DE2159365A1 - Device for exposure compensation in devices for X-ray photography - Google Patents

Description

DIPI INS. KLAUS BEHN DIPI INS. KLAUS BEHN DIPL.-PHYS. ROBERT MÜNZHUBER 21 PATENT LAWYERS

MUNICH 22 Wl DEN MAYERSTRASSE S TEL. (OB11) 22 25 SO-29 51 92

November 30, 1971

Pp / My

MEDINOVA AB, Ankdammsgatan 40, 171 43 Solna / Sweden

Device for exposure compensation in devices for the

X-ray photography

The invention relates to an apparatus for X-ray photography and in particular a device in such X-ray photography apparatus, with their Help to balance the average exposure or the average radiation intensity in the image plane of the device so that the average exposure over the entire area of the image receiving medium used is substantially is constant.

As is well known, an apparatus for X-ray photography has in its basic components one Radiation source, usually an x-ray tube, an object level in which the object to be x-rayed is located is located, and an image plane which is on the opposite side of the object plane to the radiation source and in which an image recording medium or a corresponding arrangement

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Merck, Plnck Co., Munich, No. 30 464 I Bankhaus H. Aufhäuser, MQnohen, No. 361300 Postacheck! Munich 2OB 04 Telegram address! Patent senior; "

is appropriate. This image recording medium can, for example be a radiation sensitive PiIm, a fluorescent display screen or an electronic one Image intensifier. An important problem with such devices for X-ray recording arises from the fact on that the mean intensity in different parts of the radiation leaving the object to be examined is very high shows large differences, with which the average exposure of the corresponding different areas of the image reproduction medium is excited very differently, which can be attributed to different thicknesses, densities and absorption properties of the individual areas of the object is. As a result, it is often impossible to have an exposure or au-lighting over the entire area of the image display medium to achieve within a predetermined range of the image reproduction medium, the so-called exposure latitude. This means that some parts of the Höntgen image are overexposed, whereas other parts may be underexposed, and in these areas the image contrasts become insufficient so that they do not have the desired and required information about the object examined by the X-ray radiation able to freeze more. The most common method for The solution to this problem is to take two or more recordings of the object with different radiation intensities and / or to make different exposure times. However, this method has, inter alia, the disadvantages that the test

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The total time necessary for the recordings is extended, that the film costs increase and that the object, for example a Human being exposed to a significantly larger total radiation dose will. Furthermore, if very thick parts of the object are x-rayed, the thinner parts will be made Parts of the object, for example the patient, exposed to an unnecessarily high dose of radiation. This unnecessarily high Radiation intensity in the thinner parts of the object also generates highly scattered secondary radiation, which causes a diffuse exposure or a fogged background on the image receiving medium, which also causes a results in reduced image contrast.

In order to eliminate these disadvantages, it has already been proposed to reduce the average radiation intensity in the equalize different areas of the image plane in such a way «, that the average radiation intensity and thus the average exposure within the various Areas of the image plane or of the image recording medium essentially is made evenly. Two different methods have been proposed for this task. In the one Methods are radiation-absorbing bodies, in general made of metal, placed in the beam path between the radiation source and the object plane, with the shape, the thickness in the direction of radiation and the position in relation to the radiation path of these radiation-absorbing bodies are selected in such a way that

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that the absorption caused by these bodies is essentially reversed in the different regions of the radiation is proportional to the absorption of the corresponding parts of the radiation in the illuminated object. Devices of this type are, for example, in US patent application 111,828, US patent specification 1,535,359, the German Patent specification 1,079,448 and Swiss patents 243 731 and 254 461 are described.

The other, already proposed method consists in that a diaphragm, which oscillates or rotates in a plane perpendicular to the radiation direction, is placed in the beam path, generally between the radiation source and the object plane. The shape, the position relative to the radiation and the oscillating or rotating movement of this diaphragm are selected so that the total exposure time for the different areas of the object is made substantially proportional to the absorption values of the different areas of the object. Devices of this type are, for example, in the Swiss Patent 154,209 and _s the German patents 1023315, 1193796 described and 1,017,024.

Known devices of the types described above have the common significant disadvantage that for each type of object to be x-rayed, for example skull,

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Body, limbs, etc., specially shaped absorber bodies or panels are necessary. Furthermore, the absorber body or diaphragms are manually adjusted relative to the radiation based on an estimate of the absorption value, in the different areas of the object to be x-rayed. This manual operation is time consuming and requires trained staff and only gives in the best of pail a rough and relatively imprecise compensation of the absorption differences in the different parts of the object and mostly just compensates for the differences in absorption due to the differences in the dimensions of the object in the direction of radiation, i.e. due to the thickness of the object. Therefore it is not possible in this way to detect differences in absorption to compensate, caused by structural differences in the different areas of the object are. Furthermore, it has so far only been possible to add geometrically very large absorption differences in the object compensate, i.e. absorption differences with an expansion within the object, which is essentially the

tion of the object itself corresponds in the direction perpendicular to the direction of radiation. Absorption differences that are geometrical are much more closely related to each other, i.e. with a higher spatial frequency, could not be compensated so far will.

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It is therefore the object of the invention to provide an improved device in devices for radiation recording for a Balancing the average exposure in the different areas of the image plane using this facility can have basically known elements, such as radiation-absorbing filters, which are in the radiation path are inserted between the radiation source and the object plane, and different absorption values within the different which have areas of a plane which is essentially perpendicular to the direction of radiation. The establishment however, the invention operates automatically and produces a significantly more accurate and finer compensation for the average exposure in the image plane.

The device according to the invention consists of a compensation filter arrangement with radiation-absorbing Means which have such a changeable shape or shape that their absorption values are within the various ranges the radiation from the radiation source can be changed and selected independently of one another from control elements for determining the absorption values of this compensation filter arrangement in the various areas of the Radiation, the form of the radiation absorbing means depending on the given to the control elements Control signals is changeable, and from the radiation

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source arranged from beyond the object plane Radiation detectors for recording the average intensity values of the various areas of radiation and to generate values corresponding to these intensity values Output signals, the control signals to the control elements which control the absorption values of the compensation filter arrangement determine in the different areas of radiation from the output signals of these radiation detectors are derived.

