EP4676168A1

EP4676168A1 - Controlling a high voltage generator

Info

Publication number: EP4676168A1
Application number: EP24185890.1A
Authority: EP
Inventors: Sven HAGEMEISTER; Uwe FRITZSCHE
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2024-07-02
Filing date: 2024-07-02
Publication date: 2026-01-07
Also published as: WO2026008384A1

Abstract

A high voltage generator for an X-ray source is controlled 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;
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;
a blanking filament current that is lower than the operational filament current to allow the filament temperature to decrease during the first part of the emission pauses, such that the filament temperature reaches an intercooler filament temperature, wherein the intercooler temperature is (i) lower than the operational filament temperature and (ii) at a level resulting in a non-zero emission current at an operational X-ray source voltage when the filament is at the intercooler filament temperature; and
a boosting filament current that is higher than the blanking filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second part of the emission pauses.

Description

FIELD OF THE INVENTION

The invention relates to a controller for controlling a high voltage generator providing power to 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 during an imaging run using a series of short X-ray pulses.
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 deviations or drift in temperature levels over multiple pulses.

SUMMARY OF THE INVENTION

It is an object of the invention to provide improved accuracy of 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 that is lower than the operational filament current to allow the filament temperature to decrease during the first part of the emission pauses, such that the filament temperature reaches an intercooler filament temperature, wherein the intercooler temperature is (i) lower than the operational filament temperature and (ii) at a level resulting in a non-zero emission current at an operational X-ray source voltage when the filament is at the intercooler filament temperature; and
provide a boosting filament current that is higher than the blanking filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second part of the emission pauses.

