Device, system and method for controlling a position of an anti-scatter grid in an X-ray image acquisition system

The present invention relates to a device for controlling a position of an anti-scatter grid in an X-ray image acquisition system, the device (10) comprising: a measurement unit (12); a control unit (14); and a shifting unit (16); wherein the measurement unit (12) is configured to determine an X-ray beam focus position (37) of an X-ray radiation source of the X-ray image acquisition system with respect to an X-ray detector of the X-ray image acquisition system; wherein the control unit (14) is configured to generate a shifting signal based on a displacement (18) between the X-ray beam focus position (37) and a grid focus position (35) of the anti-scatter grid; and wherein, based on the shifting signal, the shifting unit (16) is configured to shift an anti-scatter grid of the X-ray image acquisition system in at least one direction to align the anti-scatter grid with the X-ray beam focus position (37), provides an improved anti-scatter grid for X-ray acquisition systems. The invention provides the use of an improved anti-scatter grid (26) for X-ray acquisition systems (20).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/057359, filed on Mar. 25, 2019, which claims the benefit of European Patent Application No. 181643125.5, filed on Mar. 27, 2018 These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a device, a system and a method for controlling a position of an anti-scatter grid in an X-ray image acquisition system.

BACKGROUND OF THE INVENTION

For acquiring X-ray images, an X-ray radiation source emits X-ray radiation from a focal spot that is defined by the position where an electron beam hits an anode of the X-ray radiation source. The X-ray radiation travels through an object and gratings to an X-ray detector. On the travelling path, the X-ray radiation is scattered which results in a significant source of noise in the X-ray image. Scatter can be reduced using an anti-scatter grid, which is a plate in front of the X-ray detector that has lead or a similarly high absorbing material such as tungsten strips that are positioned such that only X-ray radiation originating from the focal spot can pass through wherein other (scattered) X-ray radiation will be absorbed.

In computed tomography systems two-dimensional anti-scatter grids having a height of several cm are used which absorb a significant amount of scatter. However, in C-arm systems the anti-scatter grid only has a height of 2 to 3 mm since C-arm X-ray systems are not infinitely rigid. Depending on the orientation, speed and acceleration the exact position of the focal spot with respect to the X-ray detector may vary.

U.S. Pat. No. 5,469,429 A relates to a device which aligns the focal spot to a predetermined position in a computed tomography system. The device detects the focal spot of the X-ray radiation on the anode of the X-ray tube. Then, the device adjusts the position of the focal spot to the predetermined position by repositioning the anode or by changing the path of the electron beam.

SUMMARY OF THE INVENTION

There may be a need for a device and a method which provides the use of an improved anti-scatter grid for X-ray acquisition systems.

The object of the present invention is solved by the subject-matter of the independent claims; further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply also for the system, the X-ray image acquisition system, the method, the computer program element, and the computer readable medium.

According to an aspect of the present invention, an X-ray image acquisition system is provided, comprising an X-ray radiation source and an X-ray detector connected to at least one C-arm as a support structure, and an anti-scatter grid arranged between an object receiving space and the X-ray detector. The system further includes a device for controlling a position of the anti-scatter grid, comprising a measurement unit, a control unit and a shifting unit. The measurement unit is configured to determine an X-ray beam focus position of the X-ray radiation source with respect to the X-ray detector. The control unit is configured to generate a shifting signal based on a displacement between the X-ray beam focus position and a grid focus position of the anti-scatter grid. The shifting unit is configured to, based on the shifting signal, shift the anti-scatter grid in at least one direction to align the anti-scatter grid with the X-ray beam focus position.

The device therefore adapts the position of the anti-scatter grid to align the grid focus position of the anti-scatter grid to the X-ray beam focus position. The device first measures the focus position of the X-ray radiation beam in the X-ray radiation source. Furthermore, the displacement between the measured X-ray beam focus position and the grid focus position of the anti-scatter grid of the X-ray image acquisition system is determined. Depending on the displacement, a shifting signal is generated which comprises the information how much the anti-scatter grid should be shifted in order to align the grid focus position to the X-ray beam focus position. The shifting unit then shifts the anti-scatter grid according to the information of the shifting signal. A displacement between the X-ray radiation source and the anti-scatter grid which may for example occur due to deformations of the structure of the X-ray image acquisition system may therefore be compensated by shifting the anti-scatter grid into a position in which the X-ray radiation may pass the anti-scatter grid. Due to the compensation of a misalignment between the X-ray beam focus position and the grid focus position thick anti-scatter grids, i.e. anti-scatter grids having a high grid ratio, may be used. The use of anti-scatter grids having a high grid ratio results in an improvement of the image quality since the contrast of the X-ray image is improved due to the reduction of scatter.

