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.