Since in the device according to the invention, the compensation filter arrangement Using radiation absorbing agents with variable shape, their absorption values can be changed can be changed essentially independently of one another within the various ranges of radiation, and the control elements, which change the shape of these radiation-absorbing means and thus the absorption values of the compensation arrangement determine to work according to the output signals of the radiation detectors, the average Measuring intensity values of the different areas of the radiation leaving the object becomes an automatic one Compensation of the average radiation intensity in the Image plane created with an accuracy that is as high as the appearance of the radiation-absorbing used Funds allowed. Accordingly, the average exposure is completely automatically based on a quantum

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titative measurement of the radiation intensity values in the various Areas of the radiation leaving the object balanced. The limits for balancing the average Exposures are essentially determined only by the shape of the compensation filter arrangement. With a filter arrangement according to the invention, which basically consists of a layer of a moldable, radiation-absorbing substance with a thickness that can be changed in the direction of radiation within the various areas or sections thereof Layer, it is possible to very precisely and completely compensate for the different absorption values in the different areas of the object to be x-rayed. Compared to the known devices for the same task ^ has the device according to the The invention also has the advantage that no manual adjustment is necessary, which saves time and operation even a less skilled staff allows no more differently shaped absorber bodies for the different Types of objects to be transilluminated are necessary for correct exposure of the image recording medium in all sections of the picture is achieved so that details in the structure of the object on all image sections despite the limited effective range of the image recording medium can be recognized, and that the total radiation dose to which the object, for example the patient, is exposed is, is significantly lower than with an exposure

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which, is less fully balanced.

Embodiments of the invention are shown in the drawing for example, show:

Pig. 1 schematically shows a basic structure of the device according to the invention;

2 schematically shows a first simple embodiment the device according to the invention, "in which the radiation-absorbing Means in the compensation filter arrangement from a number of solid bodies of radiation-absorbing Consist of material that can be moved relative to one another and to the beam path to change the position;

3 schematically shows a device that has been developed a little further according to the invention, in which the compensation filter arrangement of solid bodies from radiation-absorbing Consists of material which can be moved relative to one another and to the beam path;

Fig. 4 is a schematic side view, partly in Section, of a compensation filter arrangement according to the invention, in which the radiation absorbing means consist of a radiation-absorbing liquid enclosed in a shallow chamber which is essentially is arranged perpendicular to the radiation direction and changes its thickness in the different areas of the radiation can be;

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Fig. 5 is a top plan view, partially in section, of the compensation filter arrangement shown in Fig. 4;

6 schematically shows the shape of a flexible screen,

'one side in the liquid-filled chamber of the in Figures 4 and 5 form the compensation filter arrangement shown;

FIG. 7 shows a cross section through this screen shown in FIG. 6 along the section VII-VII;

. 8 shows a cross section through the screen shown in FIG. 6 along the section VIII-VIII;

9 schematically shows an embodiment of the device according to the invention, in which the compensation filter arrangement a layer of moldable or formable, radiation-absorbing material Comprises material lying in a shallow tray;

Figure 10 is a cross-section of the schematic of a compensation filter arrangement according to the invention, in which the radiation absorbing means consists of a layer of a radiation absorbing, Inside there are loose powder, which is carried in a shallow bowl and crossed through the air pressure gradient acting layer is maintained in a stable, formable or malleable shape;

11 is a diagram of another embodiment of the Device according to the invention, wherein the compensation filter arrangement has radiation-absorbing means,

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which consists of a layer of a radiation-absorbing, internally loose powder, which is deposited with a variable thickness on a flat bowl and covered by a air pressure gradients generated transversely to the powder layer in the shell are kept in a stable, immobile state will; and

12 schematically shows a device for depositing the radiation-absorbing, powdery material in the Shell of the compensation filter arrangement shown in FIG.

Fig. 1 shows only very schematically a device for recording radiation with a radiation source 1, which in is generally an X-ray tube, an object plane 2 in which is to be examined by the X-rays Object 3 is located, and an image plane 4 in which the image reproduction medium 5 is located. In the example shown a radiation-sensitive film is assumed for the image reproduction medium, but it goes without saying that that uses a fluorescent display screen, electronic image intensifier, or similar arrangement as well could be.

. Due to the different thickness and composition of the object 3, the average radiation intensity - as already discussed above - in different

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those areas of the passing through the object 3 Radiation levels can vary, causing unacceptable fluctuations in exposure in these areas would result in the film 5, which would result in the disadvantages described above.

To compensate for the absorption differences in the different areas of the object 3 and thus the exposure of the film 5, an apparatus according to the invention is provided. This device consists of a compensation filter arrangement 6, which is in the beam path between radiation source 1 and object plane 2, preferably close to the radiation source 1 is inserted. The compensation filter arrangement 6 is shown only very symbolically in FIG. 1, but a number of different Embodiments of such a compensation filter arrangement described below. The fundamental characteristic feature of this compensation filter arrangement lies in absorbent filter elements, the type and shape of which can be changed in such a way that the absorption values are within the different areas of radiation can be changed or selected essentially independently, however, without any local discontinuity occurring in the absorption, the corresponding shadow images on the film 5 could generate. Furthermore, there is the compensation filter arrangement 6-with electrically working control

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elements 7 provided, "or coupled to them, by means of which the absorption values of the compensation filter arrangement 6 in the different areas of the radiation can be determined in relation to the control signals given to the control elements. The arrangement according to the invention also has radiation detectors 8a" to 8e, which, viewed from the radiation source 1, lie beyond the object plane 2 in order to receive or measure the intensity strength influenced by the compensation filter arrangement 6 and the object 3 in the various regions of the radiation. These radiation detectors produce output signals that represent values of this intensity. In the example shown in Fig. ^ 1 these radiation pick-up elements consist of six separate radiation detectors 8a to 8e, which pick up or measure the radiation intensity in six different areas of the radiation} it is assumed that the control elements 7 the absorption values of the compensation filter arrangement 6 in can change rich the same six Strahlungsbe- M. The output signals from the radiation detectors 8a to 8e are connected to the respective differential amplifiers 9a to 9e which also receive general reference signals from a terminal 10. The output signals from the amplifiers 9a to 9e are given as control signals to the control elements 7 for the compensation filter arrangement 6.

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It can be seen from this that the arrangement according to the invention is a closed control system which is automatic the adjustment of the compensation filter arrangement operates so that the average intensity in the Image plane 4 in the different areas of the radiation that is recorded by the radiation detectors 8a to 8e, becomes essentially constant and assumes a value which is determined by the amplitude of the reference signal at terminal 10 is determined.

