Institute for Systems and Robotics - Lisboa and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001, Lisbon, Portugal.
Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK.
MAGMA. 2022 Oct;35(5):779-790. doi: 10.1007/s10334-021-00991-4. Epub 2022 Jan 8.
Histogram-based metrics extracted from diffusion-tensor imaging (DTI) have been suggested as potential biomarkers for cerebral small vessel disease (SVD), but methods and results have varied across studies. This work aims to assess the impact of mask selection for extracting histogram-based metrics of fractional anisotropy (FA) and mean diffusivity (MD) on their sensitivity as SVD biomarkers.
DTI data were collected from 17 SVD patients and 12 healthy controls. FA and MD maps were estimated; from these, histograms were computed on two whole-brain white-matter masks: normal-appearing white-matter (NAWM) and mean FA tract skeleton (TBSS). Histogram-based metrics (median, peak height, peak width, peak value) were extracted from the FA and MD maps. These were compared between groups and correlated with the patients' cognitive scores (executive function and processing speed).
White-matter mask selection significantly impacted FA and MD histogram metrics. In particular, significant interactions were found between Mask and Group for FA peak height (p = 0.027), MD Median (p = 0.035) and MD peak width (p = 0.047); indicating that the mask used affected their ability to discriminate between groups. In fact, MD peak width showed a significant 8.8% increase in patients when using TBSS (p = 0.037), but not when using NAWM (p = 0.69). Moreover, the mask may have an effect on the correlations with cognitive measures. Nevertheless, MD peak width (TBSS: r = - 0.75, NAWM: r = - 0.71) and MD peak height (TBSS: r = 0.65, NAWM: r = 0.62) remained significantly correlated with executive function, regardless of the mask.
The impact of the processing methodology, in particular the choice of white-matter mask, highlights the need for standardized MRI data-processing pipelines.
基于体素的各向异性分数（FA）和平均扩散系数（MD）直方图指标已被提议作为脑小血管病（SVD）的潜在生物标志物，但不同研究之间的方法和结果存在差异。本研究旨在评估提取 FA 和 MD 直方图指标的掩模选择对其作为 SVD 生物标志物的敏感性的影响。
从 17 例 SVD 患者和 12 例健康对照者中收集弥散张量成像（DTI）数据。估计 FA 和 MD 图；从这些图中，在两个全脑白质掩模（正常表现白质（NAWM）和平均 FA 束骨架（TBSS））上计算直方图。从 FA 和 MD 图中提取直方图指标（中位数、峰高、峰宽、峰值）。比较组间差异，并与患者的认知评分（执行功能和处理速度）相关。
白质掩模选择对白质 FA 和 MD 直方图指标有显著影响。特别是，在 Mask 和 Group 之间发现了显著的交互作用，FA 峰高（p=0.027），MD 中位数（p=0.035）和 MD 峰宽（p=0.047）；这表明使用的掩模影响了它们区分组间的能力。事实上，当使用 TBSS 时，MD 峰宽在患者中增加了 8.8%（p=0.037），但当使用 NAWM 时则没有（p=0.69）。此外，掩模可能对与认知测量的相关性有影响。然而，MD 峰宽（TBSS：r=-0.75，NAWM：r=-0.71）和 MD 峰高（TBSS：r=0.65，NAWM：r=0.62）仍然与执行功能显著相关，与掩模无关。
处理方法的影响，特别是白质掩模的选择，突出了需要标准化 MRI 数据处理流程。
