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The effect of slice order and thickness on fMRI activation data using multislice echo-planar imaging
A M Howseman1, S Grootoonk, D A Porter
1Wellcome Department of Cognitive Neurology, Institute of Neurology, London, WC1N 3BG, United Kingdom.
Neuroimage
|April 7, 1999
Summary
Multislice echo-planar imaging (EPI) for fMRI is primarily driven by BOLD contrast, not blood flow effects. Thicker slices in EPI increase the detected visual cortex activation volume.
Area of Science:
- Neuroimaging
- Functional Magnetic Resonance Imaging (fMRI)
Background:
- Multislice echo-planar imaging (EPI) is a standard fMRI technique sensitive to BOLD and potential T1 contrast.
- T1 contrast from blood inflow could theoretically alter activation maps based on slice acquisition order.
Purpose of the Study:
- To investigate the dominance of BOLD (T2*) versus T1 contrast in whole-brain multislice EPI fMRI.
- To evaluate the impact of slice thickness on fMRI activation in the visual cortex.
Main Methods:
- fMRI experiments with visual stimulation were conducted using varying repetition times (TR).
- Slice acquisition order was manipulated to assess T1 inflow effects.
- fMRI Z scores and activated voxel counts were analyzed across slice thicknesses from 1 to 8 mm.
Main Results:
- Consistent fMRI activation maps were observed across different TRs (6.0, 3.0, 1.5 s), indicating T2*-BOLD dominance.
- Maximum fMRI Z scores remained similar across slice thicknesses.
- The volume of significantly activated visual cortex increased with greater slice thickness.
Conclusions:
- Whole-brain multislice EPI fMRI is predominantly influenced by T2*-BOLD contrast.
- Increasing slice thickness enhances the detection of activated brain regions, though maximum activation intensity is unaffected.