Computer tomograph

Abstract

The invention relates to a computed tomography apparatus which operates with a plurality of rigidly arranged X-ray tubes. The X-ray tubes have at least one cathode which is correspondingly arranged for emitting electrons and an associated anode arrangement which comprises at least one anode, wherein each cathode has an orientation angle with respect to a geometric central axis of the computed tomography apparatus and a tangent plane which is applied at a focal spot of the anode has a surface normal which forms an anode angle with the central axis and X-ray radiation which emanates from the focal spot is directed onto an X-ray detector which is offset in an axial direction with respect to the X-ray tube at an average reflection angle. A quotient which is formed from the sum of the orientation angle and the reflection angle and the anode angle is at least two ninths and at most two, wherein each cathode constitutes a common action with the electrode arrangement of the X-ray tube for generating a focal spot at one of at least three selectable positions on the anode arrangement.

Description

TECHNICAL FIELD

[0001] The invention relates to a computed tomography apparatus whose X-ray emitter-detector arrangement does not rotate during operation of the computed tomography apparatus. BACKGROUND

[0002] Such a computed tomography apparatus is known, for example, from WO 2018 / 086744 A2. This computed tomography apparatus is suitable, inter alia, for X-ray imaging in computed tomography of a human head and has a rotationally fixed gantry with a plurality of X-ray emitters and X-ray detectors which are fixedly arranged around a geometric central axis of the computed tomography apparatus. Here, the X-ray emitters and the associated detectors are staggered in the direction of the central axis. The gantry is generally movable in the longitudinal direction of the computed tomography apparatus, that is to say in the direction of the central axis.

[0003] An apparatus for X-ray technology is described in RU 2164 081 C2, which has an electron source arranged centrally in the apparatus, which emits an electron beam which is directed onto an anode arranged as an X-ray source, which anode encloses an object to be examined annularly.

[0004] A further computed tomography apparatus is described in DE 102 37 546 B4. Here, an X-ray computed tomography apparatus is involved which comprises a filter, wherein the filter and the direction-dependent intensity distribution of the dispersed X-ray beam are coordinated. Thereby, a heel effect, which occurs in particular in the inclined anode of the X-ray tube, should be countered. SUMMARY

[0005] It is the task of the invention to give a computed tomography apparatus comprising a fixed gantry which is further improved with respect to the prior art, which is characterized by a particularly good space utilization while at the same time advantageous X-ray technology properties.

[0006] According to the application, this task is solved by a computer tomography apparatus having the features of the application. A computer tomography apparatus is therefore proposed, which comprises a plurality of X-ray tubes arranged at a defined angular position around a geometrical center axis, which are components of radiator-detector elements, which together form a radiator-detector ring, which can be opened by a shift of at least one of the radiator-detector elements, wherein each X-ray tube has at least one cathode arranged for emitting electrons and has an associated anode arrangement comprising at least one anode, each cathode having an orientation angle a with respect to the emission direction of the electrons, and a tangent plane imposed on the focal spot of the anode has a face normal, which forms an anode angle β with the center axis, and the X-ray radiation emanating from the focal spot is directed onto an X-ray detector with an average reflection angle γ measured with respect to a radial line through the focal spot, which is arranged offset with respect to the X-ray tube in an axial direction about the geometrical center axis of the computer tomography apparatus, wherein the quotient formed by the sum of the orientation angle a and the reflection angle γ and the anode angle β is at least two thirds and at most two, and each cathode is configured to interact with the electrode arrangement of the X-ray tube for generating the focal spot at one of at least three selectable positions on the anode arrangement. The computer tomography apparatus has in the basic design known per se a plurality of X-ray tubes arranged at a defined angular position, that is to say non-rotatably around the geometrical center axis of the computer tomography apparatus. The X-ray tubes are components of radiator-detector elements, which together form a radiator-detector ring, which can be opened by a shift of at least one of the radiator-detector elements.

[0007] Each X-ray tube has at least one cathode, typically a plurality of cathodes, arranged for emitting electrons and an associated anode, wherein each cathode has an orientation angle a defined by the average emission direction of the electrons measured with respect to the geometrical center axis of the radiator-detector ring. The electrons emitted from the cathode are incident on the surface of the anode in a manner known in principle, forming a focal spot. A tangent plane imposed centrally on the focal spot has a face normal, which forms an anode angle β with the center axis of the radiator-detector ring and thereby of the entire computer tomography apparatus. The X-ray radiation emanating from the focal spot is directed onto an X-ray detector with an average reflection angle γ measured with respect to a radial line through the focal spot, which intersects the center axis orthogonally, wherein the reflection angle γ is measurable between the central beam of the X-ray beam emanating from the focal spot and the radial line. The X-ray detector is arranged offset with respect to the X-ray tube in an axial direction about the geometrical center axis of the computer tomography apparatus.

