Abstract: Apparatus for examining a body by means of penetrating radiation such as X- or .gamma.- rays has a radiation beam assembly comprising a member with a radiation source for producing a collimated beam of penetrating radiation, and a member with detector means for receiving radiation from the source. Guide means slidably mount the members on a support structure containing a circle of reconstruction within which the body is located. The members are located on opposite sides of the center of the circle of reconstruction and are translatable as a unit in parallel paths to cause the beam to sweep through and define the plane of the circle of reconstruction. A flexible connection links the members together for maintaining a fixed spatial relationship therebetween during translation at least while the beam sweeps through the circle of reconstruction.