Journal
NEUROIMAGE
Volume 63, Issue 3, Pages 1178-1187Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.neuroimage.2012.08.045
Keywords
BOLD calibration; Hyperoxia; fMRI; CMRO2; Blood oxygenation
Funding
- Medical Research Council
- EPSRC
- EPSRC [EP/I026924/1] Funding Source: UKRI
- MRC [G0901321] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/I026924/1] Funding Source: researchfish
- Medical Research Council [G0901321] Funding Source: researchfish
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Calibration of the BOLD signal is potentially of great value in providing a closer measure of the underlying changes in brain function related to neuronal activity than the BOLD signal alone, but current approaches rely on an assumed relationship between cerebral blood volume (CBV) and cerebral blood flow (CBF). This is poorly characterised in humans and does not reflect the predominantly venous nature of BOLD contrast, whilst this relationship may vary across brain regions and depend on the structure of the local vascular bed. This work demonstrates a new approach to BOLD calibration which does not require an assumption about the relationship between cerebral blood volume and cerebral blood flow. This method involves repeating the same stimulus both at normoxia and hyperoxia, using hyperoxic BOLD contrast to estimate the relative changes in venous blood oxygenation and venous CBV. To do this the effect of hyperoxia on venous blood oxygenation has to be calculated, which requires an estimate of basal oxygen extraction fraction, and this can be estimated from the phase as an alternative to using a literature estimate. Additional measurement of the relative change in CBF, combined with the blood oxygenation change can be used to calculate the relative change in CMRO2 due to the stimulus. CMRO2 changes of 18 +/- 8% in response to a motor task were measured without requiring the assumption of a CBV/CBF coupling relationship, and are in agreement with previous approaches. (C) 2012 Elsevier Inc. All rights reserved.
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