[0008] According to the application, the following relationships are given between the angles a, β, γ:

[0009] 2 / 9 ≤ (<a + γ) / β ≤ 2

[0010] This relationship applies to all X-ray beams which respectively emanate from a focal spot. Here, each cathode acting as electron emitter is configured to cooperate with an electrode arrangement in the same X-ray tube for generating a focal spot on one of at least three selectable positions on an anode arrangement of the X-ray tube. The different, electron-emitter-adjustable positions of the focal spots are here arranged side by side along the circumferential direction of the radiator-detector ring, that is to say distributed at different angular positions around the central axis of the computed tomography apparatus. In particular, the focal spots which can be generated with the sole electron emitter are arranged equidistantly on the circumference of the radiator-detector ring. The angular distance between the individual focal spots is for example a few degrees or in the extreme case only a fraction of a degree, wherein in each case the individual focal spots are distinguishable from one another. The switching between the different discrete focal spot positions by means of the actuation of the electrode arrangement is also referred to as beam toggling. Due to the beam toggling, the total number of possible focal spot positions corresponds to a multiple of the number of electron emitters of the computed tomography apparatus. The beam toggling can be carried out in the same manner not only in at least one displaceable radiator-detector element for the purpose of opening the radiator-detector ring but also in the remaining radiator-detector elements.

[0011] The present application proceeds from the following considerations:

[0012] The electrons emitted from the cathode of an X-ray tube incorporated in a computed tomography apparatus can in principle be emitted in a main propagation direction which is parallel to the central axis of the computed tomography apparatus, wherein a mechanism influencing the electron radiation, in particular in the form of a focus electrode, can be provided. By the electrons impinging on the anode of the X-ray tube, a focal spot is formed on the anode surface. Typically, the X-ray tube is constructed such that the electrons impinge on the anode surface at an angle which is not equal to 90°. For example in the case of a substantially linear electron source, an equally elongated shape of the focal spot is produced.

[0013] The elongated shape of the focal spot can be optically shortened in such a way that the X-ray beam is shaped by a light shield which is reflected obliquely from the surface of the anode.

[0014] However, it is to be considered here that a portion of the surface of the X-ray beam close to the anode is weakened by the heel effect. The emitted X-ray radiation should radiate the further away from the plane perpendicular to the central axis of the computed tomography apparatus in which the focal spot is located, the more this effect occurs. However, it is necessary for the X-ray source and the associated detector not to be located in a common plane. In order to reduce the heel effect, it is possible to arrange the X-ray tube as a whole inclined with respect to the central plane of the computed tomography apparatus, that is to say to select an orientation angle a which is greater than zero. This of course enlarges the required construction space in the radial direction with respect to the central axis of the computed tomography apparatus.

[0015] The object conflict set out is considered according to the application as follows, namely that the quotient formed from the sum of the orientation angle a of the X-ray tube and the reflection angle γ as the numerator and the anode angle β as the denominator is at least two-thirds and at most two. In particular, it is possible to realize a design in which the quotient is at least two-fifths and at most eight-fifths, for example at least 1 and at most 1.6. In all cases, the quotient is dimensionless.

[0016] The possibility of opening the radiator-detector ring which does not necessarily have a circular basic shape provides practical advantages not only in the preparation of the examination in X-ray technology but also in activities which are carried out after the first X-ray technology research and before the examination in another X-ray technology, that is to say in the present case computed tomography, especially in medical operations. In particular, the position of the patient on the patient couch can remain unchanged even if the generation of the computed tomography recording is interrupted in order to carry out an operation in which the closed radiator-detector arrangement becomes an obstacle. In such a case, the movable portion of the radiator-detector ring can be moved away from the working area, wherein the remaining rigid portion of the radiator-detector ring remains in its original position which is required for the computed tomography imaging. In the renewed computed tomography examination, therefore, no renewed adjustment of the position of the patient or of the radiator-detector ring is necessary if it is not desired to change the volume to be examined.

