X-ray systems

Abstract

The invention relates to an X-ray system (10) comprising an anode (20), a cathode (30) comprising an electron emitter filament (40) and a focusing grid electrode (50), the system further comprising a high voltage power supply (60), at least one low-medium voltage power supply (70), and a controller (80). The controller is configured to control the high voltage power supply to apply a first high voltage between the anode and the cathode, and to control the high voltage power supply to apply a second high voltage between the anode and the cathode. The second high voltage is greater than the first high voltage, and the high voltage power supply repeatedly switches between applying the first high voltage and applying the second high voltage. The controller is configured to control the low-medium voltage power supply to apply at least two voltages to the focusing grid electrode to form a focused electron beam on the anode from electrons emitted from the electron emitter filament. During application of the first high voltage, the controller is configured to control the low-medium voltage power supply to form a first size of the focused electron beam on the anode. During application of the second high voltage, the controller is configured to control the low-medium voltage power supply to form a second size of the focused electron beam on the anode. The second size of the focused electron beam on the anode is smaller than the first size of the focused electron beam on the anode. During application of the second high voltage between the anode and the cathode, the controller is configured to control the low-medium voltage power supply to periodically move the second size of the focused electron beam on the anode such that an effective spot size of the focused electron beam on the anode increases.

Description

Technical Field

[0001] The invention relates to an X-ray system, a controller, a method of operating an X-ray system, a computer program element for controlling an X-ray system, a computer program element for controlling a controller, and a computer-readable medium. Background Art

[0002] Some X-ray tubes used for medical CT imaging use a combination of electrostatic electron beam forming and temperature-limited emission. The emission current depends on the filament temperature. While the emission current is controlled by the filament temperature, the tube voltage and the focusing grid electrode voltage also affect the emission.

[0003] In kVp switching (kVp-S), the tube voltage is switched between successive acquisition intervals (e.g., 80 kV and 140 kV). X-ray generation is much more efficient at high voltages. At the same filament temperature, the difference in X-ray output dose between 80 kV and 140 kV tubes can easily be as much as a factor of 7. For spectral imaging, the flux in the low-kV and high-kV intervals should be roughly the same to obtain good spectral material separation. In some cases, the flux imbalance between low and high kV can be partially compensated by a longer integration period at low tube voltage.

[0004] When a sufficiently high X-ray dose is required, kVp-S imaging using high gantry rotation speeds and high speeds presents a particular problem. Rapid imaging is then required, where the acquisition time for each projection is short, and the detector integration period (IP) must be very short. To deliver the required X-ray dose within the short IP time, the emission current must be high. This means that the X-ray tube is often operated at maximum X-ray tube anode load at high kVp during the on-off cycle. When the tube voltage is switched to a lower kVp, the emission current drops (e.g., by 20%-30%). Furthermore, a lower kVp generates a smaller number of photons with lower energy. Filament temperature changes only slowly and is typically fixed, so temperature cannot be used to increase the emission current and, therefore, X-ray emission at lower tube voltages (e.g., 80 kV). As mentioned above, an overall higher X-ray dose may be required, which also means that to achieve this within a short IP time, the duration of the lower kVp cannot be increased; instead, the duration of the higher kVp may need to be increased to provide a higher X-ray dose. As described above, this may result in the X-ray dose for the low kVp interval being approximately 7 times less than the X-ray dose for the high kVp interval.

[0005] The strong difference in X-ray flux between low and high kVp IPs results in very different signal-to-noise ratios (SNRs) in the acquired data. This large SNR difference is a serious problem for spectral data processing, which works best at the same SNR level.

[0006] There is a need to solve this problem. Summary of the Invention

[0007] It would be very advantageous to have an improved technique for fast kVp switching that increases the SNR in acquired low kVp intervals.The invention is defined by the independent claims, while advantageous embodiments are defined by the dependent claims.

[0008] In a first aspect, an X-ray system is provided, comprising: an anode; a cathode comprising an electron emitter filament and a focusing grid electrode; a high-voltage power supply; at least one low- and medium-voltage power supply; and a controller. The controller is configured to control the high-voltage power supply to apply a first high voltage between the anode and the cathode. The controller is configured to control the high-voltage power supply to apply a second high voltage between the anode and the cathode, wherein the second high voltage is greater than the first high voltage. The controller is configured to control the high-voltage power supply to repeatedly switch between applying the first high voltage and applying the second high voltage (kVp switching cycle). The controller is configured to control the at least one low- and medium-voltage power supply to apply at least two voltages to the focusing grid electrode to form a focused electron beam on the anode from electrons emitted from the electron emitter filament. The controller is configured to control the at least one low- and medium-voltage power supply to change at least one voltage applied to the focusing grid electrode, thereby shifting the focused electron beam on the anode. While the first high voltage is applied between the anode and the cathode, the controller is configured to control the at least one low- and medium-voltage power supply to form a focused electron beam of a first size on the anode. During the application of a second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to form a focused electron beam of a second size on the anode, wherein the focused electron beam of the second size on the anode is smaller than the focused electron beam of the first size on the anode. During the application of the second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode. During the application of the second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode, thereby increasing the effective spot size of the focused electron beam on the anode. The electron beam can be moved at a frequency greater than 1 kHz, preferably greater than 10 kHz, and more preferably equal to or greater than 20 kHz. By rapidly moving the focus relative to the integration period of the X-ray detector, the effective spot size of the electron beam on the anode can be increased. The effective spot size during the application of the second high voltage can be the same as or similar to the spot size of the focused electron beam during the application of the first high voltage.

