WO2018115325A1

WO2018115325A1 - System and method of x-ray dark field analysis

Info

Publication number: WO2018115325A1
Application number: PCT/EP2017/084163
Authority: WO
Inventors: Lars Bager Christensen
Original assignee: Teknologisk Institut
Priority date: 2016-12-22
Filing date: 2017-12-21
Publication date: 2018-06-28

Abstract

Detection of foreign bodies in food is important to prevent such contaminated products from reaching consumers. Light-weight fibrous foreign bodies such as paper, wood and insects are hard to detect even with traditionally X-ray systems. A dark field X-ray system and method for in-line food scanning in production environments to detect light-weight fibrous foreign bodies comprises an X-ray source for emitting X-rays, a movable object support (3) such as a conveyor belt, optionally a phase grating (5), an analyzer grating (6) where the grating elements of the two gratings may be angled according to each other, a scintillator (7) for converting X-rays into light waves, aspherical lenses (9, 10) and a detector (11) e.g. a camera. Reconstruction algorithms in a processor reconstruct a dark-field image from a number of successively obtained images of the object while this passes the gratings. Light-weight fibrous foreign bodies are easily detected in such dark-field images.

Description

System and method of X-ray dark field analysis

The invention relates to an X-ray dark field system and a method based on this system which can be used for fast scanning of objects such as food objects.

Especially the system and method is suitable for detection of organic foreign bodies such as paper, wood and insects in food products by using X-ray dark-field imaging with a grating interferometer and a detector comprising a scintillator converting X- ray radiation into visible light. In-line inspection of objects such as food products under transport at production companies can be used e.g. to identify foreign bodies in food products. Background of invention

Foreign bodies should not be present in food products. Foreign bodies in products reduce the quality and thus the value of the products. Higher quality and food safety requires sensitive and efficient techniques capable of identifying foreign bodies early in a production process and by using non-destructive methods. Some foreign bodies may be detected by systems based on X-ray absorption. However, absorption of X-rays by foreign bodies only makes it possible to detect fairly hard and heavy materials. Other types of detection systems are required to detect other types of foreign bodies, such as light-weight fibrous materials.

WO2015/169463 ( ilted-grating approach for scanning-mode X-ray grating interferometry') describes a scanning-mode grating interferometer design, in which a grating is tilted to form Moire fringes perpendicular to the grating lines. The sample is then translated along the fringes, and each line detector records a different phase step for each slice of the sample. The system includes an X-ray source, a phase grating (Gl), an analyzer grating (G2), optionally a source grating (GO), a position-sensitive detector such as a line-sensitive detector, means to move the object to be analyzed or to move the system, and means to analyze the obtained images. X-rays are thus detected directly by the detector.

Lin et al, 2015 (Grating-based phase-contrast imaging of tumor angiogenesis in lung metastases, Plos One 10(3) : e0121438.doi : 10.1371/journal. pone.0121438) describes a system for obtaining phase-contrast images. The system is a computed tomography (CT) system with an X-ray source, a phase grating (Gl), an absorption grating (G2), a scintillator and an X-ray CCD camera. The elongated elements of the gratings Gl and G2 are parallel and stepping hereof is performed during analysis. US 2015/0055743 (Apparatus and method for X-ray phase contrast imaging) describes an X-ray phase contrast imaging apparatus and method of operating the same. The apparatus passes X-rays generated by an X-ray source through, in succession, a source grating, an object of interest, a phase grating, and an analyzer grating. The system is a CT-system where the X-ray source, the source grating, the phase grating, and the analyzer grating move as a single entity relative to an object of interest, which is stationary. The phase grating and the analyzer grating remain in fixed relative location and fixed relative orientation with respect to one another. The detected X-rays are converted to a time sequence of electrical signals from which phase contrast images are obtained .

However, existing X-ray systems fail to detect light fibrous materials such as wood splinters, paper, cloth fibers and insects as these materials have a low contrast with X-ray absorption. Control of products to obtain the requested quality is of outmost importance and performing such control with a high speed and as an in-line process in the manufacturing environment is requested . The invention described herein makes it possible to perform fast quality control of products especially of food and feed products being transported by a conveyor belt and especially in respect of detecting foreign bodies. A simple cost-effective system can be established based on a translatory movement of the object relative to a fixed x-ray source and a fixed detector. It in particular does so by employing CCDs, cameras, or, in particular video cameras sensitive in the visible part of the electromagnetic spectrum as detectors. CCD detectors and cameras with them come at a very low cost, because of their wide use in consumer electronics, including smart-phones.

A simple detector system of the X-ray system creates a flexible system and also reduces the system price which is advantageously for e.g. food producing companies that may require multiple scanning systems for controlling if foreign bodies are present in the produced products e.g . by controlling products at multiple locations in the company such as at different production lines.

