Several strategies have been developed to prevent artifacts. In this article, different artifacts in CT imaging and various techniques to prevent then will be elaborated.
Different researchers have classified artifacts in different manner. While some experts have classified artifacts based on appearance, like ring artifacts, shading artifacts and streak artifacts (Goldman, 2007, 222), others have classified them based on the causes (Yazdi and Beaulieu, 2008, 135). In this articles, classification by Yazdi and Beaulieu (2008, 135) will be used.
Patient-based artifacts occur because of some attributes in the body of the patients. The most common patient-based artifacts are metallic artifacts. These artifacts occur due to presence of irremovable metals in the body of the patient like hip prosthesis, dental filling, fracture fixation rods, cardiac prosthesis, chemotherapy ports and surgical clips. Metallic artifacts appear like streaks on images. They occur because of improper and inaccurate correction of beam hardening within the back projection that is filtered. As such, metals absorb photons heavily and cause overestimation of activity in the metallic region. This is the reason why patients are asked to remove all metallic objects in their body prior to entering the scan room. Several techniques have been developed to prevent on minimize metallic artifacts in CT images (Yazdi and Beaulieu, 2008, 136). One such strategy is to disregard data related to projections from metal objects and reconstruct image only based on projection data from non-corrupted regions. However, this method is very costly for regular scans and convergence problems occur frequently. Another strategy is to reconstruct images by manually identifying the missing projections and replacing them with non-missing projections of the surrounding areas. This method is known as projection-interpolation method. Other strategies to