METHOD FOR DETERMINING A RELATIVE POSITION OF AN OBJECT IN RELATION TO AN X-RAY IMAGING APPARATUS

Abstract

A method is provided for determining a relative position of an object in relation to an x-ray imaging apparatus for creating an x-ray and a recorded image. The method includes brining an object in a ray path of the x-ray into a first position. The x-ray is created with a first focus point by an x-ray source and a first recorded image of the object in the first position is created by the x-ray focused on a first focus point. In the first recorded image, at least one defined geometry in and/or on the object is imaged. A measure for a change in the focus point towards a second focus point is undertaken at the x-ray source. The x-ray with the second focus point is created by the x-ray source and a second recorded image of the object in the first position is created by the x-ray focused on the second focus point. In the second recorded image, the at least one defined geometry is imaged. A distance from the object to the x-ray source and/or to the x-ray detector is determined based on the change in the focus point, as well as on the basis of the imagings of the at least one defined geometry in the first and the second recorded image.

Claims

1. A method for determining a relative position of an object in relation to an x-ray imaging apparatus having an x-ray source with a variable focus point for creating an x-ray and an x-ray detector for creating a recorded image, the method comprising: bringing the object in a ray path of the x-ray into a first position, wherein the x-ray is created with a first focus point by the x-ray source and by the x-ray focused on the first focus point; creating a first recorded image of the object in the first position, wherein at least one defined geometry in the object and/or on the object is imaged in the first recorded image; undertaking a measure for a change in focus point towards a second focus point at the x-ray source, wherein the x-ray with the second focus point is created by the x-ray source and by the x-ray focused on the second focus point; creating a second recorded image of the object in the first position, wherein the at least one defined geometry is imaged in the second recorded image; and determining a distance from the object to the x-ray source and/or to the x-ray detector based on the change in the focus point and the imagings of the at least one defined geometry in the first recorded image and the second recorded image.

2. The method of claim 1, wherein a same part of a collimator of the x-ray source is imaged in both the first recorded image and the second recorded image, wherein a value of the change in the focus point is established based on the respective imaging of the part of the collimator in the first recorded image and the second recorded image, and wherein the value of the change is included for the determination of the distance of the object to the x-ray source and/or to the x-ray detector.

3. The method of claim 2, wherein the at least one defined geometry in the object comprises a tissue structure of a patient, a structure implanted into the patient, or a combination thereof.

4. The method of claim 2, wherein a marker is attached to a part of a body of a patient, and wherein the marker is imaged as the at least one defined geometry on the object.

5. The method of claim 2, wherein a plurality of defined geometries each at a different distance from the x-ray source and/or from the x-ray detector is imaged in the first recorded image and the second recorded image, wherein the respective distance to the x-ray source or to the x-ray detector is established for each defined geometry of the plurality of defined geometries, and wherein the distance of the object to the x-ray source or to the x-ray detector is established based on the established distances of the plurality of defined geometries.

6. The method of claim 2, wherein structures imaged in the first recorded image are related to a reference point, wherein, in the second recorded image, a change in the corresponding imaged structures in relation to the reference point occurring through the change in the focus point is corrected such that the structures imaged in the second recorded image each have a same relationship to the reference point as the respective structures imaged in the first recorded image, and wherein a corrected second recorded image is created based on this same relationship to the reference point.

7. The method of claim 1, wherein the at least one defined geometry in the object comprises a tissue structure of a patient, a structure implanted into the patient, or a combination thereof.

8. The method of claim 1, wherein a marker is attached to a part of a body of a patient, and wherein the marker is imaged as the at least one defined geometry on the object.

9. The method of claim 1, wherein a plurality of defined geometries each at a different distance from the x-ray source and/or from the x-ray detector is imaged in the first recorded image and the second recorded image, wherein the respective distance to the x-ray source or to the x-ray detector is established for each defined geometry of the plurality of defined geometries, and wherein the distance of the object to the x-ray source or to the x-ray detector is established based on the established distances of the plurality of defined geometries.

