WO2011000784A1

WO2011000784A1 - X-ray tube, mammography apparatus and method for generating x-ray images

Info

Publication number: WO2011000784A1
Application number: PCT/EP2010/059052
Authority: WO
Inventors: Sven Fritzler; Peter RÖHRER; Peter Schardt
Original assignee: Siemens Aktiengesellschaft
Priority date: 2009-07-03
Filing date: 2010-06-25
Publication date: 2011-01-06
Also published as: DE102009033074A1

Abstract

The invention relates to a X-ray tube (1) with an anode (2) and a cathode (4) for generating an electron beam (8, 8a, 8b) between the cathode (4) and the anode (2), wherein a deflection unit (6) for deflecting the electron beam (8, 8a, 8b) is disposed between the cathode (4) and the anode (2). The deflection unit (6) allows the electron bean (8, 8a, 8b) to be selectively aimed at least at a first focal spot position (10), and a different second focal spot position (10a, 10b, 10c, 10d), on the anode (2). Furthermore, the invention relates to a mammography apparatus with an X-ray tube (1) and an X-ray detector (14), wherein the X-ray tube (1) is movably mounted for capturing X-ray images of the female breast (18) from various angles, and to a method for generating X-ray images of the female breast (18) with such a mammography apparatus.

Description

description

X-ray tube, mammography device and method for generating X-ray images

The invention relates to an X-ray tube and a mammography device and a method for generating X-ray images of the female breast with a mammography device. Mammography is a procedure in which the chest of a

X-ray examination is subjected. It is used for the early detection of breast cancer. In order to be able to recognize such changed breast tissue with high reliability, an isotropic three-dimensional representation of the breast tissue with very high spatial resolution is required for this purpose.

A method used in mammography is tomosynthesis. Several X-ray images of the breast are made from different angular positions, from which a plurality of slice images are then processed into a 3D image.

Volume data set is reconstructed. However, even with this method only a limited depth resolution is achieved in the representation of the breast tissue. To carry out mammography X-ray devices are used with an X-ray tube in which electron beams are generated with a heatable cathode, which are accelerated to an anode serving as a target and generate there X-rays when hitting. The area of the anode which the electron beam impinges on is called the focal spot. The impact of the electron beam on the anode generates heat, which heats the anode in the area of the focal spot. This heating is greater, the greater the power of the electron beam and the smaller the focal spot. To avoid damage to the anode, it must therefore be cooled. In order to meet the demand for a high resolution in the presentation of the breast tissue, there are already approaches in which an X-ray tube is used, which allows a Steh anode tube a nearly complete representation of the chest to the chest. For technical reasons, however, either very large focal spots or very long recording times are required, which must be accepted as a disadvantage. In order to ensure the short recording times required for an X-ray examination, it is necessary to work with the highest possible power of the electron beam. Since anode heat dissipation is limited by the anode cooling, a standing anode tube can only provide limited power density in the focal spot. Thus, the X-ray tube with high performance can only with short recording times at large

Burning spots are operated, but this leads to a poor resolution or small focal spots can be realized with a good resolution, but this can only be worked with low power, which then leads to long recording times.

The use of a rotary anode tube, which can be operated with a small focal spot for high resolution and high performance for short recording times, has the disadvantage that due to technical reasons, the breast can not be fully taken up to the chest, as caused by the turntable with drive larger space requirement of the rotary anode, a suitable arrangement of the X-ray tube within the housing of an X-ray machine with respect to the creation of an X-ray image of the breast is prevented.

It is an object of the invention to provide an X-ray tube, in which the mentioned disadvantages are avoided. It is another object of the invention to provide a mammographic device and a method for generating X-ray images of the female breast with a mammography device. The first object is achieved with an X-ray tube having the features of claim 1. According to the invention, this comprises an anode, which is preferably designed as a standing anode, and a cathode for generating an electron beam between the cathode and the anode. Between cathode and anode, a deflection unit for deflecting the electron beam is arranged, with which the electron beam is selectively adjustable to at least a first and a deviating from this second focal spot position on the anode. In other words, the focal spot position is varied by the deflection of the electron beam. In this case, several different second focal spot positions can be adjustable.

By using the deflection unit, the electron beam can be selectively deflected to a plurality of focal spot positions that are different from each other. The individual focal spot positions can thereby smear one another during continuous operation of the x-ray tube, resulting in an overall enlarged focal spot. It is also possible that the electrons produced by the electron beam

Burning spots on the anode overlap, but ideally these are spatially separated so that overheating of the anode is avoided by distributing the heat generated when the electron beam strikes the anode to a plurality of focal spots and thus to a larger area. The X-ray tube can therefore be operated with a significantly higher power electron beam than an X-ray tube with a fixed focal plane stationary anode without increasing the focal spot.

