EP3836187A1 - X-ray tubes with low extra-focal x-ray radiation - Google Patents

Abstract

The invention relates to a rotary piston X-ray tube, a rotary piston X-ray tube, an X-ray device and a computer tomograph.

The rotary piston X-ray tube according to the invention has
- a vacuum housing,
- a cathode and
- an anode plate with a ring-shaped focal path for generating X-rays by means of electrons,
- wherein the anode plate is conical and the annular focal path is arranged on a lateral surface of the anode plate,
- wherein the cathode and the anode plate are arranged non-rotatably relative to one another in the vacuum housing,
- The cathode having a cathode carrier and a plurality of field effect emitter needles arranged in a ring on the cathode carrier for emitting the electrons and
- The cathode is designed in such a way that the emitted electrons impinge on the focal path at an angle of incidence of less than 15 °.

Description

The invention relates to a rotary piston X-ray tube, a rotary piston X-ray tube, an X-ray device and a computer tomograph.

In a conventional rotary piston X-ray tube, a cathode is usually placed centrally over an anode. Electrons emitted by the cathode are usually deflected by means of an electromagnetic and / or an electrostatic device towards a focal path of the anode, in particular focused, in order to generate X-rays. Typically, an angle of incidence of the deflected electrons on the anode is large, for example greater than 30 °, with a comparatively large number of electrons being scattered back. A disadvantage can arise if the backscattered electrons at least partially strike an annular exit window of the rotary piston x-ray tube, with extra-focal x-ray radiation being generated and typically reducing the image quality.

In the US 2018/0 075 997 A1 describes an X-ray tube with cathode parts arranged in a ring shape, which can be switched individually.

The invention is based on the object of specifying a rotary piston X-ray tube, a rotary piston X-ray tube, an X-ray device and a computer tomograph with lower extra-focal X-ray radiation.

The object is achieved by the features of the independent claims. Advantageous refinements are described in the subclaims.

• ein Vakuumgehäuse,
• eine Kathode und
• einen Anodenteller mit einer ringförmigen Brennbahn zur Generierung von Röntgenstrahlung mittels Elektronen auf,
• wobei der Anodenteller kegelförmig ist und die ringförmige Brennbahn auf einer Mantelfläche des Anodentellers angeordnet ist,
• wobei in dem Vakuumgehäuse die Kathode und der Anodenteller relativ zueinander drehfest angeordnet sind,
• wobei die Kathode einen vom Vakuumgehäuse zumindest teilweise beabstandeten Kathodenträger und mehrere ringförmig auf dem Kathodenträger angeordnete Feldeffekt-Emitternadeln zur Emission der Elektronen aufweist und
• wobei die Kathode derart ausgebildet ist, dass die emittierten Elektronen in einem Einfallswinkel kleiner 15° auf der Brennbahn auftreffen.

The rotary piston X-ray tube according to the invention has

• a vacuum housing,
• a cathode and
• an anode plate with a ring-shaped focal path for generating X-rays by means of electrons,
• wherein the anode plate is conical and the annular focal path is arranged on a lateral surface of the anode plate,
• wherein in the vacuum housing the cathode and the anode plate are rotatably arranged relative to each other,
• wherein the cathode has a cathode carrier at least partially spaced apart from the vacuum housing and a plurality of field effect emitter needles arranged in a ring on the cathode carrier for emitting the electrons, and
• wherein the cathode is designed in such a way that the emitted electrons strike the focal path at an angle of incidence of less than 15 °.

The angle of incidence of the electrons is defined in such a way that an angle of incidence of 0 ° corresponds to a perpendicular impingement of the electrons on a surface of the focal path.

The rotary piston x-ray tube is particularly suitable for medical imaging and / or imaging-based material testing. The rotary piston X-ray tube differs from a conventional rotary anode X-ray tube in that the cathode of the rotary piston X-ray tube typically rotates together with the anode plate of the rotary piston X-ray tube. In a conventional upright anode x-ray tube, neither the cathode nor the anode typically rotates relative to a vacuum housing of the upright anode x-ray tube. The electrons are typically accelerated from the cathode to the anode plate, for example with an acceleration voltage greater than 20 kV and / or less than 150 kV.

