Apparatus for eliminating cross-fogging in biplane radiography

Film changers used in biplane radiography are provided with shields having radiolucent and radiopaque sections which are alternately disposed in front of the x-ray film presented by the film changers for exposure. Operation of the two shields is synchronized to dispose the radiopaque portion of one shield in front of one changer when the radiolucent portion of the other shield is disposed in front of the other changer such that scattered radiation cannot reach film in the one changer and fog it when an image is being recorded by the other changer. In one disclosed embodiment of the invention, the shield is a flexible endless belt with alternating radiopaque and radiolucent sections mounted for rotation in a loop around the film changer. In a second disclosed embodiment of the invention, planar discs having alternating radiopaque and radiolucent sectors are rotated in front of the film changers. In yet another embodiment of the invention, planar members, each having one radiopaque and one radiolucent section, are mounted for reciprocal movement in front of the film changers.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to the art of taking x-ray pictures of a common 
object along two sight lines and, more particularly, to means for 
preventing cross-fogging of the x-ray pictures in such an arrangement. 
2. Prior Art: 
In a radiographic practice known as angiography, a radiopaque or contrast 
material is injected into the blood or lymphatic vessels of a patient and 
its progress through these vessels is observed by taking a series of x-ray 
pictures. The contrast materials currently used are toxic and, therefore, 
the amount injected into the patient must be limited. However, often it is 
necessary in this practice to obtain x-ray pictures in multiple 
projections, such as the front and side and so forth. In order to 
accommodate this requirement while minimizing both time of examination and 
the amount of contrast material used, pairs of x-ray tubes and film 
changers at right angles to each other have been used simultaneously, thus 
obtaining two orthogonal projections for each injection of contrast 
material. 
It is well known that x-rays interact with the matter being x-rayed to 
produce scattering. This phenomenon, known as the Compton effect, produces 
noise on the x-ray film. While means have been devised to diminish the 
effect of scattered radiation on the primary film, namely the Potter-Bucky 
grid which is placed between the object being x-rayed and the film to 
absorb radiation which is not parallel to the line of sight of the 
picture, no attention has been focused on diminution of noise caused by 
scattered radiation from the second axis in a two axis angiogram. 
It is a primary object of this invention to provide means to eliminate 
cross-fogging between the two axes of a two axis angiogram. 
It is another object of this invention to eliminate such cross-fogging by 
means which are simple, reliable and inexpensive. 
SUMMARY OF THE INVENTION 
According to the invention, cross-fogging in biplane radiography is 
eliminated by shields having radiolucent and radiopaque portions which are 
alternately disposed in front of the film changers. Means are provided to 
synchronize the two shields such that the radiopaque portion of one shield 
is disposed in front of the film presented for exposure by its associated 
film changer when the radiolucent portion of the other shield is disposed 
in front of the film presented for exposure by the other film changer. 
In one embodiment of the invention, the shield is in the form of a flexible 
endless belt having alternating radiolucent and radiopaque sections. The 
belt is mounted such that it forms a loop surrounding the film changer. 
In another embodiment of the invention, the shield is a planar member 
mounted for movement in a plane parallel to the plane of the film 
presented for exposure. This shield may comprise a disc having alternating 
sectors of radiolucent and radiopaque material which is rotated in a plane 
parallel to and in front of the film or it may be a planar member having 
one radiopaque and one radiolucent section which is mounted for reciprocal 
movement in front of the film changer.

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.