Effect on BOLD sensitivity due to susceptibility-induced echo time shift in spiral-in based functional MRI

Area of Science:

• Neuroimaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Susceptibility artifacts arise from magnetic field inhomogeneity at air/tissue interfaces in fMRI.
• These artifacts cause geometric distortions and signal loss in brain images.
• Susceptibility gradients shift the effective echo time, impacting blood-oxygen-level dependent (BOLD) sensitivity.

Purpose of the Study:

• To investigate the impact of susceptibility gradients on effective echo time shifts.
• To quantify the resulting changes in BOLD sensitivity.
• To identify brain regions affected by BOLD sensitivity loss in fMRI.

Main Methods:

• Analysis of susceptibility gradients and their effect on echo time.
• Modeling of BOLD sensitivity changes in relation to susceptibility gradients.
• Examination of fMRI data, specifically using spiral-in trajectories.

Main Results:

• Susceptibility gradients induce significant shifts in effective echo time.
• BOLD sensitivity is directly influenced by these echo time shifts.
• Regions like the orbitofrontal cortex exhibit substantial BOLD sensitivity loss with spiral-in trajectories.

Conclusions:

• Susceptibility artifacts critically affect BOLD signal quantification in ventral brain regions.
• The choice of fMRI trajectory, such as spiral-in, exacerbates BOLD sensitivity loss.
• Understanding these artifacts is crucial for accurate fMRI studies of brain function.