The vacuum housing usually comprises metal and / or glass. The vacuum housing can be cylindrical. The Vacuum housing can be partially conical. In particular, the glass can have an annular exit window of the vacuum housing. The ring-shaped exit window of the vacuum housing advantageously enables the x-ray radiation generated on the focal path to exit the vacuum housing. The metal of the vacuum housing is typically grounded, in particular connected to a protective conductor. In particular, an electric current from electrons scattered back at the anode can be carried away via the metal of the vacuum housing. The vacuum housing is usually evacuated.

The conical anode plate is typically frustoconical. The anode plate is advantageously rotationally symmetrical. The conical anode plate can essentially correspond to a flat disk with a radius that varies along a z-axis. An interior angle of the conical anode plate, in particular an anode angle, is typically greater than 0 ° and less than 90 °, advantageously between 1 ° and 40 °, particularly advantageously between 7 ° and 20 °. The outer surface of the anode plate, in particular a surface with the radius varying along the z-axis, in particular has the focal path. The annular focal path with an extension along the z-axis greater than zero can in particular be conical, in particular with an interior angle less than 90 °, wherein the interior angle of the focal path can essentially correspond to the interior angle of the conical anode plate.

The anode plate typically has a first material layer for generating the X-ray radiation. The first material layer has, for example, tungsten and / or gold. The anode plate can additionally have a second material layer with a higher thermal conductivity and / or with a higher thermal capacity than the first material layer, in particular for cooling the first material layer. The second material layer has, for example, titanium-zirconium-molybdenum and / or copper. The first The material layer and the second material layer can in particular be arranged in overlapping layers in the anode plate. In particular, the outer surface of the conical anode plate has the first material layer.

The ring-shaped focal path of the anode plate can in particular be arranged, typically embossed, by the impingement of the electrons. The focal path particularly identifies a region of the anode plate with the strongest interaction with the impinging electrons during operation of the anode plate. The focal path is arranged in particular on the anode plate where the anode plate has the first material layer. The focal path of the anode plate is in particular ring-shaped due to the rotation of the anode plate. As a result, the generation of heat from the impinging electrons can advantageously be distributed over a larger area of the anode plate than if, instead of the annular focal path, a stationary focal point, in particular the conventional upright anode, interacts with the electrons.

The annular focal path usually has a varying focal point. The varying focal spot typically varies with time and / or typically depends on the rotation of the anode plate. The varying focal spot is in particular the area of the focal path which interacts with the electrons to generate the X-ray radiation at the respective point in time. In particular, the focal spot is the region of the focal path at which the electrons strike, in particular when the at least one field effect emitter needle of the plurality of field effect emitter needles is switched on.

The rotationally fixed arrangement of the cathode and the anode plate has the effect, in particular, that the cathode and the anode plate rotate together at the same rotational speed. Usually the vacuum housing with the cathode and the Anode plate connected in such a way that the vacuum housing, the cathode and the anode plate rotate together at the same rotational speed, in particular, in other words, cannot be rotated relative to one another.

The cathode carrier enables, in particular, the arrangement of the multiple field effect emitter needles. In particular, the cathode carrier is not part of the vacuum housing. The cathode carrier is at least partially spaced from the vacuum housing. The cathode carrier is spaced apart from the vacuum housing, in particular in an edge region of the cathode carrier. The cathode carrier can have a central area in which the cathode carrier is connected to the vacuum housing. The cathode carrier can be ring-shaped and / or plate-shaped and / or rotationally symmetrical. The cathode support can, for example, have metal and / or a heat-resistant plastic, for example epoxy resin. The cathode carrier with the multiple field effect emitter needles usually has the same rotational speed as the cathode.

