WO2008017369A2

WO2008017369A2 - Method for measuring an object using an x-ray sensor system

Info

Publication number: WO2008017369A2
Application number: PCT/EP2007/006402
Authority: WO
Inventors: Marco Erler
Original assignee: Carl Zeiss Industrielle Messtechnik Gmbh
Priority date: 2006-08-05
Filing date: 2007-07-19
Publication date: 2008-02-14
Also published as: WO2008017369A3; DE102006036692A1

Abstract

The invention relates to a method for measuring an object (1; 103) using an X-ray sensor system having an X-radiation source (101) emitting X-rays (102) in the direction of the object (1; 103) and a detector (106) detecting the X-rays (102), wherein the surface of the object (1; 103) is brought into contact with a substance (6) which has an X-ray attenuation coefficient which is higher than the X-ray attenuation coefficient of the material of the surface of the object (1; 103).

Description

Method / to measure an object by means of X-ray analysis

The invention relates to a method for measuring an object by means of an X-ray sensor system. which emits X-rays and a substance which absorbs X-rays. The invention also relates to the use of a substance for attenuating x-rays directed at the object.

Using X-ray sensors, an object can be X-rayed and the resulting image examined. Particularly efficient fluoroscopy and examination can be achieved with computed tomography. In comparison with conventional X-ray images, it has the advantage that no overlapping of image features occurs and the object can be viewed and evaluated in individual cross-sectional layers. Such a procedure works well and reliably. Difficulties can arise, however, if the object to be examined has a plurality of materials which cause a greatly different weakening of the incident X-rays.

After passing an X-ray beam through a highly attenuating material in an object, the X-ray beam hardly has low energy components so that the bremsstrahlung spectrum has a higher level of high energy radiation than low energy radiation. An X-ray beam is always "harder" after passing through the object than before it has passed through the object, so that a weakly absorbing material, which is also present in the object to be examined, is penetrated by hard radiation with almost no weakening, so that it is in one Such a situation occurs, for example, in a plastic part which is riddled with metal wires in its interior A brake radiation spectrum suitable for the examination of such an object is set by the selection of the tube high voltage such that all object points Generally, the gray value is not linearly dependent on the tube high voltage (ie the generated spectrum) and linearly dependent on the tube current (ie the beam intensity) absorbing object parts a ..ha rtes "spectrum with a relatively high Tube high voltage must be selected, the intensity can not be chosen arbitrarily. Weakly absorbing object parts thus cause only little change in intensity and produce only a low contrast at the detector. If the object to be examined also consists of plastic on its outer surface, the edges of the object in front of the object background can only be inaccurately determined. In this case, metrological examinations on the object are subject to a large measurement uncertainty.

Alternatively, if X-rays with a relatively narrow frequency band are used ("monochromatic spectrum"), filtering out of "soft" radiation by the object can be excluded, but also in this case materials with low X-ray attenuation are difficult or impossible to achieve Background, which also weakens X-rays only slightly.

It is therefore an object to present objects with materials which strongly and slightly weaken X-rays by means of X-ray sensor technology in such a way that the contour can be determined by the low and strongly weakening materials with a low measurement uncertainty.

This object is achieved by a method having the features of claim 1. Advantageous embodiments emerge from the features of the dependent claims.

In the method according to the invention for measuring an object by means of X-ray sensor system which has an X-ray source which emits X-rays towards the object and a detector which detects the X-rays, the surface of the object is brought into contact with a substance which forms an X-ray source. Has attenuation coefficient higher than the X-ray attenuation coefficient of the material of the object surface.

This makes it possible to delineate more clearly the contour of an object in front of the object background in an X-ray image. The surface of the object then appears with a grayscale contrast in front of the background, so that materials which form the outer surface of an object and relatively weakly absorb and scatter X-rays can be identified. In addition, highly debilitating materials in the Radiography continues to be well recognized. On the one hand, the selection of the substance can be made dependent on which material the object surface is made up of. If the object surface has different materials, the substance can be selected according to which material is present at a location of particular interest for a metrological examination. It should be noted that the term "surface" means, on the one hand, an outer surface that is visible from the outside, and on the other hand, it may be a surface that lies in the region of an object that is separated from a substance only by a gap Pore, an undercut or the like, although accessible from the outside, but from the outside is no longer visible., Such access is preferably without further aids (eg injection needle) possible.

