EP4676167A1 - Controlling a high voltage generator for an x-ray source - Google Patents

Controlling a high voltage generator for an x-ray source

Info

Publication number
EP4676167A1
EP4676167A1 EP24185881.0A EP24185881A EP4676167A1 EP 4676167 A1 EP4676167 A1 EP 4676167A1 EP 24185881 A EP24185881 A EP 24185881A EP 4676167 A1 EP4676167 A1 EP 4676167A1
Authority
EP
European Patent Office
Prior art keywords
current
filament
ray
operational
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
EP24185881.0A
Other languages
German (de)
French (fr)
Inventor
Sven HAGEMEISTER
Uwe FRITZSCHE
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 EP24185881.0A priority Critical patent/EP4676167A1/en
Priority to PCT/EP2025/067463 priority patent/WO2026008358A1/en
Publication of EP4676167A1 publication Critical patent/EP4676167A1/en
Pending legal-status Critical Current

Links

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
    • H05G1/54—Protecting or lifetime prediction

Definitions

  • the invention relates to a controller for controlling a high voltage generator for an X-ray source, in particular during a pulsed X-ray imaging run.
  • the invention also relates to a high voltage generator, an X-ray imaging system, a method for controlling a high voltage generator, a computer program element, and a computer-readable medium.
  • X-ray imaging is considered an important imaging modality in medical imaging.
  • X-ray sources like X-ray tubes are used to generate X-ray radiation that passes through a subject and impinges on an X-ray detector.
  • the X-ray tube typically includes a cathode with a filament and an anode.
  • a filament current When a filament current is applied to the filament, the filament current heats the filament, causing the filament to expel electrons (thermionic emission), creating a space charge a short distance away from the filament.
  • a peak X-ray tube voltage is applied across the cathode and the anode, and causes a beam of the electrons to accelerate from the cathode and impinge the anode.
  • the X-ray tube current represents the number of electrons per second flowing from the cathode to the anode.
  • Electrostatic or magnetic focusing with e.g. grid electrodes or quadrupoles can be applied to control a size of and steer the beam of electrons.
  • An interaction of the electrons with the material of the anode produces heat and radiation, including X-rays, which pass through a tube window, into an examination region, to the X-ray detector.
  • X-ray radiation may need to be generated in a pulsed manner.
  • pulsed X-ray image acquisition X-ray images are acquired using a series of short X-ray pulses. Such a series of pulses is called an imaging run.
  • a crucial part in an X-ray source is thus the cathode filament.
  • the filament needs to have a specific, elevated temperature to reach the desired emission current during an X-ray pulse.
  • X-ray sources used e.g. in cardio-vascular X-ray systems may show a wear-out of their cathode filaments. The wear-out may be the result of evaporation of the tungsten they consist of. There may thus be a need to provide X-ray sources in particular for pulsed operation with increased filament lifetime and hence increased field life.
  • WO2023117733 A1 relates to operating a filament of an X-ray tube.
  • a control device for pulsed operation of a generator for an X-ray tube is provided.
  • the X-ray tube may be controlled to provide a plurality of X-ray pulses, wherein two subsequent pulses are temporally separated by an emission pause.
  • the emission pause comprises at least a first part and a second part.
  • a filament current is provided to a cathode filament of the X-ray tube such that, in the emission pause between two subsequent pulses, during a first part of the pause a first filament current is provided and during a second part of the pause a second filament current is provided, the first filament current being lower than the second filament current.
  • Such an 'intercooler' or 'intercooling scheme' can thus be used to significantly extend the lifetime of an X-ray source.
  • a 'intercooler' or 'intercooling scheme' can thus be used to significantly extend the lifetime of an X-ray source.
  • a controller for controlling a high voltage generator for an X-ray source.
  • the controller is configured to control the high voltage generator to:
  • the filament temperature of a subsequent pulse can be corrected.
  • the correction is done by modifying the boosting and/or blanking time. In this way, drift of the operational filament temperature over several pulses can be avoided and errors from variations in X-ray emission can be reduced.
  • the duration of blanking may be increased and/or the duration of boosting may be reduced, to correct for the deviation for the following pulse.
  • the duration of blanking may be reduced and/or the duration of boosting may be increased, to correct for the deviation for the following pulse.
  • an emission current data model is used.
  • the emission current data model may be or include a static or adaptive look-up table comprising combinations of emission currents and filament currents for at least one operational X-ray source voltage.
  • the controller may be configured to populate and/or update the look-up table, e.g. during calibration runs.
  • the emission current data model may be or include a digital twin of the X-ray source, to simulate the relation between emission currents and filament currents.
  • the emission current data model may use machine learning and may be trained to provide an emission current as output data when a filament current and an X-ray source voltage is provided as input data.
  • the expected emission current of the X-ray pulse is determined using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the controller is further configured to:
  • the filament temperature data model may be or include a static or adaptive look-up table comprising changes in filament temperature over time when a boosting or blanking current is applied, for at least one operational X-ray source voltage.
  • the filament temperature data model may be used to predict the effect on filament temperature, and hence on emission current, when providing a boosting or blanking current for a certain time, i.e. when heating or cooling the filament.
  • the controller may be configured to populate and/or update such a look-up table, e.g. during calibration runs.
  • the filament temperature model may be populated by measurements of emission currents over time for various applied blanking or boosting currents, at a known X-ray source voltage. Measured emission currents may subsequently be converted to filament currents (equivalent to filament temperatures) using the emission current data model.
  • the filament temperature model may, alternatively or additionally, model the changes of emission currents over time, when blanking or boosting currents are applied. Outputs in the form of emission currents may be converted to filament temperatures or equivalent filament currents, using the emission current data model.
  • determining the adaptation comprises determining a delta in boosting or blanking time units using the filament temperature model.
  • the deviation in measured and expected emission current, relating to a difference in filament temperatures can be linearized to a delta in boosting or blanking time units.
  • the delta in boosting or blanking time units may be in the form of integer units, such as integers of milliseconds.
  • the controller is configured to provide the delta in boosting or blanking time units as an error input to a proportional-integral control algorithm, and to receive the adapted duration of providing the blanking current and/or duration of providing the boosting current as output from the proportional-integral control algorithm.
  • a proportional-integral control algorithm with the temperature difference as an error input is a fast and efficient way to regulate the boosting and/or blanking times between pulses to correct for any deviations in emission current.
  • the controller is configured to control the high voltage generator to provide an intercooler hold current during a third part of the emission pause, wherein
  • the holding part can be optimized to the emission pause, such as preferably an emission pause of fixed duration.
  • a high voltage generator for providing power to an X-ray source.
  • the high voltage generator comprises the controller according to any of the embodiments of the first aspect.
  • an X-ray imaging system for pulsed X-ray imaging, the X-ray imaging system comprising: an X-ray detector for detecting X-ray radiation; an X-ray source for generating X-ray radiation; and the high voltage generator according to the second aspect.
  • a method for controlling a high voltage generator for an X-ray source comprises:
  • the expected emission current of the X-ray pulse is determined using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the method further comprises:
  • a computer program element which, when being executed by a controller, is adapted to cause the controller to perform the method according to the fourth aspect.
  • the computer program element may be made available for download from a server, e.g. via the internet.
  • a computer-readable medium having stored thereon the computer program element mentioned above.
  • WO2023117733A1 describes the concept of a filament intercooler to increase filament lifetime.
  • thermionic X-ray tubes electrons emitted by a heated cathode are accelerated through a strong electric field in vacuum towards an anode where they generate "Bremsstrahlung” also known as X-rays in case they are generated by an X-ray tube.
  • the amount of X-ray is proportional to the emission current running between anode and cathode.
  • the emission current is a function of the voltage between cathode and anode and the temperature of the cathode.
  • Cathodes usually comprise strips or coils of a metal with a high melting point, such as Tungsten, called filaments. When they are heated, the metal of the filaments evaporates and eventually the filament gets so thin at a certain location that it breaks. This describes a general wear mechanism for thermionic X-ray tubes.
  • X-ray tubes may be operated in pulsed mode. Rather than producing a constant amount of X-ray, they produce short pulses of high intensity in series called pulsed X-ray imaging runs. This mode of operation supports detectors that may need a reset time where there is no X-ray produced between two imaging frames. Further, with short intense pulses there is less blurring of the image by movement.
