Multi-contrast T2(⁎)-relaxometry upon visual stimulation at 3T and 7T.

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Biophysics

Background:

• Quantifying effective transverse relaxation time T2(⁎) is crucial for understanding brain activity.
• Advanced MRI models are needed to accurately capture signal decay, especially at higher field strengths.

Purpose of the Study:

• To quantify the mean change in T2(⁎) in active brain regions at 3T and 7T.
• To compare a mono-exponential decay model with an extended model incorporating mesoscopic field gradients.
• To assess model cross-talk and parameter correlations.

Main Methods:

• Visual checkerboard stimulation experiment with healthy volunteers.
• Segmented multi-contrast echo-planar imaging (EPI) sequence at 3T and 7T.
• Multi-step (non-)linear least-squares fitting for BOLD-signal time courses.

Main Results:

• Baseline T2(⁎) and stimulus-correlated changes (∆T2(⁎)) were determined for both models at 3T and 7T.
• Observed dependence of T2(⁎) values on initial intensity (S0) and inflow effects.
• Mono-exponential model showed better stability, while the extended model is promising but limited by contrast acquisition.

Conclusions:

• The extended model shows potential for dynamic neurofunctional measurements.
• Inflow effects significantly influence measured relaxation times.
• Further optimization is needed for the extended model's clinical application in neuroimaging.