Method and apparatus for automatic adjustment of the position of x-ray focus of an x-ray imaging system

Abstract

Automatic adjustment of the X-ray focusing position in an X-ray imaging system is described. The position (P) of the X-ray focus (FFS) on the anode (23) of the X-ray source (6) in the scanning unit (2) of the X-ray imaging system (1) is described. F The method involves determining the combined actual position of the X-ray focusing (FFS) using a combination of the measured position of the X-ray focusing (FFS) and a model-based position of the X-ray focusing (FFS), where the model-based position is determined based on the measured value of the deflection current. Based on the combined actual position and the target position, manipulation variables are determined, and adjustments are performed to correct the position of the X-ray focusing (FFS) based on the determined manipulation variables. F The deviation from the target position is described. Additionally, the adjustment device (50) is described. Furthermore, the X-ray imaging system (1) is described.

Description

Technical Field

[0001] This invention relates to a method for adjusting the position of X-ray focusing on the anode of an X-ray beam source in a scanning unit of an X-ray imaging system. Furthermore, this invention relates to an adjustment device. Additionally, this invention relates to an X-ray imaging system. Background Technology

[0002] With the help of modern imaging methods, two-dimensional or three-dimensional image data is usually generated. This two-dimensional or three-dimensional image data can be used to visualize the patient to be imaged, such as a human or animal, and can also be used for other applications.

[0003] Computed tomography (CT) is used to achieve a special type of medical imaging. In a CT system, three-dimensional slice images of the interior of the object to be examined are generated by means of two-dimensional image detection processing. For this purpose, the imaging system generates individual images of the patient from different solid angles, i.e., the volume calculation (image) of the image is determined based on these images. This imaging system typically has an X-ray source that rotates around the object to be examined and an X-ray detector that rotates with it. The aforementioned functional elements are rotatably supported in a gantry housing (also called a gantry frame) about a system axis, which is arranged in a ring around the object receiving space. Electrons are emitted from the cathode in the X-ray source and accelerated to the anode (also called the anode plate). On the anode plate, electrons are focused onto a so-called focal spot (also called X-ray focus), which causes the emission of an X-ray beam. Figure 1 A general schematic diagram of a computed tomography (CT) system is shown to illustrate its general structure.

[0004] When rotating the imaging system, the rotation angle will be... Assigned to the imaging system. The direction of rotation in the detector plane is called... Orientation. Oriented perpendicular to the direction of the rotation axis of the imaging system. The direction of the direction is called the z-direction, which is the direction parallel to the z-axis or the system axis.

[0005] When the focal spot is at a fixed position on the anode plate of the X-ray source, regarding the rotation angle The maximum possible optical resolution in the z-direction is limited by the physical resolution of the X-ray detector. To further increase this resolution, a method called jump focusing (also known as "flying focal spot," abbreviated as "FFS") has been developed. In this method, the position of the focal spot on the anode is recorded chronologically according to the different positions of the focal spot in the X-ray source, thereby allowing the position of the focal spot on the anode to be determined from the detector's viewpoint. It is offset by half the resolution in both the direction of rotation and in the z-direction. Therefore, in The resolution of imaging in the azimuth and z-direction can be doubled in each case. The shifting of the focal spot on the anode can also be performed in more than two stages, allowing for further increases in resolution depending on the number of stages. For this method, the position of the focal spot on the anode plate in the X-ray source must be dynamically changed from one recording to the next. The recording time for each recording is sometimes in the range of several hundred μs, for example, 250 μs. Due to the potential to improve imaging through shorter recording times, recording times are being further reduced in the context of new developments, for example, to 100 μs. When the position of the X-ray beam changes on the X-ray detector, the image becomes blurred. The smaller the motion blur, the shorter the time for position changes compared to the total recording time at the jump position. By reducing the recording time at each jump position, it is necessary to shorten the time required to change the jump position so as not to increase motion blur.

[0006] In addition, the following effects contribute to motion blur:

[0007] -Mechanical tolerances in the anode plate, and

[0008] - The deflection effect of the electron beam caused by the stray field of the anode driver.

[0009] In addition, to reduce such effects, the focal spot position or the position of the X-ray focus is usually detected by a position detection unit and adjusted in a closed control loop.

[0010] The position of the X-ray focused on the anode is recorded via a slit in the X-ray shield outside the main X-ray exit. The X-ray light strikes a position detection element through the slit, which determines the X-ray focus. Position in the z-direction and z-direction. Since the slit is located outside the main X-ray exit, measurements are obtained to measure... Location, the Location included Figure 9 The one shown The coupling between the position and the z-position. Therefore, firstly, the determined position is not the actual position of the X-ray focus on the anode, and thus the determined position must be transformed.

[0011] So far, through Magnetic deflection of X-ray focusing in the z-direction and therefore in the z-direction and thus in The dynamic position of the X-ray focusing is achieved by deflecting the X-ray beam in the z-direction and in the z-direction. The X-ray focusing position is adjusted via a closed control loop. Traditionally, the control loop can be designed as a cascaded control loop, for example, with an internal current control loop and an external position control loop. In this case, the dynamics of the control loop are essentially determined by the dynamics of position detection, and in particular by the dead time of position detection and the transmission of position measurements. Due to the processing time of analog and digital electronic signal processing, the dead time of position detection and the transmission of position measurements cannot be significantly reduced. Due to the necessary suppression of interfering signals such as noise, the dynamics of position detection cannot be further increased. Therefore, in a cascaded control loop, the dynamics cannot be significantly increased further.

