DE102016226032A1 - Optical arrangement for the suppression of artifacts in X-ray examinations and method for their production - Google Patents

Abstract

The present invention relates to an optical arrangement for suppressing artifacts generated by diffraction or scattering in X-ray examinations and a method for producing such an optical arrangement.

Description

The present invention relates to an optical arrangement for suppressing artifacts generated by diffraction or scattering in X-ray examinations and a method for producing such an optical arrangement.

In general, X-rays of atoms are absorbed as a function of their atomic number and mass. The principle is that heavy atoms absorb x-rays more strongly than light atoms. This principle is used in a variety of imaging modalities, so that X-ray examinations are popular as analytical methods not only in the field of medicine, but also in the fields of biology, structural analysis, geology and archeology.

In the simple X-ray fluoroscopy method, a sample is X-rayed. The sample is partially transparent to X-radiation, i. a portion of the radiation is absorbed within the sample, the remaining radiation emerges from the sample. Behind the plane in which the sample is located, a detector is positioned, which detects the residual X-radiation reached by the sample and reproduces it as an intensity image. These so-called fluoroscopic images are two-dimensional images with information about the internal structure of the sample.

An extension of the X-ray fluoroscopy method is the X-ray computed tomography (CT). In the case of CT, software is used to combine multiple fluoroscopic images into a three-dimensional representation of the specimen. The individual fluoroscopic images are usually achieved by rotation of the sample to be measured or by rotation of the X-ray detector and source around the sample.

In the field of medicine, the sample corresponds to a part of the human body, which consists of tissue and bone with different density and therefore allows a resolution of the various structures.

In addition to absorption and transmission, there is also the possibility that the X-ray radiation in the sample is diffracted or scattered. This is problematic in view of the quality of the obtained X-ray image, since the X-rays are deflected by the diffraction or scattering and impinge on another point of the detector.

This creates a falsified image on the fluoroscopic image. Image areas in which the diffracted X-ray quanta impinge have an increased intensity, while in other areas the intensity is lower. The diffraction effect causes a blurred, blurred image. The diffracted x-ray quanta cause a "halo" around the object, the image contrast is reduced and the edges of the object are not clearly imaged.

This effect is one of the artifacts in the X-ray examination and depends on the material and geometry of the sample. For high-density materials and high-atomic-number elements, as well as for edges and density transitions in the sample, diffraction and scattering are more pronounced.

In order to minimize bending effects, various approaches have already been developed. The most common approach is the so-called strip louvre. The louvre diaphragm, also known as the "Bucky shutter", was developed as early as 1912 and is still standard equipment for X-ray machines.

The louvre diaphragm uses thin lead slats as X-ray absorbers, which are alternately paired with radiolucent slats. Diffracted radiation is absorbed in the lead lamellae, the detector receives only the direct X-ray radiation, which radiates parallel to the lead lamellae.

The disadvantage here, however, is the stripe pattern of the X-ray image, which is produced when the Bucky aperture is used purely statically.

The lamella is therefore set in some X-ray instruments by means of rapid vibrations perpendicular to the lamellar direction in vibration. As a result, the radiation-absorbing regions of the louver diaphragm move over the detector and it is ensured that each subarea of the detector is exposed to the X-ray radiation during the measurement.

This method has the disadvantage that the X-ray diffraction is eliminated only in one direction (perpendicular to the slats). Diffraction parallel to the slats can hit the detector unhindered. In addition, the method requires a periodic deflection of the diaphragm, so that the absorption of the lamellar structure is not detected by the detector (so-called line artifacts). Especially with measurements with a long measurement time, especially with CT measurements, this can cause problems.

The US 7,148,082 B2 and the US 7,236,560 B2 provide alternatives to the Bucky aperture. These patents provide that a thin lead foil is formed into a honeycomb structure. These honeycombs are placed in front of the detector and avoid diffraction effects. The structure is permanently placed in front of the detector.

The disadvantage of these approaches is the high cost, which is necessary for the production of the honeycomb structure. The dimensions of the honeycomb are in the range of several millimeters. The aperture can therefore be shielded for coarse line detectors with detector areas in the range of a few square millimeters. In modern high-resolution area detectors consisting of 512 ² , 1024 ² , 2048 ² or more single detectors with edge lengths of 100 microns to 500 microns, this method is no longer applicable.