Because the intercooler filament temperature is chosen such that a non-zero measurable emission current can be generated at the intercooler filament temperature when a known operational high X-ray source voltage is provided, the filament temperature level and corresponding equilibrium filament current, as well as the blanking and boosting filament currents and/or duration, can be determined and calibrated with accuracy. Extrapolation of filament temperature during e.g. cool-down can therefore be avoided, since the filament temperature corresponds to the measurable emission current at a known high voltage. This is advantageous in that the accuracy of repeated boosting/blanking between operational temperature and intercooler temperature for multiples of pulses/pauses can be improved. Although it is predetermined to be at a level sufficient to generate a measurable emission current, the filament intercooler temperature leads to reduced filament degradation during pulsed operation, since it is lower than the operational filament temperature. Preferably, the controller is configured to control the high voltage generator to measure the intercooler filament temperature emission current at an operational X-ray source voltage.
A pulsed X-ray imaging run comprises multiple X-ray pulses, where subsequent X-ray pulses are separated by an emission pause. Each emission pause, or a plurality of the several emission pauses, comprises a first part for blanking and a second part for boosting. The operational X-ray source voltage accelerates electrons from the cathode towards the anode of the X-ray source, to generate X-ray emission at the anode. The operational X-ray source voltage may or may not be applied continuously during a pulsed X-ray imaging run. By way of example, X-ray pulses may be controlled by varying or shutting down the X-ray source voltage, and/or by using an electron grid of the X-ray source to block electrons emitted from the cathode.
The controller may comprise or otherwise interact with a processor, such as but not limited to 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 controller may comprise or otherwise interact with a memory for storing data, long term and/or short term. The controller is configured to interact with the high voltage generator, e.g. by providing a control signal. The controller may be separate from the high voltage generator, or may be, at least partly, integrated with the high voltage generator.
According to an embodiment, the controller is further configured to control the high voltage generator to provide a predetermined stand-by filament current, such that the filament is at a stand-by filament temperature before and/or after the pulsed X-ray imaging run, and wherein the intercooler filament temperature is higher than the stand-by filament temperature.
This is advantageous, since an even lower stand-by filament temperature can be used to further decrease risk of filament degradation outside of the pulsed X-ray imaging runs. The stand-by filament current is preferably larger than zero, such that a next imaging run can be started with reduced filament preparation time.
According to an embodiment, the predetermined stand-by filament current is determined such that no emission current is generated at the operational X-ray source voltage when the filament is at the stand-by filament temperature.
This is preferred, since when the stand-by filament current, and corresponding filament temperature, is so low that no emission current is generated at the operational X-ray source voltage, no filament degradation will occur.
According to an embodiment, the filament intercooler temperature is predetermined as a highest filament temperature at which filament degradation at the operational X-ray source voltage is less than 5% higher, preferably less than 1% higher, than filament degradation at the stand-by filament temperature at the operational X-ray source voltage.
It may be preferred that the intercooler filament temperature is chosen to be as high as possible, to improve accuracy, within an acceptable range of filament degradation.
According to an embodiment, the filament intercooler temperature is predetermined as a lowest filament temperature at which a measurable emission current is generated at the operational X-ray source voltage.
It is advantageous to choose the filament intercooler to be as low as possible for optimal reduction of filament degradation, while still being large enough to generate a measurable emission current for improved accuracy of the intercooler operation.
According to an embodiment, the controller is configured to store an emission data table, wherein the emission data table comprises pairs of measured filament currents and emission currents, and wherein the intercooler filament temperature corresponds to a filament temperature in equilibrium at the lowest measured filament current in the emission data table.
The emission data table may advantageously be used for calibration of emission currents and filament currents, e.g. in relation to one or several X-ray source operational voltages. The emission data table may be used to accurately determine the suitable boosting and/or blanking currents and/or the time during which the boosting and/or blanking currents are applied. The emission data table may be static during one or several pulsed imaging runs. The emission data table may be adapted during a pulsed imaging run. By using the lowest filament temperature and filament current corresponding to a measured emission current in the emission data table, the degradation is kept as low as possible. At the same time, because the filament temperature corresponds to a measured pair in the data table, which may also be used to determine boosting and blanking currents and/or the time during which the boosting and blanking currents are applied, the accuracy of the boosting and blanking can be improved. Preferably, boosting and blanking currents are fixed, and only the time for applying such currents is adapted to optimize the pulsed X-ray imaging.
According to an embodiment, the controller is configured to control the high voltage generator to provide a predetermined intercooler hold current during a third part of the emission pauses, wherein the third part of the emission pause is between the first part and the second part of the emission pause, and wherein the intercooler hold current holds the filament temperature at the intercooler filament temperature.
Since the intercooler filament temperature is higher than e.g. the stand-by filament temperature, the difference in temperature between the operational filament temperature and the intercooler filament temperature may be comparatively low and the combined blanking and boosting times may not take the entire emission pause. 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.
According to an embodiment, the operational X-ray source voltage is between 40 kV to 200 kV, and preferably between 80 kV to 140 kV.
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 controlling the high voltage generator to:

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.
Fig. 6 shows an example of a timing diagram for boosting and blanking a filament.

