Improvements in parallel imaging accelerated functional MRI using multiecho echo-planar imaging.

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Blood-oxygenation-level-dependent (BOLD) functional MRI (fMRI) is crucial for neuroscience research.
• Conventional single-echo EPI sequences can suffer from signal dropout and geometric distortions, limiting BOLD fMRI sensitivity.
• Parallel imaging acceleration is often used to reduce scan times but can further impact signal quality.

Purpose of the Study:

• To evaluate the performance of multiecho EPI compared to single-echo EPI for BOLD fMRI at 1.5 T.
• To assess the benefits of parallel imaging acceleration in multiecho EPI sequences.
• To determine if multiecho EPI offers advantages in signal-to-fluctuation-noise ratio and activation detection.

Main Methods:

• Implementation of multiecho EPI and single-echo EPI sequences for BOLD fMRI at 1.5 T.
• Utilized a time-normalized breath-hold task with a block design.
• Employed parallel imaging acceleration factors (R = 1-3) with up to four echo trains per excitation.
• Conducted experiments on five human subjects across three scanning sessions.

Main Results:

• Multiecho EPI demonstrated significantly higher signal-to-fluctuation-noise ratio and a greater number of activated voxels compared to single-echo EPI across all reduction factors.
• Nonaccelerated single-echo EPI showed reduced performance compared to three-echo multiecho EPI with R = 2.
• Parallel imaging accelerated multiecho EPI reduced geometric distortions and signal dropout while enhancing BOLD signal sensitivity, especially in regions with short T*(2).

Conclusions:

• Multiecho EPI offers substantial advantages over conventional single-echo EPI for BOLD fMRI.
• Parallel imaging accelerated multiecho EPI improves image quality and signal sensitivity throughout the brain.
• This advanced multiecho EPI technique is highly beneficial for standard BOLD fMRI experiments.