  • WO2023117733A1 describes controlling an X-ray tube to provide a plurality of pulses to generate the electron beam with the desired emission current for generating the plurality of X-ray pulses, wherein two subsequent pulses of the plurality of pulses are temporally separated by an emission pause. That is, during the pulses, the filament current provided corresponds to a normal operational current level that, at the corresponding tube voltage, results in emitting an electron beam at the desired emission current from the cathode towards the anode.
  • the emission pause comprises at least a first part and a second part.
  • the generator is controlled to adjust, in the emission pause between the two subsequent pulses, the filament current providing a first filament current during the first part of the pause and a second filament current during the second part of the pause.
  • the first filament current is lower than the second filament current and preferably also lower than the operational current level. In effect, the first filament current is too low to maintain the filament at a temperature needed for emitting an electron beam. As a result, the filament temperature decreases during the first part of the emission pause.
  • the second filament current is provided as an intermediate heat-up current to prepare the filament for subsequently emitting the desired emission current of an electron beam during the following X-ray pulse.
  • the second filament current is higher than the operational current level.
  • the temperature of the filament may be restored to its operational value needed for emitting the electron beam.
  • WO2023117733 A1 describes providing the first and second filament current, i.e. blanking and boosting are implemented in between subsequent pulses within an imaging run, in order to save filament wear. That is, a current provided to the filament of the X-ray tube is firstly reduced in between subsequent pulses of the imaging run to the first filament current, causing the filament to cool down. Shortly before the next pulse, an increased boosting current is used as the second filament current so that the filament is back at the operating temperature at the start of the pulse. This is repeated throughout the pulsed imaging run, preferably in between adjacent X-ray pulses.
  • the inventors of the present invention have found that over multiple X-ray emission pulses during a pulsed run, drift in the filament temperature may occur. If the amount of energy that is each time applied during boosting and withdrawn during blanking is not the same, such differences may accumulate and lead to drift of the operational filament temperature level and corresponding level of X-ray radiation, which may eventually trigger errors in the system. In the present application, it is therefore suggested to monitor and correct the filament temperature of a subsequent pulse, by determining deviations between expected emission current and measured emission current of a previous pulse. Such correction is done by modifying the boosting and/or blanking time. In this way, drift of the operational filament temperature over several pulses can be avoided and errors from variations in X-ray emission can be reduced.
  • Fig. 1 schematically shows a controller 10 for controlling a high voltage generator, according to embodiments of the invention.
  • the controller may comprise or otherwise interact with a processor 12 and a memory 14.
  • the processor 12 may be a computer, a computer network, and/or another programmable apparatus, such as a single and/or multi core processing unit, a graphics processing unit, an accelerated processing unit, a digital signal processor, a field programmable gate array, an application-specific integrated circuit, etc.
  • the memory 14 may be configured for storing long term and/or short term, data.
  • the controller is illustrated as a separate unit with a frame 24. However, it is noted that the controller may be a distributed system, with processing done locally or remotely.
  • controllers may be integrated with a high voltage generator or other parts of an imaging system.
  • the controller is configured to provide an output signal 20 to control the high voltage generator 50.
  • the communication between the controller 10 and the high voltage generator 50 may be wired and/or wireless.
  • the controller 10 is configured to receive an input signal 16. In Fig. 1 this is illustrated with input from a signal source 18.
  • the signal source may be part of an X-ray imaging system.
  • the controller may be configured to receive an input signal from the generator 50 as the signal source 18. However, alternatively, or additionally, the controller may be configured to receive an input signal from a user interface, a sensor etc.
  • the controller 10 is configured to control the high voltage generator 50 to provide power to the X-ray source 102 to generate a plurality of X-ray pulses during a pulsed X-ray imaging run. During an X-ray imaging run, subsequent X-ray pulses are temporally separated in time by an emission pause.
  • the controller 10 is configured to control the high voltage generator 50 provide an operational filament current to heat a filament of a cathode of the X-ray source 102 to an operational filament temperature during the X-ray pulses.
  • the operational filament temperature corresponding to the operational filament current, is at a suitable level to generate a desired X-ray imaging emission current during the X-ray pulses.
  • the operational X-ray source voltage may be between 40 kV to 200 kV, preferably between 80 kV to 140 kV.
  • the emission current may be on the order of hundreds of mA, such as 100-200 mA.
  • the operational filament current may be between 3-6 A.
  • the controller 10 is configured to control the high voltage generator 50 to provide a blanking filament current during a first part of the emission pauses, preferably at the beginning of each emission pause.
  • the blanking filament current is lower than the operational filament current, e.g. 1-2 A and may even be 0 A.
  • the low blanking filament current allows the filament temperature to decrease to an intercooler filament temperature, which is low enough to reduce filament degradation and hence save filament lifetime.
  • the controller 10 is configured to receive a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse.
  • the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage.
  • the measured emission current may be received via the input signal 16.
  • the emission current may be measured by and received from the high voltage generator 50, which would in that case also function as the signal source 18.
  • the controller may be configured to control the high voltage generator to measure the emission current.
  • the emission current may be received from the imaging system with which the controller operates.
  • the measured emission current is received for multiple X-ray emission pulses during an imaging run, such that deviations may be monitored over time.
  • the operational filament current and the operational source voltage may be received during an imaging run. However, the operational filament current and the operational source voltage are preferably predetermined as constant values or predetermined to change according to a predetermined sequence.
  • the operational filament current and the operational source voltage may be received in advance of an imaging run and may be stored in the memory 14.
  • the controller 10 is configured to determine an expected emission current of the X-ray pulse based on the known operational filament current and the operational X-ray source voltage. In this way, the expected emission current and the measured emission current may be compared for a particular pulse.
  • the controller 10 may use an emission current data model to determine the expected emission current from the known operational filament current and the operational X-ray source voltage.
  • the emission current data model may be or include a static or dynamic look-up table, such as pre-stored in the memory 14 or received as a signal input 12, comprising combinations of emission currents and filament currents for at least one operational X-ray source voltage.
  • the controller may be configured to populate and/or update the look-up table, e.g. during calibration runs.
  • the emission current data model may be or include a digital twin of the X-ray source, to simulate the relation between emission currents and filament currents.
  • the emission current data model may use machine learning and may be trained to provide an emission current as output data when a filament current and an X-ray source voltage is provided as input data.
  • the controller 10 is configured to adapt the duration of providing the blanking current during and/or adapt the duration of providing the boosting current.
  • the controller is configured to correct the operational filament temperature of a subsequent X-ray pulse when there is a deviation between the measured emission current and the expected emission current.
  • the changed duration of providing the blanking current and/or boosting current does not change the total duration of the emission pause.
  • the controller 10 may be configured to convert the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model, and to use a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  • the filament temperature model may be stored in the memory 14 and/or or may be received by the controller 10.
  • the filament temperature data model may be or include a static or adaptive look-up table comprising changes in filament temperature over time when a boosting or blanking current is applied, for at least one operational X-ray source voltage.
  • the filament temperature data model may be used to predict the effect on filament temperature, and hence on emission current, when providing a boosting or blanking current for a certain time, i.e. when heating or cooling the filament.
  • the controller may be configured to populate and/or update such a look-up table, e.g. during calibration runs.
  • the filament temperature model may be populated by measurements of emission currents over time for various applied blanking or boosting currents, at a known X-ray source voltage. Measured emission currents may subsequently be converted to filament currents (equivalent to filament temperatures) using the emission current data model.
  • the filament temperature data model may be or include a digital twin of the X-ray source, to simulate the relation between filament temperature over time for different applied filament currents during boosting or blanking.
  • the filament temperature data model may use machine learning and may be trained to provide a filament temperature over time as output data when a filament current and an X-ray source voltage is provided as input data.
  • the filament temperature model may model the changes of X-ray source emission currents over time, when blanking or boosting currents are applied to the filament.
