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Echo time dependence of BOLD contrast and susceptibility artifacts
Maria Luisa Gorno-Tempini1, Chloe Hutton, Oliver Josephs
1Wellcome Department of Cognitive Neurology, Institute of Neurology, 12 Queen Square, London WC1N 3BG, United Kingdom.
Neuroimage
|January 5, 2002
Summary
Shorter echo times improve blood oxygenation level-dependent (BOLD) contrast in functional MRI (fMRI) for brain regions without susceptibility artifacts. However, this does not fully recover signal loss in anterior temporal lobes near air-filled sinuses.
Area of Science:
- Neuroimaging
- Functional Magnetic Resonance Imaging (fMRI)
- Brain Imaging Techniques
Background:
- Echo-planar imaging (EPI) enables rapid whole-brain acquisition but suffers signal loss near air-filled sinuses due to magnetic field inhomogeneities.
- This signal loss particularly affects temporal lobe imaging, impacting language studies and other research.
- Reducing echo time (TE) can enhance signal-to-noise ratio and mitigate signal loss in susceptible brain regions.
Purpose of the Study:
- To investigate the echo time (TE) dependence of blood oxygenation level-dependent (BOLD) contrast in fMRI.
- To assess the influence of TE on BOLD signal in brain regions affected by magnetic susceptibility artifacts.
- To compare brain activation patterns using dual echo-time sequences (TE = 40 ms vs. TE = 27 ms).
Main Methods:
- Utilized a dual echo-time functional MRI sequence to acquire whole-brain images at two different echo times (TE = 40 ms and TE = 27 ms).
- Employed a face-processing paradigm (famous faces vs. scrambled faces) known to activate fusiform gyri and anterior temporal lobes.
- Compared BOLD signal changes and activation patterns between the two echo times in regions with and without susceptibility artifacts.
Main Results:
- Robust BOLD signal activations were detected at the lower TE (27 ms) in non-susceptible regions like the fusiform gyri, enabling faster scanning.
- Signal loss was reduced at the lower TE compared to the longer TE (40 ms).
- Despite signal reduction, the lower TE was insufficient to fully recover BOLD signal in anterior temporal lobe regions susceptible to magnetic field inhomogeneities.
Conclusions:
- Optimizing echo time (TE) in fMRI can improve signal detection in less susceptible brain areas, allowing for accelerated data acquisition.
- Susceptibility artifacts in regions like the anterior temporal lobes remain a significant challenge for BOLD fMRI, even with reduced TE.
- Further methodological advancements are needed to overcome signal loss in air-tissue interfaces for comprehensive brain imaging.