Summary of invention As existing X-ray systems fail to detect light fibrous materials such as wood splinters, paper, cloth fibers and insects such light-weight materials may be present as foreign bodies when a consumer purchases a food product. The invention described herein makes it possible to perform quality control of products especially of food and feed products and especially in respect of detecting foreign bodies comprising light-weight fibrous material . The X-ray system is based on dark-field images which is a measure of the scattering properties of the object to be analyzed or rather of the foreign objects which may be present in or at the object and where the scattering properties is due to microstructures within the object and/or foreign bodies.

An X-ray system which should be capable of detecting light-weight fibrous material must be designed to detect the scattered X-rays from material comprising fibers. Such a system for e.g. in-line fast scanning detection is described herein.

The invention relates to a dark field radiology or tomography system especially for food and/or feed scanning, the system comprises a. At least one X-ray source for emitting X-rays used to analyze an object, the X-rays at least being directed towards an object to be analyzed, b. An movable object support such as a conveyor belt for supporting and transporting an object to be analyzed during the analysis,

c. At least one grating located after the object support in the propagation direction of the emitted X-rays, and

d. At least one scintillator for converting X-rays which has passed the at least one grating into light waves in the visible spectrum.

The system may further comprise one or more of the features:

• Said at least one grating may be at least two gratings located after the

object support in the propagation direction of the emitted X-rays, the gratings are a phase grating (Gl) and an analyzer grating (G2) which each has grating elements that are parallel to each other, and the at least two gratings (Gl, G2) are positioned after each other according to the propagation direction of the X-rays and with the phase grating being located closest to the object support, and the gratings are located such that the grating elements of the phase grating (Gl) and of the analyzer grating (G2) are angled according to each other,

• At least a third grating, such as a source grating (GO), located between the X-ray source and the object support,

• At least one optical element, such as at least one aspherical, e.g, cylindrical, lens located after the at least one scintillator,

• At least one camera sensitive in the visible part of the electromagnetic

spectrum located after the at least one optical element,

• At least one processor obtaining information at least from the at least one camera, the processor comprising algorithms capable of analyzing the obtained information and capable of producing dark field images. In the system all features except the object support may be stationary whereby the object support may transport an object to be analyzed pass the features of the system. Such a system may be an in-line system for detecting foreign bodies in food products in the production environments such as at abattoirs or other food producing companies.

The system is based on a method for obtaining dark field images of an object, the method comprises the steps of: a. Directing X-rays towards an area suitable for an object to be analyzed, b. Transporting an object to be analyzed substantially perpendicular to the X- ray propagation direction and transporting the object through the cone beam of X-rays,

c. Passing X-rays which has passed through the object to be analyzed through at least one grating,

d. Directing the X-rays towards at least one scintillator for converting the X- rays which has passed the at least one grating into light waves in the visible spectrum,

e. Detecting the light waves to obtain image information,

f. Analyzing the detected light waves to produce at least one dark field image of the object.

The method may further comprise one or more of the steps:

• Passing X-rays which has passed through the object to be analyzed through at least two gratings, such as a phase grating (Gl) and an analyzer grating (G2)

• Directing the X-rays through at least a third grating, such as a source

grating (GO), before the X-rays pass through the object to be analyzed,

• Directing the light waves into at least one optical element, such as at least one aspherical, e.g. cylindrical, lens,

• Directing the light waves emitted from the at least one aspherical lens into at least one camera to obtain image information from the light waves,

• Directing the image information to at least one processor, processing the image information by algorithms capable of analyzing the obtained information and capable of producing dark field images from the processed image information.

Analyzing of information to produce at least one dark field image of the object to be analyzed may further comprise analyzing the at least one dark field image to determine presence of bodies with refractive index different from the main part of the object to be analyzed, such bodies may be foreign bodies. Phase contrast images as well as absorption images may be obtained simultaneously with the dark field image. The different kind of images may be combined in an analysis of a product to be analyzed, e.g. dark field images and phase contrast images may be used for such an analysis.

The invention also relates to use of the system or of the method for analyzing an object, such as analyzing a food product such as meat, beverages, bread, cakes and biscuits, fruits, vegetables, convenience food, confectionary, dairy products. Brief description of figures

Fig. 1 illustrates an X-ray dark-field system e.g. for in-line inspection of objects.

Fig. 2 illustrates an example of an interference pattern to be detected by a detector.

Fig. 3 illustrates the principle of reconstruction of images. Detailed description of the invention

An aspect of the invention relates to a dark field radiology or tomography system, which system comprises: a. At least one X-ray source for emitting X-rays used to analyze an object, the X-rays at least being directed towards an object to be analyzed,

b. A movable object support such as a conveyor belt for supporting and

transporting an object to be analyzed during the analysis,

c. At least one grating located after the object support in the propagation direction of the emitted X-rays,

d. At least one scintillator for converting X-rays which has passed the at least one grating into light waves in the visible spectrum,

e. At least one detector sensitive in the visible part of the electromagnetic spectrum for detecting said light waves, and

f. At least a processor capable of analyzing detected light waves.

