DE102009008700B4 - Method for creating X-ray images and X-ray machine - Google Patents

Abstract

A method for generating X-ray images of an examination subject with an X-ray apparatus, comprising an adjustable C-arm (13) which holds an X-ray detector (15) and an X-ray source (14), a system control device (16), an image processing unit (17), a patient support device and at least one deformation determining device, wherein
at least one X-ray image of the examination subject is recorded (step 20) and processed by means of the image processing unit (17),
- A deformation of the patient support device in all three spatial directions is determined, and
- Based on the deformation caused by the deformation of the patient support device distortion of the examination subject on the at least one X-ray image is determined and at least partially compensated (step 23).

Description

The invention relates to a method for generating X-ray images of an examination subject with an X-ray apparatus, comprising an adjustable C-arm, which holds an X-ray detector and an X-ray source, and an X-ray apparatus for carrying out such a method.

With novel C-arm-based X-ray devices, not only 2D X-ray images but also 3D volumetric images can be generated by taking 2D x-ray images around a subject at different angulations during rotation of the C-arm and then reconstructing them into a 3D volumetric image. Further, with C-arm X-ray machines during an interventional procedure, 2D X-ray images can be taken and displayed with spatial information, e.g. be superimposed with a previously created 3D volume image, also of other modalities or with graphics drawn in the volume.

In the case of the C-arm based X-ray machines, in the course of the generation and processing of the X-ray images, e.g. In the processing of 2D X-ray images or the reconstruction of 3D volume images, but also in the superimposition of 2D X-ray images and 3D volume images stiffness-related plant-specific influencing factors adversely affect the X-ray images and generate errors in the overlay.

It is an object of the present invention to provide a method which makes it possible to improve the quality of X-ray images recorded with a C-arm X-ray apparatus, in particular also in the reconstruction of 3D volume images and the superposition of 2D X-ray images with 3D volume images. Furthermore, it is an object of the invention to provide a suitable for carrying out the method X-ray machine.

From the DE 199 50 793 A1 For example, an x-ray device and a method for determining imaging parameters are known, wherein the corresponding intrinsic imaging parameters are newly determined online for the purpose of avoiding influences of gravitational influences of the c-arm on the imaging at each x-ray exposure.

From the DE 10 2004 041 897 A1 a device for determining the position in medical examinations is known, wherein, for example, by means of measuring strips, the deflection of a table top of a patient table can be determined.

The object is achieved by a method for generating X-ray images according to claim 1 and of an X-ray device according to claim 9. Advantageous embodiments of the invention are the subject of the dependent claims.

In the method according to the invention for producing X-ray images of an examination subject with an X-ray apparatus comprising an adjustable C-arm which holds an X-ray detector and an X-ray source, a system control device, an image processing unit, a patient support apparatus and at least one deformation determination apparatus, at least one X-ray image of the examination subject is taken and processed by the image processing unit, a deformation of the patient support device in all three spatial directions is determined and determined based on the deformation caused by the deformation of the patient support device distortion of the examination object on the at least one X-ray image and at least partially compensated. By the method according to the invention, stiffness-related influencing factors, in particular the influence of the weight of the patient on the patient bed, are taken into account and corrected if necessary. The weight of the patient and the weight of, for example, the X-ray source and the X-ray detector lead to deformations of the X-ray device. These deformations are determined by the method according to the invention and serve as the basis for a correction of the rigidity-related plant-specific influencing factors. As a result, a significant improvement in the quality of the generated X-ray images can be achieved.

According to one embodiment of the invention, a plurality of 2D X-ray images of the examination object is recorded at different positions of the support relative to the examination subject and reconstructed by the image processing unit to a 3D volume image and it is caused by the deformation of the patient support device distortion of the examination subject on the at least taken into account and at least partially compensated for an X-ray image. In particular in the reconstruction of volume images from a plurality of X-ray images, stiffness-related influencing factors have a strong effect on the quality of the reconstructed volume image. Since the 2D X-ray images are recorded at different angulations of the C-arm and this is deformed differently at different angulations, the errors in the volume image are generally not reproducible. The invention provides a way to prevent errors and thus significantly improve the quality of the volume image.