[0017] The radiator-detector ring is preferably constructed from an odd number of radiator-detector elements independently of its shape. With an odd number of radiator-detector elements it is possible to make it so that no docking position between two radiator-detector elements precisely diametrically opposite another such docking position. If the focal spot is in the edge region of a radiator-detector element, that is to say close to a docking position between two sectors of the radiator-detector ring, the X-ray radiation emanating from this focal spot is incident on two X-ray detectors arranged next to one another in the circumferential direction, for example detectors involving photon counting. The use of line detectors is likewise considered. In this connection reference is made to WO 2019 / 057339 Al.

[0018] Independently of the shape, for example straight or curved, of the individual radiator-detector elements, the orientation angle a of the cathode, which can be adjusted by the angular position of the entire X-ray tube, can be greater than zero, in particular greater than 5°. This means that the electron beam emanating from the cathode is directed at least slightly radially outwards, that is to say away from the central axis of the computed tomography apparatus. The orientation angle is preferably not greater than 30°.

[0019] The anode angle β is for example at least 10° and at most 60°. In the case of an anode angle β of 10° and an arbitrary, preferably positive, orientation angle a, the plane, that is to say the face normal of the tangent plane, placed onto the anode in the focal spot forms an angle of 10° with the central axis of the computed tomography apparatus. The average reflection angle γ of the reflection of the X-ray radiation involved in the focal spot is for example at least 5° and at most 30°.

[0020] If for example an orientation angle a of 12°, an anode angle β of 20° and a reflection angle γ of 10° are selected, the quotient is 1.1. Equally for example a construction can be realized in which the orientation angle a = 30°, the anode angle β = 30° and the reflection angle γ = 18°. In this case a quotient (a + γ) / β of 1.6 results. A quotient of less than 1, namely two-fifths, is for example given in a construction with an orientation angle a of 0°, an anode angle β of 30° and a reflection angle γ of 12°. The same value of (a + γ) / β also results in a construction with an orientation angle a of 6°, an anode angle β of 45° and a reflection angle γ of 12°.

[0021] According to a possible first construction form of the computer tomograph apparatus, a radiator-detector ring formed by the radiator-detector elements depicts a split circle, wherein at least one radiator-detector element, which is configured as a sector, is displaceable, in particular deflectable, relative to the remaining radiator-detector elements. If there are a plurality of deflectable sectors, the sectors can be rigidly connected to one another, for example, and be deflectable as a whole out of the remaining radiator-detector ring. Alternatively, it is possible to support the plurality of deflectable sectors on the remaining radiator-detector ring in the manner of a gull-wing door.

[0022] According to another possible construction form, a radiator-detector ring formed by the radiator-detector elements depicts a polygon, in particular a rectangle, wherein there can be a plurality of rigidly interconnected radiator-detector elements, which are deflectable relative to the remaining radiator-detector ring. In any construction form, in the case of a uniform configuration of all radiator-detector elements, the handling of the elements can take place in a uniform manner, regardless of whether individual radiator-detector elements are elements provided for opening.

[0023] The possibilities for handling that can also be utilized in this case are explained, for example, in WO 2019 / 042587 A2. In the manufacture of cathodes that constitute the electron emitter, any of the solutions mentioned in the documents WO 2018 / 086737 Al and WO 2018 / 141485 Al can be employed, for example. In general, the X-ray tube of the computer tomograph apparatus can be configured to generate a series of X-ray pulses that differ from one another with respect to different parameters, in particular the duration of the individual pulses and the X-ray dose and the frequency of the X-ray radiation.

[0024] The anode is preferably a stationary anode, that is to say an anode that does not rotate within the anode housing. The anode can be a liquid-cooled anode, that is to say an anode configured to be flowed through by a coolant, or an anode configured without cooling channels. In the last-mentioned case, the anode is referred to simply as an uncooled anode.

[0025] An anode as explained in DE 10 2017 008 810 Al can be used, for example. The construction of the cathode that can be used as electron emitter of the computer tomograph apparatus can be chosen, for example, from the possibilities selected in WO 2019 / 057338 Al, which claims priority from the patent application DE 10 2017 008 810 Al.

[0026] The cathode is constructed in a preferred design for field emission of electrons. In particular, the cathode has nanorods, for example carbon nanotubes. Examples of possible materials for the cathode are listed in WO 2018 / 086737 Al.

[0027] According to one possible extension, each radiator-detector element has at least one first type of electron emitter and at least one second type of electron emitter, wherein the different emitter types within the radiator-detector element differ from one another with respect to their material and / or geometry.

