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

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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. ΔCBVa 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. Magn Reson Med 60:1518–1523, 2008.
Funding Information
  • National Institutes of Health (EB003375, EB003324, NS44589, RR17239)