A projection-domain iterative algorithm for metal artifact reduction by minimizing the total-variation norm and the negative-pixel energy

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.

Reducing metal artifacts by restricting negative pixels

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.

Three-dimensional CT angiography study on the relations between the vertebral artery and atlantoaxial joint

Background The vertebral artery （VA） and atlantoaxial joint （AAJ）, with complicated structures, are located in the depths of the head-neck boundary area, the regional anatomy of which cannot be shown globally and directly. This study aims to evaluate three-dimensional CT angiography （3DCTA） in displaying the AAJ, atlantoaxial segment of the vertebral artery （ASVA） and the identification of their interrelations. Methods Sixty-eight subjects without pathology of the ASVA and AAJ were selected from head-neck CTA examination. All the 3D images were formed with volume rendering （VR） together with techniques of separating, fusing, opacifying and false-coloring （SFOF）. On the 3D images, the ASVA and AAJ were observed, and their interrelations were measured. Results All the 3DCTA images were of high quality and up to our requirements. They could clearly and directly show the ASVA, ascending along the AAJ. There were 5 curves in the course of the ASVA, of which 2 curves were away from the atlantoaxial joint, one in the 2rid curve of 0.0 mm-5.4 mm, the other in the 4th of 2.6 mm-9.2 mm. There was no significant difference in the measurements between left and right （P 〉0.05）. The curved parts of the ASVA slightly expanded, with the biggest diameter of 5.6 mm in the 4th curve. Statistical comparison shows that the left ASVA is larger than the right （P 〈0.05）. Variations of the ASVA were found in 8 cases and of the AAJ in 12. Conclusions 3DCTA can globally and directly demonstrate the structures of the AAJ, ASVA and their interrelations. The 3D imaging data make up and enrich the research contents of regional anatomy and lay the foundation for related study and applications.