Device for rotating an X-ray grating, X-ray phase contrast imaging device with such a device, and method for rotating an X-ray grating

Abstract

Device for rotating an X-ray grating (1) about an axis of rotation (20) aligned parallel to the beam path during X-ray imaging, comprising: - a grid frame (2) in which the X-ray grid (1) is clamped, - a base plate (21) on which the grid frame (2) is rotatably arranged, and - a drive unit (3) configured to rotate the lattice frame (2), characterized by: - bearing rollers (6) arranged on the base plate (21), in which the grid frame (2) is rotatably and without play clamped, - a pre-tensioned tension spring (7) whose first end (13) is connected to the lattice frame (2) and whose second end (14) is connected to the base plate (21) such that the tension spring (7) is arranged tangentially to a rotational movement about the axis of rotation (20), and - a lever arm (8) formed on the lattice frame (2) which can be moved about the axis of rotation (20) by the drive unit (3).

Description

Field of the invention

[0001] The invention relates to a device for rotating an X-ray grid about a rotation axis aligned parallel to the beam path during X-ray imaging, comprising a grid frame in which the X-ray grid is clamped, a base plate on which the grid frame is rotatably mounted, and a drive unit that rotates the grid frame. The invention also relates to an associated X-ray phase contrast imaging device and a method for rotating an X-ray grid. Background of the invention

[0002] Movable X-ray grids are used primarily in X-ray phase-contrast imaging. X-ray phase-contrast imaging is an X-ray imaging technique that combines the absorption of X-rays by an object with the phase shift of the X-rays as they pass through the object. The information content of this type of imaging is significantly higher than that of pure absorption imaging, because absorption provides precise images of the highly absorbing bones, while phase contrast produces sharp images of soft tissue structures. This allows for earlier detection of pathological changes such as the development of tumors, vascular constrictions, or pathological changes in cartilage.

[0003] The transmission of X-rays through matter is described by a complex refractive index. The imaginary part of the refractive index indicates the strength of absorption, while the real part of the refractive index indicates the phase shift of the X-ray wave passing through a material. In phase-contrast imaging, the phase information of the local phase or the local phase gradient of the wavefront passing through an object is determined. Analogous to X-ray tomography, tomographic representations of the phase shift can also be reconstructed based on a large number of images.

[0004] There are several ways to achieve X-ray phase-contrast imaging. The known solutions essentially involve using special arrangements and methods to visualize the phase shift of X-rays passing through an object as intensity fluctuations. One common method is grating phase-contrast imaging, also known as Talbot-Lau interferometry, which is widely described in the literature, including in European Patent Application EP 1 879 020 A1. The core of the Talbot-Lau interferometer is three X-ray gratings (so-called interference gratings) arranged between an X-ray source and an X-ray detector.

[0005] In addition to the classic absorption image, such interferometers can display two additional measurements in the form of additional images: the phase-contrast image and the dark-field image. The phase of the X-ray wave is determined by interference with a reference wave using the interferometric grating arrangement.

[0006] EP 1 879 020 A1 discloses an arrangement with an X-ray source and a pixelated X-ray detector, between which an object to be irradiated is arranged. A source grating, also called a coherence grating, is arranged between the focal spot of the X-ray tube and the object. It is used to simulate multiple line sources with spatial partial coherence of the X-ray radiation, which is an essential prerequisite for interferometric imaging.

[0007] A diffraction grating, also known as a phase grating or Talbot grating, is placed between the object and the X-ray detector. The diffraction grating imposes a phase shift of typically pi on the wavefront.

[0008] An absorption grating between the diffraction grating and the X-ray detector is used to measure the phase shift generated by the object. The wavefront in front of the object is "bent" by the object. The three X-ray gratings must be arranged parallel to each other and at precise distances from each other.

[0009] The X-ray detector is used for the location-dependent detection of X-ray quanta. Since the pixelation of the X-ray detector is generally insufficient to resolve the interference fringes of the Talbot pattern, the intensity pattern is scanned by shifting one of the gratings (= "phase stepping"). The scanning occurs stepwise or continuously perpendicular to the direction of the X-ray beam and perpendicular to the slit direction of the absorption grating. This allows three different types of X-ray images to be recorded or reconstructed: the absorption image, the phase-contrast image, and the dark-field image.