  • the controller may be configured to convert model outputs in the form of emission currents to filament temperatures or equivalent filament currents, using the emission current data model.
  • Determining the adaptation of the boosting and/or blanking times may include determining a delta in boosting or blanking time units, preferably integer units, using the filament temperature model.
  • a delta in boosting or blanking time units preferably integer units
  • the emission current data model static dependency of emission current and filament current
  • the filament temperature model change in temperature and hence emission current over time for a certain applied boosting or blanking current
  • the deviation in measured and expected emission current, relating to a difference in filament temperatures can be linearized to a delta in boosting or blanking time units.
  • the controller 10 may be configured to provide such a delta in boosting or blanking time units as an error input to a proportional-integral control algorithm, and to receive the adapted duration of providing the blanking current and/or duration of providing the boosting current as output from the proportional-integral control algorithm.
  • the controller 10 may be configured to control the high voltage generator 50 to provide an intercooler hold current between blanking and boosting.
  • the intercooler hold current holds the filament temperature at a corresponding intercooler filament temperature.
  • the duration of providing the intercooler hold current and/or the level of the intercooler hold current may be adapted based on the adaptation of the duration of providing the blanking current and/or the boosting current.
  • the holding part can be optimized to the emission pause, such as preferably an emission pause of fixed duration.
  • Fig. 2 schematically shows an example of a high voltage generator 50 for providing power to an X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run.
  • the generator 50 in this example comprises a controller 10 as described above.
  • the example high voltage generator 50 includes an electric power input 52, an electric transformer arrangement 54, and an electric power output 56.
  • the electric power input 52 is connectable to an electric power supply configured to provide an input in form of electric energy.
  • the electric power input 52 is connected to the electric transformer arrangement 54.
  • the electric transformer arrangement 54 is configured to transform the voltage input into suitable DC high-voltage and suitable electric current for pulsed operation of the X-ray source.
  • the electric power output 56 is configured to provide a suitable high-voltage and suitable electric currents.
  • the electric power output 56 is connectable to the X-ray source.
  • the controller 10 is configured to control said generator components, e.g. the electric transformer arrangement 54.
  • a frame 58 indicates the option of arranging the controller 10, the electric power input 52, the electric transformer arrangement 54 and the electric power output 56 in a common structure or housing. However, they can also be arranged in a separate manner.
  • a first arrow 60 indicates an input signal supply.
  • a second arrow 62 indicates an electric output.
  • Fig. 3 schematically shows an example of X-ray imaging system 100.
  • the X-ray imaging system 100 comprises an X-ray source 102 for generating X-ray radiation. Further, the X-ray imaging system 100 comprises an example of the controller 10 according to one of the preceding examples, and an example of the generator 50 for voltage supply of the X-ray source according to the preceding example.
  • the X-ray source 102 comprises an anode and a cathode (not shown in detail).
  • the cathode comprises at least one cathode filament for emitting at least one electron beam towards the anode.
  • the controller 10 controls an operation of the cathode filament by controlling the generator 50.
  • the X-ray source 102 is mounted to an end of a C-arm 106, which is equipped with a detector 108 at the other end.
  • a subject support 110 is shown. Further, a display arrangement 112 is indicated near the subject support 110.
  • the C-arm and other equipment can be mounted to ceiling support structures.
  • a console 114 with e.g. mouse, keypad, tablet, and control knobs plus displays for actively controlling the X-ray imaging system 100 is shown in the lower right foreground in Fig. 3 .
  • a connection line 104 indicates the data connection of the console 114 with the controller 10 and the generator 50.
  • Fig. 4 illustrates a method 400 for controlling a high voltage generator 50 for an X-ray source.
  • the method includes:
  • the expected emission current of the X-ray pulse may be determined (460) using an emission current data model with the operational filament current and the operational X-ray source voltage as input.
  • the method 400 may further include:
  • emission current characteristics may be measured over the entire operating range of the tube.
  • Various measurements with varying filament currents If and tube voltages Ut may be performed and stored with the resulting emission current Ie in an emission current data table. From such a data table, the suitable filament current If for the whole operating range can be read out or calculated via interpolation.
  • the blank and boost curves may be converted such that the equivalent filament current in equilibrium, i.e. corresponding to a filament temperature, is calculated for each measurement. This information may be captured in a filament temperature model, such as a look-up table.
  • the filament current If is an equivalent for the filament temperature in equilibrium.
  • Blank and boost measurements and corresponding filament temperature model as described above allows for a prediction of the filament temperature when boosting or blanking for a certain duration from a filament temperature Ifstart.
  • the emission pause between the pulses is used to cool down the filament and to heat it up again before the next pulse.
  • the blank and boost times may be calculated before the imaging run, from the measurements described above, and applied during the pauses of the run. In this way, the filament wear out is reduced and the lifetime of the lifetime enhanced.
  • a pulse-to-pulse temperature regulation may be implemented. Such regulation compares the measured emission current to the nominal expected emission current of the previous pulse. Based on the direction and size of the deviation, the regulation may correct the temperature for coming pulses by moving the precalculated cool down or heat up times in the opposite direction.
  • the drift compensation may make use of a so-called PI control algorithm.
  • compensation is far from straightforward due to the non-linear relation between the emission current Ie, the filament temperature If and the time needed to adjust the filament temperature.
  • a proposed solution is to linearize the relation using the adaptation data described above.
  • the corresponding filament current If may be calculated using the emission current data table.
  • the results may then be converted into boosting or blanking steps, using a filament temperature model.
  • the boosting or blanking steps depending on if the actual emission current was higher or lower than the nominal expected emission current, may be fed into the PI control algorithm as an error.
  • the correction of the blank and/or boost time may be output by the algorithm.
  • the emission pause should preferably not be extended as the acquisition generally has a fixed timing. The correction will therefore preferably limit boost or blank time. If the emission is too high, then boost steps are omitted. If the emission is too low, then blank steps are omitted.
  • a temperature regulation is exemplified with the timing diagram in Fig. 5 .
  • the solid curve illustrates the filament temperature, which may be expressed in an equilibrium filament current Ifeq on the y-axis.
  • the x-axis illustrates time in milliseconds.
  • X-ray imaging pulses are illustrated by the rectangles, separated by an emission pause. It is noted that the diagram is intended to illustrate the principle of temperature regulation and may not be to scale. E.g. the emission pauses between X-ray pulses may be much longer, such as hundreds of milliseconds. Similarly, the pulses may be tenths or milliseconds long.
  • Fig. 5 shows three pulses.
  • the first pulse to the left has a correct operational filament temperature and the X-ray source generates an expected nominal emission current Ie nom with an operational X-ray source high voltage applied. This also leads to generating an expected X-ray dose from the X-ray source during the pulse.
  • the filament temperature is blanked for 13 ms, by applying a blanking current, and then boosted for 8 ms, by applying a boosting current. This saves filament lifetime as compared to keeping the filament temperature at the operational temperature during the entire pause.
  • the filament temperature is slightly too hot during the second pulse. This deviation in filament temperature from the expected temperature is detected by measuring the emission current Ie. In this case, the actual emission current Ie is larger than the expected nominal emission current Ie nom. A delta in emission current between measured and expected emission currents can be determined.
  • the blanking and boosting for a following emission pause may be regulated This may be done by converting the difference in emission current to a change, preferably a reduction, in units of blanking or boosting, using e.g. a filament temperature model.
  • the filament temperature is too high.
  • the delta in emission current corresponds to a correction by reducing the boosting time with 2 ms. This leads to the filament temperature being at the correct filament temperature again after boosting and in time for the third pulse.
  • the filament is at operational filament temperature 2 ms early and therefore held longer at operational temperature.
  • the filament may be kept at the low intercooler temperature between blanking and boosting, here for 2 ms, to optimize the reduction in filament degradation.
  • the blanking time may be increased, and the boosting time decreased during the same pause.
  • the regulation with adapted blanking and/or boosting time may extend over multiple emission pauses before the filament temperature is at its expected levels again and the delta between expected and measured emission current is zero or close to zero. It is also to be understood that if the measured emission current would be to low instead, to indicate that the filament temperature is lower than expected instead of higher, the blanking time would be reduced instead, and/or the boosting time would be increased.

