X-ray emission device and method of assembly

An X-ray emission device and a method of assembly of the device having a casing with a window and an X-ray tube place in the casing. The tube comprises an anode assembly equipped with an anode, a cathode assembly equipped with a cathode and an envelope containing the anode and the cathode. The longitudinal positioning of the X-ray tube in the casing is produced on the anode side. The angular positioning of the X-ray tube in the casing on a longitudinal axis is produced on the anode side. A bayonet on the casing fastens a rotation axis support for the anode. The cathode is fixed in an angular position predetermined in relation to the bayonet by pins.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 0006467 filed May 19, 2000, the entire contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention concerns the field of radiology apparatus and, in particular, the assembly of such an apparatus.

A radiology apparatus used, for example, in mammography, RAD or RF conventional radiology and neurological or even vascular (peripheral or cardiac) radiology generally comprises: an X-ray tube and a collimator for forming and delimiting an X-ray beam; an image receiver, generally a radiological image intensifier and a video camera, or even a solid-state detector; a positioner carrying the X-ray tube and collimator assembly on one side and image receiver on the other, movable in space on one or more axes, and a table for supporting a patient. An example of such an apparatus is disclosed in EP-A-972,490 and the apparatus has use in x-ray imaging.

An X-ray tube mounted, for example, in a medical radiology apparatus comprises a cathode and an anode, both contained in a vacuum-tight envelope, for electric insulation between the two electrodes. The cathode produces an electron beam which is received by the anode on a small surface constituting a focus from which the X-rays are emitted.

On application of a high voltage by a generator at the terminals of the cathode and anode, a so-called anode current is established in the circuit through the generator producing the high voltage. The anode current crosses the space between the cathode and anode in the form of an electron beam which bombards the focus.

In order to obtain a high-energy electron beam, the electrons are accelerated by an intense electric field produced between the cathode and anode. For that purpose, the anode is brought to a very high positive potential in relation to the cathode. That potential can exceed 150 kV. To produce those potentials, high-voltage supply devices are used.

A part of the X-ray emission from the focus crosses the envelope and then the window of the casing. The window being of small dimensions, the cathode, anode and window have to be mounted in given relative positions that are precise and reproducible. Furthermore, the collimator is mounted outside the casing and is crossed by the X-ray beam. As a result, the position of the focus and the position of the axis of propagation of the X-ray beam, in other words, the position of the X-ray beam, have to be perfectly defined, notably, in relation to the casing. The position of the point of emission or focus of the X-ray beam is determined by three translations and three rotations of the X-ray tube in relation to the casing in a three-dimensional reference. Two of the positions in translation and two of the positions in rotation are obtained by design. However, the position in translation along the axis of rotation of the anode and the position in rotation on the same axis require adjustments requiring highly skilled labor, a considerable time and tools. In particular, it often proves indispensable to carry out X-ray emissions following which the apparatus is disassembled in order to perfect the adjustment and is reassembled, and so on until obtaining the desired positioning making it possible to satisfy radiation protection standards and to obtain good-quality images. Such an apparatus is disclosed in WO A 97/44809.

BRIEF DESCRIPTION OF THE INVENTION

An embodiment of the invention is directed to an economical method of assembly of x-ray tube for a radiology apparatus.

An embodiment of the invention is directed to a method of assembly with positioning obtained by design.

The method of assembly, according to one aspect of the invention, is intended for a radiology apparatus X-ray emission means. The emission means comprises a casing opened by a window and an X-ray tube placed in the casing. The X-ray tube comprises an anode assembly equipped with an anode, a cathode assembly equipped with a cathode and an envelope. The anode and the cathode are placed in the envelope in order to emit an X-ray beam passing through the window. The longitudinal positioning of the X-ray tube in the casing is produced on the anode side and the angular positioning of the X-ray tube in the casing on a longitudinal axis is produced on the anode side.

