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Coupling between cerebral blood flow and cerebral blood volume: Contributions of different vascular compartments.

ABSTRACT: A better understanding of the coupling between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is vital for furthering our understanding of the BOLD response. The aim of this study was to measure CBF-CBV coupling in different vascular compartments during neural activation. Three haemodynamic parameters were measured during a visual stimulus. Look-Locker flow-sensitive alternating inversion recovery was used to measure changes in CBF and arterial CBV (CBVa ) using sequence parameters optimized for each contrast. Changes in total CBV (CBVtot ) were measured using a gadolinium-based contrast agent technique. Haemodynamic changes were extracted from a region of interest based on voxels that were activated in the CBF experiments. The CBF-CBVtot coupling constant ?tot was measured as 0.16 ± 0.14 and the CBF-CBVa coupling constant ?a was measured as 0.65 ± 0.24. Using a two-compartment model of the vasculature (arterial and venous), the change in venous CBV (CBVv ) was predicted for an assumed value of baseline arterial and venous blood volume. These results will enhance the accuracy and reliability of applications that rely on models of the BOLD response, such as calibrated BOLD.

SUBMITTER: Wesolowski R

PROVIDER: S-EPMC6492110 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Project description:UnlabelledQuantification of β-amyloid (Aβ) in vivo is often accomplished using the distribution volume ratio (DVR), based on a simplified reference tissue model. We investigated the local relationships between DVR and cerebral blood flow (CBF), as well as relative CBF (R1), in nondemented older adults.MethodsFifty-five nondemented participants (mean age, 78.5 y) in the Baltimore Longitudinal Study of Aging underwent (15)O-H2O PET CBF and dynamic (11)C-PiB PET. (15)O-H2O PET images were normalized and smoothed using SPM. A simplified reference tissue model with linear regression and spatial constraints was used to generate parametric DVR images. The DVR images were regressed on CBF images on a voxel-by-voxel basis using robust biologic parametric mapping, adjusting for age and sex (false discovery rate, P = 0.05; spatial extent, 50 voxels). DVR images were also regressed on R1 images, a measure of the transport rate constant from vascular space to tissue. All analyses were performed on the entire sample, and on high and low tertiles of mean cortical DVR.ResultsVoxel-based analyses showed that increased DVR is associated with increased CBF in the frontal, parietal, temporal, and occipital cortices. However, this association appears to spare regions that typically show early Aβ deposition. A more robust relationship between DVR and CBF was observed in the lower tertile of DVR, that is, negligible cortical Aβ load, compared with the upper tertile of cortical DVR and Aβ load. The spatial distributions of the DVR-CBF and DVR-R1 correlations showed similar patterns. No reliable negative voxelwise relationships between DVR and CBF or R1 were observed.ConclusionRobust associations between DVR and CBF at negligible Aβ levels, together with similar spatial distributions of DVR-CBF and DVR-R1 correlations, suggest that regional distribution of DVR reflects blood flow and tracer influx rather than pattern of Aβ deposition in those with minimal Aβ load. DVR-CBF associations in individuals with a higher DVR are more likely to reflect true associations between patterns of Aβ deposition and CBF or neural activity. These findings have important implications for analysis and interpretation of voxelwise correlations with external variables in individuals with varying amounts of Aβ load.

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Coupling between cerebral blood flow and cerebral blood volume: Contributions of different vascular compartments.

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