘TBSS’ folder of each template. As the mask of the lower cingulum would be required for the skeleton process (ref. 1), we compensated the difference between SACT template and FMRIB58_FA template by registering the FMRIB58_FA template to the corresponding SACT template. Then, the warp field were applied to the mask of the lower cingulum corresponding to the FMRIB58_FA template.<br>Ref.1:S.M. Smith, M. Jenkinson, H. Johansen-Berg, D. Rueckert, T.E. Nichols, C.E. Mackay, K.E. Watkins, O. Ciccarelli, M.Z. Cader, P.M. Matthews, and T.E.J. Behrens. Tract-based spatial statistics: Voxelwise analysis of multi-subject diffusion data. NeuroImage, 31:1487-1505, 2006.本研究基于380名学龄儿童的大样本扩散成像数据集，构建了SACT模板（SACT template）。本研究提供了两类扩散张量（diffusion tensor, DT）模板：一类适配全年龄段（6~12岁），另一类适配单个具体年龄。 下载所得的数据包含四个文件夹，分别对应不同类型的模板。具体而言，全年龄段扩散张量模板（'SACT_06_12_DT.nii.gz'）与CHN-PD模板（https://helab.bnu.edu.cn/chn-pd/）处于同一空间坐标系下。配套的各向异性分数（fractional anisotropy, FA）与扩散张量迹图（即3倍平均扩散率，平均扩散率（mean diffusivity, MD））亦已提供，对应文件为'SACT_06_12_DT_fa.nii.gz'与'SACT_06_12_DT_tr.nii.gz'。'SACT_06_12_mask.nii.gz'为全脑掩膜文件。 类似地，单年龄段模板可于对应单年龄段文件夹中获取，例如'/Age_Specific_SACT/Age_06_07'，其中'06_07'代表6至7岁的年龄区间。为便于使用基于扩散张量的配准方法（DTI-TK）处理SACT模板，本研究还提供了经零填充的配套模板，将模板矩阵尺寸统一为256×256×256，此类文件存放于后缀为'DTI_TK'的文件夹中。 此外，扩散张量模板以六分量的下三角顺序存储，依次为Dxx、Dyx、Dyy、Dzx、Dzy与Dzz，该存储顺序符合NIfTI标准的规范。扩散系数的单位为10⁻³mm²·s⁻¹。 最后，为便于在基于纤维束的空间统计分析（tract-based spatial statistics, TBSS，参考文献1）中便捷精准地使用SACT模板，我们在每个模板的'TBSS'文件夹下提供了'SACT_LowerCingulum_1mm.nii.gz'文件。由于骨架化步骤（参考文献1）需要扣带回下束的掩膜文件，本研究通过将FMRIB58_FA模板配准至对应SACT模板，校正了SACT模板与FMRIB58_FA模板间的空间差异，随后将得到的形变场应用于FMRIB58_FA模板对应的扣带回下束掩膜文件。 参考文献1：S.M. Smith、M. Jenkinson、H. Johansen-Berg、D. Rueckert、T.E. Nichols、C.E. Mackay、K.E. Watkins、O. Ciccarelli、M.Z. Cader、P.M. Matthews 与 T.E.J. Behrens. 基于纤维束的空间统计分析：多被试扩散成像数据的体素级分析. 《NeuroImage》，31卷：1487-1505，2006年。