title: Cortical depth dependent functional responses in humans at 7T: improved specificity with 3D GRASE.
abstract: Ultra high fields (7T and above) allow functional imaging with high contrast-to-noise ratios and improved spatial resolution. This, along with improved hardware and imaging techniques, allow investigating columnar and laminar functional responses. Using gradient-echo (GE) (T2* weighted) based sequences, layer specific responses have been recorded from human (and animal) primary visual areas. However, their increased sensitivity to large surface veins potentially clouds detecting and interpreting layer specific responses. Conversely, spin-echo (SE) (T2 weighted) sequences are less sensitive to large veins and have been used to map cortical columns in humans. T2 weighted 3D GRASE with inner volume selection provides high isotropic resolution over extended volumes, overcoming some of the many technical limitations of conventional 2D SE-EPI, whereby making layer specific investigations feasible. Further, the demonstration of columnar level specificity with 3D GRASE, despite contributions from both stimulated echoes and conventional T2 contrast, has made it an attractive alternative over 2D SE-EPI. Here, we assess the spatial specificity of cortical depth dependent 3D GRASE functional responses in human V1 and hMT by comparing it to GE responses. In doing so we demonstrate that 3D GRASE is less sensitive to contributions from large veins in superficial layers, while showing increased specificity (functional tuning) throughout the cortex compared to GE.
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, United States of America.
authors.forename: Federico
authors.initials: F
authors.lastname: De Martino
authors.forename: Jan
authors.initials: J
authors.lastname: Zimmermann
authors.forename: Lars
authors.initials: L
authors.lastname: Muckli
authors.forename: Kamil
authors.initials: K
authors.lastname: Ugurbil
authors.forename: Essa
authors.initials: E
authors.lastname: Yacoub
authors.forename: Rainer
authors.initials: R
authors.lastname: Goebel
mesh_terms: D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010775:Photic Stimulation