With the tube according to the invention, it is thus possible to realize a small focal spot, which in practice may have a diameter of less than 100 μm, while simultaneously achieving high power for a required high resolution. The use of a standing anode also allows a suitable arrangement of the X-ray tube near the end of the housing, which allows the breast to be taken up to the thorax. In a preferred embodiment of the invention, the anode is designed as a transmission anode. In this case, the X-radiation is transmitted through the anode and not emitted as usual, from the surface of the anode.

In a further preferred embodiment of the invention, the deflection unit comprises a coil, by means of which an electromagnetic field is generated which causes a deflection of the electron beam.

The deflection of the electron beam is virtually power-free when it is electrostatically deflected. In this case, the deflection unit comprises electrodes, with the aid of which an electric field is generated, which deflects the electron beam.

With regard to the mammography device, the object is achieved with a mammography device according to claim 5. Accordingly, a mammography device comprises an X-ray tube and an X-ray detector, wherein the X-ray tube for receiving X-ray images of the female breast from different angular positions is movably mounted. It is also possible that with the X-ray tube in addition to the rotational movement about an axis of rotation and a translational movement along this axis is performed so that it is moved on a spiral path. The x-ray tube is preferably pivotably mounted in a pivoting plane perpendicular to the receiving surface of the x-ray detector.

A particularly simple embodiment of the deflection unit arises when the focal spot positions lie along a line in the pivoting plane of the x-ray tube and thus the electron beam can only be deflected in one direction. With regard to the method, the object is achieved with a method for generating X-ray images of the female breast according to claim 8. Accordingly, a first x-ray image is generated with a mammography device from a first position of the x-ray tube, wherein the electron beam is set to a first focal spot position of the anode and then from a second, from the first deviating position of the X-ray tube, a second X-ray image is generated, wherein the electron beam is adjusted to a second, deviating from the first focal spot position.

As a result, several focal spots are produced one after the other in chronological succession. This also changes the recording geometry and the corresponding projection angle at which the recording of the X-ray image takes place. This must be taken into account in a later image processing. Therefore, in the case of a reconstruction method, an unambiguous assignment of the respective focal spot position and the associated X-ray image must be known.

For further explanation of the invention reference is made to the embodiments of the drawings. 1 shows a longitudinal section through an X-ray tube according to the invention, FIG.

2 is a front view of an X-ray tube according to the invention opposite to the beam direction,

Fig. 3 is a mammography device with an X-ray tube.

According to FIG. 1, an X-ray tube 1 comprises an anode 2 and a cathode 4. The anode 2 is configured as a standing anode and can be embodied as a tungsten anode, cast in copper. Alternatively, a structure is conceivable that provides a very thin tungsten layer on a high thermal conductivity graphite carrier. In addition, the anode 2 may comprise a cooling, not shown. Between anode 2 and cathode 4 a deflection unit 6 is arranged, which in this example is formed by a coil.

During operation of the x-ray tube 1, the cathode 4 has, for example, a negative high-voltage potential, while the anode 2 is brought to ground potential. The cathode 4 is flowed through by a heating current, so that an electron beam 8 is generated between the cathode 4 and the anode 2. The electron beam 8 impinges on a first focal spot position 10 of the anode 2, so that in this case X-rays are generated, which are shown simplified by the central beam 12 and exit in the beam direction 13 from the X-ray tube 1. The impact of the electron beam on the anode 2 leads to its heating in the focal spot 10 tion. This heating is the greater, the greater the power of the electron beam.

By means of the deflection unit 6, a variable e-lektromagnetisches field can now be generated within the X-ray tube 1 between the anode 2 and the cathode 4, by means of which the electron beam 8 can be deflected.

While the path of the electron beam 8 results without deflection by a field generated by the deflection unit 6, the paths of the electron beams 8a, 8b shown in dashed lines in FIG. 2 are caused by a change in the electromagnetic field. Such a deflection of the electron beams 8a, 8b results in each case in a second focal spot position 10a, 10b on which the electron beams 8a, 8b impinge on the anode 2, which deviate from the first focal spot position 10 and are spatially separated therefrom. In this case, the focal spot positions 10, 10a, 10b are arranged along the line 11. By deflecting the electron beam 8 to the different focal spot positions 10, 10 a, 10 b, different areas of the anode are heated when the electron beam impinges on the anode 2. The resulting is thus distributed over a larger area, resulting in an overall that the anode 2 is not overheated in a focal spot position 10, 10 a, 10 b. The X-ray tube 1 can therefore be operated with an electron beam 8 with significantly higher power than an X-ray tube 1 with a stationary focal spot with a high resolution, ie a very small focal spot size, without this resulting in overheating of the X-ray tube 1 and thus leads to damage.