Furthermore, it is evident that the degree of accuracy and perfection in balancing the average Exposure in the image plane 4 is mainly determined by the appearance of the compensation filter arrangement 6 is, but in particular by the number of different radiation sections in which the absorption values of the compensation filter arrangement are independent of one another can be changed or selected.

In FIG. 1, the radiation detectors 8a to 8e are seen from the radiation source 1 on the other side of the image plane arranged. In this case, the compensation filter arrangement 6 can be set so that when the film lies in its receiving position, this film and the film cassette are transparent to the radiation and the radiation detectors 8a to 8e sufficient sensitivity

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have, so that the setting of the compensation filter arrangement can be chosen to be so low that the radiation intensity from the radiation source 1 does not produce any image Can cause exposure on the film 5 ". On the other hand, the setting of the compensation filter arrangement 6 must be without Any film 5 can be carried out in the image plane 4, the film only being brought into the image plane 4 afterwards and the real exposure is performed for radiation recording of the object. To avoid that ^ Object 3 »exposing the patient to an unnecessarily large radiation dose is the compensation filter arrangement 6 preferably set for a considerably lower radiation intensity than the intensity required for the following Radiation recording of the object on the imaging medium is used.

On the other hand, the radiation detectors 8a to 8e could of course also be located between the object plane 2 and the image plane 4

are arranged, in which case the detectors ent- ^ neither would have to be sufficiently translucent so as not to have any shadow images on the image recording medium in the beam path 5, or they would have to be attached in a way that allows them to be used after adjustment the compensation filter arrangement 6, but before the actual recording exposure of the image recording medium to remove from the beam path.

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Furthermore, an arrangement according to the invention can be distinguished in such a way that the removal of the filter arrangement 6 is made possible from the beam path, with the conductor arrangement set outside the beam path and then back to a previously precisely “determined position within the beam path before the exposure to be recorded of the object can be brought. In this case, however, acts it is evident during the adjustment of the compensation filter arrangement not a closed control system, which is why the different absorption values in the different areas of the ladder arrangement through the controls 7 can be set to values as a function of the control signals from the differential amplifiers 9a to 9e which complement each other to the absorption values of the object 3 in their respective different areas.

Fig. 2 shows a simple embodiment of a device according to the invention, in which the previously adjustable compensation filter arrangement consists of two solid bodies 11a and 11b consists of radiation-absorbing material, which can be moved relative to one another and to the rays of the radiation source 1 in a plane essentially perpendicular to the direction of radiation. Are the The absorber body is wedge-shaped, so the degree of absorption of the radiation areas passing through these absorber bodies can be by changing the position of these absorber bodies

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be ized. The absorber bodies are moved by servomotors 12a and 12b, which are driven by the output signals of the differential amplifier 13a and 13b can be controlled. These two differential amplifiers are on the one hand by the output signals of the radiation detectors 14a and Hb, respectively, which act on those passing through the absorber bodies 11a and 11b Radiation components are excited, and on the other hand by a reference signal of a radiation detector 15 »the on the middle Radiation component responds which has an intensity that is essentially independent of the position ™ of the absorber bodies 11a, 11b having. Accordingly, the two absorber bodies 11a, 11b are automatically moved into a position in which all radiation detectors 14a, 14b and 15 essentially receive the same radiation intensity, whereby a balanced average exposure of the edge and middle parts of the film 5 is reached.

Pig. 3 shows an embodiment of the invention that uses {| can be used on a so-called under table, i.e. for an apparatus mainly used for radiography of the trunk a patient 3 is used. In this embodiment of the invention, too, the compensation filter arrangement consists of one Number of solid bodies made of a radiation-absorbing material, which can be moved relative to one another and to the beam path are. A row of absorber bodies 16a, 16b and 16c are in front of the patient 3 on each side of the median plane.

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seen, which are rotatably connected to each other. Of simplicity for the sake of this, the corresponding arrangement of absorber bodies is on the other side of the central plane through the patient 3 not shown in the drawing. In the example shown, three are rotatably connected to one another Absorber body 16a to 16c provided on each side. This rotatably connected absorber body can, for example, from of the type described in detail in U.S. Patent Application 113,013. The slewing rings between the Absorber bodies 16a to 16c and the free ends of the two outer absorber bodies 16a and 16c are equipped with four servomotors 17a, 17b, 17c and 17d connected in any suitable manner, so that the absorber body in a substantially can be moved in the direction perpendicular to the beam path. Each of these servomotors 17a to 17d is controlled by the Output signal of the associated differential amplifier driven. For the sake of simplicity, the drawing shows only the amplifier 16a for the servo motor 17a. In the same way as in the foregoing a number of radiation detectors 19a, 19b, 19c and 19d are arranged below the object plane, in which the patient 3 is located in order to receive the intensity values of the radiation areas that are transmitted by the position of the absorber body 16a to 16c can be influenced. In the example shown, these are radiation detectors 19a to 19d are elongated and extend parallel to the direction in which the absorber bodies 16a to 16c are

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can be moved away. Furthermore, an elongated reference detector 20 is provided, which in the central plane through the Patient 3 is arranged and accordingly picks up the intensity of the central region of the radiation. The output signal this reference detector 20 is used as a reference signal for all servomotors, and it is accordingly used in FIGS Differential amplifier 18a given for the servo motor 17a. In the same way, the output signals from the radiation detectors 19a to 19d are used as control signals for the servomotors 17a to 17d, and therefore the output signal is given from radiation detector 19a to amplifier 18a for servo motor 17a. The signals for the servomotor ver ~ stronger, for example the amplifier 18a, however, are sent to the amplifier via a potentiometer 21 for the reference signal from the reference detector 20 and via another potentiometer for the output signal from the associated radiation detector transmitted, for example the potentiometer 22a for the Aus ™ output signal from the detector 19a. These potentiometers work in connection with the actual position of a main diaphragm 23, which is used to delimit the radiation from the radiation source 1 is used. This diaphragm basically consists of four diaphragm plates, which can be moved in pairs relative to one another and determine the size of a rectangular aperture. The potentiometer 21 for the reference signal from the reference detector 20 works depending on the position of the aperture plates, which determine the size of the aperture in the longitudinal

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direction of the reference detector 20 ″, whereas the potentiometer for the output signals from the other radiation detectors, for example the potentiometer 22a for the output signal of the detector 19a, work depending on the position of the diaphragm plates, which work in parallel with the size of the diaphragm opening It should also be noted that here a potentiometer 22 is provided for each radiation detector 19. With the aid of these potentiometers 21 and 22a a compensation for the shimmering effect of the main screen 23 on the detectors 20 and 19 is achieved compensation is necessary because the detectors are not point-shaped but oblong. It is clear that without such a dependent of the illuminated parts of the radiation detectors compensating the positions of the absorber body have been changed when the setting of the main orifice is changed 23, which is of course undesirable as this becomes a fe would lead to a noble setting of the absorber body.