The multiple field effect emitter needles are preferably arranged in a continuous ring. Alternatively or additionally, the plurality of field effect emitter needles can be arranged in a ring in a plurality of rows with different radii. A distance between the plurality of field effect emitter needles is preferably so small and / or the speed of rotation is so high that thermal overloading of a connected field effect emitter needle can be avoided. In principle, it is conceivable that the multiple field effect emitter needles are subdivided into different pixels, which can preferably be switched on or off in groups. At least one field effect emitter needle of the plurality of field effect emitter needles can preferably be switched on or off individually, in particular independently of the other field effect emitter needles. The multiple field effect emitter needles, in particular in the arrangement in multiple rows, advantageously allow one To be able to specify focal point with different sizes. The rotary piston x-ray tube therefore advantageously has no electromagnetic and / or electrostatic deflection device. The multiple field effect emitter needles are preferably suitable for a flying focal spot control in the z and / or phi direction. Usually, the multiple field effect emitter needles can be switched on or off so quickly that it is possible to block the flow of electrons, in particular without a blocking grid, and / or that despite the rotation of the rotary piston X-ray tube relative to an examination subject, the direction of the X-rays and / or the Focal spot can be kept essentially constant on the annular focal path.

At least one field effect emitter needle of the plurality of field effect emitter needles has silicon and / or carbon. The at least one field effect emitter needle can in particular be a carbon nanotube or a silicon nanotube. Advantageously, the at least one field effect emitter needle is connected to a current limiting device which can prevent overloading of the at least one field effect emitter needle. Typically, the plurality of field effect emitter needles are at least partially constructed identically and / or are arranged in groups, for example in pixels.

Switching on the at least one field effect emitter needle typically includes applying a voltage to the at least one field effect emitter needle, whereby electrons are emitted from the at least one field effect emitter needle according to a field effect at a tip of the emitter needle. The electrons emitted in this way typically hit the anode plate. Switching off the at least one field effect emitter needle typically includes blocking the applied voltage. In comparison to a conventional thermionic electron emission, the voltage is advantageously low, whereby the at least one field effect emitter needle with a significantly higher clock frequency, for example in the kHz and / or MHz range, can be controlled. Usually, a number of the switched off field effect emitter needles outweighs a number of the switched on field effect emitter needles. An angle range in which the connected field effect emitter needles are located is typically less than 90 °. In this case, the field effect emitter needles are typically switched off in an angular range of 270 °. In this case, for example, every fourth field effect emitter needle of the plurality of field effect emitter needles could be switched on. The at least one field effect emitter needle is typically switched on and off in a clocked manner. The clock typically correlates with the speed of rotation.
The fact that the electrons strike the focal path at such a steep angle, in particular at the angle of incidence less than 15 °, has the following advantages in particular:
A proportion of the electrons scattered back at the anode is advantageously smaller than in the case of a larger angle of incidence. In this case, the efficiency of the rotary piston X-ray tube is preferably increased. Typically, the electrical current of the backscattered electrons, which is carried away via the metal of the vacuum housing, is lower.

Another advantage is, in particular, that the backscattered electrons have an angle of reflection which is equally steep in comparison to the angle of incidence, as a result of which fewer backscattered electrons preferably impinge on the annular exit window. In this way, the extra-focal X-ray radiation can advantageously be reduced in comparison with a larger angle of incidence.

It is furthermore advantageous that the rotary piston x-ray tube does not have an electromagnetic and / or electrostatic deflection device, because this reduces the weight of the rotary piston x-ray tube compared to a conventional rotary piston x-ray tube with such a tube Deflector. The rotary piston X-ray tube according to the invention has, in particular, an electron-optical mapping from 1 to 1, as a result of which advantageously no electromagnetic and / or electrostatic deflection device is required.

The embodiments described below are advantageously in addition to the embodiment according to claim 1, in which the angle of incidence is less than 15 °, preferably for an angle of incidence less than 5 °, particularly advantageously suitable for an angle of incidence essentially equal to 0 °.

One embodiment provides that the cathode carrier is conical, the multiple field effect emitter needles being arranged on an inside of the conical cathode carrier and the cone of the cathode carrier having an internal angle such that the emitted electrons strike the focal path at an angle of incidence of less than 15 ° . The conical cathode carrier can have a flat, in particular a disk-shaped cover side. The top side is in particular the central area of the cathode carrier. The cathode carrier, in particular the inside of the cathode carrier, is preferably designed to be essentially complementary to the anode plate, in particular to the outer surface of the anode plate. The conical cathode carrier advantageously enables the vacuum housing to be made smaller and / or a weight of the cathode carrier to be reduced because the shape of the cathode carrier is adapted to the shape of the anode plate. The shape of the cathode carrier can in particular dictate the shape of the vacuum housing, the cathode carrier being at least partially spaced from the vacuum housing. The cone of the cathode carrier particularly advantageously has an interior angle such that the emitted electrons impinge on the focal path at the angle of incidence less than 5 ° or at the angle of incidence essentially equal to 0 °.

