Control device for an x-ray tube and method for operating an x-ray tube

Abstract

The invention relates to a control device for an X-ray tube (2), comprising a housing (29) that is designed as a shield, in which an anode current regulating unit (1) is arranged and which is connected to a cathode power supply unit (18), a plurality of cathode voltage switches (20, 21, 22, 23, 24) which are to be connected to in each case a cathode (4), and a programmable assembly (25), in which the control of the cathodes (4) is determined. The cathode power supply unit (18), the cathode voltage switches (20, 21, 22, 23, 24) and the programmable assembly (18) are also arranged in the housing (29).

Claims

1. A control device for an X-ray tube, the X-ray tube comprising an anode configured as an X-ray emitter and a plurality of cathodes for generating electron beams directed at the anode; the control device comprising: a housing configured as a shield; an anode current regulating unit connected to a cathode power supply unit; a plurality of cathode voltage switches, and a plurality of cathodes, each of the plurality of cathode voltage switches being connectable to a cathode; a programmable assembly, in which control of the cathodes is determined, wherein the anode current regulating unit, the cathode power supply unit, the cathode voltage switches and the programmable assembly are arranged in the housing; a plurality of focusing electrodes associated with individual cathodes of the plurality of cathodes, and an extraction grid provided between the cathodes and the focusing electrodes, wherein the extraction grid is grounded independently of the focusing electrodes; wherein the programmable assembly comprises a field programmable gate arrangement (FPGA), a microcontroller, and a multiplexer, the FPGA being programmable so that a pulse sequence is triggered in real time, wherein timing of the pulse sequence occurs solely through the FPGA, and wherein the multiplexer is configured to switch between a desired voltage level for a boost and for an actual pulse of the pulse sequence.

2. The control device of claim 1, wherein the cathode voltage switches are configured as a high-voltage switch bank with a plurality of MOSFETs.

3. The control device of claim 2, wherein said device comprises a discharge circuit configured for discharging capacitances formed by the cathodes including feed lines, which is connected to the cathode voltage switches.

4. The control device of claim 1, wherein the programmable assembly is configured for storing operating parameters measured during operation of the X-ray tube.

5. The control device of claim 1, wherein the cathodes comprise field emission cathodes.

6. The control device of claim 5, wherein the cathodes comprise nanosticks, and wherein the nanosticks are electron emitters and are at least one of carbon nanotubes, nanotubes made of lanthanum hexaboride, and nanotubes made of cerium hexaboride.

7. The control device of claim 1, wherein the cathodes comprise dispenser cathodes.

8. The control device of claim 1, further comprising an anode voltage supply unit.

9. The control device of claim 8, wherein the anode voltage supply unit is configured for pulsed operation of the anode.

10. The control device of claim 8, wherein the anode voltage supply unit comprises a Marx generator.

Description

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is a an overview of an X-ray apparatus.

(2) FIGS. 2-3 provide a focusing device suitable for the X-ray apparatus according to FIG. 1.

(3) FIGS. 4-5 show the focusing device incorporated in the X-ray apparatus according to FIG. 1.

(4) FIG. 6-7 depict an additional possible embodiment of a focusing device suitable for the X-ray tube according to FIG. 1.

(5) FIG. 8 is a schematic representation of a control device for the X-ray apparatus according to FIG. 1.

(6) FIG. 9 shows the theoretical design of an anode power supply unit of the x-ray apparatus according to FIG. 1.

(7) FIG. 10 shows a signal chain for controlling a current source for supplying power to the cathodes of the X-ray apparatus according to FIG. 1.

(8) FIG. 11 provides a block diagram, the structure of a high-voltage switch bank, which is supplied with power via the power source in FIG. 10.

(9) FIG. 12 shows a switch for pulsed operation of the anode of the X-ray apparatus according to FIG. 1.

(10) FIG. 13 provides a power supply circuit of an anode of an additional X-ray apparatus.

(11) FIG. 14 depicts an alternative embodiment for controlling an anode of an X-ray apparatus.

(12) FIG. 15 provides the theoretical design of a circuit for pulsed operation of an anode of an x-ray apparatus with variable voltage levels.

(13) FIG. 16 is a diagram of properties of a component of the circuit according to FIG. 15.

(14) FIG. 17 is a block diagram of the structure of a cathode control device of the X-ray apparatus according to FIG. 1.