10. The method of claim 1, wherein structures imaged in the first recorded image are related to a reference point, wherein, in the second recorded image, a change in the corresponding imaged structures in relation to the reference point occurring through the change in the focus point is corrected such that the structures imaged in the second recorded image each have a same relationship to the reference point as the respective structures imaged in the first recorded image, and wherein a corrected second recorded image is created based on this same relationship to the reference point.

11. The method of claim 10, wherein a video sequence is created based on the first recorded image and the corrected second recorded image.

12. A method for automatic positioning of an object in relation to an x-ray imaging apparatus having an x-ray source with a variable focus point to create an x-ray and an x-ray detector to create a recorded image, the method comprising: predetermining a required distance of the object to the x-ray source and/or to the x-ray detector; bringing the object in a ray path of the x-ray into a first position, wherein the x-ray is created with a first focus point by the x-ray source and by the x-ray focused on the first focus point; creating a first recorded image of the object in the first position, wherein at least one defined geometry in the object and/or on the object is imaged in the first recorded image; undertaking a measure for a change in focus point towards a second focus point at the x-ray source, wherein the x-ray with the second focus point is created by the x-ray source and by the x-ray focused on the second focus point; creating a second recorded image of the object in the first position, wherein the at least one defined geometry is imaged in the second recorded image; and determining an actual distance of the object to the x-ray source and/or to the x-ray detector based on the change in the focus point and the imagings of the at least one defined geometry in the first recorded image and the second recorded image; and changing a relative position of the object in relation to the x-ray imaging apparatus as a function of the predetermined required distance and the actual distance determined.

13. The method of claim 12, wherein a radiation dose of the x-ray source is set as a function of the established actual distance from the object to the x-ray source.

14. An x-ray imaging apparatus comprising: an x-ray source having a variable focus point configured to create an x-ray; and an x-ray detector configured to create a recorded image, wherein the x-ray imaging apparatus is configured to determine a distance from the object to the x-ray source and/or to the x-ray detector based on at least two different imagings of defined geometries on or in an object positioned in a ray path of the x-ray, which is shown on at least two different recorded images of the x-ray imaging apparatus when the at least two different recorded images have each been recorded with x-rays with a different focus point.

15. The x-ray imaging apparatus of claim 14, wherein the x-ray imaging apparatus is a C-arm device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] An exemplary embodiment of the disclosure is explained below based on the figures. In the figures, in schematic diagrams in each case:

[0032] FIG. 1 depicts an example of a C-arm device in a cross-sectional diagram.

[0033] FIG. 2 depicts an example of a determination of the distance from an object in the C-arm device according to FIG. 1 by various focus points in the x-ray source in a geometrical diagram.

[0034] FIG. 3 depicts an example of two recorded images of the C-arm device according to FIG. 1 created by different focus points.

[0035] FIG. 4 depicts an example of an x-ray tube in a longitudinal cross-section.

[0036] FIG. 5 depicts an example of a method for determining a relative position of an object in relation to the C-arm device according to FIG. 1 in a block diagram.

[0037] Parts and variables corresponding to one another are provided with the same reference characters in all figures in each case.

DETAILED DESCRIPTION

[0038] FIG. 1 depicts a schematic in a cross-sectional diagram of an x-ray imaging device 1, which in the present example is embodied as a C-arm device 2. The C-arm device 2 has a C-arm 4, on which at the end 6 shown at the top in the diagram an x-ray tube 8 is arranged as an x-ray source 10. Furthermore collimators 12 are arranged in the immediate vicinity of the x-ray tube 8 at the upper end 6 of the C-arm 4, which align an x-ray 14 generated by the x-ray tube 8 on a ray path 16. An x-ray detector 20 is arranged on the end 18 of the C-arm 4 shown at the bottom in FIG. 1. Not shown here in FIG. 1 are additional components for signal processing and bundling of the image data 20 created by the x-ray detector 18.

