Graphical Derivation of the Steady-State Magnetization in Balanced SSFP MRI
Zun Z, Nayak K
University of Southern California
Balanced steady-state free precession (SSFP) exhibits different steady-state signal depending on flip angle and resonance-offset, producing a well-known banding artifact. The steady-state magnetization can be derived from matrix calculations based on excitation, relaxation, and off-resonance precession that should cancel one another in the steady state. Matrix derivations are accurate, but do not provide an intuition behind the signal variation and the banding artifact. In this work, a new graphical derivation of the SSFP signal is presented. For given T1 and T2, the steady-state signal is uniquely determined by a new parameter, the effective flip angle, which is a function of flip angle and off-resonance precession within TR, and along with T2/T1, uniquely determines steady-state magnetization.