Analytic Solution of the Optimum Flip Angle for Pass-Band SSFP fMRI Prescribes High Flip Angle Acquisitions

Steve Patterson¹, ², Chris Bowen, ¹²

Most pass-band SSFP fMRI studies employ the signal-optimizing flip angle (&[alpha] _s), which maximizes on-resonant signal and produces a flat pass-band signal vs. off-resonance profile. In this work we derive an analytical expression for the BOLD contrast-optimizing flip angle (&[alpha] _c). Using literature-reported relaxation times for grey matter, we found that &[alpha] _c ≈ &[alpha] _s + 20^o for B₀ from 1.5-7T. We tested our result against Monte Carlo simulations of SSFP fMRI BOLD contrast at 3T and found that the BOLD contrast-optimizing flip angle maximizes on-resonant BOLD contrast (23% increase from &[alpha] _s) and produces a flat pass-band BOLD contrast vs. off-resonance profile.