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 (Delta CBVa) term whenever venous contributions are minimized. Stimulation-induced Delta CBVa 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 Delta CBVa response in somatosensory cortical regions. Transverse relaxation rate change (Delta R-2) without MT was -0.43 +/- 0.15 s(-1), and MT ratio decreased during stimulation. Delta CBVa 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 Delta R-2 without MT. Simulations show that Delta CBVa quantification errors due to potential venous contributions are small for our conditions. Magn Reson Med 60: 1518-1523, 2008. (C) 2008 Wiley-Liss, Inc.