Selective Image Area Control of X-Ray Film Exposure Density

This invention relates to an improved system for determining the x-ray exposure required for photography.

Medical diagnosis of internal human tissue is frequently performed by the use of motion picture x-ray techniques, particularly when the tissue of interest, such as, for example, the beating heart, is in motion. The technique involves use of an x-ray tube aimed at the patient, a fluorescent screen disposed on the opposite side of the patient, an image intensifier which views the fluorescent screen and increases the brightness of the image, and a motion picture film camera which records the moving image. A television system is often used to provide a display as the x-ray image is panned, so that the particular site of interest can be properly positioned while the motion picture film is being exposed.

Proper exposure of the motion picture film requires accurate information with respect to light content of the image which is to be photographed. This is presently obtained by extracting and directing at a photomultiplier exposure sensing system, a small sample of a portion of the light contained in a collimated beam formed from the visible image produced by the image intensifier. Since any part of the collimated beam is composed of light from all parts of the image, what is sensed is only an average sample which is representative of the total amount of light in the entire image. Since the image of the subject contains areas of both high and low x-ray absorptivity, it is difficult to determine accurately from a sample of the entire image the optimum exposure required for the particular body portion of interest which is only a part of that total image. Since, with the presently used system, the operator has no control over the location of the light sample taken, the result is often an unsatisfactory exposure.

The patient must then be subjected again to x-radiation in order to obtain a better picture. Since it is desirable to minimize exposure of the patient to x-radiation, it is advantageous and less potentially harmful to the patient to determine initially, the optimum exposure required for the particular body portion of interest.

It is an object of this invention to provide an arrangement fo enabling the optimum exposure required for photographing a particular area of interest to be obtained the first time x-ray radiation takes place.

Another object of this invention is to provide a novel and improved arrangement for enabling optimum x-ray exposure required for a particular portion of a body of interest, using motion pictures.

The foregong and other objects of the invention may be achieved in a system in which the light output of an x-ray image intensifier is passed through a collimating lens and then onto a beam splitting mirror which passes a portion of the light to a television camera and a portion of the light to a film camera. The television camera is used to produce an image from which it can be determined whether the part of the body of interest is being x-rayed or whether the person being x-rayed or the x-ray machine must be relocated to produce an image of the portion of the body of interest. In accordance with this invention, there is interposed between the film camera and the beam splitter, a second smaller beam splitter, which permits some light to pass therethrough to be imaged on the lens of the film camera, and which also directs a portion of the received light onto an imaging lens. The imaging lens focuses the image on a mask. The mask has an aperture whose diameter is selected to define the specific area of interest of the region of the body being x-rayed. The light passing through the image mask falls on a photomultiplier, which is used to sense the intensity of the light received whereby a determination of the correct exposure required for properly photographing the desired portion of the body can be achieved.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawing.

The drawing represents a schematic diagram which illustrates both the prior art system presently being used, as well as an embodiment of this invention.

An x-ray machine 10 projects x-rays at a patient 12. X-rays passing through that patient impinge upon an image intensifier 14. The output of the image intensifier is collimated by a lens 16 disposed on the opposite side thereof. The collimated light falls upon a beam splitting mirror 18 which splits the light and directs one portion at a motion picture camera 20, and permits a second portion to pass therethrough to be directed at a television camera 22.

In accordance with the prior art, a small mirror 24 is positioned in the collimated light beam, and intercepts and diverts a portion of the light for perception by the photomultiplier exposure sensing system 26. As previously indicated, since any part of the collimated beam is composed of light from all parts of the image, what is sensed is only an average sample which is representative of the total amount of light in the entire image. Since the image of the subject contains areas of high and low x-ray absorptivity, it is difficult to determine accurately from this sample, the optimum exposure required for a particular body portion of interest, which is only a part of that total image. Also, since the operator has no control over the location of the light sample taken, the result is often an unsatisfactory exposure.

In accordance with this invention, the light reflected from the beam splitting mirror 18 is directed at another beam splitting mirror 24. The light passing therethrough will still impinge upon the film camera 20 to be photographed. The light redirected by the mirror 24 is directed at an imaging lens 26, which in turn directs it at a mask 28, located at the image position. The mask will have a central aperture, (or an adjustable diaphragm) which will enclose the central portion of an area of interest. Accordingly, a photomultiplier 30, which is used for intensity sensing, and for controlling the x-ray beam intensity, for example, is positioned to receive the light passing through the aperture of the mask. It therefore senses only the light included in the image which exists in the predetermined area of interest. Accordingly, it will indicate more accurately, the quantity of this light and can thus provide an output signal which is applied to the x-ray machine 10 to establish the x-ray beam intensity provided by the x-ray machine 10. Thereby an accurate exposure of the film for the area of interest is achieved. The camera lens aperture may be left wide open so that the patient will have the minimum of x-ray exposure for the part of the body being photographed. This occurs because the x-ray beam intensity is altered for exposure requirements, rather than altering the film camera controls.

There has accordingly been described and shown a novel and useful arrangement for accurately determining the exposure required for photographing an area of interest in a subject being x-rayed, the first time, and with a minimum of x-ray exposure for the patient.