Monitoring a focal spot

Abstract

The present invention relates to an X-ray imaging system (100). The X-ray imaging system includes: an X-ray source (110) for generating X-ray radiation (118) at an X-ray focal spot (116); a detector (120) including detector pixels (122) for detecting the X-ray radiation (118) from the X-ray source (110); and an antiscattering grid (130) located between the X-ray source (110) and the detector (120), wherein the antiscattering grid (120) includes grid cells aligned with the detector pixels. According to the invention, most of the grid cells are focusing grid cells (132) that focus toward a common focusing area, wherein at least one of the grid cells is a monitoring grid cell (134) that focuses toward a focusing area different from the common focusing area; and the processing unit (140) is configured to read out detector signals from detector pixels (122), wherein the processing unit (140) is configured to determine the change in the focal spot by analyzing the detected X-ray radiation (118) transmitted through the monitoring grid cell (134).

Description

Technical Field

[0001] This invention relates to X-ray imaging systems, anti-scattering grids, methods for determining focal spot variations, computer program units, and computer-readable media. Background Technology

[0002] US20210290195A1 describes an apparatus and method for correcting signal variations in pixels of a primary photoelectric conversion element in a radiation detection apparatus due to focal spot position drift. An edge reference detector is positioned within the coverage area of ​​a fan-beam but adjacent to the primary detector, outside the scanning field of view. Signal variations in the edge reference detector pixels under the shadow of an antiscattering grid are used to estimate real-time focal spot movement, which in turn is used to estimate shadow / signal variations on the primary detector pixels within the scanning field of view.

[0003] US20170209106A1 describes a CT scanning system comprising: a rotatable gantry having an opening for receiving a subject to be scanned; an X-ray tube; and a detector including a pixel imaging area and a pixel calibration area. The system further comprises: a patient precollimator positioned between the X-ray tube and the detector, the patient precollimator having a first aperture and a second aperture that respectively transmit X-rays to at least a portion of the pixel imaging area and the pixel calibration area; a motor configured to move the patient precollimator; and a computer programmed to: determine the focal spot position using energy derived from X-rays falling on the pixel calibration area, and based on the determination, command the motor to adjust the position of the patient precollimator.

[0004] WO2010133920A1 describes an antiscattering arrangement, a radiation detector, and an inspection device including such an arrangement. The antiscattering arrangement includes an actuator capable of tilting an antiscattering grid such that the focusing axis of the antiscattering grid can be adjusted to different focal spots of the radiation source.

[0005] A computed tomography (CT) scanner is an example of an X-ray imaging system. A CT scanner typically consists of an X-ray tube mounted on a rotating gantry, opposite an X-ray detector. The X-ray tube rotates around an examination area located between the X-ray tube and the detector, emitting multi-color X-ray radiation that passes through the examination area. Power is supplied to the X-ray tube using a high-voltage generator.

[0006] The detector detects radiation passing through the inspection area and generates projection data indicating that radiation. The reconstructor reconstructs the projection data to generate volumetric image data, which can be displayed, captured, archived, transmitted to another device, etc.

[0007] The detector comprises detector pixels that convert detected X-ray photons into electrical signals indicative of those photons. For each rotation of the gantry, the detector pixels detect and convert X-ray photons over multiple integration periods, each corresponding to a different angular position range. The duration of each integration period depends on the rotational speed of the gantry and the number of integration periods within each scan rotation. At the beginning of each integration period, the integrator of the detector pixels is reset, and then the integrator receives and integrates the electrical signal during the integration period. The integrated signal forms the projected data for that integration period.

[0008] X-ray tubes typically consist of an anode and a cathode with a filament. A filament current is applied to the filament, heating it and causing it to emit electrons (thermoe emission), thus creating a space charge shortly after the filament. A peak tube voltage is applied between the cathode and anode to accelerate the electron beam from the cathode and strike the anode. The X-ray tube current, or emission current, represents the number of electrons flowing from the cathode to the anode per second. Electrostatic or magnetic focusing with, for example, grid electrodes or quadrupoles can be used to control the size and direction of the electron beam. The interaction of electrons with the anode material generates heat and radiation, including X-rays, which pass through the tube window into the inspection area and reach the detector.

[0009] The surface region on the anode that receives the electron beam is called the focal spot. The size of the focal spot is a factor affecting the image quality of X-ray image data. For example, the focal spot size affects spatial resolution, where a smaller focal spot size produces greater spatial resolution (e.g., less focal spot blurring due to geometric magnification) compared to a larger focal spot size. The size and / or location of the focal spot may depend on the X-ray tube voltage, beam focusing voltage, and tube current.