[0012] Therefore, there is a problem of developing an adjustment device to control the position of the jump focus in order to improve dynamics. Summary of the Invention

[0013] This objective is achieved by the method for adjusting the position of the X-ray focus on the anode of the X-ray source in the scanning unit of the X-ray imaging system according to this patent, by the adjustment device according to this patent, and by the X-ray imaging system according to this patent.

[0014] In the method according to the invention for adjusting the position of the X-ray focus on the anode of the X-ray source in the scanning unit of an X-ray imaging system (preferably a computed tomography system), the adjustment of the deflection current of the X-ray focus in the X-ray beam source of the scanning unit and the adjustment of the position of the X-ray focus are performed via a common control unit and a common control system in a common control loop. The point of impact of the electron beam on the anode or the electron beam in the X-ray source on the anode plate should be referred to as the X-ray focus.

[0015] In this method, the combined actual position of the X-ray focus is determined by combining the measured position of the X-ray focus and the model-based position of the X-ray focus, which is determined based on the measured value of the deflection current. Based on the combined actual position and the target position of the X-ray focus on the anode, a manipulation variable, preferably a voltage, is determined to generate a deflection current for deflecting the electron beam from the X-ray source. Based on the determined manipulation variable, adjustments are performed to correct any deviation between the X-ray focus position and the target position. To determine the measured position and target position of the X-ray focus, individual coordinate values, such as the X-ray focus's... Coordinates (also known as coordinates) The position and the z-coordinate of the X-ray focus (also known as the z-position) can be determined and used to correct the corresponding coordinates of the X-ray focus position.

[0016] Compared to conventional adjustment methods for adjusting the position of the jump focus, according to the present invention, instead of cascaded adjustment, single-loop adjustment of the X-ray focus position is performed based on the position calculated using a dynamic model based on the measured current. In this way, the problem of idle time occurring during position detection can be advantageously reduced. Therefore, more dynamic control of the X-ray focus position, especially the jump focus position, is achieved. This results in a significant improvement in control dynamics and a reduction in susceptibility to disturbances in position control, especially for highly dynamic jump focuses, and thus leads to improved image quality. Due to the higher control dynamics, the target position of the X-ray focus can be adjusted more effectively. The jump transition from one position to the next in the X-ray focus is shorter in time, and the transition time exhibits significantly increased reproducibility.

[0017] The adjustment device according to the invention includes a control loop for adjusting and controlling the position of the X-ray focus on the anode of the X-ray source of the scanning unit of an X-ray imaging system (preferably a computed tomography system). The control loop includes a device model unit for determining a combined actual position of the X-ray focus by combining a measured position of the X-ray focus with a model-based position of the X-ray focus, the model-based position of the X-ray focus being determined based on a measured value of a deflection current. A portion of the control loop is also an adjustment unit for generating a manipulation variable based on the combined actual position and the target position, preferably a voltage for generating a deflection current of a magnet that controls the electron beam generating the X-ray focus. Additionally, the control loop includes a plant for correcting deviations between the X-ray focus position and the target position based on the determined manipulation variable.

[0018] The adjustment device according to the invention shares the advantages of the method according to the invention for adjusting the position of the X-ray focus on the anode of the X-ray source in the scanning unit of an X-ray imaging system.

[0019] The X-ray imaging system according to the invention, preferably a computed tomography system, has a scanning unit with an X-ray source and an X-ray detector. The X-ray source and X-ray detector are preferably part of a rotating imaging system. The X-ray imaging system according to the invention further includes: a control unit for controlling the rotating imaging system or the X-ray source and X-ray detector; and an adjustment device according to the invention for controlling the position of the X-ray focus at the anode of the X-ray source. The X-ray imaging system according to the invention shares the advantages of the adjustment device according to the invention.

[0020] Many of the components of the regulating device according to the invention can be designed as software components. This is particularly applicable to the device model unit, regulating unit, and parts of the device. However, in principle, some of these components can also be implemented in the form of software-supported hardware such as FPGAs, especially when particularly fast calculations are involved. Similarly, the required interface, for example if it only concerns the transfer of data from other software components, can be designed as a software interface. However, it can also be designed as a hardware-based interface controlled by suitable software.

[0021] The software-based implementation offers the advantage that the computer unit or control unit of an existing X-ray imaging system can be easily retrofitted via software updates to operate in accordance with the invention. In this regard, this objective is also achieved through a corresponding computer program product having a computer program that can be directly loaded into the memory device of the computer unit or control unit of the X-ray imaging system, and including a program portion to execute all steps for carrying out the method according to the invention when the computer program is executed in the computer unit or control unit of the X-ray imaging system.

[0022] In addition to the computer program, such a computer program product may optionally include other components such as documentation and / or additional components, including hardware components for using the software, such as hardware keys (software dongles, etc.).

[0023] Computer-readable media, such as memory sticks, hard disks, or other transferable or permanently mounted data carriers, that store program portions of a computer program that can be read and executed, may be used as storage devices for transfer to and / or storage on the computer unit of the X-ray imaging system. For example, the computer unit may have one or more cooperating microprocessors, or something similar for this purpose.

[0024] Furthermore, particularly advantageous configurations and developments of the invention arise from the dependent claims and the following description and drawings, whereby an independent claim of one claim class can also be developed in a manner similar to a dependent claim of another claim class and its descriptive portion.

[0025] In the method according to the invention for adjusting the position of X-ray focusing on the anode of the X-ray source in the scanning unit of an X-ray imaging system, preferably, the detection of the X-ray focusing position and the dead time for detecting the X-ray focusing position are modeled by a device model based on the deflection current as an input value. Therefore, a model-based position of X-ray focusing is simulated. Additionally, a model-based measurement position of X-ray focusing and the dead time occurring when measuring the measurement position are also simulated. The two model-based quantities are preferably combined with each other. In the case of the model-based measurement position, information about the measurement process itself is also included.

