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Journal of Visualized Experiments
Article . 2012 . Peer-reviewed
Data sources: Crossref
Journal of Visualized Experiments
Article . 2012 . Peer-reviewed
Data sources: Crossref
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High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain

Authors: Sucharit, Katyal; Clint A, Greene; David, Ress;

High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain

Abstract

Functional MRI (fMRI) is a widely used tool for non-invasively measuring correlates of human brain activity. However, its use has mostly been focused upon measuring activity on the surface of cerebral cortex rather than in subcortical regions such as midbrain and brainstem. Subcortical fMRI must overcome two challenges: spatial resolution and physiological noise. Here we describe an optimized set of techniques developed to perform high-resolution fMRI in human SC, a structure on the dorsal surface of the midbrain; the methods can also be used to image other brainstem and subcortical structures. High-resolution (1.2 mm voxels) fMRI of the SC requires a non-conventional approach. The desired spatial sampling is obtained using a multi-shot (interleaved) spiral acquisition (1). Since, T(2)* of SC tissue is longer than in cortex, a correspondingly longer echo time (T(E) ~ 40 msec) is used to maximize functional contrast. To cover the full extent of the SC, 8-10 slices are obtained. For each session a structural anatomy with the same slice prescription as the fMRI is also obtained, which is used to align the functional data to a high-resolution reference volume. In a separate session, for each subject, we create a high-resolution (0.7 mm sampling) reference volume using a T(1)-weighted sequence that gives good tissue contrast. In the reference volume, the midbrain region is segmented using the ITK-SNAP software application (2). This segmentation is used to create a 3D surface representation of the midbrain that is both smooth and accurate (3). The surface vertices and normals are used to create a map of depth from the midbrain surface within the tissue (4). Functional data is transformed into the coordinate system of the segmented reference volume. Depth associations of the voxels enable the averaging of fMRI time series data within specified depth ranges to improve signal quality. Data is rendered on the 3D surface for visualization. In our lab we use this technique for measuring topographic maps of visual stimulation and covert and overt visual attention within the SC (1). As an example, we demonstrate the topographic representation of polar angle to visual stimulation in SC.

Related Organizations
Keywords

Imaging, Three-Dimensional, Mesencephalon, Image Processing, Computer-Assisted, Humans, Magnetic Resonance Imaging

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
8
Average
Average
Average
bronze