Optimized 3 T EPI of the amygdalae

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging
• Functional Magnetic Resonance Imaging

Background:

• Standard gradient-recalled (GR) echo-planar imaging (EPI) parameters are often inadequate for high-resolution fMRI in specific brain regions like the limbic system at 3 Tesla.
• Intravoxel dephasing significantly impacts signal-to-noise ratio (SNR) and T2* in the amygdalae, necessitating optimized imaging parameters.

Purpose of the Study:

• To systematically establish optimal parameters for single-shot GR EPI-based fMRI of the limbic region at 3 Tesla.
• To mitigate intravoxel dephasing in the amygdalae by optimizing SNR and T2* for improved functional study reliability.
• To assess the implications of optimized parameters on temporal resolution and brain coverage.

Main Methods:

• Systematic evaluation of imaging parameters including matrix size, slice thickness, and in-plane resolution for EPI-based fMRI at 3 Tesla.
• Measurement of main magnetic field variations across the amygdalae to determine optimal slice orientation (oblique axial).
• Quantification of T2* time in the amygdalae using standard and optimized EPI protocols, and reference FLASH scans.

Main Results:

• Conventional parameters (64x64 matrix, 4-6 mm slices) were found inadequate for 3T fMRI in the limbic region.
• An oblique axial orientation was determined most suitable due to magnetic field variation patterns.
• Optimized EPI protocol with ~1.7 mm in-plane resolution and 2.0-2.5 mm slice thickness increased amygdala T2* to 48 ms (from 22 ms) and SNR by 60%.

Conclusions:

• Careful optimization of EPI protocols is crucial for reliable single-subject fMRI results in the limbic region at 3 Tesla.
• The proposed high-resolution EPI protocol significantly enhances SNR and BOLD sensitivity in the amygdalae, making functional studies feasible.
• Optimized parameters mitigate intravoxel dephasing, leading to more accurate and sensitive fMRI measurements in this brain region.