(15) FIG. 18 is a diagram of a current pulse generated with the cathode control device of the x-ray apparatus according to FIG. 1.

LIST OF SYMBOLS

(16) 1. X-ray apparatus 2. X-ray tube 3. Control device 4. Electron source, cathode 5. Anode 6. Focusing device 7. Ceramic substrate 8. Metallization 9. Emitter layer 10. Extraction grid 11. Focusing electrode 12. Focusing electrode 13. X-ray window 14. Anode power supply unit 15. Voltage supply unit of the focusing electrode 12 16. Voltage supply unit of the focusing electrode 11 17. Voltage supply unit of the extraction grid 18. Voltage supply unit of the cathodes 19. Anode current control unit 20. Cathode voltage switch 21. Cathode voltage switch 22. Cathode voltage switch 23. Cathode voltage switch 24. Cathode voltage switch 25. Programmable module 26. Microcontroller 27. FPGA 28. Cathode control device 29. Housing 30. Exterior housing 31. Anode controller 32. Step-down converter 33. Royer oscillator 34. Transformer 35. Cascade circuit 36. User interface 37. Digital signal processor 38. FPGA 39. Optocoupler 40. FPGA 41. Digital-analog converter 42. Switching element 43. Multiplexer 44. Connection 45. Connection 46. Voltage monitoring 47. Gate driver 48. Logic building block 49. Optocoupler 50. Inverter 51. Trigger signal 52. Gyrator circuit 53. Phase shift PWM controller 54. Oil tank 55. Controller 56. Alternating current-direct current converter 57. Gate driver 58. Gate driver 59. Optocoupler 60. High-voltage switch 61. Line voltage connection 62. Inverter 63. Transformer 64. Alternating current-direct current converter 65. Marx generator 66. Circuit 67. Measuring device 68. Discharge circuit BP Reference potential CoV Compensator voltage CR1 . . . CR4 Control loop EB Electron beam EP Discharge phase GA1, GA2 Grid connections HA Heating connection I.sub.A-actual Anode actual current I.sub.A-S Anode current setpoint IC Inductor current I.sub.E Emitter current IER Inductor energy recovery phase I.sub.F1 Current through focusing electrode 11 I.sub.F2 Current through focusing electrode 12 I.sub.G Grid current IP Idling phase KS Constant current level PE Peak PPC Prepulse compensation PrPh Preload phase PuPh Pulse phase duration RS Ramp start RE Ramp end RV Ramp shift Sig Output signal SR Voltage decline phase t, t.sub.0, t.sub.1 Time T1, T2, T3 Trigger signals U.sub.A Anode voltage U.sub.F1, U.sub.F2 Voltage of focusing electrodes 11, 12 U.sub.G Grid voltage VI Comparison current VSi Comparison signal XR X-ray radiation

DETAILED DESCRIPTION

(17) Unless stated otherwise, the explanations that follow pertain to all exemplary embodiments. Corresponding parts or parameters are labeled with the same reference symbols in all Figures.

(18) An X-ray apparatus 1 comprises an X-ray tube 2 and a control device 3. Components of the X-ray tube 2 are a cathode 4 as electron source and an anode 5, which is struck by an electron beam EB generated by the cathode 4, generating X-rays XR. Between the electron source 4 and the anode 5, a focusing device 6 for the electron beam EB is located.

(19) In the exemplary embodiment according to FIG. 1, the electron source 4 is designed as a field emission cathode. Here, on a ceramic substrate 7, a metallization 8 and an emitter layer 9 containing carbon nanotubes are located. An extraction grid 10 is at a slight distance from the emitter layer 9.

(20) The focusing device 6 comprises various focusing electrodes 11, 12 connected sequentially. Design variants of the focusing electrodes 11, 12 are sketched in FIGS. 2 to 7. In each case, the X-rays XR generated at a focal spot of the cathode 5 pass through an X-ray window 13 from the X-ray tube 2. A corresponding detector for the X-ray apparatus is not shown.

(21) The control device 3 used for operating the x-ray tube 2 comprises an anode power supply unit 14, which supplies the anode 5 with high voltage. The electric current actually flowing through the anode 5 is designated as I.sub.A-actual. In contrast, I.sub.A-S designates the anode setpoint.

