measurements are consistent, so any error of measurement will usually reflect itself as an error in the reconstructed image (Barrett, and Keat, 2004, 1680). Artifacts have a major role to play in diagnostic accuracy because their presence can degrade the quality of image of computed tomography or CT scan. In this article, various types of CT artifacts and strategies to avoid or minimize them will be discussed.
Based on their appearance, there are several categories of CT artifacts and they are shading artifacts, streak artifacts,ring artifacts (Goldman, 2007, 222), distortion (Barrett, and Keat, 2004, 1680), slab artifacts, step artifacts and blurring artifacts (Siemens, 2).
Beam hardening effects is the most common shading artifact. they are due to imperfect correction of beam hardening and occur in almost all CT images. They appear as "nonuniformities in the CT numbers of a uniform material, such as CT numbers that are lower at the center of a uniform phantom than at the periphery" (Goldman, 2007, 222). The nonuniformities are most of the time less than 5HU and usually unapparent unless viewed through a narrow window. larger hardening occurs if the scan is passing through a contrast medium or thick bone regions. Shading artifacts can also occur due to scattering. But scattering is uncommon in recent scanners.
Streak artifacts are very common and are encountered in almost all scanners. they occur mainly due to bad detector measurements or inconsistent measurements. Such inconsistencies occur due to metals, partial volume effects, motion, insufficient intensity of X-ray and malfunctioning of the tube arc (Goldman, 2007, 222). (Goldman, 2007, 222).
Ring artifacts or partial ring or arc artifacts occur due to drift in calibration, errors, measurement inaccuracies and imbalances. The current generation CT scanners have corrective algorithms and are able to detect inaccuracies in measurements (Goldman, 2007, 222).