From the in Pig. 2 and 3 shown embodiments of the invention and from what has been described above it is evident that the degree of accuracy and perfection in compensating for the exposure, which is achieved by the arrangement according to the invention is achieved with solid absorber bodies, largely from the number of absorber bodies, from their Shape, the arrangement to one another and the possible

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changes in their positions depend on one another. It should also be mentioned that it might be necessary for different types of objects to be x-rayed and different arrangements of absorber bodies are available. For one To fully compensate the exposure, it may be necessary to move a large number of them against each other To have absorber bodies that must have such a shape and must be movable relative to one another in this way, that they do not cause any discontinuity in the absorption, since such discontinuities correspond to shadow images were bring. Accordingly, a compensation filter arrangement with movable solid bodies made of a radiation-absorbing material still have certain disadvantages.

These disadvantages are largely addressed in a compensation filter arrangement des in the Pig. 4 to 8 turned off. In this filter arrangement that consists radiation-absorbing medium consisting of a liquid 24 which is enclosed in a thin and flat chamber 25, which can be arranged in a plane substantially perpendicular to the direction of radiation. This radiation-absorbing Liquid 24 can, for example, be mercury, any other liquid metal, or a solution or a stable suspension of a radiation-absorbing substance such as an aqueous solution of oesium acetate. The flat chamber 25 has a flat bottom 26

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and a top cover that. consists of an elastic, flexible screen 27, "for example made of Q-umrni,". The perimeter side the chamber 25 is in communication with a container (not shown in the drawing), the radiation-absorbing Contains liquid 24, it being provided that the chamber 25 is always filled with liquid. One Number of stiff but flexible wires 28 are attached to the top of the rubber cover 27 at various points, the over the surface of the diaphragm 27 in a certain pattern, for example a triangular grid pattern (Fig. 5) are distributed. These wires 28 lead through corresponding channels 29 in a plate-shaped guide part 30, which is arranged directly above the liquid chamber 25. The other ends of the wires 28 are at separate ends Servomotors 31 coupled, which are arranged around the guide part 30. It is conceivable that the wires and the associated channels 29 in the guide part 30 interact in the manner of Bowden cables. By means of the servomotors 31 and the wires 28 coupled to it, the various parts of the flexible screen 27 can either be removed from the floor 26 of the chamber 25 can be withdrawn, whereby the thickness of the liquid layer 24 increases, or they can be in Direction of the bottom 26 are pressed, whereby the thickness of the liquid layer is reduced. In this way it is possible to determine the thickness of the liquid layer in the chamber 25 and thus the absorption value of the filter arrangement

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within each section of the filter assembly corresponding to the connection points of the wires 28 to the diaphragm 27 change. Since the diaphragm 27 is elastically flexible, the thickness of the liquid layer 24 can be changed smoothly, so that there are no sudden differences in absorption between the adjacent parts of the filter assembly can.

The flexible screen 27 preferably has greater strength within the parts enclosed by the connection lines between connection points of the wires 28 than in those parts which extend along and directly adjacent to these connection lines. This can be achieved with a diaphragm as shown in FIGS. In this diaphragm, the area 32 which lies within the connection lines between the connection points 33 for the wires 28 is thicker and accordingly stronger than the areas 34 which extend along and directly adjacent to the connection lines between the connection points 33 of the wires.

Liquid chamber 25, wires 28 and guide part 30 are made of a material that has a low Has radiation absorption factor, and, since all dimensions of these elements are essentially the same and constant over the entire filter arrangement, they are not applied to any

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significant differences in absorption in the beam path Have a share.

The servomotors 31 for the wires 28 are of course controlled by appropriate radiation detectors, which are arranged beyond the object plane, this process being essentially in connection with the Pig. 1 described has been. Accordingly, a corresponding radiation detector must be provided for each servomotor 31, and these radiation detectors should be in one to the pattern of the connection points of the wires 28 on the flexible screen 27 corresponding pattern can be arranged. One should realize that the degree of accuracy and perfection the exposure compensation can increase or decrease, depending on whether the number of with the different points on the flexible screen 27 connected wires 28 is larger or smaller.

This compensation filter arrangement consists of one large number of individual elements, since the number of radiation detectors and the number of servo circuits must be the same the number of different sections of the filter arrangement in which the absorption values can be changed independently of one another meant to be. In this regard, the compensation filter arrangement as shown in Pig. 9 is shown, a more advantageous embodiment.

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Pig. 9 shows schematically]! a device for recording radiation, consisting of a radiation source 1, the object 3 to be x-rayed and the image recording medium in the form of a radiation-sensitive film 5. The previously adjustable compensation filter arrangement consists in this Pail consists of a flat shell 35 which is attached in a plane substantially perpendicular to the direction of radiation and carrying a layer of a moldable or imageable mixture 36 containing a radiation absorbing substance. The formable mixture 36 can consist, for example, of a powder which is mixed in this way with a suitable binding compound is that the powder particles stick together, or from a paste or a gelatinous mass. the Absorption values of the piiter arrangement in different areas the radiation are determined by the thickness of the layer 36 in the corresponding sections on the shell 35, and this thickness of the radiation absorbing layer can be obtained by forming or molding the top surface of the layer to be changed. For this purpose, the embodiment shown consists of a container or distributor 37, which carries the formable, radiation-absorbing mixture in itself and which moves over the shell 35 in the direction of arrow 38 can be. At the lower rear edge of the distributor 37 is an elongated, slot-shaped discharge opening for the radiation absorbing mixture is provided which extends across the shell 35. The lower edge of this au-

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Dispensing opening can preferably be through the bottom plane of the tray 35, whereas the upper edge of the dispensing opening is formed by an elastically flexible lip or spatula 39 is, for example, by a rubber band. A number of servomotors 40a to 40e are connected to this spatula 39 in such a way that that this can be moved essentially in the direction of radiation, creating different spaces for Bottom 35 of the shell can arise in different sections along the opening. The fact that the servomotors 40a to 40e continuously the spaces between the various sections of the spatula 39 and the bottom of the bowl 35, while the distributor 37 is simultaneously moving in the direction 38 relative to the shell 35, it is possible in the shell 35 is a layer of the malleable and radiation-absorbing To produce mixture 36 with different thickness and thus different absorption.

