Method of and system for reducing metal artifacts in images generated by x-ray scanning devices

• US 6,721,387 B1
• Filed: 06/13/2002
• Issued: 04/13/2004
• Est. Priority Date: 06/13/2001
• Status: Active Grant

• Current Assignee: Analogic Corporation
• Original Assignee: Analogic Corporation
• Inventors: Simanovsky, Sergey, Naidu, Ram, Bechwati, Ibrahim, Karimi, Seemee S., Crawford, Carl R.
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US10/171,116
• Time in Patent Office: 670 Days
• Field of Search: 378/4, 378/8, 378/15, 378/901
• US Class Current: 378/8
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4488 Means for cooling A61B6/045 takes precedence
• CPC Class Codes: A61B 6/5258 involving detection or reduction of artifacts or noise
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating

Abstract

A method of reducing metal artifacts in a computed tomography (CT) system includes:

A. generating a preliminary image from input projection data collected by the CT system;

B. identifying metal objects in the preliminary image;

C. generating secondary projections from the input projection data by removing projections of objects having characteristics that may cause the objects to be altered in a final artifact-corrected image.

D. extracting the projections of metal objects identified in step B from the secondary projection data generated in step C.

E. generating corrected projections by removing the projections of the metal objects extracted in Step D from the input projection data.

F. generating a final image by reconstructing the corrected projections generated in step E and inserting the metal objects identified in Step B into the final image.

Claims

1. A method of reducing metal artifacts in a computed tomography (CT) system comprising:

A. generating a preliminary image from input projection data collected by the CT system;

B. identifying metal objects in the preliminary image;

C. generating secondary projections from said input projection data by removing projections of objects having characteristics that may cause the objects to be altered in a final artifact-corrected image;

D. extracting the projections of metal objects identified in step B from the secondary projection data generated in step C;

E. generating corrected projections by removing the projections of the metal objects extracted in Step D from said input projection data;

F. generating a final image by reconstructing said corrected projections generated in step E and inserting the metal objects identified in Step B into the final image;

2. The method of claim 1 wherein Step B includes identifying objects in the preliminary image having intensities which are greater than a predetermined amount.

3. The method of claim 2 wherein Step B further includes selection of metal objects which generate artifacts.

4. The method of claim 1 wherein step C includes identifying objects in the preliminary image having characteristics which may cause the objects to be altered in a final artifact-corrected image.

5. The method of claim 4 wherein step C further includes generating a modified image by setting pixels in the preliminary image which are not included in the objects identified in step C to a calculated value.

6. The method of claim 5 wherein the calculated value is equal to mean value of the preliminary image determined using pixels other than the pixels included in the objects identified in step B.

7. The method of claim 5 wherein step C further includes reprojecting the modified image and subtracting the reprojections from the input projection data to generate secondary projections which contain the input projection data with the projections of objects identified in step C removed.

8. The method of claim 1 wherein step D includes identifying at least one region in the secondary projections which contain the projections of metal objects identified in step B.

9. The method of claim 8 wherein step D further includes determining a baseline value of each of said at least one regions.

10. The method of claim 9 wherein said baseline value of each of said at least one region is determined by linear interpolation between projection data surrounding said at least one region.

11. The method of claim 10 wherein step D further includes subtracting each baseline value from the secondary projection values in its respective region to generate projection data corresponding to said metal projections in each region.

12. The method of claim 1 wherein said objects identified in step C include objects in said preliminary image having at least one dimension which is less than a predetermined length.

13. The method of claim 12 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from the mean intensity of the preliminary image by more than a predetermined threshold.

14. The method of claim 1 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from a mean intensity of the preliminary image by more than a predetermined threshold.

16. The method of claim 4 wherein said objects identified in step C include objects in said preliminary image having at least one dimension which is less than a predetermined length.

17. The method of claim 16 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from the mean intensity of the preliminary image by more than a predetermined amount.

