In vivo measurement of changes in venous blood‐oxygenation with high resolution functional MRI at 0.95 Tesla by measuring changes in susceptibility and velocity

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Abstract
High‐resolution functional imaging experiments at 0.95 Tesla have been performed to determine the changes in oxygen saturation in pial veins during motor activation by measuring both flow and susceptibility changes in the blood. Averaging across subjects, mean values for the change of the oxygenation level, δY = 0.16 ± 0.08 (n = 7) and δY = 0.13 ± 0.09 (n = 4), were obtained from the susceptibility sensitive and the flow sensitive acquisitions, respectively. The results suggest that the increase in blood flow is largely uncoupled from the oxygen consumption. The quoted errors reflect mainly the inter‐subject variability. In addition, low‐resolution echo planar imaging (EPI) measurements were performed on the same volunteers to quantify signal intensity changes. Using the measured change in oxygenation, the observed signal changes in the EPI experiments can be attributed to a 5% venous blood volume.