Method for calibrating an X-ray image

1. Method for calibrating at least one 2D X-ray image of an object to be imaged, which is recorded by means of an X-ray device in that X-rays produced by an X-ray source radiate through the object and are recorded by means of an X-ray detector, wherein an already existing 3D model comprising a first structure of the object is compared to the 2D X-ray image, wherein an actual image positional relationship of the X-ray source and the X-ray detector relative to the object, and/or relative to one another, is determined for the 2D X-ray image, wherein for the comparison of the 3D model with the 2D X-ray image and taking into account a predetermined image positional relationship, a virtual 2D projection image is produced by applying a virtual projection method to at least one part of the 3D model, wherein the first structure in the 2D x-ray image is compared to the first structure in the virtual 2D projection image, wherein deviations are identified during the comparison of the first structure in the 2D X-ray image with the virtual 2D projection image, wherein the image positional relationship is incrementally changed within the framework of an optimization method, and a new virtual 2D projection image is generated after each change until the deviations are smaller than a defined threshold value.

2. The method according to claim 1 , wherein the 2D X-ray images are recorded step-by-step from different recording angles during a movement of the X-ray source and the X-ray detector around the object, wherein by using a reconstruction method and knowing the determined image positional relationships of the 2D X-ray images, a 3D X-ray image of the object, or a panoramic tomographic image of the object, is generated from the recorded 2D X-ray images.

3. The method according to claim 1 , wherein the first structure of the object is an upper jaw, a lower jaw, a group of teeth, a dental prosthesis part, a filling, an inlay, the entire object, a part of the object, a head of a patient and/or an individual tooth.

4. The method according to any of claim 1 , wherein the existing 3D model of the first structure is recorded by an optical three-dimensional surface measurement method, wherein the 3D model includes only one surface of the first structure, wherein during the comparison, a surface edge of the first structure in the 2D X-ray image is compared with a surface edge of the first structure in the virtual 2D projection image.

5. The method according to any of claim 1 , wherein the existing 3D model of the first structure is generated by recording an impression of the first structure with the aid of an optical three-dimensional surface measurement method, wherein the 3D model includes only one surface of the structure, wherein during the comparison, a surface edge of the structure in the 2D X-ray image is compared with a surface edge of the structure in the virtual 2D projection image.

6. The method according to claim 1 , wherein the existing 3D model of the first structure has been recorded by means of a three-dimensional volume measurement method, and contains volume data of the structure, wherein for the comparison, the structure in the 2D X-ray image is compared with the simulated projection of the structure in the virtual 2D projection image.

7. The method according to claim 1 , wherein in the virtual projection method, not only the image positional relationship of the X-ray source and the X-ray detector relative to the object, but also the thickness of the first structure to be imaged and thus the X-ray attenuation by the structure and/or the material of the first structure, as well as the X-ray attenuation dependent thereon, are taken into account.

8. The method according to claim 1 , wherein for the implementation of the optimization method, the predetermined image positional relationship from a known calibration is used as the starting solution.

9. The method according to claim 1 , wherein when comparing the 2D X-ray image with the virtual 2D projection image, a degree of similarity is calculated for the determination of the deviations, wherein a gradient difference method, a direct difference method, a correlation method, a cross-correlation method of a first and/or a higher order, a statistical method or a method of least-squares errors is used.

10. The method according to claim 1 , wherein a first structure of the object is selected in a first step to determine first actual image positional relationships of the 2D X-ray images for this first structure, wherein a second structure of the object is selected in a second step to determine second actual image positional relationships of the 2D X-ray images for the second structure.

11. The method according to claim 10 , wherein a first 3D X-ray image is reconstructed using the first actual image positional relationships and a second 3D X-ray image is reconstructed using the second actual image positional relationships, wherein a first region in the first 3D X-ray image, which displays the first structure in sharp focus, is subsequently merged with a second region in the second 3D X-ray image, which displays the second structure in sharp focus, to one overall 3D X-ray image of the object.

12. The method according to claim 10 , wherein the first structure is a lower jaw or a part of the lower jaw and the second structure is an upper jaw or a part of the upper jaw.