Investigating the effective temporal resolution in a task-based functional MRI experiment at 7 T MRI using a dynamic...

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Functional Magnetic Resonance Imaging (fMRI)

Background:

• fMRI studies increasingly aim to measure time delays in brain responses.
• High sampling rates are crucial for accurately discerning these time delays.
• Ultra-high field MRI and accelerated imaging techniques enable higher sampling rates.

Purpose of the Study:

• To define and quantify the effective temporal resolution (ETR) of fMRI scans.
• To investigate the impact of various scanning and paradigm parameters on ETR.
• To assess ETR in different brain regions with varying tissue properties.

Main Methods:

• Utilized a dynamic phantom to generate a "ground truth" signal with controlled onset delays.
• Quantified ETR by systematically varying parameters: echo time (TE), repetition time (TR), voxel size, contrast-to-noise ratio (CNR).
• Examined multi-echo echo-planar imaging (EPI) and fMRI paradigm parameters (block length/density).

Main Results:

• Multi-echo EPI data acquisition improved ETR, reducing it significantly.
• ETR was estimated at 151 ms (cortex) and 248 ms (basal ganglia) with a 600 ms TR when using multi-echo data.
• Low CNR substantially increased ETR, sometimes exceeding the TR; physiological fluctuations also impacted ETR.

Conclusions:

• Demonstrated the feasibility of achieving very short ETR in fMRI for studying time responses.
• Emphasized the critical need to evaluate the attainable ETR for specific experimental conditions and brain regions.
• Highlighted the influence of CNR and tissue properties on achievable temporal resolution in fMRI.