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Recent Advances in High-Resolution MR Application and Its Implications for Neurovascular Coupling Research.

Harel N, Bolan PJ, Turner R, Ugurbil K, Yacoub E - Front Neuroenergetics (2010)

Bottom Line: However, a significant lack of knowledge exists regarding the cluster of intermediate-sized vessels, mainly the intracortical, connecting these two groups of vessels and where, arguably, key blood flow regulation takes place.Here, we summarize recent cutting-edge MR applications for studying neurovascular and functional imaging, both in humans as well as in animal models.If indeed such a correlation between functional (neuronal) and structural (vascular) units exist as a fundamental intrinsic cortical feature, one could conceivably delineate functional domains in cortical areas that are not known or have not been identified.

View Article: PubMed Central - PubMed

Affiliation: Center for Magnetic Resonance Research, Department of Radiology, School of Medicine, University of Minnesota Minneapolis, MN, USA.

ABSTRACT
The current understanding of fMRI, regarding its vascular origins, is based on numerous assumptions and theoretical modeling, but little experimental validation exists to support or challenge these models. The known functional properties of cerebral vasculature are limited mainly to the large pial surface and the small capillary level vessels. However, a significant lack of knowledge exists regarding the cluster of intermediate-sized vessels, mainly the intracortical, connecting these two groups of vessels and where, arguably, key blood flow regulation takes place. In recent years, advances in MR technology and methodology have enabled the probing of the brain, both structurally and functionally, at resolutions and coverage not previously attainable. Functional MRI has been utilized to map functional units down to the levels of cortical columns and lamina. These capabilities open new possibilities for investigating neurovascular coupling and testing hypotheses regarding fundamental cerebral organization. Here, we summarize recent cutting-edge MR applications for studying neurovascular and functional imaging, both in humans as well as in animal models. In light of the described imaging capabilities, we put forward a theory in which a cortical column, an ensemble of neurons involved in a particular neuronal computation is spatially correlated with a specific vascular unit, i.e., a cluster of an emerging principle vein surrounded by a set of diving arteries. If indeed such a correlation between functional (neuronal) and structural (vascular) units exist as a fundamental intrinsic cortical feature, one could conceivably delineate functional domains in cortical areas that are not known or have not been identified.

No MeSH data available.


Co-registration of fMRI maps with the underlying vascular model. (A) A representative axial slice across marginal gyrus in the cat primary visual cortex. Orange-to-yellow colors represent voxels that exhibit BOLD signal changes that was correlated with the stimulus paradigm. (B) 3D surface rendering of the veins and arteries (blue and red, respectively) within the imaged volume overlaid with iso-amplitude contour lines of the BOLD signals changes.
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Figure 3: Co-registration of fMRI maps with the underlying vascular model. (A) A representative axial slice across marginal gyrus in the cat primary visual cortex. Orange-to-yellow colors represent voxels that exhibit BOLD signal changes that was correlated with the stimulus paradigm. (B) 3D surface rendering of the veins and arteries (blue and red, respectively) within the imaged volume overlaid with iso-amplitude contour lines of the BOLD signals changes.

Mentions: In several cats we obtained functional MR images signals from the primary visual cortex following a visual stimulation task. Eight slices with image resolution of 250 μm × 250 μm × 500 μm were acquired. The functional maps were confined to primary visual cortex and followed the expected pattern of activation (Harel et al., 2002, 2006; Zhao et al., 2004). Figure 3A shows a BOLD functional map for a single axial slice across primary visual cortex (area 18); in addition, a 3-D surface rendering of the vessels (similar to Figure 2C) is displayed (Figure 3B). Several interesting features are evident from the data: first, the pattern of the stimulus-induced MR signal changes in the transverse plane had a patchy appearance and was found to be non-uniform across the cortex. As expected from theoretical and modeling studies, it appears that the regions with larger BOLD changes are associated with regions of large principal veins (blue). More intriguingly, these patterns of activations changed as a function of distance from the surface (i.e., deeper into the gray matter) implying the involvement of different vascular compartments (Harel et al., 2006). These features are more evident when the fMRI signal changes are plotted as iso-amplitude contour lines and are combined with the vascular model as shown in Figure 3B. These preliminary experimental data demonstrate the feasibility of potentially detecting stimulus-induced blood flow changes at extreme high-resolutions and throughout the gray matter volume. Furthermore, these signal changes can now be spatially correlated with the underlying vascular system, relating these blood flow changes to a specific subset of the vascular units within the imaged volume.


