Center for Functional and Metabolic Mapping (CFMM), Robarts Research Institute, University of Western Ontario, London, Ontario, Canada.
Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada.
PLoS One. 2019 Apr 29;14(4):e0215974. doi: 10.1371/journal.pone.0215974. eCollection 2019.
Neurite Orientation Dispersion and Density Imaging (NODDI) is a diffusion MRI (dMRI) technique used to characterize tissue microstructure by compartmental modelling of neural water fractions. Intra-neurite, extra-neurite, and cerebral spinal fluid volume fractions are measured. The purpose of this study was to determine the reproducibility of NODDI in the rat brain at 9.4 Tesla.
Eight data sets were successfully acquired on adult male Sprague Dawley rats. Each rat was scanned twice on a 9.4T Agilent MRI with a 7 ± 1 day separation between scans. A multi-shell diffusion protocol was implemented consisting of 108 total directions varied over two shells (b-values of 1000 s/mm2 and 2000 s/mm2). Three techniques were used to analyze the NODDI scalar maps: mean region of interest (ROI) analysis, whole brain voxel-wise analysis, and targeted ROI analyses (voxel-wise within a given ROI). The coefficient of variation (CV) was used to assess the reproducibility of NODDI and provide insight into necessary sample sizes and minimum detectable effect size.
CV maps for orientation dispersion index (ODI) and neurite density index (NDI) showed high reproducibility both between and within subjects. Furthermore, it was found that small biological changes (<5%) may be detected with feasible sample sizes (n < 6-10). In contrast, isotropic volume fraction (IsoVF) was found to have low reproducibility, requiring very large sample sizes (n > 50) for biological changes to be detected.
The ODI and NDI measured by NODDI in the rat brain at 9.4T are highly reproducible and may be sensitive to subtle changes in tissue microstructure.
神经突方向分散和密度成像（NODDI）是一种扩散磁共振成像（dMRI）技术，用于通过对神经水分数的区室建模来描述组织微观结构。测量内神经突、外神经突和脑脊髓液体积分数。本研究的目的是确定 9.4T 下大鼠大脑 NODDI 的可重复性。
成功采集了 8 个成年雄性 Sprague Dawley 大鼠的数据。每只大鼠在 9.4T 安捷伦 MRI 上扫描两次，两次扫描之间间隔 7±1 天。实施了一种多壳扩散方案，共包含 108 个方向，在两个壳之间变化（b 值为 1000 s/mm2 和 2000 s/mm2）。使用三种技术分析 NODDI 标量图：感兴趣区域（ROI）的平均值分析、全脑体素分析和靶向 ROI 分析（在给定 ROI 内的体素分析）。变异系数（CV）用于评估 NODDI 的可重复性，并提供有关必要样本量和最小可检测效应量的见解。
各向异性分散指数（ODI）和神经突密度指数（NDI）的 CV 图在受试者之间和受试者内均具有高度的可重复性。此外，还发现，较小的生物学变化（<5%）可能通过可行的样本量（n<6-10）检测到。相比之下，各向同性体积分数（IsoVF）的可重复性较低，需要非常大的样本量（n>50）才能检测到生物学变化。
9.4T 下大鼠大脑中 NODDI 测量的 ODI 和 NDI 具有高度可重复性，并且可能对组织微观结构的细微变化敏感。
