Patent Number: 047529474
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary radiation diaphragm for X-ray examination devices, and in particular to such a radiation diaphragm having at least one pair of diaphragm plates adjustable in opposite directions relative to each other. 2. Description of the Prior Art A primary radiation diaphragm having two diaphragm plates movable in opposite directions relative to each other for limiting the extent of an X-ray beam is described in German OS 1,800,879. In this known radiation diaphragm, the edges of the adjustable plates are wedge-shaped so that the x-radiation is not completely absorbed by the diaphragm at the region close to the edge thereof. This serves two purposes. First, a good gating of the diagnostically relevant image region is possible, so that substantially no image regions not containing useful image information are bright enough to interfere with viewing of the relevant image. Second, when using a picture reproduction device, such as a monitor, for introducing instruments into the examination subject, it is assured that the instrument can be seen before entry into the diagnostically relevant region. In this known primary radiation diaphragm, the diaphragm edges limiting the X-ray beam are straight. In practice, such a straight edge does not always correspond to the desired limitation of the image field. Particularly, for gating the regions surrounding the heart, a curved edge contour is desirable so that the image field can be optimally adpated to the shape of the heart. A diaphragm system having plates with differently shaped edges which can be moved above each other is described in USLP 3,980,407. Different shapes at the gated field can be achieved using the same diaphragm plates in this manner. SUMMARY OF THE INVENTION It is an object of the present invention to provide a primary radiation diaphragm which permits a plurality of different image field shapes to be achieved by the use of two diaphragm plates. It is a further object of the present invention to provide a primary radiation diaphragm which permits rectangular gating as well as gating corresponding to the heart contour using the same set of plates as may optionally be needed. Another object of the present invention is to provide such a primary radiation diaphragm which is capable of individual adaptation for examination of respective patients. The above objects are achieved in accordance with the system disclosed herein wherein the diaphragm plates are adjustably mounted in two spaced planes and the path of adjustment is selected large enough such that the X-ray beam is optionally limitable by each diaphragm plate with one of two edges disposed perpendicular to the path of movement during adjustment. Individual adjustment means are provided for each of the diaphragm plates. In the primary radiation diaphragm described herein, the diaphragm plates are arranged in pairs, with the plates in each pair being capable of movement past each other over each other, so that different shapes of gating are possible by selective use of the different shaping of the two edges of a single diaphragm plate. These edges are disposed perpendicular to the path of adjustment movement of the plates.