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EP4391728A1 - Emissionsstromsteuerung für hv-generatoren - Google Patents

Emissionsstromsteuerung für hv-generatoren Download PDF

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Publication number
EP4391728A1
EP4391728A1 EP22214527.8A EP22214527A EP4391728A1 EP 4391728 A1 EP4391728 A1 EP 4391728A1 EP 22214527 A EP22214527 A EP 22214527A EP 4391728 A1 EP4391728 A1 EP 4391728A1
Authority
EP
European Patent Office
Prior art keywords
voltage
emission current
ray source
kvp
reference emission
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22214527.8A
Other languages
English (en)
French (fr)
Inventor
Roland Proksa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips NV filed Critical Koninklijke Philips NV
Priority to EP22214527.8A priority Critical patent/EP4391728A1/de
Publication of EP4391728A1 publication Critical patent/EP4391728A1/de
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/34—Anode current, heater current or heater voltage of X-ray tube
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/265—Measurements of current, voltage or power

Definitions

  • the present invention relates to an apparatus and a method for determining a reference emission current of an X-ray source for a peak-kilovoltage (kVp) switching spectral scan, to a system that comprises the apparatus, to a method for controlling an emission current of an X-ray source, to a computer program product, and to a computer-readable medium.
  • kVp peak-kilovoltage
  • an X-ray tube is governed by the high voltage applied between an anode and a cathode of this tube, as well as by the electric heating current with which a filament of the cathode is taken to high temperature.
  • the high voltage is typically supplied by a high-voltage generator.
  • the electrons are extracted from the cathode and projected at high speed into the anode.
  • the anode target which is struck by these electrons, then emits X-rays, which can be used to produce X-ray exposures, or more generally X-ray images.
  • the high voltage applied is directly related to the energy of the X-photons emitted.
  • the high-voltage generator also controls the emission current of the X-ray tube. This means that mainly the temperature of the cathode defines the emission current. Currently the high-voltage generator measures the emission current and adapts the filament heating to reach the emission current target.
  • This simple control method may be challenged for kVp-switching.
  • Rapid kVp-switching (kVp-S) is a spectral imaging technique that switches the voltage (kVp) rapidly between successive measurement intervals to obtain spectral information.
  • a theoretically optimal kVp-switching generator should switch infinitely fast and should have small waveform ripple. The fast change of the emission current makes the measurement and the entire control difficult.
  • an apparatus for determining a reference emission current of an X-ray source for a kVp-switching spectral scan comprises an input, a processor, and an output.
  • the input is configured to receive a measurement of a tube voltage of the X-ray source.
  • the tube voltage has a peak voltage switching between a first voltage and a second voltage.
  • the first voltage is higher than the second voltage.
  • the processor is configured to analyze the received measurement of the tube voltage to determine a time constant of a falling voltage transition slope during a kVp-switching cycle, and to determine the reference emission current of the X-ray source based on the determined time constant of the falling voltage transition slope.
  • the output is configured to provide the determined reference emission current of the X-ray source, which is usable for controlling an emission current of the X-ray source.
  • the apparatus as disclosed herein measures the time constant of the falling voltage transition to estimate a reference emission current, which is usable for controlling the emission current for fast kVp-switching.
  • the method as disclosed herein may allow to control the emission current for fast kVp-switching that does not suffer or suffer less from variation of the emission current during the fast-switching cycles.
  • the reference emission current is an emission current at a reference tube voltage.
  • the rapid change of the emission current within the switching cycles may require a new definition of a reference value.
  • a reference tube voltage e.g. 140 kVp.
  • the reference current 1140 we refer to this definition and call the reference current 1140 by way of example.
  • the reference current may be defined for a reference tube voltage 80 kVp, 100 kVp, or any other tube voltage.
  • a voltage range is defined between a third voltage and a fourth voltage that is lower than the third voltage, the third voltage being equal to or lower than the first voltage and the fourth voltage being equal to or greater than the second voltage.
  • the processor is configured to determine the reference emission current of the X-ray source based on a time constant of a falling voltage transition from the third voltage to the fourth voltage.
  • a system comprising an X-ray source, a voltage generator configured to supply a voltage for operating the X-ray source, and an apparatus according to the first aspect and any associated example.
  • the X-ray source is configured to generate X-rays.
  • the apparatus is configured to determine a reference emission current of the X-ray source.
  • the voltage generator is configured to control a filament heating of the X-ray source to keep the reference emission current stable over time.
  • a method for determining a reference emission current of an X-ray source for a kVp-switching spectral scan comprises:
  • the reference emission current is an emission current at a reference tube voltage.
  • a voltage range is defined between a third voltage and a fourth voltage lower than the third voltage, the third voltage being equal to or lower than the first voltage and the fourth voltage being equal to or greater than the second voltage.
  • the reference emission current of the X-ray source is determined based on a time constant of a voltage transition from the third voltage to the fourth voltage.
  • a method for controlling an emission current of an X-ray source comprises:
  • a computer program product comprising instructions which, when executed by a processor, cause the processor to carry out the steps of the method of the third aspect and any associated example or the method of the fourth aspect and any associated example.
  • the X-ray system 100 comprises an X-ray source 10 configured to project a beam of X-rays 12 through an object 14.
