Functional MRI with magnetization transfer effects: determination of BOLD and arterial blood volume changes.

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.