According to a further embodiment of the invention, at least one 2D X-ray image of the examination object is recorded and superimposed by means of the image processing unit with a previously created 3D volumetric image and the distortion of the examination object caused by the deformation of the patient positioning device is taken into account and at least partially reflected on the at least one X-ray image balanced. The application of such overlay methods is mainly used in interventional procedures. Here, errors in the overlays can lead to damage and injury to the patient. For this reason, the use of the invention is particularly advantageous.

According to the invention, the deformation of the patient support device is determined in all three spatial directions. In this way, the effect of the deformation can be determined and compensated particularly precisely.

According to a further embodiment of the invention, resistance changes are measured by means of strain gauges arranged on the patient support device and from this the deformation is determined. Strain gauges are commercially available components that can be installed and used easily and effortlessly. A particularly precise measuring method of such strain gauges is based on the measurement of resistance changes.

Conveniently, a deformation of the C-arm is determined in all three spatial directions.

According to the invention, a deformation of the examination object caused by the deformation of the patient couch is determined on the basis of the deformation and taken into account on the at least one X-ray image. Such a distortion is caused, for example, by a deformed patient couch, since the patient is stored at one end of the X-ray image by a distance lower than at the other end. This is especially important when imaging a large area of the patient on the radiograph. From the magnitude of the deformation, the size of the distance can be calculated and from this the distortion can be determined.

Advantageously, in addition to the deformation caused by the deformation of the patient bed offset or a shift of the imaged examination subject on the at least one X-ray image can be determined and taken into account. Such an offset or displacement appears, for example, on a laterally recorded X-ray image of an examination object on a deformed patient bed. If a plurality of X-ray images or an X-ray image and a volume image are to be superimposed, which were created with differently shaped patient couches, large errors occur. If the offset or displacement is calculated based on the deformation, the offset or displacement on the corresponding X-ray image can be corrected to produce a defect-free overlay.

According to one embodiment of the invention, the distortion or the offset or the displacement on the X-ray image is corrected in particular by means of an image processing. The image processing can correct distortion by applying an algorithm to the X-ray image or, for example, by negatively shifting, correcting the offset or displacement.

The X-ray apparatus for generating X-ray images of an examination subject includes an adjustable C-arm holding an X-ray detector and an X-ray source, a system control device, an image processing unit, and a patient support apparatus comprising at least one deformation determining device for determining the deformation of the patient support device, wherein the image processing unit is configured is to determine on the basis of the deformation caused by the deformation of the patient support device distortion of the examination subject on the at least one X-ray image and at least partially compensate. Expediently, the x-ray device has a calculation unit which is designed to use the deformation to determine a distortion of the examination subject on the at least one x-ray image caused by the deformation of the patient support device.

According to one embodiment of the invention, the deformation determination device has at least one strain gauge. Strain gauges are commercially available components that can be installed and used easily and effortlessly.

Conveniently, the at least one strain gauge is arranged on the patient support device for a determination of the deformation of the patient support device.

Conveniently, a strain gauge is disposed on the C-arm for a determination of the deformation of the C-arm.

According to a further embodiment of the invention, the strain gauge is formed from an X-ray transparent material. This is particularly advantageous when the strain gauge on the patient support device is arranged. By means of an X-ray-transparent material, it is possible to arrange the strain gage at a location which is particularly favorable for the measurement, without it producing a disturbing image on the X-ray image.

