BLOOD-OXYGEN-LEVEL DEPENDENT (BOLD)
The MR-contrast discovered by Seiji Ogawa in 1990 which is used in fMRI for mapping brain activity. It is based on a reduction of the diamagnetic properties (towards paramagnetic, but not in absolute susceptibility measures) of hemoglobin in the switch from the oxygenated to the deoxygenated state. It affects the surrounding tissue (extra-vascular signal) as well as in the vasculature itself (intra-vascular signal). The contrast as used in cognitive neuroimaging usually refers to a percentage increase (positive BOLD) in MR-signal intensity by 1-10% in activated brain areas (hyperemia). Less commonly used signal decreases (negative BOLD) seem to be an indicator of deactivated brain. The exact change in intensity is in dependence on neural activity perturbations from an interplay of hyperemic change in cerebral blood flow (CBF), oxygen consumption(CMRO2) and cerebral blood volume (CBV).
- ↑ Ogawa S, Lee TM, Kay AR, Tank DW Brain magnetic resonance imaging with contrast dependent on blood oxygenation PNAS (1990)
- ↑ Bandettini PA, Wong EC, Hinks RS, Tikofsky RS, Hyde JS Time Course EPI of Human Brain Function during Task Activation MRM Vol 25 pp390-397 (1992)
- ↑ Ogawa SJ, Tank DW, Menon R, Ellermann JM, Kim S-G, Merkle H, Ugurbil K Intrinsic signal changes accompanying sensory stimulation: Functional brain mapping with magnetic resonance imaging PNAS Vol 89 pp5951-5955 (1992)
- ↑ Kwong KK, Belliveau JW, Chesler DA, Goldberg IE, Weisskoff RM, Poncelet BP, Kennedy DN, Hoppel BE, Cohen MS, Turner R, Cheng HM, Brady TJ, Rosen BR Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation. PNAS Vol 89(12) pp5675-5679 (1992)