A method for determining a set of B1 field maps for different transmit channels includes determining a first partial B1 field map having absolute B1 amplitudes for each transmit channel. A gradient echo technique operating with a single gradient echo image is used to determine a relative partial B1 field map having relative B1 amplitudes for each transmit channel. A spatial weighting function for mapping the relative B1 amplitudes onto absolute B1 amplitudes is determined taking into account the first partial B1 field maps and the relative partial B1 field maps of all the transmit channels. The spatial weighting function is used to determine second partial B1 field maps from the relative partial B1 field maps. The B1 field map for each transmit channel is determined from the first and the second partial B1 field map for the respective transmit channel taking into account the subregions and/or the error values.