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Abstract

Controlling a high voltage generator for an X-ray source includes: providing (410) power to the X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by an emission pause comprising a first part and a second part; providing (420) an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses; providing (430) a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature; providing (440) a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature; receiving (450) a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage; determining (460) an expected emission current of the X-ray pulse, in dependence on the operational filament current and the operational X-ray source voltage; and adapting (470) the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapting the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.

Description

    FIELD OF THE INVENTION
  • The invention relates to a controller for controlling a high voltage generator for an X-ray source, in particular during a pulsed X-ray imaging run. The invention also relates to a high voltage generator, an X-ray imaging system, a method for controlling a high voltage generator, a computer program element, and a computer-readable medium.
    • BACKGROUND OF THE INVENTION
  • X-ray imaging is considered an important imaging modality in medical imaging. X-ray sources like X-ray tubes are used to generate X-ray radiation that passes through a subject and impinges on an X-ray detector. The X-ray tube typically includes a cathode with a filament and an anode. When a filament current is applied to the filament, the filament current heats the filament, causing the filament to expel electrons (thermionic emission), creating a space charge a short distance away from the filament. A peak X-ray tube voltage is applied across the cathode and the anode, and causes a beam of the electrons to accelerate from the cathode and impinge the anode. The X-ray tube current, or emission current, represents the number of electrons per second flowing from the cathode to the anode. Electrostatic or magnetic focusing with e.g. grid electrodes or quadrupoles can be applied to control a size of and steer the beam of electrons. An interaction of the electrons with the material of the anode produces heat and radiation, including X-rays, which pass through a tube window, into an examination region, to the X-ray detector.
  • For various reasons, for example restrictions in certain flat X-ray detectors, X-ray radiation may need to be generated in a pulsed manner. In such pulsed X-ray image acquisition, X-ray images are acquired using a series of short X-ray pulses. Such a series of pulses is called an imaging run.
  • A crucial part in an X-ray source is thus the cathode filament. The filament needs to have a specific, elevated temperature to reach the desired emission current during an X-ray pulse. X-ray sources used e.g. in cardio-vascular X-ray systems may show a wear-out of their cathode filaments. The wear-out may be the result of evaporation of the tungsten they consist of. There may thus be a need to provide X-ray sources in particular for pulsed operation with increased filament lifetime and hence increased field life.
  • WO2023117733 A1 relates to operating a filament of an X-ray tube. In order to provide X-ray tubes with improved wear out, a control device for pulsed operation of a generator for an X-ray tube is provided. The X-ray tube may be controlled to provide a plurality of X-ray pulses, wherein two subsequent pulses are temporally separated by an emission pause. The emission pause comprises at least a first part and a second part. A filament current is provided to a cathode filament of the X-ray tube such that, in the emission pause between two subsequent pulses, during a first part of the pause a first filament current is provided and during a second part of the pause a second filament current is provided, the first filament current being lower than the second filament current. By operating the filament in this way, the filament temperature can be reduced, resulting in significantly less wear and longer lifetime of the X-ray tube.
  • Such an 'intercooler' or 'intercooling scheme' can thus be used to significantly extend the lifetime of an X-ray source. During repeated changes of the filament current, and hence the corresponding filament temperature, via so called 'boosting' and 'blanking', it is important to avoid or correct deviations or drift in temperature levels over multiple pulses.
    • SUMMARY OF THE INVENTION
  • It is an object of the invention to provide improved correction of filament temperature during repeated boosting and blanking of the filament temperature.
  • The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.
  • According to a first aspect of the invention, there is provided a controller for controlling a high voltage generator for an X-ray source. The controller is configured to control the high voltage generator to:
    • provide power to the X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by a respective emission pause comprising a first part and a second part;
    • provide an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses;
    • provide a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature; and
    • provide a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature.
  • In accordance with the invention, the controller is further configured to:
    • receive a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage;
    • determine an expected emission current of the X-ray pulse in dependence on the operational filament current and the operational X-ray source voltage; and
    • adapt the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapt the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.
  • By determining deviations between expected emission current and measured emission current of a previous pulse, the filament temperature of a subsequent pulse can be corrected. The correction is done by modifying the boosting and/or blanking time. In this way, drift of the operational filament temperature over several pulses can be avoided and errors from variations in X-ray emission can be reduced. E.g., if the measured emission current is larger than the expected emission current (operational filament temperature during the pulse is too high), the duration of blanking may be increased and/or the duration of boosting may be reduced, to correct for the deviation for the following pulse. Similarly, if the measured emission current is smaller than the expected emission current (operational filament temperature during the pulse is too low), the duration of blanking may be reduced and/or the duration of boosting may be increased, to correct for the deviation for the following pulse.
  • In an embodiment, an emission current data model is used. The emission current data model may be or include a static or adaptive look-up table comprising combinations of emission currents and filament currents for at least one operational X-ray source voltage. The controller may be configured to populate and/or update the look-up table, e.g. during calibration runs. The emission current data model may be or include a digital twin of the X-ray source, to simulate the relation between emission currents and filament currents. The emission current data model may use machine learning and may be trained to provide an emission current as output data when a filament current and an X-ray source voltage is provided as input data.
  • According to an embodiment of the invention, a total duration of each emission pause remains constant before and after the adaptation. It is advantageous to control the high voltage generator to keep the total duration of each emission pause, comprising the blanking and boosting, constant during the X-ray imaging run. This is because the pulsed X-ray acquisition may have a fixed timing. Hence, when changing the duration of blanking and/or boosting, the emission pause should neither be extended nor reduced. If the sum of duration of the first part with blanking and the second part with boosting is reduced, the emission pause may be controlled to comprise a third part where the filament is kept at a stable temperature. It may be advantageous to reduce the blanking time if the measured emission current is too low and to reduce the boosting time if the measured emission current is too high. In this way, there is no risk that the boosting plus blanking times extend beyond the total duration of the emission pause.
  • According to an embodiment of the invention, the controller is further configured to control the high voltage generator to measure the measured emission current. This is advantageous, since the controller can control when the measurement of the 'measured emission current' is performed and provide an efficient feedback loop based on the outcome of the measurement. Modern high voltage generators are generally equipped to measure the emission current when used together with an X-ray source.
  • According to an embodiment of the invention, the expected emission current of the X-ray pulse is determined using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the controller is further configured to:
    • convert the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model; and
    • use a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  • Due to a very non-linear relationship between emission current and filament temperature, accurate regulation of boosting and/or blanking time may be challenging. Therefore, it is advantageous to convert the difference in emission currents to a difference in temperature values, such as a difference in equilibrium filament current corresponding to the respective temperature. From this difference, there is a more linear relationship with the effect of blanking and boosting time, and the regulation can be improved
  • The filament temperature data model may be or include a static or adaptive look-up table comprising changes in filament temperature over time when a boosting or blanking current is applied, for at least one operational X-ray source voltage. Hence, the filament temperature data model may be used to predict the effect on filament temperature, and hence on emission current, when providing a boosting or blanking current for a certain time, i.e. when heating or cooling the filament. The controller may be configured to populate and/or update such a look-up table, e.g. during calibration runs.
  • The filament temperature model may be populated by measurements of emission currents over time for various applied blanking or boosting currents, at a known X-ray source voltage. Measured emission currents may subsequently be converted to filament currents (equivalent to filament temperatures) using the emission current data model.