Based on the disadvantages of the prior art apertures, it was an object of the present invention to provide an optical arrangement which effectively reduces the diffraction and scattering artifacts in the X-ray image and instead does not produce any further artifacts. Furthermore, the optical arrangement should be able to fulfill its function even using modern, high-resolution detectors. Finally, the optical arrangement should be easy and inexpensive to produce. Furthermore, a manufacturing process should be specified, with which the optical arrangement including aperture can be made.

According to the invention the object is achieved by providing an optical arrangement with the features of claim 1 and the method having the features of claim 12.

The inventive optical arrangement for suppressing diffraction or scattering artifacts in X-ray examinations includes at least one aperture and a detector unit having a plurality of individual detectors, the aperture having a matrix of X-ray absorbing material having a plurality of optical channels of X-ray transmissive material in that the optical channels are formed from a positive mask made of a plastic, each optical channel is assigned to a single detector and the dimensions of the optical channels are selected such that only the X-ray scattering radiation and / or X-ray diffraction radiation passes through the diaphragm which is located at the end of the detector unit optical channel forms a maximum scattering angle of 10 ° with the undiffracted and unscattered X-rays.

In this way, the single detectors can be effectively shielded from diffracted X-ray quanta. All X-ray quanta that are not located directly from the X-ray source to the detector are absorbed by the aperture.

In an advantageous variant of the optical arrangement, the dimensions of the optical channels are chosen so that only the X-ray scattering radiation and / or X-ray diffraction radiation passes through the diaphragm, which at the detector unit facing the end of the optical channel at most a scatter angle of 5 °, preferably 3 °, especially preferably 2 °, forms with the undiffracted and unscattered X-rays.

The occurring artifacts can be minimized. At the same time, the resolution of the X-ray image is increased.

mit der Länge des optischen Kanals L im Verhältnis steht, wobei α der maximal zulässige Streuwinkel an dem der Detektoreinheit zugewandten Ende des optischen Kanals ist.Furthermore, it is preferred that the optical arrangement is designed such that the end of the optical channels, which faces away from the detector unit, has a maximum extent b which, according to formula (I) $$\alpha ={\text{tan}}^{-1}\left(b\text{/}L\right)$$

is related to the length of the optical channel L, where α is the maximum allowable scattering angle at the end of the optical channel facing the detector unit.

This allows a highly flexible adaptation of the optical arrangement to the individual requirements in the X-ray examination. The geometry of the optical channels need not be refined beyond what is necessary.

The optical channels of the optical arrangement in one embodiment have the shape of a cylinder, a prism, a truncated cone and / or a cuboid, preferably the shape of a cylinder with a circular cross section, a cylinder with an elliptical cross section and / or an oblique cylinder, particularly preferably the shape a cylinder with a circular cross section.

In each of the embodiments, it is crucial that the optical channels have a larger dimension in the direction of the incident X-radiation than perpendicular to the direction of the incident X-ray radiation, so that they fulfill their shielding function.

Advantageously, the optical channels in the matrix are arranged without overlapping, preferably parallel and isolated from one another, particularly preferably at regular intervals, in particular at positions of an at least partially regular grating.

The matrix can be divided in a preferred embodiment, for example, in several rectangular areas, within which the optical channels are each arranged on a regular grid. Adjacent rectangular areas have different grating structures or grids with different grating constants, on the positions of which the optical channels are arranged.

The optical arrangement can also be characterized in that the optical channels contained therein have a base area whose surface area is in each case not more than 5.00 mm ² , preferably not more than 1.00 mm ² , particularly preferably not more than 0.50 mm ² , in particular not more than 0. 10 mm ² .

The X-ray absorbing material in the optical arrangement preferably consists of a chemical element with an atomic number of at least 9 or of an oxide of a chemical element with an atomic number of at least 9, wherein the chemical element is preferably selected from the group consisting of zirconium, tin, Lead, bismuth, tungsten, yttrium, copper, silver and mixtures thereof. Particularly preferred for the X-ray absorbing material include zirconia and yttria.

