1. A magnetic resonance scanner, comprising: a main magnet which generates a B 0 field; gradient coils and a gradient coil controller which generates gradients across the B 0 field; one or more RF coils which transmit B 1 pulses and receive magnetic resonance signals; an RF transmitter which transmits B 1 pulses to the RF coils to excite and manipulate resonance; an RF receiver which demodulates received resonance signals into data lines; one or more processors connected to the gradient coil controller ( 28 ), the RF transmitter, and the RF receiver which are programmed to: control the RF transmitter and the gradient coil controller to implement an interleaved multi-slice 2D imaging sequence which in each of a plurality of TRs generates a first and second navigation data lines and at least one image data line for each of a plurality of slices; reconstruct the first navigation data lines from the plurality of slices into a first navigation projection image; reconstruct the second navigation data lines from the plurality of slices into a second navigation projection image; and compare successive navigation projection images to detect and adjust for 3D motion.