Titration of the BOLD effect: Separation and quantitation of blood volume and oxygenation changes in the human cerebral cortex during neuronal activation and ferumoxide infusion

Most functional magnetic resonance imaging (fMRI) techniques are sensitive to susceptibility variations and rely on the change in blood oxygenation le vel in response to neuronal activation (BOLD), The BOLD effect is accompani ed by a change in cerebral blood flow (rCBF) and cerebral blood volume (rCB V). Intravascular contrast agents, such as magnetite nanoparticles, can be used to measure changes in rCBV, A new measuring protocol has been develope d that enables the separate quantification of changes in blood volume and o xygenation levels. A combination of alternating acoustic stimulation blocks and infusion of a superparamagnetic contrast agent offers the possibility to disentangle the competing influences of oxygenation and blood volume cha nges. Serial blood sampling during infusion was used to assess the actual c ontrast agent concentration during infusion in order to calculate absolute blood volume changes during neuronal resting and activation states. Magn Re son Med 42:829-836, 1999, (C) 1999 Wiley-Liss, Inc.