Exploring structure and function of sensory cortex with 7 T MRI

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In this paper, we present an overview of 7 T magnetic resonance imaging (MRI) studies of the detailed function and anatomy of sensory areas of the human brain. We discuss the motivation for the studies, with particular emphasis on increasing the spatial resolution of functional MRI (fMRI) using reduced field-of-view (FOV) data acquisitions. MRI at ultra-high-field (UHF) – defined here as 7 T and above – has several advantages over lower field strengths. The intrinsic signal-to-noise ratio (SNR) of images is higher at UHF, and coupled with the increased blood-oxygen-level-dependent (BOLD) signal change, this results in increased BOLD contrast-to-noise ratio (CNR), which can be exploited to improve spatial resolution or detect weaker signals. Additionally, the BOLD signal from the intra-vascular (IV) compartment is relatively diminished compared to lower field strengths. Together, these properties make 7 T functional MRI an attractive proposition for high spatial specificity measures. But with the advantages come some challenges. For example, increased vulnerability to susceptibility-induced geometric distortions and signal loss in EPI acquisitions tend to be much larger. Some of these technical issues can be addressed with currently available tools and will be discussed. We highlight the key methodological considerations for high resolution functional and structural imaging at 7 T. We then present recent data using the high spatial resolution available at UHF in studies of the visual and somatosensory cortex to highlight promising developments in this area.HighlightsMagnetic resonance imaging, MRI, at 7 T can provide increased BOLD contrast-to-noise ratio compared to lower field strengths.For many neuroscience applications, fMRI at 7 T has clear advantages: (a) with voxel sizes of 1 mm3 and below, spatially resolving small brain structures becomes possible; (b) measuring weaker signals such as biases across cortical maps in individual participants is easier; (c) the sensitivity of functional signals from methods other than gradient-echo EPI based BOLD contrast become more robust and usable.We show recent results of mapping somatosensory and visual areas with a reduced field-of-view (FOV) at high spatial resolution, and summarize methodological advances in using these methods.

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