Abstract: Radiology instrument comprising an X-ray tube linked with a plane detector. A support device comprises a pedestal of overall L-shape resting on the floor, with a substantially horizontal base, a substantially vertical post and an axis of rotation passing through one end of the base, the post being fixed to the other end of the base and being parallel to the axis, a bracket which is fixed to the top of the post and can rotate about a horizontal axis, and a C-shaped arm which is mounted on the bracket and is capable of rotating about an axis substantially perpendicular to the horizontal axis by sliding on bracket, the tube and the detector being mounted on bow and facing one another, the axis of the bracket the axis of the arm being secant at a point in space referred to as the isocenter. The instrument comprises a means for moving the isocenter continuously along a longitudinal axis of a patient held static.