[0009] In this way, the filament temperature of a standard X-ray tube can be increased and the focusing grid electrode adjusted so that, for a first high cathode-to-anode voltage of, for example, 80 kV, an electron spot size of, for example, 1 mm can be maintained at the anode. However, at this filament temperature, operating the cathode at a second high cathode-to-anode voltage (e.g., 140 kV) will produce an electron spot size of 1 mm at the anode, which will result in an emission current at this cathode / anode voltage, and thus, a system power exceeding the maximum achievable value—typically, systems with standard cathodes are operated at maximum power at 140 kV. Therefore, operating the focusing grid electrode at 140 kV produces a spot size smaller than 1 mm (the spot size at 80 kV), for example, 0.8 mm. This results in a reduction in the emission current generated by a 1 mm spot size, but the associated power can be maintained at the system's maximum power. In fact, the power can be at its maximum. However, when the electron beam spot size is smaller, the spatial resolution of the 140 kV system (0.8 mm spot size) will be greater than that of the 80 kV system (1 mm spot size), and the difference in spatial resolution can lead to image quality issues. Thus, the smaller spot size at 140 kV is shifted at a high frequency relative to the integration period of the X-ray detector, and this shifting increases the effective focused electron spot size. The shifting can be controlled so that the spatial resolution at 140 kV is the same as that at 80 kV, for example by shifting the focused electron beam at 140 kV so that its effective spot size (within the integration period of the X-ray detector) is the same as that at 80 kV. Thus, due to the increased electron filament temperature, and operating within the system power limitations at high voltages without spatial resolution issues, the resulting X-rays produced per unit time at 80 kV can be increased relative to those produced by previous standard X-ray tubes. Standard X-ray tubes have two focusing grid electrodes. The average of the medium and low voltages controls the size of the focal spot, and the difference in these voltages will affect the focal spot position.

[0010] In this way, since the X-rays per unit time at 80 kV can be increased, the X-ray flux at 80 kV can be increased relative to that at 140 kV relative to the level previously achieved, and the resulting signal-to-noise ratio of the energy spectrum material decomposition is improved. It is worth noting that throughout this application, the low voltage is exemplified by 80 kV and the high voltage is exemplified by 140 kV, as these may be typical voltages suitable for energy spectrum imaging using kVp switching. However, the scope of the present invention is not limited to these exact voltages, and it will be understood by those skilled in the art that other high and low voltages may also be selected to obtain sufficient energy spectrum separation during the dual energy X-ray imaging cycle. For example, but not limited to, a low voltage selected in the range of 60–100 kV and a high voltage selected in the range of 120-160 kV.

[0011] Relative to the dose previously achieved, a fixed X-ray dose can be maintained, but as the X-rays produced per unit time at 80 kV increase, for the set "low" cathode to anode high voltage of 80 kV, the time period of the "high" cathode to anode high voltage of 140 kV can be reduced due to the larger X-ray flux produced in the set time period, thereby resulting in a reduction in the total X-ray dose period, thereby providing faster imaging due to the shorter projection acquisition time (IP time).

[0012] In an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to periodically move the focused electron beam of the second size over the anode with a sinusoidal modulation.

[0013] In an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with square wave modulation.

[0014] In an example, during application of a first high voltage between the anode and cathode, the controller is configured to control at least one low-medium voltage power supply to operate the focusing grid electrode in a first operating mode. During application of a second high voltage between the anode and cathode, the controller is configured to control at least one low-medium voltage power supply to operate the focusing grid electrode in a second operating mode. The controller is configured to control the high-voltage power supply to change the voltage applied between the anode and cathode from the first high voltage to the second high voltage, and when the voltage is at a set voltage between the first high voltage and the second high voltage, the controller is configured to switch the operation of the focusing grid electrode from the first operating mode to the second operating mode. The set voltage is an intermediate voltage between the first high voltage and the second high voltage. The set voltage is preferably within a range of 10% to 90% of the difference between the first high voltage and the second high voltage, and more preferably within a range of 20% to 80% of the difference between the first high voltage and the second high voltage. For example, when the first high voltage is 80 kV and the second high voltage is 140 kV, the set voltage may be 100 kV. The set voltage may be selected to optimize system performance. The setting voltage may be the point at which the detector integration period for "low" energy X-rays transitions with the detector integration period for "high" energy X-rays during spectral imaging.

[0015] In an example, the controller is configured to control an amplitude difference of the sinusoidal modulation or an amplitude difference of the square wave modulation during a period in which the voltage applied between the anode and the cathode changes from the set voltage to the second high voltage.

[0016] In an example, the amplitude difference of the sinusoidal modulation or the amplitude difference of the square wave modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0017] In an example, the product of the emission current and the set voltage is at a maximum power level during the period when the set voltage is applied between the anode and the cathode.

[0018] In other words, the controller holds the cathode-to-anode voltage at a "low" voltage (e.g., 80 kV) for a period of time, then ramps the cathode-to-anode voltage up to a "high" voltage (e.g., 140 kV) for a period of time, then holds the cathode-to-anode voltage at 140 kV for a period of time, and this forms a cycle in which dual-energy x-rays are produced, thereby providing spectral imaging. Then, the controller does the reverse, returning to 80 kV, producing a second cycle in which dual-energy x-rays are produced, thereby providing spectral imaging. At 80 kV, the controller controls the focusing grid electrodes of the cathode for focusing and moving the spot of electrons on the anode to provide a first "stationary" spot at a higher emission temperature than normal. Because the thermal spreading of the electrons is greater than before, the focusing grid electrodes of the cathode are operated at a greater focusing concentration than before to maintain the same focal spot size as before - e.g., 1 mm. But now at 80 kV, more x-rays per unit time are produced from the anode than before. When the controller rapidly increases the cathode-to-anode voltage from 80 kV to 140 kV, for simplicity the focusing grid electrodes initially remain in the same configuration as at 80 kV. At an intermediate cathode-to-anode voltage (e.g., 100 kV), the controller switches to a second focal grid electrode configuration that will form a focal spot on the anode that is less than 1 mm, e.g., 0.8 mm. The electron emitter remains at the same temperature, and at the switching point of 100 kV the size of the formed spot drops below 0.8 mm, and the emission current drops. As the cathode-anode voltage increases from 100 kV to 140 kV, the electron focal spot size increases to 0.8 mm, and the emission current increases. However, the controller maintains this 0.8 mm electron spot size and this emission current, but changes the appropriate focusing grid electrode voltage differences to about the average to move the focal spot, thereby producing an effective focal spot size that is greater than 0.8 mm, e.g., 1 mm.

[0019] During kVp switching, the cycle time of the kVp switching period as described above can be on the order of tenths to hundreds of microseconds, possibly up to a few milliseconds. Thus, the transition of tube voltage and emission current can be very rapid. The transition time between energy levels, i.e., the transition time between the "high" and "low" voltage plateaus (i.e., from high to low or from low to high) can be shorter than 300 μβ, such as, preferably between 30 μβ and 200 μβ, or even shorter. (See, e.g., the top graph in Figure 6-8 .)