[0010] The X-ray grids must be able to be moved and aligned very precisely and without play, both linearly and rotationally. It must be ensured that the necessary mechanical components are located outside the beam path. One known method for moving the X-ray grids is using hexapods.

[0011] German Patent Application DE 25 18 669 A1 discloses an X-ray filter that can be rotated against a spring force acting on a lever arm. The filter, together with the receiver, rests on a rotating plate.

[0012] The published patent application DE 10 2012 211 751 A1 discloses a wedge filter which can be displaced translationally against a spring force and which is arranged on a rotatable gear wheel. Summary of the invention

[0013] It is an object of the invention to provide a device, an X-ray phase contrast imaging device and a method in which a play-free rotation of an X-ray grid is ensured.

[0014] According to the invention, the stated object is achieved with the device, the X-ray phase contrast imaging device, and the method of the independent patent claims. Advantageous further developments are specified in the dependent claims.

[0015] According to the invention, the geometry of a grid frame supporting the X-ray grid is designed so that it can rotate concentrically with the beam path. Four bearing rollers mounted on the grid frame serve as the counterbearings or abutments of the grid frame. Two of these bearing rollers are positioned on the running surfaces of the grid frame using eccentric bolts to ensure a backlash-free circular motion. The grid frame is preloaded by a tension spring acting tangentially on it and driven by a tangential cable connected to an electric drive.

[0016] The tension spring's preload allows for a backlash-free change in the direction of rotation. The cable can also be designed as a pulley system for additional reduction to increase the resolution in X-ray phase-contrast imaging. This is also possible by installing a lever on the lattice frame, to which the cable engages.

[0017] A pulley block is a device that reduces the amount of force required, for example, to move loads. A pulley block consists of fixed and loose pulleys and a rope.

[0018] The invention claims a device for rotating an X-ray grid about an axis of rotation aligned parallel to the beam path in X-ray imaging. The device comprises: - a grid frame in which the X-ray grid is clamped, - a base plate on which the grid frame is rotatably mounted, - a drive unit designed to rotate the lattice frame, - bearing rollers arranged on the base plate, in which the grid frame is clamped rotatably and without play, - a pre-tensioned tension spring, the first end of which is connected to the lattice frame and the second end of which is connected to the base plate in such a way that the tension spring is arranged tangentially to a rotational movement about the axis of rotation, and - a lever arm formed on the lattice frame, which can be moved around the axis of rotation by the drive unit.

[0019] The device offers the advantage of ensuring backlash-free rotation of an X-ray grid, even when reversing the direction of movement. The lever reduces the drive unit's speed. This device allows for cost reduction. Furthermore, it can be individually configured for each new setup through the geometry of the frame and the design of the cable pull.

[0020] In a further development, the lever arm can be arranged opposite the tension spring with respect to the axis of rotation.

[0021] In a further embodiment, the device has an electric drive of the drive unit, which can move the lever arm.

[0022] In a further embodiment, the electric drive can be rigidly connected to the base plate.

[0023] In a further embodiment, the device has a cable pull unit of the drive unit, comprising at least one cable pulley and a pull rope running around the cable pulley, wherein the first rope end of the pull rope is connected to the lever arm and the second rope end of the pull rope is connected to the electric drive.

[0024] In another embodiment, the traction cable can be redirected multiple times. This allows for gear reduction.

[0025] In a further development, the cable pull unit can be designed as a pulley block, with cable pulleys being arranged on the lever arm and moving with it.

[0026] In a further development, the electric drive can be a stepper motor.

[0027] In a further development, the device comprises a push rod that moves the lever arm and a piezoelectric linear electric motor that allows the push rod to be moved linearly. This embodiment is an alternative to the cable pull.

[0028] In a further embodiment, the grid frame can be rectangular, with the corners cut off and the bearing rollers positioned on them.