[0010] Unwanted focal spot variations can lead to inconsistencies in imaging data and image artifacts, and can also serve as indicators of X-ray source malfunction. High spatial resolution X-ray imaging techniques, such as photon counting, are particularly sensitive to focal spot variations. Therefore, improvements in the detection of X-ray focal spot variations are needed. Summary of the Invention

[0011] The object of this invention is, in particular, to provide improved monitoring of focal spot changes.

[0012] This invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.

[0013] According to a first aspect, an X-ray imaging system is provided. The X-ray imaging system includes: An X-ray source, used to generate X-ray radiation at the X-ray focal spot; The detector includes detector pixels for detecting X-ray radiation from the X-ray source; An anti-scattering grid is located between the X-ray source and the detector, wherein the anti-scattering grid includes grid cells aligned with the detector pixels, wherein most of the grid cells are focusing grid cells focused towards a common focusing area, and wherein at least one of the grid cells is a monitoring grid cell focused towards a focusing area different from the common focusing area; and A processing unit is configured to read out detector signals from the detector pixels, wherein the processing unit is configured to determine the changes in the focal spot by analyzing the detected X-ray radiation transmitted through the monitoring grid unit.

[0014] The anti-scattering grid according to the invention, comprising a focusing grid unit and at least one monitoring grid unit with a different focusing area, improves the monitoring of focal spot changes. Focal spot changes can be variations in size and / or position. Early detection of small focal spot changes avoids inconsistencies in imaging data and image artifacts. Furthermore, focal spot movement and / or size changes over time can invalidate previous calibrations, shorten X-ray source lifespan, etc. Therefore, monitoring focal spot movement and / or size can improve image quality, aid in calibration management, and provide early triggering for preventative and corrective maintenance and service actions.

[0015] Preferably, the anti-scattering grid is placed near or adjacent to the detector. The anti-scattering grid can be bonded to the detector. The anti-scattering grid can be a 1D anti-scattering grid, a 2D anti-scattering grid, or a hybrid anti-scattering grid including 1D and 2D areas. The portion of the grid that includes at least one monitoring grid cell is preferably a 2D anti-scattering grid having multiple grid cells in the "length" direction and multiple grid cells in the "width" direction.

[0016] The grid cells have a predetermined height and are formed between walls (also referred to as partition walls). The walls of each grid cell attenuate X-ray radiation and form channels through which X-ray radiation can pass. The walls of the anti-scattering grid may include at least one high-Z material for attenuating X-ray radiation. A high-Z material is a material (element) with a high atomic number Z. Such a material provides good absorption of X-ray or gamma-ray radiation, which is advantageous for, for example, absorbing scattered radiation passing through the grid cells. The high-Z material is preferably a metal. Preferably, the high-Z material is tungsten (Wolfram, W, atomic number Z = 74). Other examples of high-Z materials include molybdenum (Mo, atomic number 42), tantalum (Ta, atomic number 73), niobium (Nb, atomic number 41), lead (Pb, atomic number 82), bismuth (Bi, atomic number 83), rhenium (Re, atomic number 75), silver (Ag, atomic number 47), and gold (Au, atomic number 79). The high-Z material preferably has an atomic number Z greater than 40, more preferably greater than 70. The wall may alternatively, additionally, or in combination comprise an alloy containing at least one high-Z material.

[0017] The detector may have detector pixels arranged in rows and columns. Similarly, the anti-scattering grid may have grid cells arranged in rows and / or columns. Preferably, the channel of each grid cell is aligned with a corresponding detector pixel or a set of corresponding detector pixels. Each grid cell may have the same or similar size as the other grid cells. Preferably, the vast majority (>90%) of the grid cells are focusing grid cells, and only a small portion (<10%) are monitoring grid cells.

[0018] The focusing grid cells (i.e., most of the grid cells of the anti-scattering grid) are focused onto a common focal region. Radiation spatially oriented from the common focal region toward the focusing grid cells will be absorbed less through the channels of the focusing grid cells compared to radiation from another direction other than the common focal region. For example, the walls of each focusing grid cell can be tilted and / or shaped such that the channels of each focusing grid cell point toward the common focal region. The virtual longitudinal axes of the channels through each focusing grid cell can substantially intersect at the same point or along the same line. The common focal region can have a size on the order of the focal spot size (e.g., approximately 0.1 mm to 5 mm) in at least one direction. Preferably, the common focal region intersects with the default or default average position of the X-ray source focal spot in use. In this way, X-ray radiation radiated in the beam from the X-ray focal spot can pass directly through the channels of the focusing grid cells to reach the detector.

