Asymmetric spin echo multi-echo echo planar imaging (ASEME-EPI) sequence for pre-clinical high-field fMRI.

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)

Background:

• Gradient-recalled echo (GRE) acquisitions in fMRI offer high sensitivity but are prone to signal loss and lack microvasculature specificity.
• Spin echo (SE) acquisitions provide better specificity but at the cost of reduced sensitivity.
• High-field preclinical fMRI faces challenges with susceptibility-induced signal loss and T2* decay.

Purpose of the Study:

• To introduce and evaluate Asymmetric Spin Echo Multi-Echo Echo Planar Imaging (ASEME-EPI) for high-field preclinical fMRI.
• To combine the benefits of GRE and SE techniques for improved fMRI performance.
• To assess ASEME-EPI's ability to enhance specificity and signal recovery in challenging imaging conditions.

Main Methods:

• Developed and implemented ASEME-EPI, utilizing a spin echo readout followed by two asymmetric spin echo GRE readouts.
• Conducted a feasibility study on a 9.4 T pre-clinical MRI system using visual stimulation in northern tree shrews.
• Compared ASEME-EPI with conventional GRE echo planar imaging (GRE-EPI) and SE echo planar imaging (SE-EPI).

Main Results:

• ASEME-EPI achieved a BOLD contrast-to-noise ratio (CNR) comparable to GRE-EPI.
• ASEME-EPI demonstrated improved specificity in activation maps, confining activity to the primary visual cortex (V1).
• The technique successfully recovered signal in areas with severe field inhomogeneity where GRE-EPI failed.

Conclusions:

• ASEME-EPI offers a promising compromise between GRE sensitivity and SE specificity for high-field preclinical fMRI.
• The multi-echo nature and initial SE readout contribute to denoising and signal recovery.
• ASEME-EPI shows potential for overcoming T2* decay challenges and improving localization in preclinical neuroimaging.