Research And Implementation Of Metal Artifacts Reduction And CT Value Calibration In Dental Computed Tomography

Dental X-ray Computed Tomography (CT) is playing an important role in diagnosis of dental diseases. Having measured the x-ray attenuation through across-section of an object in different directions, the distribution of the x-ray attenuation in this cross-section is constructed by a computer, and then it will be diplayed to assist doctors to locate the position of focus of infection. Compared with the commercial CT, dental CT has many advantages, for example, low dose and radiation. However, a series of problems and challenges of dental CT still need to be solved in clinical examination. The accuracy of CT value and metal artifacts are prominent issues. Therefore, some researches on CT value calibration and Metal Artifact Reduction (MAR) were promoted in this thesis, which mainly include the contents as follows:In view of metal artifacts, this thesis contains two aspects to reduce metal artifacts. The first method is compensate the projection data of metal projection region by interpolation. The second method is iterative reconstruction calibration methods. This method reconstruct image by using the nonmetal projection data. The thesis implements the ART iterative reconstruction calibration method and MLEM calibration method. The third metal artifact correction method based on the weighting projection data, this method uses three parts projection data, including the template image projection data, spline interpolation projection data and corrected projection data. A corrected image by using the weighted three parts data was obtained. The method not only implement the data continuity in each projection angle, and also implements the data continuity between angle and angle.In view of the current shortage of present commercial CT value correction method, this thesis presents a suitable CT value correction method for dental CT, this method takes into full consideration about the presence of image noise and artifacts in the reconstructed image.The new method was applied to simulate metal artifact image with the image SNR improved by 22%. The improved CT value correction method can improve the accuracy of CT value. The ROI of water phantom image was improved by 53%.