Article
High-resolutionMR (7 Tesla) microscopy of the human hippocampus
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Published: | September 11, 2012 |
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Questions: The human hippocampal formation is morphologically affected in many neurological disorders such as Alzheimer's disease or mesial temporal lobe epilepsy (mTLE). Its internal structure remains, however, difficult to recognize at 1.5T or 3T magnetic resonance imaging (MRI). We aimed to anatomically delineate all compartments and layers of the human hippocampus along its entire anterior-posterior axis combining high-field 7T MRI and histological sections from same tissue specimens.
Methods: Eight post-mortem human hippocampus specimens were examined on a 7T experimental scanner using different acquisition protocols:
- 1.
- Anatomical subregions and layers along the anterior-posterior axis of the hippocampus were characterized on T2-weighted coronal sections. MRI findings were validated by coregistration with histological sections of the very same specimens.
- 2.
- Three-dimensional T2-weighted imaging and coronal planes with different angulations were acquired to anticipate the arched shape of the hippocampal head.
- 3.
- Fractional anisotropy and color fiber orientation maps were used to visualize intrahippocampal projections and fiber tracts.
Results: Ten clearly recognizable layers were defined by MR-intensity differences between anatomical boundaries of the hippocampus and confirmed by exact confrontation with histology. These findings were best visible at the hippocampal mid-body-level. We were able to distinguish all these hippocampal subregions also in the hippocampal head combining three-dimensional T2-weighted images and oblique planes. Fractional anisotropy and color fiber orientation maps reliably visualized intrahippocampal projections as well as fiber tracts connecting the hippocampus with the mesial temporal lobe.
Conclusion: High resolution MR-microscopy identified anatomical subregions and sublayers as well as distinct intra- and parahippocampal fiber tracts along the entire anterior-posterior axis of the human hippocampus, and will be a promising tool for the investigation of subtle pathology in neurological or neurodegenerative disorders.