Patent Number: 046413359
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a primary-beam collimator which permits the restriction of three beam pyramids originating from three focal points: F1, F2 and FN. Focal points F1 and F2 serve to create pairs of stereo images, while focal point FN is used to produce regular radiographs. Beam restriction in planes parallel to the stero base (i.e., line F1-F2) is achieved as in the case of regular primary-base shutters, with the aid of first-stage and second-stage pairs of shutter leaves, 1a, 1b. Restriction in planes orthogonal to the stereo base is achieved during stereo operation (i.e., alternative activation of focal points F1, F2) with the aid of first-stage shutter leaves 2a (restricting the beam from F1), and 2b (restricting the beam from F2), and the second-stage shutter leaves 3a and 3b. Shutter leaves 2a, 2b, and 3a, 3b can be adjusted in a plane perpendicular to the central-beam axis of the restricted pyramid-shaped beam, in which the stereo base is located. Inner positions of leaves 2a, 2b have been represented by dash-dot lines. Internal restriction of the beam pyramids is achieved by means of the swiveling shutter leaves 4a (for point F1) and 4b (for point F2). Shutter leaves 4a, 4b swivel about axes 5a, 5b, and can also be adjusted in a direction parallel to the stereo base on guides 14 (FIG. 3). Shutter leaves 2a, 2b, 3a, 3b, and the swiveling shutter leaves 4a, 4b, are operated by a stepping motor (not shown). Their movements are coordinated by a microcomputer. In order to obtain pairs of stereo radiographs, shutter leaves 1a, 1b, 2a, 2b, 3a, 3b, and 4a, 4b are positioned as represented by solid lines, resulting in the shaping of two beam pyramids (I and II). When shifting from stereo to regular operation, the microcomputer coordinates the movements of the shutter to new positions. Shutter leaves 2a, 3a, and swiveling shutter leaf 4a which, during stereo operation, restrict beam pyramid I at the top and the bottom, as shown in FIG. 1, now become the top restriction of beam pyramid III (with the vertex in FN). The same is valid for the bottom restriction, which is obtained with the aid of shutter leaves 2b, 3b, and 4b. According to FIG. 3, the swiveling shutters 4a, 4b are constructed so as to allow free movement to shutter-leaf pairs 1a, 1b and filter frames 6a, 6b, 6c, 6d in a cross-section adjacent to axes 5a, 5b. During the stereo operation, restriction is achieved by external surfaces 7a, 7b (FIG. 2) of swiveling shutters 4a, 4b, while during regular operation restriction is performed by the internal surfaces 8a, 8b. The swivel movement of swiveling shutters 4a, 4b takes place over a guide link 9 (FIG. 2). In the space between the swiveling shutters 4a, 4b and shutter-leaf pair 1a, 1b a sighting device 10a, 10b, 10c may be provided, consisting of a light bulb and two mirrors (FIG. 1). For the operation of an image-intensifier tube with a circular entrance filter, it is possible to add an octagonal diaphragm 11, which is only schematically shown in the figures. In the space between the swiveling shutters 4a, 4b an additional spring-operated swiveling shutter 12 may be introduced, as shown in FIGS. 2 and 3. During stereo operation with slight beam restriction, this swiveling shutter 12 closes the gap between the swiveling shutters 4a and 4b, cutting off scatter radiation. During regular operation, swiveling shutter 12 is kept open by shutter leaf 2a, now positioned along shutter leaf 4a, with the aid of a linkage rod 13. An essential feature of the primary-beam collimator as shown in FIGS. 1 to 3 is the following: The shutter leaves 1a, 1b, 2a, 2b, 3a, 3b, and 4a, 4b are constructed and can be adjusted so that beam pyramids I and II, from focal points F1 and F2, respectively, can be individually controlled. For the restriction by planes perpendicular to the stereo base F1-F2, two internal shutter leaves 4a, 4b are provided, adjustable between two external shutter leaves 2a, 2b. The internal shutter leaves 4a, 4b are constructed so that, when brought to their external position, they permit the free emission of a central beam-pyramid III from a central focal point FN and, in conjunction with the external shutter leaves 2a, 2b, they close the external openings in the path of beam pyramids I, II. The above-described primary-beam collimator can be used, as needed, for either regular or stereo shutter operation. There has thus been shown and described a beam collimator for x-ray apparatus which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawing which discloses the preferred embodiment thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.