Preferably the dark field radiology or tomography system as described herein is used for food scanning such as for scanning of carcasses, meat pieces, minced meat, such as intermediate products or final products in the food industry. When scanning such products the purpose may be for identifying foreign objects which should not be present in food products, such foreign objects may be objects comprising fibers or other structures which interfere with the X-rays such that the interference is detectable in dark field X-ray. Such foreign objects may be lightweight fibrous material and may comprise wood, paper, cardboard, grains, straws, insects or parts hereof, etc. The X-ray source may be any suitable X-ray source. Preferred is X-rays with low energies such as below 100 keV. The X-ray source may be a conventional X-ray tube with an X-ray focal spot. The X-ray source may also be an X-ray source selected from the group of X-ray sources consisting of a hot filament X-ray source and a field emission X-ray source. The system comprises a movable object support such as a conveyor belt for supporting and transporting an object to be analyzed during the analysis. The analysis of the objects such as food products incl. meat pieces is to be performed quickly preferably with a conveyor belt speed used at abattoirs or other food producing companies. The movable object support is preferably a conveyor belt which can transport the object to be analyzed pass the X-ray source and the detection facilities. The objects to be scanned at an in-line scanning system may be transported with a speed of 20 m/min and if the detector has a pixel size of 0.5 cm the system should be capable of obtaining 500-700 such as 600 frames or images per second . The system may comprise one or two gratings located after the object support.

When the system comprises only a single grating in the form of a phase grating Gl located after the object support, the detector as described elsewhere herein preferably has many small pixels to be capable of detecting details in the interference pattern generated by the Gl grating and the product amendments. The system may further comprise one or more of the features:

• At least two gratings located after the object support in the propagation direction of the emitted X-rays, the grating may be a phase grating (Gl) and an analyzer grating (G2) which each may have grating elements that are parallel to each other, and the at least two gratings (Gl, G2) can be positioned after each other according to the propagation direction of the X- rays and with the phase grating Gl being located closest to the object support, and the gratings can be located such that the grating elements of the phase grating (Gl) and of the analyzer grating (G2) can be angled according to each other, • At least a third grating, such as a source grating (GO), located between the X-ray source and the object support,

• At least one optical element, such as at least one aspherical, e.g. cylindrical, lens located after the at least one scintillator,

· At least one camera located after the at least one optical element,

• At least one processor obtaining information at least from the at least one camera, the processor comprising algorithms capable of analyzing the obtained information and capable of producing dark field images,

• A radiation safe casing for shielding X-rays from escaping into the

surroundings.

The system may be based on a grating interferometry technique with two gratings located after the object support and where each grating comprises a number of linear grating elements. In such an installation grating elements of the phase grating (G l) and of the analyzer grating (G2) are preferably angled according to each other. The grating elements of the phase grating (Gl) will thus be misaligned when compared to the grating elements of the analyzer grating (G2). The phase grating (G l) and the analyzer grating (G2) should preferably both be fixed during the analysis where the objects to be analyzed are transported through the X-ray beam and a number of images are obtained of the moving object. The phase grating (Gl) creates an interference pattern of the received X-rays in the area between the phase grating (Gl) and the analyzer grating (G2), where the latter due to its location in respect to this interference pattern filter out specific interference relations and only let certain other interference relations pass to the scintillator. If the grating elements of the two gratings Gl and G2 are parallel these interference relations would be similar all over the scintillator and thus all over the camera's detector such that the pixel size of the detector is without importance for registration for the interference pattern. Even with large detector pixels it is thus possible to translate the analyzer grating (G2) and gradually filter out any displacement of the formed interference pattern. If the grating elements of the analyzer grating (G2) instead are located with a small angle to the grating elements of the phase grating (Gl) the created interference relations which can be registered by the camera will not be similar throughout the detection area. One of the axes of the camera will hereby correspond to a continuous displacement of the two grating's mutual location in contrast to the gradual displacement mentioned above. When transporting objects to be analyzed on a conveyor belt the translation of the object in a system with one of Gl and G2 angled with respect to the other can be performed e.g. parallel with the phase grating (G l) such that a certain section of an object will be registered with different interference relations by the camera at a certain time (t= l). A part of the same section e.g. a single row of pixels in the camera will at a slightly later time (t=2) be registered with a different interference relation at the neighbor row (r=2) of pixels in the camera. Again at a corresponding later time (t=3) the part of the section will be registered with a third interference relation at the next row (r=3) of pixels in the camera. This registering by the camera of a part of a section (e.g. a row) of an object with different interference relations can be performed until the time where the section (e.g. row) has passed the last row of pixels in the camera corresponding to the last interference relation between the phase grating (Gl) and the analyzer grating (G2). The phase grating (Gl) and the analyzer grating (G2) may be placed with an angle between the grating elements of the phase grating (Gl) and the grating elements of the analyzing grating (G2) corresponding to exactly on grating period of the phase grating (G l). The registration will hereby comprise a number of images of the object though as a large number of interference relations corresponding to the number of pixels in the camera along the moving direction of the conveyor belt. The recorded images of the object are analyzed by the processor with a