[0026] The device model is preferably used for focusing X-rays based on deflection current. The location is modeled. Additionally, the slit... The measurements of position and / or z-position are modeled using measurement dynamics and dead time. The two model variables determined in this way are then compared with… The measured values ​​of position and / or z-position are compared. The sum of the negative values ​​of the measured position, the model position, and the model position adjusted using the measured model is used as the actual value of the adjustment unit. The determination of the model value is advantageously applied to the actual value measurement in a timely manner. If the measured value is available, it is compared with the model value that generates a delay from the dead time. If no measured value is available, the model value can still be used to maintain the adjustment. In this way, accelerated adjustment and shortened transition time during the jump focus are achieved. This process is similar to how the Smith predictor works.

[0027] In the method according to the invention for adjusting the position of the X-ray focus on the anode of the X-ray source in the scanning unit of an X-ray imaging system, the path gain of the adjusting unit and the path gain of the device are particularly preferably adapted to the tolerances in the device and the tolerances of the measured deflection current and the position of the X-ray focus. For proper parameterization of the system model, the path gain and the gain of the adjusting unit must be adapted to the actual device because tolerances actually exist in the device. This adaptation is performed as follows: in the first measurement, the magnitudes of the measured value and the model value are within... The jump focus is determined at two distinct locations in the z-direction and z-direction. The difference between the measured and model values ​​at each location gives the jump distance. The path gain is now adjusted so that the jump distances for the measured and model values ​​are the same.

[0028] Furthermore, in the method according to the invention, a filter can be used to suppress the effects of high-frequency interference on the adjustment unit. As explained in detail later, the filter only suppresses high-frequency interference and is not based on any actual change in the position of the jump focus. Such disturbances may occur, for example, due to irregularities in the anode plate or due to measurement noise. In the filter implementation, the measurement position of the X-ray focus (preferably...) The difference signal is formed by subtracting the model value or the value of the measured position based on the model from the measured position (and / or z-position). The high-frequency component of this difference signal is then extracted via a high-pass filter, and then subtracted from the model value of the device model, i.e., the combined actual position of the X-ray focus. In this way, the high-frequency components of the measured signal generated by the manipulation variables of the adjustment unit and mapped via the model are also visible to the adjustment unit because they occur simultaneously in the measurement and are not captured by the high-pass filter since the model value is subtracted from the measured value before being filtered and extracted by the high-pass filter. This means that only the high-frequency components not generated by the adjustment unit are filtered out. High-frequency interference, such as high-frequency noise generated by slits in the anode plate or in position measurements at low radiation doses, is significantly reduced. Therefore, the focus position remains significantly more stable and reproducible at the desired position on the anode plate during a single recording. Consequently, any blurring in the imaging caused by the movement of the X-ray focus due to jump transitions and perturbations is significantly reduced.

[0029] In the method according to the invention, X-ray focusing is very particularly preferably controlled as a jump focusing with a predetermined trajectory of the X-ray focusing position on the anode of the X-ray source. During the jump, preferably, there is a jump focusing... Changes in position or z-position. It is particularly preferred to alternately change the jump focus. The position and the z-position of the jump focus. The jump focus is also preferably jumping back and forth between four positions.

[0030] Furthermore, preferably, in the method according to the invention, the position where the X-rays are focused includes... Position and z-position, and execute Geometric decoupling of z-position and z-position detection. The coupling problem is that changes in z-position cause [variables] in the detection system. Changes in location. During decoupling, based on measurements... The actual X-ray focusing is calculated using the position and the measured z-position. Location, where geometric coupling is compensated. This function can be used to determine... The target value of the location and the value used to determine it The actual value of the location. The position offset value is determined as the decoupling correction value. This can be calculated during the adjustment step. For this purpose, the values ​​for the measured position and the model position are calculated for both. The position and two z-positions are determined. This can be derived from... The adjustment offset is calculated by the difference between the average position and the distance in the z-direction. Therefore, the X-ray focusing is composed of jumps in the z-direction. The disturbances in location are significantly reduced or eliminated.

[0031] During decoupling, from the X-ray focused The corrected offset value is subtracted from the position. Additionally, the distance between the two z-positions of the X-ray focus is corrected to a corrected z-distance using a correction function and multiplied by the z-position of the X-ray focus. Finally, this result is multiplied by the value from... The result of subtracting the offset value from the position is decoupled. Location is the final result.

[0032] The method according to the invention is very particularly preferably designed such that the operation of controlling the position of the X-ray focus on the X-ray detector is dynamically switched between the operation of adjusting the position of the X-ray focus. In our nomenclature, "control" of the position refers to open-loop control. In contrast, "adjustment" refers to closed-loop control. Thus, the advantageous improvement of the aforementioned adjustment of the focus also extends to the open-loop controlled mode. Device models are also used for this hybrid adjustment / controlled operation because they depict the behavior of both dynamic and static devices. For example, in the case of so-called beam blanking, the position can continue to be pre-controlled for a period of time when there is no tube current flow, and therefore the position of the X-ray focus cannot be measured, so that it can be quickly adjusted when the X-ray beam is subsequently turned on. The controlled mode can also be used for recording with very low X-ray doses. In this case, the X-ray dose may be insufficient to capture the position of the X-ray focus. When switching from the adjustment operation to the open-loop operation, only the position of the X-ray focus is used. The model values ​​of position and / or z-position are used as position signals for the adjustment unit. The measurements for the position and / or z-position, and the corresponding modeling measurements, are each set to a value of 0. Additionally, it is necessary to add... The stationary offset value of the model value at the location. This offset value corresponds to the position when switching between two different modes. The measured value of the location and The difference between the modeled measurements of the position. To switch back to control operation, the original structure must be switched back. This means that during control operation, the measurements of the X-ray focus position determined only during closed-loop operation and the model-based measurements are set to the value "0". To calculate... The correct offset values ​​for the position are needed again when changing to a control or closed-loop operation. Therefore, the zero values ​​of the measurements and the model-based measurements are reset during the transition to control operation.

