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  High-resolution CMRO2 in gray matter of macaque visual cortex

Bohraus, Y., Logothetis, N., & Goense, J. (2012). High-resolution CMRO2 in gray matter of macaque visual cortex. Poster presented at 42nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012), New Orleans, LA, USA.

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Bohraus, Y1, 2, Author              
Logothetis, NK1, 2, Author              
Goense, J1, 2, Author              
1Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497798              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_1497794              


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 Abstract: Commonly used fMRI signals measure local vascular and neural changes, with the former underlying a certain degree of spatiotemporal blurring. To minimize the latter, methods can be used that are less sensitive to partial volume effects. One such methodology capitalizes on high resolution, voxel-by-voxel CMRO2 measurements. Here we combined such measurements with so-called calibrated BOLD methodology to acquire CBF and BOLD maps during visual stimulation. Calibration was done by estimating a normalization factor (M) assessed in hypercapnia conditions, reflecting the upper limit of BOLD signal-changes. Quantitative description and interpretation of the data was done by using a model with parameters α, relating relative changes of CBV to CBF according to Grubb’s law (α=0.38), and β linking blood oxygenation to relaxivity (β=1.5). To improve the model, α was selected to account for changes in venous CBV only (α=0.23), i.e. to account for CBV-changes that are relevant to the BOLD signal, rather than to total CBV alterations. Alternatively, the model was compared to a more detailed model and showed highest accuracy with α=0.14 β=0.91. We determined the CMRO2 in anesthetized macaques at 7T high resolution to separate the visually induced percent changes in CMRO2 (CMRO2) in gray matter from white matter and vessel signals. We subsequently repeated the calculations using the aforementioned α β parameters in order to reassess the robustness of the results. CBF and BOLD signals were acquired simultaneously with a triple-echo sequence. The CMRO2 changes, M and n (ratio of fractional CBF to CMRO2) were calculated in V1 and V2. At a resolution of 1x1x3 mm3, the average CMRO2 was 12±5 (mean ± sem) with M=0.29 ± 0.05. The coupling constant n was 2.1 ± 0.4. Similar values were obtained for α=0.23. The calibration constant M slightly increased using α=0.14 β=0.91 but remained consistent with the value of 0.3-0.4 in gray matter at 7T. CMRO2 changes n were not very sensitive to the choice of parameters. For resolution of 0.5x0.5x3mm3 the results suggested higher CMRO2 changes in gray matter than in white matter with a possible peak in layer IV, being the main input layer in macaque monkey. CBF and BOLD percent changes during visual stimulation and hypercapnic challenge were increased at a resolution of 0.5x0.5x3mm3 compared to 1x1x3 mm3. In conclusion, using the calibrated BOLD method, we found high-resolution CMRO2 changes of 12-14 and coupling ratios of 1.8-2.1, and demonstrated differences in CMRO2 measured in gray and white matter. The reported results were found to be robust and insensitive to changes in the α β parameters at high field.


 Dates: 2012-10
 Publication Status: Published in print
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 Identifiers: BibTex Citekey: BohrausLG2012
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Title: 42nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012)
Place of Event: New Orleans, LA, USA
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Title: 42nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012)
Source Genre: Proceedings
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Pages: - Volume / Issue: - Sequence Number: 95.03 Start / End Page: - Identifier: -