reconstruction algorithm capable of turning the images into at least one dark-field image. An automated image assessment algorithms aimed at large volume scanning may be included in the system. Hereby it becomes possible to identify e.g. light-weight fibrous material if present in or at the scanned object.

In a preferred embodiment all features of the system except the object support are stationary whereby the object support may transport an object to be analyzed pass the features of the system. Such a stationary system would be preferred for in-line systems for scanning e.g. intermediate products or final products in production environments in food producing companies.

The system may also be a system where all features of the system except the object support are configured to move as a single entity relative to an object of interest such that the single entity may move around the object support supporting and optionally transporting an object to be analyzed.

Further details of the X-ray dark field imaging apparatus are presented below. The X-ray dark field imaging apparatus may comprises an X-ray source configured to provide X-ray illumination at an exit port thereof; a source grating (GO) configured to receive the X-ray illumination at a source grating entrance port and configured to provide a plurality of X-ray beams at a source grating exit port; a phase grating (Gl) having a plurality of phase grating elements, the phase grating (Gl) situated at a distance I from the source grating (GO), the phase grating (Gl) configured to receive X-rays at a phase grating entrance port and to provide X-rays at a phase grating exit port; an analyzer grating (G2) having a plurality of analyzer grating elements, the analyzer grating (G2) situated at a distance d from the phase grating (Gl), the analyzer grating (G2) configured to receive X-rays at an analyzer grating entrance port and to provide X-rays at an analyzer grating exit port, the phase grating (Gl) and the analyzer grating (G2) having a fixed location and a fixed orientation relative to each other and with one of the phase grating (Gl) and analyzer grating (G2) slightly angled in respect of the other such that the phase grating elements of the two gratings are non-parallel in one dimension in the direction of the X-ray beams.

A scintillator may receive X-rays from the analyzer grating (G2) and exhibits flashes of lights producing a ight image' in the visible part of the electromagnetic spectrum corresponding to the 'X-ray image' received by the scintillator. The ight image' may exit the scintillator on the opposite site of the scintillator in respect of the scintillator side receiving the X-rays. The Night image' may be reflected out of the direction of the X-rays beams by a reflector, where a first aspherical, e.g.

cylindrical, lens converts the width or length of the light image into a dimension capable of being detected by a CCD camera (vision camera) or a video camera sensitive in the visible part of the electromagnetic spectrum; a second aspherical, e.g. cylindrical, lens converts the other of the width or length of the light image into another dimension capable of being detected by a CCD camera or a video camera. The final dimension of the Night image' may have a length-to-width relation of 4: 3, converted from an 'X-ray image' with e.g. a length-to-width relation of 10 :4. The conversion may thus be a contraction of the Night image' in the length and width, and this contraction may be different in respect of the length and width and may be performed sequential in any order. By directing the Night image' out of the direction of the X-rays, the detector such as a camera or video camera is not in the X-ray propagation direction whereby noise is reduced or omitted as noise would occur if the detector was in the X-ray propagation direction due to direct radiation into the detector. Furthermore when the detector is located out of the X-ray propagation direction the electronic elements of the camera are also protected from the X-rays. By selecting the aspherical lenses to convert the Night image' to a needed conversion factor it is possible to use any vision system as the detector. Hereby the degree of details which is required when analyzing a specific kind of objects can be adjusted as a compromise between the degree of details and the measuring velocity (capacity) by selecting between common cameras and aspherical lenses available on the market.

The system may further comprise a detector such as a camera or a video camera, in particular a video camera sensitive in the visible part of the electromagnetic spectrum positioned to receive light emitted from the scintillator and optionally converted by at least one aspherical lens. The detector may within a short receive a number of ight images' corresponding to a sequence of ight images' when an object is moved pass the phase grating (G l) and analyzer grating (G2) which are angled according to each other. As the object to be analyzed is moved and the detector at the same time receives Night images' of the scattered X-rays, each small section (point or pixel) of the object will be observed with different grating conditions because of the angled gratings. The Night images' are thus obtained with different grating conditions and an interference pattern is created which is to be analyzed. A number of these Night images' are required to produce an entire image of the object under transport. The number of Night images' which should be used to produce an entire image is dependent on how the phase grating (Gl) and the analyzer grating (G2) are angled according to each other e.g. 7 Night images' are required for one point where these 7 Night images' have different phase conditions.

