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 α tot was measured as 0.16 ± 0.14 and the CBF‐CBVa coupling constant α 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.
Highlights
The relationship between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is critical for an accurate understanding of the haemodynamics that underlie blood oxygenation level dependent (BOLD) fMRI, and a greater understanding of cerebral haemodynamics will lead to more precise quantification of the BOLD response.[1,2]
The former shows CBF‐weighted (Figure 2A) and CBVa‐weighted (Figure 2B) Look‐Locker flow‐sensitive alternating inversion recovery (LL‐FAIR) difference images as a function of post‐label delay time averaged over all experimental timepoints; note the higher CNR of the CBVa‐weighted data
It has been shown that the accuracy of the calibrated BOLD method for quantifying stimulus evoked oxygen metabolism changes is critically dependent on accurate knowledge of CBF‐CBVv coupling.[26,27]
Summary
The relationship between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is critical for an accurate understanding of the haemodynamics that underlie blood oxygenation level dependent (BOLD) fMRI, and a greater understanding of cerebral haemodynamics will lead to more precise quantification of the BOLD response.[1,2] Early studies suggested that the majority of CBV change in response to neuronal activation occurs in venous vessels.[3,4] This led to the adoption of a CBF‐CBV coupling model based on a power law relationship that was characterized using PET measurements of CBF and total CBV (CBVtot).[5] it is well known that arterial CBV (CBVa) increases on activation, and that this occurs to a much greater degree than total CBV, despite the lower baseline CBV of the arterial compartment.[6,7,8] the use of a CBF‐CBVtot.
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