(22) The value of the anode setpoint, I.sub.A-S is entered into an anode current control unit 19. The anode current control unit 19, as the power source, constitutes a central unit of a current control loop, which can be of various types, as will be further explained in the following.

(23) Independently of the detailed design of the anode current control, the control device 3 includes a voltage supply unit 15 of the focusing electrode 12 and a voltage supply unit 16 of the focusing electrode 11. In addition, a voltage supply unit 17 of the extraction grid 10 is present. The voltage supply unit 17 comprises an insulating transformer. With this, galvanic separation between the reference potential designated as BP in FIG. 8 and the ground, also shown in FIG. 8, is present. This separation is of decisive significance for avoiding damage to the X-ray tube 2 in case of a flashover from the anode 5. If charged particles are emitted by the anode 5, these are deflected by the focusing electrodes 11, 12, so that the potential of the focusing electrodes 11, 12 is briefly elevated. If a galvanic connection were to exist between the focusing electrodes 11, 12 on one hand and the extraction grid 10 on the other hand, the potential of the extraction grid 10 would also be increased as a result. This in turn would result in increased emission of the electron source 4, which would result in an avalanche-like increase in the release of particles form the anode 5. An effect of this type, which could have negative consequences extending to destruction of the cathode 4, is avoided by separating the reference potential BP on which the extraction grid 10 lies, from the focusing electrodes 11, 21. The potential of the focusing electrodes 11, 12 is designated by U.sub.F1, U.sub.F2 and falls in the range between minus 10 kV and plus 10 kV. U.sub.g designates the potential of the extraction grid 10, which falls in the range between minus 5 kV and plus 5 kV.

(24) The anode current control unit 19 is connected with a voltage supply unit 18 of the cathodes 4 and a cathode switch arrangement 20. In addition, the anode current control unit 19 is connected with a programmable assembly 25, which comprises a microcontroller 26 and a FPGA (Field Programmable Gate Arrangement) 27. The components 18, 19, 20, 25 mentioned are assembled into a cathode control device 28, which is located in a housing 29 designed as a shield. An external housing 30 shown in broken lines in FIG. 8 also surrounds the other components of the control device 3.

(25) These additional components include, among other things, the anode power supply unit 14. As is apparent from FIG. 9, the anode power supply unit 14, comprises an anode controller 31, a step-down converter 32, a Royer oscillator 33, a transformer 34 and a cascade circuit 35. The cascade circuit 35 supplies an outlet voltage U.sub.A, which is applied to the anode 5. The signal delivered by the anode current control unit 19, which is conducted to the cathode switch arrangement 20, is generally designated by Sig.

(26) The control of the emitter current source, i.e., the anode current control unit 19, is visualized in FIG. 10. Here, 36 designates a user interface, 37 a digital signal processor, 38 an FPGA, 39 an optocoupler, 40 another FPGA, 41 a digital-analog converter and 42 a switching element, which connects the two digital-analog converts 41 with the anode current control unit 19.

(27) The signal Sig delivered by the anode current control unit 19 is conducted to the cathode switch arrangement 20, as is sketched in FIG. 11. The cathode switch arrangement 20 comprises individual cathode voltage switches 21, 22, 23, 24, the number of which corresponds to the number of cathodes 4 to be controlled. The emitter current is designated by I.sub.E. The voltage applied to the individual emitters, i.e., cathodes 4, is monitored with the aid of the voltage monitor 46. The voltage monitor 46 is connected to a gate driver 47, which interacts with the cathode voltage switches 21, 22, 23, 24 via a multiplexer 43. Additional connections of the multiplexer 43 are designated with 44, 45. The gate driver 47 is connected over an optocoupler 49 with a logic module 48, which is at a low voltage level.

(28) With the aid of the circuit according to FIG. 11, current pulses are generated, more information about which is shown in FIG. 18. The current pulse is a rectangular pulse extending from time t.sub.0 to time t.sub.1. To approach the desired rectangular form with the emitter current I.sub.E as closely as possible, at the beginning of the pulse, the signal Sig describes a peak PE, with which parasitic capacitances are balanced out. In this way a constant current level KS is achieved practically over the entire pulse.