[0019] At least one monitoring grid cell is focused on a focal area or point different from the common focal area. Radiation spatially emitted from different focal areas toward the monitoring grid cell will be absorbed less through the channel of the monitoring grid cell compared to radiation from, for example, the common focal area or another region not within the focal spot of the monitoring grid cell. For example, the walls of the grid monitoring cell may be tilted and / or shaped such that the channel through which X-ray radiation can pass points to a focal area different from the common focal area. Alternatively or additionally, the grid monitoring cell may include lenses to modify the focal area. Preferably, the focal area of ​​the monitoring grid cell does not (or to a lesser extent) intersect with the default or default average position of the X-ray source focal spot in use. In this way, X-ray radiation passing through the monitoring grid cell from the focal spot may be sensitive to changes in the size and / or position of the focal spot. Based on the analysis of the detected radiation passing through the monitoring grid cell, changes in the focal spot can be monitored with improved sensitivity.

[0020] The processing unit may include a processor or otherwise interact with a processor, such as, but not limited to, a computer, a computer network, and / or another programmable device, for example, a single-core 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.

[0021] According to an embodiment, the monitoring grid unit is located on the periphery of the antiscattering grid, and X-ray radiation passing through the monitoring grid unit is detected using peripheral detector pixels. In this way, by monitoring changes in the focal spot using detectors and one or more peripheral pixels of the antiscattering grid, interference to the detection area of ​​the field of view used for image formation is minimal or nonexistent. Therefore, image quality within the field of view is not affected by monitoring grid units or pixels having different focal areas compared to other grid units. Furthermore, the peripheral monitoring grid unit can be used to detect signals with a high signal-to-noise ratio, thereby improving sensitivity to changes in the focal spot.

[0022] According to an embodiment, the processing unit is configured to determine the change in the X-ray focal spot by comparing the detected X-ray radiation transmitted through the monitoring grid unit with the detected radiation transmitted through at least one of the focusing grid units.

[0023] According to an embodiment, the anti-scattering grid includes at least two monitoring grid units, wherein a first monitoring grid unit has a different focal region than a second monitoring grid unit, wherein the first and second monitoring grid units have respective focal regions different from a common focal region, and wherein the processing unit is configured to determine changes in the X-ray focal spot by comparing detected X-ray radiation transmitted through the first monitoring grid unit with detected radiation transmitted through the second monitoring grid unit. By comparing radiation passing through at least two monitoring grid units with different focal regions, more precise information about whether / how the focal spot has changed can be derived.

[0024] According to an embodiment, the anti-scattering grid includes at least four monitoring grid units having mutually distinct focal zones, wherein the at least four monitoring grid units each have a focal zone on each side of the common focal zone, and wherein the processing unit is configured to determine the change in the X-ray focal spot by comparing detected X-ray radiation transmitted through each of the at least four monitoring grid units. By comparing the radiation passing through the monitoring grid units with focal zones on any side of the common focal zone (e.g., in the "top," "bottom," "left," and "right" positions), the change in the focal spot in each direction can be accurately monitored.

[0025] According to an embodiment, the processing unit is configured to determine a burnt spot breathing or oscillation phenomenon (e.g., oscillation on the anode trajectory) by comparing changes in the burnt spot at multiple time points.

[0026] According to an embodiment, the processing unit is configured to output alarms and / or suggested maintenance actions based on the determined changes in the focal spot. In this way, timely and possible preventive or corrective actions can be taken to optimize imaging and / or prevent system downtime.

[0027] According to an embodiment, the processing unit is configured to determine a correction signal for offsetting the determined focal spot variation and / or for processing imaging data to correct the determined focal spot variation. In this way, the correction signal can be used (e.g., by adapting a signal for controlling electrostatic or magnetic focusing of the electron beam) to correct the determined focal spot variation, thereby adjusting the acquired image, etc., to account for the effects of the focal spot variation. The correction signal can be used directly during image (post-)processing, or during subsequent scans in a calibration process, etc.