The servomotors 40a to 40e are controlled by the signals from respective differential amplifiers 41a to 41e, on the one hand a reference signal and on the other hand the output signals of the corresponding, elongated Radiation detectors 42a to 42e received below the image plane 4 to one another and to the direction of movement 38 of the distributor 37 are arranged in parallel.

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Furthermore, a blend plate 43 is with a Slit-shaped opening 44 arranged below the shell 35. The opening slot 44 is parallel to the spatula 39 of the Distributor 37 and the blend plate 43 is moved in the same direction as the distributor 37 in such a way synchronously with this ", that the part of the radiation which passes through the opening slot 44 is identical to the part of the radiation is passed through the tray 35 and through the radiation absorbing layer 36 adjacent to the spatula 39 of the manifold 37 passes through.

This compensation filter arrangement is preset in the following way: If with the shaping or formation of the Layer of the radiation-absorbing mixture 36 is started in the tray 35 ", the manifold 37 is in an" on the drawing shown on the far right. The radiation component from the radiation source 1 runs through the slot opening 44, shines through the right part of the object 3, which is to be X-rayed, and falls on the right Parts of the radiation detectors 42a to 42e. Move in conjunction with the control signals from the amplifiers 41a to 41e the servomotors 40a to 40e the lip or spatula 39 in such a position that the formable layer 36 in the Shell 35 is given such a thickness that the sum of the absorption in this layer and in the object 3 is essentially constant and over the entire radiation part that

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passes through the opening slit, what becomes uniform means that all detectors 42a to 42e receive an essentially equally strong radiation intensity. While the manifold 37 and the diaphragm 45 are moved to the left in the drawing, the position of the spatula 39 is according to and then changed by the servomotors 40a to 40e in such a way that the radiation-absorbing layer 36 in the shell 35 is molded over the entire surface of the shell in order to obtain absorption values which are essentially reversed are proportional to the absorption values of the object 3 within the corresponding radiation areas.

After this pre-setting of the compensation filter arrangement the aperture 43 is removed from the beam path, so that the entire object 3 for radiation recording of the rays can be transilluminated.

After the X-ray exposure of the object, the distributor 37 is brought into its initial position, this manifold having such a shape that during its backward movement the layer of radiation-absorbing Mixture 36 in the bowl 35 is leveled.

In the case of the one just described and shown in FIG Compensation filter arrangement was assumed that the formable layer arranged, radiation-absorbing mi-

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Mixture 36 in the shell 35 has such an internal consistency, for example that of a paste, a gelatinous Mass or a powder mixed with a suitable binding substance that the upper surface of the Layer can be easily formed or shaped and then can maintain its shape. It has, however has shown that it is also possible to use an internally dissolved and freely movable powder of a radiation-absorbing material to use, for example a plastic material with radiation-absorbing substance. The upper surface Of course, a layer of such an internally dissolved powder cannot be formed or formed without special precautions be shaped so that the amount of depressions and elevations required by the invention with relative steep sides is reached. It has been shown, however, that it is possible to have such a layer with internally loose and floating powder in an extremely stable state, with the top surface of the layer formed with depressions and elevations on very steep sides or can be shaped, these remaining essentially unchanged after the shaping process by an air pressure gage is built up across the layer from the upper side to the lower side. Such a pressure gradient can preferably be produced in that the shell carrying the powder layer has a bottom which is permeable to air, but not to the powder, and that

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Means for generating a reduced air pressure are provided below this perforated bottom in the shell are. The air-permeable bottom of the shell can for example consist of a stretched, fine fabric.

Fig. 10 shows schematically and in cross section a compensation filter arrangement according to the invention, the is based on the principle described above. This compensation filter arrangement can basically be used in the same way as in Pig. 9 shown Filter arrangement.

The filter arrangement shown in Fig. 10 thus has a shell 35, which is in the same way as the filter arrangement in Fig. 9 is suitable to carry a layer 36 of radiation-absorbing material in this Case consists of internally loose and freely movable powder. In contrast to the filter arrangement shown in FIG however, the filter arrangement in FIG. 10 has one Tray 35 with perforated bottom 45, which is for. Air is permeable, but not for the powder material 36. In addition a suction chamber 46 is provided below the air-permeable bottom 45. This suction chamber 46 is in a known manner shown only schematically on the drawing and is connected to an air pump 47, whereby a reduced air pressure can be produced in this suction chamber 46. as

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Result of this reduced pressure in the chamber 46 and as The result of the air flow through the powder layer 36 and the air-permeable base 45 is created within the powder layer 36 an air pressure gradient. Under the action of this pressure gradient the powder layer assumes an extremely stable state so that the upper surface of the powder layer receives can be easily formed or shaped, while maintaining depressions and bumps with very steep planks.

The formation of the top surface of the powder layer 36 is used to create a desired variable Thickness carried out in a manner similar to that of the Filter arrangement according to Pig. 9 »by using an elongated, elastically flexible scraper or a corresponding scraper knife 48, which extends transversely to the shell 35, is moved over the shell in the direction of arrow 49, and at the same time the scraper 48 is set by servomotors 40a to 40e at a desired distance from the bottom 45 of the tray. As described above, this distance between scraper 48 and bottom 45 of the tray can be in different sections be different along the length of the scraper. During its movement over the tray 55 in the direction 49 digs itself, the scraper 48 in the powder layer 36 and leaves with a molded or formed powder layer 36a different thickness behind. The excess powder

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material from the surface of the original leather layer 36 is removed by suction into a container 51 through an elongated suction nozzle 50 located at the top of the Scraper 48 is located. The servomotors 40a to 40e control the position of the scraper 48 and are operated in the same way as in FIG the one in Pig. 9, the conductor arrangement illustrated is controlled by signals from the radiation detectors 42a to 42e; included the scraper 48 is moved synchronously with the slit screen 43 via the shell 35. After shaping or formation of the Powder layer 36 becomes the exposure of the object for radiation recording carried out in the manner described above. Before repeating the training Powder layer 36 in the tray 35 for radiation recording Another object occurs, that is removed from the shell 35 during the previous shaping of the layer 36 Powder material replaced again, so that again a powder layer 36 of substantially uniform thickness is produced which can then be treated again in the manner described above.

