Patent Number: 052356272
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to an X-ray diagnostic system, and is concerned in particular with a diagnostic system with an X-ray camera supported by an arm, which is provided with a system for compensating offsets in an X-ray irradiated field. 2. Description of the Prior Art A conventional X-ray diagnostic system, such as a system for diagnosing circulatory organs includes an arm which supports an X-ray source such as an X-ray tube at one end and an X-ray camera opposing the X-ray tube at the other end. The arm is usually formed in a C-shape or an .OMEGA.-shape in order to maintain sufficient inner space to permit the X-ray tube and X-ray camera to be set at various positions around the patient. However, a large arm bends from the weight of an X-ray tube and its accessories, and causes offsets in the X-ray irradiated field. As a result of the offsets, not only the required part radiographed is, but also parts of the patient are irradiated inadvertently when an autocollimator is used. This problem become more serious when larger the X-ray diagnostic systems are used. Conventional systems solve the above-mentioned problems in the following manner; (i) Utilization of an arm with more rigid members to reduce the amount of bending. (ii) Changing the location and angle at which heavy devices such as an X-ray tube, an X-ray diaphragm device or an image intensifier are attached so that the amount of bending is decreased. However, it is not always possible to utilize large and rigid arms, because these require a lot of space and as a result insufficient space is provided for operating the devices. In the future, X-ray diaphragm devices and image intensifiers are expected to become larger and heavier, thus exacerbating the problem will be more serious. It is very difficult to eliminate the offsets of the X-ray irradiated field for every position and angle of the arm simply by changing the locations and angles at which the image intensifier or the X-ray tube are attached. Therefore, the use of a conventional X-ray diagnostic system with a large arm leads to substantial offsets in the irradiated field. This makes it difficult to irradiate at an exact location and to prevent unwanted irradiation of the patient. SUMMARY OF THE INVENTION The present invention has been made in an attempt to solve the above-described drawbacks, and therefore has an object of providing an X-ray diagnostic system that makes it possible to eliminate offsets in X-ray irradiated fields when a holding arm is used for a large X-ray diagnostic system. An X-ray diagnostic system of the invention comprises an X-ray camera unit for radiographing a patient as an object; a holding means for holding the X-ray tube and the X-ray camera unit in opposition and maintaining sufficient operating space between them; a seeking means for seeking a offset in an X-ray irradiated field; a controlling means for controlling the X-ray diaphragm unit according to an output of the seeking means. Preferably, the seeking means comprises a first measuring device for measuring an angle of rotation of the arm around an axis of the patient, a second measuring device for measuring an angle of rotation of the arm in a plane including the axis, and a third measuring device for measuring a distance SID. Preferably, the movable X-ray diaphragm unit includes a plurality of movable wings for limiting an X-ray irradiated field. Preferably, the controlling means is provided with a compensating table for calculating compensating amounts according to data from the seeking means, and further provided with a seeking means for seeking compensating amounts experimentally according to data from the seeking means and the offsets of the X-ray irradiated field. These and other objects, features and advantages of the present invention will be more apparent from the following description of a preferred embodiment, taken in conjunction with the accompanying drawings.