Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
  • H01J35/08—Anodes; Anti cathodes
  • H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
  • H01J35/153—Spot position control
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/06—Cathode assembly
  • H01J2235/068—Multi-cathode assembly
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/081—Target material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/086—Target geometry

Definitions

• the invention relates to an X-ray source having a plurality of electron sources spaced apart in a longitudinal direction and to an X-ray system having such an X-ray source.
• Tomographic imaging X-ray methods such as those used for non-destructive material testing, but especially in medicine, illuminate the examination subject from different directions.
• the individual projections obtained in this way are then calculated into a spatial image of the examination object.
• the illumination of the examination object from different directions is achieved by a movement of the X-ray source.
• CT computed tomography
• the to- mosynthesis represents another medical examination procedure with the help of which a spatial image of the examination object, in this case the breast, can be obtained.
• the breast is illuminated from directions in a restricted angular range.
• the X-ray source is moved with respect to the examination subject.
• a movement of the X-ray source always involves technical problems. For example, high inertia forces occur during fast movement, which must be withstood by the mechanical design of the X-ray source.
• the X-ray source must be supplied with electrical energy and cooling water; Both supply lines must follow the movement of the X-ray source or through technically complex measures, such as grinding contacts or rotary unions for a movement of the X-ray source can be upgraded.
• the object of the present invention is to provide an X-ray source as well as an X-ray system with such an X-ray source which is suitable for the emission of a plurality of X-ray beams. is net and is improved in terms of their X-ray power.
• the X-ray source according to the invention has a plurality of electron sources spaced apart from one another in a longitudinal direction and a common anode, which is arranged opposite to the latter and likewise extends in the longitudinal direction.
• the electrons emanating from the electron sources strike the anode at spatially spaced locations, thus producing separate emission centers each associated with an electron source.
• the anode of the x-ray source is rotatable about a longitudinally oriented axis.
• an X-ray source having the features mentioned, the electrons striking the anode generate emission centers on the anode at spatially spaced locations. In this way, it is possible to construct an X-ray source which is suitable for emitting a plurality of X-ray beams but has only one anode.
• the common anode is designed to be rotatable. Instead of a focal spot, the electron beam impinging on the anode rotating during operation of the X-ray source generates a focal spot path which extends along the circumference of the anode. The area of this focal spot is much larger compared to the focal spot produced on a fixed anode.
• the volume of the anode which is heated by the impinging electrons.
• the introduced into the anode material thermal performance is thus distributed over a larger volume.
• more anode material is compared with a comparative anode.
• the X-ray source according to the invention therefore has a higher thermal load capacity. This effect has a particularly positive effect on an X-ray source which has a large number of emission centers.
• the axis of rotation of the anode extends in the longitudinal direction of the X-ray source.
• the spaced apart electron sources are also arranged along this longitudinal direction.
• the electrons emanating from the electron sources cause longitudinally spaced emission centers on one and the same anode.
• This geometry makes it possible to realize an X-ray source with separate emission centers and at the same time to use a rotating anode.
• the X-ray source advantageously has a mechanically very simple structure, since only one common anode with a single axis of rotation can be used to generate the separate emission centers.
• the anode is a rotary body; Preferably, this is cylindrical.
• the anode typically rotates at high frequency during operation of the x-ray source.
• rotational bodies are often easy to produce and highly resistant to centrifugal forces (inertial forces).
• the anode of the X-ray source is exposed to various loads.
• high centrifugal forces act on the anode material on the other hand, the anode is strongly heated by the impinging electrons.
• the anode in the region of the focal spot path must consist of the material suitable for the desired X-ray emission.
• the material causing a desired X-ray emission is also referred to below as the anode material.
• Such an anode material is tungsten, for example.
• the X-ray emission used is generally the brake spectrum, including the material-specific and characteristic X-ray lines. By using appropriate filters, the low-energy parts of the brake spectrum can be filtered out.
• an anode should satisfy as many requirements as possible at the same time.
• this should be mechanically resilient, and provide the desired X-ray emission.
• the X-ray source is improved in that its anode is a composite anode of a base body and a cover layer, which serves as an anode material.
• the base body and the cover layer have different material compositions.
• the structure and the selected material composition of such a composite anode can be flexibly adapted to the loads occurring.
• the cover layer occupies at least a portion of the lateral surface of the anode. This portion will also preferably extend along the circumference of the anode.
