EP3685420B1 - Mbfex tube - Google Patents

Description

The invention relates to an MBFEX tube (MBFEX=Multibeam Field Emission X-Ray) for an X-ray device, which is also referred to as a multi-focus field emission X-ray tube. Such X-ray tubes are, for example, from the treatise: Yang Lu, Hengyong Yu, Guohua Cao, Jun Zhao, Ge Wang, Otto Zhou, Medical Physics 2010, Vol. 37, pp. 3773 - 3781 and the U.S. 7,751,528 B2 known, the cathodes containing carbon nanotubes for the field emission of electrons. The MBFEX tubes described there are intended for use in computer tomographs in which, instead of rotating an x-ray emitter, sequential electrical switching of individual fixed x-ray emitters is carried out.

In connection with electron emitters that contain nanorods, in particular carbon nanotubes, reference is also made to the documents by way of example WO 2018/086737 A1 and WO 2018/086744 A2 referred.

Different MBFEX tubes, which in the U.S. 7,751,528 B2 are described, have fixed X-ray emitters, in each of which a cathode is associated with an anode. Thus, there is a total of a large number of cathodes and a corresponding large number of anodes. While the anodes are connected to a high DC voltage potential, the cathodes are to be controlled individually.

DE 10 2010 011661 shows a multifocus X-ray tube which has a fixed anode (A) and a plurality of fixed cathodes (KH, KL) in a vacuum vessel, which are connected to the cathode voltage source (KSV) via a plurality of cathode leads. The cathodes can be designed as CNT field emitters, for example, and are aligned with the anode to generate X-ray sources. The high voltage for beam generation can be applied to the anode while the cathodes are grounded.

The object of the invention is to provide an MBFEX tube that is simple to manufacture and structurally compact compared to the prior art and to expose the high-voltage bushings and the cathode leads to only a minimum of radiation from secondary electrons or ions.

According to the invention, this object is achieved by the proposed MBFEX tube having the features of claim 1 . The object is also achieved by an arrangement made up of a plurality of MBFEX tubes according to claim 24. The MBFEX tube can be manufactured according to claim 25 and can be operated according to claim 27.

The proposed MBFEX tube is intended for an X-ray device and has in a vacuum tube an anode which is fixedly arranged therein and is designed as a cold finger and a plurality of cathodes which are fixedly arranged in rows. In turn, the vacuum tube has a plurality of cathode leads and no more than two high-voltage feedthroughs. In this case, a coolant tube is arranged in a high-voltage bushing, in which another tube, that is to say the coolant inner tube, is arranged. In this case, either the outer or the inner tube can function as a coolant supply tube, with the respective other tube being provided as a coolant discharge tube.

The coolant supply pipe and the coolant discharge pipe are provided for cooling the anode with a liquid coolant. The cathodes are provided for the field emission of electrons and are each aligned with respect to their main electron emission direction to the common anode for generating X-ray sources. The X-ray sources on the anode emit X-ray beams each having a main X-ray emission direction. The X-ray sources are preferably arranged in rows on the anode.

The proposed MBFEX tube is based on the first idea of designing the anode of the proposed MBFEX tube itself as a cooling device in the form of a cold finger to solve the anode cooling problem that exists with MBFEX tubes according to the prior art. With this in mind, in the proposed MBFEX tube, the anode is designed to be hollow, with the cavity being clamshell designed to allow both coolant supply and exhaust. For example, it acts the inner tube around the coolant supply tube and the outer tube concentrically surrounding the inner tube around the coolant discharge tube.

The anode including the coolant tubes is closed at one end. The transition between the coolant supply pipe and the coolant discharge pipe is formed at this end of the elongated anode. Among other things, low-viscosity silicone oils, in particular those with a boiling point of more than 450° C., are suitable as liquid coolants. Insulating oils sold under the "Shell Diala" brand name can also be used as coolants to cool the anode.

The design of the anode as a cold finger not only corresponds to a particularly advantageous compact design, but also has the advantage that both the coolant discharge pipe and the coolant supply pipe can be connected to one of the two ends of the anode through a passage through the vacuum tube with a coolant Circulation device is connected.

The anode contains, for example, molybdenum and/or tungsten and optionally has a coating on the outer surface which is suitable for the emission of X-rays. According to an advantageous development, surface sections of the anode that are positioned at an angle relative to the elongated basic shape are formed by attachments of the anode. In this case, the individual attachments have different angles of inclination in relation to the elongated base body of the anode. In this way, it is possible with a particularly high level of efficiency to align the X-ray radiation produced at the individual attachments by impinging electrons in the direction of the isocenter of the X-ray system comprising the MBFEX tube. This result can also be achieved by producing the surface sections mentioned by grinding the anode. A coating of the anode can be located either on its entire surface or only on sections of the surface, namely on the attachments or in the cuts.

The anode of the x-ray tube is preferably designed as a non-rotating anode. For the purpose of further improved cooling, the anode can in principle also be rotated about its own axis.

The manufacture of small passages through a vacuum tube for X-ray devices can be easily accomplished in terms of manufacturing technology with regard to sealing against the outside atmosphere. The cathode leads of the proposed MBFEX tube are provided as connections for the cathodes to an electrical voltage, typically at a level of a few kV, in particular up to 4 kV, and are designed, for example, as wire leads. If, for example, the vacuum tube is made of glass, cathode feed lines in the form of wires can be simply melted into the vacuum tube, with such feedthroughs having a high and long-lasting seal.

Larger bushings, for example for electrical high-voltage connections or for pipes, in a vacuum tube, on the other hand, have to be sealed in a complex manner. It is therefore advantageous to avoid a large number of such larger feedthroughs on a vacuum tube. In terms of a second basic idea, this is achieved with the proposed MBFEX tube in that the coolant discharge tube is guided through a high-voltage bushing together with the coolant supply tube. The high-voltage bushings are intended for connecting the anode to an electrical high voltage. The anode is preferably connected to a high voltage at the end of the anode.