[0020] The electron emitter temperature, the 80-100 kV focus grid electrode settings, and the 100-140 kV focus grid settings (electron beam movement) can be selected so that the maximum system power (emission current x cathode to anode voltage) is maximized at 140 kV and at the switching voltage of 100 kV (which will be lower than the maximum in the 80-99 kV region - up to the switching point), providing the best system configuration.

[0021] In an example, the product of the emission current and the second voltage is at a maximum power level during the second high voltage being applied between the anode and the cathode.

[0022] In an example, the system includes an X-ray detector. During the second high voltage being applied between the anode and the cathode, the controller is configured to control the at least one low- medium voltage power supply to move the second size of focused electron beam on the anode at a frequency greater than a detection integration period of the detector.

[0023] In an example, during the second high voltage being applied between the anode and the cathode, the controller is configured to control the at least one low- medium voltage power supply to move the second size of focused electron beam on the anode such that the effective size of the focused electron beam on the anode is equal to the first size of focused electron beam.

[0024] In a second aspect, a controller is provided. The controller is suitable to be included in an X-ray system, such as the X-ray system described above. The controller is configured to control at least one low- medium voltage power supply to apply at least two voltages to a focus grid electrode of a cathode of an X-ray tube to form a first size of focused electron beam on an anode of the X-ray tube, wherein the first size of focused electron beam is formed from electrons emitted from an electron emitter filament of the cathode when a high voltage power supply applies a first high voltage between the anode and the cathode. The controller is configured to control the at least one low- medium voltage power supply to apply at least two voltages to the focus grid electrode of the cathode to form a second size of focused electron beam on the anode, wherein the second size of focused electron beam is formed from electrons emitted from the electron emitter filament when the high voltage power supply applies a second high voltage between the anode and the cathode. The second size of focused electron beam focused on the anode is smaller than the first size of focused electron beam focused on the anode, and the second high voltage is greater than the first high voltage. The high voltage power supply repeatedly switches between applying the first high voltage and applying the second high voltage. The controller is configured to control the at least one low- medium voltage power supply to vary the at least one voltage applied to the focus grid electrode of the cathode to periodically move the second size of focused electron beam on the anode such that an effective spot size of the focused electron beam on the anode increases.

[0025] Thus, a new controller can replace the standard controller of an existing X-ray system with a standard X-ray tube (which controls the X-ray tube to focus the electron beam), and since the electron emitter can work at a higher temperature, and the low energy X-rays emitted per unit time increases proportionally to the high energy X-rays emitted per unit time for the standard controller, the system performance can be immediately improved while keeping the system within its power capability range. The signal-to-noise ratio can be improved without loss of spatial resolution, resulting in an improved material decomposition capability.

[0026] The new controller does not need to control the high voltage power supply, and can only control the focusing grid electrode of the cathode. The new controller can be provided with information about how the high voltage power supply is operated. The new controller can control the high voltage power supply. Like the existing controller, the controller of the present invention can be provided with information about the integration period of the associated X-ray detector, and can control such detector itself.

[0027] In an example, the controller is configured to control the high voltage power supply to apply a first high voltage between the anode and the cathode, and the controller is configured to control the high voltage power supply to apply a second high voltage between the anode and the cathode.

[0028] In a third aspect, a method of operating an X-ray system is provided, the method comprising:

[0029] controlling, by a controller, at least one low-medium voltage power supply to form a first size of focused electron beam on an anode during application of a first high voltage between the anode and a cathode by a high voltage power supply, wherein the cathode comprises an electron emitter filament and a focusing grid electrode; the at least one low-medium voltage power supply applying at least two voltages to the focusing grid electrode to form the first size of focused electron beam on the anode;

[0030] controlling, by the controller, the at least one low-medium voltage power supply to form a second size of focused electron beam on the anode during application of a second high voltage between the anode and the cathode by the high voltage power supply, wherein the at least one low-medium voltage power supply applies at least two voltages to the focusing grid electrode to form the second size of focused electron beam on the anode, wherein the second size of focused electron beam on the anode is smaller than the first size of focused electron beam on the anode, wherein the second high voltage is greater than the first high voltage, and the high voltage power supply repeatedly switches between applying the first high voltage and applying the second high voltage; and

[0031] At least one low-medium voltage power supply is controlled by a controller to move the focused electron beam of the second size on the anode, and wherein the at least one low-medium voltage power supply changes at least one voltage applied to the focusing grid electrode, thereby periodically moving the focused electron beam of the second size on the anode, so that the effective spot size of the focused electron beam on the anode increases.

[0032] In one aspect, a computer program element for controlling the system according to the first aspect is provided, which computer program element is configured to perform the method according to the third aspect when the computer program element is executed by a processor.

[0033] In one aspect, a computer program element for controlling a controller according to the second aspect is provided, which, when executed by a processor, is configured to perform the method according to the third aspect.

[0034] Hence, according to various aspects, a computer program element is provided for controlling one or more systems / controllers as described above, which, if executed by a processor, is adapted to perform a method as described above.

[0035] According to another aspect, a computer-readable medium storing the aforementioned computer unit is provided.

[0036] The computer program element may for example be a software program, but may also be an FPGA, a PLD or any other suitable digital device.

[0037] Advantageously, the benefits provided by any aspect described above also apply to all other aspects, and vice versa.

