Steady-state functional MRI using spoiled small-tip fast recovery imaging.

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Functional MRI (fMRI) typically relies on T2*-contrast and long echo times.
• Existing fMRI methods are susceptible to B0 artifacts like geometric distortions and signal dropout.
• A new steady-state sequence, small-tip fast recovery (STFR), has been proposed to address these limitations.

Purpose of the Study:

• To evaluate the efficacy of the STFR sequence for functional brain imaging.
• To compare STFR performance against established blood oxygen level dependent (BOLD) fMRI techniques.
• To assess STFR's potential for high-resolution imaging with reduced artifacts.

Main Methods:

• Monte Carlo Bloch simulations were employed to model steady-state signals for both BOLD and STFR during rest and activation.
• In vivo STFR fMRI experiments were conducted using a tailored tip-up radiofrequency pulse in the motor cortex of multiple subjects.
• Functional activation maps were generated and analyzed for reliability.

Main Results:

• Simulations predicted a functional signal in STFR primarily driven by intravoxel dephasing, with minimal influence from spin diffusion.
• STFR demonstrated comparable activation maps and signal changes to BOLD fMRI during finger-tapping tasks.
• The reliability of STFR functional activation maps was found to be comparable to BOLD fMRI.

Conclusions:

• STFR can generate functional contrast effectively, even with a short echo time (TE).
• This sequence presents a viable alternative to conventional long-TE T2*-based fMRI.
• The observed functional contrast in STFR is attributed to the interplay between T2*-like dephasing and the specific tip-up pulse design.