Magnetic resonance monitoring of a target (30) uses the detected magnetic resonance to determine movement such as diffusion of contrast agent relative to the object, and uses the movement to discriminate (50, 60) a part of the contrast agent which is bound to the target, from the rest of the contrast agent. The need for clearing agents can be avoided or reduced, and hence imaging is instantaneous. A "stationary spin map" of the object can be formed by comparing the movements in the different directions, and determining if the differences between them are less than a given threshold. Determining isotropic movement in this way for a number of locations on the object allows the map to be generated.