The invention relates to an X-ray image device of the type in which the X-ray image to be formed is built up with the aid of an elongated X-ray detector which is capable of converting incident X-ray radiation into a light image and which performs during operation a scanning movement in a housing of the device in a direction transverse to the longitudinal direction of the elongated X-ray detector.

Such an X-ray image device may, for example, be a device for slit radiography, such as is described, for example, in the Dutch Patent Application 8303156. In the case of such a device for slit radiography, an object or a patient is scanned with the aid of a flat, fan-shaped X-ray beam which is moved during at least one scanning stroke transversely to the surface of the fan-shaped beam. Behind the object or the patient, an elongated X-ray detector moves synchronously with the X-ray beam in such a way that the radiation transmitted through the patient or the object always falls essentially on the X-ray detector. The X-ray detector converts the X-ray radiation received into a light image which can be used to expose a photographic film and/or to generate electrical signals representing the X-ray image. The flat, fan-shaped beam can be obtained, for example, with the aid of an X-ray source which interacts with a slit diaphragm. The X-ray source and the slit diaphragm can be moved jointly or with respect to one another in such a way that the beam leaving the slit diaphragm performs the desired scanning movement. The diaphragm may, if desired, be provided with slit control means such as those described in the Dutch Patent Application 8400845. The invention is, however, also applicable to other types of devices which comprise an elongated X-ray detector which performs a scanning movement in order to scan a predetermined area. An example is described in Dutch Patent Application 9102063.

An elongated X-ray detector suitable for use in

an X-ray image device of the type described above is, for example, an X-ray image intensifier tube as described in Dutch Patent 183914. For use in an X-ray image device suitable for thorax examination, the X-ray image intensifier tube must have an image surface of approximately 400 to 500 mm. This dimension corresponds to the width of the thorax in most people and of the fan- shaped beam. In the scanning direction, the image surface can be, for example, approximately 25 mm high. In order to be able to form a complete thorax image, the X-ray image intensifier tube must traverse an area of approximately 400 x 400 mm ² , which is achieved by allowing the X-ray image intensifier tube to perform a scanning movement in a direction transverse to the longitudinal direction of the X-ray image intensifier tube. During the scanning movement, the X-ray image intensifier tube produces a varying output image which can be used to expose a photographic film, but which is preferably projected onto a photosensitive electronic device which converts the incident light into corresponding electrical signals. The electrical signals can then be stored or used to form a video image or the like, optionally after further processing.

To convert the output signal of the X-ray image intensifier into electrical signals, an elongated CCD device (CCD = charge-coupled device) is generally used. Such CCD devices are obtainable commercially, but have much smaller dimensions than the output window of the elongated X-ray image intensifier tube. A suitable CCD device is, for example, the Dalsa I-FI-2048 which has 2048 x 96 image elements and a sensitive area of 28.7 x 1.34 mm. The output image of the elongated image intensifier tube can be imaged for this purpose in reduced size on the CCD device. For this purpose, use can be made of a camera which comprises a lens system which reduces the size of the output image of the X-ray image intensifier tube to dimensions suitable for the CCD device and images the output image of the X-ray image

intensifier tube on the CCD device. The necessary reduction factor β is, in the given example, approximately 16, which results in a fairly large spacing d (Figure 1) between the X-ray image amplifier tube and the camera and consequently in a relatively large depth of the housing of the X-ray image device. A drawback of a large depth of the housing of the X-ray image device is the large installation space which such an X-ray device takes up and also the effort involved in installing and/or moving such a bulky X-ray device. Another aspect is that the housing of the X-ray image device has to be lightproof. The bigger the housing is, the greater is the chance generally of a locally incomplete sealing.

There is therefore a need for an X-ray image device having a more compact construction than the known

X-ray image devices. For this purpose, according to the invention, an X-ray image device of the type described above is one wherein at least one mirror is mounted in the housing of the device and at least partially receives the light image formed by the X-ray detector during operation in every position of the X-ray detector during the scanning movement and reflects it to at least one camera which moves synchronously together with the X-ray detector and which is mounted near one of the ends of the elongated X-ray detector.

The invention will be described in more detail below with reference to the accompanying drawing of some exemplary embodiments.

