The invention relates to a method of MR imaging, wherein a portion of a body (10) placed in the examination volume of a MR device (1) is subjected to an imaging sequence (IMG) of RF pulses and switched magnetic field gradients. The imaging sequence (IMG) is a stimulated echo sequence including i) at least two preparation RF pulses (α) radiated toward the portion of the body (10) during a preparation period (21), and ii) one or more reading RF pulses (β) radiated toward the portion of the body (10) during an acquisition period (22) temporally subsequent to the preparation period (21). One or more FID signals (I1) and one or more stimulated echo signals (I2) are acquired during the acquisition period (22). A B1 map indicating the spatial distribution of the RF field of the RF pulses within the portion of the body (10) is derived from the acquired FID (I1) and stimulated echo (I2) signals. It is an object of the invention to provide an improved B1 mapping method which can be applied in magnetic resonance angiography (MRA) and, in particular, in cardiac imaging, where the acquisition of a complete B1 map needs to be performed within the diastolic phase of the heartbeat. The invention proposes that the portion of the body (10) is subjected to a suppression sequence (BB) for suppression of MR signals emanating from blood prior to the imaging sequence (IMG). Moreover, the invention relates to a MR device (1) and to a computer program for a MR device (1).
