Methods for correcting a non-uniform power response of a radiofrequency (“RF”) transmit coil used in magnetic resonance imaging (“MRI”) are described. Transmit power response data for an RF transmit coil are processed to compute RF amplitude scaling factors for the RF transmit coil as a function of transmit frequency offset. The RF amplitude scaling factors can be used to correct transmitted RF power, and thus flip angle, to be more uniform over a range of transmit frequency offsets, as may be encountered when imaging with lower field MRI systems or MRI systems with high strength or asymmetric gradients.