The system may also comprise a controller, which in a CT-system may be configured to control the motion of the X-ray source, the source grating, the phase grating, the analyzer grating, the scintillator, the aspherical lenses, and the detector relative to the moving object of interest as a function of time.

An analyzer module which may be part of a processer may be configured to receive and record the images from the detector such as from a camera or from a video camera as a function of time, and be configured to manipulate the received signals with respect to time, configured to generate a dark field image of at least a portion of the object of interest from the received signals, and configured to perform at least one action selected from the group of actions consisting of recording the X-ray dark field image, transmitting the X-ray dark field image to a data handling system, and displaying the X-ray dark field image to a user. The analyzer module may be a general purpose programmable computer provided with instructions recorded on a machine readable medium. Algorithms may be used in the analyzer to analyze the images acquired by the detector.

Preferably the X-ray source, the source grating, the phase grating, and the analyzer grating, the scintillator, the aspherical lenses and the camera/video are configured to be stationary relative to an object of interest which is preferably moving during X-ray treating, such as being moved by a conveyor belt. However, the X-ray source, the source grating, the phase grating, and the analyzer grating, the scintillator, the aspherical lenses and the camera/video may also be configured to function as a unity and move around an object of interest which is preferably moving through the X-ray cone beam, such as being moved by a conveyor belt, hereby the system can be a CT-system e.g. with a conveyor belt transporting objects to be scanned through the CT-system and thus generating a helix trajection.

Another object of the invention relates to a method for obtaining dark field images of an object, the method may comprise the steps of a. Directing X-rays towards an area suitable for an object to be analyzed, b. Transporting an object to be analyzed substantially perpendicular to the X- ray propagation direction and transporting the object through the cone beam of X-rays,

d. Directing the X-rays towards at least one scintillator for converting the X- rays which has passed the at least one grating into light waves in the visible part of the electromagnetic spectrum,

e. Detecting the light waves to obtain image information,

f. Analyzing the detected light waves to produce at least one dark field image of the object to be analyzed.

The method may further comprise one or more of the steps:

• Passing X-rays which has passed through the object to be analyzed through at least two gratings, such as a phase grating (Gl) and an analyzer grating (G2),

• Directing the X-rays through at least a third grating, such as a source

grating (GO), before the X-rays pass through the object to be analyzed,

• Directing the light waves obtained from at least one scintillator into at least one optical element, such as at least one aspherical, e.g. cylindrical lens,

• Directing the light waves emitted by the at least one aspherical lens into at least one camera to obtain image information from the light waves,

• Directing the image information to at least one processor, processing the image information by algorithms capable of analyzing the obtained information and capable of producing dark field images from the processed image information. Preferably time is a part of the method to obtain Night images' which can be used to construct a dark field image of an object to be analyzed. With 'time' is meant that a number of ight images' are obtained in respect of a single point or a section of the object to be analyzed and these Night images' are obtained with different interference patterns as the object is moved along a single grating or along the angled phase grating (Gl) and the analyzer grating (G2) . A pre-defined number of Night images' are used to construct information for such a single object point or section in a dark field image. The pre-defined number of 'light images' used to construct a dark-field image may be e.g. 6, 7, 8, 9, 10 etc. The method may preferably comprise the steps of: a. Directing X-rays towards an area suitable for an object to be analyzed, b. Directing the X-rays through a source grating (GO),

c. Directing the X-rays which have passes the source grating (GO) towards an object to be analyzed, where the object is moving e.g. on a conveyor belt, d. Letting X-rays which has passed through the object to be analyzed through at least a phase grating (Gl) and an analyzer grating (G2),

e. Directing the X-rays further towards at least one scintillator for converting the X-rays which has passed the at least two gratings into light waves, f. Reflecting the light waves by a reflector such that the reflected light waves become non-parallel to the X-ray direction through the phase grating (Gl) and the analyzer grating (G2),

g. Directing the light waves through a first aspherical lens for converting the length or width into a dimension suitable for a camera,

h. Directing the light waves from step g) through a second aspherical lens for converting the length or width not converted in step g) into a dimension suitable for a camera,

i. Directing the light waves from step h) into at least one camera to obtain image information from the light waves,

j. Directing the image information to at least one processor, processing the image information by algorithms capable of analyzing the obtained information and capable of producing dark field images from the processed image information.

