Common artifacts in computerized tomography : A review

A computed tomographic (CT) image is a display of the anatomy of a thin slice of the body developed from multiple X-ray absorption measurements made around the body's periphery. Unlike conventional tomography, in which the image of a thin slice is created by blurring out the information from unwanted regions, the CT image is constructed mathematically, using data arising only from the section of interest. Generating such an image is confined to cross sections of the anatomy that are oriented essentially perpendicular to the axial dimension of the body. 1 An artifact is any distortion or error in an image that is unrelated to the subject being studied. Artifacts are relatively common in CT imaging and may be considered as a source, or type, of noise. Their cause may not always be obvious. However, there are a number of different effects that may be responsible for artifacts in CT. Because artifacts in CT arise as a result of the interaction between the subject and the machine, it is useful to classify the artifacts by the nature of the error made in the scanning process. In CT, artifacts may be produced by: • Errors in X-ray attenuation measurements; • Alterations in the energy spectrum of the X-ray beam (beam hardening) as it passes through the patient; • The presence of high-density foreign materials in the body; • Partial-volume averaging effect; • Motion of the patient; • Quantum mottle (noise); • Malfunction of the detector arising from errors in detector calibrations and balance, geometric effects, or a machine peculiarity; or • Inadequate temperature, humidity, or the presence of small dust particles within the computer that causes an inadequacy in the reconstruction algorithm. This article will present common arti-facts such as streaks, rings, and black and white bands that appear in CT studies. This review addresses causes of arti-facts, their effects on the quality of the radiographic image, and procedures that can be used to reduce the presence of such artifacts. The reduction of artifacts enhances CT interpretive accuracy and helps to establish a correct diagnosis. Method During a 1-year period, 7197 CT studies were performed in a large (600-bed) teaching hospital. Within this total number of studies, 432 repeat studies were performed due to image artifacts. These repeat studies were collected and classified according to the cause of the artifacts viewed. The study included both inpa-tients and outpatients, but not all CT …