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Co-analysis of Brain Structure and Function using fMRI and Diffusion-weighted Imaging
Published on: November 8, 2012
BOLD background gradient contributions in diffusion-weighted fMRI--comparison of spin-echo and twice-refocused
André Pampel1, Thies H Jochimsen, Harald E Möller
1Max Planck Institute for Human Cognitive and Brain Sciences, Magnetic Resonance Unit, Leipzig, Germany. anpa@cbs.mpg.de
NMR in Biomedicine
|March 18, 2010
Summary
Interactions between diffusion gradients and magnetic susceptibility in vessels affect apparent diffusion coefficient (ADC) measurements in diffusion-weighted functional MRI (DFMRI). Monte-Carlo simulations reveal these cross-terms cause functional ADC increases and signal changes in DFMRI.
Area of Science:
- Magnetic Resonance Imaging
- Biophysics
- Neuroimaging
Background:
- Diffusion-weighted functional magnetic resonance imaging (DFMRI) is sensitive to changes in apparent diffusion coefficient (ADC) during neural activity.
- Susceptibility gradients around blood vessels can interact with diffusion gradients, potentially confounding ADC measurements.
Purpose of the Study:
- To investigate the impact of cross-terms between diffusion gradients and vessel susceptibility on ADC measurements in DFMRI.
- To quantify the influence of these interactions on extravascular signal and ADC changes.
Main Methods:
- Monte-Carlo (MC) simulations were employed to numerically integrate Bloch equations.
- A vascular model with randomly oriented cylinders and varying susceptibility was used to simulate random walks.
Main Results:
- Cross-terms were found to cause a functional increase in ADC.
- A descending percent signal change with increasing diffusion weighting was observed.
- The twice-refocused spin-echo sequence partially suppressed these effects compared to standard Stejskal-Tanner diffusion weighting.
Conclusions:
- Interactions between diffusion gradients and vessel susceptibility significantly influence DFMRI ADC measurements.
- The observed effects can lead to misinterpretation of functional activation.
- Sequence choice, such as the twice-refocused spin-echo, can mitigate but not entirely eliminate these artifacts.
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