The invention is also directed to an X-ray emission device intended for a radiology apparatus. The device comprises a casing opened by a window and an X-ray tube placed in the casing. The X-ray tube comprises an anode assembly equipped with an anode, a cathode assembly equipped with a cathode and an envelope, the anode and the cathode being placed in the envelope in order to emit an X-ray beam passing through the window. The anode assembly comprises a means of longitudinal positioning of the X-ray tube in the casing and a means of angular positioning of the X-ray tube in the casing on a longitudinal axis.

The invention is also directed to an X-ray emission device intended for a radiology apparatus. The device comprises a casing opened by a window and an X-ray tube placed in the casing. The X-ray tube comprises an anode assembly equipped with an anode, a cathode assembly equipped with a cathode and an envelope, the anode and the cathode being placed in the envelope in order to emit an X-ray beam passing through the window. The anode assembly comprises a bayonet for angularly positioning the X-ray tube in the casing on a longitudinal axis and for fastening the X-ray tube to the casing.

A radiology apparatus X-ray emission device is thus obtained, the X-ray beam of which is positioned with great precision, while being simple to assemble.

DETAILED DESCRIPTION OF THE INVENTION

The anode assembly comprises an anode shaft integral with the anode, a rotation axis support and an electric drive motor of the anode equipped with a stator and a rotor, one reference surface is formed on the rotation axis support, one reference surface is formed on the casing and both reference surfaces are brought in contact.

In one embodiment of the invention, the axial distance between the reference surface of the rotation axis support and the zone of the anode from which the X-ray beam is emitted is predetermined.

In one embodiment of the invention, the axial distance between the reference surface of the casing and the window is predetermined.

In another embodiment of the invention, the rotation axis support is fastened by a bayonet on the casing. The cathode can be fixed in an angular position predetermined in relation to the bayonet.

The cathode assembly comprises feed pins and crossing the envelope, the pins are fastened in an angular position predetermined in relation to the cathode. In an embodiment of the invention, the cathode assembly being integral with a portion of the envelope, the portion of the envelope is fastened on another portion of the envelope integral with the anode assembly, with the pins in an angular position predetermined in relation to the anode assembly. In an embodiment of the invention, the pins are fastened in a position aligned with the cathode.

In an embodiment of the invention, the angular positioning of the X-ray tube in the casing on a longitudinal axis is accomplished by contact of a bayonet of the anode assembly with a surface integral with the casing.

The surface integral with the casing can be formed by the bottom of a ramp formed in a flange integral with the casing.

The bayonet is generally integral with a non-revolving part of the anode assembly. A means complementing the bayonet can be integrated with the casing.

The anode assembly may comprise a reference surface capable of cooperating with a corresponding reference surface formed on the casing. The reference surface can be machined.

The cathode assembly may comprise feed pins crossing the envelope, the pins being fastened in an angular position predetermined in relation to the cathode. The cathode assembly being integral with a portion of the envelope, the portion of the envelope is fastened on another portion of the envelope integral with the anode assembly, with the pins in an angular position predetermined in relation to the anode assembly.

In an embodiment of the invention, the pins are in a position aligned with the cathode.

In an embodiment of the invention, the anode assembly comprises an anode shaft integral with the anode, a rotation axis support and an electric drive motor of the anode equipped with a stator and a rotor. One reference surface is provided on the rotation axis support, one reference surface is provided on the casing and both reference surfaces are in contact.

In an embodiment of the invention, the rotation axis support comprises a bayonet capable of cooperating with a corresponding part of the casing for the fastening of the axis support.

As shown inFIG. 1, the radiology apparatus contains an L-shaped stand1with a generally horizontal base2and a generally vertical support3fastened to an end4of the base2. At the opposite end5, the base2contains an axis of rotation parallel to the support3and on which the stand is capable of turning. A support arm6is fastened at a first end to the top7of the support3, rotating on an axis8. The support arm6can take the shape of a bayonet. A C-shaped circular arm9is maintained by another end10of the support arm6. The C-shaped arm9is capable of sliding rotating on an axis13relative to the end10of the support arm6.

