An X-ray scanner comprises an array (12) of X-ray detectors (16) arranged in cylindrical configuration around an imaging volume (28), and a multi-focus X-ray source (20) which extends in a helical configuration around the outside of the detector array (12). A helical gap (24) in the detector array (12) allows X-rays from the source (20) to pass through the patient (26) in the imaging volume (28), and onto the detectors (16) on the opposite side of the scanner. The source (20) is controlled so that the X-rays are produced from a number of source points along the helical locus (23) to produce a tomographic image. As the patient is stationary and the source point varied electrically, the scanning rate is sufficient to produce a series of images which can be displayed as a real time three-dimensional video image.