One embodiment provides that at least one field effect emitter needle pedestal is arranged between the multiple field effect emitter needles and the cathode carrier in such a way that the emitted electrons strike the focal path at an angle of incidence of less than 15 °. The at least one field effect emitter needle pedestal can in particular be wedge-shaped and / or rotationally symmetrical and / or ring-shaped. This embodiment is particularly compatible with the conical cathode support. Alternatively, the at least one field effect emitter needle pedestal can be arranged on a flat cathode carrier in such a way that the emitted electrons impinge on the focal path at the angle of incidence less than 15 °, preferably less than 5 ° or at the angle of incidence essentially equal to 0 °.

One embodiment provides that at least one field effect emitter needle of the plurality of field effect emitter needles is arranged at a distance of less than 5 cm from the focal path. The distance is particularly advantageously less than 2 cm. The distance can be called electron distance and / or E distance. This embodiment makes it possible to reduce the size of the rotary piston X-ray tube, in particular because no electromagnetic and / or electrostatic deflection device is arranged between the cathode and the anode plate. Typically, the distance is equal to or greater than 1 mm per 10 kV acceleration voltage.

One embodiment provides that the anode plate is mounted rotatably about an axis of rotation at a rotational speed, the rotary piston X-ray tube having a circuit device and the circuit device being designed to switch on at least one field effect emitter needle of the plurality of field effect emitter needles as a function of the rotational speed. The speed of rotation is particularly dependent on a frequency of rotation of the anode plate. The circuit device can, in particular, determine and / or specify the rotational speed of the anode plate. Typically the circuit device is designed to switch off the at least one connected field effect emitter needle of the plurality of field effect emitter needles as a function of the rotational speed. The axis of rotation typically corresponds to the z-axis. The speed of rotation is typically greater than 50 Hz, particularly advantageously greater than 140 Hz, typically less than 200 Hz.

• die Drehkolben-Röntgenröhre und
• ein Röntgenstrahlergehäuse auf, wobei das Röntgenstrahlergehäuse, ein Austrittfenster, ein Kühlmedium und die Drehkolben-Röntgenröhre aufweist.

A rotary piston X-ray source according to the invention has

• the rotary piston X-ray tube and
• an X-ray tube housing, the X-ray tube housing having an exit window, a cooling medium and the rotary piston X-ray tube.

The cooling medium can in particular be liquid and / or gaseous. The cooling medium includes, for example, air and / or oil and / or water.

The rotary piston X-ray tube is typically mounted in the rotary piston X-ray tube so as to be rotatable about the axis of rotation. In particular, the cathode and the anode plate are rotatably mounted relative to the x-ray emitter housing, in particular at the same rotational speed.

The exit window is in particular stationary relative to the annular exit window. In other words, a main area of the annular exit window, which is typically closest to the exit window of the x-ray emitter housing, typically changes continuously due to the rotation of the vacuum housing. This main area of the ring-shaped exit window and the exit window of the x-ray emitter housing allow in particular the exit of the x-ray radiation from the vacuum housing and from the x-ray tube housing in such a way that a patient and / or an object can be x-rayed with the x-ray radiation. The main area of the annular exit window typically depends on the focal point. Typically, the Circuit device specify the varying focal point, in particular on the focal path, for example by switching on or off the at least one field effect emitter needle, preferably depending on the rotation of the anode plate, whereby the electrons of the at least one switched on field effect emitter needle on the anode plate in the focal point preferably hit.

One embodiment provides that the rotary piston X-ray tube is rotatably supported in the X-ray tube housing, the rotary piston X-ray tube having a circuit device and the circuit device being designed in such a way that at least one field effect emitter needle of the multiple field effect emitter needles is dependent on the exit window of the X-ray tube housing to turn on. The circuit device is therefore preferably designed so that the patient and / or the object can be transilluminated with X-ray radiation, the X-ray radiation emerging from the ring-shaped exit window and the exit window of the x-ray tube housing.