The C-shaped arm9supports an X-ray emission means11and an X-ray detector12in diametrically opposite positions facing each other. The detector12contains a flat detection surface. The direction of the X-ray beam is determined by a straight line joining a focal point of the emission means11to the center of the flat surface of the detector12. The axis of rotation of the stand1, the axis8of the support arm6and the axis13of the C-shaped arm9are secant at a point14called isocenter. In mid-position, those three axes are perpendicular to one another. The axis of the X-ray beam also passes through point14.

A table15, provided to accommodate a patient, possesses a longitudinal orientation aligned with axis8in rest position.

AsFIG. 2shows, the X-ray emission means11comprises a cathode16and an anode17contained in an envelope18transparent to X-rays. The assembly or X-ray tube19consisting of the cathode16, the anode17and the envelope18is in turn contained in a casing20opaque to X-rays, except for a part situated opposite the X-ray beam emitted by the anode17, which consists of a window21of material transparent to X-rays. The space between the transparent envelope18and the opaque casing20is filled with oil22used for electric insulation and for cooling of the X-ray source.

As is well known, the cathode16emits an electron beam that strikes the turning anode17, which re-emits an X-radiation from a focal surface. The X-ray beam emitted by the anode17consists of radiation emanating from that focal surface, but also of extrafocal parasite radiations which are eliminated, preferably as close as possible to the emission source.

More precisely, referring toFIGS. 3 to 6, it can be seen that the anode assembly referenced23comprises elements that are at the same voltage as the anode17. The anode assembly23comprises a turning part24and of a non-turning part25. The turning part24contains, in addition to the anode17, a support shaft26of the anode17and a rotor27, for example, of cage winding type. Roller bearings, not represented, can be provided to support the turning part24at high angular velocities in the order of 10,000 revolutions per minute.

The non-turning part25is generally cylinder-shaped and placed radially between the shaft26it supports and the rotor27, placed in turn inside and at a short distance from a tubular portion28of the casing18. Outside and around the tubular portion28, an electric insulator29and a stator30are arranged. The rotor27, the electric insulator29and the stator30form an electric motor capable of driving the anode17. The electric insulator29and the stator30are supported by the casing20and are separated by a short distance from the tubular portion28.

The non-turning part25is provided, at its end opposite the anode17, with a ring-shaped reference surface31, whose axial distance from the anode17and, in particular, from the X-ray emission focus32, is determined by the manufacturing dimensions of the intermediate parts such as the shaft26and the bearings and known with great precision. A pin33is fastened to the non-turning part25beyond the reference surface31. The pin33is in turn connected to a high-voltage supply, not represented, by means of a bushing34formed in the casing20. In other words, the axial distance between the focus32and the reference surface31is constant and reproducible.

The tubular portion28of the envelope18ends in a collar35, tightly fastened, for example, by welding to the non-turning part25in order to enable a vacuum to be maintained inside the envelope18.

From the reference surface31and axially toward the pin33, the non-turning part25is provided with a cylindrical surface36extending from the narrow diameter of the reference surface31and with an end surface37. The casing20contains a flange39provided with a ring-shaped tubular portion40of diameter adapted to that of the cylindrical surface36. The tubular portion40is provided with a radial end surface41forming a reference surface capable of being in contact with reference surface31.

On the cylindrical surface36, a transverse bayonet38is formed, containing two diametrically opposite fingers38aand38bdirected radially outward. The fingers38aand38bare of unequal lengths, the length being taken between the cylindrical surface36and the free end of each finger38a,38b. The precise angular position of the non-turning part25can thus be determined and not at just π radians, as in case the fingers were of equal lengths.

