8.5: Presentation session: BRAiN measurements and imaging technologies: “Data-driven evaluation and optimization of acquisition strategies for ultra-high-field functional MRI at 7 Tesla”

Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is commonly performed using 2D single-shot echo-planar imaging (EPI). However, challenges with EPI at 7 Tesla (T) include significant geometric distortions (due to low bandwidth (BW) in the phase-encode (PE) direction) and amplification of physiological noise. Recent studies have suggested that 3D multi-shot sequences such as PRESTO may offer comparable BOLD contrast-to-noise ratio with increased volume coverage and decreased geometric distortions. A four-way comparison was performed at 7T between 2D and 3D acquisition sequences at two in-plane resolutions. The quality of fMRI data was evaluated via independent metrics of prediction and reproducibility using NPAIRS (Non-parametric Prediction, Activation, Influence and Reproducibility re-Sampling). Activation maps were optimized for each acquisition strategy by selecting the number of principal components that jointly maximized prediction and reproducibility, and showed good agreement in sensitivity and specificity for positive BOLD changes. High-resolution EPI exhibited the highest z-scores of the four acquisition sequences; however, it suffered from the lowest BW in the PE direction (resulting in the worst geometric distortions) and limited spatial coverage, and also caused subject discomfort through peripheral nerve stimulation (PNS). In comparison, PRESTO had the second highest z-scores (higher than EPI for a matched in-plane resolution), the highest BW in the PE direction (producing images with superior geometric stability), the potential for whole-brain coverage, and no reported PNS. This study provides evidence to support the consideration of using multi-shot acquisition sequences in lieu of single-shot EPI for ultra-high-field BOLD fMRI at 7T and above.