15. A method of reducing metal artifacts in a computed tomography (CT) system comprising:

A. generating a preliminary image from input projection data collected by the CT system;

B. identifying metal objects in the preliminary image which have generated metal artifacts in the preliminary image;

C. identifying objects in the preliminary image having characteristics which may cause the objects to be altered in a final artifact-corrected image;

D. generating a modified image by setting pixels in the preliminary image which are not included in objects identified in step C to a mean value of the preliminary image;

E. reprojecting the modified image;

F. subtracting the reprojections from the input projection data to generate secondary projections containing the preliminary image with the objects identified in step C removed;

G. identifying at least one region in the secondary image which contains projections of metal objects identified in step B;

H. determining a baseline value of each of said at least one regions;

I. subtracting each baseline value from the secondary projection values in its respective region to generate projection data corresponding to said metal object in each region;

J. Subtracting said metal projection data from said input projection data to generate corrected projections;

K. reconstructing said final artifact-corrected image by;

a. reconstructing corrected projections; and

b. superimposing said metal objects identified in step B into said corrected image.

18. The method of claim 15 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from a mean intensity of the preliminary image by more than a predetermined amount.

19. The method of claim 15 wherein, in step G, said baseline value of each of said at least one region is determined by linear interpolation between projection values surrounding said at least one region.

20. A system for reducing metal artifacts in a computed tomography (CT) system comprising:

a tunnel having a platform disposed therein for receiving an object to be scanned;

an x-ray source for directing x-rays at the object to be scanned;

a detector array including a plurality of detectors for receiving said x-rays within said tunnel; and

processing means for reducing metal artifacts in images of the object reconstructed from the x-rays detected by said detectors, said processing means performing the steps of;

A. generating a preliminary image from input projection data collected by the CT system;

B. identifying metal objects in the preliminary image;

C. generating secondary projections from said input projection data by removing projections of objects having characteristics that may cause the objects to be altered in a final artifact-corrected image;

D. extracting the projections of metal objects identified in step B from the secondary projection data generated in step C;

E. generating corrected projections by removing the projections of the metal objects extracted in Step D from said input projection data;

F. generating a final image by reconstructing said corrected projections generated in step E and inserting the metal objects identified in Step B into the final image.

21. The system of claim 20 wherein Step B includes identifying objects in the preliminary image having intensities which are greater than a predetermined amount.

22. The system of claim 21 wherein Step B further includes selection of metal objects which generate artifacts.

23. The system of claim 20 wherein step C includes identifying objects in the preliminary image having characteristics which may cause the objects to be altered in a final artifact-corrected image.

24. The system of claim 23 wherein step C further includes generating a modified image by setting pixels in the preliminary image which are not included in the objects identified in step C to a calculated value.

25. The system of claim 24 wherein the calculated value is equal to mean value of the preliminary image determined using pixels other than the pixels included in the objects identified in step B.

26. The system of claim 24 wherein step C further includes reprojecting the modified image and subtracting the reprojections from the input projection data to generate secondary projections which contain the input projection data with the projections of objects identified in step C removed.

27. The system of claim 20 wherein step D includes identifying at least one region in the secondary projections which contain the projections of metal objects identified in step B.

28. The system of claim 27 wherein step D further includes determining a baseline value of each of said at least one regions.

29. The system of claim 28 wherein said baseline value of each of said at least one region is determined by linear interpolation between projection data surrounding said at least one region.

30. The system of claim 29 wherein step D further includes subtracting each baseline value from the secondary projection values in its respective region to generate projection data corresponding to said metal projections in each region.

31. The system of claim 20 wherein said objects identified in step C include objects in said preliminary image having at least one dimension which is less than a predetermined length.

32. The system of claim 31 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from the mean intensity of the preliminary image by more than a predetermined threshold.

33. The system of claim 20 wherein said objects identified in step C include objects in said preliminary image having an intensity which differs from a mean intensity of the preliminary image by more than a predetermined threshold.