  • The filament temperature data model may be or include a digital twin of the X-ray source, to simulate the relation between filament temperature over time for different applied filament currents during boosting or blanking. The filament temperature data model may use machine learning and may be trained to provide a filament temperature over time as output data when a filament current and an X-ray source voltage is provided as input data.
  • The filament temperature model may, alternatively or additionally, model the changes of emission currents over time, when blanking or boosting currents are applied. Outputs in the form of emission currents may be converted to filament temperatures or equivalent filament currents, using the emission current data model.
  • According to a further embodiment of the invention, determining the adaptation comprises determining a delta in boosting or blanking time units using the filament temperature model. In this way, with the combination of the emission current data model (static dependency of emission current and filament current) and the filament temperature model (change in temperature and hence emission current over time for a certain applied boosting or blanking current), the deviation in measured and expected emission current, relating to a difference in filament temperatures, can be linearized to a delta in boosting or blanking time units. The delta in boosting or blanking time units may be in the form of integer units, such as integers of milliseconds.
  • According to a further embodiment of the invention, the controller is configured to provide the delta in boosting or blanking time units as an error input to a proportional-integral control algorithm, and to receive the adapted duration of providing the blanking current and/or duration of providing the boosting current as output from the proportional-integral control algorithm. Using a proportional-integral control algorithm with the temperature difference as an error input is a fast and efficient way to regulate the boosting and/or blanking times between pulses to correct for any deviations in emission current.
  • According to an embodiment of the invention, the controller is configured to control the high voltage generator to provide an intercooler hold current during a third part of the emission pause, wherein
    • the third part of the emission pause is between the first part and the second part of the emission pause,
    • the intercooler hold current holds the filament temperature at the intercooler filament temperature, and
    • the controller is further configured to adapt the duration of the providing the intercooler hold current and/or the level of the intercooler hold current based on the adaptation of the duration of providing the blanking current and/or the boosting current.
  • By holding the filament temperature at the intercooler temperature during a third holding part (instead of boosting too soon), filament degradation can be kept as low as possible. Furthermore, by adapting the intercooler hold current and/or its duration according to the adaptation of the duration of providing the blanking current and/or the boosting current, the holding part can be optimized to the emission pause, such as preferably an emission pause of fixed duration.
  • According to a second aspect of the invention, there is provided a high voltage generator for providing power to an X-ray source. The high voltage generator comprises the controller according to any of the embodiments of the first aspect.
  • According to a third aspect of the invention, there is provided an X-ray imaging system for pulsed X-ray imaging, the X-ray imaging system comprising: an X-ray detector for detecting X-ray radiation; an X-ray source for generating X-ray radiation; and the high voltage generator according to the second aspect.
  • According to a fourth aspect of the invention, there is provided a method for controlling a high voltage generator for an X-ray source. The method comprises:
    • providing power to the X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by a respective emission pause comprising a first part and a second part;
    • providing an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses;
    • providing a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature;
    • providing a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature;
    • receiving a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage;
    • determining an expected emission current of the X-ray pulse, in dependence on the operational filament current and the operational X-ray source voltage; and
    • adapting the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapting the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.
  • According to an embodiment of the invention, the expected emission current of the X-ray pulse is determined using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the method further comprises:
    • converting the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model; and
    • using a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  • According to a fifth aspect, there is provided a computer program element, which, when being executed by a controller, is adapted to cause the controller to perform the method according to the fourth aspect. The computer program element may be made available for download from a server, e.g. via the internet.
  • According to a sixth aspect, there is provided a computer-readable medium having stored thereon the computer program element mentioned above.
  • These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • Exemplary embodiments of the invention will be described in the following with reference to the following drawings:
    • Fig. 1 schematically shows an example of a controller for controlling a high voltage generator.
    • Fig. 2 schematically shows an example of a high voltage generator for providing power to an X-ray source.
    • Fig. 3 schematically shows an example of an X-ray imaging system.
    • Fig. 4 shows an example of a method for controlling a high voltage generator.
    • Fig. 5 shows an example of a timing diagram for boosting and blanking a filament.
    DETAILED DESCRIPTION OF EMBODIMENTS
  • WO2023117733A1 , incorporated herein by reference, describes the concept of a filament intercooler to increase filament lifetime. In thermionic X-ray tubes, electrons emitted by a heated cathode are accelerated through a strong electric field in vacuum towards an anode where they generate "Bremsstrahlung" also known as X-rays in case they are generated by an X-ray tube. The amount of X-ray is proportional to the emission current running between anode and cathode. Apart from cathode surface size, surface conditions and material, which are "fixed" in a particular tube design, the emission current is a function of the voltage between cathode and anode and the temperature of the cathode. Cathodes usually comprise strips or coils of a metal with a high melting point, such as Tungsten, called filaments. When they are heated, the metal of the filaments evaporates and eventually the filament gets so thin at a certain location that it breaks. This describes a general wear mechanism for thermionic X-ray tubes.
  • For imaging, X-ray tubes may be operated in pulsed mode. Rather than producing a constant amount of X-ray, they produce short pulses of high intensity in series called pulsed X-ray imaging runs. This mode of operation supports detectors that may need a reset time where there is no X-ray produced between two imaging frames. Further, with short intense pulses there is less blurring of the image by movement.
  • WO2023117733A1 describes controlling an X-ray tube to provide a plurality of pulses to generate the electron beam with the desired emission current for generating the plurality of X-ray pulses, wherein two subsequent pulses of the plurality of pulses are temporally separated by an emission pause. That is, during the pulses, the filament current provided corresponds to a normal operational current level that, at the corresponding tube voltage, results in emitting an electron beam at the desired emission current from the cathode towards the anode.
  • The emission pause comprises at least a first part and a second part. The generator is controlled to adjust, in the emission pause between the two subsequent pulses, the filament current providing a first filament current during the first part of the pause and a second filament current during the second part of the pause. The first filament current is lower than the second filament current and preferably also lower than the operational current level. In effect, the first filament current is too low to maintain the filament at a temperature needed for emitting an electron beam. As a result, the filament temperature decreases during the first part of the emission pause.
  • Preferably, the second filament current is provided as an intermediate heat-up current to prepare the filament for subsequently emitting the desired emission current of an electron beam during the following X-ray pulse. Preferably, the second filament current is higher than the operational current level. Thus, at the beginning of the following pulse, the temperature of the filament may be restored to its operational value needed for emitting the electron beam.
  • WO2023117733 A1 describes providing the first and second filament current, i.e. blanking and boosting are implemented in between subsequent pulses within an imaging run, in order to save filament wear. That is, a current provided to the filament of the X-ray tube is firstly reduced in between subsequent pulses of the imaging run to the first filament current, causing the filament to cool down. Shortly before the next pulse, an increased boosting current is used as the second filament current so that the filament is back at the operating temperature at the start of the pulse. This is repeated throughout the pulsed imaging run, preferably in between adjacent X-ray pulses.
  • The inventors of the present invention have found that over multiple X-ray emission pulses during a pulsed run, drift in the filament temperature may occur. If the amount of energy that is each time applied during boosting and withdrawn during blanking is not the same, such differences may accumulate and lead to drift of the operational filament temperature level and corresponding level of X-ray radiation, which may eventually trigger errors in the system. In the present application, it is therefore suggested to monitor and correct the filament temperature of a subsequent pulse, by determining deviations between expected emission current and measured emission current of a previous pulse. Such correction is done by modifying the boosting and/or blanking time. In this way, drift of the operational filament temperature over several pulses can be avoided and errors from variations in X-ray emission can be reduced.