Analyzing of information to produce at least one dark field image of the object to be analyzed may further comprise analyzing the at least one dark field image to determine presence of bodies with refractive index different from the main part of the object to be analyzed, such bodies may be foreign bodies. The method may further comprise a step where the produced dark-field images or the images obtained by the camera or video camera are analyzed to identify if foreign bodies such as light-weight fibrous material are present in the analyzed object. If such foreign bodies are identified a further step of the method may include removing the analyzed object from the conveyor belt or production line or removing the foreign body or foreign bodies from the analyzed object. Removing foreign bodies is preferably only performed when the analyzed objects are meat pieces and the foreign bodies are located on the surface of the meat pieces. Objects with foreign bodies located inside the object are preferably not used for human food .

A further aspect of the invention relates to use of the system as described herein for analyzing an object, such as analyzing a food product such as meat, beverages, bread, cakes and biscuits, fruits, vegetables, convenience food, etc. optionally the use may be performed by the method as described herein. Meat pieces may be any meat piece. The use may be for analyzing meat pieces at abattoirs or other food producing companies for the presence of the foreign bodies. At abattoirs use of the method may be for analyzing boneless meat pieces or boneless meat products e.g . belly pieces and minced meat,

The use of the system is preferably for analyzing food products for determining whether foreign bodies are present in or at the food product.

Yet a further aspect of the invention relates to use of the method as described herein for analyzing an object, such as analyzing a food product such as a meat, beverages, bread, cakes and biscuits, fruits, vegetables, convenience food, etc. optionally the use may be performed in the system as described herein. According to another aspect, the invention relates to a method of making an X-ray dark field image of an object of interest. The method comprises the steps of passing X-rays generated by an X-ray source through, in succession, a source grating, an object of interest, a phase grating, an analyzer grating, and to a scintillator. The signal, i.e. the visible light emitted from the scintillator may be reflected away from the X-ray beam direction, converted by e.g. two aspherical lenses to a ight image' with a width-to-length ration of e.g. 3 :4 which is detected by a camera or a video camera sensitive in the visible part of the electromagnetic spectrum. Reconstruction algorithms are used to produce at least one dark field image based on light images obtained from an object. An image may be

reconstructed as described in respect of Fig. 3. Preferably the method is performed such that the X-ray source, the source grating, the phase grating, the analyzer grating, the scintillator, the aspherical lenses and the detector are stagnant and fixed relative to each other. The object to be analyzed can be transported e.g. by a conveyor belt through the X-ray beam during analysis. As described elsewhere the number of images/frames obtained may be about 600 per second. The time used to scan an object is thus dependent on the length of the object in the transport direction.

When performing the analysis in CT-scanning mode the method may be performed such that the X-ray source, the source grating, the phase grating, the analyzer, the scintillator, the aspherical lenses and the detector grating move as a single entity relative to an object of interest which may be under transport through the CT- scanner, the phase grating and the analyzer grating remaining in fixed relative location and fixed relative orientation with respect to one another.

The method further comprise analyzing the signals received by the camera or video camera representative of the X-rays as a function of time to generate an X-ray dark field image of the object of interest; and performing at least one action selected from the group of actions consisting of recording the X-ray dark field image, transmitting the X-ray dark field image to a data handling system, and displaying the X-ray dark field image to a user. The handling system may be a system handling analyzed objects such as removing analyzed objects where e.g. foreign bodies are identified from e.g. a conveyor belt.

Detailed description of the figures

Fig. 1 illustrates an X-ray dark-field system for e.g. in-line inspection of objects. X- rays are emitted from an X-ray source 1), are passing a source grating (GO) 2, pass an object 4 to be analyzed and which is transported by a movable object support 3 such as a conveyor belt. X-rays which have passed through the object pass through the movable object support 3 moving in a moving direction 14, a phase grating (Gl) 5, an analyzer grating (G2) 6 to a scintillator 7 where the X-rays are converted into visible light which by a reflector 8 are directed out of the X-ray propagation direction 13. Directing the visible light out of the X-ray propagation path has the advantage that the detector, i.e. the CCD or other image sensor, be it included in a camera or not, is not hit by the X-ray radiation which could cause undesired noise in the CCD or other image sensor, even if they are adapted to visual light. To utilize the detector in full, the ight image' obtained from the scintillator 7 is converted into a predetermined length-to-width ratio of e.g. 4: 3 by an aspherical, e.g. cylindrical, lens (A) 9 and an aspherical, e.g. cylindrical, lens (B) 10 such that the ight image' is suitable to become detected by a camera or video camera 11. Standard cameras come in more or less standardized aspect ratios and of course 4: 3 is not the only ratio that may be used . Since this part of the invention operates in the visible part of the electromagnetic spectrum, the optical

components used are readily available at low cost, due to mass production The detected signals from the ight image' are forwarded to a processer 12 capable of analyzing the signals and based on a number of such Night images' producing a dark field X-ray image or equivalent information capable of being analyzed in respect of e.g. the structure of the analyzed object such that e.g. foreign bodies on and/or in the object can be detected.