[0039] The C-arm 4 furthermore has a control unit 26 within its housing 24, which is configured to create finished recorded images 28 from the image data 20 and also control all the relevant processes for the creation of the recorded images 28 in the x-ray imaging apparatus 1, thus for example the start time and the value of the anode voltage of the x-ray tube 8, or also the respective operating voltages of detector modules in the x-ray detector 18. The control unit 26 is shown here for the sake of simplicity as an integrated unit but may also be realized however by different decentralized units, which take over the required functions. The control unit 26 here has the required number of processors, physical memory chips, microcontrollers, baseboards, and the like.

[0040] The housing 24 of the C-arm 4 is mounted on a chassis 30, so that the C-arm device 2 as such for creating the recorded images 28 may be moved to different deployment locations, and moreover is able to be moved in relation to a patient 32 of whom a region of their body is to be imaged by x-ray imagings. The patient 32 lies on a patient couch 34 here. In order now to image an object 36, (e.g., a part of the body of the patient 32 or also a bone structure by the C-arm device 2), the C-arm 4 on the chassis 30 will be brought into a suitable position in relation to the patient 32 for this purpose. The recorded images 28 created may then be output via a data connection 38 to a computer not shown in any greater detail for graphical display etc.

[0041] During the creation of the recorded images 28, however, the distance DSO from the object 36 to the x-ray source 10 is unknown, as is the distance DOI from the object to the x-ray detector 18. Only the fixed predetermined distance DSI from the x-ray source 10 to the x-ray detector 18 is known here. In a way still to be illustrated, the distance DSO and also the distance DIO may now be determined based on the various recorded images, which are each created with a different focus point in the x-ray tube 8.

[0042] FIG. 2 depicts schematically in a geometrical illustrative diagram the ray path 16 for the x-ray 14 according to FIG. 1, wherein to create the ray 14 in FIG. 2 a first focus point 40 is used once and a second focus point 42 is used once. The diagram in FIG. 2 is not to be seen here as true-to-scale. The distance DSO from the x-ray source 10 to the object 36 or also the distance DOI from the object to the image plane 46 and thus to the detector 18 may be established here as the relative position PR of the object 36 (which is given by a part of the body or a body tissue structure of the patient 32 according to FIG. 1). For the x-ray focused on the first focus point 40, an edge 44 of the collimator 12 in the image plane 46, which is given by the x-ray detector 18, is imaged at IK1 (dotted-line ray). A defined geometry 48 in the object 36, which is given in the present case by a delimitation of a bone 50, is imaged by the x-ray focused at the first focus point 40 on a point IG1 in the image plane 46 (dotted-line ray). The corresponding image points in the image plane 46 for the edge 44 of the collimator 12 and for the geometry 48 are given by the x-ray focused on the second focus point 42 by IK2 or IG2 (dashed ray in each case).

[0043] Because the vertical distance DSK from the first focus point 40 or second focus point 42 to the edge 44 of the collimator 12 for both focus points 40, 42 may be assumed in the present example as the same (if this assumption is not made, the respective vertical distances of the focus points 40, 42 to the edge 44 are still known, the equations below are to be adapted here in a simple manner), and is known, the distance DF between the first focus point 40 and the second focus point 42 may be established from the distance DSI between the x-ray source 10 and the x-ray detector 18, the distance DSK from a focus point to the edge 44 of the collimator 12 as well as from the distance DIK of the two image points IK1 and IK2 in the image plane 46 via a simple set of rays. The result is provided in equation (i) below:

DF=DSK.Math.DIK/(DSIDSK)(i)

[0044] On the basis of the distance DF of the two focus points 40, 42 established in this way, using similar considerations, the distance DSO from the x-ray source 10 to the object 36 may be established from the distance DIG of the two image points IG1 and IG2 of the defined geometry 48 as provided in equation (ii) below:

DSO=DF.Math.(DSIDSO)/DIG=>DSO=DF.Math.DSI/(DF+DIG),(ii)

with DF according to equation (i). A determination of the distance DIO from the object 36 to the x-ray detector 18 may be carried out in a similar way. Instead of the edge of the bone 50, or in addition thereto, a separately provided marker, not shown in any greater detail in FIG. 2, may be attached to the object 36 as the defined geometry.