[0028] Depending on the dimensions of the radiator-detector arrangement, the computed tomography apparatus can be suitable, for example, for examining a human head, for examining a chest or for a whole-body examination.

[0029] The detector of the computed tomography apparatus is constructed, for example, as a semiconductor detector. With regard to a particularly high sensitivity, a photon-counting detector is advantageous as a component of the computed tomography apparatus. In this regard, the document DE 10 2014 215 548 Al is exemplarily mentioned. BRIEF DESCRIPTION OF DRAWINGS

[0030] A number of embodiments of the application are further illustrated below with the aid of the drawings. Herein in the drawings:

[0031] Figure 1 A schematic view of a computed tomography apparatus is shown;

[0032] Figure 2 A simplified end view of a computed tomography apparatus according to the application is shown, which comprises an open radiator-detector ring; Figure 1

[0033] A view according to Figure 3 of a computed tomography apparatus, which comprises a closed radiator-detector ring; Figure 2

[0034] Figure 4 and 5 A view according to Figure 2 and 3 of a modified design form of a computed tomography apparatus is shown;

[0035] Figure 6 and 7 Further views according to Figure 2 and 3 of a design form of a computed tomography apparatus, which comprises a rectangular radiator-detector ring;

[0036] Figure 8 and 9 ​Schematic diagram showing details of a computer tomograph comprising a circular, split radiator-detector ring.

[0037] The following explanations apply to all embodiments unless stated otherwise. Components that correspond to one another or act in principle identically are denoted by the same reference signs in all figures. DETAILED DESCRIPTION

[0038] The computer tomograph generally designated 1 is designed in particular for the investigation of a human head, that is to say is constructed as a head CT device. Reference is made to the document WO 2018 / 086744 A2 cited at the outset for the principle construction of the computer tomograph 1.

[0039] The computer tomograph 1 is shown in Figure 1 a roughly schematic sectional view in which the median axis MA of the computer tomograph 1 lies in the drawing plane. The z direction of a Cartesian coordinate system is given by the median axis MA. The x and y axes of the coordinate system open out into a plane that is orthogonal to the drawing plane. The gantry generally designated 2 of the computer tomograph has the basic shape of a ring that lies in the x-y plane. This means that the plane in which the gantry 2 lies is oriented perpendicularly to the median axis MA.

[0040] In the embodiment, the X-ray tube 3 has an elliptical, non-circular shape in cross section as derived from Figure 1 Alternatively, for example, an X-ray tube whose cross-sectional shape is circular or polygonal, for example square, hexagonal or octagonal, can also be used.

[0041] The gantry 2 has a plurality of X-ray tubes 3 that are distributed in a rigid angular arrangement about the median axis MA in the operation of the computer tomograph 1. The associated X-ray detector 4, that is to say a semiconductor detector, is likewise provided in a ring-shaped space about the median axis MA. The entire arrangement consisting of the X-ray tubes 3 and the X-ray detector 4 is not rotatable, but is only movable in the z direction, that is to say in the longitudinal direction of the median axis MA. For this purpose, the gantry 2 is mounted on a movable stand 7. The plane in which the X-ray tubes 3 lie is moved relative to the plane in which the X-ray detector 4 lies in the axial direction, that is to say in the z direction.

[0042] Each X-ray tube 3 has a plurality of cathodes 5 as electron emitters. The associated anodes are designated 6 and are counted as anode arrangements 9 of the corresponding X-ray tube 9. The means for influencing the electron beam designated ES, in particular a focusing electrode, are not shown in Figure 1The beam center is not shown. The electron beam ES forms an angle with the median axis MA, which is referred to as the orientation angle a of the cathode 5. In embodiments, the orientation angle a is greater than zero. This means that the electrons emitted from the cathode 5 have a component of motion radially outward with respect to the median axis MA.

[0043] The focal spot, generally denoted BF, on which the electrons emitted from the cathode 5 impinge on the anode 6. In embodiments, the anode 6 is not rotatable, that is to say is configured as a stationary anode. Alternatively, a rotating disk anode can be used. In such a case, the electron beam ES is preferably oriented parallel to the rotation axis of the rotating disk anode. The orientation angle a thus corresponds to the angle of inclination of the rotation axis of the rotating disk anode with respect to the median axis MA.