Recent Advances in High-Resolution MR Application and Its Implications for Neurovascular Coupling Research.

Harel N, Bolan PJ, Turner R, Ugurbil K, Yacoub E - Front Neuroenergetics (2010)

Co-registration of fMRI maps with the underlying vascular model. (A) A representative axial slice across marginal gyrus in the cat primary visual cortex. Orange-to-yellow colors represent voxels that exhibit BOLD signal changes that was correlated with the stimulus paradigm. (B) 3D surface rendering of the veins and arteries (blue and red, respectively) within the imaged volume overlaid with iso-amplitude contour lines of the BOLD signals changes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2967427&req=5

Figure 3: Co-registration of fMRI maps with the underlying vascular model. (A) A representative axial slice across marginal gyrus in the cat primary visual cortex. Orange-to-yellow colors represent voxels that exhibit BOLD signal changes that was correlated with the stimulus paradigm. (B) 3D surface rendering of the veins and arteries (blue and red, respectively) within the imaged volume overlaid with iso-amplitude contour lines of the BOLD signals changes.
Mentions: In several cats we obtained functional MR images signals from the primary visual cortex following a visual stimulation task. Eight slices with image resolution of 250 μm × 250 μm × 500 μm were acquired. The functional maps were confined to primary visual cortex and followed the expected pattern of activation (Harel et al., 2002, 2006; Zhao et al., 2004). Figure 3A shows a BOLD functional map for a single axial slice across primary visual cortex (area 18); in addition, a 3-D surface rendering of the vessels (similar to Figure 2C) is displayed (Figure 3B). Several interesting features are evident from the data: first, the pattern of the stimulus-induced MR signal changes in the transverse plane had a patchy appearance and was found to be non-uniform across the cortex. As expected from theoretical and modeling studies, it appears that the regions with larger BOLD changes are associated with regions of large principal veins (blue). More intriguingly, these patterns of activations changed as a function of distance from the surface (i.e., deeper into the gray matter) implying the involvement of different vascular compartments (Harel et al., 2006). These features are more evident when the fMRI signal changes are plotted as iso-amplitude contour lines and are combined with the vascular model as shown in Figure 3B. These preliminary experimental data demonstrate the feasibility of potentially detecting stimulus-induced blood flow changes at extreme high-resolutions and throughout the gray matter volume. Furthermore, these signal changes can now be spatially correlated with the underlying vascular system, relating these blood flow changes to a specific subset of the vascular units within the imaged volume.

Bottom Line: However, a significant lack of knowledge exists regarding the cluster of intermediate-sized vessels, mainly the intracortical, connecting these two groups of vessels and where, arguably, key blood flow regulation takes place.Here, we summarize recent cutting-edge MR applications for studying neurovascular and functional imaging, both in humans as well as in animal models.If indeed such a correlation between functional (neuronal) and structural (vascular) units exist as a fundamental intrinsic cortical feature, one could conceivably delineate functional domains in cortical areas that are not known or have not been identified.

View Article: PubMed Central - PubMed

Affiliation: Center for Magnetic Resonance Research, Department of Radiology, School of Medicine, University of Minnesota Minneapolis, MN, USA.

ABSTRACT
The current understanding of fMRI, regarding its vascular origins, is based on numerous assumptions and theoretical modeling, but little experimental validation exists to support or challenge these models. The known functional properties of cerebral vasculature are limited mainly to the large pial surface and the small capillary level vessels. However, a significant lack of knowledge exists regarding the cluster of intermediate-sized vessels, mainly the intracortical, connecting these two groups of vessels and where, arguably, key blood flow regulation takes place. In recent years, advances in MR technology and methodology have enabled the probing of the brain, both structurally and functionally, at resolutions and coverage not previously attainable. Functional MRI has been utilized to map functional units down to the levels of cortical columns and lamina. These capabilities open new possibilities for investigating neurovascular coupling and testing hypotheses regarding fundamental cerebral organization. Here, we summarize recent cutting-edge MR applications for studying neurovascular and functional imaging, both in humans as well as in animal models. In light of the described imaging capabilities, we put forward a theory in which a cortical column, an ensemble of neurons involved in a particular neuronal computation is spatially correlated with a specific vascular unit, i.e., a cluster of an emerging principle vein surrounded by a set of diving arteries. If indeed such a correlation between functional (neuronal) and structural (vascular) units exist as a fundamental intrinsic cortical feature, one could conceivably delineate functional domains in cortical areas that are not known or have not been identified.

No MeSH data available.