CORRECTION OF SPATIAL ARTIFACTS IN RADIOGRAPHIC IMAGES

• US 20130328919A1
• Filed: 06/07/2012
• Published: 12/12/2013
• Est. Priority Date: 06/07/2012
• Status: Active Grant

• Current Assignee: Varex Imaging Corporation
• Original Assignee: Varian Medical Systems Incorporated (Siemens AG)
• Inventors: Holt, Kevin Matthew
• Granted Patent: US 9,752,995 B2
• Time in Patent Office: Days
• US Class Current: 345/629
• CPC Class Codes: G01N 2223/3307 source and detector fixed; object moves
• CPC Class Codes: G01N 2223/401 image processing
• CPC Class Codes: G01N 2223/631 large structures, walls
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 2340/125 wherein one of the images is motion video

Abstract

The present invention encompasses methods, apparati, and computer-readable media for correcting spatial artifacts in composite radiographic images of an object (1). A method embodiment of the present invention comprises the steps of generating the composite image from a plurality of views of the object (1); estimating a shift profile; and re-generating the image by shifting the views using the shift profile.

Claims

1. A method for correcting spatial artifacts in a composite radiographic image of an object, said method comprising the steps of:

generating the composite image from a plurality of views of the object;

estimating a shift profile; and

re-generating the image by shifting the views using the shift profile.

2. The method of claim 1 wherein the shift profile is represented by s[k], where k is a view number.

3. The method of claim 1 further comprising performing, between the estimating step and the re-generating step, the step of applying a smoothing filter to the shift profile.

4. The method of claim 1 wherein the re-generating step is accomplished by interpolation.

5. The method of claim 4 wherein the interpolation is from the group of interpolations consisting of bi-linear, cubic, B-spline, and sinc.

6. The method of claim 1 wherein the step of estimating a shift profile utilizes an optimization algorithm.

7. The method of claim 6 wherein the optimization algorithm is applied to find the shift profile that minimizes a sum of a set of penalty functions such that the answer at least approximately satisfies a set of zero or more hard constraints.

8. The method of claim 7 wherein the penalty function(s) comprise(s) at least one function from the group consisting of a squared error function, an absolute error function, and a Huber function.

9. The method of claim 7 wherein each penalty function and each constraint is from one of two classes of criteria:

a shift criterion class and an image criterion class.

10. The method of claim 9 wherein each class is represented by at least one penalty function or constraint.

11. The method of claim 9 wherein the shift criterion class is enforced by at least one step from the following:

using finite differences;

encouraging derivatives of the shift profile to be small;

hard penalizing a Fourier or other transform;

soft penalizing a Fourier or other transform;

using group sparsity.

12. The method of claim 9 wherein the image criterion class is satisfied by at least one step from the following:

performing an edge detection on the image, producing a corrected image, and encouraging edges in the corrected image to have a desired shape;

calculating a displacement field and encouraging some component of the shift profile to be similar to the displacement field; and

encouraging the corrected image to be smooth.

13. The method of claim 12 wherein the step of encouraging the corrected image to be smooth comprises at least one of:

encouraging total energy in the gradient of the corrected image to be small;

using a Total Variation semi-norm;

using a Huber function.

14. The method of claim 7 wherein the problem is solved using a convex programming solver.

15. The method of claim 1 wherein the composite radiographic image is produced by x-rays.

16. The method of claim 1 wherein the object is imaged by an imager, and there is relative movement between the object and the imager.

17. The method of claim 1 wherein more than one image is re-generated using the same shift profile.

18. The method of claim 1 wherein only some subset of the views is processed.

19. The method of claim 18 comprising the following steps:

processing the image to identify one or more artifact-related features;

identifying one or more subsets of views relative to locations of the artifact-related feature(s); and

processing only the identified subset(s) of views.

20. The method of claim 19 where the artifact-related features are wheels on a car or truck.

21. At least one computer-readable medium containing computer program instructions for correcting spatial artifacts in a composite radiographic image of an object, said instructions performing the steps of:

generating the composite image from a plurality of views of the object;

estimating a shift profile; and

re-generating the image by shifting the views using the shift profile.

22. Apparatus for correcting spatial artifacts in a radiographic image of an object, said apparatus comprising:

means for generating a composite image from a plurality of views of the object;

coupled to the generating means, means for estimating a shift profile; and

coupled to the estimating means, means for re-generating the image by shifting the views by using the shift profile;

23. The apparatus of claim 22 wherein the estimating means includes an optimization algorithm that is applied to find the shift profile that minimizes a sum of a set of penalty functions such that the answer at least approximately satisfies a set of zero or more hard constraints.