Investigating the BOLD effect during infusion of Gd-DTPA using rapid T*2 mapping

This work aimed to investigate the effects of administering Gd-DTPA on the BOLD effect, and to determine the feasibility of using this approach to measure fractional changes in blood volume and blood oxygenation on neuronal activation during a visual paradigm. A linear relationship between cortical R-2(*) and the intravascular concentration of Gd-DTPA was demonstrated. The change in R2* in the visual cortex on activation at 3 T (in the absence of Gd-DTPA) was found to be 1.38 +/- 0.31 s(-1) (N = 4). The fractional change in total blood volume during visual activation was calculated to be 28% +/- 7% (N = 4). The absolute increase in venous blood oxygenation on activation (AY) was estimated to be 21% +/- 4% (N = 4) (assuming HCT = 0.4, resting blood oxygenation = 60%, fraction of volume change that was venous 36%, and the resting venous fraction of the blood volume 70%). Simulations showed that the estimated change in venous blood oxygenation was sensitive to the assumed venous blood fraction, and that the estimated fractional change in blood oxygenation was insensitive to whether the change in blood volume occurred in the arterial or venous network.