The Artifacts Produced on the Images during CT Scans

The following are the types of artifacts that can occur in a CT scan: streaking, rings, distortion, and shading. Streaking is usually due to a single measurement inconsistency. rings are due to individual detector calibration errors. distortion is due to helical reconstruction, and shading, which is due to the gradual deviation of a group of channels or views from the actual measurement (Barrett and Keat 2004).The causes for the origin of artifacts can be based on the following causes: physics-based artifacts, patient-based artifacts, helical and multisection artifacts, scanner-based artifacts, and artifacts due to other causes.1. Physics-based artifacts are related to the processes involved in CT data acquisition.a. Beam hardening is the preferential absorption of lower energy photons leaving only the higher energy photons during the passage of photons through a dense object (Anschel, Romanelli, and Mazumdar 2007). It is seen as a dark area immediately near an object of high attenuation (Gay and Woodcock 2007). Beam hardening gives rise to two types of artifacts: cupping artifacts and dark bands or streaks (Barrett and Keat 2004)b. Photon starvation-as the x-ray beam travels horizontally, a great deal of attenuation occurs and only few photons reach the detectors. The image, therefore, has horizontal streaks (Barrett and Keat 2004.)c. Undersampling is the presence of a large interval between projections. View aliasing is radiating fine stripes from a dense structure. Ray aliasing is stripes occurring close to the structure (Barrett and Keat 2004.)2. Patient-based artifacts occur when the patient moves during the CT scan or if the patient has any metallic objects (removable or non removable) in their body. Metal objects cause streaking artifacts (Barrett and Keat 2004) because x-ray absorption results in incomplete projection profiles (Bushong 2000). Patient movement results in shading or streaking.One of the most prevalent artifacts in CT scanning is due to respiratory motion. This artifact occurs when there is a discrepancy between the chest position on the CT image. As a result, curvilinear cold areas can occur, and this is the most common type (Sureshbabu and Mawlawi, 2005). Streaking or shading artifacts can also result if any part of the patient lies outside the scanning field (incomplete projection) (Barrett and Keat 2004.)

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