Focusing electrodes are fixedly arranged in the vacuum tube between the cathodes and the anode and can be connected to an electrical voltage, for example, via electrical leads in the cathode leads. The focusing electrodes are located in the space between extraction grids, which are closely spaced from the cathodes, and the anode.

Structures of the extraction grating can be produced particularly precisely by laser processing. In particular, a picosecond or femtosecond laser for structuring suitable for extraction grids. The precise manufacture of the extraction grid is an essential prerequisite for the electrons emitted from the cathode to reach the anode with a high degree of transmission. During operation of the MBFEX tube, the electron source, including the extraction grid, is exposed to thermal stress, among other things. In order to minimize deformations of the extraction grid due to these loads, a special design of the extraction grid is preferred:

The extraction grid basically has a basic shape adapted to the shape of the associated electron source, ie cathode, in particular a rectangular basic shape. The long sides of this rectangle are formed by so-called edge strips of the extraction grid. The two edge strips are integrally connected to one another by grid strips running transversely to them. The transition areas between the grid strips and the edge strips are of particular importance for the absorption of thermally induced deformations. A curved transition between the grid strip and the edge strip has proven to be particularly advantageous. In this case, the curvatures at the two ends of the grid strip are preferably aligned in opposite directions. If, for example, in a plan view of the extraction grid, one end of the grid strip is curved upwards at its transition to the edge strip, the other end of the grid strip is curved downwards at the transition to the opposite edge strip. The lattice strips thus each have an elongated S-shape, the distance between the individual lattice strips being at least approximately constant over their entire length. Each grid strip connects to the edge strip at a non-right angle. Instead of an elongated S-shape of the grid strip, it can also have any other shape suitable for length compensation. For example, arc-shaped, for example semi-circular, curved sections can be integrated into each grid strip, in particular near the transition areas to the edge strips. It is also possible to design sections of the grid strips with simple or Z-shaped bends, preferably in a rounded shape. In all cases, the distance between adjacent grid strips is preferably constant over the entire length of the grid strips.

The distance between each point of the extraction grid and the electron emitter is constant to a very good approximation not only when the MBFEX tube is cold, but also at all times during normal operation. In addition to the extraction grid, components of the focusing device can also be precisely processed with pulsed laser radiation. Like the focusing components, the extraction grid can be made of steel, for example, in particular stainless steel.

The x-ray beams, which can be generated at the x-ray sources on the anode, each have a direction with the maximum intensity of the emitted x-ray radiation, which corresponds to the respective main x-ray emission direction. Such a main x-ray emission direction is present in all x-ray sources that are different from a spherical beam source. The geometry of the X-ray beam detected by the X-ray detector depends not only on the focusing of the electron beam but also on the collimation of the X-ray radiation. In this case, an X-ray window in the vacuum tube can be designed as a collimator device and/or a collimator device can be attached in front of an X-ray window on the vacuum tube.

With the MBFEX tube, for example, fan-shaped X-ray beams (fan beam) and/or conical X-ray beams (cone beam) can be generated. Each individual X-ray source formed on the anode can, for example, be approximately in the form of a point, surface or line. The cross-sectional profile of the X-rays in the isocenter of the X-ray system, in particular a tomography system, depends primarily on the collimation of the X-rays, in addition to the shape of the X-ray source.

In the proposed MBFEX tube, the cathodes are preferably arranged in a fixed row in such a way that, in cooperation with the focusing electrodes on the anode, a likewise row-like arrangement of X-ray sources is produced. The cathodes are intended for sequential electrical activation. The proposed MBFEX tube can be used in a computer tomograph instead of a rotating X-ray source.

In the embodiment of the MBFEX tube according to the invention, the high-voltage bushings and the cathode leads are arranged in a row and opposite the anode on the vacuum tube. This means that - viewed in the cross section of the MBFEX tube - the cathode supply lines and high-voltage bushings on the one hand and the anode on the other hand are diametrically opposed. With such an arrangement, the high voltage feedthroughs and cathode leads are exposed to only a minimum of secondary electron or ion radiation. Particularly advantageously, such an arrangement also allows the proposed MBFEX tube to be easily installed in an X-ray device, for example in the gantry of a computer tomograph.

Individual advantageous developments of the proposed MBFEX tube are discussed below.

In a preferred configuration of the proposed MBFEX tube, its cathodes have carbon nanotubes. The very high electrical and thermal conductivity of carbon nanotubes enables a high current carrying capacity without significant heat development on the individual carbon nanotubes themselves. Carbon nanotubes have a low field strength threshold of less than 2 V/m for the field emission of electrons. The field strength threshold value for cathodes for emitting electrons, which have carbon nanotubes, can be reduced even further by arranging the carbon nanotubes in the preferred vertical direction on the cathode surface. Since single-wall carbon nanotubes are semiconductors and multi-wall carbon nanotubes are metallic conductors, multi-wall carbon nanotubes are particularly suitable for applications as electron emitters on the cathodes of the proposed MBFEX tube. It is therefore particularly advantageous to operate the proposed MBFEX tube, which has cathodes containing carbon nanotubes, with a relatively low-power power supply.

In addition to carbon nanotubes, other types of nanorods, also known generally as nanosticks, are also suitable for the emission of electrons within the MBFEX tube. In a preferred embodiment, field emission cathodes are formed from such nanosticks as cathodes of the x-ray tube.

The nanosticks of the cathode are preferably made of a material which, with regard to the quantum mechanical field emission effect, has the lowest possible electron work function for the field emission of electrons. The nanosticks here have a uniform or non-uniform composition and are designed either as hollow bodies, ie tubes, or solid. In this case, the cathodes can have nanosticks of the same type or a mixture of different types of nanosticks, the type of nanosticks relating to their material composition and material modification.