  • the object 14 may include, but are not limited to, a human subject, pieces of baggage, or other objects desired to be scanned.
  • the X-ray source 10 may be an X-ray tube producing X-rays having a spectrum of energies that range e.g., from 30 keV to 200 keV.
  • the X-rays 14, after being attenuated by the object 14, impinges upon a radiation detector 16.
  • the radiation detector 16 produces an electrical signal that represents the intensity of an impinging X-ray beam 12.
  • the radiation detector 16 may be e.g., a scintillation-based detector or a direct-conversion type detector.
  • the X-ray source 10 is an X-ray tube connected to a high-voltage generator, such as the high-voltage generator 18 illustrated in FIG. 1 .
  • the high-voltage generator 18 supplies the high-voltage for operating the X-ray tube.
  • the X-ray tube may include one or more filaments positioned within a cathode that emit electrons towards an anode when the high voltage is applied thereto, when a current is driven through the one or more filaments.
  • the high-voltage generator 18 typically controls the emission current of the X-ray tube. Most X-segments have heat limited emission. This means that mainly the temperature of the cathode defines the emission current. In the prior art, the high-voltage generator measures the emission current and adapts the heating to reach the emission current target. The temperature change may be a relatively slow process, e.g., hundreds of milliseconds because heating and cooling are slow processes.
  • This simple emission control method may be challenged for kVp-switching. If the tube voltage (kVp) is rapidly switched, fast electrical field effects impact the emission current. For example, if the tube voltage is changed from 80 kVp to 140 kVp, the emission current may change by 20%-30% although the filament temperature stays constant. In addition, it may be necessary to adjust the focal spot (FS) to maintain the same size for 80 kVp and 140 kVp. If the FS is controlled by electrodes, a change of the steering voltages may change the emission current as well (e.g., 20%-30%). These two effects will impact the emission current rapidly within the switching cycles.
  • FS focal spot
  • the fast change of the emission current makes the measurement and the entire control difficult.
  • the problem may be further increased for time-based dose modulation.
  • the dose of a kVp-S acquisition can be changed dynamically during the scan by changing the duty cycle of the kVp-waveform.
  • the present disclosure proposes a novel method to control the emission current for fast kVP-switching that does not suffer or suffer less from variation of the emission current during the switching cycles.
  • the apparatus 20 may comprise various physical and/or logical components for communicating and manipulating information, which may be implemented as hardware components (e.g., computing devices, processors, logic devices), executable computer program instructions (e.g., firmware, software) to be executed by various hardware components, or any combination thereof, as desired for a given set of design parameters or performance constraints.
  • Fig. 1 may show a limited number of components of the apparatus 20 by way of example, it can be appreciated that a greater or a fewer number of components may be employed for a given implementation.
  • the apparatus 20 may be embodied as, or in, a device or apparatus, such as a server, workstation, or mobile device.
  • the processor 24 may comprise one or more microprocessors, which execute appropriate software.
  • the software may have been downloaded and/or stored in a corresponding memory, e.g., a volatile memory such as RAM or a non-volatile memory such as flash.
  • the software may comprise instructions configuring the one or more processors to perform the functions as described herein.
  • the processor may be implemented as dedicated hardware to perform some functions and/or a programmable device (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.
  • a programmable device e.g., one or more programmed microprocessors and associated circuitry
  • the functional units of the apparatus 20, e.g., the input 22, the one or more processors 24, and the output 26 may be implemented in the device or apparatus in the form of programmable logic, e.g., as a Field-Programmable Gate Array (FPGA), or as an application-specific integrated circuits (ASIC).
  • FPGA Field-Programmable Gate Array
  • ASIC application-specific integrated circuits
  • each functional unit of the apparatus may be implemented in the form of a circuit.
  • the apparatus 20 may reside in a system console (not shown), e.g., running as a software.
  • the input 22 is configured to receive a measurement of a tube voltage u(t) of the X-ray source.
  • the tube voltage u(t) has a peak voltage switching between a first voltage and a second voltage.
  • the first voltage is higher than the second voltage.
  • the tube voltage may be acquired during regular operation, e.g. by measuring the voltage at the output of the high-voltage generator 18.
  • FIG. 2 shows an exemplary waveform of a tube voltage that was measured at the output of the high-voltage generator 18.
  • the tube voltage u(t) has a peak voltage switching between a first voltage 140 kVp and a second voltage 80 kVp.
  • the exemplary waveform shown in FIG. 2 also demonstrates a duty cycle change for time-based dose modulation. After the fourth cycle, the kVp high time is increased.
  • the last stage may comprise a diode and a capacitor.
  • the last stage may comprise a diode and a capacitor.
  • the voltage before the diode will be lowered and the diode decouples the capacitor and the tube. Consequently, the emission current of the tube will discharge the capacitor.
  • the falling voltage transition slopes of the waveform show no ripple because the high-voltage generator is decoupled from the output and the output voltage just shows the "smooth" discharge of the capacitor by the "smooth" transition current.
  • FIG. 3 shows a zoom into one of the smooth falling transition slopes, i.e., falling transmission slope 28, shown in FIG. 2 .
  • the capacitance including e.g., parasitic capacitors of the cable, tube etc.
  • the voltage transition of the output can be measured and used to estimate the emission current. This will be explained in detailed hereinafter.
  • the filament temperature and the steering voltage to form the focal spot to be constant.
  • the emission current that discharges the output capacitor depends on the reference current 1140 times a tube voltage dependent function f(u), which is typically a simple linear function.
