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Optimized EPI for fMRI studies of the orbitofrontal cortex
R Deichmann1, J A Gottfried, C Hutton
1Wellcome Department of Imaging Neuroscience, Institute of Neurology, London WC1N 3BG, UK. r.deichmann@fil.ion.ucl.ac.uk
Neuroimage
|June 20, 2003
Summary
This study presents a new method to reduce magnetic susceptibility artifacts in functional magnetic resonance imaging (fMRI) using echo planar imaging (EPI). The technique improves signal recovery in the orbitofrontal cortex without sacrificing temporal resolution for event-related studies.
Area of Science:
- Magnetic Resonance Imaging
- Neuroimaging
- Biophysics
Background:
- Gradient-echo echo planar imaging (EPI) is susceptible to image distortions and signal loss near air/tissue interfaces due to magnetic susceptibility gradients.
- These artifacts compromise functional magnetic resonance imaging (fMRI) studies, particularly in brain regions like the temporal lobes and orbitofrontal cortex.
- Blood oxygenation level-dependent (BOLD) effect-based fMRI studies are sensitive to these susceptibility-induced signal alterations.
Purpose of the Study:
- To present a novel method for signal recovery in specific regions of the orbitofrontal cortex affected by magnetic susceptibility gradients.
- To reduce the impact of in-plane and through-plane susceptibility gradients during EPI acquisition.
- To ensure the method is compatible with event-related fMRI studies by preserving temporal resolution.
Main Methods:
- Optimization of imaging slice orientation to minimize the influence of in-plane susceptibility gradients.
- Application of a moderate preparation gradient pulse, similar to z-shimming, for partial compensation of through-plane susceptibility gradients.
- Evaluation of the method's effectiveness in recovering signals in the orbitofrontal cortex.
Main Results:
- The proposed method effectively reduces image distortions and signal losses caused by susceptibility gradients in the orbitofrontal cortex.
- Optimization of slice orientation and the use of a preparation gradient pulse significantly improved signal recovery.
- The technique maintains high temporal resolution, crucial for event-related functional neuroimaging.
Conclusions:
- This method offers a viable solution for enhancing signal quality in susceptibility-prone brain regions during EPI-based fMRI.
- The preservation of temporal resolution makes it suitable for event-related functional studies.
- The technique advances the capability to study brain function in challenging areas like the orbitofrontal cortex.