According to a particular embodiment, the circuit device is designed to switch on the at least one field effect emitter needle of the multiple field effect emitter needles as a function of the rotational speed and of the predeterminable focal point on the focal path and in particular of the exit window of the x-ray tube housing. Typically, the speed of rotation and a position of the predeterminable focal point can be converted into one another.

An X-ray device according to the invention has the rotary piston X-ray source and an X-ray detector. The X-ray detector is typically arranged opposite the exit window of the rotary piston X-ray tube. Between the X-ray detector and the exit window of the rotary piston X-ray emitter is in particular the patient for medical imaging and / or the object for the Material testing can be positioned. The x-ray detector is designed, in particular, to detect the x-ray radiation illuminating the patient and / or the object. An image, in particular a medical one, can preferably be reconstructed based on the captured X-ray radiation. In particular, the image has a higher image quality due to the reduced extra-focal radiation.

The invention is described and explained in more detail below using the exemplary embodiments shown in the figures. Basically, in the following description of the figures, structures and units that remain essentially the same are named with the same reference symbols as when the respective structure or unit first appeared.

Fig. 1

eine Drehkolben-Röntgenröhre und

Fig. 2

einen Computertomographen.

Show it:

Fig. 1

a rotary piston X-ray tube and

Fig. 2

a computed tomograph.

Fig. 1 shows a rotary piston X-ray tube 10 in a cross section along an axis of rotation of the rotary piston X-ray tube 10. The rotary piston X-ray tube 10 has a vacuum housing 11, a cathode 12 and an anode plate 13. The anode plate 13 has an annular focal path 14 for generating X-rays by means of electrons. The anode plate 13 is conical and, due to a flat top side, is frustoconical in this embodiment. The annular focal path 14 is arranged on a jacket surface 15 of the anode plate 13. In the vacuum housing 11, the cathode 12 and the anode plate 13 are arranged in a rotationally fixed manner relative to one another, because in this exemplary embodiment they are firmly connected to the vacuum housing 11. The cathode 12 has a cathode carrier 16 at least partially spaced apart from the vacuum housing 11 and a plurality of field effect emitter needles 17 arranged in a ring on the cathode carrier 16 for emission of electrons on. The cathode 12 is designed in such a way that the emitted electrons impinge on the focal path 14 at an angle of incidence of less than 15 °. The vacuum housing 11 has an annular exit window 18. The cathode carrier 16 has a central area without field effect emitter needles.

A further area is shown on a rear side of the anode plate 13, which can be designed in particular for additional cooling of the anode plate 13. Alternatively or additionally, this further area can connect the anode plate 13 to the vacuum housing.

Schematically shown in Fig. 1 is a particularly advantageous embodiment in which the angle of incidence is less than 5 ° because the field effect emitter needles 17 are arranged quasi parallel to the lateral surface 14 and the annular focal path 14. In principle, it is conceivable that the angle of incidence is essentially equal to 0 °. In this case, the field effect emitter needles 17 are typically arranged parallel to the lateral surface 15 and the annular focal path 14.

In this exemplary embodiment, the cathode carrier 16 is conical. The multiple field effect emitter needles 17 are arranged on an inner side of the conical cathode carrier 16. The cone of the cathode carrier 16 has an interior angle such that the emitted electrons impinge on the focal path 14 at the angle of incidence less than 15 °.

In Fig. 1 the alternative or additional embodiment is not shown, with at least one field effect emitter needle pedestal being arranged between the multiple field effect emitter needles 17 and the cathode carrier 16 such that the emitted electrons impinge on the focal path 14 at an angle of incidence of less than 15 °.

Depending on the configuration of the rotary piston X-ray tube 10, at least one field effect emitter needle of the plurality of field effect emitter needles 17 is arranged at a distance A of less than 5 cm from the focal path 14. The distance A is particularly advantageously less than 2 cm.

