Abstract
We compared the sensitivity of standard single-shot 2D echo planar imaging (EPI) to three advanced EPI sequences, i.e., 2D multi-echo EPI, 3D high resolution EPI and 3D dual-echo fast EPI in fixed effect and random effects group level fMRI analyses at 3T. The study focused on how well the variance reduction in fixed effect analyses achieved by advanced EPI sequences translates into increased sensitivity in the random effects group level analysis. The sensitivity was estimated in a functional MRI experiment of an emotional learning and a reward based learning tasks in a group of 24 volunteers. Each experiment was acquired with the four different sequences. The task-related response amplitude, contrast level and respective t-value were proxies for the functional sensitivity across the brain. All three advanced EPI methods increased the sensitivity in the fixed effects analyses, but standard single-shot 2D EPI provided a comparable performance in random effects group analysis when whole brain coverage and moderate resolution are required. In this experiment inter-subject variability determined the sensitivity of the random effects analysis for most brain regions, making the impact of EPI pulse sequence improvements less relevant or even negligible for random effects analyses. An exception concerns the optimization of EPI reducing susceptibility-related signal loss that translates into an enhanced sensitivity e.g. in the orbitofrontal cortex for multi-echo EPI. Thus, future optimization strategies may best aim at reducing inter-subject variability for higher sensitivity in standard fMRI group studies at moderate spatial resolution.
Highlights
The optimization of functional MRI pulse sequences is based on a well-balanced trade-off between several requirements
All three advanced echo planar imaging (EPI) methods increased the sensitivity in the fixed effects analyses, but standard single-shot 2D EPI provided a comparable performance in random effects group analysis when whole brain coverage and moderate resolution are required
The upper row (Fig. 2a) presents activation t-maps resulting from a random effects analysis obtained for the four sequences overlaid on a single subject anatomical image
Summary
The optimization of functional MRI (fMRI) pulse sequences is based on a well-balanced trade-off between several requirements. Typical fMRI studies benefit from whole brain coverage and high spatial resolution on the one hand, and high temporal resolution as well as high sensitivity and specificity on the other hand. To achieve high sensitivity to the blood-oxygen level dependent (BOLD) effect across the entire brain, a compromise between high general BOLD sensitivity due to pronounced T2*-weighting and reduced susceptibility-related signal dropouts in frontal and deep brain regions (Weiskopf et al, 2007a) has to be achieved. Physiological noise contributions due to e.g. heart pulsation, respiration and head motion need to be minimized (Birn et al, 2006; Chang and Glover, 2009; Glover et al, 2000; Krüger and Glover, 2001).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
