Introduction

Magnetic resonance imaging (MRI) shows slight spatial variations in brain white matter (WM). We used quantitative multi-parametric MRI to evaluate in what respect these inhomogeneities could correspond to WM subtypes with specific characteristics and spatial distribution.

Materials and methods

Twenty-six controls (12 women, 38 ±9 Y) took part in a 60-min session on a 3T scanner measuring 7 parameters: R₁ and R₂, diffusion tensor imaging which allowed to measure Axial and Radial Diffusivity (AD, RD), magnetization transfer imaging which enabled to compute the Macromolecular Proton Fraction (MPF), and a susceptibility-weighted sequence which permitted to quantify R₂* and magnetic susceptibility (χ_m). Spatial independent component analysis was used to identify WM subtypes with specific combination of quantitative parameters values.

Results

Three subtypes could be identified. t-WM (track) mostly mapped on well-formed projection and commissural tracts and came with high AD values (all p < 10⁻¹⁸). The two other subtypes were located in subcortical WM and overlapped with association fibers: f-WM (frontal) was mostly anterior in the frontal lobe whereas c-WM (central) was underneath the central cortex. f-WM and c-WM had higher MPF values, indicating a higher myelin content (all p < 1.7 10⁻⁶). This was compatible with their larger χ_m and R₂, as iron is essentially stored in oligodendrocytes (all p < 0.01). Although R₁ essentially showed the same, its higher value in t-WM relative to c-WM might be related to its higher cholesterol concentration.

Conclusions

Thus, f- and c-WMs were less structured, but more myelinated and probably more metabolically active regarding to their iron content than WM related to fasciculi (t-WM). As known WM bundles passed though different WM subtypes, myelination might not be uniform along the axons but rather follow a spatially consistent regional variability. Future studies might examine the reproducibility of this decomposition and how development and pathology differently affect each subtype.

中文翻译：

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多参数定量MRI显示三种不同的白质亚型

介绍

磁共振成像（MRI）显示脑白质（WM）的轻微空间变化。我们使用定量多参数MRI来评估这些不均匀性在哪些方面可以对应于具有特定特征和空间分布的WM亚型。

材料和方法

26位对照（12名女性，38±9 Y）在3T扫描仪上参加了60分钟的会议，测量了7个参数：R ₁和R ₂，扩散张量成像，可以测量轴向和径向扩散率（AD，RD） ），磁化转移成像，这使计算大分子质子分数（MPF），并且其允许量化R A磁化率加权序列₂ *和磁化率（χ_米）。使用空间独立成分分析来确定具有定量参数值的特定组合的WM亚型。

结果

可以确定三种亚型。t-WM（轨迹）主要映射在格式良好的投影和连合面上，并具有较高的AD值（所有p <10 ^-18）。另外两个亚型位于皮质下WM中，并与缔合纤维重叠：f-WM（额叶）大部分位于额叶的前部，而c-WM（中央）在中央皮质的下面。f-WM和c-WM的MPF值较高，表明髓磷脂含量较高（所有p <1.7 10 ^-6）。这与它们的较大的χ兼容_米和R ₂，作为铁基本上存储在少突胶质细胞（所有P <0.01）。尽管R ₁本质上显示相同，但​​相对于c-WM，其在t-WM中的较高值可能与其较高的胆固醇浓度有关。

结论

因此，f-和c-WMs的铁含量比与fasciculi（t-WM）有关的WM的结构更少，但具有更多的髓鞘，并且可能在铁含量方面具有更高的代谢活性。正如已知的WM束通过不同的WM亚型一样，髓鞘形成可能沿着轴突不均匀，而是遵循空间一致的区域变异性。未来的研究可能会检查这种分解的可再现性，以及发育和病理学如何不同地影响每种亚型。