Preferably, the method uses a substance having an X-ray attenuation coefficient higher or lower than the attenuation coefficient of each material contained in the interior of the object which is not contained in the surface of the object. This not only better captures the contour of the object against the background. In addition, the substance can always be easily distinguished from the material that is inside the object, without the need for direct contact with the substance. This increases the security in the evaluation of image information. Furthermore, materials that are not accessible from the outside can be reliably identified.

It is advantageous if a fluid is used as the substance. A fluid can be applied relatively easily to an object. This can be done, for example, by immersing the object in the substance and remaining immersed in this substance during X-ray irradiation. The distance traveled by the X-rays through this substance, the intensity of the radiation, which can still be detected by the arranged behind the object detector. If the beam intensity can only be increased insignificantly due to the X-ray source used, the object can only be wetted with the substance. In this case, the goal is to achieve wetting that is as complete as possible, whereby only partial wetting is sufficient if only certain areas of the object are to be measured. Wetting of the surface is preferable to a complete immersion of the object in the substance, even if that Object has very small dimensions. This ensures that the X-rays are still absorbed to a significant extent by the object and not by the substance. In this way, even with small parts, a lower measurement uncertainty can be achieved than without the use of a substance.

As an alternative to a fluid, it is also possible to use a powder or a very fine-grained material with any desired X-ray attenuation. By vibration, it is possible to densify such a powder well, so that the object to be examined is well wrapped. Thus, as described above, also the contour of the object can be detected well.

Preferably, the substance with which the surface of the object comes into contact, iodine or barium. Iodine has the atomic number 53, and barium has the atomic number 56. Since the X-ray absorption is proportional to the third power of the atomic number, these elements can be used as so-called "positive contrast agents." They therefore increase the contrast to an object. which has elements with a lower atomic number.

Preferably, the substance used is an aqueous solution which has a dissolved salt based on iodine and an alkali metal or alkaline earth metal. This can be, for example, sodium iodide. Such a substance is advantageous since it has a very high solubility in water, dissolves rapidly at room temperature, does not react with plastics, iron and aluminum in the dissolved state and can be used to produce concentrations whose X-ray attenuation coefficient corresponds approximately to that of iron. It is also advantageous that sodium iodide is harmless to health, can be washed off a surface without discoloration and can be produced in a wide concentration range. In addition, sodium iodide does not decompose or decompose for long periods of time (years), is insensitive to light, and is chemically stable at room temperature or temperatures common in sample pretreatments.

Instead of sodium iodide, other salts of iodine may be used. Care must be taken that no metal is present in the test object which has a lower electronegativity coefficient than the metal of the salt. Otherwise it could happen that the iodine reacts chemically with the metal of the measurement object and, for example, the surface of the object is attacked. Alternatives to sodium iodide may also be salts of triiodo-benzoic acid as water-soluble contrast agents or oily iodine compounds.

The invention also relates to the use of a substance for attenuating X-rays directed at an object to be measured. According to the invention, it is proposed to bring the substance into contact with a surface of the object to be examined. The term "surface" here primarily refers to a surface that is accessible from the outside without further aids, and which does not necessarily have to be visible from the outside.Thus, in addition to an interior region of an object, an outside area of an object to be measured, for example an X-ray, can be easily weakened In this way, the contour of the object can be better recognized in an X-ray image, the substance preferably having iodine, since iodine has a high attenuation coefficient for X-rays.

Advantages and developments of the invention will be explained with reference to the following figures, in which:

Fig. 1 is a schematic, highly simplified representation of a computer tomograph; Fig. 2 is an X-ray image showing a side view of an object to be measured which is partly in contact with an X-ray absorbing substance; FIG. 3 shows a first reconstructed recording of a plane through the object, taken along the section line A-A in FIG. 2, by means of a computer tomograph; FIG. FIG. 4 shows a second reconstructed recording of a plane through the object, taken along the section line B-B in FIG. 2, by means of a computer tomograph; FIG. 5 shows a schematic cross-sectional view for explaining the sectional plane B-B in FIG.