[0038] The above aspects and examples will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Exemplary embodiments will be described below with reference to the accompanying drawings:

[0040] Figure 1 A schematic diagram illustrating an example of an X-ray system;

[0041] Figure 2 An example of a method of operating an X-ray system is shown;

[0042] Figure 3 A conventional X-ray tube cathode is shown, shown in 3D on the left and in cross-section on the right;

[0043] Figure 4 The typical behavior of a conventionally controlled standard X-ray tube is shown;

[0044] Figure 5 Shows a new way to control Figure 4 Behavior of a standard X-ray tube;

[0045] Figure 6 Shown Figure 4 Examples of cathode-anode voltages for standard X-ray tubes and new control cathode focusing grid electrodes;

[0046] Figure 7 Shown Figure 4 Examples of cathode-anode voltages for standard X-ray tubes and new control cathode focusing grid electrodes;

[0047] Figure 8 Shown Figure 4 Examples of cathode to anode voltages for standard X-ray tubes and new control cathode focus grid electrodes; and

[0048] Figure 9 The spectral performance in terms of signal-to-noise ratio (SNR) in spectral images obtained at a given patient X-ray radiation intensity is shown. DETAILED DESCRIPTION

[0049] Figure 1An X-ray system having a controller 80 is provided, which can replace the controller of an existing system. The X-ray system 10 includes an anode 20 and a cathode 30, wherein the cathode 30 includes an electron emitter filament 40 and a focusing grid electrode 50. For example, there may be two focusing grid electrodes, one on either side of the electron emitter filament, but three or four focusing grid electrodes may also be provided. The system 10 also includes a high-voltage power supply 60, at least one low- and medium-voltage power supply 70, and a controller 80. The controller is configured to control the high-voltage power supply to apply a first high voltage between the anode and the cathode. The controller is configured to control the high-voltage power supply to apply a second high voltage between the anode and the cathode, wherein the second high voltage is greater than the first high voltage. The controller is configured to control the at least one low- and medium-voltage power supply to apply at least two voltages to the focusing grid electrode, so that electrons emitted from the electron emitter filament form a focused electron beam at the anode. The controller is configured to control the at least one low- and medium-voltage power supply to vary at least one voltage applied to the focusing grid electrode, thereby shifting the focused electron beam at the anode. During a period of applying a first high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to form a focused electron beam of a first size on the anode. During a period of applying a second high voltage between the anode and the cathode, the controller is configured to control the at least one medium-low voltage power supply to form a focused electron beam of a second size on the anode, wherein the focused electron beam of the second size on the anode is smaller than the focused electron beam of the first size on the anode. During a period of applying the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode.

[0050] In an example, the at least one low-medium voltage power supply is a single voltage unit that can generate two or more independent voltages, wherein one voltage can be varied while the other(s) remain constant, and the two voltages can be varied simultaneously, for example, one voltage being in antiphase with the other (e.g., in the form of a sine wave and a cosine wave), such that the average value of the two voltages remains constant. As described above, if there are three or four focal grid electrodes, then there can be three or four low-medium voltage power supplies, but again, more complex power supplies can provide the necessary voltages. In other words, the at least one low-medium voltage power supply can apply the necessary voltages to the focal grid electrodes of existing standard cathodes of standard X-ray tubes, and in fact, to more complex cathodes of X-ray tubes having more than two focal grid electrodes.

[0051] In an example, at least one low-medium voltage power supply is two or more voltage units that can generate two or more independent voltages, where one voltage can be varied while the other(s) remain constant, and the two voltages can be varied simultaneously, for example, one voltage is in antiphase with the other voltage (e.g., in the form of a sine wave and a cosine wave) such that the average value of the two voltages remains constant.

[0052] In an example, the controller is configured to control at least one low-medium voltage power supply to vary at least two voltages applied to the focal grid electrode to move the focused electron beam on the anode.

[0053] Therefore, the focal spot size for both the filament temperature and the cathode-to-anode high voltage is controlled by, for example, the average voltage across the two focusing grid electrodes. A voltage change on one electrode will cause the focal spot to shift sideways, but the focal spot size will change slightly as the average voltage across the two electrodes changes. Therefore, as the voltage on one electrode increases, the voltage on the other can be decreased, keeping the average constant. The focal spot will shift again, but the focal spot size will remain virtually unchanged.

[0054] This also means that when the controller controls at least one low-medium voltage power supply to apply at least two voltages to the focusing grid electrodes so that electrons emitted by the electron emitter filament form a focused electron beam on the anode, this may mean that one focusing grid electrode is maintained at a first voltage and a second focusing grid electrode is maintained at a second voltage, and wherein the first voltage and the second voltage are the same - to provide a focus at a central neutral position - or wherein the first voltage is different from the second voltage, wherein the focus will be offset from the central neutral point. This is what is meant by "at least two voltages."

[0055] According to an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size over the anode.

[0056] According to an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with a sinusoidal modulation.

[0057] According to an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with square wave modulation.

[0058] According to an example, during application of a first high voltage between the anode and the cathode, the controller is configured to control the at least one low- medium voltage power supply to operate the focusing grid electrode in a first operating mode. During application of a second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to operate the focusing grid electrode in a second operating mode. The controller is configured to control the high voltage power supply to change the voltage applied between the anode and the cathode from the first high voltage to the second high voltage, and during this change, when the voltage is at a set voltage between the first high voltage and the second high voltage, the controller is configured to switch the operation of the focusing grid electrode from the first operating mode to the second operating mode.

[0059] According to an example, the controller is configured to control the amplitude difference of the sinusoidal modulation during the change of the voltage applied between the anode and the cathode from the set voltage to the second high voltage.

[0060] According to an example, the controller is configured to control the amplitude difference of the square wave modulation during the change of the voltage applied between the anode and the cathode from the set voltage to the second high voltage.

[0061] According to an example, the amplitude difference of the sinusoidal modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0062] According to an example, the amplitude difference of the square wave modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0063] According to an example, the product of the emission current and the set voltage is at a maximum power level during application of the set voltage between the anode and the cathode.

[0064] In other words, the controller holds the cathode-to-anode voltage at a "low" voltage (e.g. 80 kV) for a period of time, then ramps the cathode-to-anode voltage to a "high" voltage (e.g. 140 kV) over a period of time, then holds the cathode-to-anode voltage at 140 kV for a period of time, and this period of time is a cycle in which dual-energy X-rays are produced, thereby providing spectral imaging. Then, the controller does the reverse, returning to 80 kV, producing a second cycle in which dual-energy X-rays are produced, thereby providing spectral imaging. At 80 kV, the controller controls the focusing grid electrodes of the cathode for focusing and moving the spot of electrons on the anode to provide a first "stationary" spot at a higher emitter temperature than normal. Because the thermal spreading of the electrons is greater than before, the focusing grid electrodes of the cathode are operated at a greater focusing concentration than before to maintain the same focal spot size as before - e.g. 1 mm. But now at 80 kV, more X-rays per unit time are produced from the anode than before. When the controller rapidly increases the cathode-to-anode voltage from 80 kV to 140 kV, for simplicity the focusing grid electrodes initially remain in the same configuration as at 80 kV. At an intermediate cathode-to-anode voltage (e.g. 100 kV), the controller switches to a second focusing grid electrode configuration which will form a focal spot on the anode which is less than 1 mm, e.g. 0.8 mm. The electron emitter remains at the same temperature, at the switching point of 100 kV the size of the spot formed drops below 0.8 mm, and the emission current drops. As the cathode-to-anode voltage increases from 100 kV to 140 kV, the electron focal spot size increases to 0.8 mm, and the emission current increases. However, the controller maintains this 0.8 mm electron spot size and this emission current, but changes the appropriate focusing grid electrode voltage differences to about the average to move the focal spot, thereby producing an effective focal spot size which is greater than 0.8 mm, e.g. 1 mm.

