Dental X-Ray Diagnostic Device

The present invention is directed to a dental X-ray diagnostic device for producing panoramic layer exposures of the subject particularly of a jaw. The device comprises an X-ray source which is mounted on a rotating arm of a carriage, a cassette which accepts the X-ray film and is mounted to rotate on the arm so that the film is moved during an exposure as the arm rotates both the source and cassette around the subject and a slit diaphragm disposed in the beam path between the source and the subject for limiting the width of the beam of radiation projected from the source.

A dental X-ray diagnostic device for producing panoramic layer exposures of a subject such as a jaw of a patient are known and have been sold. An example is disclosed in a Siemens brochure entitled ORTHOPANTOMOGRAPH No. MD 80/1238. As disclosed in this brochure, the diagnostic device provides a panoramic layer exposure or a panograph of a jaw as the patient's skull is fixed in a special support mount and the device has a mechanism which rotates the X-ray tube and the cassette containing the film around the patient so that the entire jaw can be imaged on the film with a single exposure. The image gained with this device is a layered image which is only sharp for the subject at a very specific layer depth while the zones adjacent the specific depth are blurred. The thickness of the sharply imaged zone is thereby proportional to the radius of curvature of the layer form and inversely proportional to the slit width of the X-ray beam. In the known devices which have a constant slit width over the entire motion sequence, the so-called normal layer, which comprises the jaw area including the front teeth, has a different layer thickness because of the different curvatures of the patient's jaw.

In order to achieve an appropriate radiation intensity for the entire area to be imaged without those areas for which such an intensity is not required being overloaded radiation-wise, it is known from German OS No. 2,753,119 to design a diaphragm which is positioned between the radiation source and the subject to be exposed with a wedge-shaped slit which converges downward. With the assistance of such a wedge-shaped slit diaphragm, the intensity of the radiation is greater in the upper area of the jaw than in the lower area. Thus, differing layer thicknesses of the subject in the vertical plane can be taken into consideration but the X-ray beam remains constant as viewed over the entire exposure of the jaw.

Due to the tighter curvature of the jaw in the area of the front teeth, a lower layer thickness is present there. This provides disadvantages particularly given subjects whose jaws depart from the normal shape. For example, if the dentitions with teeth are extremely slanted or with projecting canine, the images of these slanted teeth or projecting canines will not always have sufficient sharpness.

The present invention is directed to the object of achieving an improvement in the construction of a diagnostic device which will have the goal of attaining a layer thickness which is optimally matched to the subject over the entire exposure. To accomplish these goals, the present invention is directed to an improvement in a dental X-ray diagnostic device for producing panoramic layer exposures of the subject, particularly panoramic layer exposures of a jaw, said device comprising an X-ray source, carriage means having an arm for supporting the X-ray source, a cassette-accepting X-ray film, said cassette being mounted for relative movement on the arm of the carriage means, said carriage means moving both the X-ray source and the cassette around the subject with the cassette being moved relatively on the arm and a slit diaphragm means being positioned between the source and the subject for limiting the width of the beam of radiation being projected from the source. The improvement comprises adjustment means for changing the effective width of the slit diaphragm means during an exposure.

The present invention is directed to the perception that taking into consideration that the sharply imaged zone of an exposure principally depends on the radius of curvature of the subject to be exposed and on the width of the beam of X-rays. It is proposed for achieving the desired object to make the effective slit width of the diaphragm which is disposed between the radiation source and the cassette variable during the exposure. This diaphragm variation in terms of its effective slit width can be provided in place of the already existing primary or secondary diaphragm or can be provided as an additional diaphragm. It is particularly advantageous to couple this to the primary diaphragm so that the patient thereby receives the lowest radiation dose and to accomplish the coupling by use of a cam plate. This can be adjustably mounted for translational movement. A particularly simple execution of the variable diaphragm being mounted for rotation are on a vertical axis and by so doing the edges limiting the slit thus form the effective slit width which limits the width of the X-ray beam.

FIG. 1 is a side view of a dental X-ray diagnostic means for producing a panoramic layer in accordance with the present invention with portions in section; and

FIG. 2 is a plan view of the device according to FIG. 1 with portions in section and illustrating two different positions of the source.

The principles of the present invention are particularly useful when incorporated in a dental X-ray diagnostic device for producing panoramic layer exposures of a patient's jaw. The basic structure of such a device is known as mentioned by the above cited brochure.

The device essentially consists of an arm 1 of a carriage which is mounted for height adjustment on a support. The arm 1 carries a cassette 2 which accepts an X-ray film which is illustrated in FIG. 2 as being in a curved path 13. As illustrated, the cassette 2 is mounted for rotation about an axis on the arm 1. On the opposite end of the arm 1 an X-ray source 3 having two diaphragms 4 and 5 is provided. The diaphragm 4 is a slit diaphragm and is variable in terms of its effective slit width while the diaphragm 5 is a standard primary diaphragm. The arm 1 with the film cassette 2 and the X-ray source 3 having the two diaphragms 4 and 5 will be rotated in a known manner around the patient's head 6 during an exposure. During the rotation, the effective gating of the X-ray beam proceeding from the radiation source 3 is varied by means of twisting or rotating the diaphragm 4. To accomplish this, the diaphragm 4 is mounted by mounting means in the arm 1 to rotate around a vertical bearing axis 7. In addition, the diaphragm is connected to a lever 8 which on the other end has a cam follower 9 which is held on a radial cam 11 by a spring 10. In comparison to the rotating arm 1, the radial cam 11 is stationarily disposed and the cam has a shape which determines the angular position of the diaphragm 4 with reference to the cental beam focus which is indicated by the line 12.

As illustrated in FIG. 2, the diaphragm 4 is shown in two different positions. In the position indicated by I, the full slit width of the diaphragm is utilized. In the position indicated by II, the diaphragm has been rotated so that its effective width 4' is smaller. Thus, due to the rotation of the diaphragm on the axis 7 between the position illustrated at I and the position II, the effective slit width has become narrower. Due to this constriction of the slit width, the thickness of the layer in which a sharp image will be obtained is increased so that object points which according to the previous method would lie outside of the layer thickness and would be blurred now or sharply imaged.

The cam plate 11 is designed in such a manner that the effective slit width becomes narrower when exposing the area of the front teeth. Thus, the layer thickness for obtaining sharp images is increased in this area. In the area of the temporomaxillary joints, however, the full slit width is given and thus the normal layer thickness will be achieved.

In FIG. 2, a secondary diaphragm 14 is disposed directly in front of the position 13 for the film. The secondary diaphragm advantageously correspondingly proportionally couples to the variable diaphragm 4 so that an optimum limitation of the ray beam is given while avoiding scattered rays.

It has proved to be particularly advantageous to compensate the radiation intensity over the entire cycle range in accordance with the varying slit width of the diaphragm 4. For example, it is desirable to increase the intensity when the slit width becomes smaller. By so doing, over-exposures or, respectively, under-exposures, can be avoided.

Although various minor modifications may be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent granted hereon, all such modifications as reasonably and properly come within the scope of our contribution to the art.