Metal artifacts reduction in cone beam reconstruction
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.
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 2D projection images;
forming a 3-D image metal mask that contains metal voxels in the first 3-D-image;
for each measured 2D projection image, forward projecting the 3-D image metal mask to form a projection metal mask of pixels resulting therefrom in a corresponding 2D projection metal image;
forming a metal obstruction 3-D map that indicates the extent to which each voxel in the first 3-D-image is obstructed by metal;
forming a plurality of composite 2D projection images, wherein each composite 2D projection image is formed by modifying measured 2D projection image data for pixels for said each measured 2D projection image within the projection metal mask of the corresponding 2D projection metal image with calculated 2D projection image data for the corresponding pixels;
reconstructing a metal artifact reduced 3-D image from the plurality of composite 2D projection images;
modifying non-metal voxels in the metal artifact reduced 3-D image identified by the metal obstruction 3-D map, where the modified non-metal voxels include voxels that are not neighbors of the metal voxels;
and
displaying the modified metal artifact reduced 3-D image.
2. The method of claim 1 wherein modifying the one or more non-metal voxels of the metal artifact reduced 3-D image comprises computing differences between corresponding pixel values for a plurality of measured 2D projection images and a plurality of corresponding calculated 2D projection images and wherein the one or more non-metal 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 modified 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 modified non-metal voxels of the 3-D prior image are set according to this calculated value.
5. The method of claim 1 further comprising storing or transmitting the modified metal artifact reduced 3-D image.
6. The method of claim 1 further comprising displaying the first 3-D image along with the modified metal artifact reduced 3-D image.
7. 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 in a corresponding projection metal image by forward projecting the 3-D image metal mask;
forming a plurality of composite projection images, wherein each composite projection image is formed by modifying measured projection image data for pixels for said each measured projection image within the projection metal mask of the corresponding projection metal image with calculated projection image data for the corresponding pixels;
reconstructing a metal artifact reduced 3-D image from the plurality of composite projection images;
identifying non-metal voxels in the metal artifact reduced 3-D image that are affected by metal attenuation in the measured projections;
modifying the affected non-metal voxels in the metal artifact reduced reconstruction based on an amount of modification to the measured projections used to produce the composite projection, where the modified affected non-metal voxels include voxels that are not neighbors of the metal voxels;
and
displaying one or more portions of the modified metal artifact reduced 3-D image.
8. The method of claim 7 further comprising generating and storing a plurality of calculated projection images using forward projection of the modified metal artifact reduced 3-D image.
9. The method of claim 7 wherein the measured projection images are acquired from a cone-beam computed tomography system.
10. The method of claim 7 further comprising displaying one or more of the measured projection images, projection metal masks, or composite projection images.
11. The method of claim 7 further comprising generating a metal obstruction 3-D map that indicates the extent to which each voxel in the first 3-D image is obstructed by metal.