[0033] Under controlled operation, even if position measurement is temporarily unavailable, the position of the jump focus can be advantageously kept relatively stable. When beam blanking is used in conjunction with the position adjustment according to the invention, due to the controlled operation when the X-ray beam is turned off, a stable X-ray focus position can be quickly achieved again after the electron beam is turned back on. Therefore, both options lead to optimal imaging with almost no motion blur.

[0034] To determine the model-based position of X-ray focusing, preferably, the device model unit of the adjustment device according to the present invention is configured to simulate and / or combine the model-based position of X-ray focusing and / or the dead time of the measured position of X-ray focusing and the measured position of X-ray focusing based on the deflection current by the device model of the adjustment path, i.e., the device.

[0035] As already described in conjunction with the relevant methods, the device model is used to preferably focus X-rays based on the deflection current. The location is modeled. Additionally, the slit... Position measurement is modeled using measurement dynamics and dead time. The two model variables determined in this way are then compared with… The measured values ​​of the position are compared. The sum of the negative values ​​of the measured position, the model position, and the model position adjusted using the measured model is used as the actual value of the adjustment unit.

[0036] As explained in conjunction with the relevant methods, the determination of the model values ​​is advantageously adapted in terms of time to the actual value measurements. If the measured values ​​are available, they are compared with the model values ​​that generate a delay from the dead time. If no measured values ​​are available, the model values ​​can still be used to maintain the adjustment. In this way, accelerated adjustment and shortened transition time during the focus jump are achieved. Attached Figure Description

[0037] The invention will now be described in more detail with reference to the accompanying drawings, based on exemplary embodiments. In the various figures, the same components are given the same reference numerals.

[0038] Figure 1 A schematic diagram of a computed tomography (CT) system is shown.

[0039] Figure 2 A schematic diagram of the X-ray source for a computed tomography (CT) system is shown.

[0040] Figure 3 The method for measuring X-ray beams is shown. A device for the z-component and z-component.

[0041] Figure 4 It shows Representation of jump focus in the -z plane.

[0042] Figure 5 A schematic diagram of an adjustment device according to an exemplary embodiment of the present invention is shown.

[0043] Figure 6 It shows Figure 5 A schematic diagram of the device model shown.

[0044] Figure 7 Detailed illustration Figure 5 The slot filter has already been shown.

[0045] Figure 8 Detailed illustration Figure 5 The decoupling unit shown in the figure

[0046] Figure 9 It shows in Detailed explanation of the coupling of X-ray beams in the z-direction and the z-direction.

[0047] Figure 10 A flowchart illustrating a method for controlling the position of the X-ray focus of an X-ray source in a medical imaging apparatus according to an exemplary embodiment of the present invention is shown.

[0048] Figure 11 The measurement curve and X-ray focusing are shown. Representation of the difference curve between the measured values ​​and model values ​​of the coordinates and z-coordinates. Detailed Implementation

[0049] Figure 1 A schematic diagram of a computed tomography (CT) system 1 is shown to illustrate its general structure. The device includes a gantry 2 having a fixed portion 3 (also called a gantry frame) and a rotatable portion 4 (also called a rotor or roller) capable of rotating or rotating about a system axis z. The rotating portion 4 has an imaging system (X-ray system) 4a comprising an X-ray source 6 and an X-ray detector 7, which are arranged opposite to each other on the rotating portion 4. The X-ray source 6 and the X-ray detector 7 together form the imaging system 4a. When the CT system 1 is in operation, the X-ray source 6 emits X-rays 8 in the direction of the X-ray detector 7, penetrating the object being measured (e.g., patient P), and is detected by the X-ray detector 7 in the form of measurement data or measurement signals.

[0050] exist Figure 1In the image, a patient bed 9 for positioning patient P can also be seen. The patient bed 9 includes a bed base 10 on which a patient support plate 11, configured for actual positioning of patient P, is arranged. The patient support plate 11 can be adjusted relative to the bed base 10 in the system axis z direction (i.e., in the z-direction) so that it can be introduced together with patient P into the opening 12, i.e., the patient receiving area 12 of the gantry 2, for recording the X-ray projection of patient P. The computational processing of the X-ray projection recorded by the imaging system 4a, or the reconstruction of slice images, 3D images, or 3D datasets based on the measurement data or signals of the X-ray projection, is performed in the image computer 13 of the computed tomography system 1, wherein the slice images or 3D images can be displayed on the display device 14. The image computer 13 can also be designed as a control unit for controlling the imaging processing of the gantry 2 and, in particular, the imaging system 4a.