Suitable materials in pure or doped form for the field emission of electrons are, in addition to single- or multi-walled carbon nanotubes, single- or multi-walled hetero-nitrogen-carbon nanotubes, rare earth borides, in particular lanthanum hexaboride and cerium hexaboride, metal oxides, in particular TiO ₂ , MnO, ZnO and Al ₂ O ₃ , metal sulfides, in particular molybdenum sulfide, nitrides, in particular boron nitride, aluminum nitride, carbon nitride, gallium nitride, carbides, in particular silicon carbide, silicon. Rod-shaped, optionally hollow, elements made of polymeric materials are also suitable as starting products for the production of the nanosticks, which emit electrons when the cathodes are in operation. The nanosticks of the cathodes are optionally made from starting products which only partially, in particular in the form of a coating, have polymer materials.

In a particularly preferred embodiment, the cathodes have nanosticks on the surface in a preferred vertical direction, ie in the direction of the anode. When operating the X-ray emitter and at a sufficient distance from each other are at the Very strong electric fields can be generated at the tips of the nanosticks, which considerably simplifies the emission of electrons.

In a possible embodiment of the proposed MBFEX tube, more than one type of cathode is arranged in the vacuum tube, with the term "type" being able to refer both to the geometry and to other properties of the cathodes, for example the materials. In principle, cathodes of the same and different types can be sequentially electrically controlled in any desired manner. In addition to the cathodes themselves, there may also be differences in focus. Together with properties such as the surface geometry of the individual cathodes, different electron beams and ultimately different X-ray beams can thus be generated.

The nanorods of the cathode have, for example, a length of less than 20 μm and a diameter of less than 10 nm, with a density of at least 10 ⁶ nanorods per cm ² being given, based on the area of the cathode.

A screen printing process is suitable for producing the cathode containing nanorods. In comparison to conventional methods, in particular to the method of electrophoretic deposition (EPD), a particularly uniform layer thickness and a relatively smooth surface of the emitter can thus be achieved. A layer designed for the emission of electrons with a thickness of less than 20 μm and a mean roughness value (Ra) of less than 2.5 μm is preferably formed by at least one type of cathode. The high quality of the emitter layer, together with a constant distance to the extraction grid, contributes to a high transmission rate of the electron source of the X-ray tube of up to 90% and more. The high transmission rate is also favored by the fact that the nanorods are mainly aligned in the vertical direction, caused by the screen printing process, in relation to the substrate surface on which the emitter layer is located.

It is also possible, within one and the same MBFEX tube, to use both cathodes with carbon nanotubes and completely different types of cathodes, for example cathodes with tungsten tips, which work in a different, fundamentally known manner. Dispenser cathodes can also be used within the MBFEX tube. In this regard, reference is made to the documents DE 10 2011 076 912 B4 and DE 10 2010 043 561 A1 referred.

If the cathodes are designed as field emission cathodes, the complete emitter arrangement preferably has the following layer structure:
A flat carrier element, in particular in the form of a ceramic circuit board, is provided as the bottom layer of the emitter arrangement. The ceramic circuit board is made of corundum, for example. The emitter layer is on the ceramic circuit board. In areas next to the flat emitters, the ceramic circuit board is covered by a metal intermediate plate, which is also known as a spacer. On the intermediate metal plate, which is connected to a defined electrical potential, there is a so-called grid plate including the extraction grid assigned to the individual emitters. The grid plate in turn is covered by a plate made of electrically insulating material, in particular ceramic, which is generally referred to as the upper insulating layer. The designation "upper" layer has no connection with the orientation of the electron emitter in space, but simply means that the named layer is arranged closest to the anode of the X-ray tube. The layer structure described is also suitable for other X-ray tubes that are not claimed as a whole.

In a particularly preferred development of the proposed MBFEX tube, the anode at least partially encloses a designated examination area. In this case, the x-ray sources and the main x-ray emission directions also at least partially enclose the examination area. The examination area is provided for positioning an examination object in an X-ray device.

For example, the MBFEX tube is curved as a whole, which means that even as a single X-ray tube it partially encloses the examination area. A more extensive enclosing of the examination area can be realized in various ways: For example, the MBFEX tube can extend over a very large angle, in extreme cases up to almost 360°, ie it can have an almost closed ring shape. Alternatively, it is possible to assemble a ring shape from individual MBFEX tubes. The individual MBFEX tubes can either be curved or straight. In the latter case, the arrangement of all MBFEX tubes has a polygonal shape. Incomplete polygon shapes or ring shapes, such as L-shapes, U-shapes or semicircular shapes, can also be produced by combining several MBFEX tubes, with not all MBFEX tubes of such arrangements necessarily having the same shape.

With an arc-shaped anode of the MBFEX tube arranged concavely around the examination area, the focal spot blur can be reduced in a computer tomograph compared to conventional designs and a higher and more constant image resolution can be achieved, especially if the anode is designed as a circular arc. If the anode is in the form of an arc of a circle, then all of the X-rays are aligned equally to an examination object. Among other things, by minimizing the number of high-voltage bushings, the examination object can be X-rayed from practically all circumferential positions using a single MBFEX tube.

The proposed MBFEX tube is characterized by a compact and robust design that is particularly easy to produce compared to the prior art and is particularly suitable for computer tomographs to replace a rotating X-ray source. The vacuum tube in which the X-rays are generated is preferably made of metal.

With the help of different types of cathodes, which are arranged in one and the same MBFEX tube, different X-ray images which differ differ from each other in terms of dose, can be generated. This provides a simple possibility for dose modulation. The number of MBFEX tubes in an X-ray system, the shape of the individual MBFEX tubes and the geometric arrangement of the MBFEX tubes in relation to one another are not subject to any restrictions. Likewise, the MBFEX tube or a plurality of MBFEX tubes can be combined within an X-ray system with X-ray tubes of other types. In general, x-rays of different wavelengths, as provided for multi-energy or dual-energy recordings, can be generated by different settings of the anode voltage.

