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Jascha Swisher, John Sexton, John Gore, Chris Gatenby, Frank Tong; High-resolution retinotopic mapping at 7 Tesla with multishot 3D sequences. Journal of Vision 2010;10(7):922. doi: 10.1167/10.7.922.
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© ARVO (1962-2015); The Authors (2016-present)
High-field (>4T) MRI offers great promise for high-resolution functional imaging of human visual cortex, but a number of technical issues have slowed the pace of its adoption. In particular, susceptibility-induced geometric distortions become more severe at high resolution and high field strength. Such effects are especially worrisome in topographic mapping studies, which typically rely on accurate coregistration between functional and anatomic images in order to render activity patterns on inflated or flattened representations of the cortical surface. We used polar angle retinotopic mapping of the early visual areas at 7T as a test case to compare the single-shot, 2D EPI sequences commonly used for functional MRI with alternative, multi-shot 3D sequences (3D-FFE and 3D-PRESTO) that achieve similar spatial and temporal resolutions, but are less prone to susceptibility effects. Images were acquired at 4 isotropic spatial resolutions (1.12mm, 1.67mm, 2mm, and 3mm) using both 2D-EPI and 3D-FFE/3D-PRESTO sequences. We found marginally higher functional SNR (median √F statistic of activation in the grey matter of V1) for the EPI sequences across all resolutions. However, the lower distortion of the multi-shot 3D sequences lead to noticeable improvements in the smoothness and regularity of the surface-based retinotopic maps, particularly at the highest spatial resolutions. Such sequences may therefore provide a useful alternative to standard EPI imaging at high field strength and high resolution, especially in applications where geometric distortion is of concern, such as surface-based mapping of visual cortex.
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