[0051] Figure 2 A cross-sectional view of the arrangement of an imaging system 4a is shown, which includes an X-ray source 6 and an X-ray detector 7, outlined in dashed lines. The X-ray source 6 includes a cathode 22 from which an electron beam E is emitted in the z-direction. The electron beam E is focused and deflected by a deflection unit 25, which is designed as an electromagnetic deflection coil. Furthermore, the electron beam E strikes a rotatably mounted anode 23, which can rotate about the z-axis. When the X-ray source 6 is in operation, the anode 23 is set to rotate by an electric actuator (not shown). When the X-ray source 6 is in operation, a high voltage is applied between the cathode 22 and the anode 23, causing the aforementioned electron beam E to be emitted from the cathode 22 and act on the anode 23. Therefore, the anode 23 is at a predetermined position P. F The X-ray focusing FFS is located where the electron beam E acts on its edge region, and this location can be used... The z-coordinates clearly describe how the electron beam E is properly deflected by deflection unit 25. The electron beam E strikes the material of anode 23, and there forms the previously mentioned focal spot or X-ray focused focal spot (FFS).

[0052] The obtained X-ray radiation 8 emerges laterally from the X-ray source 6 through the exit window. The object O between the X-ray source 6 and the detector 7 is also... Figure 2 As shown in the diagram, object O is acted upon by X-ray beam 8 and casts a shadow on X-ray detector 7. The position of the focal spot (FFS) is typically affected by various perturbation variables during operation. To compensate for the focal spot movement caused by these perturbation variables, electromagnetic deflection unit 25 generates a corresponding, time-varying deflection field with opposite orientation. For this purpose, electromagnetic or electrostatic deflection unit 25 is connected to a control unit (not shown) that provides a control signal based on a previously recorded correlation characterizing the focal spot movement as... Figure 2The operating parameters of the electric actuator are not shown in the diagram. As already mentioned, if a so-called jump focus is to be generated, the movement of the focus can also be desired and intentionally controlled. In this case, the control unit controls the movement of the focus. Position P of X-ray focusing FFS in the z-direction and z-direction F The change is a function of time.

[0053] exist Figure 3 The diagram schematically illustrates the X-ray focusing FFS used to measure X-ray beam 8. A device 30 for the first and second components of the X-ray beam 8. Device 30 includes an anode 23 (also referred to as a plate). The second component of the X-ray beam 8 reflected by the anode 23 is guided through a slit 31 in the X-ray beam shield and detected by a so-called position element 32. To achieve a jump-focused FFS, the coordinates of the incident point of the X-ray beam 8 (i.e., the X-ray focused FFS) are changed. and z.

[0054] exist Figure 4 The diagram illustrates the movement of the jump-focusing FFS. The jump-focusing FFS changes its position P on the anode at defined time intervals. F X-ray focusing FFS Location or z position POS z Or two coordinates POS z Change simultaneously. directional jump range This indicates the X-ray focusing FFS during the jump. Location The change in z distance z dist This indicates the change in z-position during the jump.

[0055] Figure 5 A schematic diagram of a position adjustment device 50 according to an exemplary embodiment of the present invention is shown. The position adjustment device 50 includes a single-loop control loop having a single device, i.e., an adjustment path. The control loop includes a device model unit 51, which records information for adjusting the position. Current that deflects X-ray beam 8 in direction and decoupling Location Both are used as input variables. The input variables, including the current, are processed by device model unit 51. and decoupling Location Based on input variables , Device model unit 51 generates actual variables that can be modeled. The actual variable Then it passes through the slit filter 52.

[0056] The slit filter 52 is used to suppress the influence of high-frequency interference on the position adjustment unit 53, in combination with Figure 7 Detailed explanation.

[0057] In addition to the input variables of the filter In addition, the position adjustment unit 53 also... -z decoupling unit 54 receives two target values POS Z_soll ,Should -z decoupling unit 54 executes according to equation (2) (see below). -z decoupling. Two target values. POS Z_soll The target of the X-ray beam Location and the target z-position POS of the X-ray beam Z_soll The position adjustment unit 53 is based on the target value. POS Z_soll and decoupling actual value POS z_ist The process determines the manipulated variable, i.e., the necessary coil voltage. The voltage of the coil Applied to electromagnetic deflection unit 25 (see Figure 2 ) magnetic coils to achieve the target value POS Z_soll .

[0058] Now, on device 55, the jump focus FFS is being calibrated. Location .

[0059] Then, position element 32 (see reference) Figure 3 ) Perform the measurement of the position of the X-ray focusing FFS, the measurement Location It was determined that Location They are not yet decoupled.

[0060] The one that has not yet been decoupled Location With the measured z-position POS Z_ist Together, they are input into decoupling unit 54, which uses the above-described... Location and z position POS Z_ist Decoupling is determined according to equation (2). Measurement location .

[0061] Decoupling Measurement location The data is sent to device model unit 51, which processes the decoupling in the manner described above. Measurement location and the current of the deflection coil Decoupling Measurement location It is also sent directly to the slit filter 52.

[0062] Figure 6 Detailed illustration Figure 5 The device model unit 51 shown. First, based on the deflection current. Using device model 51a, calculate model-based Location Furthermore, the measurement in the slit with a dead time is simulated using the measurement device model 51b and the dead time simulation unit 51c, and the measurement is determined. Variables of location simulation measurement (Also known as model-based measurement location). These two variables , The measurement and the already decoupled data are handled in the following manner. Position value Perform offset:

[0063] (1).

[0064] The calculation method is similar to that of the classic Smith predictor. Figure 7 After the filtering shown in the figure, the result (i.e., the actual Location The actual value of the position adjustment unit 53 is used in the form of a filter. For low-frequency or constant components of the signal, the model-based... Location Compared with model-based Measurement location Same. In this case, only decoupling. The measurement position is maintained as the actual position in equation (1). Location For high-frequency signal components, these components are reduced in measurement due to the filter characteristics in position detection. This means that in model-based... Measurement location The middle will also be reduced. In this case, model-based... Location The proportion in the middle is directly transmitted to the actual Location .