DETAILED DESCRIPTION OF EMBODIMENTS

WO2023117733 A1 , 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 generally "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 may get 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 each two adjacent X-ray pulses.
The inventors of the present invention have found that instead of blanking the filament current down to a level that is as low as possible and where no degradation takes place, it may be advantageous to specifically choose to decrease the filament temperature to a predetermined temperature level where some electron emission still occurs, and where an emission current can be measured if a tube voltage is applied. Because the emission current can in that way be measured and/or calibrated also at the lowest filament temperature after blanking (during the intercooling phase), the accuracy of blanking and boosting back to the correct operational filament temperature during each pause between subsequent pulses may be improved. Filament temperature may therefore be monitored, via the emission current, which means that calibration and/or adaptation of the current levels may be accurately performed. Although some filament degradation may occur due to the electron emission at the lowest intercooling filament temperature, this may be at negligible levels. Hence, accuracy of repeated boosting and blanking may be improved, while filament lifetime is still saved.
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 and/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 may be configured to receive an input signal 16. In Fig. 1 this is illustrated with input from a user interface 18. However, alternatively, or additionally, the controller may be configured to receive an input signal from the generator 50, an X-ray imaging system, a sensor etc.
The controller 10 is configured to control the high voltage generator 50 to provide power to an X-ray source to generate a plurality of X-ray pulses during a pulsed X-ray imaging run. Each pulsed X-ray imaging run includes multiple X-ray pulses with pauses between pairs of X-ray pulses. Such a pause between a pair of pulses can be divided in at least a first part for blanking and a second part for boosting. Sharp pulses in X-ray emission from the X-ray source may be achieved by rapidly switching the X-ray source voltage on and off. Alternatively, or additionally, the X-ray pulses may be achieved by gridding the emission, such as with grid electrodes. The controller 10 is configured to control the high voltage generator 50 to provide a filament current to heat a filament of a cathode of the X-ray source, such that an electron beam can be generated via thermionic emission. The controller 10 is configured to control the high voltage generator 50 to provide an operational filament current during the X-ray pulses of a pulsed X-ray imaging run. In this way, the desired X-ray imaging radiation can be achieved during each of the pulses.
The controller 10 is further configured to control the high voltage generator 50 to provide a predetermined blanking filament current to decrease the filament temperature during the first part (blanking part) of each of, or a plurality of, the emission pauses. The filament temperature is reduced in this way until the filament temperature reaches an intercooler filament temperature. The intercooler temperature is thus lower than the operational filament temperature, which reduces filament degradation during the emission pause.
The controller 10 is further configured to control the high voltage generator 50 to provide a predetermined boosting filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second (boosting) part of each of, or the plurality of, the emission pauses. In this way, the temperature of the filament is brought back to operational temperature again to prepare for the next X-ray emission pulse.
During an emission pause between pulses, the temperature of the filament is thus brought down to the intercooler filament temperature with a low blanking current and subsequently brought up to operational temperature again with a larger boosting current. This scheme is repeated between each pair, or between multiple selected pairs, of pulses during the pulsed X-ray imaging run, in order to reduce unnecessary filament degradation.
The intercooler filament temperature chosen at a level where a non-zero measurable emission current can be generated at an operational X-ray source voltage. In this way, the filament temperature transitions can be accurately monitored and calibrated. Based on this information, boosting and blanking may be accurately adapted if necessary.
When the filament is at the intercooler filament temperature, the corresponding emission current can thus be measured when an operational X-ray source voltage is applied. The operational X-ray source voltage is preferably in the range of kV, and more preferably between 40 kV to 200 kV, such as between 80 kV to 140 kV.
Preferably, the controller 10 is configured to control the high voltage generator 50 to measure the emission current. Preferably, the emission current at the intercooler filament temperature is measured outside of an imaging run, such as during a calibration run or tube conditioning. During X-ray pulsed imaging runs, there is preferably no X-ray emission during emission pauses. When measuring the emission current, a small amount of X-ray radiation is generated by the X-ray source. The level of the emission current and corresponding level of X-ray radiation is significantly lower compared to when the filament is at operational temperature. The emission current at the intercooler filament temperature may be on the order of single milliamperes or even lower. The intercooler temperature may be the lowest possible filament temperature at which a measurable emission current is generated at the operational X-ray source voltage.
