Patent Number: 049967010
Section: summary

The invention relates to a method for slit radiography in which use is made of an X-ray source and a slit diaphragm placed in front of the X-ray source to form a fan-shaped X-ray beam with which a body to be investigated is at least partially scanned to form an X-ray shadow image on an X-ray detector placed behind the body, which fan-shaped X-ray beam is formed by a number of sectors situated next to each other, and in which the transmitted X-ray radiation is controlled instantaneously for each sector during the scanning movement by means of controllable beam sector modulators acting in conjunction with the slit diaphragm. In addition, the invention relates to a device for applying the method. Such a method and such a device are known from Dutch patent application No. 8400845. According to the technique known from Dutch patent application No. 8400845, to control the quantity of X-ray radiation transmitted through the slit diaphragm at each point of time, use is made of attenuation elements which are placed near or in the slit of the slit diaphragm and act as beam sector modulators, which are each able to control a sector of the fan-shaped X-ray beam, and which, depending on the attenuation occurring in the associated sector and caused by the body to be investigated are controlled in a manner such that the attenuation elements extend to a lesser or greater degree into the X-ray beam. If the attenuation caused by the irradiated body in a certain sector and at a certain instant is large, the attenuation element associated with said sector is moved completely or largely out of the X-ray beam. On the other hand, if the attenuation caused by the body in a certain sector at a certain instant is low, then the associated attenuation element is brought further into the X-ray beam. The advantage of this technique is that equalized X-ray photographs can be obtained therewith, i.e. X-ray photographs which have a good contrast both in the light parts and in the dark parts. If, therefore, a photograph is made in this manner, for example, of the upper part of a patient's body, the radiologist can find sufficient information in the same photograph relating to both the chest and the abdomen of the patient, whereas previously two different photographs were necessary to obtain the same information. The known technique has the drawback that at the instant when the soft tissues of the patient are irradiated, the X-ray radiation still transmitted in the sector concerned is relatively hard, whereas soft radiation is adequate for the soft tissues and is also to be preferred. The object of the invention is, therefore, to simplify and to improve the known technique and in general to make available an effective method and equipment for producing equalized X-ray photographs. For this purpose, according to the invention, a method of the type described is characterized in that the X-ray radiation is cyclically modulated in a predetermined manner for all the sectors taken together and that the controllable beam sector modulators are individually controlled in order to select cyclically a part of the X-ray radiation for each sector, which cyclic selection is synchronized with the predetermined cyclic modulation of the X-ray radiation. A device for slit radiography, comprising an X-ray source, a slit-type diaphragm, placed in front of the X-ray source, which forms a fan-shaped X-ray beam with which a body to be investigated can be scanned at least partially to form an X-ray shadow image of the scanned part of the body on an X-ray detector placed behind the body, a control signal generator which, during operation, provides a signal representing the transmission of the body for each sector of the X-ray beam to control means, controllable beam sector modulators which act together with the slit diaphragm and which, under the control of signals from the control means, are able to influence the X-ray beam for each sector, is characterized, according to the invention, by modulation means for providing an X-ray beam modulated in a predetermined cyclical manner.