Reduction of beam hardening induced metal artifacts using consistency conditions

2019 ◽  
Author(s):  
Shiras Abdurahman ◽  
Robert Frysch ◽  
Georg Rose
Keyword(s):  
Beam Hardening ◽  
Metal Artifacts ◽  
Consistency Conditions

scholarly journals Contrast Enhancement Method Based on Gray and Its Distance Double-Weighting Histogram Equalization for 3D CT Images of PCBs

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
Lei Zeng ◽  
Bin Yan ◽  
Weidong Wang
Keyword(s):  
Printed Circuit Boards ◽  
Histogram Equalization ◽  
Ct Images ◽  
3D Ct ◽  
Circuit Boards ◽  
Beam Hardening ◽  
Metal Artifacts ◽  
Low Contrast ◽  
Image Histogram ◽  
Enhancement Method

Cone beam computed tomography (CBCT) is a new detection method for 3D nondestructive testing of printed circuit boards (PCBs). However, the obtained 3D image of PCBs exhibits low contrast because of several factors, such as the occurrence of metal artifacts and beam hardening, during the process of CBCT imaging. Histogram equalization (HE) algorithms cannot effectively extend the gray difference between a substrate and a metal in 3D CT images of PCBs, and the reinforcing effects are insignificant. To address this shortcoming, this study proposes an image enhancement algorithm based on gray and its distance double-weighting HE. Considering the characteristics of 3D CT images of PCBs, the proposed algorithm uses gray and its distance double-weighting strategy to change the form of the original image histogram distribution, suppresses the grayscale of a nonmetallic substrate, and expands the grayscale of wires and other metals. The proposed algorithm also enhances the gray difference between a substrate and a metal and highlights metallic materials. The proposed algorithm can enhance the gray value of wires and other metals in 3D CT images of PCBs. It applies enhancement strategies of changing gray and its distance double-weighting mechanism to adapt to this particular purpose. The flexibility and advantages of the proposed algorithm are confirmed by analyses and experimental results.

scholarly journals Reducing metal artifacts by restricting negative pixels

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Gengsheng L. Zeng ◽  
Megan Zeng
Keyword(s):  
Computed Tomography ◽  
Objective Function ◽  
Ct Scans ◽  
Filtered Backprojection ◽  
Beam Hardening ◽  
Metal Artifacts ◽  
X Ray ◽  
X Ray Computed ◽  
Set Up ◽  
True Values

AbstractWhen 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 naïve 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.

Beam Hardening Correction Using Cone Beam Consistency Conditions

2018 ◽  
Vol 37 (10) ◽  
pp. 2266-2277 ◽  
Author(s):  
Shiras Abdurahman ◽  
Robert Frysch ◽  
Richard Bismark ◽  
Steffen Melnik ◽  
Oliver Beuing ◽  
...  
Keyword(s):  
Cone Beam ◽  
Beam Hardening ◽  
Consistency Conditions ◽  
Beam Hardening Correction

Empirical Beam Hardening and Ring Artifact Correction for X‐Ray Grating Interferometry (EBHC‐GI)

2020 ◽  
Author(s):  
Brandon J. Nelson ◽  
Shuai Leng ◽  
Elisabeth R. Shanblatt ◽  
Cynthia H. McCollough ◽  
Thomas Koenig
Keyword(s):  
Beam Hardening ◽  
Artifact Correction ◽  
X Ray ◽  
Ring Artifact

scholarly journals Bootstrap bounds on closed Einstein manifolds

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
James Bonifacio ◽  
Kurt Hinterbichler
Keyword(s):  
Compact Riemannian Manifold ◽  
Tree Level ◽  
Conformal Field Theories ◽  
Einstein Manifolds ◽  
Consistency Conditions ◽  
Conformal Field ◽  
Geometric Data ◽  
Conformal Bootstrap ◽  
Laplacian Operators ◽  
Kaluza Klein

Abstract A compact Riemannian manifold is associated with geometric data given by the eigenvalues of various Laplacian operators on the manifold and the triple overlap integrals of the corresponding eigenmodes. This geometric data must satisfy certain consistency conditions that follow from associativity and the completeness of eigenmodes. We show that it is possible to obtain nontrivial bounds on the geometric data of closed Einstein manifolds by using semidefinite programming to study these consistency conditions, in analogy to the conformal bootstrap bounds on conformal field theories. These bootstrap bounds translate to constraints on the tree-level masses and cubic couplings of Kaluza-Klein modes in theories with compact extra dimensions. We show that in some cases the bounds are saturated by known manifolds.

scholarly journals String defects, supersymmetry and the Swampland

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Carlo Angelantonj ◽  
Quentin Bonnefoy ◽  
Cezar Condeescu ◽  
Emilian Dudas
Keyword(s):  
Supersymmetry Breaking ◽  
Dimensional Theory ◽  
Consistency Conditions ◽  
Tensor Multiplet ◽  
Microscopic Origin

Abstract Recently, Kim, Shiu and Vafa proposed general consistency conditions for six dimensional supergravity theories with minimal supersymmetry coming from couplings to strings. We test them in explicit perturbative orientifold models in order to unravel the microscopic origin of these constraints. Based on the perturbative data, we conjecture the existence of null charges Q∙Q = 0 for any six-dimensional theory with at least one tensor multiplet, coupling to string defects of charge Q. We then include the new constraint to exclude some six-dimensional supersymmetric anomaly-free examples that have currently no string or F-theory realization. We also investigate the constraints from the couplings to string defects in case where supersymmetry is broken in tachyon free vacua, containing non-BPS configurations of brane supersymmetry breaking type, where the breaking is localized on antibranes. In this case, some conditions have naturally to be changed or relaxed whenever the string defects experience supersymmetry breaking, whereas the constraints are still valid if they are geometrically separated from the supersymmetry breaking source.

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