In order to achieve a further increase in performance of the X-ray tube 1, however, the electron beam 8 can be deflected not only along the line 11 but also perpendicular thereto, as indicated by the further dashed lines

Focal spot positions 10c, 10d is illustrated. Thus, a distribution of the resulting upon impact of the electron beam on the anode heat is achieved on an even larger surface of the anode 2. FIG. 3 shows a mammography apparatus with an X-ray tube 1 and an X-ray detector 14 spaced apart from it in the beam direction 13 with its receiving surface 16 facing the X-ray tube 1. Between the receiving surface 16 of the X-ray detector 14 and the X-ray tube 1 is a breast 18, which serves as an examination object of X-ray images to be produced.

The x-ray tube 1 is pivotably mounted in the direction of arrow 22 in a pivot plane 20 which is perpendicular to the receiving surface 16 of the x-ray detector 14. This makes it possible to make X-ray images of the breast 2 from different angular positions, by means of which an isotropic three-dimensional representation of the breast tissue with very high spatial resolution is to be made possible.

According to the method of the invention, a first x-ray image is obtained from the x-ray tube 1 from a first position generated, wherein the electron beam 8 is set to a first focal spot position 10 on the anode 2.

After this first recording, the X-ray tube 1 is pivoted in the direction of arrow 22 in the pivoting plane 20, so that it is located in a deviating from the first second position, as shown in phantom in Fig. 3.

From this second position, a second X-ray image is then generated, wherein the deflecting unit 6 generates an electromagnetic field, so that the electron beam deflected thereby is adjusted to a second focal spot position 10a deviating from the first one. The focal spot positions 10, 10a lie on a line 11, which lies in the pivoting plane 20 in this case. During the preparation of an X-ray image from an angular position, a different area of the anode 2 is heated by the impact of the electron beam 8, 8a, while the remaining area of the anode can cool down. This results in that the anode 2 is not overheated in a focal spot position 10, 10a, so that the x-ray tube 1 can be operated with an electron beam 8 with significantly higher power.

To further increase the power, the electron beam 8 can be deflected not only along this line 11 but also perpendicular thereto, as is illustrated by the further focal spot positions 10c, 10d shown in dashed lines in FIG. Thus, a distribution of the resulting upon impact of the electron beam on the anode 2 heat is achieved on an even larger surface of the anode 2.

Thus, several X-ray images with high resolution, so a small focal spot and high performance can be made in a short time. Overheating of the anode 2 is thereby avoided. This means that several focal spots are produced one after the other in chronological order with this method. This aspect must be taken into account in the later image processing become. Therefore, in the case of a reconstruction method, an unambiguous assignment of the respective focal spot position and the associated X-ray image must be known.

Claims

claims

1. X-ray tube (1) having an anode (2) and a cathode (4) for generating an electron beam (8, 8a, 8b) between cathode (4) and anode (2), wherein between the cathode (4) and anode (2) a deflection unit (6) for deflecting the electron beam (8, 8a, 8b) is arranged, with which the electron beam (8, 8a, 8b) selectively to at least a first focal spot position (10) and a deviating from this second focal spot position ( 10a, 10b, 10c, 10d) on the anode (2) is adjustable.

2. X-ray tube (1) according to claim 1, wherein the anode (2) is designed as a transmission anode.

3. X-ray tube according to claim 1 or 2, wherein the deflection unit (6) comprises a coil.

4. X-ray tube according to claim 1 or 2, wherein the deflection unit (6) comprises electrodes.

5. Mammography device with an X-ray tube (1) according to one of the preceding claims and an X-ray detector (14), wherein the X-ray tube (1) for receiving X-ray images of the female breast (18) is movably mounted from different angular positions.

6. Mammography device according to claim 5, wherein the X-ray tube (1) in a pivoting on the receiving surface (16) of the X-ray detector (14) perpendicular pivot plane (20) is pivotally mounted.

7. A mammography apparatus according to claim 6, wherein the focal spot positions (10, 10a, 10b) lie along a line in the pivot plane (20) of the X-ray tube (1).

8. A method for generating X-ray images of the female breast (18) with a mammography device according to one of the claims. 5 to 7, wherein from a first position of the X-ray tube (1), a first X-ray image is generated, wherein the E- lektronenstrahl (8) is set to a first focal spot position (10) on the anode (2) and then from a second in that a second X-ray image is generated from the first deviating position of the X-ray tube (1), the electron beam (8a) being adjusted to a second focal spot position (10a) deviating from the first one.