In the tubular portion40, two ramps42are hollowed out in dimensions adapted to the bayonet38, open on the side of the radial surface41and of identical shape. The ramps42can be spiral or even L-shaped with a roughly axial entry zone and a roughly radial locking zone. In any event, the ramps42are provided with bottoms43of angular position defined in relation to the flange39in which the bottoms43are formed and, consequently, of angular position defined in relation to the casing20and to the window21. The angular position of the bayonet38in relation to the cathode16is also precisely defined. In other words, contact of the bayonet38with the bottoms43of the ramps42secures the angular positioning of the X-ray tube19in the casing20.

The flange39is fastened by means of a plurality of screws44axially oriented on a radial surface45of a ring46fastened inside a tubular part47of the casing20. The tubular part47also supports the window21. The flange39is angularly positioned relative to the window21. The positioning can be secured by means of a slug integral with the ring46or flange39or by means of a circumferentially irregular distribution of screws44, for example, with three screws44spaced two-by-two 90°.

The axial position of reference surface41relative to the center of the window21is defined and known with great precision. Thus, the axial position of the focus32relative to the center of the window21is defined and known with great precision by design and not by adjustment with successive approximations.

The cathode assembly referenced48as a whole contains elements that are at the same voltage as the cathode16. The cathode assembly48comprises, in addition to the cathode16, an arm forming a cam49and supporting the cathode16and a center part50supporting the arm49and in contact with the end of the envelope18opposite the anode17.

A plurality of parallel pins51, three here, tightly cross the envelope18, being axially oriented. One of the pins can be coaxial with the shaft26and the other pins placed in the same plane, for example, the cut plane ofFIG. 2. The pins51are connected to a high-voltage supply, not represented, by means of a bushing52formed in the casing20.

The angular positioning of the cathode16relative to the longitudinal axis of the tube19, which is also the axis of rotation of the anode17, makes it possible to emit the X-rays properly in relation to the window21. The angular positioning is obtained by means of pins51which are mounted and fastened in a given position relative to the cathode16and then relative to the bayonet38.

In the example illustrated, the pins51are arranged in a plane passing the longitudinal axis of the tube19and perpendicular to a plane passing through the cathode16and through the longitudinal axis of the tube19. The positioning can be carried out before the final closure of the envelope18when it is still divided into a part integral with the pins51and a part integral with the collar35. On final closure of the envelope18, in other words, on sealing of its two parts, the pins51are angularly positioned in a given and precise manner in relation to the bayonet38. In the example illustrated, the pins51and the bayonet38are coplanar. The angular orientation of the bayonet38and cathode15relative to the longitudinal axis of the tube19is constant. The angular orientation is obtained on the manufacture of the tube19and is therefore predictable.

Once the X-ray tube19is mounted and sealed, it is brought into a casing20equipped with the flange39, insulator29and stator30. The cylindrical surface36is presented and engaged in the bore of the tubular portion40, the bayonet38entering the ramps42. The X-ray tube19is turned on its longitudinal axis until the bayonet38is brought in contact with the bottoms43of the ramps42. The differences in lengths between the fingers38aand38bthen makes it possible to know the angular position of the X-ray tube19. The angular position of the window21integral with the casing20is also known and defined. Consequently, the angular position of the cathode16is entirely and precisely defined in relation to the window. The bayonet38serves both as a means of fastening and as a means of angular positioning.

The angular positioning is thus achieved. The longitudinal positioning is secured by contact between the reference surfaces31and41and maintained by the bayonet38tightened in the ramps42.

A threaded portion can possibly be provided on the non-turning part25beyond the radial surface37in order to cooperate with a nut, not represented, and complete the locking.

The bushing52is then fastened in the casing20and the pins51are fastened to the bushing52.

A simple and safe assembly method is thus obtained, avoiding a complex calibration including the stages of assembly, X-ray emission, disassembly, adjustment and reassembly, possibly repeated multiple times. The cost of assembly and the risk of radiation exposure of personnel are thus reduced.

Various modifications in structure and/or steps and/or function may be made by one skilled in the art without departing from the scope of the invention.