Department of Clinical Neurophysiology, University Medical Center, Georg-August University Göttingen, Göttingen, Germany.
Neuroimage. 2011 Jun 1;56(3):1164-70. doi: 10.1016/j.neuroimage.2011.02.029. Epub 2011 Feb 13.
Voxel-based morphometry (VBM) is a widely applied method in computational neurosciences but it is currently recommended to compare only data collected at a single MRI scanner. Multi-site VBM would be a desirable approach to increase group size and, thus, statistical power. We aimed to assess if multi-site VBM is feasible on similar hardware and compare the magnitude of inter- and intra-scanner differences. 18 healthy subjects were scanned in two identical 3T MRI scanners using different head coil designs, twice in scanner A and once in scanner B. 3D T1-weighted images were processed with SPM8 and FSL4.1 and compared as paired t-test (scan versus re-scan) on a voxel basis by means of a general linear model (GLM). Additionally, coefficient-of-difference (coeffD) maps were calculated for respective pairs of gray matter segmentations. We found considerable inter-scanner differences clearly exceeding a commonly used GLM significance threshold of p<0.05 (FWE corrected). The spatial pattern of detected differences was dependent on whether SPM8 or FSL4.1 was used. The inclusion of global correcting factors either aggravated (SPM8) or reduced the GLM detected differences (FSL4.1). The coeffD analysis revealed markedly higher variability within the FSL4.1 stream both for the inter- and the intra-scanner comparison. A lowered bias cutoff (30 mm FWHM) in SPM8 improved the comparability for cortical areas. Intra-scanner scan/re-scan differences were generally weaker and did not exceed a p<0.05 (FWE corrected) threshold in the GLM analysis. At 3T profound inter-scanner differences are to be expected that could severely confound an unbalanced VBM analysis. These are like related to the receive bias of the radio-frequency hardware.
体素基形态测量学（VBM）是计算神经科学中广泛应用的方法，但目前仅建议比较在单个 MRI 扫描仪上收集的数据。多站点 VBM 将是一种增加组大小的理想方法，从而提高统计能力。我们旨在评估多站点 VBM 是否在类似硬件上可行，并比较扫描仪之间和扫描仪内部的差异幅度。18 名健康受试者在两台相同的 3T MRI 扫描仪上使用不同的头部线圈设计进行扫描，在扫描仪 A 中扫描两次，在扫描仪 B 中扫描一次。使用 SPM8 和 FSL4.1 处理 3D T1 加权图像，并通过一般线性模型（GLM）在体素基础上作为配对 t 检验（扫描与重新扫描）进行比较。此外，还为各自的灰质分割对计算了系数差异（coeffD）图。我们发现，扫描仪之间的差异非常大，明显超过了通常使用的 GLM 显著性阈值 p<0.05（FWE 校正）。检测到的差异的空间模式取决于使用 SPM8 还是 FSL4.1。使用全局校正因子会加剧（SPM8）或减少 GLM 检测到的差异（FSL4.1）。coeffD 分析表明，在 FSL4.1 流中，无论是扫描仪之间还是扫描仪内部的比较，都存在明显更高的可变性。SPM8 中的偏差截止值降低（30mm FWHM）可改善皮质区域的可比性。在 GLM 分析中，扫描仪内扫描/重新扫描差异通常较弱，且不超过 p<0.05（FWE 校正）阈值。在 3T 下，预计会出现深刻的扫描仪间差异，这可能会严重混淆不平衡的 VBM 分析。这些差异与射频硬件的接收偏差有关。