  • Fig. 1 schematically shows a controller 10 for controlling a high voltage generator, according to embodiments of the invention. The controller may comprise or otherwise interact with a processor 12 and a memory 14. The processor 12 may be a computer, a computer network, and/or another programmable apparatus, such as a single and/or multi core processing unit, a graphics processing unit, an accelerated processing unit, a digital signal processor, a field programmable gate array, an application-specific integrated circuit, etc. The memory 14 may be configured for storing long term and/or short term, data. In the example in Fig. 1, the controller is illustrated as a separate unit with a frame 24. However, it is noted that the controller may be a distributed system, with processing done locally or remotely. Furthermore, parts of or the entire controller may be integrated with a high voltage generator or other parts of an imaging system. The controller is configured to provide an output signal 20 to control the high voltage generator 50. The communication between the controller 10 and the high voltage generator 50 may be wired and/or wireless.
  • The controller 10 is configured to receive an input signal 16. In Fig. 1 this is illustrated with input from a signal source 18. The signal source may be part of an X-ray imaging system. The controller may be configured to receive an input signal from the generator 50 as the signal source 18. However, alternatively, or additionally, the controller may be configured to receive an input signal from a user interface, a sensor etc.
  • The controller 10 is configured to control the high voltage generator 50 to provide power to the X-ray source 102 to generate a plurality of X-ray pulses during a pulsed X-ray imaging run. During an X-ray imaging run, subsequent X-ray pulses are temporally separated in time by an emission pause.
  • The controller 10 is configured to control the high voltage generator 50 provide an operational filament current to heat a filament of a cathode of the X-ray source 102 to an operational filament temperature during the X-ray pulses. With an operational X-ray source voltage applied, the operational filament temperature, corresponding to the operational filament current, is at a suitable level to generate a desired X-ray imaging emission current during the X-ray pulses. The operational X-ray source voltage may be between 40 kV to 200 kV, preferably between 80 kV to 140 kV. The emission current may be on the order of hundreds of mA, such as 100-200 mA. The operational filament current may be between 3-6 A.
  • The controller 10 is configured to control the high voltage generator 50 to provide a blanking filament current during a first part of the emission pauses, preferably at the beginning of each emission pause. The blanking filament current is lower than the operational filament current, e.g. 1-2 A and may even be 0 A. The low blanking filament current allows the filament temperature to decrease to an intercooler filament temperature, which is low enough to reduce filament degradation and hence save filament lifetime.
  • The controller 10 is configured to control the high voltage generator 50 to provide a boosting filament current during a second part of the emission pauses. The boosting filament current is higher than the blanking filament current in order to increase the filament temperature again from the intercooler filament temperature to the operational filament temperature. The boosting filament current may be 7-10 A. In this way, the filament is brought back to a temperature level suitable for X-ray emission.
  • The controller 10 is configured to receive a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse. The measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage. The measured emission current may be received via the input signal 16. The emission current may be measured by and received from the high voltage generator 50, which would in that case also function as the signal source 18. The controller may be configured to control the high voltage generator to measure the emission current. The emission current may be received from the imaging system with which the controller operates. The measured emission current is received for multiple X-ray emission pulses during an imaging run, such that deviations may be monitored over time. The operational filament current and the operational source voltage may be received during an imaging run. However, the operational filament current and the operational source voltage are preferably predetermined as constant values or predetermined to change according to a predetermined sequence. The operational filament current and the operational source voltage may be received in advance of an imaging run and may be stored in the memory 14.
  • The controller 10 is configured to determine an expected emission current of the X-ray pulse based on the known operational filament current and the operational X-ray source voltage. In this way, the expected emission current and the measured emission current may be compared for a particular pulse. The controller 10 may use an emission current data model to determine the expected emission current from the known operational filament current and the operational X-ray source voltage. The emission current data model may be or include a static or dynamic look-up table, such as pre-stored in the memory 14 or received as a signal input 12, comprising combinations of emission currents and filament currents for at least one operational X-ray source voltage. The controller may be configured to populate and/or update the look-up table, e.g. during calibration runs. The emission current data model may be or include a digital twin of the X-ray source, to simulate the relation between emission currents and filament currents. The emission current data model may use machine learning and may be trained to provide an emission current as output data when a filament current and an X-ray source voltage is provided as input data.
  • The controller 10 is configured to adapt the duration of providing the blanking current during and/or adapt the duration of providing the boosting current. The controller is configured to correct the operational filament temperature of a subsequent X-ray pulse when there is a deviation between the measured emission current and the expected emission current. Preferably, the changed duration of providing the blanking current and/or boosting current does not change the total duration of the emission pause.
  • The controller 10 may be configured to convert the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model, and to use a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current. The filament temperature model may be stored in the memory 14 and/or or may be received by the controller 10. The filament temperature data model may be or include a static or adaptive look-up table comprising changes in filament temperature over time when a boosting or blanking current is applied, for at least one operational X-ray source voltage. The filament temperature data model may be used to predict the effect on filament temperature, and hence on emission current, when providing a boosting or blanking current for a certain time, i.e. when heating or cooling the filament. The controller may be configured to populate and/or update such a look-up table, e.g. during calibration runs. The filament temperature model may be populated by measurements of emission currents over time for various applied blanking or boosting currents, at a known X-ray source voltage. Measured emission currents may subsequently be converted to filament currents (equivalent to filament temperatures) using the emission current data model. The filament temperature data model may be or include a digital twin of the X-ray source, to simulate the relation between filament temperature over time for different applied filament currents during boosting or blanking. The filament temperature data model may use machine learning and may be trained to provide a filament temperature over time as output data when a filament current and an X-ray source voltage is provided as input data. The filament temperature model may model the changes of X-ray source emission currents over time, when blanking or boosting currents are applied to the filament. The controller may be configured to convert model outputs in the form of emission currents to filament temperatures or equivalent filament currents, using the emission current data model.
  • Determining the adaptation of the boosting and/or blanking times may include determining a delta in boosting or blanking time units, preferably integer units, using the filament temperature model. In this way, with the combination of the emission current data model (static dependency of emission current and filament current) and the filament temperature model (change in temperature and hence emission current over time for a certain applied boosting or blanking current), the deviation in measured and expected emission current, relating to a difference in filament temperatures, can be linearized to a delta in boosting or blanking time units. The controller 10 may be configured to provide such a delta in boosting or blanking time units as an error input to a proportional-integral control algorithm, and to receive the adapted duration of providing the blanking current and/or duration of providing the boosting current as output from the proportional-integral control algorithm.
  • The controller 10 may be configured to control the high voltage generator 50 to provide an intercooler hold current between blanking and boosting. The intercooler hold current holds the filament temperature at a corresponding intercooler filament temperature. The duration of providing the intercooler hold current and/or the level of the intercooler hold current may be adapted based on the adaptation of the duration of providing the blanking current and/or the boosting current.
  • By holding the filament temperature at the intercooler temperature during a third holding part (instead of boosting too soon), filament degradation can be kept as low as possible. Furthermore, by adapting the intercooler hold current and/or its duration according to the adaptation of the duration of providing the blanking current and/or the boosting current, the holding part can be optimized to the emission pause, such as preferably an emission pause of fixed duration.
  • Fig. 2 schematically shows an example of a high voltage generator 50 for providing power to an X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run. The generator 50 in this example comprises a controller 10 as described above. Furthermore, the example high voltage generator 50 includes an electric power input 52, an electric transformer arrangement 54, and an electric power output 56. The electric power input 52 is connectable to an electric power supply configured to provide an input in form of electric energy. The electric power input 52 is connected to the electric transformer arrangement 54. The electric transformer arrangement 54 is configured to transform the voltage input into suitable DC high-voltage and suitable electric current for pulsed operation of the X-ray source. The electric power output 56 is configured to provide a suitable high-voltage and suitable electric currents. The electric power output 56 is connectable to the X-ray source. The controller 10 is configured to control said generator components, e.g. the electric transformer arrangement 54.