In the compensation filter arrangement according to the invention according to Pig. 10 is the radiation-absorbing, powder-shaped Material initially arranged in a layer of uniform thickness in the tray 35, then this layer by removing different ropes, the original layer is given the desired, different thickness.

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However, it is also possible to place the radiation-absorbing, powder-like material on the air-permeable base 45 the shell 35 ″ from the beginning in a layer with the desired, different thickness to be deposited, wherein at the same time, an air pressure gradient across the deposited powder layer is maintained in the manner described above it becomes that this powder layer remains in a stable state and maintains its different thickness.

Pig. 11 shows schematically and by way of example a compensation filter arrangement which works in this way.

The compensation filter arrangement shown in FIG. 11 also has, like the conductor arrangement in Pig. 10 ₈ a bowl 35 with a perforated bottom 45 "which is permeable to air", but not for the radiation-absorbing powdery material, and a suction chamber 46 arranged below the bottom 45 of the bowl and connected to an air pump 47. Purely the deposition of the desired, radiation-absorbing powder layer 36 in different thicknesses. A device 52 is provided on the shell 35, which emits a fine jet 53 of the radiation-absorbing powder which is directed into the shell 35. This arrangement 52 is related to a directional element 54 which directs the powder jet 53 over the entire surface of the shell 35

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measured a predetermined scan pattern can be deleted and also changes the strength of the powder jet, i.e. the flow rate of the powdery material in the jet " By moving the powder jet 53 over the tray 35 'in a linear scanning pattern, i.e. in one process works like a TV picture tube, and through the simultaneous Modulation of the strength of the powder jet 53, it is accordingly possible to hit the bottom 45 of the shell 35 to deposit a powder layer with different thicknesses, which due to the acting through the layer Pressure-oil gradient in a stable, immobile state is held.

The radiation-detecting elements for recording or measuring the intensity of those passing through the object 3 Radiation consist in this Pail of an arrangement for an electronic scanning of the radiation image of the Object 3, being scanned in a predetermined pattern and generating a video signal that at each moment the intensity of the part of the radiation image just scanned is proportional. Like in Pig. 11 shown, can this device for electronically scanning the radiation image of the object 3 is an image intensifier known per se 55, which converts the radiation image into a corresponding optical image, and a television eye 56 can see this optical image. The pick-up tube 56 generates in known

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ter way, a video signal that corresponds to the intensity values of the scanned points in the radiation image of the object proportional amplitude ". This video signal from the Pick-up tube 56 is fed to assembly 54 via a signal connection line. Sync signals or other those Signals related to image scanning of the pickup tube 56 " likewise supplied to the arrangement 54 via the signal connecting line 57. In the arrangement 54, the key signals and the video signal from the pickup tube 56 on the one hand for controlling the scanning movement of the powder jet 53 on the shell 35 and on the other hand used for changing the intensity of the powder jet in such a way that the powder jet 53 is moved over the tray 35 along the scanning pattern which corresponds to the scanning pattern of the pickup tube 56 and the intensity of the powder jet 53 is changed in accordance with the variable amplitude of the video signal.

Mg. 12 shows schematically and using an example an embodiment of the assemblies 52 and 54 for creating and controlling the powder jet 53 in a filter assembly disclosed in Pig. The type illustrated in FIG. 11. The arrangement 52 for The generation of the fine powder jet 53 consists of a cylindrical container 58 with the powdery material is filled and in which a rotatable paddle wheel is mounted, which is driven by a suitable motor 60 will. A thin tube 61 extends through the

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cylindrical outer wall into the container 58 such that the inner end of the tube passes the blades of the wheel 59. The blade ends have recesses for the end of the tube 61 to pass through. By turning the paddle wheel 59, the powdery material in the container 58 is forced through the thin tube 61 as a finely focused powder jet to resign.

The arrangement 54 for controlling the powder jet 53 has two pairs of deflection plates 62 and 63 for the electrostatic Deflection of the beam 53 in two orthogonal directions. By applying a suitable electrical Potential at the deflector plates 62 and 63, it becomes possible to direct the powder jet 53 in a desired direction and in one Deflect desired angle, whereby the powder jet 53 over the shell 35 according to the desired scanning pattern can be moved. The necessary deflection voltages for the deflection plates 62 and 63 are provided by a control unit 64, in which the video signal from the pickup tube 56 is fed via the signal line 57. Pure the Intensity modulation of the powder jet 53 is provided another pair of electrostatic deflector plates 65, which can be fed from the control unit 64 with a deflection voltage with such a large amplitude that the Powder jet 53 is deflected very sharply in the direction indicated by the dashed arrow 66, as a result of which the powder jet

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the shell 35 is not reached at all, but instead is collected in a container not shown in the drawing will. By pulse modulating the supply voltage for the baffles 65, a pulse rate or a Pulse ratio, which changes depending on the video signal from the pickup tube 56, it is obviously possible to vary the total amount of powder in the powder jet 53 reaching the tray 35 according to the amplitude of the video signal.

Instead of the intensity modulation of the powder jet 53 in the manner described above, it would also be possible to use a To use powder jet with constant flow rate and the scanning speed of the jet over the cup 35 such to vary the amount of powder deposited in cup 35 within any given range of the scan pattern of the powder jet proportional to the amplitude of the video signal for that given area of the scan pattern will. It should also be noted that in a ladder arrangement this lyps the final radiation absorbing powder layer 36 in the tray 35 gradually over a period of time which takes a few scan cycles of the pickup tube 56 and thus the powder jet 53 includes.

Since an arrangement according to the invention makes it possible to achieve a good balance of the average exposure

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To achieve different areas on the image recording medium, there is also the possibility of an automatic exposure control system to use in the radiation recorder with very good results. Previous attempts at automatic Using exposure control systems in radiation recorders often gives unsatisfactory results because the automatic exposure control is mostly based on the radiation intensity in an image section which is of little importance, resulting in an incorrect exposure of the much more interesting parts of the image because the mean exposure is not uniform in all areas of the image. In connection with an arrangement according to the invention, which brings a very good compensation of the exposure over the entire image, can, however, the automatic Exposure control system can be driven without difficulty, maintaining a correct relationship to the signals consists of the radiation detectors, which record the radiation intensity in the image plane.