In an example, the anti-scatter grid is arranged between an object receiving space and the X-ray detector, the object receiving space being a space between the X-ray radiation source and the X-ray detector. The anti-scatter grid may for example be arranged close in front of the X-ray detector. In another example, the anti-scatter grid may be arranged on the X-ray detector.

In an example, the shifting unit is connected to an anti-scatter grid of the X-ray image acquisition system.

According to an example, the control unit is configured to determine the displacement based on an analysis of an X-ray image that is acquired by the X-ray detector.

In an example, the analysis of an X-ray image comprises a contrast analysis.

In an example, the determination of the displacement is performed based on the anti-scatter grid position with respect to the X-ray radiation source.

In an example, the control unit is configured to determine whether the X-ray image depicts a shadow of the anti-scatter grid, the shadow indicating the displacement.

According to an example, the shifting unit is configured to shift the anti-scatter grid in at least one direction that is arranged in a plane being parallel to an X-ray impact surface of the X-ray detector.

In an example, the anti-scatter grid is a 1D grid.

According to an example, the shifting unit is configured to shift the anti-scatter grid in two directions. In an example, the anti-scatter grid is a 2D grid. This further improves the scatter removal.

According to an example, the shifting unit comprises at least one control member that is configured to move the anti-scatter grid.

In an example, the control member is a motor.

According to an example, the measurement unit is configured to determine the X-ray beam focus position during an acquisition of an X-ray image with the X-ray image acquisition system. Deviations of the alignment between the X-ray beam focus position and the grid focus position may therefore be compensated during the acquisition of an X-ray image. Hence, a repeated image acquisition on the same position due to low contrast is avoided.

In an example, the measurement unit is configured to determine the actual position during a calibration procedure before the acquisition of an X-ray image with the image acquisition system.

According to an example, the X-ray radiation source and the X-ray detector are mounted to opposing sections of the C-arm as at least one support structure; and wherein the support structure is configured to rotate the two opposing attachment sections around the object receiving space.

In an example, the X-ray image acquisition is one of the group of a two-dimensional image acquisition system, a three-dimensional image acquisition system, or a mobile system.

According to an example, the control unit is configured to generate the shifting signal based on the X-ray detector's angular position, speed, and/or acceleration.

In an example, the anti-scatter grid comprises a grid ratio in the range of 8:1 to 16:1, preferably in the range of 10:1 to 16:1, most preferably in the range of 12:1 to 16:1. The grid ratio is defined to be the ratio of the grid height to the grid interspace width.

In an example, the anti-scatter grid is a high ratio grid, i.e. a “thick” anti-scatter grid.

Further examples and advantages of the X-ray image acquisition system may be derived from the above description. Thus, it is referred to the above description.

According to the present invention, also a method for controlling a position of an anti-scatter grid in a C-arm X-ray image acquisition system is provided, the method comprising the following steps: a) determining an X-ray beam focus position of an X-ray radiation source of an X-ray image acquisition system with respect to an X-ray detector of the X-ray image acquisition system using a measurement unit; b) generating a shifting signal based on a displacement between the X-ray beam focus position and the grid focus position using the control unit: c) shifting the position of the anti-scatter grid in at least one direction based on the shifting signal using a shifting unit to align the anti-scatter grid with the X-ray beam focus position in the X-ray radiation source.

Further examples and advantages of the method may be derived from the above description. Thus, it is referred to the above description.

According to the present invention, also a computer program element for controlling an apparatus according to the above description is provided, which, when being executed by a processing unit, is adapted to perform the method according to the above description.

According to the present invention, also a computer readable medium having stored the program element according to the above description is provided.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1aand 1bshow an X-ray image acquisition system20comprising an X-ray radiation source22, an X-ray detector24, an anti-scatter grid26, at least one support structure32, and a device10for controlling a position of an anti-scatter grid in an X-ray image acquisition system. The device10comprises a measurement unit12, a control unit14, and a shifting unit16.

In an embodiment of the invention, the X-ray image acquisition system20may be a two-dimensional X-ray image acquisition system.

In another embodiment of the invention, the X-ray image acquisition system20may be a three-dimensional X-ray image acquisition system.

