Patent Number: 062597671
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an X-ray device which includes an X-ray imaging apparatus and an X-ray generator for powering an X-ray source which co-operates with the X-ray imaging apparatus and also includes a diaphragm unit which is connected to the X-ray source and includes an adjustable diaphragm aperture in order to preset an exposure field on an X-ray image detection device, the diaphragm aperture being adjustable on the one hand by a drive unit which is controlled by a control system and on the other hand by adjusting means for manual adjustment of the diaphragm aperture. 2. Description of the Related Art X-ray devices of this kind are known for the formation of Bucky images. Such devices utilize image detection devices in the form of film/foil combinations of various formats which are accommodated in suitably dimensioned cassettes. The examiner then selects the cassette format required for the next X-ray exposure and inserts the cassette into the X-ray device. The X-ray device is provided with a measuring device for measuring the cassette format. The control system then adjusts the diaphragm aperture in dependence on the measured cassette format so that the exposure field corresponds to the cassette format or the format of the film present therein. Such X-ray devices require manual adjustment of the exposure field only if the examiner wishes to constrict the exposure field. Since recently so-called "digital" X-ray detectors are used as the image detection devices; such detectors include a large number of (for example, 2000.times.2000) detector elements which are arranged in the form of a matrix, are sensitive to light or X-rays and generate electric signals which are dependent on the X-ray intensity and are processed in the X-ray device. The X-ray device may comprise various imaging units, for example a grid exposure table for forming X-ray images of a supine patient and/or a grid wall stand for forming X-ray images of a standing patient; each of these units is provided with only a single digital detector of this kind whose dimensions, therefore, have to correspond to the largest possible exposure format (for example, 43.times.43 cm). Automatic adjustment of the diaphragm aperture to the format of this image detector, however, would in most cases require a rather substantial manual restriction of the exposure field, thus complicating the use of such an apparatus. Citation of a reference herein, or throughout this specification, is not to be construed as an admission that such reference is prior art to the Applicants' invention of the invention subsequently claimed. SUMMARY OF THE INVENTION It is an object of the present invention to simplify the use of an X-ray device whose imaging unit (units) has (have) an image detector which has each time only a single (maximum) format. On the basis of an X-ray device of the kind set forth this object is achieved in that there is provided a storage device which co-operates with the control system and in which a respective set of exposure parameters is stored for each of a number of organs, that each set contains, in addition to the exposure parameters for the X-ray detector, an adjustment value for adjusting the exposure field, and that, when an organ is selected, the adjustment value is fetched and the exposure field is adjusted, by way of the control system and the drive unit, in conformity with the adjustment value associated with the selected organ. The use of a storage device in which respective sets of exposure parameters are stored for various organs has since long been known in the X-ray imaging technique. According to such so-called APR (Anatomically Programmed Radiography) methods, essentially exposure parameters for the X-ray generator, for example the voltage to the X-ray tube, the current through the X-ray tube and the exposure duration, are stored in an organ-dependent manner in order to be fetched and adjusted when the relevant organ is selected. The invention is based on the recognition of the fact that the size of the exposure field is correlated to the organ or to the body region to be imaged by way of the subsequent X-ray exposure. Therefore, for each organ the size of the required exposure field is stored additionally. The stored adjustment value is fetched when the relevant organ is selected and controls, via the control system and the drive unit, the diaphragm unit in such a manner that the preset exposure field is adjusted. After that, the examiner need only slightly change the exposure field, if at all. During manual adjustment of the exposure field the examiner is present in the vicinity of the patient who is arranged, for example on a patient table. However, the other adjusting operations, for example selection of an organ, triggering of an X-ray exposure etc., are carried out at a control desk or a workstation which is situated in a room other than that in which the patient is present. In the embodiment wherein the control system is programmed in such a manner that, after actuation of the adjusting means, the manual adjustment of the exposure field is carried out or preserved independently of an adjustment value fetched before or after that, it is ensured that the manual adjustment made for the exposure of the relevant organ is not overwritten by an adjustment value stored for this organ so that it is canceled again. The appropriately programmed control system then consists effectively of a diaphragm controller which is arranged to control the drive unit and the diaphragm unit, as well as of the workstation which controls all components of the X-ray device as well as the overall exposure procedure. The further embodiment wherein the control system is programmed in such a manner that after an X-ray exposure or a change of a patient to be examined an exposure field adjusted by actuation of the adjusting means is adjusted in conformity with the relevant adjustment value fetched, however, enables a change-over to be made from the manual adjustment to the stored adjustment values when an X-ray exposure or change of patient has taken place after the manual adjustment. Bucky exposures or exposures on the wall stand are generally executed with a given distance between the X-ray source and the image detector, for example 1.15 m. In that case each exposure field corresponds to a given diaphragm aperture. However, it is often desirable to increase or decrease the distance between the X-ray source and the image detector. Therefore, the further embodiment wherein the distance between the X-ray source and the X-ray image detection device is adjustable, further comprising means for measuring this distance, and wherein the control system is programmed in such a manner that in dependence on the measured distance the diaphragm aperture has a value such that the size of the exposure field on the image detection device assumes its preset value, ensures that when said distance is changed, the diaphragm aperture is also readjusted in such a manner that the desired exposure field is obtained in the plane of the image detector. The invention can be used with an image detector indicating a flat detector with light-sensitive or X-ray sensitive detector elements which are arranged in the form of a matrix. The invention, however, can in principle be used for all imaging units involving only a single format of the image detector.