In some cases it could be beneficial to the possibility to have to change the degree of exposure compensation so that only partial compensation is achieved. Included It might be easier to recognize anatomical structures from experience, from viewing the images is obtained without any contrast compensation. Such a variable partial compensation can be achieved with an

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Order can be achieved according to the invention, "in which the servomotors controlling the presetting of the compensation filter arrangement are provided with a negative feedback from their output to their input. In Pig Shaft is connected to the absorber body 11a and also to a suitable signal converter W , which generates an electrical signal proportional to the angle of rotation of the servo motor 12a, which is thus proportional to the position of the absorber body 11a, this signal being fed back in phase opposition to the differential amplifier 13a of the servo motor 12a is. By changing the degree of feedback it is obviously possible to change the degree of compensation in the radiographic image.

It is also possible to adjust the degree of exposure or contrast compensation by using radiation to change different energies, i.e. a different voltage on the X-ray tube, namely at the Presetting of the compensation filter arrangement before the radiographic exposure of the object in the following real irradiation for the purpose of recording. The degree of contrast compensation changes in the process radiographic image, since a change in the radiation energy unequal changes in absorption in the too

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translucent object and in the heavy one, the radiation-absorbing one Substance in the compensation filter arrangement performing elements.

The choice · of the compensation filter arrangement too The radiation absorbing substance used is also an important factor for correct exposure compensation on a whole Höntgen picture. So far, in general Absorber body made of aluminum is used. This has the disadvantage that those parts of the radiation that pass through thin and pass through weakly absorbing areas of the object and consequently also through parts of the compensation filter arrangement with a high absorption capacity, there is a shift in the energy distribution spectrum of the radiation experience higher energy values, i.e. towards a harder radiation. As this harsher radiation makes the object easier penetrates, the parts of the object with low absorption, that is, generally the thinner areas of the object Object with lower image contrast placed in the recording device than the areas of the object with higher absorption, generally the thicker areas of the object. However, this can be avoided when used as radiation absorbing Substance in the compensation filter arrangement, a substance is selected whose K absorption edge is within of the energy distribution spectrum of the radiation used for the X-ray exposure is and preferably

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close to the energy value for the maximum intensity of the used Radiation. In the case of X-rays, this means that the radiation-absorbing substance adheres to an absorption edge should, which corresponds to an energy that multiplied by the factor 1.2 Ms 2.0 and preferably 1.4, results in the voltage, which is applied to the X-ray tube during the X-ray exposure. However, this value is not critical, but the voltage applied to the tube can be changed within a comparatively wide range without this as a result, the improved contrast ratios were lost. Suitable radiation absorbing substances are preferred Rare earth metals that meet the above conditions for those commonly used on X-ray tubes Tension filling such as those used in the examination of skeleton and bones and many other cases of softness Tissue constructions are used.

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Claims (1)

