Evaluation of highly accelerated simultaneous multi-slice EPI for fMRI.

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• Echo planar imaging (EPI) is the standard for blood oxygen level-dependent (BOLD) functional MRI (fMRI).
• Simultaneous multi-slice (SMS) techniques accelerate EPI acquisition by combining multiband (MB) and simultaneous image refocusing (SIR) factors.
• SMS methods enable faster whole-brain imaging, crucial for capturing dynamic neural activity.

Purpose of the Study:

• To evaluate the impact of various simultaneous multi-slice (SMS) acceleration combinations on BOLD fMRI data quality.
• To determine optimal SMS acceleration strategies for maximizing signal-to-noise ratio and information content.
• To compare the BOLD information content at different repetition times (TRs) using accelerated EPI.

Main Methods:

• Evaluated SMS accelerations up to N=48 using different combinations of multiband (M) and simultaneous image refocusing (S) factors at 3T with a 32-channel head coil.
• Assessed data quality using temporal signal-to-noise ratio (tSNR), BOLD contrast-to-noise ratio (CNR), and information content from checkerboard and movie clip tasks.
• Compared BOLD information content across different repetition times (TRs), including 300ms-600ms and 2s.

Main Results:

• At low accelerations (N≤6), S=1 with varying M yielded the best tSNR and BOLD CNR.
• At higher accelerations (N>8), S=2 demonstrated maximal BOLD CNR and information content.
• Faster TRs (300ms-600ms) captured significantly more BOLD information per unit time compared to a TR of 2s.

Conclusions:

• Simultaneous image refocusing (S=2) is beneficial for high-acceleration SMS-EPI in fMRI, particularly for maximizing BOLD CNR and information.
• Optimizing SMS acceleration parameters is critical for achieving high-quality fMRI data.
• Faster repetition times significantly enhance the efficiency of BOLD information acquisition in task-based fMRI.