[0044] The face normal FN of the tangent plane TE, on which the anode 6 is placed and in which the focal spot BF lies, forms an anode angle β with the median axis MA. The anode angle β is at least 10° and not more than 45° in all embodiments illustrated in the figures.

[0045] The X-ray radiation RS emanates from the focal spot BF, wherein, in Figure 1 Only the central beam of the X-ray beam is sketched in the center. The orientation of the X-ray radiation RS to be used for imaging is determined by means of a light shield in a manner known per se. For the emission of the X-ray radiation RS, the X-ray tube 3 has an X-ray window 8.

[0046] The X-ray radiation RS emanates from the X-ray tube 3 at an average reflection angle γ measured with respect to a radial line RL. The radial line RL is oriented orthogonally to the median axis MA and intersects the median axis MA and the center of the focal spot BF. That is, a reflection angle γ of zero degrees means that the X-ray radiation RS is oriented exactly in the radial direction, that is to say orthogonally to the median axis MA. On account of the axial misalignment of the X-ray detector 4 with respect to the X-ray tube 3 about the median axis MA, the reflection angle γ must be greater than zero. In the embodiments described, the reflection angle γ is at least 5°, however not more than 30°.

[0047] The sum of the reflection angle γ and the orientation angle a is at least one twelfth of the anode angle β and at most twice the anode angle β.

[0048] The cathode 5 is configured as a field emission cathode in embodiments. Here, a plurality of cathodes 5 is respectively assigned to a common anode 6 in each X-ray tube S. Here, each X-ray tube S can respectively have a plurality of cathodes 5, 25 of uniform or different configuration as electron emitters.

[0049] Each X-ray tube 3 is part of a radiator-detector element 11, 12, 13, 14, also one X-ray detector 4 each can be counted as such a radiator-detector element. The totality of the radiator-detector elements 11, 12, 13, 14 forms a non-rotating radiator-detector ring 10, which constitutes the gantry 2 and which, in accordance with Figures 1 to 5 and the embodiments 8 and 9, has a circular shape. In accordance with Figure 6 and 7 the embodiments, the radiator-detector ring 10 has a square basic shape, which, contrary to this, has no influence on the essential function of the same, which is important in terms of X-ray technology as well as in terms of handling. No housing is provided, which surrounds the gantry 2.

[0050] In all cases, the term "fixed" in the sense of the arrangement of the radiator-detector ring 10 is to be understood in such a way that, in the acquisition of the X-ray technology, no rotation of the radiator-detector unit around the central axis MA of the gantry 2 is given. Rather, by means of the X-ray tubes 3 and the associated X-ray detectors 4, which are distributed around the entire circumference of the gantry 2, a fan-shaped beam of X-ray radiation RS can be generated, which respectively emanates from the focal spot BF on the anode 6 of the X-ray tube 3.

[0051] In accordance with Figures 1 to 5 the embodiment, the radiator-detector ring 10 is constructed from a total of three radiator-detector elements 11, 12, 13, wherein the radiator-detector element 11 is fitted on the stand 7 and thus applies as a fixed radiator-detector element. Contrary to this, the radiator-detector elements 12, 13 enable the opening of the radiator-detector ring 10, so that this can be, for example, slid from the side over the patient couch 15.

[0052] For the opening of the radiator-detector ring 10, in the case Figures 1 to 3 a sole hinge 16 is provided, which is arranged between the radiator-detector elements, that is to say the sectors 11, 13. The sectors 12, 13, which in total extend over approximately 240° on the circumference of the radiator-detector ring 10, are in this case rigidly connected to one another and jointly deflect when opening and closing the ring 10.

[0053] In accordance with Figure 4 and 5 the embodiments, the following distinguishes from the construction form in accordance with Figures 1 to 3 , namely that there are two hinges 16, 17, on which the sector 13 or the sector 12 is deflectably hinged. The radiator-detector elements 12, 13 are thus openable in the pattern of a winged door.

[0054] In accordance with Figure 4 and 5Embodiments of the application have in common with the embodiments according to Figures 1 to 3 the structural form that in this case the plurality of radiator-detector elements 12, 13, 14, which together depict a U-shape, are jointly deflectable. By virtue of the flat shape of the entire sector, also the fixed sector 11, the examination region is particularly well accessible in the open radiator-detector ring 10.

[0055] Figure 8 and 9 Details of the X-ray tube 3 and of other components of X-ray technology are illustrated figuratively, which are applicable to all embodiments set forth. The radiator arrangement of the X-ray tube 3 is designated 18.

