使用弥散磁共振成像技术对活体人脑海马体的宏观结构和微观结构进行成像。

Mapping the macrostructure and microstructure of the in vivo human hippocampus using diffusion MRI.

机构信息

Robarts Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.

Neuroscience Graduate Program, University of Western Ontario, London, Ontario, Canada.

出版信息

Hum Brain Mapp. 2023 Nov;44(16):5485-5503. doi: 10.1002/hbm.26461. Epub 2023 Aug 24.

Abstract

The hippocampus is classically divided into mesoscopic subfields which contain varying microstructure that contribute to their unique functional roles. It has been challenging to characterize this microstructure with current magnetic resonance based neuroimaging techniques. In this work, we used diffusion magnetic resonance imaging (dMRI) and a novel surface-based approach in the hippocampus which revealed distinct microstructural distributions of neurite density and dispersion, T1w/T2w ratio as a proxy for myelin content, fractional anisotropy, and mean diffusivity. We used the neurite orientation dispersion and density imaging (NODDI) model optimized for grey matter diffusivity to characterize neurite density and dispersion. We found that neurite dispersion was highest in the cornu ammonis (CA) 1 and subiculum subfields which likely captures the large heterogeneity of tangential and radial fibres, such as the Schaffer collaterals, perforant path, and pyramidal neurons. Neurite density and T1w/T2w were highest in the subiculum and CA3 and lowest in CA1, which may reflect known myeloarchitectonic differences between these subfields. Using a simple logistic regression model, we showed that neurite density, dispersion, and T1w/T2w measures were separable across the subfields, suggesting that they may be sensitive to the known variability in subfield cyto- and myeloarchitecture. We report macrostructural measures of gyrification, thickness, and curvature that were in line with ex vivo descriptions of hippocampal anatomy. We employed a multivariate orthogonal projective non-negative matrix factorization (OPNNMF) approach to capture co-varying regions of macro- and microstructure across the hippocampus. The clusters were highly variable along the medial-lateral (proximal-distal) direction, likely reflecting known differences in morphology, cytoarchitectonic profiles, and connectivity. Finally, we show that by examining the main direction of diffusion relative to canonical hippocampal axes, we could identify regions with stereotyped microstructural orientations that may map onto specific fibre pathways, such as the Schaffer collaterals, perforant path, fimbria, and alveus. These results highlight the value of combining in vivo dMRI with computational approaches for capturing hippocampal microstructure, which may provide useful features for understanding cognition and for diagnosis of disease states.

摘要

海马体经典地分为中观亚区,其中包含不同的微观结构,这些微观结构有助于其独特的功能作用。目前,使用基于磁共振的神经影像学技术来描述这种微观结构具有挑战性。在这项工作中,我们使用扩散磁共振成像(dMRI)和一种新的基于表面的海马体方法,揭示了神经突密度和分散、T1w/T2w 比(作为髓鞘含量的替代物)、各向异性分数和平均扩散率的不同微观结构分布。我们使用优化用于灰质扩散的神经突方向分散和密度成像(NODDI)模型来描述神经突密度和分散。我们发现,神经突分散在 CA1 和 subiculum 亚区最高,这可能捕捉到了切线和放射纤维的巨大异质性,如 Schaffer 侧支、穿通路径和锥体细胞。神经突密度和 T1w/T2w 在 subiculum 和 CA3 中最高,在 CA1 中最低,这可能反映了这些亚区之间已知的髓鞘结构差异。使用简单的逻辑回归模型,我们表明,神经突密度、分散和 T1w/T2w 测量值在亚区之间是可分离的,这表明它们可能对亚区细胞和髓鞘结构的已知变异性敏感。我们报告了宏观结构的回转轴率、厚度和曲率测量值,这些值与海马体解剖学的离体描述一致。我们采用了一种多变量正交投影非负矩阵分解(OPNNMF)方法来捕获海马体的宏观和微观结构的共变区域。这些聚类在中线-侧线(近端-远端)方向上高度可变,可能反映了形态、细胞构筑轮廓和连接的已知差异。最后,我们表明,通过检查相对于经典海马体轴的扩散的主要方向,我们可以识别出具有刻板微观结构取向的区域,这些区域可能映射到特定的纤维通路,如 Schaffer 侧支、穿通路径、齿状回和穹窿。这些结果强调了将体内 dMRI 与计算方法相结合以捕获海马体微观结构的价值,这可能为理解认知和诊断疾病状态提供有用的特征。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/077c/10543110/3b93144a0abd/HBM-44-5485-g006.jpg

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