[0065] The electron emitter temperature, the focusing grid electrode settings from 80 kV to 100 kV, and the focusing grid settings (electron beam movement) from 100 kV to 140 kV can be selected so that the maximum system power (emission current x cathode-to-anode voltage) is at a maximum at 140 kV, and at a maximum at the switching voltage of 100 kV (which will be lower than the maximum in the 80-99 kV region), thereby providing an optimal system configuration.

[0066] According to an example, the product of the emission current and the second voltage is at a maximum power level during the second high voltage is applied between the anode and the cathode.

[0067] According to an example, the system includes an X-ray detector 90. During the second high voltage is applied between the anode and the cathode, the controller is configured to control at least one low intermediate voltage power supply to move the second size of focused electron beam on the anode at a frequency greater than a detection integration period of the detector.

[0068] According to an example, during application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode such that the effective size of the focused electron beam on the anode is equal to the focused electron beam of the first size. In an example, the temperature of the electron emitter filament is constant.

[0069] As mentioned above, Figure 1 The present invention also relates to a controller that can, for example, replace the aforementioned controller. Reference is now made to a new controller 80. According to an example, the controller is configured to control at least one low- and medium-voltage power supply 70 to apply at least two voltages to the focusing grid electrode 50 of the cathode 30 of an X-ray tube to form a focused electron beam of a first size on the anode 20 of the X-ray tube. When the high-voltage power supply 60 applies a first high voltage between the anode and the cathode, electrons emitted from the electron emitter filament 40 of the cathode form a focused electron beam of the first size. The controller is configured to control the at least one low- and medium-voltage power supply to apply at least two voltages to the focusing grid electrode of the cathode to form a focused electron beam of a second size on the anode. When the high-voltage power supply applies a second high voltage between the anode and the cathode, electrons emitted from the electron emitter filament form a focused electron beam of a second size. The electron beam of the second size focused on the anode is smaller than the electrons of the first size focused on the anode, and the second high voltage is greater than the first high voltage. The controller is configured to control the at least one low- and medium-voltage power supply to vary at least one voltage applied to the focusing grid electrode of the cathode, thereby shifting the focused electron beam of the second size on the anode.

[0070] Thus, the standard controller (which controls the X-ray tube to focus the electron beam) of an existing X-ray system with a standard X-ray tube can be replaced with the new controller, and because the electron emitter can operate at a higher temperature and the number of low-energy X-rays emitted per unit time increases proportionally to the number of high-energy X-rays emitted per unit time for the standard controller, system performance can be immediately improved while keeping the system within its power capabilities. The signal-to-noise ratio can be improved without sacrificing spatial resolution, resulting in improved material resolution capabilities.

[0071] The controller does not need to control the high voltage power supply, but only the focusing grid electrode of the cathode, but needs to be provided with information about how the high voltage power supply is operating, but can control the high voltage power supply when necessary. For existing controllers, the controller can provide information about the integration period of the relevant X-ray detector and can also control such detector itself if necessary.

[0072] According to an example, the controller is configured to control the high voltage power supply 60 to apply a first high voltage between the anode and the cathode, and the controller is configured to control the high voltage power supply to apply a second high voltage between the anode and the cathode.

[0073] In an example, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode.

[0074] In an example, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with a sinusoidal modulation.

[0075] In an example, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with square wave modulation.

[0076] In an example, during application of a first high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to operate the focusing grid electrode in a first operating mode. During application of a second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to operate the focusing grid electrode in a second operating mode. The controller is configured to control the high voltage power supply to change the voltage applied between the anode and the cathode from the first high voltage to the second high voltage, and when the voltage is at a set voltage between the first high voltage and the second high voltage, the controller is configured to switch the operation of the focusing grid electrode from the first operating mode to the second operating mode.

[0077] In an example, the controller is configured to control an amplitude difference of the sinusoidal modulation during a period in which the voltage applied between the anode and the cathode changes from the set voltage to the second high voltage.

[0078] In an example, the controller is configured to control an amplitude difference of the sinusoidal modulation during a period in which the voltage applied between the anode and the cathode changes from the set voltage to the second high voltage.

[0079] In an example, the difference in amplitude of the sinusoidal modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0080] In an example, the amplitude difference of the square wave modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0081] In an example, the controller is configured to be in communication with the X-ray detector 90, and the controller is configured to control at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode at a frequency greater than a detection integration period of the X-ray detector.

[0082] In an example, the controller is configured to control at least one low-medium voltage power supply to move the second-sized focused electron beam on the anode so that an effective size of the focused electron beam on the anode is equal to the first-sized focused electron beam.

[0083] Figure 2 An example of the basic steps of a method 100 of operating an X-ray system is shown. The method comprises:

[0084] Controlling 110 at least one low-medium voltage power supply by a controller to form a focused electron beam of a first size on an anode during a period in which a first high voltage is applied between the anode and a cathode by a high voltage power supply, wherein the cathode includes an electron emitter filament and a focusing grid electrode; the at least one low-medium voltage power supply applies at least two voltages to the focusing grid electrode to form the focused electron beam of the first size on the anode;

[0085] The at least one low-medium voltage power supply is controlled 120 by the controller to form a focused electron beam of a second size on the anode during a period in which a second high voltage is applied between the anode and the cathode by the high voltage power supply, wherein the at least one low-medium voltage power supply applies at least two voltages to the focusing grid electrode to form a focused electron beam of the second size on the anode, wherein the focused electron beam of the second size on the anode is smaller than the focused electron beam of the first size on the anode, and wherein the second high voltage is greater than the first high voltage, and,

[0086] At least one low-medium voltage power supply is controlled 130 by a controller to move the second-sized focused electron beam over the anode, and wherein the at least one low-medium voltage power supply varies at least one voltage applied to the focusing grid electrode to move the second-sized focused electron beam over the anode.