[0028] According to a second aspect, an antiscattering grid is provided for use in an X-ray imaging system according to an embodiment of the first aspect, wherein the antiscattering grid comprises grid cells, wherein a majority of the grid cells are focusing grid cells focused toward a common focal region, wherein at least one of the grid cells is a monitoring grid cell, and wherein the monitoring grid cell focuses toward a focal region different from the common focal region. Radiation spatially emitted from the common focal region toward the focusing grid cell will be absorbed less through the channel of the focusing grid cell compared to radiation from another direction other than the common focal region. Similarly, radiation spatially emitted from a focal region different from the common focal region toward the monitoring grid cell will be absorbed less through the channel of the monitoring grid cell compared to radiation from, for example, the common focal region or another region not in the focal spot of the monitoring grid cell.

[0029] According to an embodiment, the anti-scattering grid includes at least four monitoring grid units with different focusing areas, wherein the at least four monitoring grid units have a focusing area on each side of the common focusing area.

[0030] According to an embodiment, the anti-scattering grid is manufactured using 3D additive manufacturing or 3D subtractive manufacturing techniques. By manufacturing the anti-scattering grid based on a 3D model, the focusing area, shape, etc., of each grid unit (e.g., one or more monitoring grid units) can be precisely controlled. This allows for more accurate monitoring of focal spot changes. Examples of such 3D additive manufacturing or 3D subtractive manufacturing techniques include metal laser sintering, electron beam powder melting, and etching-assisted laser micromachining.

[0031] According to embodiments, the antiscattering grid is a monolithic grid or a stacked single-grid structure. By fabricating the antiscattering grid as a monolithic grid or a stacked single grid (i.e., constructed as a single unit without horizontal tiling), image detection and / or monitoring of focal spot variations can be improved because, for example, edge effects from tiling structures are avoided. 3D additive manufacturing or 3D subtractive manufacturing is advantageous for realizing such monolithic or stacked single grids. In the context of this invention, a stacked single grid is a single grid unit constructed from multiple layers or stacked or laminated sheets of material. Each layer or sheet may include more than one material. Different layers or sheets may include different materials.

[0032] According to a third aspect, a method is provided for determining focal spot variations of an X-ray source in an X-ray imaging system. The method includes: The detector receives a detector signal, the detector including detector pixels for detecting X-ray radiation from the X-ray source, wherein an antiscattering grid is located between the X-ray source and the detector, wherein the antiscattering grid includes grid cells aligned with the detector pixels, wherein most of the grid cells are focusing grid cells focusing towards a common focusing area, wherein at least one of the grid cells is a monitoring grid cell focusing towards a focusing area different from the common focusing area; and The changes in the focal spot are determined by analyzing the detected X-ray radiation transmitted through the monitoring grid unit.

[0033] According to a fourth aspect, a computer program unit is provided, which, when executed by a processing unit, is adapted to cause the processing unit to perform the method according to a third aspect. The computer program unit or product may be downloadable (e.g., via the Internet) from a server.

[0034] According to a fifth aspect, a computer-readable medium is provided on which the computer program units described above are stored. The medium may be non-transient. For example, the medium may be a floppy disk, CD, DVD, or solid-state storage device.

[0035] These and other aspects of the invention will become apparent and elucidated with reference to the embodiments described below. Attached Figure Description

[0036] Figure 1 An X-ray imaging system is illustrated schematically.

[0037] Figure 2 The illustration schematically depicts X-ray radiation detected from the default focal spot position and the changed focal spot position.

[0038] Figure 3 The illustration schematically depicts X-ray radiation detected from the default focal spot position and the changed focal spot position.

[0039] Figure 4 The diagram schematically illustrates an anti-scattering grid with four monitoring grid pixels having different focal areas.

[0040] Figure 5 The method for determining the focal spot variation of an X-ray source is illustrated schematically. Detailed Implementation

[0041] Figure 1An X-ray imaging system 100 according to an embodiment of the present invention is schematically illustrated. The system includes an X-ray source 110 for generating X-ray radiation 118. The X-ray source 110 in the figure includes a cathode 112 and an anode 114. Preferably, the anode 114 is a rotating anode. The X-ray radiation 118 is generated at a focal spot 116 on the anode, where electrons emitted from the cathode 112 strike the anode 114. The X-ray imaging system 100 also includes a detector 120 having detector pixels 122. The detector pixels 122 can detect the X-ray radiation 118 with spatial resolution. The X-ray imaging system 100 includes an antiscattering grid 130. The antiscattering grid 130 is located between the X-ray source 110 and the detector 120. Typically, the antiscattering grid 130 is positioned close to the detector 120, for example, directly adjacent to or adjacent to the detector 120. The object to be imaged by the X-ray imaging system 100 is typically positioned between the X-ray source 110 and the antiscattering grid 130. The antiscattering grid 130 comprises a plurality of focusing grid cells 132. Each focusing grid cell 132 is focused toward the same common focal region. The walls of each focusing grid cell 132 may be tilted and / or shaped such that the channel of each grid cell 132 points toward the common focal region. The virtual longitudinal axes of the channels passing through each focusing grid cell may substantially intersect at the same point or on the same line. The common focal region may have a size on the order of the focal spot size (e.g., approximately 0.1 mm to 5 mm) in at least one direction.