Irrespective of the design of the cathodes, successive X-ray pulses of different wavelengths can be generated by the MBFEX tube in a preferred process. In this way, different materials within the examination volume can be distinguished from one another with a particularly high degree of reliability and at the same time a short recording time.

In terms of low susceptibility to faults and avoidance of damage, or at least minimization of damage, in the event of any faults, it has proven to be particularly advantageous to ground various components of the MBFEX tube that are to be set to zero potential in different ways. This applies specifically to focusing electrodes and the extraction grid directly in front of the electron emitters, which contain carbon nanotubes or other nanosticks:
While passive focusing electrodes are grounded via a housing in a preferred embodiment, the extraction grid is grounded independently of said housing, for example via a separate grounding line which can be assigned to a unit for controlling the electron emitter.

The advantage of the separate grounding of focusing electrodes and extraction grid comes into play if the potential of the focusing electrodes - despite existing grounding - due to the very high potential at which the anode is located due to a flashover located, is briefly raised. If the extraction grid were grounded together with the focusing electrodes at this moment, this would result in a correspondingly increased potential of the extraction grid and thus in an increased voltage difference between the carbon nanotubes and the extraction grid. Due to the given, strongly pronounced voltage dependence of the electron emission of the carbon nanotubes, the electron emission would increase extremely as a result, which would entail the risk of damaging the X-ray tube. Such a risk of damage is avoided by separately grounding the focusing electrodes on the one hand and the extraction grid on the other.

Fig. 1

ein erstes Ausführungsbeispiel einer MBFEX-Röhre 1 in schematischer Aufsicht auf eine als Kreisbogen ausgebildet Anode 30,

Fig. 2

das erste Ausführungsbeispiel einer MBFEX-Röhre 1 in schematisierter Seitenansicht,

Fig. 3

ein zweites Ausführungsbeispiel einer MBFEX-Röhre 1 mit einer geraden, linienförmig ausgebildeten Anode 30,

Fig. 4

das zweite Ausführungsbeispiel einer MBFEX-Röhre 1 mit geschnittener Ansicht der Anode 30,

Fig. 5

eine Hochspannungsdurchführung 52 der MBFEX-Röhre 1 nach Fig. 3,

Fig. 6, 7

Teilansichten einer Gittervorrichtung 43 der MBFEX-Röhre 1 des ersten Ausführungsbeispiels eines Computertomographen,

Fig. 8, 9

Teilansichten der Gittervorrichtung 43 der MBFEX-Röhre 1 des zweiten Ausführungsbeispiels eines Computertomographen,

Fig. 10, 11

Teilansichten einer alternativen Ausgestaltung einer Gittervorrichtung 43 einer MBFEX-Röhre 1,

Fig. 12

eine Emitteranordnung 33 einer MBFEX-Röhre 1 in Explosionsdarstellung,

Fig. 13

eine obere Isolierlage 48 der Emitteranordnung 44 nach Fig. 12,

Fig. 14

ein Gitterblech 47 der Emitteranordnung 44 nach Fig. 12,

Fig. 15

eine Extraktionsgitterelektrode 71 des Gitterblechs 47 nach Fig. 14,

Fig. 16

ein Metall-Zwischenblech 46 der Emitteranordnung 44 nach Fig. 12,

Fig. 17, 18

die Vorderseite einer Keramikplatine 45 der Emitteranordnung 44 nach Fig. 12,

Fig. 19

die Rückseite der Keramikplatine 45 der Emitteranordnung 44 nach Fig. 12,

Fig. 20

ein Detail der Keramikplatine 45,

Fig. 21

ein Detail einer MBFEX-Röhre 1 mit zwei unterschiedlichen Sorten von Kathoden 41, 42,

Fig. 22, 23

ein Beispiel einer insgesamt ringförmigen Anordnung mehrerer MBFEX-Röhren 1 in zwei verschiedenen Ansichten,

Fig. 24, 25

ein Beispiel einer insgesamt polygonförmigen Anordnung mehrerer MBFEX-Röhren 1 in zwei Ansichten analog Fig. 22 und 23,

Fig. 26, 27

ein mehrere, jeweils als Röntgenquelle fungierende Aufsätze 33 aufweisende Anode 30 einer MBFEX-Röhre 1,

Fig. 28

in dreidimensionaler Darstellung die Form einer Kathode 40 einer MBFEX-Röhre 1 sowie zum Vergleich eine herkömmliche Kathodenform,

Fig. 29

in einem Diagramm Strom- und Spannungspulse beim Betrieb der MBFEX-Röhre 1.

The proposed MBFEX tube is explained in more detail below with the aid of a drawing in which various exemplary embodiments are summarized. Shown here, in a partially simplified representation:

1

a first exemplary embodiment of an MBFEX tube 1 in a schematic plan view of an anode 30 designed as a circular arc,

2

the first exemplary embodiment of an MBFEX tube 1 in a schematic side view,

3

a second exemplary embodiment of an MBFEX tube 1 with a straight, line-shaped anode 30 ,

4

the second exemplary embodiment of an MBFEX tube 1 with a sectional view of the anode 30 ,

figure 5

a high-voltage bushing 52 of the MBFEX tube 1 after 3 ,

Figures 6, 7

Partial views of a grating device 43 of the MBFEX tube 1 of the first exemplary embodiment of a computer tomograph,

Figures 8, 9

Partial views of the grating device 43 of the MBFEX tube 1 of the second exemplary embodiment of a computer tomograph,

10, 11

Partial views of an alternative embodiment of a grating device 43 of an MBFEX tube 1 ,