[0087] In an example, during application of the second high voltage between the anode and the cathode, the method includes controlling, by the controller, at least one low-medium voltage power supply to periodically move the focused electron beam of a second size over the anode.

[0088] In an example, during application of the second high voltage between the anode and the cathode, the method includes controlling, by a controller, at least one low-medium voltage power supply to periodically move the focused electron beam of a second size on the anode in a sinusoidally modulated manner.

[0089] In an example, during the application of the second high voltage between the anode and the cathode, the method includes controlling, by a controller, at least one low-medium voltage power supply to periodically move the focused electron beam of a second size on the anode in a square wave modulation manner.

[0090] In an example, during application of a first high voltage between the anode and the cathode, the method includes controlling, by a controller, at least one low-medium voltage power supply to operate the focusing grid electrode in a first operating mode, and during application of a second high voltage between the anode and the cathode, the method includes controlling, by the controller, at least one low-medium voltage power supply to operate the focusing grid electrode in a second operating mode. The method may then include controlling, by the controller, the high voltage power supply to change the voltage applied between the anode and the cathode from the first high voltage to the second high voltage, and may include switching, by the controller, the operation of the focusing grid electrode from the first operating mode to the second operating mode when the voltage is at a set voltage between the first high voltage and the second high voltage.

[0091] In an example, the method includes controlling, by a controller, an amplitude difference of the sinusoidal modulation during a period in which a voltage applied between the anode and the cathode changes from a set voltage to a second high voltage.

[0092] In an example, the method includes controlling, by a controller, an amplitude difference of square wave modulation during a period in which a voltage applied between the anode and the cathode is changed from a set voltage to a second high voltage.

[0093] In an example, the difference in amplitude of the sinusoidal modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0094] In an example, the amplitude difference of the square wave modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

[0095] In an example, during application of the set voltage between the anode and the cathode, the product of the emission current and the set voltage is at a maximum power level.

[0096] In an example, during application of the second high voltage between the anode and the cathode, a product of the emission current and the second voltage is at a maximum power level.

[0097] In an example, during application of the second high voltage between the anode and the cathode, the method includes controlling, by the controller, at least one low-medium voltage power supply to move the focused electron beam of a second size on the anode at a frequency greater than a detection integration period of the detector.

[0098] In an example, during application of the second high voltage between the anode and the cathode, the method includes controlling, by a controller, at least one low-medium voltage power supply to move the focused electron beam of a second size on the anode so that an effective size of the focused electron beam on the anode is equal to the focused electron beam of the first size.

[0099] In an embodiment, the temperature of the electron emitter filament is constant.

[0100] Now refer to Figure 3-8An X-ray system having a new controller and a new method of operating an X-ray system are described in detail.

[0101] It has been recognized that while electron emission from conventional cathodes is controlled via filament temperature, the tube voltage and the focusing grid electrode voltage also affect emission. It has been recognized that the filament temperature can be increased and the focusing grid electrode voltage varied to provide the same focal spot size at 80 kV, but now with an increased electron emission current and, therefore, an increased X-ray emission per unit time from the anode. In order to keep the increased filament temperature within the 140 kV power requirement, it has been recognized that the focusing grid electrode voltage can be varied to provide a reduced spot size while maintaining an emission current equivalent to that previously provided at a 140 kV tube voltage, and wherein, for example, the X-ray tube can still be operated at maximum power. However, during the detector's 140 kV high hold interval, the focusing grid electrode voltage is varied around an average value to maintain the instantaneous focal spot size, but to shift the focal spot to provide an increased effective spot size, equivalent to that at 80 kV and the low kVp interval. In this way, the spatial resolution in the low kVp and high kVp intervals can be the same, but the flux in the low kVp interval can be increased, resulting in an increased signal-to-noise ratio for material resolution.

[0102] Thus, a method of operating a standard X-ray tube is provided that improves the performance of kVp switching with high emission currents by rapidly oscillating the focal spot during a portion of the kVp switching cycle.

[0103] To help explain this new technology, we introduce an existing typical cathode design. Figure 3 A typical cathode design is shown. The filament is embedded in a cup with deflection grids (focusing grid electrodes) on both sides (A and B). The grid voltage is used to position the focal spot (FS) and determine the focal spot size. The common portion of the voltage defines the FS size. A high voltage confines the emitted electron beam and forms a small focal spot (and vice versa). The voltage difference between the grids can be used to position the focal spot. The common voltage also affects emission by changing the electric field. Grids A and B can have different voltages.

[0104] From the perspective of image reconstruction, the focal spot (FS) size should be similar for low and high kVpIP. Projections with different FS sizes will result in different spatial resolutions, which may cause serious problems in spectral data processing (material decomposition) and should be avoided.

[0105] During the kVp switching cycle, the FS size is affected by the kVp. At higher kVp levels, the FS is typically larger. To address this issue, conventional X-ray tube controllers dynamically adjust the FS size during the kVp cycle to maintain a constant FS size. Conventional controllers determine the size and position of the FS by applying appropriate voltages to the focal grid electrodes.

[0106] Figure 4 The typical behavior of a standard X-ray tube with a standard cathode operated with a conventional controller is shown.