[0056] An emitter structure assembly 19 for generating an electron beam ES, which impinges onto the anode arrangement 9 and thereby generates a focal spot BF, is present in each X-ray tube 3. The focal spot BF does not necessarily have a substantially point-like structure. Rather, an elongated focal spot BF can be generated in principle in a known manner, wherein the position of the focal spot BF is understood in each case as the position of the point thereof.

[0057] According to Figure 8 , the emitter structure assembly 19 has different cathodes 5, 25 in order to generate different doses and / or wavelengths of X-ray radiation. In each case, electrons are extracted from the cathodes 5, 25 by means of an extraction grid 20, wherein the electron beam ES is deflectable in a defined manner by means of an electrode arrangement 21 having a plurality of electrodes 22, 23. The plurality of cathodes 5, 25 is jointly arranged on a circuit board 24.

[0058] The entire anode arrangement 9, which interacts with the emitter structure assembly 19 of the X-ray tube 3, extends over an angle a' on the circumference of the radiator-detector ring 10, which angle results from the number of radiator-detector elements 11, 12, 13, 14, that is to say sectors of the radiator-detector ring 10, wherein in Figure 8 the arrangement outlined in Fig. 1, five sectors, that is to say 120° sectors, of like extent are given.

[0059] The angle a' of the extension of the anode arrangement 9 along the circumferential direction of the radiator-detector ring 10 is slightly less than 120° in the case of Figure 8 Fig. 2. The angle β' is also significantly closer to 72°, which angle is given by the extension of the X-ray detector 4 over the circumference of the radiator-detector ring. In other words: the gaps formed between the individual X-ray detectors 4 over the circumference of the radiator-detector ring 10 are significantly narrower than the gaps formed between the individual radiator arrangements 18. The plurality of possible focal spot positions extends over an angle γ' within the X-ray tube 3, which is less than the angle a'.

[0060] The electrode arrangement 21 is configured for deflecting the electron beam ES alternatively onto the focal spot BF or a focal spot BF which is offset in comparison therewith in the circumferential direction of the radiator-detector ring 10 + , BF - . With regard to the arrangement according to Figure 8 and 9 , the focal spot BF + is deflected in the clockwise direction and the focal spot BF - is deflected in the counter-clockwise direction. The deflection of the electron beam which represents the offset of the focal spot BF is also referred to as beam switching and enables the focal spot BF - , BF, BF + to be positioned particularly densely on the circumference of the radiator-detector ring 10. Here, a total number of several hundred focal spot positions which corresponds to several times the number of electron emitters (cathodes 5, 25) can be achieved, which at the same time facilitates a saving-quality construction of the computed tomography apparatus 1 while high-quality imaging.

[0061] List of reference signs

[0062] 1 computed tomography apparatus

[0063] 2 table

[0064] 3 X-ray tube

[0065] 4 X-ray detector

[0066] 5 cathode, electron emitter

[0067] 6 anode

[0068] 7 gantry

[0069] 8 X-ray window

[0070] 9 anode arrangement

[0071] 10 radiator-detector ring

[0072] 11 radiator-detector element

[0073] 12 radiator-detector element

[0074] 13 radiator-detector element

[0075] 14 radiator-detector element

[0076] 15 patient couch

[0077] 16 hinge

[0078] 17 hinge

[0079] 18 radiator arrangement

[0080] 19 emitter structure assembly

[0081] 20 extraction grid

[0082] 21 electrode arrangement

[0083] 22 electrode

[0084] 23 electrode

[0085] 24 circuit board

[0086] 25 cathode of second type, electron emitter

[0087] a orientation angle

[0088] b anode angle

[0089] g reflection angle

[0090] a' angle, at which the anode arrangement of the radiator-detector element extends

[0091] a' angle, at which the anode arrangement of the radiator-detector element extends

[0092] b' angle, at which the detector of the radiator-detector element extends

[0093] b' angle, at which the detector of the radiator-detector element extends

[0094] g' angle range, at which the possible focal spot of the anode arrangement lies

[0095] g' angle range, at which the possible focal spot of the anode arrangement lies

[0096] BF focal spot (in general)

[0097] BF + , BF - focal spot, which is generated by means of the electron emitter (in a middle position and in two positions which are offset along the circumference of the radiator-detector ring)

[0098]

