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Art"],"published-print":{"date-parts":[[2021,12]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>When the object contains metals, its x-ray computed tomography (CT) images are normally affected by streaking artifacts. These artifacts are mainly caused by the x-ray beam hardening effects, which deviate the measurements from their true values. One interesting observation of the metal artifacts is that certain regions of the metal artifacts often appear as negative pixel values. Our novel idea in this paper is to set up an objective function that restricts the negative pixel values in the image. We must point out that the na\u00efve idea of setting the negative pixel values in the reconstructed image to zero does not give the same result. This paper proposes an iterative algorithm to optimize this objective function, and the unknowns are the metal affected projections. Once the metal affected projections are estimated, the filtered backprojection algorithm is used to reconstruct the final image. This paper applies the proposed algorithm to some airport bag CT scans. The bags all contain unknown metallic objects. The metal artifacts are effectively reduced by the proposed algorithm.<\/jats:p>","DOI":"10.1186\/s42492-021-00083-z","type":"journal-article","created":{"date-parts":[[2021,6,1]],"date-time":"2021-06-01T04:01:08Z","timestamp":1622520068000},"update-policy":"http:\/\/dx.doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Reducing metal artifacts by restricting negative pixels"],"prefix":"10.1186","volume":"4","author":[{"given":"Gengsheng L.","family":"Zeng","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Megan","family":"Zeng","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"297","published-online":{"date-parts":[[2021,6,1]]},"reference":[{"key":"83_CR1","doi-asserted-by":"publisher","unstructured":"Gjesteby L, De Man B, Jin YN, Paganetti H, Verburg J, Giantsoudi D et al (2016) Metal artifact reduction in CT: where are we after four decades? 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US Patent 7444010, 28 Oct 2008"},{"key":"83_CR11","unstructured":"Manhart M, Psychogios M, Amelung N, Knauth M, Rohkohl C (2017) Improved metal artifact reduction via image quality metric optimization. Paper presented at the 14th international meeting on fully three-dimensional image reconstruction in radiology and nuclear medicin, Xi\u2019an Jiaotong University, Xi\u2019an, 18-23 June 2017"},{"key":"83_CR12","doi-asserted-by":"publisher","unstructured":"Boyd SP, Vandenberghe L (2004) Convex optimization. Cambridge University Press, Cambridge https:\/\/doi.org\/10.1017\/CBO9780511804441","DOI":"10.1017\/CBO9780511804441"},{"key":"83_CR13","doi-asserted-by":"publisher","unstructured":"Calafiore GC, El Ghaoui L (2014) Optimization models. 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