Furthermore, the plastic for the positive mask in the optical arrangement according to the invention can be temperature-resistant and be selected from the group consisting of injection-moldable polymers, in particular PE, PEEK and PA, castable polymers, in particular epoxides and phenols and mixtures thereof, wherein the plastic for reinforcement and fibers , preferably fibers selected from the group consisting of glass fibers, carbon fibers, ceramic fibers, textile fibers, in particular cotton fibers, polyester fibers and aramid fibers and mixtures thereof, may have.

The plastic used for the positive mask should be characterized in particular by a sufficient rigidity, a high short-term temperature resistance to solder melting at up to 150 ° C, a micro injection molding capability and a sufficient radiopacity.

It is also a preferred variant of the invention, when the positive mask is removed from the matrix in the optical arrangement after the preparation of the matrix according to the principle of the lost form.

The optical arrangement according to any one of the preceding claims may also be characterized in that the diaphragm has a protective layer, wherein the protective layer is preferably made of epoxy resin, and more preferably has a thickness of 0.5 mm to 5.0 mm, in particular of 1.0 mm up to 2.0 mm.

The aperture is advantageously in the optical arrangement in the form of a flat or curved plate with a thickness of 1 mm to 10 mm, in particular from 3 mm to 6 mm, and preferably has holes for attachment in the optical arrangement and positioning in front of the detector unit ,

1. a) Herstellen einer Positivmaske aus Kunststoff durch Spritzgießen von mindestens einem Formkörper in Form einer Bodenplatte mit einer Vielzahl von Ausstülpungen,
2. b) Überschichten der Positivmaske mit einem Röntgenstrahlung absorbierenden Matrixmaterial zur Herstellung einer Blende, bei dem aus der Vielzahl von Ausstülpungen optische Kanäle erzeugt werden und
3. c) Positionieren der Blende relativ zu einer Detektoreinheit, so dass jeder optische Kanal einem Einzeldetektor der Detektoreinheit zugeordnet ist, wobei das Röntgenstrahlung absorbierende Matrixmaterial vor oder nach dem Überschichten der Positivmaske erhitzt wird.

The process according to the invention for the preparation comprises the following steps:

1. a) producing a positive mask from plastic by injection molding of at least one shaped body in the form of a base plate with a plurality of protuberances,
2. b) overlaying the positive mask with an X-ray absorbing matrix material to produce a diaphragm in which optical channels are generated from the plurality of protuberances and
3. c) positioning the aperture relative to a detector unit such that each optical channel is associated with a single detector of the detector unit, wherein the X-ray absorbing matrix material is heated before or after the positive mask is overlaid.

The production of the positive mask in injection molding makes it possible to produce protuberances in any cross section. Cylindrical, rectangular and complex contours can be produced and these can be arranged in accordance with the position of the individual detectors.

In the method we also preferably prepared a positive mask, which consists of at least one shaped body in the form of a bottom plate with a plurality of protuberances, wherein the protuberances particularly preferably a length of 1 to 15 mm, most preferably from 2 mm to 7 mm, in particular from 3 mm to 5 mm.

It is also advantageous if the positive mask produced by injection molding of at least one shaped body in the form of a bottom plate with a plurality of protuberances is so covered with the matrix material that the ends of the protuberances are not completely covered and preferably 500 .mu.m to 1000 .mu.m exposed ,

It is also preferable that the positive mask is overcoated with the matrix material by placing the positive mask in a frame and sealing it, melting the matrix material and then pouring it into the frame, or subsequently lowering the frame into a pan with the liquid matrix material.

In particular, solders based on lead alloys or bismuth alloys are used as the matrix material. These have a melting temperature of less than 150 ° C and allow the positive mask, which is formed from a plastic, largely maintains its structure during this process step. After cooling, a flat structure of X-ray-absorbing matrix material (cooled solder) can form, which has solidified around the radio-opaque positive mask.

Furthermore, it is favorable if the surface of the panel is milled and / or ground flat after the cooling of the matrix material, wherein the milled and / or ground surface is preferably provided with a protective layer.