12

an emitter assembly 33 of an MBFEX tube 1 in an exploded view,

13

an upper insulating layer 48 of the emitter assembly 44 after 12 ,

14

a grid plate 47 of the emitter arrangement 44 after 12 ,

15

an extraction grid electrode 71 of the grid sheet 47 after 14 ,

16

a metal shim 46 of the emitter assembly 44 after 12 ,

17, 18

the front of a ceramic circuit board 45 of the emitter assembly 44 after 12 ,

19

the back of the ceramic board 45 of the emitter assembly 44 after 12 ,

20

a detail of the ceramic plate 45 ,

21

a detail of an MBFEX tube 1 with two different types of cathodes 41 , 42 ,

22, 23

an example of an overall ring-shaped arrangement of several MBFEX tubes 1 in two different views,

24, 25

analogous to an example of an overall polygonal arrangement of several MBFEX tubes 1 in two views 22 and 23 ,

26, 27

an anode 30 of an MBFEX tube 1, which has several attachments 33 each functioning as an X-ray source,

28

a three-dimensional representation of the shape of a cathode 40 of an MBFEX tube 1 and, for comparison, a conventional cathode shape,

29

in a diagram current and voltage pulses during operation of the MBFEX tube 1.

All the exemplary embodiments of the proposed MBFEX tube 1 explained below are intended for a computer tomograph and have a vacuum tube 20 with an X-ray window 21 . An anode 30 designed as a cold finger is fixedly arranged in the vacuum tube 20 of all exemplary embodiments. The anode 30 contains tungsten.

The first two exemplary embodiments of the proposed MBFEX tube show in the vacuum tube 20 a plurality of cathodes 40 of a uniform type arranged in a fixed manner and the exemplary embodiment 21 such cathodes 41 , 42 of two different types, the cathodes 40 , 41 , 42 being provided for the field emission of electrons. The cathodes 40, 41, 42 are each aligned with the common anode 30 for generating X-ray sources Q with respect to the electron main emission direction e of the electron beams E that can be generated. The cathodes 40, 41, 42 are fixed in rows in such a way that on the anode 30 an arrangement of X-ray sources Q can also be produced in rows. The cathodes 40, 41, 42 are provided for sequential electrical control. The x-ray bundles X each have a main x-ray emission direction x .

A grating device 43 is aligned with each x-ray source Q in each of the exemplary embodiments. The grid devices 43 are fixedly arranged in the vacuum tube 20 between the cathodes 40, 41, 42 and the anode 30. FIG. Each grating device 43 has an extraction grating. The extraction grids are arranged at a short distance in front of the cathodes 40, 41, 42 and are provided for the extraction of electrons in the form of an electron beam E from the cathodes 40, 41, 42 . The extraction grids are in the Figures 1 to 4 not marked.

The vacuum tube 20 of all exemplary embodiments in turn has a plurality of cathode feed lines 50 and two high-voltage bushings 51, 52 . The cathode leads 50 are provided as connections for the cathodes and the grid devices 43 to an electrical voltage of a few kV and are designed as wire leads. The high-voltage bushings 51, 52 are provided for the end connection of the anode to an electrical high voltage of several 10 kV. Typically, the high voltage is in the range of 10 kV to 420 kV. Values in the upper range of this interval are selected, for example, in X-ray systems for examining larger objects in the non-medical field.

A coolant discharge pipe 31 with an internal coolant supply pipe 32 is guided through a high-voltage bushing 52 . The coolant discharge pipe 31 and the coolant supply pipe 32 are provided for cooling the anode 30 with a liquid, electrically non-conductive coolant by means of a circulating device.

In all exemplary embodiments of the proposed MBFEX tube 1 , the cathodes 40, 41, 42 in cooperation with the anode 30 can generate X-ray pulses of uniform or alternating energy. An example is in 29 the time course of an emitter current EC, an anode current AC, and the grid-emitter voltage GEV are recorded. The diagram after 29 shows actual measurement data. The high transmittance of approx. 90%, which indicates the ratio of anode current AC to emitter current EC, should be emphasized. In the present case, the anode current AC 52.2 mA and the emitter current EC 58.2 mA determined from the measured voltage values. This extremely favorable ratio between the anode current AC and the emitter current EC results primarily from the high quality of the emitter arrangement 44 of the x-ray tube 1, which is described in more detail below.

The first embodiment of the proposed MBFEX tube 1 is based on the 1 and the 2 explained in more detail. In the first exemplary embodiment, the anode 30 is designed as an arc of a circle.

The 1 Figure 12 shows a schematic top view of the anode 30 with the vacuum tube 20, the grid devices 43 and the high voltage feedthroughs 51, 52 not visible. The 1 is not to scale. The anode 30, the cathodes 40 and the grid devices 43 are arranged within the vacuum tube 20. FIG. In this case, the cathodes 40 are located on a carrier 6 made of metallized ceramic. The anode 30 is fixed in the vacuum tube 20 independently of the cathodes 40 . The x-ray sources Q are arranged in such a way that the x-ray beams X generated are aligned with an examination region U in their respective main x-ray emission directions x .

The examination area U is provided for the positioning of an examination object, in particular a patient.

The 2 shows the proposed MBFEX tube 1 in its first embodiment in a cross-sectional side view. In the 2 the coolant supply pipe 32, the cathode leads 50 and the high-voltage bushings 51, 52 are not visible. The cathodes 40 have multi-walled carbon nanotubes on their surface in a preferred vertical direction. In this context, "perpendicular" is to be understood as meaning an orientation directed towards the anode 30 .

The second embodiment of the proposed MBFEX tube 1 is based on the 3 and the 4 explained in more detail. The second exemplary embodiment differs from the first exemplary embodiment only in that the anode 30 is linear.

