Metal artifact reduction based on sinogram correction in CT

A CT image including metallic objects suffers from strong metal artifacts such as shades and streaks. Most metal artifact reduction algorithms based on filtered back-projection have tried to make a metal-free projection data by modifying the original data on the metal-traces in the sinogram. Although those algorithms are able to reduce metal artifacts, they tend to produce new artifacts and distort non-metallic regions. In this paper, we propose a novel algorithm for reducing metal artifacts while preserving non-metallic region with minimum distortion. In the algorithm, we first generate a metal-free image by removing metallic regions in the initially reconstructed image and interpolating the intensities of metallic regions with those of non-metallic surrounding pixels. Based on the metal-free image, we obtain a reprojection data. We then apply a high-pass filter (HPF) for the reprojection data and interpolate overlapping regions along the metal-trace direction. We merge the processed reprojection data with the low-pass filtered projection data after replacing metal-trace regions with linearly interpolated values. The final reconstructed image is then obtained by using this merged projection data. The proposed algorithm provides much better performance compared with the existing algorithms by effectively reducing shade artifacts between metallic objects without introducing shape distortion of non-metallic objects.