[0042] Preferably, the common focusing region intersects with the default or default average position of the X-ray source focal spot 116 during use. In this way, X-ray radiation 118 radiated in the beam from the default X-ray focal spot 116 (and therefore from the common focusing region) can pass directly through the channel of the focusing grid unit 132 to reach the detector 120.

[0043] The antiscattering grid 130 includes at least one monitoring grid element 134. Preferably, the antiscattering grid 130 includes at least two monitoring grid elements 134, and more preferably at least four monitoring grid elements 134. In contrast to the focusing grid element 132, each monitoring grid element 134 focuses toward a different focusing area than the common focusing area. X-ray radiation 118 from the X-ray source can penetrate through each monitoring element 134 and reach the corresponding detector pixel 122. Preferably, at least one monitoring grid element 134 is located at the periphery of the antiscattering grid. In this way, the monitoring grid elements can be used to monitor the focal spot 116 with little or no interference to the imaging in the field of view of the imaging system 100. Suitable for applications such as... Figure 1The anti-scattering grid 130 of the imaging system 100 shown can preferably be manufactured using 3D additive manufacturing or 3D subtractive manufacturing techniques. Examples of 3D additive manufacturing or 3D subtractive manufacturing techniques include metal laser sintering, electron beam powder melting, and etching-assisted laser micromachining.

[0044] Imaging system 100 includes a processing unit 140. Processing unit 140 is connected to detector 120 and configured to read out detector signals from detector pixels 122. The processing unit may also be connected to other parts of imaging system 100, such as an X-ray source, and / or a high-voltage generator (not shown), and / or an electron beam optics device (not shown), and / or a user interface (not shown), etc. The connection between processing unit 140 and the detector and / or parts of the imaging system can be wired or wireless. The processing unit may include processor 142 or otherwise interact with processor 142. The processing unit may include memory 144 or otherwise interact with memory 144. Processing unit 140 may be located in or near imaging system 100, or may be positioned (partially) away from imaging system 100. Processing unit 142 may be a distributed computing system.

[0045] Processing unit 140 is configured to analyze detected X-ray radiation 118 transmitted through at least one monitoring grid cell 134. Detector signals from detector pixels 122 provide information about, for example, changes in the intensity of detected X-ray radiation transmitted through monitoring grid cells 134. Processing unit 140 can compare the detected radiation transmitted through monitoring grid cells 134 over time and / or can compare the detected radiation transmitted through monitoring grid cells 134 with the detected radiation transmitted through at least one of the focusing grid cells. In an example where the antiscattering grid 130 has multiple monitoring grid cells 134, the processing unit can additionally or alternatively compare the detected radiation between monitoring grid cells 134. Based on the analysis of the detected radiation transmitted through at least one monitoring grid cell 134, the processing unit can determine changes in the focal spot. The detected changes in the focal spot can be changes in the size and / or position of the focal spot compared to a default size and / or position. The determined changes in the focal spot can also be temporary changes, such as determined focal spot breathing, focal spot oscillations on the anode focal spot trajectory, etc. When the imaging system 100 utilizes the "jumping" of the focal spot between multiple focal spot positions, the processing unit can be configured to determine the deviation from the default average focal spot position, the deviation of the jump magnitude, etc.

[0046] The processing unit 140 can be configured to output alarms and / or suggested maintenance actions based on determined focal spot changes. In this way, timely and possible preventive or corrective actions can be taken to optimize imaging and / or prevent system downtime. Such alarms and / or suggested actions can be output to users, service personnel, etc., locally or remotely via appropriate hardware (e.g., user interface, imaging workstation, device for audible signals, device for visible signals, device for tactile signals, etc.).

[0047] Processing unit 140 can be configured to determine a correction signal. The correction signal can be used (e.g., via controlling electron beam optics, X-ray source parameters such as cathode filament current, X-ray source voltage, etc.)) to counteract determined variations in the focal spot. Alternatively or additionally, the control signal can be used for image correction, such as correcting deviations in the image acquired by imaging system 100 caused by variations in the focal spot. The correction signal can be used directly during image (post)processing, during the calibration process, or for subsequent scans, etc.