[0065] Figure 7 Device 70 is shown, which illustrates in detail its cooperation with adjacent or upstream device model unit 51. Figure 5 The slit filter 52 has already been shown. (As combined with...) Figure 6 As explained, device model unit 51 generates the actual Position value And also output Location value or decoupling Measurement location as well as Location simulation measurement variables In X-ray focusing FFS Location measurement At certain points, due to the slits in the anode plate structure, regular dips and overshoots occur. These act as high-frequency interferences to the control loop. Even at low X-ray intensities, measurement noise can cause high-frequency interferences that are not based on any actual change in the position of the X-ray focusing FFS. Without filtering, this interference will cause a reaction in the control loop, which will then lead to an actual shift in the position of the X-ray focusing FFS, resulting in motion artifacts.

[0066] Therefore, the device model unit 51 generates actual value and possible modeling and decoupling of measurements Position value and Variables of location simulation measurement The data is transmitted to slit filter 52. In slit filter 52, the two values—the measurement and the decoupling—are... Position value and Variables of location simulation measurement Subtract. The result is Diff. mess_mod This corresponds to the deviation between the model and reality, and includes both low-frequency and high-frequency components. It utilizes the measured signal. High-frequency components, difference signal Diff mess_mod This includes actual errors due to the irregularity of the rotating anode or high-frequency interference due to measurement noise. The variable Diff is obtained from this variable via a high-pass filter 52a. mess_mod Extracting high-frequency components Diff mess_mod_hf The high-pass filter 52a is part of the slit filter 52, and it diffs the high-frequency components. mess_mod_hf From the actual possible modeling value Subtract from the middle. Then, for the actual model that has already corrected for high-frequency interference effects... value It is sent to the position adjustment unit 53.

[0067] Figure 8 Detailed illustration Figure 5 The decoupling unit 54 shown is used to compensate for geometric coupling from the measured or predetermined target location. Location Measurement or predetermined z-position POS of X-ray focused FFS z Calculate actual decoupling Location The decoupling unit 54 is used for both the target value path and the actual value path. For decoupling, from... Location Subtract from the middle to combine Figure 9 Offset calculated in the manner described .

[0068] Additionally, calculate the measured or predetermined distance z between the two z positions. dist The reciprocal value of z dist_rec And the reciprocal value z dist_rec Multiply by the z-position POS, which is the measured or predetermined target position. z Then, multiply the result by the factor from... Location Subtract offset The result is decoupling Location This is the final result.

[0069] Therefore, it is necessary Location offset value This serves as a correction value for the decoupling function. This offset value can be calculated during the adjustment process. For this purpose, for two The position and two z-positions are used to re-determine the values ​​of the measured position and the model position. Then, it can be determined from... The offset value is calculated by the difference between the average position and the distance in the z-direction. (See also) Figure 9 ).

[0070] Figure 9 It shows in Detailed illustration 90 of the coupling of X-ray beams in the z-direction and the z-direction. Figure 9 The diagram shows four jump positions (FFS) for X-ray focusing. These jump positions are at the z-position, R-position, and... They differ in location. Because in The coupling of deflection in the directional and z-direction directions is erroneously detected by position element 32 of the X-ray beam. Coordinates. This error is decoupled in Figure 9 The jump positions FFSFD1, FFSFD2, FFSFD3, and FFSFD4 are symbolized by four error-decoupled jump points. For comparison, [further details are needed]. Figure 9 The diagram shows four correctly decoupled locations: FFSCD1, FFSCD2, FFSCD3, and FFSCD4. Furthermore, in... Figure 9 The diagram also shows the two undecoupled positions of the jump focus, FFSND1 and FFSND2.

[0071] Correction, the so-called It is generated by the following equation:

[0072] (2).

[0073] Calculate the new method as follows : The old one at the last jump position Reduce the number of jump positions between incorrectly decoupled jump positions FFSFD1, FFSFD2, FFSFD3, FFSFD4 and correctly decoupled jump positions FFSCD1, FFSCD2, FFSCD3, FFSCD4. Deviation aw pz_1234 and the R amplitude of the jump focus. R The quotient multiplied by the jump focusing distance r of the slit 31 in the X-ray shielding is used to focus the light. dist The amplitude of R is determined by the combination of Figure 4 and Figure 8 The explanation of the z jump z dist That is, the distance between the two z positions is generated. Since the geometry of anode 23 is known, the R amplitude is... R Jump from z to z in an explicit way dist Generates. Formula (2) is generated by the second set of rays, where R amplitude is... R The distance r to the jump focus FFS of slit 31 dist The quotient equals Deviation aw pz_1234 And new The business.

[0074] Figure 10 A flowchart 1000 is shown illustrating a method for controlling the position of the X-ray focus of an X-ray source in a medical imaging apparatus according to an exemplary embodiment of the present invention. In step 10.I, firstly, based on the measured deflection current... and the already decoupled measurement location To the actual variables Modeling was performed. In step 10.II, the influence of high-frequency interference on the adjustment process was suppressed, and the actual variables of the filter were... Confirmed. For details on filtering, refer to [reference needed]. Figure 6 The description. In step 10.III, to combine Figure 8 and Figure 9 The description method decouples the expected variables POS z_soll .

[0075] In step 10.IV, based on actual variables and Location decoupling expected variable To perform position adjustment, i.e., manipulate the variable used to generate the deflection current. voltage The result is calculated and applied to device 55 in step 10.V. In step 10.VI, a position measurement is performed, and the measured value is determined. Location In step 10.VII, then, based on the measurement Location and the measured z-position POS Z_ist To execute -z decoupling, such as combining Figure 8 and Figure 9 As explained. In step 10.VIII, the measurements are decoupled. Location This can be used in steps 10.I and 10.II. Then, the adjustment process continues with step 10.I.

