A method and system are described for compensating for non-uniformity of excitation field B1+ in magnetic resonance imaging (MRI) of an object. The variation in the RF excitation field B1+ is measured over a region of interest (ROI) in the object, the B1+ field causing nuclear spins in the object to flip at a flip angle when B1+ is applied to the object. The flip angle profile is designed to be proportional to a reciprocal of the measured variation in the excitation field B1+. One or more control parameters of the estimated flip angle profile is adjusted, in accordance with the measured variation in B1+, so as to cancel out variation in actual flip angle until a profile of the actual flip angle is achieved that is substantially uniform throughout the ROI.