Apparatus for X-ray bone densitometry of the hip joint in which an image of the hip joint is taken with the patient in a standing position comprising an X-ray source (24) and a detector (48) arranged on opposite sides of a patient receiving space with a height adjustable saddle (56) being provided for the patient to straddle. The appropriate height for the X-ray source and the detector are determined by the positioning of the saddle engaged with the crotch of the patient. Also disclosed is X-ray apparatus comprising a fan beam X-ray source (24) and a detector assembly (48) comprising a linear array of a plurality of detectors extending in the plane of the fan beam with means for scanning the source and the detector such that the source is scanned back and forth in a direction transverse to the plane of the fan beam and the detector array is scanned in said direction to remain in said fan beam and is incrementally indexed in a selected direction in the plane of the fan beam in a series of small steps to bring each detector in said array through a series of overlapping positions in said fan beam and is then indexed through a larger distance in said selected direction to move each detector in said fan beam by a distance equal to said length of said array or a major faction thereof.