As a protective layer is, for example, an epoxy resin, which can be poured onto the panel. After curing, this protective layer can give the panel additional mechanical stability.

In addition, it is desirable that after cooling the matrix material, holes be drilled in the aperture for attachment in the optical assembly and positioning in front of the detector unit.

The positioning of the diaphragm ultimately depends advantageously on the X-ray source. Parallel alignment of aperture and detector is preferred in synchrotron radiation, while positioning of the aperture is to be selected at an angle between 180 ° and 360 ° to the X-cone detector.

The positive mask can be produced in a variant of the method by injection molding of at least two moldings in the form of a bottom plate with a plurality of protuberances, wherein the at least two moldings are assembled to form the positive mask and the arrangement of the protuberances differs between at least two moldings.

Finally, it is preferable if the positive mask is removed in a step after the overlaying of the method so that cavities are formed at the location of the optical channels in the aperture.

The cavities absorb less total X-ray radiation as compared to the plastic optical channels, so that the proportion of X-rays arriving at the detector with respect to the incident X-rays is higher overall.

The following figures are intended to illustrate the invention without wishing to reduce it to the specific embodiments.

1 schematically shows an embodiment of the invention, the aperture, which can avoid X-ray diffraction from an angle of 2, 1 ° when using a detector unit with a dimension of 200 microns x 200 microns in an optical arrangement. Beams with a diffraction angle less than 2.1 ° ( 3 ), the optical channels ( 1 ) happen. Beams with a larger diffraction angle are emitted from the diaphragm ( 2 ) absorbed. The channels ( 1 ) have special dimensions, namely a length between 3 mm and 5 mm and a diameter of 0, 15 mm to 0, 18 mm.

2 schematically shows a projection of a positive mask with which a diaphragm according to the invention can be produced. The width or the diameter ( 4 ) of the protuberances is smaller than the distance ( 5 ) between the protuberances. The length ( 6 ) of the protuberances is of the same order of magnitude as the thickness of the bottom plate.

The width or the diameter ( 4 ) of the protuberances may for example be 150 microns, while the distance between the protuberances is 250 microns. The length ( 6 ) of the protuberances is from 3 to 5 mm.

3 shows an embodiment according to the invention of an optical arrangement with optical channels (FIG. 1 ), which are in an aperture ( 2 ) are arranged from an X-ray absorbing material. Also shown are the single detector elements ( 7 ) located in the detector unit ( 8th ) are arranged. It can also be seen that each individual detector element ( 7 ) is assigned to an optical channel.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7148082 B2 [0014]
• US 7236560 B2 [0014]

Claims (19)

Optical arrangement for suppressing artifacts generated by diffraction or scattering during X-ray examinations, comprising at least one diaphragm and a detector unit with a multiplicity of individual detectors, the aperture comprising a matrix of X-ray absorbing material having a plurality of X-ray transparent material optical channels, the optical channels being formed of a positive plastic mask, each optical channel being associated with a single detector, and the dimensions of the optical channels are selected so that only the X-ray scattering radiation and / or X-ray diffraction radiation passes through the diaphragm, which at the end of the optical channel facing the detector unit maximally forms a scattering angle of 10 ° with the undiffracted and unscattered X-radiation. Optical arrangement according to Claim 1 , characterized in that the dimensions of the optical channels are selected so that only the X-ray scattering and / or X-ray diffraction radiation passes through the diaphragm, which at the detector unit facing the end of the optical channel maximum a scattering angle of 5 °, preferably 3 °, particularly preferably 2 °, with the undiffracted and unscattered X-rays. Optical arrangement according to one of the preceding claims, characterized in that the end of the optical channels, which faces away from the detector unit, has a maximum extent b, which according to formula (I) $$\alpha ={\text{tan}}^{-1}\left(b\text{/}L\right)$$