Figure 1 shows diagrammatically in side view/cross section an example of an X-ray image device according to the prior art;

Figure 2 shows diagrammatically the device of Figure 1 in plan view;

Figure 3 shows diagrammatically in plan view a first exemplary embodiment of a device according to the invention;

Figure 4 shows diagrammatically in plan view a second exemplary embodiment of a device according to the

invention;

Figure 5 shows diagrammatically in plan view a third exemplary embodiment of a device according to the invention; and Figure 6 shows diagrammatically in plan view a fourth exemplary embodiment of a device according to the invention.

Figures 1 and 2 show diagrammatically in side view and plan view an example of a known X-ray image device 1. The device shown comprises an X-ray source 2 provided with a slit diaphragm 3 via which a flat, fan- shaped X-ray beam 4 is directed onto a patient 6 to be investigated or onto an object to be investigated placed in front of a housing or cabinet 5. In the example shown, the X-ray source 2 can swivel together with the slit diaphragm 3 round an axis 6, as shown by an arrow 7. The fan-shaped X-ray beam 4 swivels during this process in a direction transverse to the surface of the fan- shaped X-ray beam, as indicated in Figure 1 by an arrow 8, in order to scan the patient or the object, or at least a relevant part thereof, with the X-ray beam during one or more working strokes.

The cabinet 5 has a front wall 9 which is transparent to X-ray radiation and behind which there is an elongated X-ray detector 10. The X-ray detector is coupled to the X-ray source 2, which swivels during operation, in such a way, not shown in greater detail, that the X-ray radiation transmitted by the patient or the object 6 always falls on the entry window of the X-ray detector 10. The X-ray detector 10 therefore moves synchronously with the flat, fan-shaped beam 4, as indicated by arrows 11.

The X-ray detector 10 is designed to convert the X-ray radiation incident at the input side into a light image which is produced at the output side. In the example shown, a tubular X-ray detector is used having an elongated cathode 12 which is sensitive to X-ray radiation and which emits electrons under the influence

of incident X-ray radiation. Situated opposite the cathode 12 is an elongated anode 13. The emitted electrons move under the influence of a high voltage, prevailing in operation between the cathode and the anode, from the cathode to the anode. The anode converts the incident electrons into light quanta. The light image thus formed at the anode side is projected via a lens or a lens system 14 onto a photographic film or, as shown, onto a photosensitive semiconductor device, such as a CCD 15, which converts the light image into corresponding electrical signals which can be processed and/or stored in a device not shown. The lens system 14 and the film or semiconductor device form part of a stationary camera which is placed at a distance from the X-ray detector 10 so that the camera can receive the output image of the X-ray detector 10 in every position of the X-ray detector 10 and can project it onto the semiconductor device or film.

The associated distance d between the X-ray detector and the camera is relatively large so that a fairly deep housing 5 is necessary and must be completely lightproof.

Figure 3 shows diagrammatically in plan view a first example of a device according to the invention. In Figure 3 and in Figures 4 to 6 inclusive, the parts of the X-ray device which are not essential for a good understanding of the invention are not shown. In Figure 3, the image surface at the anode or the output window of the X-ray detector 10 is indicated by 20. Arranged near one of the ends of the elongated strip-shaped image area 20 is a camera 21 having a lens or lens system 22 and, in this example, a photosensitive semiconductor device 23, referred to below as a CCD. The camera 21 can be moved together with the X-ray detector 10 when the X-ray detector 10 traverses a scanning path. For this purpose, the X-ray detector 10 and the camera 21 may be mounted, for example, on a common support. Such a support is indicated diagrammatically at 24. The support 24 can

also form a carriage or be mounted on a carriage which is driven during operation by means of a suitable drive means in order to traverse the scanning path.

Arranged opposite the X-ray detector 10 and the camera 21 is a mirror 25 which reflects the image surface

20 of the X-ray detector in the direction of the lens system 22 of the camera 21. In this example, the mirror

25 is a single, fixed flat mirror, but this is not strictly necessary. In this embodiment, the mirror 25 has a length corresponding to the scanning path perpendicular to the surface of the drawing. By using the mirror 25, the depth needed for the housing of the

X-ray device is approximately halved, which provides an appreciable space saving and reduces the probability of light leakages.