As an example, the operational filament current may be between 4-6 A, such as 5 A. Each X-ray emission pulse may have a duration or pulse width on the order of milliseconds, such as 10 ms. The emission pause between pulses may be on the order of hundreds of milliseconds, such as 100-150 ms. During boosting and blanking, the change in filament temperature depends on the respective boosting or blanking current as well as on the duration of the respective boosting or blanking period during the emission pause. A blanking current may be 1-2 A or even lower. A boosting current may be in the range of 7-10 A, such as 8 A. The intercooler filament temperature corresponds to an equilibrium temperature when an intercooler filament current is applied. Such a corresponding intercooler filament current is lower than the operational filament current, but large enough to generate an emission current at an operational X-ray source voltage. The intercooler filament current may be e.g. between 3-4 A. A typical emission current during X-ray emission at the operational filament temperature, i.e. during the X-ray emission pulses at the operational X-ray source voltage, may be in the order of 100-200 mA. The comparable low non-zero emission current when the filament is at the intercooler filament temperature may be on the order of low tenths or single milliamperes, such as less than 25 mA, preferably less than 10 mA, more preferably less than 5 mA.
The controller 10 may be configured to control the high voltage generator 50 to provide a stand-by filament current before and/or after a pulsed X-ray imaging run. When the stand-by filament current is provided, the filament reaches in equilibrium a stand-by filament temperature, which is lower than the intercooler filament temperature. Preferably, the stand-by filament temperature is so low that no emission current is generated, or at least not measurable, when an operational X-ray source voltage is applied. In this way, filament degradation will be very small during such stand-by periods. Also, no significant degradation of the anode occurs for the same reason. The stand-by filament current and temperature are preferably not lower than necessary to avoid X-ray emission. In this way, start-up time may be limited when going from stand-by to operation of the filament again when starting a new pulsed X-ray imaging run. The stand-by filament current may be around 2-3 A. The filament intercooler temperature may be predetermined as a highest filament temperature at which filament degradation at the operational X-ray source voltage is less than 5% higher, preferably less than 1% higher, than filament degradation at the stand-by filament temperature at the operational X-ray source voltage.
In order to control heating and cooling of the filament with boosting and blanking, a data look-up table with pairs of measured filament currents and emission currents at a known voltage range may be used. Such a data table may be created with calibration runs, before imaging with the system. Such a data table may be adapted during and/or between pulsed X-ray imaging runs. When using such a data table, the intercooler filament temperature may advantageously be predetermined as the filament temperature corresponding to the lowest measured filament current in the data table.
During an emission pause between two X-ray pulses, the sum of time it takes to blank the filament temperature from operational filament temperature to intercooler temperature and the time to boost filament temperature back from intercooler temperature to operational filament temperature again may not take up the entire pause. In such a case, it may be advantageous to hold the filament temperature at the intercooler filament temperature to avoid boosting too early. In this way, filament degradation may be reduced. The controller 10 may therefore be configured to control the high voltage generator 50 to provide a predetermined intercooler hold current during a third part of the emission pauses, wherein the third part of the emission pause is between the first blanking part and the second boosting part of the emission pause, and wherein the intercooler hold current holds the filament temperature at the intercooler filament temperature.
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 providing power to an X-ray source 102. The method 400 includes controlling the high voltage generator 50 to provide 410 power to the X-ray source 102 to generate a plurality of X-ray pulses during a pulsed X-ray imaging run. 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.
The method 400 further includes controlling the high voltage generator 50 to provide 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.
The method 400 further includes controlling the high voltage generator 50 to provide 430 a blanking filament current that is lower than the operational filament current to allow the filament temperature to decrease during the first part of the emission pauses, such that the filament temperature reaches an intercooler filament temperature, wherein the intercooler temperature is (i) lower than the operational filament temperature and (ii) at a level resulting in a non-zero emission current at an operational X-ray source voltage when the filament is at the intercooler filament temperature.
The method 400 further includes controlling the high voltage generator 50 to provide 440 a boosting filament current that is higher than the blanking filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second part of the emission pauses.
The intercooler filament temperature is thus determined to be at a level where a non-zero, measurable, emission current can be generated at an operational X-ray source voltage. In this way, the filament temperature can be accurately monitored via the measured emission current. Based on this information, boosting and blanking may be accurately adapted if necessary.
