The impact of EPI voxel size on SNR and BOLD sensitivity in the anterior medio-temporal lobe: a comparative group study of deactivation of the Default Mode

SD Robinson, J Pripfl, H Bauer, E Moser - Magnetic Resonance Materials …, 2008 - Springer
Magnetic Resonance Materials in Physics, Biology and Medicine, 2008Springer
Objectives To quantify the gain in time-series SNR that can be achieved in the amygdala by
reducing EPI voxel size, and to assess the extent to which this advantage is carried through
to statistical significance in a group fMRI study, using a cognitive task to trigger task-
independent deactivation of anterior medial temporal structures. Materials and methods Two
groups of seven subjects were posed number-series tasks to induce deactivation of the
Default Mode network. This is known from PET work to include the amygdala, which lies in a …
Objectives
To quantify the gain in time-series SNR that can be achieved in the amygdala by reducing EPI voxel size, and to assess the extent to which this advantage is carried through to statistical significance in a group fMRI study, using a cognitive task to trigger task-independent deactivation of anterior medial temporal structures.
Materials and methods
Two groups of seven subjects were posed number-series tasks to induce deactivation of the Default Mode network. This is known from PET work to include the amygdala, which lies in a region of high magnetic field gradient. In 3 T imaging, one group was studied with high resolution EPI with 6 μl voxels, the other with lower resolution EPI with 17 μl voxels. Field maps were acquired to allow field gradients in relevant ROIs to be assessed.
Results
Time-series SNR was 45% higher in the amygdala in the high resolution EPI data than in the low resolution data. In activation results, whilst there was good agreement between other areas, the involvement of the amygdala could only be demonstrated in the high resolution data.
Conclusion
We find that reduction in signal dephasing afforded by high resolution EPI is realized as a substantial increase in SNR and BOLD sensitivity in group fMRI data. This has allowed the first demonstration of the involvement of the amygdala in the Default Mode in fMRI.
Springer