• 1 eine Seitenansicht einer durch das Patientengewicht verformten Patientenliege;
• 2 eine Ansicht eines erfindungsgemäßen Röntgengeräts mit Verformungsbestimmungsvorrichtungen an der Patientenliege;
• 3 eine Abfolge eines erfindungsgemäßen Verfahrens zur Erstellung von Röntgenbildern;
• 4 eine Abfolge eines erfindungsgemäßen Verfahrens zur Rekonstruktion eines 3D-Volumenbilds;
• 5 eine Ansicht eines durch das Gewicht von Röntgenstrahler und Röntgendetektor verformten C-Bogens;
• 6 eine Ansicht eines C-Bogens mit mehreren Verformungsbestimmungsvorrichtungen;
• 7 eine Ansicht eines Dehnungsmessstreifens, und
• 8 eine Abfolge eines erfindungsgemäßen Verfahrens zur Überlagerung eines 2D-Röntgenbildes und eines 3D-Volumenbildes.

The invention and further advantageous embodiments according to features of the subclaims are explained in more detail below with reference to schematically illustrated embodiments in the drawing, without thereby limiting the invention to these embodiments. Show it:

• 1 a side view of a deformed by the patient's weight patient bed;
• 2 a view of an inventive X-ray device with deformation determining devices on the patient bed;
• 3 a sequence of a method according to the invention for the production of X-ray images;
• 4 a sequence of a method according to the invention for reconstructing a 3D volume image;
• 5 a view of a deformed by the weight of X-ray and X-ray detector C-arm;
• 6 a view of a C-arm with multiple deformation determining devices;
• 7 a view of a strain gauge, and
• 8th a sequence of a method according to the invention for superimposing a 2D X-ray image and a 3D volume image.

In the 1 is shown as a patient couch 10 by the weight and weight of a patient 11 is deformed. The table top of the patient bed 10 Depending on the cantilever length l, the material from which it was produced, and the weight forces involved, it is deformed at its cantilevered end by the amount d.

In the 5 is shown as the weight of an X-ray 14 and the weight of an X-ray detector 15 to a deformation of a C-arm 13 lead, with the respective deformation at different angulations of the C-arm 13 is different.

In the 2 is an inventive X-ray machine with a C-arm 13 , which is an X-ray source 14 and an X-ray detector 15 holds, and with a patient bed 10 shown. The C-arm may, for example, be arranged on a robot arm or another adjustable suspension and is preferably movable and rotatably mounted in several spatial directions. In order to determine a deformation of the patient table, at least one, in particular several, strain gauges 12 at the patient table 10 arranged. One or more strain gauges are arranged, for example, on the cantilevered end of the patient couch; but it can also be arranged on other areas of the patient bed one or more strain gauges. The positions of the strain gauges 12 serve here only as an example and can be selected as needed.

The X-ray machine also has a system controller 16 , an image processing unit 17 for example in the form of an image system and a calculation unit 18 on. control Panel 16 , Image processing unit 17 and calculation unit 18 can also be arranged together in one unit. The strain gauges are, for example, via a data line with the calculation unit 18 or the Control Panel 16 connected in order to forward the measured deformations can. By means of the calculation unit or the system control, the deformation can then be used to determine or calculate what effect the deformation has on the X-ray image and / or how great the effect actually is. From this it can then be determined how the effect can be corrected or at least reduced from the X-ray image. This information is then sent to the image processing unit 17 passed, which performs the correction.

So that strain gauges arranged on the patient table are not visible in the X-ray image, they must be positioned at the table in such a way that they do not lie in the beam path of the X-ray source. Advantageously, the strain gauges are formed from an X-ray transparent material.

In order to determine a deformation of the C-arm, at least one, in particular several, strain gauges 12 on the C-arm 13 arranged as in the 5 is shown, the strain gauges are distributed over the C-arm and at least one strain gauge each near the X-ray source 14 and a respective strain gauge next to the X-ray detector 15 is arranged. The positions of the strain gauges 12 serve here only as an example and can be selected as needed. In order to measure the deformation particularly well, it is advantageous to arrange some strain gauges at the respective ends of the C-arm.

