fMRI protocol optimization for simultaneously studying small subcortical and cortical areas at 7 ​T.

Area of Science:

• Neuroimaging
• Neuroscience
• Biophysics

Background:

• Fundamental cognitive processes depend on complex brain networks involving both cortical and subcortical regions.
• Functional magnetic resonance imaging (fMRI) is crucial for studying these networks, requiring protocols with broad blood-oxygen-level dependent (BOLD) sensitivity.
• Standard single-echo echo planar imaging (EPI) protocols present a BOLD-sensitivity trade-off between cortical and subcortical areas.

Purpose of the Study:

• To empirically compare the BOLD-sensitivity of a single-echo fMRI protocol against a multi-echo protocol.
• To evaluate protocol performance for studying iron-rich subcortical structures and cortical regions at 7 Tesla.
• To determine if multi-echo protocols can overcome the BOLD-sensitivity limitations of single-echo protocols in whole-brain fMRI.

Main Methods:

• Designed and implemented both single-echo and multi-echo EPI protocols optimized for high spatial resolution and short echo times.
• Protocols were tailored to enhance sensitivity in small, iron-rich subcortical structures while maintaining coverage and sensitivity in cortical areas.
• Empirically compared the BOLD-sensitivity performance of the two protocols across the entire brain at 7 Tesla.

Main Results:

• Both the single-echo and multi-echo fMRI protocols demonstrated comparable BOLD-sensitivity across the whole brain at 7 Tesla.
• The multi-echo protocol did not show a significant advantage in overall BOLD-sensitivity despite its design to avoid the cortical-subcortical trade-off.
• The tested protocols successfully balanced the need for subcortical sensitivity with cortical coverage.

Conclusions:

• At 7 Tesla, standard single-echo EPI protocols can achieve whole-brain BOLD-sensitivity comparable to multi-echo protocols, even when targeting subcortical structures.
• The findings suggest that the trade-offs associated with multi-echo acquisition may not be necessary for achieving adequate BOLD-sensitivity in many whole-brain fMRI applications at this field strength.
• Further research may explore specific sequence parameters or alternative acquisition strategies for optimizing fMRI BOLD-sensitivity in challenging brain regions.