[0107] To understand X-ray tube operation, the X-ray detector operates in two integration steps (IPs). In the first IP, low-energy X-rays are collected, while in the second IP, high-energy X-rays are collected. A high-voltage power supply applies 80 kV between the cathode and anode, and a conventional controller uses medium- and low-voltage power supplies to apply voltages to the focusing grid electrodes to form a 1 mm focal spot. The high voltage can be applied for a set time. The detector is collecting data in the first IP. Then, a conventional or other controller rapidly ramps the cathode-anode voltage, while the voltage applied to the focusing grid electrodes remains constant. As the cathode-anode voltage increases, the focal spot size and emission current also increase. At the set voltage (here, 100 kV), the conventional controller varies the voltage applied to the focusing grid electrodes to achieve a 1 mm focal spot size at 140 kV. The detector operates in the first IP until the 100 kV change. Starting from the 100 kV change, the detector operates in the second IP. When the focusing grid electrode voltage changes, the focal spot size and emission current immediately decrease. However, these values ​​increase as the cathode-to-anode voltage increases to 140 kV. The system is typically designed to facilitate reaching maximum power at 140 kV. The cathode-to-anode voltage is then maintained at 140 kV for a period of time, and then rapidly reduced to 80 kV. At 100 kV, the focusing grid electrode switches back to a state equivalent to the 1 mm focal spot size at 80 kV, the second IP ends, and a new first IP begins. This process then repeats.

[0108] continue Figure 4 , Figure 4 a shows the FS size for different kVp levels (80 kVp and 140 kVp). The two curves are shown for two different settings of the focusing grid electrode (1, 2). The parameters are chosen so that the FS size for 80 kVp and 140 kVp is the same for both grid settings (1 mm in this example). This ensures that the FS size is the same as requested. Figure 4 b shows the effective FS size in the case of a 100 kV switched focusing grid electrode setup. Figure 4c shows the emission current for two grid settings and kVp. Figure 4 d shows the emission current with switching of the focus grid electrode setting at 100 kV.

[0109] Now, with the new controller operation, the filament temperature is increased. During the 80-100 kV region, the controller has changed the focus grid electrode setting (to setting 3) so that the focus size remains 1 mm at 80 kV. In the 100-140 kV region, the controller has changed the focus grid electrode setting (to setting 4) to achieve a focus size of less than 1 mm and to ensure that the tube power limit (700 mA at 140 kVp) does not exceed the threshold.

[0110] Figure 5 shows the equivalent data as Figure 4 but now showing the new controller operation. All requirements have been met with these changes except one. The tube current at low kVp is increased by 36% (about 900 mA instead of 660 mA). The maximum power level at 140 kV does not exceed the threshold, and the maximum power level at 100 kV does not exceed the threshold. The focus spot size at low kVp settings remains at (1 mm). However, the FS size at 140 kVp is now too small (0.6 mm instead of 1 mm).

[0111] Therefore, the new controller can effectively create a larger FS (e.g., 1 mm) by rapidly moving a smaller (e.g., 0.6 mm) FS. The movement is fast compared to the IP time. For example, a motion at a frequency of 20 kHz will have 20 cycles in 1 ms of IP time. Fast FS motion is a well-known technique used in so-called dual focus switching (DFS) and is not explained further.

[0112] Figure 6The focus grid voltage waveform is plotted against the X-ray tube voltage. The top graph shows the tube voltage waveform in kVp-s, where the cathode-to-anode voltage is held at 80 kV for a period, rapidly increased to 140 kV and held at this voltage for a period, and then rapidly dropped to 80 kV. As described above, the detector operates in a first, low-energy integration period of tube voltages between 80 and 100 kV, and in a second, high-energy integration period of tube voltages between 100 and 140 kV. In the top graph of tube voltage versus time, the solid and dashed lines represent the lower and upper voltage ranges. The other two graphs show the focus grid electrode voltages, which have a constant average level to maintain an instantaneous focal spot size of 0.6 mm but vary to rapidly move the focal spot, creating an increased effective focal spot size "seen" by the detector. Therefore, during the low kV interval, the focus grid electrode voltage remains constant, creating a constant focal spot (FS). During the high voltage period, the focus grid electrode voltage increases and incorporates an oscillating voltage difference to shift the FS position.

[0113] like Figure 7 As shown in , the fast-moving focus grid grid electrode voltage can be tube voltage adaptive, where the applied voltage amplitude varies proportionally to the cathode-to-anode voltage so that the movement of the focus on the anode has the same amplitude during voltage modulation.

[0114] like Figure 8 As shown in , the fast moving focus grid gate electrode voltage can be a square wave, which can be achieved via a switching technique that switches between two voltages. In some cases, this can lead to higher EMI and high frequency problems that do not occur with sinusoidal modulation, such as Figure 6 and 7 shown, but this requires more complex technology than simple switching of square wave modulation.

[0115] Figure 9 The spectral performance is shown in terms of signal-to-noise ratio (SNR) in spectral images obtained at a given patient X-ray radiation intensity (expressed as a percentage of the maximum X-ray tube intensity). The spectral SNR is expressed as a percentage of a Philips dual-slice CT scanner at the same dose level. The dashed line shows the performance at conventional doses. The solid line shows how the proposed operation improves performance.

[0116] Thus, a new technique for the operation of a standard X-ray tube is provided that improves the performance of kVp switching with high emission currents by rapidly oscillating the focal spot during a portion of the kVp switching cycle.

[0117] During a kVp switching period comprising a low kVp interval and a high kVp interval, the focusing grid gate electrode is also switched between low voltage and high voltage settings.

[0118] During the low kVp interval, the grid voltage is at a low setting and remains constant over time.

[0119] During the high kVp interval, the grid voltage switches to oscillate rapidly around the high voltage setting, causing the focus to move rapidly within one detector integration period and the effective focal spot size to increase.

[0120] The result is that on-off cycling can increase the emission current and keep the focal spot size effectively constant, resulting in a better signal-to-noise ratio and, in turn, improved spectral imaging performance.

[0121] The controller described above can be used to replace conventional controllers in X-ray systems, resulting in immediate performance improvements.

[0122] In a further exemplary embodiment, a computer program or a computer program element is provided, characterized in that it is configured to perform the method steps of any method according to one of the preceding embodiments on a suitable apparatus or system.

[0123] The computer program element can therefore be stored on a computing unit, which can also be a part of an embodiment. The computing unit can be configured to perform the steps of the above method or cause the execution of the steps of the above method. In addition, it can be configured to operate the parts of the above system. The computing unit can be configured to automatically operate and / or execute the user's command. The computer program can be loaded into the working memory of a data processor. Therefore, a data processor can be equipped to perform a method according to one of the aforementioned embodiments.

[0124] This exemplary embodiment of the invention covers both a computer program that right from the start uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.

[0125] Furthermore, the computer program element may be able to provide all necessary steps to complete the flow of the exemplary embodiment of the method as described above.