(29) As is apparent from FIG. 18, the PE peak is very narrow compared to the total pulse. In particular, a rapid decrease in the PE peak takes place. The PE peak is achieved with the aid of a so-called current boost. In addition, for comparison with a non-claimed solution, a comparison signal VSi is also drawn in in FIG. 18. The comparison signal VSi generated without current boost, which in contrast to the PE peak exhibits a slow decline toward the maximum, which coincides with the maximum of the PE peak, means that the current pulse, shown in FIG. 18 as the comparison current VI, rises substantially more slowly and also falls more slowly, so that overall a rectangular shape of the current pulse is not achieved. In the case of current pulses following one another in rapid succession this also has the unwanted effect that pulses can overlap.

(30) The control device 3 offers the possibility of operating not only the cathodes 4 but also the anode 5 in pulsed mode. As is apparent from FIG. 12, the anode power supply unit 14 comprises an inverter 50 and a gyrator circuit 52, among others.

(31) The anode power supply unit 14 according to FIG. 12, which is part of the arrangement according to FIG. 1, supplies voltage pulses at a constant level, so that the X-ray apparatus 1 is operated in the single energy mode. The X-ray tube 2 comprises a plurality of X-ray sources. The cathodes provided for generating the electron beams EB in this exemplary embodiment have carbon nanotubes as emitters. An alternative, the apparatus according to FIG. 12 may be used for operating an X-ray tube with a single emitter.

(32) Prepulse compensation PPC of the control device 3 is provided for avoiding a short-term voltage decrease, a so-called drop, at the beginning of a voltage pulse, and as is indicated in FIG. 12, processes a trigger signal 51. The prepulse compensation PPC means that with the aid of the trigger signal 51, the voltage at the beginning of the pulse to be generated is elevated somewhat relative to the desired voltage level to compensate for parasitic effects, especially due to capacitances. Here, the trigger signal 51 already precedes the beginning of the voltage pulse to be generated by a few microseconds. As a result, a voltage pulse of the anode voltage U.sub.A is produced, which to a high probability represents a rectangular pulse. The anode voltage U.sub.A falls in the range from ±10 kV to ±130 kV.

(33) In contrast to FIGS. 1 to 12, FIGS. 13 and 14 relate to X-ray devices 1 that are operated with dispenser cathodes. The X-ray device 1 equipped with the anode energy supply unit 14 according to FIG. 13 has two grids within the X-ray tube 2 to which electrical voltage is applied via grid connections GA1, GA2.

(34) In addition, a heating element is present, which is to be connected via a heating connection HA.

(35) The anode power supply unit 14 according to FIG. 13 is controlled by pulse width modulation (PWM). Within the anode power supply unit 14, 53 indicates a phase-shift PWM controller, 54 an oil tank, 55 a controller, 56 an alternating current-direct current converter, 57 and 58 respectively a gate driver and 59 an optocoupler.

(36) The embodiment according to FIG. 14 differs from the exemplary embodiment according to FIG. 13 through the absence of the grid connections GA1, GA2. A high-voltage switch is designated as 60 in FIG. 14.

(37) In contrast to the arrangements according to FIGS. 13 and 14, which are intended for producing anode voltage U.sub.A with a constant level, the pulses produced using the device according to FIG. 1, which describes the anode voltage U.sub.A, from pulse to pulse lie either at a uniform level or at different voltage levels.

(38) In the last-named case, the circuit shown for use in FIG. 15, by which pulsed anode voltage U.sub.A is generated with suddenly changing levels, is suitable for use in X-ray device 1. Here, 61 designates a line voltage connection, 62 an inverter, 63 a transformer, 64 a direct current-alternating current converter, and 65 a Marx generator. A measuring device 67 is provided for measuring current and voltage. Components with which the prepulse compensation PPC is realized are parts of a circuit 66. During each individually generated voltage pulse, the current control remains in effect, as sketched in FIG. 1.

(39) The current control can be designed in the form of various control loops CR1, CR2, CR3, CR4. In all cases a certain anode current setpoint I.sub.A-S is preset. This current setpoint I.sub.A-S is compared with measured values. In the simplest case this is merely a matter of the actual anode current I.sub.A-actual. The corresponding control loop is designated by CR2. If the grid current designated by I.sub.G is also included in the control, i.e., the current flowing out through the extraction grid 10, the control loop CR4 is present. The focusing electrodes 11, 12 also play a role in the control loops CR3 and CR1. In the case of control loop CR3, the focusing electrodes 11, 12 are operated passively, i.e., at the same potential as the housing of the X-ray tube 2. On the other hand, in the case of control loop CR1, active focusing is used. In this case the focusing electrodes 11, 12 can be operated with constant or pulsed voltages on the order of −10 KV to +10 KV. The current flowing through the focusing electrodes 11, 12 is designated by I.sub.F1 and I.sub.F2 respectively. The control loop CR1 is the most complex form of current regulation overall.