In a further embodiment of the invention, the X-ray image acquisition system20may be a mobile X-ray image acquisition system.

The X-ray radiation source22emits X-ray radiation30from an X-ray beam focus position37. The X-ray radiation30travels through an object receiving space36, in which for example a patient to be examined may be present, and the anti-scatter grid26and then arrives on an X-ray impact surface43of the X-ray detector24. The anti-scatter grid26filters scattered X-ray radiation, only letting through X-ray radiation30which is emitted from the grid focus position35of the anti-scatter grid26.

The anti-scatter grid26may comprise a grid ratio in the range of 8:1 to 16:1, preferably in the range of 10:1 to 16:1, most preferably in the range of 12:1 to 16:1. The grid ratio is defined to be the ratio of the grid height to the grid interspace width. An anti-scatter grid26having a high grid ratio may be called a thick anti-scatter grid. The thick anti-scatter grid will highly reduce the scatter in the X-ray image which will highly improve the quality of the X-ray images due to the reduced signal-to-noise ratio.

InFIG. 1a, the at least one support structure32is a C-arm38. The C-arm comprises two opposing sections31,33which are arranged at opposing ends of the C-arm38. The X-ray radiation source22is attached to the first opposing section31. The X-ray detector24is attached to the second opposing section33. The at least one support structure32may rotate the two opposing sections31,33with the X-ray radiation source22and the X-ray detector24, respectively, around the object receiving space36. The rotation may be performed around an axis34which serves a rotational bearing for the support structure32.

InFIG. 1b, the at least one support structure32comprises two robotic arms39,41. The X-ray radiation source22is attached to the first robotic arm39. The X-ray detector24is attached to the second robotic arm41. The robotic arms39,41may rotate the X-ray radiation source22and the X-ray detector24around the object receiving space36. Furthermore, the robotic arms39,41are configured to arrange the X-ray radiation source22and the X-ray detector24on opposing sides of the object receiving space36during the image acquisition process. The X-ray radiation30emitted by the X-ray radiation source22may therefore travel through the object receiving space36to the X-ray detector24.

As long as the X-ray beam focus position37and the grid focus position35match, the X-ray radiation30passing the anti-scatter grid26will provide a high-quality image of an object in the object receiving space36. This is shown inFIG. 2a.

FIG. 2bshows the situation, that the X-ray beam focus position37deviates from the grid focus position35by a displacement18. The anti-scatter grid26will then filter some of the X-ray radiation30being emitted from the X-ray beam focus position37such that the image quality on the X-ray detector24will be reduced. Such a deviation may result during the image acquisition due to deformations of the at least one support structure32. The deformations may for example occur due to acceleration and/or gravitational forces during the rotation of the at least one support structure32around the object receiving space36.

In order to align the grid focus position35of the anti-scatter grid26to the X-ray beam focus position37, the shifting unit16may shift the anti-scatter grid26by a distance19, according toFIG. 2c, such that the X-ray radiation30that is emitted from the X-ray beam focus position37may pass the anti-scatter grid26. The shift of the anti-scatter grid26may be performed parallel to the X-ray impact surface43.

FIG. 3shows device10in more detail. The measurement unit12may comprise two elements which may be arranged at the X-ray radiation source22and the X-ray detector24. The measurement unit12is configured to determine the X-ray beam focus position37in the X-ray radiation source22with respect to the X-ray detector24. The X-ray beam focus position37is determined by the position in the X-ray radiation source22on which an electron beam28being emitted from a cathode21arrives at the anode23.

The measurement unit12determines the position of the X-ray detector24and compares it to the position of the X-ray beam focus position37in order to determine a displacement between the X-ray beam focus position37and the X-ray detector24. The measurement unit12may provide that determination during an image acquisition process.

For determining a displacement between the X-ray beam focus position37to the X-ray detector24, an initial alignment between the X-ray beam focus position37in the X-ray radiation source22and the grid focus position35of the anti-scatter grid26which may be arranged close to or on the X-ray detector24, respectively, may be provided. The measurement unit12may determine deviations between an initial spatial alignment of the X-ray radiation source22and the X-ray detector24during the image acquisition, i.e. during the rotation of the X-ray radiation source22and the X-ray detector24around the object receiving space36. Then, the measurement unit12may determine any displacement to the initial alignment during the image acquisition.

