Patent Number: 048037168
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to an x-ray diagnostics installation for radiographs, and in particular to such an x-ray installation having a secondary radiation grid preceding the film holder and means for moving the secondary radiation grid perpendicular to a central ray of the x-ray beam during an exposure. 2. Description of the Prior Art X-ray diagnostics installation of the type described above are known which include means for forming an electrical signal corresponding to the exposure time, and control means for controlling the speed of movement of the secondary radiation grid dependent on the exposure time, with the speed of movement being fixed. In x-ray diagnostics installations of this type, the secondary radiation grid has lamellae directed at the focus of the x-ray source for the purpose of suppressing leakage radiation emanating from the examination subject. The movement of the secondary radiation grid during an exposure is intended to prevent the lamellae from becoming visible in the resulting radiograph. In such known systems, the control circuitry for movement of the secondary radiation grid selects a rigidly prescribed rate of speed for such movement. It is not possible, however, using such a fixed speed to prevent grid streaks from becoming visible in the radiograph for all exposure times. As described in German Patent No. 884 148, the speed of the secondary radiation grid is set dependent on the exposure time, however, it is assumed that the exposure time is set before an exposure is actually undertaken, and is thus known. The system disclosed therein cannot undertake an automatic selection of the proper speed of movement of the secondary radiation grid without knowing the exposure time in advance. SUMMARY OF THE INVENTION It is an object of the present invention to provide an x-ray diagnostics installation of the type described above wherein imaging of the lamellae of the secondary radiation grid in the radiograph is reliably prevented for all exposure times by the use of an automatic exposure unit. The above object is achieved in accordance with the principles of the present invention in an x-ray diagnostics installation having an automatic exposure means wherein a signal corresponding to the exposure time is acquired from the input signal of an integrator. The input signal to the integrator is obtained from a radiation measuring chamber disposed in the path of the x-ray beam after the examination subject. The radiation detector first supplies a dose rate signal which is used after integration for de-energizing the voltage supply for the x-ray source. Given a prescribed dose for an exposure, the anticipated exposure time can be calculated from the dose rate signal. A signal corresponding to the anticipated exposure time can then be used for controlling the rate of speed of the secondary radiation movement. The speed of movement of the secondary radiation grid must be increased with a shorter exposure time.