• the cover layer extends along the circumference of the anode in the form of segments, which are spatially spaced apart in the longitudinal direction.
• the individual segments of the cover layer are each assigned to an emission center, ie in each case a focal spot path generated by the electron beam of an electron source is located on a segment.
• the anode material of the cover layer is more expensive than the material which can be used for the base body of the anode. An economical handling of the anode material of the cover layer is therefore recommended. By doing this in the form of preferably annular segments is placed on or in the base body, only as much anode material is used as is necessary to produce the desired X-ray emission.
• the base material is subject to similar requirements as conventional rotary anodes.
• the base material is required to have high heat capacity and good thermal conductivity so that the heat introduced into the anode material can be reliably dissipated.
• the anode material is primarily selected with regard to the desired X-ray emission. In order for high X-ray emission powers to be achieved, the anode material usually has a high melting temperature.
• Such an X-ray source has an anode with a cover layer which is subdivided into segments of a first segment group and into segments of a second segment group. In each case a segment of the first segment group and a segment of the second segment group are arranged in pairs in the longitudinal direction in pairs. The segments of the first
• Segment group and the segments of the second segment group have a different material composition. This means that the segments are arranged in pairs on the anode, with one segment each of the first segment group and one segment of the second segment group being combined to form a pair. The segments are arranged such that respectively Segments of different segment groups are directly adjacent.
• an X-ray source In an X-ray source according to the above embodiment, it is possible to use the X-ray emissions of two different materials without having to perform a change of the X-ray source itself.
• the electron beam is selectively directed to the segments of the first or the segments of the second segment group.
• the change of the anode material can be effected both by a displacement of the electron beam and by a displacement of the anode. Since the segments of a pair are spaced apart in the longitudinal direction, such a displacement takes place in the longitudinal direction.
• At least one of the electron sources is designed such that the electrons emanating from it strike the surface of the anode in a direction that is different from their surface normal at the point of impact of the electrons.
• the electron beam emanating from the electron source viewed in a plane containing the axis of rotation of the anode and oriented substantially perpendicular to the beam direction of the electron beam, strikes the anode in a region between its edge and its axis of rotation.
• the at least one electron source is designed in such a way that the electrons strike it in a direction oriented at least approximately perpendicular to the longitudinal direction of the anode.
• the at least one electron source and the anode are movable relative to one another such that the direction in which the emitted electrons strike the surface of the anode in a transverse direction that is oriented both perpendicular to the longitudinal direction and perpendicular to the direction of the electrons is, is adjustable.
• the at least one electron source is designed such that it is adjustable with respect to the anode in a transverse direction.
• a change in the focal spot size is brought about by the adjustment of the electron beam and / or by the displacement of the anode.
• the size of the focal spot has a direct impact on the physical spatial resolution that can be achieved with the X-ray source.
• a particularly small focal spot which would allow a high physical spatial resolution, has the disadvantage that the anode is thermally very heavily loaded.
• a large focal spot on the other hand, ensures a low thermal load on the anode, but the physical spatial resolution is lower.
• the possibility of changing the focal spot size now gives the user the freedom to set a small focal spot size, for example, with low X-ray power required, and thus to achieve a high spatial resolution. If, on the other hand, the X-ray emission power is to be particularly high, with the spatial resolution being of secondary interest, the user has the option of increasing the focal spot size to protect the X-ray source from thermal overloading.
• the object is achieved by an X-ray system with the features of claim 14.
• the X-ray system according to the invention has an X-ray source according to one of the preceding claims.
• an examination object is illuminated from a plurality of different illumination directions, wherein these are each assigned to an emission center of the X-ray source. Since the above-explained X-ray source is suitable for generating high emission powers, short exposure times can be achieved with high resolution and at the same time fixed tube with the X-ray system according to the invention.
• Fig. 3 the X-ray source acc. Fig. 1 in cross section
• Fig. 4 the anode in a cross-sectional view
• Fig. 5 is a mammography system.
• Fig. 1 shows an X-ray source 2, as it can be used for example in a mammography system for generating tomosynthetic image data sets.
• the X-ray source 2 can be used in the same way for other X-ray systems in which the examination object is illuminated from a plurality of different directions.
• the X-ray source 2 includes a plurality of juxtaposed in the longitudinal direction 3 of the Röntgenquel- Ie 2 electron sources 4i to 4 n.
