Patent Number: 042108179
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, two x-ray tubes 1 and 3 are arranged to project x-rays along two orthogonal sight lines 5 and 7 respectively. The x-rays from both tubes 1 and 3 pass through the object 8 to be x-rayed, which is normally a human or other living being. Frequently, although not necessarily, radiopaque contrast material has been injected into the blood or lymphatic vessels of the being in preparation for the radiograms. The x-rays from the tube 1 project an image of the object 8 onto x-ray film presented for exposure in a window 9 by the film changer 11. Likewise, the x-rays from the tube 3 project a planar image of the object onto film presented for exposure by the film changer 13. The film changers 11 and 13 are commercial units which sequentially present cut or rolled film for exposure. These film changers are not provided with any sort of shutter so that it can be appreciated from observing FIG. 1 that while the radiation from x-ray tube 1 forms an image on film in changer 11, scattered radiation from tube 1 will also impinge upon the film in changer 13. Since this scattered radiation is random, fogging of the film in changer 13 occurs. In a similar manner, the film in changer 11 is fogged by scattered radiation emitted by the tube 3. In order to eliminate this fogging, I propose that shields, which may take the form of flexible endless belts 15, be mounted for rotation about the changers 11 and 13 by rollers 17 at the four corners of the film changers. The belts 15 are comprised of alternate sections 19 and 21 of radiolucent and radiopaque materials respectively. The radiolucent sections may be made of plastic (e.g.) or pure rubber while the radiolucent sections may be made of lead impregnated rubber. The lower front roller 17 on changer 11 is rotated periodically by motor 23 to dispose sequentially the radiolucent sections 19 and radiopaque sections 21 in front of the window 9 in which x-ray film is presented for exposure. A pair of pinion gears 25 on the ends of the shafts 27 of the lower front rollers 17 of changers 11 and 13 synchronizes advancement of the belts 15 such that the radiopaque section 21 of the belt associated with changer 13 is in front of the film presented for exposure by that changer when the radiolucent section 19 is in front of the window 9 of changer 11 and vice-versa. Thus, when the x-ray tube 1 is energized to project an image onto the film presented for exposure by the film changer 11, the film presented by changer 13 is protected by the radiopaque portion 21 of the shield 15 and cannot be fogged by scattered radiation. The operation of the motor 23 can be automatically synchronized with the advancement of film by the film changers and energization of the x-ray tubes, if desired, or may be performed manually at the appropriate times. While the belts 15 have been illustrated as circulating around the outside of the film changers which are raised by legs 29, the belt assembly could be enclosed by a cover and made an integral part of the changer. It will also be appreciated that the belts 15 could be mounted for rotation about a vertical axis, that is, with the belt circulating around the four sides of the changer, rather than about a horizontal axis as shown. It can further be appreciated that the belts can be driven by separate electrically synchronized motors rather than by a single motor with a mechanical coupling as shown. FIG. 3 illustrates another embodiment of the invention in which the shield takes the form of a planar disc 31 mounted for rotation in front of the film 33 presented for exposure by the film changer 35. The disc 31 has alternating sectors 37 and 39 of radiolucent and radiopaque material respectively. As in the embodiment of FIGS. 1 and 2, rotation of the disc 31 may be synchronized mechanically or electrically with a similar disc mounted in front of a second film changer to place a radiopaque sector in front of one changer while a radiolucent section is in front of the other changer. As illustrated in FIG. 4, the shield may also be a planar member 41 having one radiolucent section 43 and one radiopaque section 45 mounted for reciprocal motion in a frame 47 disposed in front of the film changer 49. With the shield in the full left position as shown in FIG. 4 the radiolucent section 43 is in front of the film changer so that x-rays may reach the film 51 presented for exposure. When the shield 41 is moved to the right as seen in FIG. 4, the radiopaque section 45 is disposed in front of the film changer 49 and the film 51 is protected from scattered radiation. Again, the operation of similar shields in front of each of the film changers can be synchronized mechanically or electrically to shield alternately one film changer while an image is being recorded on film in the other changer. While the invention has herein been shown and disclosed in what is presently conceived to be the preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is not limited to the details disclosed herein but is to be accorded the full scope of the appended claims as to any and all equivalents.