[0048] Figure 2 The diagram schematically illustrates how changes in the focal spot position affect the detected X-ray radiation passing through the grid cells. Figure 2 Part (a) shows a focusing grid unit 232 positioned above detector pixel 222, between detector pixel 222 and X-ray focal spot 216. In (a), focal spot 216 is in a first (default) position. The dashed vertical axis 202 passing through the center of focal spot 216 in the first position illustrates the focusing area of ​​the focusing grid unit 232 toward the focal spot 216 in the first position. Therefore, the amount of detected X-ray radiation 218 is indicated as high by ++ in (a).

[0049] exist Figure 2 In (b), the same focused grid pixel 232 as in (a) is shown. However, in (b), the situation has changed because the X-ray focal spot is the modified focal spot 217 in the second (non-default) position. As a result, the grid cells are not focused toward the area where the modified focal spot 217 exists, and therefore the detected radiation is lower, as indicated by a +.

[0050] exist Figure 2 Part (c) shows the same focal spot situation as in (a), but in this case, it is viewed from the perspective of the monitoring grid unit 234 above the detector pixel 221. Since the monitoring grid unit 234 is not focused towards the focal spot 216 in the first (default) position, the radiation detected through the monitoring grid unit in (c) is lower than the radiation detected using the focusing grid unit in (a). This is illustrated with a + in (c).

[0051] exist Figure 2 Part (d) shows the case where the changed focal spot 217 is in the second (non-default) position, where the monitoring grid cell is the same as in (c). In the example in (d), the position change of focal spot 217 is consistent with the focusing direction of monitoring grid cell 234. Therefore, compared to (c), the detected radiation through monitoring grid cell 234 is higher, as indicated by ++. Thus, changes in the focal spot can be detected with high precision. The large relative change from the low signal in (c) to the high signal in (d) provides high sensitivity for focal spot monitoring. If the signal from detector pixel 222 below focusing grid cell 232 in (b) is compared with the signal from detector pixel 221 below monitoring grid cell 234, then the sensitivity can be further improved as the focal spot changes in the opposite direction when it changes from focal spot 216 in the first position (a and c) to focal spot 217 in the second position (b and d). Furthermore, the change in detected radiation through monitoring grid cell 234 also provides information about the direction in which the focal spot has moved. Figure 2 In the simple example, it can be clearly seen from the signal of detector pixel 221 that, due to the increase in signal, the focal spot moves from the first position in (c) to the second position in (d) along the focusing direction of the monitoring grid cell.

[0052] Figure 3 It schematically shows the relationship with Figure 2 A comparison of the same type, namely, a comparison of the focusing grid cell 232 in (a) and (b) with the monitoring grid cell 234 in (c) and (d). Figure 2 The difference is that, in Figure 3 In the middle, the focal spot moves to the third position, such as Figure 3 The modified focal spot 317 in parts (b) and (d) is shown. Figure 3 The net effect of the modified focal spot 317 on X-ray radiation passing through the focusing grid unit 232 in part (b) and Figure 2 Part (b) is basically the same. However, Figure 3 The change of part (d) in the middle and Figure 2 The change in part (d) is opposite. Figure 3 In portion (d), the focal spot 317 has further shifted out of the focal point of the monitoring grid unit 234, meaning that in (d), little or no radiation 319 is transmitted through the monitoring grid unit 234. This again illustrates how the monitoring grid unit 234 can be used to determine changes in the focal spot 317 with high sensitivity, and the change in signal can also provide information about the direction of the focal spot change. Figure 2 and Figure 3The example in the text can also be understood to mean that, for example, by using two monitoring grid cells (e.g., one focused “left” monitoring grid cell and another focused “right” monitoring grid cell), the sensitivity to position and / or size changes in either direction can be further improved.

[0053] In the case where the X-ray source 110 is characterized by a beamforming optics that enables controlled movement of the electron beam, the detector signal acquired within the monitoring grid cell can be calibrated for the focal spot position and / or for the signal used to move the electron beam. This information can be used to correct the focal spot position and / or to derive the focal spot position in a time-resolved manner for use during the image formation process.

