skilled in the art it should be recognized that while a gear and rack arrangements are shown for moving the ct scanning component to describe helical path this showing is meant to be exemplary and not limiting fig6 is a side view showing of the screening ct system 31 of fig1 and 4 a in the embodiment of fig1 4 a and 6 the ct ring 32 does not ride on a helically arranged rails instead the at least one x ray source rotates within the ring while the ring moves vertically as indicated by the arrow for third generation systems detectors 34 rotate with the at least one x ray source within the ring in fourth generation systems the detectors substantially surround the subject or patient 44 and do not rotate in the embodiment shown in fig6 the circular rail 45 with a circular rack 45 a attached thereto is shown affixed to the ct ring 32 the gears of gear boxes such as gear box 35 mesh with the vertical racks such as rack 47 attached to post in a preferred aspect of an embodiment of the invention gravity causes the rack to drive the gears of the gear boxes such as gear box 35 the gears of the gear box then rotate drive gear 48 which meshes with circular rack 45 a and causes the at least one x ray source to rotate while the ring is descending in third generation systems the detectors are also affixed to the circular rack 45 which is attached to the rotating circular rack 45 a the rail 45 and rack 45 a are shown mounted on ball bearings such as bearing 61 in race 62 in another preferred aspect of an embodiment of the invention the gear box is motorized.