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

Abstract

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 (ΔCBVa) term whenever venous contributions are minimized. Stimulation-induced ΔCBVa 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 ΔCBVa response in somatosensory cortical regions. Transverse relaxation rate change (δR2) without MT was -0.43 ± 0.15 s-1, and MT ratio decreased during stimulation. ΔCBV 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 ΔR2 without MT. Simulations show that ΔCBVa quantification errors due to potential venous contributions are small for our conditions. © 2008 Wiley-Liss, Inc.