Patent Number: 046413359
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a primary-beam collimator for a stereo radiographic x-ray diagnostic installation with an x-ray tube having dual focal points spaced at a distance from each other. In such an arrangement the object under study is x-rayed alternately from each of the focal points. By simultaneously viewing the radiograph pair--obtained from two focal points--the observer perceives a spatial image. The use of such multifocal x-ray tubes presents the problem of ensuring adequate x-ray exposure of the relevant areas of the object examined, as sourced from each of the two focal points, while avoiding the exposure of more tissue than is required. SUMMARY OF THE INVENTION The principal object of the invention is to provide a primary-beam collimator of the type described above, by means of which each pyramid-shaped beam, originating from each focal point, can be optimally controlled. This object, as well as other objects which will become apparent from the discussion that follows, are achieved, according to the invention, by providing shutters which can be adjusted so that each beam pyramid may be individually controlled for each focal point. A further advantageous development of the invention consists in providing two external shutter leaves and two internal shutter leaves arranged between the external leaves so as to restrict the beams in planes perpendicular to the stereo base--i.e., the line connecting the two focal points--with each internal shutter leaf being adjustable in the direction of its corresponding adjacent external shutter leaf. The restriction of both beam pyramids in planes parallel to the stereo base can thus be achieved by means of a pair of shutter leaves common to both beam pyramids, while the restriction in planes perpendicular to the stereo base can be controlled by means of both external and internal shutter leaves for both beams. For this purpose the internal shutter leaves may be suitably shaped so that, when adjusted to their external positions, they permit the emission of a central beam pyramid from a central focal point and, in conjunction with the external shutter leaves, they close the external shutter openings. This configuration enables regular radiographs to be taken from a central focal point under the same optimal conditions of beam restriction as in the case of stereos. For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiment of the invention and to the accompanying drawings.