The 3 shows a partially sectioned view of the MBFEX tube 1 of the second embodiment. In the 3 the coolant supply tube 32, the cathodes 40 and the grid devices 43 are not visible. As in the first exemplary embodiment of the MBFEX tube 1 , the cathode leads 50 and the high-voltage bushings 51, 52 are arranged in a row on the vacuum tube 20 and the anode 30 opposite.

The 4 shows the proposed MBFEX tube 1 in its second embodiment with a sectional view of the anode 30. In FIG 3 the cathodes 40 and grid devices 43 are also not visible. Individual features of the high voltage bushing 52 are running out figure 5 out.

An existing in all embodiments grating device 43, which in detail in different variants in the Figures 5 to 11 1 is aligned with the anode 6 , i.e. positioned between the cathodes 40, 41, 42 and the anode 6 in the vacuum tube 20. FIG . The grating device 43 includes by definition at least one extraction grid electrode 71, 73, 74 and at least one form of focusing electrodes 72, 75, 76.

The extraction grid electrodes 71,73,74 are fixed directly above the cathodes 40,41,42 and are provided for field extraction of electrons from the cathodes 40,41,42 . The focusing electrodes 72, 75, 76 are also fixed directly above each extraction grid electrode 71, 73, 74 , facing the anode 6 and provided for focusing the extracted electrons as an electron beam E onto the respective X-ray source Q to be generated. Extraction grid electrodes 71, 73, 74 are independently grounded from focusing electrodes 72, 75, 76 . The focusing electrodes 72, 75, 76 can be operated as passive or active focusing electrodes.

In the first exemplary embodiment, the grid device 43 has an extraction grid electrode 71 common to all cathodes 40 , with each individual cathode 40 being separately associated with an individual focusing electrode 72 . In the second embodiment, the grid device 43 has an extraction grid electrode 73 of a first form common to the cathodes 41 of the first kind and an extraction grid electrode 74 of a second form common to the cathodes 42 of the second kind, each individual cathode 41 of the first kind separately having a single focusing electrode 75 of a first form and each individual cathode 42 of the second type is separately associated with an individual focusing electrode 76 of a second form. The extraction grid electrodes 71, 73, 74 and the focusing electrodes 72, 75, 76 are shown in FIGS Figures 1 to 4 not marked.

For computer-aided X-ray imaging by means of tomosynthesis, a time-constant potential of typically 40 KV is applied to the anode 6 , with a uniformly pulsed electrical direct current of 30 mA flowing between the anode 6 and the respectively connected cathode 40, 41 . For computer-aided X-ray imaging using HPEC tomosynthesis on the other hand, a potential of typically 120 kV which is constant over time is present on the relevant anode, with a uniformly pulsed electrical direct current of the order of 0.5 mA flowing between the anode 6 and the respective switched cathode 40, 42 .

In all exemplary embodiments, the proposed computer tomograph has a current controller, a device controller, an electronic control system (ECS = Electronic Control System), a cathode high-voltage source (CPS = Cathode Power Supply), an anode high-voltage source (APS = Anode Power Supply) and a device controller on. The current regulator, the device control, the electronic control system, the cathode high-voltage source, the anode high-voltage source and the device control are part of an electronic control device. The current regulator, the device control and the electronic control system constitute an electronic control system.

The electronic control device has a main electric circuit and a control circuit, the main circuit and the control circuit being integrated in a DC circuit. In the main circuit, the anode high-voltage source with the anode 6 and the current regulator, the current regulator with the device controller, the device controller with the electronic control system, the electronic control system with the cathode high-voltage source and the cathode high-voltage source in parallel connection with the cathode 40, 41, 42 as well as with the respective grid device 43 electrically connected. In the control circuit, the anode high-voltage source is electrically linked to the control system via feedback. Here, the control system is provided both for the sequential switching of the cathodes 40, 41, 42, for the regulation of the extraction grid electrodes 71, 73, 74 and the focusing electrodes 72, 76, 56 of the respective grid device 43 and for the regulation of the main circuit current, whereby on The electrical voltage of the cathode high-voltage source can be adapted to the main circuit current specified with the control system.

In 21 eight cathodes 41, 42 of the MBFEX tube 1 are outlined as an example. Both the cathodes 41 of the first type and the cathodes 42 of the second type have Carbon nanotubes, but differ in terms of their geometry. The cathodes 41, 42 are arranged in rows and alternately offset in the vacuum tube 20 , the number of cathodes 41 of the first type being equal to the number of cathodes 42 of the second type. A grating device 43 and thus an x-ray source Q can each be assigned a cathode 41 of the first form and a cathode 42 of the second form. In the MBFEX tube 1 after 21 the cathodes 41 of the first type or the cathodes 42 of the second type can be sequentially controlled in any way. In this way, dual-dose X-ray images can be taken with the MBFEX tube 1 .

How from the Figures 22 to 25 shows, several MBFEX tubes 1 can be combined to form a rigid, ring-shaped or polygonal arrangement, which replaces a rotating arrangement in a computer tomograph. This applies to any configuration of MBFEX tubes 1 that has already been described and that will be explained below.

A layered structure of an emitter arrangement 44 of an MBFEX tube 1 is shown in FIGS Figures 12 to 20 illustrated. The emitter arrangement 44 comprises a ceramic circuit board 45 made of corundum as the bottom layer. The cathodes 40 are located on a conductive coating of the ceramic circuit board 45 and are produced with high geometric precision using the screen printing process. Conductor structures 66 can be seen on the back of the ceramic circuit board 45 .

A metal intermediate plate 46 is placed on the ceramic circuit board 45 . This intermediate metal plate 46 has rectangular openings 61 for the cathodes 40 . In addition, the metal intermediate plate 46 has strip-shaped openings 62 that are narrower and longer than the openings 61 on the longitudinal sides of the openings 61. The strip-shaped openings 62 have a function in degassing the vacuum tube 20. This applies both to the preparation for operation as well as for the ongoing operation of the X-ray tube 1, each in cooperation with the ceramic circuit board 45.