is related to the length of the optical channel L, where α is the maximum allowable scattering angle at the end of the optical channel facing the detector unit. Optical arrangement according to one of the preceding claims, characterized in that the optical channels are in the form of a cylinder, a prism, a truncated cone and / or a cuboid, preferably the shape of a cylinder with a circular cross section, a cylinder with an elliptical cross section and / or an oblique cylinder , Particularly preferably have the shape of a cylinder having a circular cross-section. Optical arrangement according to one of the preceding claims, characterized in that the optical channels in the matrix without intersections, preferably parallel and isolated from each other, more preferably at regular intervals, in particular on positions of an at least partially regular grating are arranged. Optical arrangement according to one of the preceding claims, wherein the optical channels have a base area whose surface area in each case not more than 5.00 mm ² , preferably not more than 1.00 mm ² , particularly preferably not more than 0.50 mm ² , in particular not more than 0.10 mm ² is. Optical arrangement according to one of the preceding claims, characterized in that the X-ray absorbing material consists of a chemical element with an atomic number of at least 9 or an oxide of a chemical element with an atomic number of at least 9, wherein the chemical element is preferably selected from the group consisting of zirconium, tin, lead, bismuth, tungsten, yttrium, copper, silver and mixtures thereof. Optical arrangement according to one of the preceding claims, characterized in that the plastic for the positive mask is temperature resistant and is selected from the group consisting of injection moldable polymers, in particular PE, PEEK and PA, castable polymers, in particular epoxides and phenols and mixtures thereof, wherein the Plastic for reinforcement preferably fibers, more preferably fibers selected from the group consisting of glass fibers, carbon fibers, ceramic fibers, textile fibers, in particular cotton fibers, polyester fibers and aramid fibers and mixtures thereof. Optical arrangement according to one of the preceding claims, characterized in that the positive mask is removed from the matrix after production of the matrix according to the principle of the lost form. Optical arrangement according to one of the preceding claims, characterized in that the diaphragm has a protective layer, wherein the protective layer is preferably made of epoxy resin, and more preferably has a thickness of 0.5 mm to 5.0 mm, in particular from 1.0 mm to 2.0 mm, has. Optical arrangement according to one of the preceding claims, characterized in that the diaphragm is in the form of a flat or curved plate having a thickness of 1 mm to 10 mm, in particular from 3 mm to 6 mm, and preferably holes for attachment in the optical arrangement and positioning in front of the detector unit. Method for producing an optical arrangement according to one of the preceding claims, comprising the following steps: a) producing a positive mask from plastic by injection molding of at least one shaped body in the form of a base plate with a plurality of protuberances, b) overlaying the positive mask with an X-ray absorbing matrix material to produce a diaphragm in which optical channels are generated from the plurality of protuberances and c) positioning the aperture relative to a detector unit such that each optical channel is associated with a single detector of the detector unit, wherein the X-ray absorbing matrix material is heated before or after overlaying the positive mask. Method according to Claim 12 , characterized in that the positive mask in at least one shaped body in the form of a bottom plate with a plurality of protuberances, wherein the protuberances preferably a length of 1 to 15 mm, more preferably from 2 mm to 7 mm, most preferably from 3 mm 5 mm. Method according to one of Claims 12 or 13 , characterized in that the positive mask produced by injection molding of at least one shaped body in the form of a bottom plate with a plurality of protuberances is so covered with the matrix material that the ends of the protuberances are not completely covered and preferably 500 microns to 1000 microns are exposed. Method according to one of Claims 12 to 14 characterized in that the positive mask is overcoated with the matrix material by placing the positive mask in a frame and sealing it, melting the matrix material and then pouring it into the frame, or subsequently lowering the frame into a pan with the liquid matrix material. Method according to one of Claims 12 to 15 , characterized in that the surface of the diaphragm is milled flat and / or ground after cooling of the matrix material, wherein the milled and / or ground surface is preferably provided with a protective layer. Method according to one of Claims 12 to 16 , characterized in that after cooling of the matrix material holes are drilled in the aperture for attachment in the optical assembly and positioning in front of the detector unit. Method according to one of Claims 12 to 17 , characterized in that the positive mask is produced by injection molding of at least two moldings in the form of a bottom plate with a plurality of protuberances, wherein the at least two moldings are assembled to form the positive mask and the arrangement of the protuberances differs between at least two moldings. Method according to one of Claims 12 to 18 , characterized in that the positive mask is removed after the overlay, so that arise at the location of the optical channels in the diaphragm cavities.

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