Fig. 2 illustrates an example of an interference pattern to be detected by a detector. The illustration is a single image or frame obtained when an object is transported in a system as described herein. Illustrated are a phase grating (Gl) 5 (shown as light grey), an analyzer grating (G2) 6 (shown as dark grey) and pixels of a detector (white squares) . To simplify the illustration no scintillator is illustrated. The phase grating (Gl) 5 and analyzer grating (G2) 6 are angled slightly according to each other. In this illustration the grating elements 16 of the analyzer grating are parallel to the pixel columns of the detector and the grating elements 15 of the phase grating are non-parallel to the pixels of the detector. The opposite could also be possible or both gratings 5, 6 could have grating elements being non-parallel to the pixel columns of the detector. Illustrated is also the moving direction of movable object support 14 and numbering of some of the pixels in the detector.

Illustrated is numbering of the pixels in the detector. The numbering first indicate the number of the row followed by the number of the column for a pixel (P). The figure illustrates in the first pixel row the pixels with the numbering Ρι,ι; P2 ; P3,i; and Ρχ,ι; X is the total number of pixel columns in the detector. The figure illustrates in the first pixel column the pixels with the numbering Ρι,ι; Pi, 2; Pi, 3 ; Pij; and Ρι,γ; Y is the total number of pixel rows in the detector and is an number between 1 and Y. The figure illustrates in the last pixel column the pixels with the numbering Ρχ,ι; Pxj; and Ρχ,γ; X multiplied with Y gives the total pixels of the detector. For the rows the row number may be represented by Y and where Y is a number between 1 and X.

During transport of an object through the X-ray cone beam a number of

images/frames are obtained of the object. An object section (i,j) will be depicted in pixel i,j at time ti also denoted Pi,j(ti), at pixel i,j+ l at time t2 denoted Pi,j+i(t2) and at pixel i,j+2 at time t3 denoted Pi,j+2(t3) etcetera until the specific object section has passed the last row of the detector. Hereby each object section of an object will be depicted Y-times corresponding to the number or rows in the detector.

Due to the scattering of the X-rays made by the phase grating (Gl) and analyzer grating (G2), and especially the difference of the scattering of X-rays from a single object section due to the angling between (Gl) and (G2), the images/frames obtained of an object/object section during the transport of the object are not similar to each other i.e. what Pi,j(ti) depicts need not be similar to what is depicted by Pi,j+i(t₂) and by Pi,j+2(t₃).

To produce a dark field image and/or phase contrast image all the images/frames of an object section are analyzed by a reconstruction algorithm to produce such a dark field image and/or phase contrast image of this object section. Performing such reconstruction for all object sections of an object result in the production of a dark field image and/or phase contrast image of the entire object. Such a dark field image and/or phase contrast image may be analyzed for the presence of e.g.

foreign bodies.

Fig. 3 illustrates the principle of reconstruction of images. The reconstruction of an image may be performed by combining images/frames obtained of an object section in different image lines which are obtained at different times of an object under transport. As the gratings causes differences in the images/frames obtained of an object section differences will occur among the different images/frames obtained, however in this figure the object is shown with an identical symbol, as only the principle of reconstruction is illustrated. The reconstruction is explained by illustrating a reconstruction of an object with a size of one pixel in the direction of transport. This object is under transport and is in this example moved one line between obtaining each image/frame. As an example 8 images/frames (frame 1 to 8) are illustrated, however another number of images/frames may be used for the reconstruction of an image. The reconstructed image for the object under transport is based on line 1 at t=l, line 2 at t=2, line 3 at t=3, line 4 at t=4, line 5 at t=5, line 6 at t=6, line 7 at t=7, and line 8 at t=8. By combining these images/frames from line 1 to 8 at time t=l to t=8 the reconstructed image for this object is obtained.

Most objects are larger than one pixel and a reconstructed image of such an object is based on the principle as described above for each line of the images/frames obtained when the object is under transport during examination. List of reference signs 1. X-ray source

2. Source grating, GO

3. Movable object support

4. Object to be analyzed

5. Phase grating, Gl

6. Analyzer grating, G2

7. Scintillator

8. Reflector

9. Aspherical lens A

10. Aspherical lens B

11. Camera or video

12. Processor

13. X-ray propagation direction

14. Moving direction of movable object support

15. Grating element of phase grating

16. Grating element of analyzer grating

Claims

ims

A dark field radiology or tomography system, said system comprising

a. At least one X-ray source for emitting X-rays used to analyze an

object, said X-rays at least being directed towards an object to be analyzed,

b. An movable object support such as a conveyor belt for supporting and transporting an object to be analyzed during the analysis, c. At least one grating located after said object support in the

propagation direction of said emitted X-rays, and

d. At least one scintillator for converting X-rays which has passed said at least one grating into light waves in the visible spectrum, e. At least one detector adapted to detect said light waves, and f. At least a processor capable of analyzing detected light waves.

