Method for determining a distance by X-ray imaging, and X-ray device

1. A method for determining a distance between a first point and a second point on an object under examination within the body of a person under examination by x-ray imaging with an x-ray device, the method which comprises:

recording a first x-ray image containing the first point, with a first relative positioning of an x-ray source to the object under examination;

recording a second x-ray image containing the first point, with a second relative positioning of the x-ray source to the object under examination;

wherein the first relative positioning and the second relative positioning are shifted relative to one another substantially in parallel to a central beam of the x-ray device;

recording a third x-ray image containing the second point, with a third relative positioning of the x-ray source to the object under examination;

recording a fourth x-ray image containing the second point, with a fourth relative positioning of the x-ray source to the object under examination;

wherein the third relative positioning and the fourth relative positioning are shifted relative to one another substantially in parallel to the central beam of the x-ray device;

determining a location of the first point in the first x-ray image and in the second x-ray image;

determining a location of the second point in the third x-ray image and in the fourth x-ray image;

carrying out a stereo reconstruction based on the locations of the first point thus determined as a corresponding landmark for obtaining a 3D position of the first point;

carrying out a stereo reconstruction based on the locations of the second point thus determined as a corresponding landmark for obtaining a 3D position of the second point; and

determining the distance between the first point and the second point from the 3D position of the first point and the 3D position of the second point.

2. The method according to claim 1 , wherein the first and second relative positioning and the third and fourth relative positioning are respectively shifted relative to one another at right angles to the central beam of the x-ray device.

3. The method according to claim 1 , wherein:

the first x-ray image and the second x-ray image record an image of a first partial area of the object under examination and have mutually different imaging scales and/or are not, or only slightly, rotated and tilted in relation to one another; and

the third x-ray image and the fourth x-ray image record an image of a second partial area of the object under examination and have mutually different imaging scales and/or are not, or only slightly, rotated and tilted in relation to one another.

4. The method according to claim 1 , wherein the step of determining the locations of the first point and the step of determining the locations of the second point are manual steps carried out manually by a user of the x-ray device.

5. The method according to claim 1 , wherein the step of determining the locations of the first point and the step of determining the locations of the second point are carried out at least partly automatically by a 2D-2D image registration of the first x-ray image with the second x-ray image and also of the third x-ray image with the fourth x-ray image.

6. The method according to claim 1 , further comprising:

determining extrinsic camera parameters for the stereo reconstruction, which describe a 3D position and an orientation of the x-ray source in the first and second and the third and fourth relative positionings; and

wherein an execution of the stereo reconstruction takes account of the extrinsic camera parameters.

7. The method according to claim 6 , wherein:

each of the first and the second and the third and the fourth x-ray image maps location marks of a location-coded marker plane; and

the extrinsic camera parameters are determined based on the mapped location marks.

8. The method according to claim 7 , wherein the marker plane is defined to substantially extend orthogonally to a central beam of the x-ray device.

9. The method according to claim 6 , which comprises determining the extrinsic camera parameters based on a monitoring of a positioning of the x-ray device between the different relative positionings.

10. The method according to claim 1 , which further comprises:

recording at least two calibration x-ray images, which each map location marks of a location-encoded marker plane, wherein the at least two calibration x-ray images are recorded with different orientations of the x-ray source to the marker plane; and

determining intrinsic camera parameters for the stereo reconstruction, which describe imaging characteristics of the x-ray device, from the calibration x-ray images based on the mapped location marks;

wherein a execution of the stereo reconstruction takes account of the intrinsic camera parameters.

11. The method according to claim 10 , wherein at least one of at least two calibration x-ray images is the first x-ray image and/or the second x-ray image and/or the third x-ray image and/or the fourth x-ray image.

12. An x-ray device, comprising:

an x-ray source and an x-ray detector;

an imaging controller configured for carrying out the following steps:

recording a first x-ray image containing a first point in an object under examination, with a first relative positioning of an x-ray source to the object under examination;

recording a second x-ray image containing the first point, with a second relative positioning of the x-ray source to the object under examination;

recording a third x-ray image containing a second point in an object under examination, with a third relative positioning of the x-ray source to the object under examination;

recording a fourth x-ray image containing the second point, with a fourth relative positioning of the x-ray source to the object under examination;

wherein the first relative positioning and the second relative positioning are shifted relative to one another substantially in parallel to a central beam of the x-ray device; and

wherein the third relative positioning and the fourth relative positioning are shifted relative to one another substantially in parallel to the central beam of the x-ray device; and

a processor configured for carrying out the following steps:

determining a location of the first point in the first x-ray image and in the second x-ray image;

determining a location of the second point in the third x-ray image and the fourth x-ray image;

carrying out a stereo reconstruction based on the determined locations of the first point as corresponding landmark for obtaining a 3D position of the first point;

carrying out a stereo reconstruction based on the determined locations of the second point as corresponding landmark for obtaining a 3D position of the second point;

determining a distance between the first point and the second point from the 3D position of the first point and the 3D position of the second point.