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...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 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.展开更多
Metal objects in X-ray computed tomography can cause severe artifacts.The state-of-the-art metal artifact reduction methods are in the sinogram inpainting category and are iterative methods.This paper proposes a proje...Metal objects in X-ray computed tomography can cause severe artifacts.The state-of-the-art metal artifact reduction methods are in the sinogram inpainting category and are iterative methods.This paper proposes a projectiondomain algorithm to reduce the metal artifacts.In this algorithm,the unknowns are the metal-affected projections,while the objective function is set up in the image domain.The data fidelity term is not utilized in the objective function.The objective function of the proposed algorithm consists of two terms:the total variation of the metalremoved image and the energy of the negative-valued pixels in the image.After the metal-affected projections are modified,the final image is reconstructed via the filtered backprojection algorithm.The feasibility of the proposed algorithm has been verified by real experimental data.展开更多
Due to the beam-hardening effect of the broad energy spectrum of the X-ray source in computed tomography,the reconstructed images usually suffer from severe artifacts when metallic objects are being imaged.Metal artif...Due to the beam-hardening effect of the broad energy spectrum of the X-ray source in computed tomography,the reconstructed images usually suffer from severe artifacts when metallic objects are being imaged.Metal artifact correction methods are usually sophisticated and not practical,especially in some non-medical applications,in which the linear attenuation coefficients are unknown.This paper suggests a simple and effective algorithm to estimate the unreliable measurements.The proposed algorithm is an iterative algorithm,in which the iteration is performed in the projection domain,while the objective function is set up in the image domain.The final image is reconstructed with the conventional filtered backprojection algorithm.The feasibility of the proposed method is verified with airport bags that contain some unknown metals.展开更多
Several bulk metallic glasses （BMGs） were selected to in vitro assess their magnetic resonance imaging （MRI） compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magne...Several bulk metallic glasses （BMGs） were selected to in vitro assess their magnetic resonance imaging （MRI） compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magnetic resonance image. The investigated metals include the Au49Ags.sPd2.3Cu26.9Si16.3, Zr61Ti2Cu2sA112, Cu50.4Nis.0Ti31Zr13 and Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2, together with pure titanium （CP-Ti） and Co-28Cr-6Mo alloy （ASTM-F799） for comparison. The artifact extent in MR images was quantitatively characterized according to the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo （FSE） sequence and gradient echo （GRE） sequence. As indicated, artifact severity of the BMGs is much less than that of the CoCrMo alloy. The AuAgPdCuSi BMG manifested the smallest arti- fact among the four BMGs, while the TiCuZrFeSnSiAg BMG is comparative to the CP-Ti. The MRI compatibility of BMGs is ranked as a sequence of the Au-, Zr-, Cu- and Ti-based alloys. Dependence of material mag- netic susceptibility on artifact extent is also the case of the BMGs, even though it does not follow a simple linear relationship within a range of △χv = 30-180 ppm. These findings are of interest to reveal that the BMGs are potentially applied in the fields associated with an interventional MRI for MRI-guided surgeries.展开更多
High-attenuation object-induced streaking and shadow artifacts in computerized to- mography （CT） are somewhat connected to the misfit of the X-ray projection data to the range space of the Radon transform. This misf...High-attenuation object-induced streaking and shadow artifacts in computerized to- mography （CT） are somewhat connected to the misfit of the X-ray projection data to the range space of the Radon transform. This misfit is mainly due to the beam hardening factor of the projection data which is unavoidable for polychromatic sources. The major difficulty in dealing with the beam hardening-induced streaking and shadow artifacts comes from its highly nonlinear nature depending on geometries of high attenuation objects. In this work, we investigate the mathematical characteristics of those streaking and shadow artifacts from the structure of the projection data. We also proposed a metal artifacts reduction method by incorporating the recent technique of the nonlinear beam-hardening corrector. Numerical simulations show that the proposed method effectively alleviates the streaking artifacts without changing the background images.展开更多
基金This research is partially supported by NIH,No.R15EB024283.
文摘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 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.
基金This research is partially supported by NIH,No.R15EB024283.
文摘Metal objects in X-ray computed tomography can cause severe artifacts.The state-of-the-art metal artifact reduction methods are in the sinogram inpainting category and are iterative methods.This paper proposes a projectiondomain algorithm to reduce the metal artifacts.In this algorithm,the unknowns are the metal-affected projections,while the objective function is set up in the image domain.The data fidelity term is not utilized in the objective function.The objective function of the proposed algorithm consists of two terms:the total variation of the metalremoved image and the energy of the negative-valued pixels in the image.After the metal-affected projections are modified,the final image is reconstructed via the filtered backprojection algorithm.The feasibility of the proposed algorithm has been verified by real experimental data.
文摘Due to the beam-hardening effect of the broad energy spectrum of the X-ray source in computed tomography,the reconstructed images usually suffer from severe artifacts when metallic objects are being imaged.Metal artifact correction methods are usually sophisticated and not practical,especially in some non-medical applications,in which the linear attenuation coefficients are unknown.This paper suggests a simple and effective algorithm to estimate the unreliable measurements.The proposed algorithm is an iterative algorithm,in which the iteration is performed in the projection domain,while the objective function is set up in the image domain.The final image is reconstructed with the conventional filtered backprojection algorithm.The feasibility of the proposed method is verified with airport bags that contain some unknown metals.
基金supported by the National Natural Science Foundation of China under Grant No.51571192
文摘Several bulk metallic glasses （BMGs） were selected to in vitro assess their magnetic resonance imaging （MRI） compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magnetic resonance image. The investigated metals include the Au49Ags.sPd2.3Cu26.9Si16.3, Zr61Ti2Cu2sA112, Cu50.4Nis.0Ti31Zr13 and Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2, together with pure titanium （CP-Ti） and Co-28Cr-6Mo alloy （ASTM-F799） for comparison. The artifact extent in MR images was quantitatively characterized according to the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo （FSE） sequence and gradient echo （GRE） sequence. As indicated, artifact severity of the BMGs is much less than that of the CoCrMo alloy. The AuAgPdCuSi BMG manifested the smallest arti- fact among the four BMGs, while the TiCuZrFeSnSiAg BMG is comparative to the CP-Ti. The MRI compatibility of BMGs is ranked as a sequence of the Au-, Zr-, Cu- and Ti-based alloys. Dependence of material mag- netic susceptibility on artifact extent is also the case of the BMGs, even though it does not follow a simple linear relationship within a range of △χv = 30-180 ppm. These findings are of interest to reveal that the BMGs are potentially applied in the fields associated with an interventional MRI for MRI-guided surgeries.
文摘High-attenuation object-induced streaking and shadow artifacts in computerized to- mography （CT） are somewhat connected to the misfit of the X-ray projection data to the range space of the Radon transform. This misfit is mainly due to the beam hardening factor of the projection data which is unavoidable for polychromatic sources. The major difficulty in dealing with the beam hardening-induced streaking and shadow artifacts comes from its highly nonlinear nature depending on geometries of high attenuation objects. In this work, we investigate the mathematical characteristics of those streaking and shadow artifacts from the structure of the projection data. We also proposed a metal artifacts reduction method by incorporating the recent technique of the nonlinear beam-hardening corrector. Numerical simulations show that the proposed method effectively alleviates the streaking artifacts without changing the background images.
