METAL ARTIFACTS REDUCTION IN CONE BEAM RECONSTRUCTION

• US 20160078647A1
• Filed: 09/11/2014
• Published: 03/17/2016
• Est. Priority Date: 09/11/2014
• Status: Active Grant

• Current Assignee: Carestream Dental Technology Topco Limited
• Original Assignee: CareStream Health Incorporated
• Inventors: Subramanyan, Krishnamoorthy, Ray, Lawrence A., Schildkraut, Jay S.
• Granted Patent: US 9,934,597 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 for reducing metal artifacts in a volume radiographic image reconstructs a first 3-D-image using measured projection images and forms a 3-D image metal mask that contains metal voxels. For each measured projection image, a projection metal mask is a projection of the 3-D image metal mask. A 3-D prior image contains voxels within the 3-D image metal mask. Voxel values of the first 3-D image outside the 3-D image metal mask are replaced with a value representative of air or soft tissue. Non-metal voxels of the 3-D prior image are modified according to a difference between a pixel value related to the nonmetal voxel and the corresponding pixel value in a calculated projection image. Composite projection images are formed by replacing measured projection image data for pixels within the projection metal mask with calculated projection image data. A metal artifact reduced 3-D image is reconstructed from composite projections.

Claims

1. A method for reducing metal artifacts in a volume radiographic image, the method executed at least in part on a computer and comprising:

reconstructing a first 3-D-image using measured projection images;

forming a 3-D image metal mask that contains metal voxels in the first 3-D image;

for each measured projection image, forming a projection metal mask that contains the pixels that are a projection of the 3-D image metal mask;

forming a 3-D prior image that contains the voxels of the first 3-D image that are within the 3-D image metal mask and replacing voxel values of the first 3-D image that are outside the 3-D image metal mask with a value that is representative of air or soft tissue;

iteratively modifying one or more of the non-metal voxels of the 3-D prior image according to a difference between a pixel value related to the nonmetal voxel in at least one measured projection image at a projection angle and the corresponding pixel value in at least one calculated projection image that is generated for the projection angle according to the 3-D prior image;

forming a plurality of composite projection images, wherein each composite projection image is formed by replacing measured projection image data for pixels within the projection metal mask with calculated projection image data for the corresponding pixels;

and

reconstructing and displaying a metal artifact reduced 3-D image from the plurality of composite projection images.

2. The method of claim 1 wherein iteratively modifying the one or more nonmetal voxels of the 3-D prior image comprises computing differences between corresponding pixel values for a plurality of measured projection images and a plurality of corresponding calculated projection images and wherein the one or more nonmetal voxels are modified two or more times.

3. The method of claim 1 further comprising forming a set of final calculated projection images using forward projection of the metal artifact reduced 3-D image.

4. The method of claim 1 in which the degree of metal obstruction of voxels in the first 3-D image is calculated and the voxels of the 3-D prior image are set according to this calculated value

5. The method of claim 1 wherein forming a 3-D prior image further comprises segmenting the first 3-D image into at least tissue and metal classes.

6. The method of claim 1 further comprising storing or transmitting the artifact-reduced 3-D image.

7. The method of claim 1 further comprising displaying the first 3-D image along with the artifact-reduced 3-D image.

8. A method for reducing metal artifacts in a volume radiographic image, the method executed at least in part on a computer and comprising:

reconstructing a first 3-D-image using measured projection images;

forming a 3-D image metal mask that contains metal voxels in the first 3-D image;

for each measured projection image, forming a projection metal mask that contains the pixels that are a projection of the 3-D image metal mask;

segmenting the first 3-D image into at least tissue and metal classes and forming a 3-D prior image that contains voxels of the first 3-D image that are within the 3-D image metal mask and replacing voxel values of the first 3-D image that are outside the 3-D image metal mask with values that are representative of air or soft tissue;

iteratively modifying one or more of the non-metal voxels of the 3-D prior image according to a difference between a pixel value related to the nonmetal voxel in at least one measured projection image at a projection angle and the corresponding pixel value in at least one calculated projection image that is generated for the projection angle according to the 3-D prior image;

forming a plurality of composite projection images, wherein each composite projection image is formed by replacing measured projection image data for pixels within the projection metal mask with calculated projection image data for the corresponding pixels;

reconstructing a metal artifact reduced 3-D image from the plurality of composite projection images;

and

displaying one or more portions of the metal artifact reduced 3-D image.

9. The method of claim 8 further comprising generating and storing a plurality of calculated projection images using forward projection of the metal artifact reduced 3-D image.

10. The method of claim 8 wherein the measured projection images are acquired from a cone-beam computed tomography system.

11. The method of claim 8 further comprising displaying one or more of the measured projection images, projection metal masks, or composite projection images.

12. The method of claim 8 further comprising generating a metal obstruction 3-D map that indicates the extent to which each voxel in the 3-D image is obstructed by metal.