• the electron sources A 1 to 4 n each comprise a cathode based on carbon nanotubes, but they can be used in parallel. rather, conventional hot cathodes are used. Beam-forming components, such as a Welteneltzy- linder are not shown for reasons of clarity.
• the electron sources A 1 to 4 n which are arranged next to each other in the longitudinal direction 3 in the manner of an array can be driven individually so that they emit, individually or in groups, an electron beam 6i... 6 n which is incident on the surface of the X-ray source during operation 2 rotating anode 8 is directed.
• the essentially cylindrical anode 8 is held rotatably in the housing 10 of the X-ray source 2 via a shaft 9 about an axis A.
• At the anode 8 is a composite anode of a base body 12 and a cover layer formed 14i to 14 n from a large number of mutually spaced apart in the longitudinal direction 3 segments.
• Each electron source A 1 to 4 n is associated with an opposing segment 14 ⁇ to 14 n .
• An emanating from the electron source A 1 E- lektronenstrahl 6 X is thus directed to the segment 14 X.
• the material of the segments 14i to 14 n determines the type of X-ray emission of the X-ray source 2.
• the segments 14i to 14 n of the cover layer of molybdenum are examples of the cover layer of molybdenum.
• the X-ray source 2 is suitable according to the number of their electron sources 4i to 4 n and segments 14 ⁇ to 14 n suitable to deliver n X-ray beam simultaneously or successively. This is done by appropriate control of the electron sources A 1 to 4 n .
• the emission centers generated by the electrons incident on the segments 14i..l4 n are spaced apart from one another in the longitudinal direction 3 in accordance with the segments 14i..l4 n themselves. Consequently, the X-ray source 2 is adapted to emit X-ray beams coming from different directions.
• the anode 8 Since, during the operation of the X-ray source 2, the anode 8 rotates about the axis A, the anode 8 is formed along the circumferential direction of the segments 14i to 14 n one from the respective electron beam 6 1 to 6 n heated focal spot.
• the width of the segments 14 ⁇ to 14 n is just chosen so that it corresponds substantially to the width of the focal spot.
• the introduced into the anode 8 heat is discharged mainly in the form of radiation again.
• the anode 8 is traversed in its interior by cooling channels, so that they can be actively cooled by a cooling medium, which is supplied for example via the axis 9 of the anode 8.
• the base body 12 and the segments 14 ⁇ to 14 n are made of different materials. While the material of the segments 14 ⁇ to 14 n determines the type of X-ray emission of the X-ray source 2, the base body 12 mainly serves to dissipate the heat introduced by the electron beams 6 1 to 6 n into the segments 14 i to 14 n . For this reason, the segments 14 ⁇ to 14 n are embedded in the surface of the base body 12, which is made of graphite because of its good thermal conductivity ability. The part of the circumferential surface of the base body 12 engaging segments 14i to 14 n extending along the periphery of the base body 12 and are preferably formed in the form of tires or rings.
• the emission of the X-ray source 2 is dependent on the material of the segments, which has the same function and function as the material of the anode in conventional X-ray sources. For this reason, the material of the segments 14i to 14 n also referred to as anode material.
• FIG. 2 shows a further X-ray source 2, which has two different anode materials.
• the X-ray source 2 is suitable for the emission of two different X-ray spectra (or in general of two different X-ray emissions).
• the anode 8 comprises segments 14 la , 14 lb to 14 na , 14 nb , which are subdivided into two segment groups with the indices a and b.
• the segments 14 to 14 na la segment group a are made of molybdenum, while the segments 14 to 14 lb nb segment group b are of tungsten.
• the segments 14 la , 14 lb to 14 na , 14 nb are combined in pairs, two segments 14 ia , 14 lb are assigned to an electron source 4 X.
• the electron beam 6 X emanating from the X-ray source 4 i is directed, with the aid of deflection coils 16, optionally as electron beam 6 ia onto the molybdenum segment 14 ia or as electron beam 6 lb onto the tungsten segment 14 lb. It is now possible to direct the electron beams 6i to 6 n of all the electron sources A 1 to 4 n either to the molybdenum segments 14 la to 14 na or to the tungsten segments 14 lb to 14 nb . In this case, the X-ray emission of the entire X-ray source 2 would be switched. But it is also possible to switch selectively only individual electron sources 4i to 4 n, so that a X-ray source 2 with mixed emission characteristics.