[0076] Figure 11 The measurement curve is shown. POS z_mess And the difference curve between the measured values ​​and model values ​​regarding the X-ray focusing position. DIFF z_mess_mod The value is represented by 110.

[0077] Measurements taken when the X-ray focus point is measured. POS z_mess At that time, the position of the X-ray focusing and the Figure 8 and Figure 9 As shown The following parameters affected by the -z decoupling are influenced by tolerances:

[0078] - Linearity error is >= + - 10% Location Gain,

[0079] - Linearity error of >= + - 10% for z-position POS z The gain, and

[0080] -For current = 0 amperes, in the X-ray source Location Offset value to zero position .

[0081] To compensate for the effects of parameter changes, the following parameters should be adjusted by the device model unit 51 and the adjustment unit 53:

[0082] -Offset value ,

[0083] - Device model unit 51 and adjustment unit 53 relative to Location The gain, and

[0084] - Device model unit 51 and adjustment unit 53 relative to z position POS z The gain.

[0085] Adjustments can be made in a single adjustment step before the imaging process, or through continuous adaptation during the imaging process.

[0086] In device model unit 51 (see Figure 6 From the measured values With model values ​​or model measurements The difference between Calculate intermediate variables, differences This reflects the difference between the measurement and the model. When the X-ray focusing position changes, this variable can be used to... Determine the accuracy of the model. One purpose of adjustment is to minimize the deviation between the model and the measurement, so that the model is fully adapted. Figure 11 It shows the so-called -z is the curve of the jump scan, where all four positions are close to the jump focus.

[0087] When determining the parameters mentioned above, via the difference curve DIFF z_mess_mod In a steady state and at time t sum_p t sum_z Determine the sum value. p_1 ,sum p_2 ,sum p_3 ,sum p_4 ,sum z_1 ,sum z_2 "p" is either "phi" or " The abbreviation for "". It can also be directly converted to the average by dividing the corresponding sum by the corresponding number of measurements. In time t... sum_p tsum_z There is a waiting time t wt , in t wt During the jump focus The transition between the position and the z-position. The differences can be summed and averaged over several readout sequences. The goal of adaptation is the difference curve. DIFF z_mess_mod By removing external disturbance variables, the model becomes smooth. Then, the difference between the model and the measurement becomes small, and the system fits optimally.

[0088] First, calculate the average from the sum:

[0089] mw p_x = sum p_x / t sum_p ,

[0090] mw z_x = sum z_x / t sum_z .

[0091] In this context, x is an integer between 1 and 4 or between 1 and 2. Furthermore, x reflects the sequence shown. And the number at the position of z.

[0092] Next, calculate the average value of the readout sequence:

[0093] mw p_12 = (mw p_1 + mw p_2 ) / 2,

[0094] mw p_34 = (mw p_3 + mw p_4 ) / 2,

[0095] mw p_1234 = (mw p_1 + mw p_2 + mw p_3 + mw p_4 ) / 4,

[0096] mw z_12 = (mw z_1 + mw z_2 ) / 2.

[0097] Third, calculate the deviation of the average:

[0098] aw p_12 = (mw p_1 - mw p_12 ) / 2 + (mwp_12 - mw p_2 ) / 2,

[0099] aw p_34 = (mw p_3 - mw p_34 ) / 2 + (mw p_34 - mw p_4 ) / 2,

[0100] aw p_1234 = (aw p_12 + aw p_34 ) / 2,

[0101] aw pz_1234 = (mw p_12 - mw p_1234 ) / 2 + (mw p_1234 - mw p_34 ) / 2,

[0102] aw z_12 = (mw z_1 - mw z_12 ) / 2 + (mw z_12 - mw z_2 ) / 2.

[0103] In the fourth step, the correction variable sppgain is used for the gain of the device model unit 51 and the adjustment unit 53. p_korr k p_korr by To calculate:

[0104] Therefore, the following parameters exist:

[0105] Jump range ,

[0106] The gain correction factor for device model unit 51: sppgain p_korr ,

[0107] The gain correction factor of the adjustment unit 53: k p_korr .

[0108] Then, we get Correction factor for the gain of device model unit 51:

[0109] .

[0110] get The correction factor for the gain of the adjustment unit 53:

[0111] .

[0112] Fifth, calculate the correction variable sppgain for the amplification of device model unit 51 and adjustment unit 53 for z. z_korr z p_korr :

[0113] Therefore, the following parameters exist:

[0114] - Jump range amp z ,

[0115] The gain correction factor for device model unit 51 of type -z: sppgain z_korr ,

[0116] -z adjustment unit 53 gain correction factor: k z_korr .

[0117] Then, the magnification correction factor of device model unit 51 of z is obtained as follows:

[0118] sppgain z_korr = (aw z_12 + ampl z ) / ampl z .

[0119] The correction factor for the gain of the adjustment unit 53 of z is obtained as follows:

[0120] k z_korr = ampl z / (aw z_12 + ampl z ) = 1 / sppgain z_korr .

[0121] Sixth, now calculate the new offset value according to equation (2). .

[0122] Finally, it should be reiterated that the methods and adjustment devices described in detail above are merely exemplary embodiments, which can be modified in various ways by those skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the relevant feature may appear more than once. Similarly, the term "unit" does not preclude the fact that the relevant component is composed of several interacting sub-components that may also be spatially distributed.

