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前期大量的MRI研究已经表明，精神分裂患者很多脑区的局部灰质体积（regional grey matter volume）出现异常变化，但是这些研究的结果似乎并不一致。而这种结果的不一致性是否是由于采用不同的工具包进行分析而导致的呢？近期，有研究者在《Brain Imaging and Behavior》杂志上发表研究论文，对精神分裂患者Voxel-based morphometry (VBM)结果的不一致性是否是由于所用工具包不同而导致的这个问题进行了研究。笔者在这里对这篇文章进行简单解读，希望大家对不同的工具包对VBM计算结果的影响有一定的认识。
数据分析方法
86名精神分裂患者和86名健康对照组进行MRI扫描，搜集T1影像。 VBM的分析分别采用两种工具包：FMRIB Software Library voxel-based morphometry(FSL-VBM)和Statistical Parametric Mapping software (SPM-VBM)。对于两种工具包，采用默认的参数设置对T1影像进行处理。具体如下：
对于FSL-VBM，采用FSL 5.0软件，具体的预处理流程如下：1）brain extracting tool (BET) was employed to cut the skull from all T1 MRI structural images；2）FSL Automated Segmentation Tool (FAST) was adopted to carry out tissue-type segmentation；3）After the careful check for segmentation quality, the segmented GM parietal volume images were then aligned to the MNI standard space (MNI152) by applying linear image registration tool FLIRT and nonlinear registration FNIRT methods. A study-specific template was created by averaging the registered images, to which the native grey matter images were then non-linearly re-registered；3）The registered GM parietal volume images were modulated for thecontraction/enlargement due to the nonlinear component of the transformation by dividing them by the Jacobian of the warp field；4）the segmented and modulated images were then smoothed with isotropic Gaussian kernels with a standard deviation (sigma = 3 mm)。 对于SPM-VBM，采用SPM8软件，具体预处理流程如下：1）T1-weighted images were manually re-oriented, placing the origin at the anterior commissure; 2) Images were then segmented into GM, WM and cerebro spinal fluid (CSF) based on standard tissue probability maps using New Segment for SPM; 3) After the careful check for segmentation quality, the Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra (DARTEL) algorithmwas employed to create a study-specific template for spatial normalization ofthe segmented GM images of each subject; 4) Images were smoothed spatially witha full width at half maximum kernel of 8-mm。 关于统计分析，对于FSL-VBM，组间GM volume的比较采用非参数置换检验，用threshold-free cluster enhancement (TFCE)来矫正多重比较（P<0.05）；对于SPM-VBM，组间GM volume的比较采用t-test，采用FDR来矫正多重比较（P<0.05）。
主要研究结果
1.被试的临床和统计学数据如图1所示。
- VBM结果。 对于FSL-VBM，精神分裂患者在frontal, temporal, parietal 以及cingulate cortices等广泛的脑区表现出GM 的降低，具体如图2和图3所示。
然而，对于SPM-VBM分析，没有发现精神分裂患者GM显著降低的脑区。但是，FSL-VBM和SPM-VBM都揭示出精神分裂患者在一些脑区表现出显著增加的GM体积，具体如图4和图5所示。
把上述具有显著差异的脑区的GM 体积提取出来，与临床数据PANSS做相关分析，发现只有GM显著降低的脑区（如bilateral superior frontal cortex, bilateral inferiorfrontal cortex, left middle frontal cortex, right superior parietal cortex,right inferior parietal cortex and right anterior cingulate cortex）与PANSS具有显著相关性，具体如图6和7所示。
总结
总之，本文的研究结果表明，不同的工具包得到的VBM结果存在一定的差异，这可能是由于不同工具包中采用的算法不同所导致的。但是哪种工具包更优，现在还不能确定，需要未来做更多的研究。
参考文献： Li C , Liu W , Guo F , et al. Voxel-basedmorphometry results in first-episode schizophrenia: a comparison of publiclyavailable software packages[J]. Brain imaging and behavior, 2019.