A typical strain gauge 12 is in the 7 shown. The strain gauge has, for example, a measuring grid film of resistance wire, which on a thin Plastic backing was laminated, etched and provided with electrical connections. The measuring principle of such strain gauges 12 is generally the following: Strain gauges change their electrical resistance during deformation, so when stretched, the resistance increases and when compressed it is reduced. The change of resistance is achieved by integration of the strain gauge 12 detected in an electrical circuit. Depending on the change in resistance, conclusions are drawn about the deformation. In addition, there are also strain gauges that use piezoelectric, voltage-optical or capacitive measuring principles. In order to detect deformations in different spatial levels, several strain gauges can be arranged in different directions or so-called rosette strain gauges can be used.

In the 3 a sequence of a method according to the invention is shown. An X-ray image of an examination subject is recorded by means of an X-ray apparatus (step 20 ). In addition, at least one deformation of the patient support device or the C-arm is determined (step 21 ), for example, by means of one or more strain gauges, the respective deformation is measured. For example, in the case of the patient bed, the deformation can be measured simultaneously with the acquisition of the X-ray image in order to obtain a particularly accurate measurement. In the case of the C-arm, for example, it is possible to fall back on measurements that have already been taken in a calibration process with a correspondingly identical position of the C-arm.

After the measurement and recording are performed, at least one effect of the deformation on the X-ray image is determined (step 22 ). For example, in the case of measuring the deformation of the patient couch 10 a distortion caused by the deformation or an offset or a displacement of the imaged examination subject on the X-ray image can be calculated. Such a calculation can be carried out by the calculation unit based on information about the deformation as well as about further geometric information of the X-ray device. Such geometric information may include the position of X-ray and X-ray detector, the position and size of the patient couch, the size of the examination subject, the size of the X-ray detector, and so on.

Subsequently, the effect is corrected during the processing of the X-ray image (step 23 ), for example, by applying an algorithm of image processing to the X-ray image. In the case of an offset or a displacement, the imaged examination object can be displaced on the X-ray image in the opposite direction of the offset or of the displacement; in the case of distortion, an equalization algorithm can be applied to the X-ray image or to parts of the X-ray image.

The deformation of the C-arm can be determined by means of one or more strain gauges before taking an X-ray image or even once as a calibration process in different angulations and positions with different distances between the X-ray source and the X-ray detector. The C-arm deformations per system can be assumed to be constant over the runtime as long as the static conditions do not change. In different systems, however, the deformation may be different. Therefore, the deformations of the C-arm are preferably determined once for each system, and e.g. involved in the calibration process.

The table deformation, however, can not be considered consistent over the life of the table because it depends on the patient's weight, the position of the patient and the cantilever length l of the table. Deformations are recaptured and included in each shot.

In the 4 or the 8th a method in the case of a 3D reconstruction of a volume image from a plurality of x-ray images or a superimposition of a volume image with an x-ray image is shown. Following the correction of the X-ray images or a 3D volume image is reconstructed (step 24 ) or a superposition of a volume image with the X-ray image (step 25 ) carried out. The X-ray image to be superimposed may, for example, be a live X-ray image during an interventional procedure, the superimposed volume image may also have been recorded and transmitted by another imaging device.

When superimposing 3D volume images and 2D X-ray images, the inventive method compensates for inaccuracies, for example that the volume image is not congruent with the X-ray image, so that additional 2D / 3D registration can be saved. Overall, it comes through the inventive method in an overlay to improve the overlay accuracy, higher quality studies and to improve the workflow for the user.

• - zumindest ein Röntgenbild des Untersuchungsobjekts aufgenommen und mittels der Bildverarbeitungseinheit verarbeitet wird,
• - zumindest eine Verformung der Patientenlagerungsvorrichtung oder des C-Bogens ermittelt wird, und
• - zumindest ein Effekt der Verformung auf das Röntgenbild bei der Verarbeitung des Röntgenbilds berücksichtigt und zumindest teilweise ausgeglichen wird.

The invention can be briefly summarized in the following way: To improve the quality of X-ray images, a method for generating X-ray images of an examination subject with an X-ray device comprising an adjustable C-arm, which holds an X-ray detector and an X-ray source, a system control device, an image processing unit Patient storage device and at least one deformation determination device, provided

• at least one X-ray image of the examination subject is taken and processed by means of the image processing unit,
• - At least one deformation of the patient support device or the C-arm is determined, and
• - At least one effect of the deformation on the X-ray image in the processing of the X-ray image is taken into account and at least partially compensated.