Additionally, in an example, a displacement18between the X-ray beam focus position37and the grid focus position35may be determined during the image acquisition by analyzing the acquired X-ray images of the X-ray detector24. A reduction of the quality of the X-ray images will indicate a misalignment between the X-ray beam focus position37and the grid focus position35. The reduction of the quality may result from a reduction of the contrast of the X-ray image and/or from the presence of a shadow of the anti-scatter grid26in the X-ray image. This may improve the determination of the displacement between the X-ray beam focus position37and the grid focus position35.

The control unit14analyzes the measured displacement18between the X-ray position37and the grid focus position35. Based on the displacement18the control unit14generates a shifting signal. The shifting signal comprises information about the distance19that the anti-scatter grid26has to be shifted in order to align the grid focus position35to the X-ray beam focus position37.

The control unit14may also base the shifting signal on the X-ray detector's24angular position, speed, and/or acceleration. The angular position, the speed, and the acceleration may be acquired by sensors on the at least one support structure32.

The shifting unit16may be attached to the anti-scatter grid26. Furthermore, the shifting unit16may comprise at least one control member that may be motor. The control member is configured to reposition the anti-scatter grid26in one dimension, i.e. along one direction.

The shifting unit16receives the shifting signal from the control unit14and shifts the anti-scatter grid26by the distance19. This shifts the grid focus position35towards the X-ray beam focus position37. The result is a realignment of the X-ray beam focus position37to the grid focus position35of the anti-scatter grid26.

FIGS. 4aand 4bshow different types of anti-scatter grids26.FIG. 4ashows a one-dimensional anti-scatter grid26. This one-dimensional anti-scatter grid26comprises a single row of X-ray radiation transparent sections25which are separated by X-ray radiation absorbing sections27. The X-ray radiation transparent sections25are arranged such that they are aligned to the grid focus position35. The one-dimensional anti-scatter grid26may reduce the scatter in one dimension.

The shifting unit16being attached to the anti-scatter grid26may reposition the anti-scatter grid26in the direction indicated by the arrow.

FIG. 4bshows a two-dimensional anti-scatter grid26. The two-dimensional anti-scatter grid26has several rows of X-ray radiation transparent sections25which are separated by X-ray radiation absorbing sections27. Also, the rows of the X-ray radiation transparent sections25are separated by X-ray radiation absorbing sections27. That two-dimensional anti-scatter grid26may reduce the scatter in two dimensions.

The shifting unit16comprises a first shifting component162and a second shifting component164. The first and the second shifting components162,164may be control members.

The first shifting component162may shift the anti-scatter grid26in a first dimension wherein the second shifting component164may shift the anti-scatter grid26in a second dimension. The first and the second dimension may be orthogonal with respect to each other indicated by the arrows. However, the first and the second dimension may also be non-orthogonal while being non-parallel.

FIG. 5shows a flowchart for the method100for controlling the position of the anti-scatter grid in an X-ray image acquisition system.

In step a), and X-ray beam focus position of an X-ray radiation source of an X-ray image acquisition system is determined101with respect to an X-ray detector of the X-ray image acquisition system using a measurement unit. The position of the X-ray detector and the X-ray radiation source may be determined in order to determine changes in the alignment of the anti-scatter grid being arranged close to or on the X-ray detector, respectively, to the X-ray beam focus position. This means, that in step a), the displacement between the grid focus position and the X-ray beam focus position may be determined.

In an example, in addition, acquired X-ray images may be analyzed102to determine a reduction of the image quality, wherein the reduction may result from a reduced contrast and/or a shadow of an anti-scatter grid in the X-ray image due to a change of alignment. This may improve the determination of the displacement between the grid focus position and the X-ray beam focus position.

In step b), a shifting signal is generated103from the displacement between the X-ray beam focus position and the grid focus position. The generation102may be performed by a control unit. The shifting signal comprises the information how much the anti-scatter grid must be repositioned in order to align the grid focus position of the anti-scatter grid to the X-ray beam focus position.

In step c), the position of the anti-scatter grid may be shifted104in at least one direction based on the shifting signal. This shifting may be performed by a shifting unit. This will align the grid focus position of the anti-scatter grid to the X-ray beam focus position in the X-ray radiation source.

In another exemplary embodiment of the present invention, a computer program or a computer program element40being shown inFIG. 1is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

Further on, the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.

According to a further exemplary embodiment of the present invention, a computer readable medium50according toFIG. 1, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it which computer program element is described by the preceding section. A computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.