The system according to claim 1, further comprising one or more of the features:

• The at least one grating is at least two gratings located after said object support in the propagation direction of said emitted X-rays, said grating are a phase grating (Gl) and an analyzer grating (G2) which each has grating elements that are parallel to each other, and said at least two gratings (Gl, G2) are positioned after each other according to the propagation direction of said X-rays and with said phase grating being located closest to said object support, and said gratings are located such that the grating elements of said phase grating (G l) and of said analyzer grating (G2) are angled according to each other

• At least a third grating, such as a source grating (GO), located

between said X-ray source and said object support,

• At least one optical element, such as at least one aspherical lens located after said at least one scintillator,

• Said at least one detector is at least one camera sensitive in the

visible part of the electromagnetic spectrum located after said at least one optical element,

• Said at least one processor obtaining information at least from said at least one camera, said processor comprising algorithms capable of analyzing said obtained information and capable of producing dark field images. The system according to any of the preceding claims, wherein all features of the system except said object support are stationary whereby said object support may transport an object to be analyzed pass said stationary features of the system.

The system according to any of the preceding claims 1 to 2, wherein all features of the system except said object support are configured to move as a single entity relative to an object of interest such that said single entity may move around said object support supporting and transporting an object to be analyzed .

A method for obtaining dark field images of an object, said method comprising the steps of

a. Directing X-rays towards an area suitable for an object to be

analyzed,

b. Transporting an object to be analyzed substantially perpendicular to the X-ray propagation direction and transporting said object through the cone beam of X-rays,

c. Passing X-rays which has passed through said object to be analyzed through at least one grating,

d. Directing said X-rays towards at least one scintillator for converting said X-rays which has passed said at least one grating into light waves in the visible part of the electromagnetic spectrum,

e. Detecting said light waves to obtain image information,

f. Analyzing said detected light waves to produce at least one dark field image of said object.

The method according to claim 6, further comprising one or more of the steps:

• Passing X-rays which has passed through said object to be analyzed through at least two gratings, such as a phase grating (Gl) and an analyzer grating (G2),

• Directing said X-rays through at least a third grating, such as a

source grating (GO), before said X-rays pass through said object to be analyzed,

• Directing said light waves into at least one optical element, such as at least one aspherical lens, • Directing said light waves emitting said at least one aspherical lens into at least one camera sensitive in the visible part of the

electromagnetic spectrum to obtain image information from the light waves,

• Directing said image information to at least one processor, processing said image information by algorithms capable of analyzing said obtained information and capable of producing dark field images from said processed image information.

The method according to any of the claims 5 or 6, wherein said method comprises the steps of:

a. Directing X-rays towards an area suitable for an object to be

analyzed,

b. Directing said X-rays through a source grating (GO),

c. Directing said X-rays which have passes said source grating (GO) towards an object to be analyzed, where said object is stationary or moving on a conveyor belt,

d. Letting X-rays which has passed through said object to be analyzed through at least a phase grating (Gl) and an analyzer grating (G2), e. Directing said X-rays further towards at least one scintillator for converting said X-rays which has passed said gratings into light waves in the visible part of the electromagnetic spectrum, f. Reflecting said light waves by a reflector such that said reflected light waves become non-parallel to the X-ray direction through said phase grating (G l) and said analyzer grating (G2),

g. Directing said light waves through a first cylindrical lens for

converting the length or width into a dimension suitable for a camera,

h. Directing said light waves from step g) through a second cylindrical lens for converting the length or width not converted in step g) into a dimension suitable for a camera,

i. Directing said light waves from step h) into at least one camera to obtain image information from the light waves,

j. Directing said image information to at least one processor, processing said image information by algorithms capable of analyzing said obtained information and capable of producing dark field images from said processed image information.

8. The method according to any of the claims 5 to 7, wherein said analyzing of information to produce at least one dark field image of said object to be analyzed further comprises analyzing said at least one dark field image to determine presence of bodies with refractive index different from the main part of said object to be analyzed, such bodies may be foreign bodies.

9. Use of the system according to any of the claims 1 to 5 for analyzing an object, such as analyzing a food product such as meat, beverages, bread, cakes and biscuits, fruits, vegetables, convenience food, etc. optionally said use is performed by the method according to any of the claims 6 to 8.

10. Use of the method according to any of the claims 6 to 8 for analyzing an object, such as analyzing a food product such as meat, beverages, bread, cakes and biscuits, fruits, vegetables, convenience food, etc. optionally said use is performed in the system according to any of the claims 1 to 5.