  • f(u) a tube voltage dependent function
  • I140 the reference current may be defined for a reference tube voltage 80 kVp, 100 kVp, or any other reference tube voltage.
  • the voltage u1 may also be referred to as a third voltage
  • the voltage u2 may also be referred to as a fourth voltage. For example, as shown in FIG.
  • u1 is defined as 120 kVp and u2 is defined as 100 kVp.
  • the time it takes to transit from u1 to u2 is ⁇ t. This time ⁇ t is proportional to I140 and a constant that can be identified in a calibration.
  • the processor 24 is configured to analyze the received measurement of the tube voltage u(t) to determine a time constant of a falling voltage transition slope, e.g., ⁇ t, during a kVp-switching cycle, and to determine the reference emission current, e.g., I140, of the X-ray source based on the determined time constant of the falling voltage transition slope e.g., based on the above-described approach.
  • a time constant of a falling voltage transition slope e.g., ⁇ t
  • I140 reference emission current
  • the apparatus 20 then provides the reference emission current, e.g., I140, via the output 26, to the high-voltage generator 18.
  • I140 reference emission current
  • the high-voltage generator 18 is configured to control the filament heating to keep the reference emission current e.g., I140, stable over time.
  • FIG. 4 shows a flowchart describing an exemplary method 200 for determining a reference emission current of an X-ray source for a kVp-switching spectral scan.
  • the method 200 may be implemented as a device, module or related component in a set of logic instructions stored in a non-transitory machine- or computer-readable storage medium such as random access memory (RAM), read only memory (ROM), programmable ROM (PROM), firmware, flash memory, etc., in configurable logic such as, for example, programmable logic arrays (PLAs), field programmable gate arrays (FPGAs), complex programmable logic devices (CPLDs), in fixed-functionality hardware logic using circuit technology such as, for example, application specific integrated circuit (ASIC), complementary metal oxide semiconductor (CMOS) or transistor-transistor logic (TTL) technology, or any combination thereof.
  • PLAs programmable logic arrays
  • FPGAs field programmable gate arrays
  • CPLDs complex programmable logic devices
  • ASIC application specific integrated circuit
  • CMOS complementary metal oxide semiconductor
  • TTL transistor-transistor logic
  • computer program code to carry out operations shown in the method 200 may be written in any combination of one or more programming languages, including an object-oriented programming language such as JAVA, SMALLTALK, C++, Python, or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages.
  • object-oriented programming language such as JAVA, SMALLTALK, C++, Python, or the like
  • conventional procedural programming languages such as the "C" programming language or similar programming languages.
  • the exemplary method may be implemented as the apparatus 20 shown in FIG. 1 .
  • the method 200 comprises a step of receiving a measurement of a tube voltage of the X-ray source.
  • the tube voltage has a peak voltage switching between a first voltage and a second voltage.
  • the first voltage is higher than the second voltage.
  • the apparatus 20 receives a measurement of a tube voltage of the X-ray source.
  • the tube voltage may be acquired during regular operation, e.g. by measuring the voltage at the output of the high-voltage generator 18.
  • FIG. 2 An exemplary waveform of the tube voltage is shown in FIG. 2 .
  • the tube voltage u(t) shown in FIG. 2 has a peak voltage switching between a first voltage 140 kVp and a second voltage 80 kVp.
  • the method 200 further comprises a step of analyzing the received measurement of the tube voltage to determine a time constant of a falling voltage transition slope during a kVp-switching cycle.
  • the apparatus 20 may determine the time constant ⁇ t of the exemplary falling voltage transition slope 28 during a kVp-switching cycle.
  • the method 200 further comprises the step of determining the reference emission current of the X-ray source based on the determined time constant of the falling voltage transition slope.
  • the apparatus 20 shown in FIG. 1 may determine the reference emission current, e.g., a reference emission current at 140 kVp, according to the above-described equation (1).
  • step 240 the method 200 further comprises the step of providing the determined reference emission current of the X-ray source.
  • the apparatus 20 provides the determined reference emission current I140 to the high-voltage generator 18.
  • FIG. 5 shows a flowchart describing a method 300 for controlling an emission current of an X-ray source.
  • the exemplary method 300 may be implemented by the high-voltage generator 18 shown in FIG. 1 .
  • the high-voltage generator 18 receives a reference emission current I140 provided by the apparatus 20 shown in FIG. 1 .
  • the reference emission current I140 may be determined according to the method 200 shown in FIG. 4 .
  • step 320 the high-voltage generator 18 controls a filament heating of the X-ray source to keep the reference emission current stable over time.
  • a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding aspects, on an appropriate system.
  • the computer program element might therefore be stored on a processor, which might also be part of an embodiment of the present invention.
  • This processor may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above-described apparatus.
  • the processor can be adapted to operate automatically and/or to execute the orders of a user.
  • a computer program may be loaded into a working memory of a data processor.
  • the data processor may thus be equipped to carry out the method of the invention.
  • This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.
  • the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.
  • a computer readable medium such as a CD-ROM
  • the computer readable medium has a computer program element stored on it, which computer program element is described by the preceding section.
  • a computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.
  • a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.
  • the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network.
  • a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • X-Ray Techniques (AREA)
EP22214527.8A 2022-12-19 2022-12-19 Emissionsstromsteuerung für hv-generatoren Pending EP4391728A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP22214527.8A EP4391728A1 (de) 2022-12-19 2022-12-19 Emissionsstromsteuerung für hv-generatoren