[0029] In a further embodiment, the grid frame can be round.

[0030] The invention also claims an X-ray phase contrast imaging device comprising an X-ray emitter, an X-ray detector and at least one device according to one of the preceding claims arranged between the X-ray emitter and the X-ray detector.

[0031] Furthermore, the invention claims a method for rotating an X-ray grating in an interferometric X-ray imaging with a device according to the invention, wherein the lever arm of the X-ray grating is moved by a predeterminable angle of less than one degree by the drive unit.

[0032] Further features and advantages of the invention will become apparent from the following explanations of several embodiments based on schematic drawings.

[0033] They show: Fig. 1: an oblique view of a device with a rectangular X-ray grid and a pulley, Fig. 2: another oblique view of a device with a rectangular X-ray grid and a pulley, Fig. 3: a side view of a device with a round X-ray grid, Fig. 4: a side view of a device with a rectangular X-ray grid and a piezo linear drive and Fig. 5: an X-ray phase contrast imaging device. Detailed description of several embodiments

[0034] Fig. 1 shows a three-dimensional view of a device for rotating an X-ray grid 1, which is clamped (fixed) in a grid frame 2, about the axis of rotation 20. During an X-ray image acquisition, the axis of rotation 20 is aligned in the direction of the X-ray radiation (along the beam path). The grid frame 2 is clamped without play in four bearing rollers 6. To achieve this, two of the bearing rollers 6 can have eccentric bearing bolts, with the aid of which the bearing rollers 6 can be adjusted against the grid frame 2. The grid frame 2 is rectangular in design, with bevelled corners. The bevelled corners form the running surfaces for the bearing rollers 6. The bearing rollers 6 are rotatably mounted on a base plate 21. This type of "clamping" allows movement of a few degrees.

[0035] At the upper edge of the lattice frame 2, a tension spring 7 is attached by its first end 13, tangential to the rotational movement of the lattice frame 2 about the rotation axis 20. The second end 14 of the tension spring 7 is connected to the base plate 21. The tension spring 7 is preloaded so that it applies a tensile stress to the lattice frame 2 at any angular position of the lattice frame 2. This ensures a backlash-free change of direction of the rotational movement.

[0036] At the lower edge of the lattice frame 2, opposite the tension spring 7 with respect to the rotation axis 20, a lever arm 8 is formed. It serves to reduce the speed of the drive unit 3. The drive unit 3 has a stepper motor 5 that is firmly connected to the base plate 21 and moves the lever arm 8 via the cable pull unit 4. The cable pull unit 4 has several cable pull pulleys 12 and a pull cable 11. The first cable end 15 is connected to the lever arm 8, and the second cable end (not visible) is connected to the stepper motor 5. Thus, a rotary movement of the stepper motor 5 is converted into a lever movement.

[0037] To further reduce the rotary motion of the stepper motor 5, the cable pulley unit 4 is designed as a pulley system. For this purpose, cable pulleys 12 are mounted on both the lever arm 8 and the base plate 21. This further reduction ensures a very precise and fine rotary motion of the X-ray grid 1. The maximum required rotary motion is less than one degree in both directions with a resolution of less than one angular minute.

[0038] Fig. 2 shows the device of the Fig. 1 in a further three-dimensional view. The base plate 21 with the bearing rollers 6 mounted on it can be seen again, which hold the grid frame 2 (with the X-ray grid 1) free of play. The corners of the rectangular grid frame 2 are significantly beveled for support. A stepper motor 5 of the drive unit 3 and a cable pull unit 4 of the drive unit 3 move the lever arm 8 of the grid frame 2. The tension spring 7 is arranged opposite the lever arm 8.

[0039] Fig. Figure 3 shows a front view of a device with a round X-ray grid 1 in a round grid frame 2. All other components are according to the Fig. 1 and Fig. 2. The bearing rollers 6, the tension spring 7, the lever arm 8, the drive unit 3 with stepper motor 5 and the cable pull unit 4 can be seen.

