The primarily intravascular magnetization transfer (MT)-independent changes in functional MRI (fMRI) can be separated from MT-dependent changes. This intravascular component is dominated by an arterial blood volume change (DeltaCBV(a)) term whenever venous contributions are minimized. Stimulation-induced DeltaCBV(a) can therefore be measured by a fit of signal changes to MT ratio. MT-varied fMRI data were acquired in 13 isoflurane-anesthetized rats during forepaw stimulation at 9.4T to simultaneously measure blood-oxygenation-level-dependent (BOLD) and DeltaCBV(a) response in somatosensory cortical regions. Transverse relaxation rate change (DeltaR(2)) without MT was -0.43 +/- 0.15 s(-1), and MT ratio decreased during stimulation. DeltaCBV(a) was 0.46 +/- 0.15 ml/100 g, which agrees with our previously-presented MT-varied arterial-spin-labeled data (0.42 +/- 0.18 ml/100 g) in the same animals and also correlates with DeltaR(2) without MT. Simulations show that DeltaCBV(a) quantification errors due to potential venous contributions are small for our conditions.
(c) 2008 Wiley-Liss, Inc.