Background: Metal artifacts appearing as streaks and shadows often compromise\nreadability of computed tomography (CT) images. Particularly in a dental CT in which\nhigh resolution imaging is crucial for precise preparation of dental implants or orthodontic\ndevices, reduction of metal artifacts is very important. However, metal artifact\nreduction algorithms developed for a general medical CT may not work well in a dental\nCT since teeth themselves also have high attenuation coefficients.\nMethods: To reduce metal artifacts in dental CT images, we made prior images by\nweighted summation of two images: one, a streak-reduced image reconstructed from\nthe metal-region-modified projection data, and the other a metal-free image reconstructed\nfrom the original projection data followed by metal region deletion. To make\nthe streak-reduced image, we precisely segmented the metal region based on adaptive\nlocal thresholding, and then, we modified the metal region on the projection data\nusing linear interpolation. We made forward projection of the prior image to make the\nprior projection data. We replaced the pixel values at the metal region in the original\nprojection data with the ones taken from the prior projection data, and then, we finally\nreconstructed images from the replaced projection data. To validate the proposed\nmethod, we made computational simulations and also we made experiments on teeth\nphantoms using a micro-CT. We compared the results with the ones obtained by the\nfusion prior-based metal artifact reduction (FP-MAR) method.\nResults: In the simulation studies using a bilateral prostheses phantom and a dental\nphantom, the proposed method showed a performance similar to the FP-MAR method\nin terms of the edge profile and the structural similarity index when an optimal global\nthreshold was chosen for the FP-MAR method. In the imaging studies of teeth phantoms,\nthe proposed method showed a better performance than the FP-MAR method in\nreducing the streak artifacts without introducing any contrast anomaly.\nConclusions: The simulation and experimental imaging studies suggest that the proposed\nmethod can be used for reducing metal artifacts in dental CT images.
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