  • A frame 58 indicates the option of arranging the controller 10, the electric power input 52, the electric transformer arrangement 54 and the electric power output 56 in a common structure or housing. However, they can also be arranged in a separate manner. A first arrow 60 indicates an input signal supply. A second arrow 62 indicates an electric output.
  • Fig. 3 schematically shows an example of X-ray imaging system 100. The X-ray imaging system 100 comprises an X-ray source 102 for generating X-ray radiation. Further, the X-ray imaging system 100 comprises an example of the controller 10 according to one of the preceding examples, and an example of the generator 50 for voltage supply of the X-ray source according to the preceding example. The X-ray source 102 comprises an anode and a cathode (not shown in detail). The cathode comprises at least one cathode filament for emitting at least one electron beam towards the anode. The controller 10 controls an operation of the cathode filament by controlling the generator 50.
  • As an example, the X-ray source 102 is mounted to an end of a C-arm 106, which is equipped with a detector 108 at the other end. A subject support 110 is shown. Further, a display arrangement 112 is indicated near the subject support 110. The C-arm and other equipment can be mounted to ceiling support structures. A console 114 with e.g. mouse, keypad, tablet, and control knobs plus displays for actively controlling the X-ray imaging system 100 is shown in the lower right foreground in Fig. 3. A connection line 104 indicates the data connection of the console 114 with the controller 10 and the generator 50.
  • Fig. 4 illustrates a method 400 for controlling a high voltage generator 50 for an X-ray source. The method includes:
    • providing 410 power to the X-ray source 102 to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by an emission pause comprising a first part and a second part;
    • providing 420 an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses;
    • providing 430 a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature;
    • providing 440 a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature;
    • receiving 450 a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage;
    • determining 460 an expected emission current of the X-ray pulse, in dependence on the operational filament current and the operational X-ray source voltage; and
    • adapting 470 the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapting the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.
  • The expected emission current of the X-ray pulse may be determined (460) using an emission current data model with the operational filament current and the operational X-ray source voltage as input. The method 400 may further include:
    • converting the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model; and
    • using a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  • It can be understood that other embodiments of the invention, as already elaborated on with respect to the controller 10, are also mutatis mutandis applicable to the method 400.
  • During adaptation of an X-ray tube 102, emission current characteristics may be measured over the entire operating range of the tube. Various measurements with varying filament currents If and tube voltages Ut may be performed and stored with the resulting emission current Ie in an emission current data table. From such a data table, the suitable filament current If for the whole operating range can be read out or calculated via interpolation. The filament current If may be seen as a function of emission current Ie and tube voltage Ut. If = f Ie , Ut
  • As a next step of adaptation, the emission current may be measured while a fixed filament current and tube voltage is applied. This is preferably done for the blank current (such as If = 0 A) and the boost current (such as If = 6 A). During such measurements, the resulting emission current is measured over time, e.g. every millisecond. The measurements during blanking give information about the cooldown behaviour of the filament and the boost measurements give information about the filament behaviour when heating up. Using the emission current data table, the blank and boost curves may be converted such that the equivalent filament current in equilibrium, i.e. corresponding to a filament temperature, is calculated for each measurement. This information may be captured in a filament temperature model, such as a look-up table. In this way, it is possible to predict the resulting emission current when a filament is boosted or blanked for a certain time. To stay at a particular emission current level, the boosting or blanking is stopped and the operational filament current for the setpoint is applied. If = f Ie Setpoint , Ut Setpoint
  • The filament current If is an equivalent for the filament temperature in equilibrium. The blank and boost measurements and corresponding filament temperature model as described above allows for a prediction of the filament temperature when boosting or blanking for a certain duration from a filament temperature Ifstart. Blank : If End = f If Start , t Blank Boost : If End = f If Start , t Boost
  • During a pulsed X-ray imaging run, the emission pause between the pulses is used to cool down the filament and to heat it up again before the next pulse. The blank and boost times may be calculated before the imaging run, from the measurements described above, and applied during the pauses of the run. In this way, the filament wear out is reduced and the lifetime of the lifetime enhanced. To reduce temperature drift between pulses, a pulse-to-pulse temperature regulation may be implemented. Such regulation compares the measured emission current to the nominal expected emission current of the previous pulse. Based on the direction and size of the deviation, the regulation may correct the temperature for coming pulses by moving the precalculated cool down or heat up times in the opposite direction.
  • The drift compensation may make use of a so-called PI control algorithm. However, compensation is far from straightforward due to the non-linear relation between the emission current Ie, the filament temperature If and the time needed to adjust the filament temperature. A proposed solution is to linearize the relation using the adaptation data described above. For both nominal and actual emission current Ie, the corresponding filament current If may be calculated using the emission current data table. The results may then be converted into boosting or blanking steps, using a filament temperature model. The boosting or blanking steps, depending on if the actual emission current was higher or lower than the nominal expected emission current, may be fed into the PI control algorithm as an error. The correction of the blank and/or boost time may be output by the algorithm. The emission pause should preferably not be extended as the acquisition generally has a fixed timing. The correction will therefore preferably limit boost or blank time. If the emission is too high, then boost steps are omitted. If the emission is too low, then blank steps are omitted.
  • A temperature regulation is exemplified with the timing diagram in Fig. 5. The solid curve illustrates the filament temperature, which may be expressed in an equilibrium filament current Ifeq on the y-axis. The x-axis illustrates time in milliseconds. X-ray imaging pulses are illustrated by the rectangles, separated by an emission pause. It is noted that the diagram is intended to illustrate the principle of temperature regulation and may not be to scale. E.g. the emission pauses between X-ray pulses may be much longer, such as hundreds of milliseconds. Similarly, the pulses may be tenths or milliseconds long.
  • Fig. 5 shows three pulses. The first pulse to the left has a correct operational filament temperature and the X-ray source generates an expected nominal emission current Ie nom with an operational X-ray source high voltage applied. This also leads to generating an expected X-ray dose from the X-ray source during the pulse. Between the first pulse and the second pulse from the left, the filament temperature is blanked for 13 ms, by applying a blanking current, and then boosted for 8 ms, by applying a boosting current. This saves filament lifetime as compared to keeping the filament temperature at the operational temperature during the entire pause. However, as seen from the solid curve above the middle pulse, the filament temperature is slightly too hot during the second pulse. This deviation in filament temperature from the expected temperature is detected by measuring the emission current Ie. In this case, the actual emission current Ie is larger than the expected nominal emission current Ie nom. A delta in emission current between measured and expected emission currents can be determined.
  • With the information that the emission current during the middle pulse is too high, quantified with a certain delta Ie, the blanking and boosting for a following emission pause may be regulated This may be done by converting the difference in emission current to a change, preferably a reduction, in units of blanking or boosting, using e.g. a filament temperature model. In this case the filament temperature is too high. The delta in emission current corresponds to a correction by reducing the boosting time with 2 ms. This leads to the filament temperature being at the correct filament temperature again after boosting and in time for the third pulse. In the example in Fig. 5, the filament is at operational filament temperature 2 ms early and therefore held longer at operational temperature. Alternatively, the filament may be kept at the low intercooler temperature between blanking and boosting, here for 2 ms, to optimize the reduction in filament degradation. As another option, the blanking time may be increased, and the boosting time decreased during the same pause.
  • It is noted that the regulation with adapted blanking and/or boosting time may extend over multiple emission pauses before the filament temperature is at its expected levels again and the delta between expected and measured emission current is zero or close to zero. It is also to be understood that if the measured emission current would be to low instead, to indicate that the filament temperature is lower than expected instead of higher, the blanking time would be reduced instead, and/or the boosting time would be increased.
  • It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed processor. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. Measures recited in mutually different dependent claims may advantageously be used in combination.