The method 400 may include controlling the high voltage generator 50 to provide a stand-by filament current before and/or after a pulsed X-ray imaging run. When the stand-by filament current is provided, the filament reaches in equilibrium a stand-by filament temperature, which is lower than the intercooler filament temperature. Preferably, the stand-by filament temperature is so low that no emission current is generated, or at least not measurable, when an operational X-ray source voltage is applied. In this way, filament degradation will be very small during such stand-by periods. Also, no significant degradation of the anode occurs for the same reason. The stand-by filament current and temperature are preferably not lower than necessary to avoid X-ray emission. In this way, start-up time may be limited when going from stand-by to operation of the filament again when starting a new pulsed X-ray imaging run. The filament intercooler temperature may be predetermined as a highest filament temperature at which filament degradation at the operational X-ray source voltage is less than 5% higher, preferably less than 1% higher, than filament degradation at the stand-by filament temperature at the operational X-ray source voltage.
Fig. 5 illustrates a schematic timing diagram showing part of a pulsed X-ray imaging run. The diagram illustrates how the filament temperature changes with a filament temperature curve 500. The y-axis of the diagram represents filament temperature or its equivalent filament current. The x-axis represents time. Starting from the left, the filament is at operational temperature. During a first X-ray pulse period 511, an operational X-ray source voltage is applied and the X-ray source 102 emits X-ray radiation with a step-increase in emission current, as schematically illustrated by the first X-ray pulse 521. Besides the X-ray source voltage, the emission pulse may also be controlled with grid electrodes of the X-ray source. A second X-ray pulse period 512 and a second X-ray pulse 522 is illustrated correspondingly. Between the X-ray pulse periods 511, 512, there is an emission pause 510.
During a first part of the emission pause 510, there is a blanking period 530. During the blanking period a low or zero filament blanking current is applied, such that the filament temperature decreases, as seen from the filament temperature curve 500. The blanking period 530 (in combination with the blanking current) is chosen such that the filament temperature decreases down to a filament intercooler temperature. The filament intercooler temperature is chosen such that an emission current is non-zero and can thus be measured when an operational X-ray source voltage is applied. The relation between filament temperature and emission current is highly non-linear. The intercooler temperature is thus chosen above a threshold where an emission current is generated, which means that it can be accurately calibrated. The timing diagram also shows a lower level of filament temperature, the stand-by filament temperature, to which the filament may be cooled down between imaging runs (not shown). The stand-by filament temperature is preferably chosen such that no emission current is generated, but only slightly lower such that the filament can quickly be heated back to operational temperature again when starting a new imaging run. Because the stand-by filament temperature does not correspond to a measurable emission current, it needs to be extrapolated and is therefore less accurate compared to the intercooler filament temperature if used during repeated imaging pulses and emission pauses during an imaging run.
During a second part of the emission pause 510, there is a boosting period 540. During this period, a comparatively high filament current is applied such that the filament temperature increases again up to the operational filament temperature to be ready for the following X-ray pulse 522. As seen from the schematic figure, the filament temperature reaches operational temperature relatively early during the emission pause 510. The filament temperature is held at operational temperature during a third part 550 of the emission pause. Compared to a situation of keeping the filament temperature at operational filament temperature during the entire emission pause, the scheme shown in Fig. 5 with blanking and boosting reduces filament degradation.
Fig. 6 schematically shows a similar timing diagram with a further reduced filament degradation. Similarly to Fig. 5, also Fig. 6 illustrates how the filament temperature changes with a filament temperature curve 600. During a first X-ray pulse period 611, an operational X-ray source voltage is applied and the X-ray source 102 emits X-ray radiation with a step-increase in emission current, as schematically illustrated by the first X-ray pulse 621. Besides the X-ray source voltage, the emission pulse may also be controlled with grid electrodes of the X-ray source. A second X-ray pulse period 612 and a second X-ray pulse 622 is illustrated correspondingly. Between the X-ray pulse periods 611, 612, there is an emission pause 610. During a first part of the emission pause 610, there is a blanking period 630. During the blanking period a low or zero filament blanking current is applied, such that the filament temperature decreases, as seen from the filament temperature curve 600. The blanking period 630 (in combination with the blanking current) is chosen such that the filament temperature decreases down to a filament intercooler temperature.
Contrary to the example above, in Fig. 6 the second part of the emission pause with the boosting period 640 does not follow immediately after the blanking period 630. Instead, a third part 650 of the emission pause takes place between the blanking 630 and boosting period 640. During the third part 650 of the emission pause, the filament temperature is held at the intercooler filament temperature before being boosted to operational filament temperature again during the boosting period 640. In this way, filament degradation during the emission pause can be further reduced, by extending the time at which the filament is at a lower intercooler filament temperature. This is of particular value for emission pauses that are relatively long, such that the sum of blanking and boosting time periods is (much) less that the total time of the emission pause. During the third part 650 of the emission pause, the filament temperature is kept at a level corresponding to a non-zero, measurable, emission current when an X-ray source voltage would be applied. This provides for improved accuracy in calibrating and controlling the temperature levels.
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