[0040] Fig. 4 shows a device for rotating an X-ray grid 1 but with a differently designed drive unit 3 than the devices of Fig. 1 to Fig. 3. The grid frame 2, which holds the X-ray grid 1, is also mounted on the base plate 21 by means of the four bearing rollers 6, and a preloaded tension spring 7 ensures a backlash-free reversal of the direction of movement. However, a push rod 9 now engages the lever arm 8. This is moved by the piezo linear motor 10 and thereby rotates the grid frame 2. The piezo linear motor 10 is firmly connected to the base plate 21, so that the drive force can be introduced into the push rod 9.

[0041] Fig. Figure 5 shows an arrangement for interferometric X-ray phase contrast imaging with three X-ray gratings 1 on a base plate 21, each arranged according to the device of Fig. 1 to Fig.4. The devices with X-ray grid 1 and base plate 21 are arranged between an X-ray emitter 18 and an X-ray detector 19.

[0042] Although the invention has been illustrated and described in detail by the embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention. List of reference symbols 1 X-ray grid 2 grid frames 3 Drive unit 4 cable pull unit 5 Stepper motor 6 Storage roller 7 tension spring 8 lever arm 9 Push rod 10 Piezo linear motor 11 Pull rope 12 cable pulley 13 first end 14 second end 15 first rope end 18 X-ray tubes 19 X-ray detector 20 axis of rotation 21 Base plate

Claims

[1] Device for rotating an X-ray grid (1) about an axis of rotation (20) aligned parallel to the beam path in X-ray imaging, comprising: - a grid frame (2) in which the X-ray grid (1) is clamped, - a base plate (21) on which the grid frame (2) is rotatably arranged, and - a drive unit (3) designed to rotate the grid frame (2), characterized by : - bearing rollers (6) arranged on the base plate (21), in which the grid frame (2) is clamped rotatably and without play, - a pre-tensioned tension spring (7), the first end (13) of which is connected to the lattice frame (2) and the second end (14) of which is connected to the base plate (21) in such a way that the tension spring (7) is arranged tangentially to a rotational movement about the axis of rotation (20), and - a lever arm (8) formed on the grid frame (2) which can be moved about the axis of rotation (20) by the drive unit (3). [2] Device according to claim 1, characterized by that the lever arm (8) is arranged opposite the tension spring (7) with respect to the axis of rotation (20). [3] Device according to claim 1 or 2, characterized by : - an electric drive (5, 10) of the drive unit (3) which is arranged to move the lever arm (8). [4] Device according to claim 3, characterized by that the electric drive (5, 10) is rigidly connected to the base plate (21). [5] Device according to claim 3 or 4, characterized by : - a cable pull unit (4) of the drive unit (3), comprising at least one cable pulley (12) and a pull rope (11) running around the cable pulley (12), - wherein the first rope end (15) of the traction rope (11) is connected to the lever arm (8) and the second rope end of the traction rope (11) is connected to the electric drive (5). [6] Device according to claim 5, characterized by that the traction cable (11) is deflected several times. [7] Device according to claim 6, characterized by that the cable pull unit (4) is designed as a pulley block, wherein cable pulleys (12) are arranged on the lever arm (8) and move with it. [8] Device according to one of claims 3 to 7, characterized by e, that the electric drive is a stepper motor (5). [9] Device according to claim 3 or 4, characterized by : - a push rod (9) moving the lever arm (8) and - a piezo linear electric motor (10) by which the push rod (9) can be moved linearly. [10] Device according to one of the preceding claims, characterized by that the grid frame (2) is rectangular, with the corners cut off and the bearing rollers (6) positioned thereon. [11] Device according to one of claims 1 to 9, characterized by that the grid frame (2) is round. [12] X-ray phase contrast imaging device comprising an X-ray emitter (18), an X-ray detector (19) and at least one device according to one of the preceding claims arranged between the X-ray emitter (18) and the X-ray detector (19). [13] Method for rotating an X-ray grid (1) in an interferometric X-ray imaging with a device according to one of claims 1 to 11, characterized by that the drive unit (3) moves the lever arm (8) of the lattice frame (2) by a predeterminable angle of less than one degree.

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