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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.


Vascular model of cat visual cortex. (A) An example of 3D time-of-flight (TOF) microangiography in the cat visual cortex. The axial excitation slab (Slab) was positioned so that its superior edge passed through the sagittal sinus (SS), as can be seen in the coronal view. Arteries, indicated by red arrows, are bright due to unsaturated blood flowing into the slab. Veins, indicated by blue arrows, are dark due to their elevated concentration of deoxyhemoglobin (the BOLD effect). (B) A dorsal view close up showing in greater details vessels classifications using the TOF and BOLD techniques; Veins: blue, Arteries: red. (C) 3D surface rendering of the vessels identified throughout the entire imaged volume. Figure modified from Bolan et al. (2006).
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Figure 2: Vascular model of cat visual cortex. (A) An example of 3D time-of-flight (TOF) microangiography in the cat visual cortex. The axial excitation slab (Slab) was positioned so that its superior edge passed through the sagittal sinus (SS), as can be seen in the coronal view. Arteries, indicated by red arrows, are bright due to unsaturated blood flowing into the slab. Veins, indicated by blue arrows, are dark due to their elevated concentration of deoxyhemoglobin (the BOLD effect). (B) A dorsal view close up showing in greater details vessels classifications using the TOF and BOLD techniques; Veins: blue, Arteries: red. (C) 3D surface rendering of the vessels identified throughout the entire imaged volume. Figure modified from Bolan et al. (2006).

Mentions: The technique of 3D TOF micro-angiography is used to generate images of the arteries and is demonstrated in Figure 2. In the exact setup as the images shown in Figure 1, a transverse slab (thickness 2 mm) was positioned in the center of the cortex, so that the superior edge of the slice passed through the sagittal sinus (Figure 2A). The vertical position of the slice is critical for producing proper flow weighting in the intracortical arteries running perpendicular to the cortical surface. The flip angle (30°) is greater than the Ernst angle for both blood and cortical gray matter so the spins inside the slice are saturated and show low signal. Blood that flows into the slice is not saturated, and therefore gives a higher signal than blood that has remained inside the slice for one or more excitations. This effect is called the TOF or inflow effect. In Figure 2A, the red arrows show an example of a bright vessel in both views. Other bright vessels are evident, particularly in the axial view in which most of the larger intracortical vessels are oriented perpendicular to the image plane. Blue arrows point to veins which are dark due to the BOLD effect (Figure 2A). Thus, Figure 2 demonstrates the ability to first, image the intracortical vessels and second, differentiate and show a clear separation of arteries and veins within the image volume across (tangential) the tissue. Figure 2B displays a vessel classification map, a single axial slice across primary visual cortex of the cat in which intracortical visible vessels were classified as vein or artery, using the TOF and BOLD effect method as described above. A large number of vessels can be identified in a single slice, as shown in Figure 2A. By combining several imaging schemes, namely susceptibility-weighted and TOF images, along with 3D image-processing and display methods, we have developed a technique by which we can identify and classify the intracortical vessels as veins or arteries in vivo.


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)

Vascular model of cat visual cortex. (A) An example of 3D time-of-flight (TOF) microangiography in the cat visual cortex. The axial excitation slab (Slab) was positioned so that its superior edge passed through the sagittal sinus (SS), as can be seen in the coronal view. Arteries, indicated by red arrows, are bright due to unsaturated blood flowing into the slab. Veins, indicated by blue arrows, are dark due to their elevated concentration of deoxyhemoglobin (the BOLD effect). (B) A dorsal view close up showing in greater details vessels classifications using the TOF and BOLD techniques; Veins: blue, Arteries: red. (C) 3D surface rendering of the vessels identified throughout the entire imaged volume. Figure modified from Bolan et al. (2006).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Vascular model of cat visual cortex. (A) An example of 3D time-of-flight (TOF) microangiography in the cat visual cortex. The axial excitation slab (Slab) was positioned so that its superior edge passed through the sagittal sinus (SS), as can be seen in the coronal view. Arteries, indicated by red arrows, are bright due to unsaturated blood flowing into the slab. Veins, indicated by blue arrows, are dark due to their elevated concentration of deoxyhemoglobin (the BOLD effect). (B) A dorsal view close up showing in greater details vessels classifications using the TOF and BOLD techniques; Veins: blue, Arteries: red. (C) 3D surface rendering of the vessels identified throughout the entire imaged volume. Figure modified from Bolan et al. (2006).
Mentions: The technique of 3D TOF micro-angiography is used to generate images of the arteries and is demonstrated in Figure 2. In the exact setup as the images shown in Figure 1, a transverse slab (thickness 2 mm) was positioned in the center of the cortex, so that the superior edge of the slice passed through the sagittal sinus (Figure 2A). The vertical position of the slice is critical for producing proper flow weighting in the intracortical arteries running perpendicular to the cortical surface. The flip angle (30°) is greater than the Ernst angle for both blood and cortical gray matter so the spins inside the slice are saturated and show low signal. Blood that flows into the slice is not saturated, and therefore gives a higher signal than blood that has remained inside the slice for one or more excitations. This effect is called the TOF or inflow effect. In Figure 2A, the red arrows show an example of a bright vessel in both views. Other bright vessels are evident, particularly in the axial view in which most of the larger intracortical vessels are oriented perpendicular to the image plane. Blue arrows point to veins which are dark due to the BOLD effect (Figure 2A). Thus, Figure 2 demonstrates the ability to first, image the intracortical vessels and second, differentiate and show a clear separation of arteries and veins within the image volume across (tangential) the tissue. Figure 2B displays a vessel classification map, a single axial slice across primary visual cortex of the cat in which intracortical visible vessels were classified as vein or artery, using the TOF and BOLD effect method as described above. A large number of vessels can be identified in a single slice, as shown in Figure 2A. By combining several imaging schemes, namely susceptibility-weighted and TOF images, along with 3D image-processing and display methods, we have developed a technique by which we can identify and classify the intracortical vessels as veins or arteries in vivo.

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.