Retinotopic mapping of the human visual cortex at a magnetic field strength of 7T.

Objective: fMRI-based retinotopic mapping data obtained at a magnetic field strength of 7T are evaluated and compared to 3T acquisitions.

Methods: With established techniques retinotopic mapping data were obtained in four subjects for 25 slices parallel to the calcarine sulcus at 7 and 3T for three voxel sizes (2.5(3), 1.4(3), and 1.1(3)mm(3)) and in two subjects for 49 slices at 7T for 2.5(3)mm(3) voxels. The data were projected to the flattened representation of T1 weighted images acquired at 3T.

Results: The obtained retinotopic maps allowed for the identification of visual areas in the occipito-parietal cortex. The mean coherence increased with magnetic field strength and with voxel size. At 7T, the occipital cortex could be sampled with high sensitivity in a short single session at high resolution. Alternatively, at lower resolution simultaneous mapping of a great expanse of occipito-parietal cortex was possible.

Conclusion: Retinotopic mapping at 7T aids a detailed description of the visual areas. Here, recent findings of multiple stimulus-driven retinotopic maps along the intraparietal sulcus are supported.

Significance: Retinotopic mapping at 7T opens the possibility to detail our understanding of the cortical visual field representations in general and of their plasticity in visual system pathologies.