[0054] Figure 4 Figure (a) illustrates a top view of an anti-scattering grid 130 having a large number of focusing grid cells 432 and including four monitoring grid cells 434, 435, 436, and 437. This anti-scattering grid can be a grid used for computed tomography in a gantry, or it can be a grid used with a flat-panel X-ray detector in, for example, a fluorescence fluoroscopy or radiographic imaging system. Figure 4 Part (b) shows a schematic diagram of the focal spot location and the focusing area of ​​the grid unit. The default position of the focal spot 416 is indicated by a circle. The focusing grid unit 432 focuses toward the common focusing area 442 (as illustrated by the striped squares surrounding the focal spot). This means that, in this example, the focusing grid unit focuses directly toward the default area of ​​the focal spot 416 to maximize the transmission of the X-ray radiation 118 generated at the focal spot 416. In contrast to the focusing grid unit 432, each of the monitoring grid units 434, 435, 436, and 437 can focus on a different area. Preferably, the four different focusing areas of the monitoring grid units 434, 435, 436, and 437 surround the common focusing area. As an example, the first monitoring grid unit 434 can focus on the area 444 "to the left" of the common focusing area 442. The second monitoring grid unit 435 can focus on the area "below" the common focusing area 442. The third monitoring grid unit 436 can be focused on the area "to the right" of the common focusing area 442. The fourth monitoring grid unit 437 can be focused on the area "above" the common focusing area 442. In this configuration, the four monitoring grid units 434, 435, 436, and 437 can be used to determine whether the focal spot position can be temporarily or permanently changed and in which direction it changes. Furthermore, the four monitoring grid units 434, 435, 436, and 437 can be used to determine whether the focal spot size has been temporarily or permanently changed, and if so, in which direction(s) the size change occurred. Figure 4The example is illustrated with two monitoring grid units 434, 435 on one side of the antiscattering grid and two monitoring grid units 436, 437 on the other side of the antiscattering grid. However, those skilled in the art will understand that many variations in the positioning and focusing of the individual monitoring grid units 434, 435, 436, 437 can achieve advantageous monitoring of the focal spot.

[0055] Figure 5 A method for determining focal spot variations in an X-ray source of an X-ray imaging system is schematically illustrated. The method includes: The system receives detector signals from a detector (510), the detector including detector pixels for detecting X-ray radiation from the X-ray source, wherein an anti-scattering grid is located between the X-ray source and the detector, wherein the anti-scattering grid includes grid cells aligned with the detector pixels, wherein most of the grid cells are focusing grid cells focused towards a common focusing area, wherein at least one of the grid cells is a monitoring grid cell focused towards a focusing area different from the common focusing area; and The changes in the focal spot 520 are determined by analyzing the detected X-ray radiation transmitted through the monitoring grid unit.

[0056] The monitoring grid unit can be located on the periphery of the anti-scattering grid, and the peripheral detector pixels can be used to detect X-ray radiation passing through the monitoring grid unit.

[0057] Variations in the 520 focal spot can be determined by comparing the detected X-ray radiation transmitted through the monitoring grid cell with the detected radiation transmitted through at least one of the focusing grid cells.

[0058] The anti-scattering grid may include at least two monitoring grid units, wherein a first monitoring grid unit has a different focal area than a second monitoring grid unit, and the first and second monitoring grid units have corresponding focal areas different from the common focal area. The change in the X-ray focal spot (520) can be determined by comparing the detected X-ray radiation transmitted through the first monitoring grid unit with the detected radiation transmitted through the second monitoring grid unit.

[0059] The anti-scattering grid may include at least four monitoring grid units having mutually distinct focal zones, wherein the at least four monitoring grid units each have a focal zone on each side of the common focal zone. The variation of the X-ray focal spot 520 can be determined by comparing the detected X-ray radiation transmitted through each of the at least four monitoring grid units.

[0060] The breathing or oscillation phenomenon of the 520 focal spot can be determined by comparing the changes of the focal spot at multiple time points.

[0061] The method may include: outputting alarms and / or suggested maintenance actions based on the determined changes in the foci.

[0062] The method may include determining a correction signal. This correction signal may be adapted to compensate for variations in the determined focal spot 520. Alternatively or additionally, such a correction signal may be adapted to process imaging data to correct for variations in the determined focal spot 520.

[0063] It should be noted that the above embodiments are illustrative rather than limiting of the invention, and those skilled in the art will be able to devise many alternative embodiments without departing from the scope of the appended claims. Any reference numerals placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several different elements and / or by means of a suitably programmed processor. In apparatus-type claims enumerating several units, several of these units may be embodied by the same item of hardware. Certain measures recited in mutually different dependent claims may be advantageously combined.