• a change of the X-ray emission of the X-ray source 2 can - as described - by a deflection of the electron beams 6i to 6 n carried out by means of deflection coils 16.
• the anode 8 can be displaced in the longitudinal direction 3 by a corresponding amount, so that the electron beams 6i to 6 n now meet the tungsten segment 14 lb to 14 nb instead of the original molybdenum segments 14 la to 14 na, for example ,
• FIG. 3 shows a cross-sectional view of the X-ray source 2 shown in FIG. 1 along the sectional plane designated III-III.
• the n emanating from the electron source 4 n electron beam 6 is incident on the rotating within the housing 10 about the axis A anode 8 in the region of the segment 14 n. Due to the electron bombardment, within the anode denmaterials of the segment 14 n an emission center 18 n caused. Usually this is also called a focal spot.
• the n outgoing X-ray beam from the emission center 18 2O n leaves the material of the segment 14 and n is the window 22 n is limited.
• the n emanating from the emission center 18 X-ray 2O n can except by the process shown in Fig.
• the emission characteristic of the X-ray source 2 can be changed by a displacement of the electron source 4 n in a transverse direction 24, which is oriented substantially perpendicular to the axis A or not in the longitudinal direction 3, which is not shown in FIG. 3.
• the cross-direction 24 is also emitted from the electron source 4 n n substantially perpendicular to the direction of the electron beam 6, oriented.
• Fig. 4 shows a detail view of the X-ray source 2 shown in Fig. 3, wherein the electron source 4 n both IH rer in Fig. Position 3 shown is also shown in a position displaced in the transverse direction 24 position as an electron source 4 n '. In accordance with this displacement, the electron beam 6 n strikes the surface of the anode 8 as now electron beam 6 n 'at a different angle.
• the irradiation direction of the two electron beams 6 n , 6 n 'before and after the displacement of the electron source 4 n is considered below relative to the surface normal N or N' of the anode 8.
• the angle between the direction of irradiation of the electron beam 6 n and the surface normal N before the shift is greater than the angle between the electron beam 6 n 'and the surface normal N' after displacement thereof.
• the position of the emission center or focal spot 18 n changes .
• a larger focal spot 18 n ensures that the thermal energy of the electrons of the incident electron beam 6 n decelerated in the anode material is distributed into a larger volume of the anode 8. As a result, the thermal load of the anode 8 decreases at the expense of a lower physical spatial resolution.
• a plane E is introduced only for clarification, containing the axis of rotation A and substantially perpendicular to the electron beams 6 n , 6 n 'oriented.
• impact points 26, 26' are constructed.
• the points of incidence 26, 26 'lying in the plane E always lie between the outer edge of the anode 8 and its axis A.
• the point of incidence 26, 26' travels selectively into an area close to the axis or into an area the edge of the anode 8.
• the X-ray source 2 can be used in X-ray machines, in which an examination object is irradiated from different directions. Examples of such X-ray devices in the field of medical technology are: mammography devices, computer tomographs (CT) or devices for rotational angiography.
• CT computer tomographs
• the use of an X-ray source 2 will be explained below by way of example with reference to the mammography system 28 shown in FIG. 5.
• the x-ray source 2 comprises schematically illustrated x-ray emitters 29 i to 29 n , which extend in the longitudinal direction 3 of the x-ray source 2.
• An X-ray emitter 29,... 29 n respectively comprises at least one electron source 4 and its associated segment 14 of the anode 8.
• the beam located between a detector 30 and a compression plate 32 Breast 34 are irradiated from different illumination directions 36i to 36 n .
• the individual X-ray emitters 29 i to 29 n are excited for emission in chronological sequence. If, for example, the emission center 29 X is excited to emit, the breast 34 is irradiated from the direction 36 i. When the emission center is excited to emit n 29, the chest 34 is illuminated from the direction n 36th
• a mammography system 28, as shown in FIG. 5, is suitable for recording tomosynthetic image data records.

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• 2008
  • 2008-07-15 DE DE102008033150A patent/DE102008033150B4/de not_active Expired - Fee Related
• 2009
  • 2009-06-09 US US13/054,371 patent/US8619946B2/en not_active Expired - Fee Related
  • 2009-06-09 CN CN2009801278666A patent/CN102099888B/zh not_active Expired - Fee Related
  • 2009-06-09 WO PCT/EP2009/057085 patent/WO2010006846A1/de active Application Filing
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