[0099] ES electron beam

[0100] FN face normal

[0101] MA median axis

[0102] RL radial line

[0103] RS X-ray radiation

[0104] TE section​

Claims

1. A computed tomography apparatus comprising a plurality of X-ray tubes (3) arranged at defined angular positions around a geometric mid-axis (MA), the X-ray tubes being components of radiator-detector elements (11, 12, 13, 14) which together form a radiator-detector ring (10) which can be opened by a shift of at least one of the radiator-detector elements (11, 12, 13, 14), wherein, Each X-ray tube (3) has at least one cathode (5, 25) provided for emitting electrons and has an associated anode arrangement (9) comprising at least one anode (6), each cathode (5, 25) with respect to the emission direction of the electrons has an orientation angle (a) with respect to the geometric median axis (MA), and a tangent plane (TE) imposed on the focal spot of the anode (6) has a face normal (FN) which forms an anode angle (b) with the median axis (MA), and the X-ray radiation (RS) emanating from the focal spot is directed onto an X-ray detector (4) at an average reflection angle (g) measured with respect to a radial line (RL) through the focal spot, the X-ray detector (4) being arranged in an axial direction with respect to the X-ray tube (3) offset with respect to the geometric median axis (MA), wherein the quotient formed from the sum of the orientation angle (a) and the reflection angle (g) and the anode angle (b) is at least two thirds and at most two, and each cathode (5, 25) is configured to interact with an electrode arrangement (21) of the X-ray tube (3) for generating the focal spot at one of at least three selectable positions on the anode arrangement (9).

2. The computed tomography apparatus of claim 1, wherein The orientation angle (a) is greater than zero and at most 30°.

3. A computed tomography apparatus as claimed in claim 1 or 2, characterized in that The anode angle (b) is at least 10° and at most 60°.

4. A computed tomography apparatus according to claim 1 or 2, characterized in that The average reflection angle (g) is at least 5° and at most 30°.

5. A computed tomography apparatus according to claim 1 or 2, characterized in that, The anode (6) is configured as a fixed anode.

6. The computed tomography apparatus of claim 5, wherein The anode (6) is configured as an uncooled anode.

7. The computed tomography apparatus of claim 5, wherein The anode (6) is configured as a liquid-cooled anode.

8. A computed tomography apparatus according to claim 1 or 2, characterized in that The quotient formed from the sum of the orientation angle (a) and the reflection angle (g) as the numerator and the anode angle (b) as the denominator is at least 2 / 5 and at most 8 / 5.

9. A computed tomography apparatus according to claim 1 or 2, characterized in that The cathode (5, 25) constitutes a field emission for electrons, and the cathode comprises nanorods.

10. The computed tomography apparatus of claim 9, wherein Each radiator-detector element (11, 12, 13, 14) has at least one cathode of a first type and at least one cathode of a second type, wherein the different cathode types within the radiator-detector element (11, 12, 13, 14) differ from one another in terms of their material and / or geometry.

11. The computed tomography apparatus of claim 9, wherein Each radiator-detector element (11, 12, 13, 14) constitutes a conversion between different X-ray frequencies and / or X-ray doses, wherein each focal spot is likewise selectable as a source of all adjustable X-ray frequencies and X-ray doses.

12. A computed tomography apparatus as claimed in claim 1 or 2, characterized in that A radiator-detector ring (10) formed by the radiator-detector elements (11, 12, 13, 14) describes a split circle, wherein at least one radiator-detector element (11, 12, 13, 14) configured as a sector is offsettable with respect to the remaining radiator-detector elements (11, 12, 13, 14).

13. The computed tomography apparatus of claim 12, wherein Each radiator-detector element (11, 12, 13, 14) to be opened is individually deflectable.

14. The computed tomography apparatus according to claim 1 or 2, characterized in that, The radiator-detector ring (10) formed by the individual radiator-detector elements (11, 12, 13, 14) describes a polygon, wherein the plurality of radiator-detector elements rigidly connected to one another are deflectable relative to the remaining radiator-detector ring (10).

15. The computed tomography apparatus according to claim 1 or 2, characterized in that, All of the radiator-detector elements (11, 12, 13, 14) have a uniform shape.

16. The computed tomography apparatus of claim 9, wherein The cathode comprises carbon nanotubes.

17. The computed tomography apparatus of claim 12, wherein At least one of the radiator-detector elements (11, 12, 13, 14) configured as a sector is deflectable relative to the remaining radiator-detector elements (11, 12, 13, 14).

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