A metal artifact reduction method for a dental CT based on adaptive local thresholding and prior image generation

Abstract

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

Dual‐energy‐based metal segmentation for metal artifact reduction in dental computed tomography

“…The CT images, I rf , reconstructed from the region‐filled projection data, will have reduced metal artifacts since the high‐intensity pixel values have been replaced with the ones of the surrounding pixels. However, when the metallic object is close to the objects of interest like teeth, it is often the case that the edge structure of the objects on the CT images is somewhat distorted by the pixel replacement . Simple pixel replacement on the metal trace on the projection data would break the line integral assumption of the projection data, leading to the generation of new artifacts on the CT images.…”

“…Simple pixel replacement on the metal trace on the projection data would break the line integral assumption of the projection data, leading to the generation of new artifacts on the CT images. To compensate the edge distortion caused by the pixel replacement, we used the image fusion technique . We fused the region‐filled CT image, I rf , with the original CT image ( I orig ) reconstructed from the original projection data to get the fused CT image ( I fused ) following the procedures introduced in the literature .…”

“…However, when the metallic object is close to the objects of interest like teeth, it is often the case that the edge structure of the objects on the CT images is somewhat distorted by the pixel replacement. 28,54 Simple pixel replacement on the metal trace on the projection data would break the line integral assumption of the projection data, leading to the generation of new artifacts on the CT images. To compensate the edge distortion caused by the pixel replacement, we used the image fusion technique.…”

“…To compensate the edge distortion caused by the pixel replacement, we used the image fusion technique. 54 We fused the region-filled CT image, I rf , with the original CT image (I orig ) reconstructed from the original projection data to get the fused CT image (I fused ) following the procedures introduced in the literature. 28 If the fusion of two images is made properly, the fused image has weaker metal artifacts than I orig , and it has better edge structure than I rf .…”

Development of a dental handpiece angle correction device

“…Accuracy not only improves the quality of the dental procedures, but also reduces the time required, allowing for minimally invasive techniques to reduce postoperative complications [ 1 ]. The accuracy of angulation is especially emphasized for tooth preparation of full-crowns and placement of implant fixtures [ 2 , 3 ]. During patient functioning, in order to keep the fixed prosthesis stable on the tooth, proper resistance and maintenance of the abutment form are necessary.…”