(40) With the diagram according to FIG. 16, reference is made to FIG. 15. Here, details of the prepulse compensation PPC are shown. In the diagram, CoV designates the compensator voltage, which is generated by the circuit 66, the compensation circuit. The compensation process is influenced by various trigger signals T1, T2, T3. Here, the trigger signal T3 influences the beginning of the pulse, which is described by the compensator voltage CoV and a shape increasing according to the absolute magnitude, in other words, it has the shape of an individual sawtooth. The duration of this pulse is designated in FIG. 16 as the pulse-phase duration PuPh. To supply the pulse in the desired amount at the right time, an internal voltage within the circuit 66, the course of which is shown in FIG. 16 directly below the three trigger signals T1, T2, T3, ramps down immediately before the beginning of the sawtooth pulse of the compensator voltage CoV. The start of this ramp is designated as the ramp start RS in FIG. 16. The ramp start RS is chronologically advanced relative to the start of the sawtooth pulse ahead of the compensator voltage CoV by a ramp shift RV. The end of the ramp of the internal voltage is designated by RE. Then a constant voltage level is maintained until, within a voltage decline phase SR, the internal voltage is returned to the initial value, namely 0 volt.

(41) The trigger signals T2 and T1 mark the end and the beginning of idling states IP. After the end of the idling phase IP shown first chronologically in FIG. 16, a preload phase PrPh begins. During this preload phase PrPh, without the compensator voltage CoV showing a deflection, an internal current in the circuit 66 drops. Since the initial current is 0 amperes, an absolute magnitude increase in the current exists here. The current is designated as the inductor current IC. The absolute minimum, i.e., the absolute magnitude maximum, of the inductor current IC, is present in the sawtooth pulse of the compensator voltage CoV. Then the current rises again within an inductor energy recovery phase IER. At the beginning of the voltage decline phase SR, the inductor current IC has again assumed the value of 0 ampere.

(42) The plurality of individual cathodes 4, which are located within the X-ray tube 2 and are controlled by the central anode current control unit 19, are shown schematically in FIG. 17. The number of cathodes 4 in this case is not subject to any theoretical imitations. If necessary, the cathodes 4 can be discharged rapidly through a discharge circuit 68, which is connected to the cathode circuit array 20. The discharge circuit 68 comprises a chain of resistors, the first end of which is grounded, while the second end of the chain of resistances is connected via a switch to the cathode 4 to be discharged during the discharging process.

(43) Although the structures, devices, methods, and systems have been described in accordance with particular embodiments, one of ordinary skill in the art will readily recognize that many variations to the particular embodiments are possible, and any variations should therefore be considered to be within the spirit and scope disclosed herein. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.

(44) The claims following this written disclosure are hereby expressly incorporated into the present written disclosure, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of the independent claims with their dependent claims. Moreover, additional embodiments capable of derivation from the independent and dependent claims that follow are also expressly incorporated into the present written description. These additional embodiments are determined by replacing the dependency of a given dependent claim with the phrase “any of the claims beginning with claim [x] and ending with the claim that immediately precedes this one,” where the bracketed term “[x]” is replaced with the number of the most recently recited independent claim. For example, for the first claim set that begins with independent claim 1, claim 3 can depend from either of claims 1 and 2, with these separate dependencies yielding two distinct embodiments; claim 4 can depend from any one of claim 1, 2, or 3, with these separate dependencies yielding three distinct embodiments; claim 6 can depend from any one of claims 1, 2, 3, or 4, with these separate dependencies yielding four distinct embodiments; and so on.

(45) Recitation in the claims of the term “first” with respect to a feature or element does not necessarily imply the existence of a second or additional such feature or element. Elements specifically recited in means-plus-function format, if any, are intended to be construed to cover the corresponding structure, material, or acts described herein and equivalents thereof in accordance with 35 U.S.C. § 112(f). Embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.