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Proposing a Hybrid Method for Reducing the Artifact of the Computed Tomography (CT) Images

Ghorbanzadeh, Mohammad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54012 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Hosseini, Abolfazl; Vosoughi Vahdat, Bijan
  7. Abstract:
  8. Over the past few decades, computed tomography (CT) has been introduced as one of the leading cross-sectional imaging techniques in a wide range of clinical applications in diagnostic radiology, oncology, and multimodal molecular imaging. Despite the recognized value of this imaging technique, the quality and accuracy of CT images can be compromised by a number of physical destructive factors. The presence of metal objects such as dental fillings, hip or knee prostheses, heart pacemakers, war fragments and spinal cages can cause and intensify image artifacts. These types of artifacts appear as black and white lines in the image, obscuring the structures and textures around the metal implant and destroying the diagnostic value of the CT images. These artifacts also affect the accuracy of treatment planning in radiation therapy, which relies on CT images to determine electron density and estimate the relative stopping power of particles. Therefore, to solve this problem, for 4 decades, algorithms called metal artifact reduction (MAR) have been proposed, which, despite years of progress, have remained insufficient. Conventional methods, in addition to reducing metal artifacts, add new artifacts to the image and inevitably destroy image information, causing the edges of the image to be lost. Also, these methods are not able to reduce the artifact in areas where there are high-density implants (jaw area). In this thesis, we present a promising method to increase the efficiency of MAR using a combination of two methods, iterative-based metal artifact reduction and sinogram correction methods, so that in addition to not adding new artifacts to the image, it also preserves the edges of the image. Contrary to conventional methods, it provides good output in almost all cases and types of implants. The embedded algorithm solves the challenges posed in the previous methods by forming the prior image using the weighted relationship between the original image and the image corrected by the linear interpolation method and applying an edge preserving filter. Adding a iterative process by reducing the weight of the original image in the output image reconstruction has helped to meet this challenge. The accuracy and precision of the proposed method has been studied by the following methods: clinical, parametric and intuitive examination, all of which show the high accuracy of the proposed method
  9. Keywords:
  10. Radiotherapy ; Artifact Reduction ; Metal Artifact ; Metal Artifact Reduction ; Normalized Mmetal Artifact Reduction (NMAR) ; Computed Tomography (CT) ; IW_NMAR Algorithm

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