Reducing artifacts in an image data set and X-ray device
Streak artifacts generated by at least one X-ray attenuating object arranged outside a reconstruction volume in a three-dimensional image data set showing the reconstruction volume are reduced. The reconstruction volume is reconstructed from two-dimensional projection images recorded from different projection directions. The object is localized in the projection images showing the object. To determine corrected projection images for the reconstruction of the image data set, the image data of the area of each projection image showing the object is corrected to remove the object. The localization of the object is performed taking into account difference images of the measured projection images and from a reconstruction data set of forward-projected comparative images reconstructed from the measured projection images.
1. A method for reducing artifacts generated by at least one X-ray attenuating object arranged outside a reconstruction volume in a three-dimensional image data set showing the reconstruction volume, which is reconstructed from two-dimensional projection images recorded from different projection directions, the method comprising:
localizing the object in the projection images showing the object; and
determining corrected projection images for the reconstruction of the image data set, the image data of the area of each projection image showing the object being corrected to remove the object, wherein the localizing of the object is performed taking into account difference images of the measured projection images and from a reconstruction data set of forward-projected comparative images reconstructed from the measured projection images.
2. The method as claimed in claim 1 , wherein localizing the object comprises localizing the object where the reconstruction volume is completely contained in all the projection images and the object has a higher density, higher attenuation coefficient, or the higher attenuation coefficient and the higher density than all naturally occurring materials in the body of a person.
3. The method as claimed in claim 2 , wherein localizing the object comprises localizing a metal object.
4. The method as claimed in claim 1 , wherein the reconstruction data set is determined by reconstruction of the reconstruction volume from the measured projection images.
5. The method as claimed in claim 4 , wherein the area showing the object is segmented in the difference images.
6. The method as claimed in claim 5 , wherein segmenting comprises using an edge detection algorithm.
7. The method as claimed in claim 5 , further comprising segmenting the reconstruction data set according to at least two material classes with assigned attenuation coefficients, according to which a virtual normalization image based on effective transmission lengths of the material classes is determined in the projection directions of the projection images for which a comparative image is determined, and, prior to the formation of the difference images, the measured projection images and the comparative images are normalized using the normalization images, wherein the corrected measured projection images are denormalized after the removal of the object.
8. The method as claimed in claim 7 , wherein the segmentation of the reconstruction data set is performed according to four material classes.
9. The method as claimed in claim 8 , wherein the segmentation is performed according to air, soft tissue, bone, and contrast medium classes.
10. The method as claimed in claim 1 , wherein the reconstruction data set is reconstructed for an object volume containing the object, the object volume being larger than the reconstruction volume, wherein, in an iterative method, in each case a three-dimensional correction data set is reconstructed from the difference images based on the current reconstruction data set and to form a new reconstruction data set added to the current reconstruction data set, wherein, following the introduction of an abort criterion, the object in the most recently determined reconstruction data set is segmented and the segmentation in the reconstruction data set is used for the localization of the object in the measured projection images.
11. The method as claimed in claim 10 , wherein introducing the abort criterion comprises introducing a minimization of a statistical variable of the image data contained in the difference images, exceeding of a prespecified number of iterations, or both as an abort condition.
12. The method as claimed in claim 11 , wherein introducing the minimization comprises introducing the minimization of an L1 standard or an L2 standard of the image data of the difference images as the statistical variable.
13. The method as claimed in claim 1 , wherein artifacts generated by the object are detected in a reconstruction from the measured projection images based on the reconstruction volume and, from the geometric properties of the artifacts, a subset of the measured projection images is selected which subset may contain the areas showing the object, wherein the determination of the difference images a correction to remove the object is performed restricted to the subset.
14. The method as claimed in claim 13 , wherein a Hough transformation is used for the detection of the artifacts.
15. The method as claimed in claim 13 , wherein the artifacts detected are streak artifacts.
16. The method as claimed in claim 1 , wherein for the determination of the corrected measured projection images, an interpolation is performed in the areas showing the object.
17. An X-ray device comprising:
an X-ray source;
an X-ray detector; and
a control device configured to:
localize an object in a projection images showing the object;
determine corrected projection images for the reconstruction of an image data set, the image data of an area of each projection image showing the object being corrected to remove the object, wherein the localizing of the object is performed taking into account difference images of the projection images and from a reconstruction data set of forward-projected comparative images reconstructed from the projection images.
18. The X-ray device of claim 17 , wherein the control device is configured to:
segment the area showing the object in the difference images using an edge detection algorithm.
19. The X-ray device of claim 17 , wherein the control device is configured to:
reconstruct the reconstruction data set for an object volume containing the object, the object volume being larger than the reconstruction volume, wherein, in an iterative method, in each case a three-dimensional correction data set is reconstructed from the difference images based on the current reconstruction data set and to form a new reconstruction data set added to the current reconstruction data set, wherein, following the introduction of an abort criterion, the object in the most recently determined reconstruction data set is segmented and the segmentation in the reconstruction data set is used for the localization of the object in the measured projection images.
20. A non-transitory computer readable storage medium having stored thereon instructions, the instructions when executed by a computing device:
localizing an object in projection images showing the object; and
determining corrected projection images for the reconstruction of an image data set, image data of the area of each projection image showing the object being corrected to remove the object, wherein the localizing of the object is performed taking into account difference images of the measured projection images and from a reconstruction data set of forward-projected comparative images reconstructed from the measured projection images.