Fig. 2 shows a computed tomograph 40 in a cross section along an axis of rotation of a rotating part 41 of the computed tomograph 40. The computed tomograph 40 does not have the rotating part 41 and a for reasons of clarity Fig. 2 stationary part shown. An X-ray device 30 is arranged on the rotating part 41.

The x-ray device 30 has a rotary piston x-ray source 20 and an x-ray detector 31.

The rotary piston X-ray tube 20 has the rotary piston X-ray tube 10 and an X-ray tube housing 21. The x-ray emitter housing 21 has an exit window 22, a cooling medium and the rotary piston x-ray tube 10.

The rotary piston X-ray emitter 10 is rotatably mounted in the X-ray emitter housing 21. The rotary piston X-ray emitter 20 has a circuit device 23 and is connected to the rotary piston X-ray emitter 10. The circuit device 23 is designed in such a way that at least one field effect emitter needle of the plurality is not in Fig. 2 Field effect emitter needles 17 shown to be switched on as a function of the exit window 22 of the X-ray emitter housing 21.

Although the invention has been illustrated and described in more detail by the preferred exemplary embodiments, the invention is nevertheless not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

Claims (12)

Rotary piston X-ray tube (10), having - a vacuum housing (11), - a cathode (12) and - An anode plate (13) with an annular focal path (14) for generating X-rays by means of electrons, - wherein the anode plate (13) is conical and the annular focal path (14) is arranged on a lateral surface (15) of the anode plate (13), - wherein in the vacuum housing (11) the cathode (12) and the anode plate (13) are arranged non-rotatably relative to one another, - The cathode (12) having a cathode carrier (16) at least partially spaced apart from the vacuum housing (11) and a plurality of field effect emitter needles (17) arranged in a ring on the cathode carrier (16) for emitting the electrons and - The cathode (12) being designed in such a way that the emitted electrons impinge on the focal path (14) at an angle of incidence of less than 15 °. Rotary piston X-ray tube (10) according to claim 1, wherein the cathode support (16) is conical, wherein the plurality of field effect emitter needles (17) are arranged on an inside of the conical cathode support (16) and wherein the cone of the cathode support (16) is such Inner angle has that the emitted electrons impinge on the focal path (14) at the angle of incidence less than 15 °. Rotary piston X-ray tube (10) according to one of the preceding claims, wherein between the multiple field effect emitter needles (17) and the cathode carrier (16) at least one field effect emitter needle pedestal is arranged such that the emitted electrons at the angle of incidence less than 15 ° impinge on the focal path (14). Rotary piston X-ray tube (10) according to one of the preceding claims, wherein at least one field effect emitter needle of the plurality of field effect emitter needles (17) is arranged at a distance (A) less than 5 cm from the focal path (14). Rotary piston X-ray tube (10) according to claim 4, wherein the distance (A) is less than 2 cm. Rotary piston X-ray tube (10) according to one of the preceding claims, wherein the anode plate (13) is rotatably mounted about an axis of rotation at a rotational speed, the rotary piston X-ray tube having a circuit device and wherein the circuit device is designed to provide at least one field effect emitter needle to switch on several field effect emitter needles depending on the speed of rotation. Rotary piston X-ray tube (10) according to one of the preceding claims, wherein the angle of incidence is less than 5 °. The rotary piston x-ray tube (10) of claim 7, wherein the angle of incidence is substantially equal to 0 °. Rotary piston X-ray source (20), having - A rotary piston X-ray tube (10) according to one of the preceding claims and - An X-ray emitter housing (21), the X-ray emitter housing (21) having an exit window (22), a cooling medium and the rotary piston X-ray tube (10). Rotary piston X-ray tube (20) according to claim 9, wherein the rotary piston X-ray tube (10) is rotatably mounted in the X-ray tube housing (21), wherein the rotary piston X-ray tube (20) has a circuit device (23) and wherein the circuit device (23) such is formed, at least one field effect emitter needle of the plurality of field effect emitter needles (17) depending on the To switch on the exit window (22) of the X-ray tube housing (21). X-ray device (30), having the rotary piston X-ray source (20) according to one of Claims 9 to 10 and an X-ray detector (31). Computed tomograph (40), comprising a stationary part and a rotating part (41), the X-ray device (30) according to claim 11 being arranged on the rotating part (41).

Images