In the ceramic circuit board 45, in addition to the cathodes 40, various strip-shaped openings 64, 65 can be seen. Here are three short, narrow openings 64 directly next to the longitudinal sides of each cathode 40. In addition, the cathodes 40 are flanked by openings 65 which are somewhat further away and are also in the form of strips. In this case, two strip-shaped openings 65 are arranged one behind the other in a line. Two pairs of such lines of strip-shaped openings 65 together with the arrangement of cathode 40 and a total of six smaller strip-shaped openings 64 lying in between describe an H-shape. This applies to all cathodes 40 on the ceramic circuit board 45 with the exception of the two outermost cathodes 40, which are only flanked on one side by strip-shaped openings 65 of the longer type.

In particular, the internal openings 64, which are very close to the cathodes 40 , contribute to the fact that during the emission of electrons, gas can also be discharged in an extremely low concentration down to individual particles to the rear of the emitter arrangement 44 . This makes a significant contribution to avoiding flashovers within the vacuum tube 20 . The relatively large strip-shaped openings 65 are required to a greater extent for sucking off gas during the production of the X-ray tube 1, in particular during baking.

The metal intermediate plate 46 has, as an integral part, a connection strip 63 as an electrical connection led from the emitter arrangement 44 to the outside. On the metal intermediate plate 46 there is a grid sheet 47, which includes the extraction grid electrodes 71 , each of which corresponds to a cathode with a precisely defined distance of 0.224 mm (in the example according to 12 ) are superior.

Details of the extraction grid electrode 71 are forthcoming 15 out. Overall, the extraction grid electrode 71 has a rectangular shape, the long sides of which are formed by completely straight edge strips 78 . The two edge strips are connected to one another by a large number of lattice strips 77 , so that the lattice structure results overall. In contrast to the edge strips 78, however, the grid strips 77 are not completely straight. Rather, a rounded transition area 79 is formed at the two ends of each grid strip 77, ie at the transition to the edge strip 78 . The rounded transition areas 79 ensure that thermally induced deformations do not occur a change in the spacing between the cathode 40 and the extraction grid 71 , but are accommodated within the in-plane extraction grid 71 without affecting the emission characteristics of the emitter assembly 44 .

The grid plate 47 is covered by an upper insulating layer 48 in the form of a plate made of a ceramic material, with which the emitter arrangement 44 is completed. The upper insulating layer 48 has, as shown in FIG 12 shows openings 49 , which are adapted to the shape of the cathodes 40 to allow the passage of electrons.

Geometric features of the cathode 40, as it is contained several times in the emitter arrangement 44 , are shown in 28 shown. To a good approximation, the cathode 40 has a cuboid structure. Over the entire electron-emitting surface of the cathode 40 , there are hardly any fluctuations in the distance between the cathode 40 and the 28 not shown extraction grid electrode 71 given. For comparison is in 28 the surface structure of a conventional cathode produced by the process of electrophoretic deposition (EPD) is indicated by dashed lines. There is no question of a smooth surface in this comparison example. Rather, there are pronounced peaks within the surface of the emission cathode, particularly at the edges of the cathode produced using the EPD process. The electrons are mainly emitted at these tips. On the one hand, this limits the service life and, on the other hand, the transmission rate of electrons. In contrast to this , the cathode 40 used in the X-ray tube 1 according to the invention emits electrons in every area section of its surface with an almost constant release rate.

An exemplary embodiment of an anode 30 which cooperates with the emitter arrangement 44 is shown in FIGS Figures 26 and 27 illustrated. On the cylindrical body of the anode 30 there are several top pieces 33, which are also referred to as anode tops or tops for short. Each of these attachments 33 has a surface 34 which is inclined relative to the base body and is coated with tungsten or another material suitable for X-ray sources. The inclinations of the various surfaces 34 differ from one another in such a way that - as in 27 is indicated - the emitted X-ray radiation X is focused in the direction of the isocenter of the X-ray emitter arrangement 10 lying in the examination area U.

Reference List

1

MBFEX tube

6

carrier

10

X-ray tube arrangement

20

vacuum tube

21

x-ray window

30

anode

31

Coolant drain pipe

32

coolant supply pipe

33

top piece

34

coated surface

40

cathode

41

Cathode of a first variety

42

Cathode of a second kind

43

grid device

44

emitter arrangement

45

ceramic circuit board

46

metal intermediate plate

47

mesh sheet

48

upper insulating layer

49

Opening in the upper insulating layer

50

cathode lead

51

high voltage bushing

52

high voltage bushing

61

Opening in the metal intermediate plate

62

strip-shaped opening in the metal intermediate plate

63

terminal strips

64

narrow strip-shaped opening

65

wider stripe-shaped opening

66

ladder structure

71

extraction grid electrode

72

focusing electrode

73

Extraction grid electrode of a first form

74

Extraction grid electrode of a second form

75

Focusing electrode of a first form

76

Focusing electrode of a second form

77

grid strips

78

edge strips

79

rounded transition area

80

ceramic carrier

81

metal layer

AC

anode current

E

electron beam

e

Electron main emission direction

EC

emitter current

GEV

grid-emitter voltage

Q

x-ray source

X

X-ray beam

x

X-ray main emission direction

u

area of study

Claims (27)

