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Robust Detection of Ocular Dominance Columns in Humans using Hahn Spin Echo BOLD fMRI at High Fields


Shmuel,  A
Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Yacoub, E., Ugurbil, K., & Shmuel, A. (2004). Robust Detection of Ocular Dominance Columns in Humans using Hahn Spin Echo BOLD fMRI at High Fields. Poster presented at 10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004), Budapest, Hungary.

Cite as: http://hdl.handle.net/21.11116/0000-0005-6412-6
Background: The ability to reliably and reproducibly map high resolution functional architecture using fMRI techniques has been a point of debate in animal as well as human studies. Several animal and human studies have successfully mapped high resolution functional organizations, however, the robustness of the phenomenon (i.e. reproducibility and demonstration in multiple subjects), which would certainly improve the credibility of the data, has been a subject of debate, with only limited reproducibility demonstrated so far. Several different techniques have been used (i.e. initial dip, blood flow, blood volume, Gradient Echo (GE) BOLD); however, which one is optimal specifically for humans, has not been established. Here we demonstrate the spatial specificity of Hahn Spin Echo (HSE) BOLD by robust mapping of ocular dominance columns in humans at 7 T. SNR and the BOLD effect both increase with field strength, while the blood signal tends to be diminished because of the rapid shortening of its T2. This bodes well for the accuracy of both GE and HSE BOLD. Previous studies in humans mapping high resolution functional architecture used GE BOLD at 4T because the CNR of GE BOLD at 4T is much higher compared to that of HSE BOLD. However, the success of GE BOLD relies on the expectation that non-specific large vessel contributions will be equivalent for the two conditions and can be cancelled out. In the HSE approach, this requirement is significantly alleviated. Furthermore, improved CNR and SNR at magnetic fields exceeding 4T make the HSE BOLD technique feasible for such high resolution studies. Methods and Results: Studies were conducted at 7 T using slab selective FOV reduction for HSE (TR/TE 6000/50 ms) and 3 image segments. Resolution (60 x 256): 0.5 x 0.5 x 3 mm3. To suppress gross subject motion, a bite bar was used. In addition, any scans with significant motion were discarded. The visual stimuli were presented through fiber optic video goggles. Imaging was performed on a region of flat cortex where the ODCs are expected to run perpendicular to the inter-hemispheric fissure. Subjects were brought back for several repeated studies to assess the reproducibility of the functional maps. Approximately the same anatomical location was selected in multiple sessions with the same subject. The maps from different sessions were co-registered to allow for (see Figure) identification of the same columns in the different sessions. The Figure presents an ODC map from one subject obtained in three different sessions (over the period of several months). Despite inevitable but small differences in the slice positioning, highly reproducible maps were obtained. Similar reproducibility was seen in 3 different subjects. Conclusions: Using HSE BOLD at very high magnetic fields (7T), we have demonstrated not only that high field fMRI can produce reliable and reproducible maps at the sub-millimeter level but also that these maps have intrinsically high spatial specificity, even to the level of cortical columns in humans. We expect HSE BOLD to be the imaging choice for high resolution applications in humans at high fields.