Claims

1. An X-ray imaging system (100), comprising: X-ray source (110), which is used to generate X-ray radiation (118) at the X-ray focal spot (116). The detector (120) includes detector pixels (122) for detecting X-ray radiation (118) from the X-ray source (110). An antiscattering grid (130) is located between the X-ray source (110) and the detector (120), wherein the antiscattering grid (120) includes grid cells aligned with the pixels of the detector, characterized in that most of the grid cells are focusing grid cells (132) focusing toward a common focusing area, wherein at least one of the grid cells is a monitoring grid cell (134), wherein the monitoring grid cell (134) focuses toward a focusing area different from the common focusing area; and characterized in that the X-ray imaging system (100) further includes: A processing unit (140) is configured to read out detector signals from the detector pixels (122), wherein the processing unit (140) is configured to determine the changes in the focal spot by analyzing the detected X-ray radiation (118) transmitted through the monitoring grid unit (134).

2. The imaging system according to claim 1, wherein, The monitoring grid unit (134) is located on the periphery of the anti-scattering grid (130), and X-ray radiation passing through the monitoring grid unit (134) is detected by peripheral detector pixels.

3. The imaging system according to claim 1 or 2, wherein, The processing unit (140) is configured to determine the change in the focal spot by comparing the detected X-ray radiation transmitted through the monitoring grid unit (134) with the detected radiation transmitted through at least one of the focusing grid units (132).

4. The imaging system according to claim 1, 2, or 3, wherein, The anti-scattering grid (130) includes at least two monitoring grid units (134), wherein the first monitoring grid unit has a different focal area than the second monitoring grid unit, wherein the first monitoring grid unit and the second monitoring grid unit have corresponding focal areas different from the common focal area, and wherein the processing unit (140) is configured to determine the change in the X-ray focal spot by comparing the detected X-ray radiation transmitted through the first monitoring grid unit with the detected radiation transmitted through the second monitoring grid unit.

5. The imaging system according to claim 4, wherein, The anti-scattering grid (130) includes at least four monitoring grid units having mutually different focal zones, wherein the at least four monitoring grid units have a focal zone on each side of the common focal zone, and wherein the processing unit is configured to determine the change in the X-ray focal spot by comparing the detected X-ray radiation transmitted through each of the at least four monitoring grid units.

6. The imaging system according to any one of the preceding claims, wherein, The processing unit (140) is configured to determine the focal breathing or oscillation phenomenon by comparing the changes of the focal at multiple time points.

7. The imaging system according to any one of the preceding claims, wherein, The processing unit (140) is configured to output alarms and / or suggested maintenance actions based on the determined changes in the foci.

8. The imaging system according to any one of the preceding claims, wherein, The processing unit (140) is configured to determine a correction signal for offsetting the determined change in the focal spot, and / or to process imaging data to correct the determined change in the focal spot.

9. A scattering shield (130) for use in an X-ray imaging system (100) according to any one of the preceding claims, wherein, The anti-scattering grid includes grid cells, wherein most of the grid cells are focusing grid cells (132) that focus toward a common focusing area, wherein at least one of the grid cells is a monitoring grid cell (134), and wherein the monitoring grid cell (134) focuses toward a focusing area different from the common focusing area.

10. The anti-scattering grid according to claim 9, wherein, The anti-scattering grid (130) includes at least four monitoring grid units with different focusing areas, wherein the at least four monitoring grid units have a focusing area on each side of the common focusing area.

11. The anti-scattering grid according to claim 9 or claim 10, wherein, The anti-scattering grid (130) is manufactured using 3D additive manufacturing technology or 3D subtractive manufacturing technology.

12. The anti-scattering grid according to claim 11, wherein, The anti-scattering grid (130) is an integral grid or a stacked single grid structure.

13. A method for determining focal spot changes of an X-ray source in an X-ray imaging system, the method comprising: Receiving (510) a detector signal from a detector, the detector comprising detector pixels for detecting X-ray radiation from the X-ray source, wherein an antiscattering grid is located between the X-ray source and the detector, wherein the antiscattering grid comprises grid cells aligned with the detector pixels, characterized in that a majority of the grid cells are focusing grid cells focused toward a common focusing area, wherein at least one of the grid cells is a monitoring grid cell, wherein the monitoring grid cell focuses toward a focusing area different from the common focusing area; and characterized in that the method further comprises: The changes in the focal spot (520) are determined by analyzing the detected X-ray radiation transmitted through the monitoring grid unit.

14. A computer program unit, when executed by a processing unit (140), is adapted to cause the processing unit to perform the method according to claim 13.

15. A computer-readable medium having stored thereon a computer program unit according to claim 14.

Images