Figures 4 and 5 show two other exemplary embodiments, in each of which two mirrors 30, 31 or 40, 41, respectively, placed at an angle to one another are used with associated cameras 32, 33 or 42, 43, respectively. The cameras are now mounted in each case at both ends of the elongated X-ray detector 10 and are preferably again mounted together with the X-ray detector 10 on a diagrammatically indicated common support 34 or 44, respectively. The mirrors 30, 31 or 40, 41, respectively, are stationary in this example and are placed in a V shape, the V shape being placed with the apex turned toward the image surface 20 in Figure 4, while the apex of the V shape is turned away from the image surface in the exemplary embodiment of Figure 5. The apex of the V shape coincides in both examples essentially with the central plane perpendicular of the image surface. In this embodiment, each of the mirrors images half, and preferably somewhat more, of the image surface on the lens system of one of the cameras, as a result of which the installation depth required is reduced further. In addition, compared with the embodiment having a single mirror, a smaller reduction of the output image of the X-ray detector 10 is necessary

and a larger CCD surface can be used. This results in a better signal/noise ratio, a better modulation transfer function (MTF) and a greater dynamic range in the electrical signals formed by the CCD. In the embodiment of Figure 5, each mirror interacts with the camera which is furthest from the mirror. The mirror 40 is situated, for example, opposite the image surface half 20a, but interacts with the camera 43 which is situated near the end of the other image surface half 20b. In the same way the mirror 41 situated opposite the image surface half 20b interacts with the camera 42 situated near the end of the image surface half 2 ₀ a.

In the examples shown, the two mirrors are adjacent to one another. It is also possible, however, to place the mirrors at some distance from one another. In principle, it is also possible to use curved mirrors instead of flat mirrors.

In addition, stationary mirrors are used in the examples shown and these have a relatively large length corresponding to the length of the scanning path perpendicular to the surface of the drawing.

As an alternative it is possible to use one or more smaller mirrors which move together with the camera(s) and the X-ray detector 10. This also opens up the possibility of mounting the mirror(s) together with the X-ray detector 10 and the camera(s) on a common support.

Such an embodiment is shown diagrammatically in Figure 6 by way of example. Figure 6 again shows an image surface 20 which represents the output image of the elongated X-ray detector 10. Placed at both ends of the image surface is a camera 50 or 51, respectively. Mounted near each camera is, in addition, a relatively small mirror 52 or 53, respectively. Both the mirrors and the cameras move during operation together with the X-ray detector 10 along the scanning path. For this purpose, the mirrors 52, 53 and the cameras 50, 51 are preferably mounted together with the X-ray detector on a

common support. Preferably, the common support is formed by the housing of the X-ray detector. Such a support is indicated diagrammatically by broken lines at 54. The mirrors 52, 53 may have a small height in the direction perpendicular to the surface of the drawing because the image to be projected onto the camera placed opposite each mirror also has only a small height. The mirrors can therefore be of strip-shaped construction and be placed at an angle with respect to the image surface 20 which is such that the half of the image surface situated near a mirror can be reflected by the mirror to the camera situated opposite. Thus, in the arrangement shown in Figure 6, the camera 50 interacts with the mirror 53, while the camera 51 interacts with the mirror 52. The support 54 may form part of a carriage or be mounted on a carriage which is coupled in a known manner to drive means and guide members so that the carriage can traverse the desired scanning path during operation.

The common carrier can advantageously be constructed as a flat, lightproof cabinet in which the X- ray detector, the cameras and the mirrors are mounted. The housing 5 of the X-ray image device no longer has to be lightproof in that case. The lightproof cabinet containing X-ray detector, cameras and mirrors can advantageously be constructed as a preassembled unit which can be mounted or removed or replaced as a single entity. The lightproof cabinet must, of course, be provided, at the position of the cathode of the X-ray detector, with a window which is essentially transparent to X-ray radiation and which may be composed, for example, of plastic or a thin metal plate.

It is pointed out that, after the above, various modifications are obvious to the person skilled in the art. Thus, the mirrors 52, 53 may in principle be of longer construction and even adjoin one another at the height of the central plane perpendicular of the image surface. In addition, the X-ray device may be provided with slit control means or image equalization means known

per se. These and similar modifications are deemed to fall within the scope of the invention.