[0045] FIG. 3 depicts a schematic of a view of a first recorded image 28a and a second recorded image 28b in the setup shown in FIG. 2, wherein the first recorded image 28a has been created with an x-ray 14 focused on the first focus point 40, and the second recorded image 28b with an x-ray focused on the second focus point 42. Clearly to be seen in the second recorded image 28b is the relative shift of the image points IG2 and IK2 of the defined geometry 48 or of the edge 44 of the collimator 12 in relation to the corresponding image points IG1, IK2, as well as the distances DIG, DIK resulting herefrom, based on which by the geometrical considerations shown in FIG. 2, the distance DSO from the x-ray source 10 to the object 36 or the distance DOI from the object 36 to the x-ray detector 18 is determined.

[0046] FIG. 4 depicts a schematic diagram of a longitudinal section of an x-ray tube 8, which as well as a cathode 51 has a rotating anode 52 as well as deflection coils 54. By the deflection coils 54, the focal spot is able to be changed on the rotating anode 52, by different strengths of deflection current being applied to the deflection coils and thus creating different strengths of magnetic field to deflect the electron beam 56. The electron beam 56 in this case may be directed to a first focal spot 58 on the rotating anode 52, so that the x-ray 14 resulting herefrom is focused on the first focus point 40, which coincides with the first focal spot 58 (dotted lines). With a change in the deflection current in the deflection coils 54, the electron beam 56 may be directed to a second focal spot 60, so that the x-ray 14 resulting herefrom is focused on the second focus point 42, which coincides with the second focal spot 60 (dashed lines).

[0047] FIG. 5 depicts schematically in a block diagram a method for determining a relative position of an object 36 in relation to an x-ray imaging apparatus 1 according to FIG. 1. In an act S1, the object 36 is brought into the ray path 16 of the x-ray 14. In the present example, a marker 62 is also attached to the object. In an act S2, a first recorded image 28a of the object 36 is created, in which inter alia the marker 62 is able to be resolved as a defined geometry 48. For the first recorded image 28a, the x-ray 14 is focused on the first focus point 40. Now, in an act S3, the first focus point 40 is shifted towards the second focus point 42, e.g., using a change in the deflection current in the deflection coils 54 according to FIG. 4. In an act S4, a second recorded image 28b of the object 36 is created by the x-ray 14 focused on the second focus point 42. Now, in an act S5, based on the different imagings in the first recorded image 28a and the second recorded image 28b of the defined geometry 48 in accordance with geometrical considerations shown in FIG. 2, the distance DSO from the x-ray source 10 to the object 36 as well the distance DOI from the object 36 to the x-ray detector 18 is determined.

[0048] In an additional act S6, the deviations visible in FIG. 4 in the imaging of corresponding structures, which are produced in relation to one another in the first recorded image 28a and the second recorded image 28b, may be corrected such that corresponding structures are imaged in the same image areas. The corrections may allow for a video sequence 64 to be created based on the first and the second recorded image 28a, 28b, on the basis of which, for example, an accompanying surgical intervention may be monitored.

[0049] The method of acts S1 to S5 may moreover be embedded in a method for automatic positioning of an object in relation to an x-ray imaging apparatus. For this, in an act S7, the distance DSO established as actual distance may be compared with a predetermined required distance Dsoll, and if there is too great a deviation, the position of the C-arm device 2 may be adapted according to FIG. 1 in an act S8. Moreover, in an adaptation of this type, the radiation strength of the x-ray source 8 may be configured to a new actual distance.

[0050] Although the disclosure has been illustrated and described in greater detail by the exemplary embodiments, the disclosure is not restricted by these exemplary embodiments. Other variations may be derived herefrom by the person skilled in the art, without departing from the scope of protection of the disclosure. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

[0051] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.