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 that is lower than the operational filament current to allow the filament temperature to decrease during the first part of the emission pauses, such that the filament temperature reaches an intercooler filament temperature, wherein the intercooler temperature is (i) lower than the operational filament temperature and (ii) at a level resulting in a non-zero emission current at an operational X-ray source voltage when the filament is at the intercooler filament temperature; and

provide a boosting filament current that is higher than the blanking filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second part of the emission pauses.
The controller (10) according to claim 1, wherein the controller is further configured to control the high voltage generator to provide a stand-by filament current, such that the filament is at a stand-by filament temperature before and/or after the pulsed X-ray imaging run, and wherein the intercooler filament temperature is higher than the stand-by filament temperature.
The controller (10) according to claim 2, wherein the predetermined stand-by filament current is determined such that no emission current is generated at the operational X-ray source voltage when the filament is at the stand-by filament temperature.
The controller (10) according to claim 2 or 3, wherein the filament intercooler temperature is predetermined as a highest filament temperature at which filament degradation at the operational X-ray source voltage is less than 5% higher, preferably less than 1% higher, than filament degradation at the stand-by filament temperature at the operational X-ray source voltage.
The controller (10) according to any of the preceding claims, wherein the filament intercooler temperature is predetermined as a lowest filament temperature at which a measurable emission current is generated at the operational X-ray source voltage.
The controller (10) according to any of the preceding claims, wherein the controller is configured to store an emission data table, wherein the emission data table comprises pairs of measured filament currents and emission currents, and wherein the intercooler filament temperature corresponds to a filament temperature in equilibrium at the lowest measured filament current in the emission data table.
The controller (10) 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 pauses, wherein the third part of the emission pause is between the first part and the second part of the emission pause, and wherein the intercooler hold current holds the filament temperature at the intercooler filament temperature.
The controller (10) according to any of the preceding claims, wherein the operational X-ray source voltage is between 40 kV to 200 kV, preferably between 80 kV to 140 kV.
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.
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 9.
A method for controlling a high voltage generator for an X-ray source, the method comprising controlling the high voltage generator to:
provide (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;

provide (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;

provide (430) a blanking filament current that is lower than the operational filament current to allow the filament temperature to decrease during the first part of the emission pauses, such that the filament temperature reaches an intercooler filament temperature, wherein the intercooler filament temperature is (i) lower than the operational filament temperature and (ii) at a level resulting in a non-zero emission current at an operational X-ray source voltage when the filament is at the intercooler filament temperature; and

provide (440) a boosting filament current that is higher than the blanking filament current to increase the filament temperature from the intercooler filament temperature to the operational filament temperature during the second part of the emission pauses.
A computer program element, which, when being executed by a controller, is adapted to cause the controller to perform the method according to claim 11.
A computer-readable medium having stored thereon the computer program element of claim 12.