Variable-rate selective excitation (VERSE) is a
powerful method to control RF power and SAR that bounds to a key condition as retaining
the RF-to-gradient amplitude ratio at each sample that preserves the rotational
behavior of on-resonance spins (1). The maintenance of VERSE condition strictly
depends on the fidelity of the local gradient fields implying that any
deviation from the nominal VERSE’d gradients will modulate the spin rotations
similar to off-resonances ultimately resulting excitation errors and the RF
pulse to converge to a significantly different peak RF power.