2; and FIG. 6 shows a third reconstructed recording of a plane through the object, made by means of a computer tomograph, along the section line C-C in FIG. 2.

FIG. 1 shows a schematic representation of a computer tomograph. The computer tomograph 100 has an X-ray source 101, the X-rays 102 kegelstrahlföπnig in the direction of an object to be examined 103 emits. The cone-shaped beams 102 strike the object 103, which is movably mounted on a manipulator 104 relative to the x-ray source 101, see reference numeral 105, and are partially absorbed, scattered, or transmitted. A detector 106 arranged behind the object 103 detects the X-rays 102 which have passed through the object 103. The detector 106 records a multiplicity of images depending on an angular position of the object 103 relative to the X-ray source 101. With a data processing 107, these images can be processed in such a way that a three-dimensional structure of the object 103 can be created ("reconstruction"), by which any desired cross-sections can subsequently be laid.

FIG. 2 shows a side view of an object 1 in a container 2, which was created by an X-ray image. The object 1 is an injection-molded part which has been placed vertically in the container, the lower portion of the injection-molded part being in a substance 6, which in this embodiment is formed as an aqueous solution based on iodine. The object 1 has a housing 3 made of plastic, wherein within the housing 3 metallic leads 4 extend in the vertical direction. In the upper area of the injection-molded part, a metallic part 5 can be seen centrally, which appears in a dark gray value in the X-ray image. This suggests that the part 5 has a higher X-ray attenuation coefficient than the metallic leads 4, which appear in a lighter gray value. The container 2 is shown with a very light gray value, mainly the funnel-shaped outer contour 7 can be seen; Sporadically horizontal transverse grooves 8 of the container 2 are visible. Due to the differences in gray value between container 2 and object 1, it becomes clear that the plastic of the container 2 weakens fewer x-rays than the plastic of the object 1. A high attenuation is achieved by the substance 6, which appears in Fig. 2 in a very dark gray value. The lower portion of the object 1 is no longer visible in the substance 6.

If the object 1 and the container 2 with the substance 6 are placed on a manipulator 9 and rotated about their own axis in, for example, 800 angular steps during a complete revolution, then these captured images can be evaluated by a data processing so that sectional views along several Create layers to let. FIGS. 3 to 4 show cross sections through the object 1 and the container 2 in a negative representation (strongly weakening regions in a light gray value, low-weakening regions in a dark gray value). FIG. 3 shows a cross section along the line AA drawn in FIG. In this level are only the plastic of the container 2, the plastic of the object 1 and the metallic leads 4 within the injection molded part. The reconstructed image of this plane shows the metallic leads 4 in a light gray value and radiating lines 10 in an extension to a row of the metallic leads 4, wherein the radiating lines appear in a dark gray value. Between the individual metallic leads 4 of a row very dark areas 1 1 can be seen.

The radiating lines 10 and the dark areas 11 are artifacts that have no actual correspondence in the object. They are undesirable in the figure, but can not be avoided for objects with differently absorbent materials without the use of the method according to the invention. They arise from the fact that, after the passage of X-rays through, for example, metals with a high attenuation coefficient, relatively low-energy X-ray components are absorbed and scattered by these metals, so that only "hard" radiation is available for further passage through an object ( "beam hardening"). Hard radiation is no longer weakened by materials with low X-ray attenuation coefficients, so that faulty image information is determined in the presence of low-attenuation materials. Furthermore, in FIG. 3 lines 12 can still be seen in a lighter grayscale, which correspond to a plastic of the housing 3; not visible are the container 2 and the outer periphery of the object 1. An image as shown in Fig. 3 has the disadvantage that on the one hand artifacts are displayed. On the other hand, real existing edges of an object to be measured are sometimes not or almost not recognizable. An image shown in FIG. 3 corresponds to a computed tomography image without the use of the method according to the invention.