1. A multibeam field emission X-ray tube, MBFEX tube, (1) for an x-ray device which comprises, in a vacuum tube (20), an anode (30) fixedly arranged therein and also designed as a cooling finger, and a plurality of fixedly arranged cathodes (40, 41, 42), wherein

   the vacuum tube (20) comprises a plurality of cathode feed lines (50) and no more than two high-voltage bushings (51, 52),

   in a high-voltage bushing (52), a coolant pipe (31) with an internal coolant inner pipe (32) is passed through,

   the coolant pipe (31) and the coolant inner pipe (32) are provided with a liquid coolant for cooling the anode (30),

   the cathodes (40, 41, 42) are provided for field emission of electrons and are in each case oriented towards the anode (30) for generating x-ray sources (Q),

   wherein the cathode feed lines (50) and the high-voltage bushings (51, 52) are arranged in a row and lying opposite the anode (30) on the vacuum tube (20).
2. The MBFEX tube (1) according to claim 1, characterized in that the x-ray sources (Q) are arranged in a row on the anode (30).
3. The MBFEX tube (1) according to claim 2, characterized in that the x-ray sources (Q) are each located on a surface section of the anode (30) which is inclined with respect to the center axis of the anode (30).
4. The MBFEX tube (1) according to claim 3, characterized in that the inclined surface sections are formed by projections of the anode (30).
5. The MBFEX tube (1) according to claim 3, characterized in that the inclined surface sections are formed by ground-in areas in the anode (30).
6. The MBFEX tube (1) according to claim 4 or 5, characterized in that the inclined surface sections of the anode (30) are coated.
7. The MBFEX tube (1) according to any one of claims 1 to 6, characterized in that the cathodes (40, 41, 42) comprise nanorods.
8. The MBFEX tube (1) according to claim 7, characterized in that at least some of the nanorods are designed as single-walled or multi-walled carbon nanotubes or as single-walled or multi-walled hetero nitrogen carbon nanotubes.
9. The MBFEX tube (1) according to claim 7 or 8, characterized in that at least some of the nanorods contain rare earth borides, metal oxides, metal sulfides, nitrides, carbides or silicon.
10. The MBFEX tube (1) according to any one of claims 7 to 9, characterized in that the nanorods have a length of less than 20 um and a diameter of less than 10 nm, wherein a density with respect to the surface area of the cathode (40, 41, 42) is at least 10⁶ nanorods per cm².
11. The MBFEX tube (1) according to any one of claims 1 to 10, characterized in that focusing electrodes (72) are arranged between at least one extraction grid (71), located above the cathodes (40, 41, 42), and the anode (30) .
12. The MBFEX tube (1) according to claim 11, characterized in that the focusing electrodes (72) are grounded separately from the extraction grid (71).
13. The MBFEX tube (1) according to any one of claims 11 or 12, characterized in that the extraction grid (71) describes a rectangular form with two mutually parallel edge strips (78) which are integrally connected to one another by grid strips (77), wherein, at the transitions between the grid strips (77) and the edge strips (78), rounded transition regions (79) are formed with which the grid strips (77) describe an elongated S-form in each case.
14. The MBFEX tube (1) according to any one of claims 1 to 13, characterized in that the vacuum tube (20) comprises different types of cathodes (40, 41, 42) which differ with respect to at least one parameter from a group of parameters, wherein the group of parameters comprises geometric parameters and material parameters.
15. The MBFEX tube (1) according to any one of claims 1 to 14, characterized in that a layer designed for the emission of electrons and having a thickness of less than 20 um and an average roughness, Ra, of less than 2.5 um is formed by at least one type of cathode (40, 41, 42).
16. The MBFEX tube (1) according to any one of claims 1 to 15, characterized in that a plurality of cathodes (40, 41, 42) is arranged on a flat support element (45).
17. The MBFEX tube (1) according to claim 16, characterized in that the flat support element has strip-shaped openings (64) of a first type and strip-shaped openings (65) of a second type, wherein a group of strip-shaped openings (64) of the first type is arranged closer next to a cathode (40) than a group of strip-shaped openings (65) of the second type, and wherein the strip-shaped openings (64) of the first type are narrower than the strip-shaped openings (65) of the second type.
18. The MBFEX tube (1) according to any one of claims 16 or 17, characterized in that the flat support element (45) is part of a layered emitter arrangement (44), which further comprises a metal intermediate plate (46), a grid plate (47) including extraction grid (71), as well as an upper insulating layer (48).
19. The MBFEX tube (1) according to claim 18, characterized in that the strip-shaped openings (64, 65) of the flat support element (45) are at least partially aligned with openings (62) in the metal intermediate plate (46).
20. The MBFEX tube (1) according to any one of claims 1 to 19, characterized in that the anode (30) is designed for two-sided feeding and discharging of coolant, wherein, at the two ends of the anode (30), in each case a coolant feed line and an associated coolant discharge line are arranged.
21. The MBFEX tube (1) according to any one of claims 1 to 20, characterized in that the anode (30) at least partially encloses an examination region (U), wherein the x-ray sources (Q) also at least partially enclose the examination region (U).
22. The MBFEX tube (1) according to claim 21, characterized in that the anode (30) has an arcuate design.
23. The MBFEX tube (1) according to any one of claims 1 to 21, characterized in that the anode (30) is designed as a rotating anode.
24. An arrangement of multiple MBFEX tubes (1) designed according to any one of claims 1 to 23, wherein an annular, arcuate, polygonal, L- or U-shaped form at least partially enclosing the examination area (U) is formed by the totality of the MBFEX tubes (1).
25. A method for producing an MBFEX tube (1) according to any one of claims 1 to 23, wherein a vacuum tube (20), an anode (30) to be placed in the vacuum tube (20) and cathodes (40, 41, 42) designed for field emission and also to be arranged in the vacuum tube (20) are provided, and wherein at least one element to be arranged between the cathodes (40,41,42) and the anode (30), which is selected from the group of elements comprising an extraction grid (71) and a focusing electrode (72), is machined by laser.
26. The method according to claim 25, characterized in that the laser machining of the element (71,72) is performed with picosecond or femtosecond clocking of the laser.
27. A method for operating an MBFEX tube (1) according to any one of claims 1 to 23, wherein the anode (30) is used for the emission of successive x-ray pulses of different wavelengths.

Images