Claims 1.] Device for exposure compensation of various Areas of an image recording medium in a device for recording radiation with a radiation source, object plane for a Object to be x-rayed and image plane for this image recording medium, characterized by a compensation filter arrangement located in the beam path between the radiation source (1) and the object plane (2) (6) with radiation absorbing means, the shape of which is so different that the absorption values this radiation absorbing means in different areas of the radiation from the source (1) im can be changed essentially independently of one another by means of control elements (7) for changing the absorption values of the Compensation filter arrangement (6) in different areas of the radiation, the shape of the radiation-absorbing Means can be changed as a function of the control signals given to the control elements, and by the radiation source (1) seen from beyond the object plane (2) arranged radiation detectors (8a-8e) for recording the average intensity values of the different areas of the radiation and for the generation of these intensity values corresponding output signals, the control signals to the control elements (7), which the absorption values of the compensation filter arrangement (6) in the different 209829/0431 determine which areas of radiation are derived from the output signals of these radiation detectors (8a-8e). 2. Device according to claim 1, characterized in that that the radiation-absorbing means of the compensation filter arrangement (6) consists of a plurality of plague bodies (16a to 16c) consist of radiation-absorbing material which, relative to the beam path and individually in a substantially bar Chen are arranged to be moved to the plane perpendicular to the radiation direction, and that the control elements (7) are servomotors (17a-17d), which are coupled to the absorber body (16a-16c) for determining the position of the latter. 3. Device according to claim 1, characterized in that the radiation-absorbing means of the compensation filter arrangement (6) consists of a layer of a formable, radiation-absorbing material, which is in an im is arranged substantially perpendicular to the radiation direction plane, and that the control elements (7) in different Regions of the layer have control elements for changing the thickness of the layer in the direction of radiation. 4. Device according to claim 3 »characterized in that the radiation-absorbing means has a flat chamber (25), which is arranged in a plane substantially perpendicular to the direction of radiation and with a 209829/0431 radiation-absorbing liquid (24) is filled, wherein one of the large walls of this chamber consists of an elastic, flexible screen (27), and that the control elements (31) is connected to the diaphragm (27) via a plurality of separately arranged points (33) on its surface, so that the distance of the diaphragm in these points to the opposite, larger wall (26) of the chamber (25) can be changed is. 5. Device according to claim 4, characterized in that the control elements are a number of servomotors (31) and have associated Bowden cables (28, 29), each Bowden cable having one of its ends with the associated servomotor (31) and at its other end with one of the points (33) on the flexible screen (27) is connected so that each Servomotor by the Bowden cable connected to it a pull or acting essentially parallel to the radiation direction Exerts pressure force on the panel in the connection point of the Bowden cable with the panel. 6. Device according to claim 4 or 5, characterized in that the connection points (33) between control elements (31,28) and diaphragm (27) in a triangular grid pattern are arranged. 09829/0431 7. Device according to one of claims 4 to 6, characterized characterized in that 'the flexible screen (27) has a lower strength within the areas (34) which extend along the connecting lines between connection points (33) of control elements (31, 28) and cover (27), than in the areas (32) of the diaphragm which are enclosed by these connecting lines. 8. Device according to claim 3, characterized in that the radiation-absorbing means have a flat shell (35) arranged in a plane substantially perpendicular to the radiation direction and a moldable layer (36) of radiation-absorbing material lying in this shell and that the control elements to change the thickness / this layer (36) have a deformation arrangement (37 , 39) for its surface. 9. Device according to claim 8, characterized in that the deformation arrangement for the upper surface of the formable layer (36) of radiation-absorbing material on this shell (35) an elongated, elastically flexible Has scraper assembly (39) that looks over the tray extends perpendicular to the radiation direction and relative to the shell in one to the radiation direction and to the longitudinal direction the scraper assembly perpendicular direction (38) is movable, and that the control elements a plurality of servo - 209 829/0 43 1 motors (40a-40e) that have been arranged with the Sc (39) are connected on the long side at intervals in such a way that the distance between the tray bottom (45) and the spatula edge the scraper arrangement (39) is changeable. 10. Device according to claim 9 »characterized in that that a distributor (37) over the tray (35) for the delivery of the radiation-absorbing material through an elongated, Slit-shaped distributor opening is movable into this bowl, the flexible spatula (39) being the upper edge the manifold opening forms. 11. The device according to claim 9, characterized in that the radiation-absorbing material consists of an internally loose and freely movable powder, that the shell (35) has a perforated bottom (45) which is permeable to air and impermeable to the powder, that one System (46, 47) is provided for generating a reduced air pressure below this bottom, whereby an air pressure gradient is established through the powder layer (36) on the shell, which keeps the powder layer in an essentially stable state, that spatula elements (48 ) dig depressions in this powder layer (36) when moving over the bowl, which are determined by the distances between the bottom (45) of the bowl and the spatula elements (43), and that a suction device (50, 51) ent the parts of the powder layer - 209829/0431 ferrite ♦ which are above the cutting edge of the spatula (48). 12, device according to claim 11, characterized in that that the suction device for the parts of the leather layer (36) has an elongated suction nozzle (50) extending along and above the cutting edge of the spatula (48), • 13 »device according to one of claims 9 to 12, characterized in that elongated, Radiation detectors (42a-42e) arranged parallel to one another and to the direction of movement (38) of the scraper arrangement (39) are provided and that a diaphragm (43) with a slot-shaped opening (44) * which extends parallel to the longitudinal direction of the scraper arrangement (39), relative to the beam path and in the same direction (38). the scraper arrangement (39) can be moved synchronously therewith in such a way that that the portion of radiation passing through the aperture (44) is equal to the radiation component that is directly applied to the scraper arrangement (39) through the layer (36) of the radiation-absorbing material in the shell (35) passes through. 14 * Device according to claim 1, characterized in that the radiation-absorbing means have a flat shell (35), which in a direction to the radiation substantially vertical. Level is arranged and the one 209829/0431 Layer (36) of an inwardly loose and freely movable radiation-absorbing powder carries, this shell having a perforated bottom (45) which is permeable to air and is impermeable to this powder, and a suction device (46, 47) below this bottom reduced air pressure is generated, creating an air pressure gradient through the powder layer (36) on the floor (45) is made, which keeps the layer in a substantially stable state, and that control elements (52,54) by the signals of the radiation indicator (55, 56) for the powder delivery on the bottom (45) of the bowl (35) can be controlled in this way are that in each part of the shell a layer (36) is formed with a thickness that is determined by the radiation intensity of the Radiation part is determined beyond the object plane, which runs through the part of the shell. 15. The device according to claim 14, characterized in that the device for powder dispensing has a system (52) for Generation of a fine, on the shell (35) directed powder jet (53) and a directional element (54) has the Powder jet moved over the bottom of the bowl according to a predetermined scanning pattern. 16, device according to claim 15, characterized in that that the directional element (54) for the movement of the powder jet (53) has an electrostatic deflection arrangement (62,63) for the Powder jet owns. 209829/0431 17. Device according to claim 15 or 16, characterized in that that the electronic display (55 »56) shows the radiation image of the object (3) behind the object plane accordingly electronically scans a predetermined scan pattern and generates an electrical video signal representative of the Intensity value of the part of the radiation image scanned at any given moment represents that the directional element (54) is controllably connected for the movement of the powder jet (53) with the image scanning device (56), so that the Powder jet in the scanning pattern over the shell (35) corresponding to the scanning pattern of the radiation image is moving / is, and that the powder jet (53) can be controlled by the video signal in such a way that one of the amplitudes during the scanning movement the amount of powder corresponding to the video signal is deposited in the bowl. 18. Device according to claim 17, characterized in that the change in the flow rate of the powder jet (53) controls a deflector (65) in response to the video signal. 19. Device according to one of claims 1 to 18, characterized characterized in that the control signal for the control elements is proportional to the difference in output signal of the Radiation indicator and a reference signal is. '" 209 829/0431 20. Device according to claim 19 »characterized in that a radiation detector for the generation of this reference signal is arranged beyond the object plane (2) as seen from the radiation source (1). 21. Device according to claim 20, characterized in that the radiation detector (20) for the generation of the Reference signal is arranged in such a way that it can be influenced by part of the radiation which has an intensity which is essentially independent of the various absorption values of the compensation filter arrangement. 22. Device according to one of claims 1 to 21, characterized in that the control elements (e.g. 12a) with a signal generator (70) are connected, which generates signals corresponding to the working position of the control elements represent the absorption values of the radiation-absorbing means (11a) determined by the control elements, these Signals in negative feedback are given to the input of the controls. 23 · Device according to claim 22, characterized in that the feedback factor is variable. 24. Device according to one of claims 1 to 23 for a device for recording radiation with variable 209829/043 Main aperture for restricting the radiation from the radiation source, characterized by signal modifying elements (21,22a), which can be influenced by adjusting the main diaphragm (23) for a modification of the control signals which are output from the radiation detectors (I9a-19d, 20) to the control elements (I7a-17 <ä) in such a way that that the setting of the compensation filter arrangement by the control elements are made essentially independent of the setting of the main panel (25). 25. Device according to one of claims 1 to 24, characterized characterized in that the radiation detectors (8a-8e) seen from the radiation source (1) behind the image plane (4) lie. 26. Device according to one of claims 1 to 24, characterized in that the radiation detectors are arranged between the object plane and the image plane and can be removed from the beam path. 27. Device according to one of claims 1 to 26, characterized in that an automatic exposure control system works as a function of the output signals of the radiation detectors. 209 829/04 31 28. Device according to one of claims 1 to 27, characterized in that the radiation-absorbing means at least one element with a K absorption line within the 3 energy spectrum for the X-ray exposure radiation used by the object. 29. Device according to claim 21, characterized in that that the K-absorption line of the radiation-absorbing element is close to the energy value of the intensity maximum for the radiation that is used in the radiological exposure of the object. 30. Device according to one of claims 28 or 29, characterized in that the K absorption line of the Radiation absorbing element corresponds to an energy that multiplied by the factor 1.2 to 2.0, preferably with a factor of 1.4, the voltage of an X-ray tube used as a radiation source for the X-ray exposure of the object. 51. Device according to one of claims 28 to 30, characterized characterized in that the radiation-absorbing element belongs to the rare earth metals. 0-9 829/0431 Read 11 e