The image shown in Fig. 4 shows a cross section along the plane BB in Fig. 2. In this plane, the substance 6 is very thinly brought into contact with the object 1 according to an embodiment of the invention. The substance 6 wets the surface of the object 1 so that X-rays pass through only a relatively thin but intensely debilitating layer. Radiating lines 10 can be seen in less pronounced form than in FIG. By contrast, the inner circumference of the container 2 and the object 1 can be seen more clearly. The inner circumference of the container 2 is shown with a circular line 13 and the outer periphery of the object I by a line 14, both lines 13. 14 appear in a middle gray value. A comparison with Fig. 3 shows that in Fig. 3, the line 14 is very weak and the line 13 is not visible at all. In Fig. 4 they appear as accurately measurable lines, since the substance 6 is in contact both with the inner periphery of the container 2 and with the outer periphery of the object 1. Even within the object gray scale gradations are still visible, see reference numeral 15.

The space between the inner circumference of the container 2 and the outer periphery of the object 1 is not filled by the substance 6 in this sectional plane BB, since the sectional plane runs just above the central liquid surface. Fig. 5 shows the course of the sectional plane BB schematically in an enlargement. The thin wetting of the inner circumference of the container 2 and the outer periphery of the object 1 is explained by the positive adhesive tension of the substance, which causes the substance 6 to creep upwards in the boundary region between substance 6 and plastic of the object 1 or plastic of the container 2 , so that in each case a contact angle θ _\ or θi is formed.

The metallic leads 4 are visible in Fig. 4 in a slightly lighter gray value than the plastic sheath 14 of the object 1 or the inner periphery 13 of the plastic container 2. This shows that there is a small but still present difference in the attenuation of X-rays between the metallic leads 4 and the substance 6. Radiating lines 10 are less pronounced than in the illustration in Fig. 3, since there is less hardening of the X-rays. This representation, shown in FIG. 4, enables a more accurate measurement of the object 1 composed of materials having different attenuation coefficients.

The reconstructed image shown in Fig. 6 shows a section through the plane CC in Fig. 2. The X-rays pass here a greater distance through the substance 6, so that a strong attenuation of the X-rays takes place. The object 1 arranged in the center of the container 2 is barely recognizable, so that on the basis of this image no precise measurement can be made. An immersion of the object 1 in the substance 6 results in the selected beam intensity and the selected path length through the substance 6 too strong absorption of X-rays. A comparison between the images in FIGS. 3, 4 and 6 leads to the result that the object 1 used can be measured very well at the selected parameters by means of X-rays if its surface is only wetted with a substance which attenuates X-rays.

Claims

claims

Method for measuring an object (1; 103) by means of X-ray sensor system which has an X-ray source (101) which emits X-rays (102) in the direction of the object (1; 103) and a detector (106) which detects the X-rays (102), wherein the surface of the object (1; 103) is brought into contact with a substance (6) having an X-ray attenuation coefficient higher than the X-ray attenuation coefficient of the material of the surface of the object (1; 103).

A method according to claim 1, wherein a substance (6) having an X-ray attenuation coefficient higher or lower than the X-ray attenuation coefficient of each material contained in the interior of the object (1; Surface of the object (1; 103) is included.

3. The method according to claim 1 or 2, wherein as the substance (6) a fluid or a powder is used.

A method according to any one of claims 1 to 3, wherein the surface of the object (1; 103) is brought into contact with the substance (6) by immersing the object (1; 103) in the substance.

5. A method according to any of claims 1 to 3, wherein the surface of the object (1; 103) is brought into contact with the substance by wetting the object (1; 103) with the substance (6).

6. The method according to any one of claims 1 to 5, wherein the substance (6) comprises iodine or barium.

7. The method according to any one of claims 1 to 6, wherein as the substance (6) an aqueous solution is used, which comprises a dissolved salt based on iodine and an alkali metal or alkaline earth metal.

8. Use of a substance (6) for attenuating X-rays (102) directed onto an object (1; 103) to be measured, wherein the substance (6) is brought into contact with a surface of an object to be examined (1;

9. Use according to claim 8, wherein the substance (6) comprises iodine.