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP22214527.8A EP4391728A1 (de) 2022-12-19 2022-12-19 Emissionsstromsteuerung für hv-generatoren

Publications (1)

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EP4391728A1 true EP4391728A1 (de) 2024-06-26

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5629844A (en) * 1995-04-05 1997-05-13 International Power Group, Inc. High voltage power supply having multiple high voltage generators
JP2013192801A (ja) * 2012-03-21 2013-09-30 Toshiba Corp Ｘ線ｃｔ装置
US9992855B2 (en) * 2014-12-30 2018-06-05 General Electric Company Energy imaging with controlled rise and fall times
US20200413525A1 (en) * 2019-06-27 2020-12-31 Shanghai United Imaging Healthcare Co., Ltd. Systems and methods for medical imaging

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5629844A (en) * 1995-04-05 1997-05-13 International Power Group, Inc. High voltage power supply having multiple high voltage generators
JP2013192801A (ja) * 2012-03-21 2013-09-30 Toshiba Corp Ｘ線ｃｔ装置
US9992855B2 (en) * 2014-12-30 2018-06-05 General Electric Company Energy imaging with controlled rise and fall times
US20200413525A1 (en) * 2019-06-27 2020-12-31 Shanghai United Imaging Healthcare Co., Ltd. Systems and methods for medical imaging

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