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. Author manuscript; available in PMC: 2010 Feb 10.
Published in final edited form as: Neuroimage. 2007 Nov 22;39(4):1510. doi: 10.1016/j.neuroimage.2007.11.015

Fig. 1.

Fig. 1

Relationship between fractional blood oxygenation level dependent (BOLD) and fractional cerebral blood flow (CBF) increases in response to brain activation for different ratios (n) of the fractional changes in CBF and cerebral metabolic rate of oxygen (CMRO2). Curves were calculated for different values of n using the BOLD signal equation (Eq. (1)) with M=0.06, α=0.4, and β=1.5. Filled circles indicate the BOLD and CBF responses for a fixed 20% increase in CMRO2, illustrating that, for the same underlying change in metabolism, the magnitude of the BOLD response is strongly dependent on n. Relatively small differences in n from 1.5 to 2 or from 2 to 3 can lead to over 100% changes in the BOLD response for the same CMRO2 change. The curve for n=∞ is the response for no change in CMRO2.