After over 200 years, 7 T magnetic resonance imaging reveals the foliate structure of the human corpus callosum in vivo.

Objective: A fine structure of the corpus callosum (CC), consisting of radial lines, is seen in historical anatomical atlases as far back as that of Vicq d'Azyr (1786). This study examines a similar pattern observed in vivo using high-resolution MR images at 7 T. Methods: 8 healthy subjects were examined with 7.0-T MRI. Anatomical images were collected with a gradient echo scan with 0.5-mm isotropic resolution, which were rated for visibility of the radial pattern. In addition, the second eigenvector of the diffusion tensor images was examined. Results: The fine radial lines are detected not only in the sagittal view but also in the axial view of the in vivo MR images. From this, it is likely that these structures are two-dimensional ribbons. Interestingly, and confirming the structural nature of these stripes, the second eigenvector of the diffusion tensor imaging data shows an extremely similar pattern of oriented foliate structure. A similar modular structure involving transient septa has been observed previously in histological sections of human fetal CC. Conclusion: The separate sets of data-the atlas of Klingler, anatomical images and second eigenvector images-all indicate a ribbon-like arrangement of the fibres in the CC. As such, they closely match the structures shown in the drawn atlases of as old as 1786. Advances in knowledge: This ribbon arrangement of fibres in the CC, previously unseen in CT or lower field MRI, can now be observed in vivo. This appears to match over two centuries of ex vivo observations.