A method of nuclear magnetic resonance imaging of a body in which the spins of a chosen nucleus in a selected slice (43) of the body are rotated through an angle appreciably greater than 90° by applying, in sequence, two substantially identical r.f. pulses (B 1 (90°), B 2 (90°)) accompanied by a magnetic field having a gradient (G 1 z, G 2 z) in a direction orthogonal to the plane of the slice (43). Each r.f. pulse is at the Larmor frequency for the chosen nuclei in the slice (43), and is effective to rotate the spins by not greater than 90° and the r.f. pulses together are sufficient to rotate the spins through the angle. The gradients of the magnetic fields are in opposite directions.