Diffusion tensor microscopy indicates the cytoarchitectural basis for diffusion anisotropy in the human hippocampus.

Area of Science:

• Neuroimaging
• Diffusion Tensor Microscopy
• Human Anatomy

Background:

• Hippocampal pathologies like Alzheimer disease and mesial temporal sclerosis can be better detected using diffusion tensor MR imaging.
• Characterizing cytoarchitectural features of diffusion anisotropy is crucial for improving imaging sensitivity and specificity.

Purpose of the Study:

• To characterize the cytoarchitectural basis of diffusion anisotropy in human hippocampus autopsy specimens.
• To establish baseline diffusion parameters for specific hippocampal subregions at high resolution.

Main Methods:

• Diffusion tensor microscopy was performed on human hippocampus autopsy specimens (n=5) using a 14.1T magnet.
• Data included 21 diffusion gradient orientations with a diffusion time of 17 ms and b-value of 1250 s/mm(2).
• Mean diffusivity, fractional anisotropy (FA), and principal fiber orientation were calculated for manually segmented hippocampal regions.

Main Results:

• High signal-to-noise ratio diffusion-weighted images clearly delineated hippocampal anatomy.
• Water diffusivity varied significantly across hippocampal regions, ranging from 1.21 x 10(-4) mm(2)/s in the fimbria to 3.48 x 10(-4) mm(2)/s in granule cells.
• Color fiber-orientation maps revealed microstructural basis for diffusion anisotropy within hippocampal laminae.

Conclusions:

• Diffusion tensor microscopy provides novel microstructural information of human hippocampal laminae.
• Ex vivo, high-field data can inform the study of injury-specific diffusion changes in susceptible regions.
• This research may lead to more specific MR imaging surrogate markers for neurodegenerative diseases and epilepsy.