[0126] According to another exemplary embodiment of the present invention, a computer-readable medium, such as a CD-ROM, a USB memory stick or the like, is proposed, wherein the computer-readable medium has a computer program element stored thereon, the computer program element being as described in the previous section.

[0127] The computer program may be stored and / or distributed on suitable media, such as optical storage media or solid-state media provided with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0128] However, the computer program may also be provided over a network like the World Wide Web and can be downloaded from such a network into the working memory of a data processor. According to a further exemplary embodiment of the invention, a medium for making a computer program element available for downloading is provided, said computer program element being arranged to perform one of the previously described embodiments of the invention.

[0129] It should be noted that embodiments of the present invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method claims, while other embodiments are described with reference to apparatus claims. However, a person skilled in the art will appreciate from the above and following descriptions that, unless otherwise indicated, any combination of features relating to different subject matters, in addition to any combination of features belonging to the same type of subject matter, is also considered to be disclosed by this application. However, all features can be combined to provide synergistic effects that exceed the simple sum of the features described.

[0130] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary rather than restrictive. The present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the appended claims.

[0131] In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may perform the functions of several items recited in a claim. Measures recited in mutually different dependent claims may be advantageously combined. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An X-ray system (10), comprising: Anode (20); a cathode (30) comprising an electron emitter filament (40) and a focusing grid electrode (50); High voltage power supply (60); at least one low-medium voltage power source (70); and A controller (80) configured to: Controlling the high-voltage power supply to apply a first high voltage between the anode and the cathode; controlling the high-voltage power supply to apply a second high voltage between the anode and the cathode, wherein the second high voltage is greater than the first high voltage; controlling the high-voltage power supply to repeatedly switch between applying the first high voltage and applying the second high voltage; controlling the at least one low-medium voltage power supply to apply at least two voltages to the focusing grid electrode to form a focused electron beam on the anode by electrons emitted from the electron emitter filament; and controlling the at least one low-medium voltage power supply to vary at least one voltage applied to the focusing grid electrode to thereby move the focused electron beam on the anode; wherein, during the period when the first high voltage is applied between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to form a focused electron beam of a first size on the anode; wherein, during the period of applying the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to form a focused electron beam of a second size on the anode, wherein the focused electron beam of the second size on the anode is smaller than the focused electron beam of the first size on the anode; and Wherein, during the period when the second high voltage is applied between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode so that the effective spot size of the focused electron beam on the anode increases.

2. The system according to claim 1, wherein: During application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with sinusoidal modulation.

3. The system according to claim 1, wherein: During application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to periodically move the focused electron beam of the second size on the anode with square wave modulation.

4. The system according to any one of claims 1 to 3, wherein: During application of the first high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to operate the focusing grid electrode in a first operating mode, wherein, during application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to operate the focusing grid electrode in a second operating mode, wherein the controller is configured to control the high voltage power supply to change the voltage applied between the anode and the cathode from the first high voltage to the second high voltage, and wherein, when the voltage is at a set voltage between the first high voltage and the second high voltage, the controller is configured to switch the operation of the focusing grid electrode from the first operating mode to the second operating mode.

5. A system according to claim 4, when dependent on claim 2 or claim 3, wherein: The controller is configured to control an amplitude difference of the sinusoidal modulation or an amplitude difference of the square wave modulation during a period in which the voltage applied between the anode and the cathode changes from the set voltage to the second high voltage.

6. The system according to claim 5, wherein: The amplitude difference of the sinusoidal modulation or the amplitude difference of the square wave modulation varies in proportion to the amplitude of the voltage applied between the anode and the cathode.

7. The system according to claim 4, wherein: During the period in which the set voltage is applied between the anode and the cathode, a product of an emission current and the set voltage is at a maximum power level.

8. The system according to any one of claims 1 to 3, wherein: During the period in which the second high voltage is applied between the anode and the cathode, a product of an emission current and the second high voltage is at a maximum power level.

9. The system according to any one of claims 1 to 3, wherein: The system includes an X-ray detector (90), and wherein, during application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode at a frequency that is greater than a frequency of a detection integration period of the detector.

10. The system according to any one of claims 1 to 3, wherein: During application of the second high voltage between the anode and the cathode, the controller is configured to control the at least one low-medium voltage power supply to move the focused electron beam of the second size on the anode so that the effective size of the focused electron beam on the anode is equal to the focused electron beam of the first size.

11. A method (100) of operating an X-ray system, the method comprising: controlling (110) at least one low-medium voltage power supply by a controller to form a focused electron beam of a first size on the anode during a period in which a first high voltage is applied between the anode and the cathode by a high voltage power supply, wherein the cathode comprises an electron emitter filament and a focusing grid electrode, and wherein the at least one low-medium voltage power supply applies at least two voltages to the focusing grid electrode to form the focused electron beam of the first size on the anode; controlling (120) the at least one low-medium voltage power supply by the controller to form a focused electron beam of a second size on the anode during application of a second high voltage between the anode and the cathode by the high voltage power supply, wherein the at least one low-medium voltage power supply applies at least two voltages to the focusing grid electrode to form the focused electron beam of the second size on the anode, wherein the focused electron beam of the second size on the anode is smaller than the focused electron beam of the first size on the anode, wherein the second high voltage is greater than the first high voltage, and wherein the high voltage power supply repeatedly switches between applying the first high voltage and applying the second high voltage; and The at least one low-medium voltage power supply is controlled (130) by the controller to move the focused electron beam of the second size on the anode, and wherein the at least one low-medium voltage power supply changes at least one voltage applied to the focusing grid electrode to periodically move the focused electron beam of the second size on the anode so that the effective spot size of the focused electron beam on the anode increases.

12. The method (100) according to claim 11, further comprising: Controlling the high voltage power supply by the controller to apply the first high voltage between the anode and the cathode; and The controller controls the high voltage power supply to apply the second high voltage between the anode and the cathode.

13. A controller (80) configured to perform the method according to claim 11 or 12.

14. A computer program element for controlling a system according to any one of claims 1 to 10, wherein the computer program element, when run by a processor, is configured to perform the method according to claim 11 or 12; or for controlling a controller according to claim 13, wherein the computer program element, when executed by a processor, is configured to perform the method according to claim 11 or 12.

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