Claims (13)

  1. A controller (10) for controlling a high voltage generator (50) for an X-ray source (102), wherein the controller is configured to control the high voltage generator to:
    provide power to the X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by a respective emission pause comprising a first part and a second part;
    provide an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses;
    provide a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature;
    provide a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature; and
    wherein the controller is further configured to:
    receive a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage;
    determine an expected emission current of the X-ray pulse in dependence on the operational filament current and the operational X-ray source voltage; and
    adapt the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapt the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.
  2. The controller (10) according to claim 1, wherein a total duration of each emission pause remains constant before and after the adaptation.
  3. The controller (10) according to claim 1 or 2, wherein the controller is further configured to control the high voltage generator to measure the measured emission current.
  4. The controller according to claim 1 or 2 or 3, wherein the expected emission current of the X-ray pulse is determined using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the controller is further configured to:
    convert the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model; and
    use a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  5. The controller according to claim 4, wherein determining the adaptation comprises determining a delta in boosting or blanking time units using the filament temperature model.
  6. The controller according to claim 5, wherein the controller is configured to provide the delta in boosting or blanking time units as an error input to a proportional-integral control algorithm, and to receive the adapted duration of providing the blanking current and/or duration of providing the boosting current as output from the proportional-integral control algorithm.
  7. The controller according to any of the preceding claims, wherein the controller is configured to control the high voltage generator to provide an intercooler hold current during a third part of the emission pause, wherein
    the third part of the emission pause is between the first part and the second part of the emission pause,
    the intercooler hold current holds the filament temperature at the intercooler filament temperature, and
    the controller is further configured to adapt the duration of the providing the intercooler hold current and/or the level of the intercooler hold current based on the adaptation of the duration of providing the blanking current and/or the boosting current.
  8. A high voltage generator (50) for providing power to an X-ray source, the high voltage generator comprising the controller (10) according to any of the preceding claims.
  9. An X-ray imaging system (100) for pulsed X-ray imaging, the X-ray imaging system comprising:
    an X-ray detector (108) for detecting X-ray radiation;
    an X-ray source (102) for generating X-ray radiation; and
    the high voltage generator (50) according to claim 8.
  10. A method (400) for controlling a high voltage generator for an X-ray source, the method comprising:
    providing (410) power to the X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run, wherein subsequent X-ray pulses of the plurality of X-ray pulses are temporally separated by a respective emission pause comprising a first part and a second part;
    providing (420) an operational filament current to heat a filament of a cathode of the X-ray source to an operational filament temperature during the plurality of X-ray pulses to generate a desired X-ray imaging emission current during the X-ray pulses;
    providing (430) a blanking filament current during the first part of the emission pauses, wherein the blanking filament current is lower than the operational filament current, to allow the filament temperature to decrease to an intercooler filament temperature;
    providing (440) a boosting filament current during the second part of the emission pauses, wherein the boosting filament current is higher than the blanking filament current, to increase the filament temperature from the intercooler filament temperature to the operational filament temperature;
    receiving (450) a measured emission current, the operational filament current, and an operational source voltage of an X-ray pulse, wherein the measured emission current is measured during the X-ray pulse at the operational filament current and the operational X-ray source voltage;
    determining (460) an expected emission current of the X-ray pulse, in dependence on the operational filament current and the operational X-ray source voltage; and
    adapting (470) the duration of providing the blanking current during the first part of a subsequent emission pause, and/or adapting the duration of providing the boosting current during the second part of the subsequent emission pause, to correct the operational filament temperature of a subsequent X-ray pulse for a difference between the measured emission current and the expected emission current.
  11. The method according to claim 10, wherein the expected emission current of the X-ray pulse is determined (460) using an emission current data model with the operational filament current and the operational X-ray source voltage as input, and the method further comprises:
    converting the measured emission current to a first filament current, corresponding to a first filament temperature, using the emission current data model; and
    using a filament temperature model with as input the first filament current or the first filament temperature, and the operational filament current or the corresponding operational filament temperature, to determine the adaptation of the duration of providing the blanking current and/or the duration of providing the boosting current.
  12. A computer program element, which, when being executed by a controller, is adapted to cause the controller to perform the method according to claim 10 or 11.
  13. A computer-readable medium having stored thereon the computer program element of claim 12.
EP24185881.0A 2024-07-02 2024-07-02 Controlling a high voltage generator for an x-ray source Pending EP4676167A1 (en)

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EP24185881.0A EP4676167A1 (en) 2024-07-02 2024-07-02 Controlling a high voltage generator for an x-ray source
PCT/EP2025/067463 WO2026008358A1 (en) 2024-07-02 2025-06-23 Controlling a high voltage generator for an x-ray source

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4505101B2 (en) * 2000-03-31 2010-07-21 東芝Ｉｔコントロールシステム株式会社 X-ray generator
DE102013200189B4 (en) * 2013-01-09 2016-03-31 Siemens Aktiengesellschaft Method and device for heating current control of a pulsed x-ray tube
WO2023117733A1 (en) 2021-12-21 2023-06-29 Koninklijke Philips N.V. Operating a filament of an x-ray tube

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4505101B2 (en) * 2000-03-31 2010-07-21 東芝Ｉｔコントロールシステム株式会社 X-ray generator
DE102013200189B4 (en) * 2013-01-09 2016-03-31 Siemens Aktiengesellschaft Method and device for heating current control of a pulsed x-ray tube
WO2023117733A1 (en) 2021-12-21 2023-06-29 Koninklijke Philips N.V. Operating a filament of an x-ray tube

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