Claims (16)

A method for generating X-ray images of an examination subject with an X-ray apparatus, comprising an adjustable C-arm (13) which holds an X-ray detector (15) and an X-ray source (14), a system control device (16), an image processing unit (17), a patient support device and at least one deformation determining device, wherein at least one X-ray image of the examination subject is recorded (step 20) and processed by means of the image processing unit (17), - A deformation of the patient support device in all three spatial directions is determined, and - Based on the deformation caused by the deformation of the patient support device distortion of the examination subject on the at least one X-ray image is determined and at least partially compensated (step 23). Method according to Claim 1 wherein a plurality of 2D X-ray images of the examination object are taken at different positions of the C-arm (13) relative to the examination subject and reconstructed by the image processing unit (17) to a 3D volume image and at least the distortion caused by the deformation of the patient support device Examined object on the at least one X-ray image in the reconstruction of the 3D volume image and at least partially compensated. Method according to Claim 1 wherein at least one 2D X-ray image of the examination object is recorded and superimposed by the image processing unit (17) with a 3D volume image and at least taken into account by the deformation of the patient support device distortion of the examination subject on the at least one X-ray image in the superposition and at least partially compensated , Method according to Claim 1 in which resistance changes are measured by means of strain gauges (12) arranged on the patient support device and from this the deformation is determined. Method according to one of the preceding claims, wherein a deformation of the C-arm (13) in all three spatial directions is determined. Method according to Claim 2 or 3 , wherein further 2D X-ray images are recorded and superimposed with the 3D volume image and the distortion is taken into account in the overlay and at least partially compensated. Method according to Claim 1 in which, based on the deformation, an offset caused by the deformation of the patient positioning device or a displacement of the imaged examination object on the at least one X-ray image is determined and taken into account. Method according to one of the preceding claims, wherein the distortion or the offset or the displacement on the X-ray image is corrected in particular by means of an image processing. X-ray machine for generating X-ray images of an examination object, having an adjustable C-arm (13) which holds an X-ray detector (15) and an X-ray source (14), with a system control device (16), with an image processing unit (17) and with a patient support device, comprising at least one deformation determination device for determining the deformation of the patient support device, wherein the image processing unit (17) is adapted to determine based on the deformation caused by the deformation of the patient support device distortion of the examination subject on the at least one X-ray image and at least partially compensate. X-ray device after Claim 9 with a calculation unit (18), wherein the calculation unit is designed to use the deformation to determine a distortion of the examination subject on the at least one X-ray image caused by the deformation of the patient positioning device. X-ray device after Claim 9 or 10 wherein the system control device (16) is adapted to control the X-ray machine such that a plurality of 2D X-ray images of the examination subject at different positions of the C-arm (13) relative to the examination subject and recorded by the image processing unit (17) to a 3D Volume image reconstructed be formed, and wherein the image processing unit (17) is adapted to take into account the distortion on the at least one X-ray image in the reconstruction of the 3D volume image and at least partially compensate. X-ray machine according to one of Claims 9 to 11 wherein the X-ray device is adapted to record 2D X-ray images and the image processing unit (17) is adapted to superimpose the 2D X-ray images with a 3D volume image and is adapted to take into account the distortion on the at least one X-ray image in the superposition and at least partially offset. X-ray machine according to one of Claims 9 to 12 wherein the deformation determining device comprises at least one strain gauge (12). X-ray device after Claim 13 wherein the at least one strain gauge (12) is disposed on the patient support device and adapted to measure a deformation of the patient support device. X-ray machine according to one of Claims 9 to 14 wherein a strain gauge (12) is disposed on the C-arm (13) and adapted to measure a deformation of the C-arm (13). X-ray machine according to one of Claims 13 to 15 wherein the strain gauge (12) is formed of an X-ray transparent material.

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