Claims

1. A method for adjusting the position (P) of the X-ray focus (FFS) on the anode (23) of the X-ray source (6) of the scanning unit (2) of an X-ray imaging system (1). F The method, in which, - The actual location of the combined X-ray focusing (FFS) It is determined by a combination of the following items: -The measurement location of the X-ray focusing (FFS) ),and -Based on deflection current The model-based location of the X-ray focusing (FFS) is determined by measurements of the X-rays. -Based on the actual location of the combination ( ) and target location ( POS z_soll ) to determine the manipulated variable ( ),as well as -Based on the determined manipulation variables ( Adjustments are performed to correct the position (P) of the X-ray focus (FFS). F ) and the target location ( POS z_soll () deviation.

2. The method according to claim 1, wherein, During the determination of the model-based position of the X-ray focus (FFS), based on the deflection current ( The following items are combined and / or calculated using the device model (51a) of the device (55): - The model-based location of the X-ray focusing (FFS), and / or - The model-based measurement location of the X-ray focusing (FFS), and - The dead time of the model-based measurement position of the X-ray focusing (FFS).

3. The method according to claim 2, wherein, In the device (55) and in the deflection current ( ) and the position of the X-ray focusing (FFS) (P F The following operations are performed during the measurement: the adjustment gain of the adjustment unit (53) and the path gain of the device (55) are adapted to the tolerance.

4. The method according to claim 3, wherein, The actual location of the X-ray focusing (FFS) combination ( The filtering is used to generate the combined actual position of the filtered data. ), to suppress the influence of high-frequency interference on the adjustment unit (53), wherein the actual position of the combined filtering ( This is determined by the following: - By measuring the position from the X-ray focusing (FFS) The difference signal (Diff) is determined by subtracting the model-based measurement location from the original measurement location. mess_mod ), - Extract the difference signal (Diff) using a high-pass filter. mess_mod High-frequency components (Diff) mess_mod_hf ),as well as -From the actual location of the combined X-ray focusing (FFS) Subtract the difference signal (Diff) from the original signal. mess_mod High-frequency components (Diff) mess_mod_hf ).

5. The method according to any one of the preceding claims, wherein, The X-ray focusing (FFS) is controlled to have a position (P) of the X-ray focusing (FFS) on the anode (23) of the X-ray source (6). F The jump focus of the predetermined trajectory.

6. The method according to claim 5, wherein, - The position of the X-ray focusing (FFS) (P F )include Location( z-position (POS) z ),as well as -Execute the above Location( ) and the z position (POS) z The geometric decoupling of ) is obtained.

7. The method according to claim 6, wherein, To calculate decoupling The location is determined based on the following factors: the X-ray focusing (FFS) Position correction offset value ( ): - The predetermined jump amplitude in the R direction (ampl) R ), -The X-ray focusing (FFS) Location( The average value of the measured values ​​and the z-position (POS) z ) deviation (aw pz _ 1234 ),as well as -Previous offset value ( ).

8. The method according to claim 7, wherein, The decoupling is determined by the following: Location: -from the above Location( Subtract the correction offset value ( ), - By measuring the distance between two z positions (z dist The recursive value of z dist_rec ) and the z position (POS) z Multiply to determine the product, and - Combine the product with the product from the Location( Subtract the correction offset value from the original value. Multiply the results of the product.

9. The method according to any one of claims 1 to 4 and 6 to 8, wherein, The method dynamically switches between the following operations: - The position of the X-ray focusing (FFS) (P F ) control operations, and - The position of the X-ray focusing (FFS) (P F The operation of adjustment.

10. The method according to claim 5, wherein, The method dynamically switches between the following operations: - The position of the X-ray focusing (FFS) (P F ) control operations, and - The position of the X-ray focusing (FFS) (P F The operation of adjustment.

11. A method for adjusting the position (P) of the X-ray focus (FFS) on the anode (23) of the X-ray source (6) of the scanning unit (2) of an X-ray imaging system (1). F The regulating device (50) includes: - Device model unit (51), used to determine the combined actual position of the X-ray focusing (FFS) by a combination of the following items ( ): -The measurement location of the X-ray focusing (FFS) ),and -Based on deflection current ( The model-based location of the X-ray focusing (FFS) is determined by measurements of the X-rays. - Adjustment unit (53), for adjusting based on the combined actual position ( ) and target location ( POS z_soll To generate manipulated variables ( ), - Device (55), for using the determined manipulation variable ( To correct the position of the X-ray focusing (FFS) (P) F ) and the target location ( POS z_soll () deviation.

12. The regulating device according to claim 11, wherein, The device model unit (51) is configured to determine the model-based position of the X-ray focusing (FFS) based on the deflection current ( The following items are calculated and / or combined using the device model (51a) of the device (55): - The model-based location of the X-ray focusing (FFS), and / or - The model-based measurement location of the X-ray focusing (FFS), and - The dead time of the model-based measurement position of the X-ray focusing (FFS).

13. An X-ray imaging system (1), comprising: - A scanning unit (2) including an X-ray source (6) and an X-ray detector (7). - A control unit (13) for controlling the X-ray source (6) and the X-ray detector (7). - The position (P) of the X-ray focusing (FFS) of the anode (23) of the X-ray source (6) as described in claim 11 or 12 F ) adjustment device (50).

14. A computer program product having a computer program that can be directly loaded into the storage unit of a control unit (13) of an X-ray imaging system (1), the computer program having a program portion that, when executed in the control unit (13), performs all the steps of the method according to any one of claims 1 to 10.

15. A computer-readable medium storing a program portion executable by a computer unit, such that when the program portion is executed by the computer unit, all steps of the method according to any one of claims 1 to 10 are performed.

Images