Abstract: In a scanner for computed tomography an X-ray source and a multiple cell X-ray detector are mounted on a rotatable support on opposite sides of the rotational axis for orbiting about a body to thereby scan it with a diverging X-ray beam. The source and detector are each on a carriage which enables driving them jointly toward or away from the axis of rotation while the body stays fixed so that regardless of the width of the body portion its boundaries will be substantially tangent to the boundary rays of the beam and after penetrating the body the beam and the X-ray image which it entrains will always cover the entire length of the detector and use all of its cells.