Purpose: To determine retrospectively the frequency of two artifact patterns that mimic pathologic lesions on computed tomographic (CT) head images acquired in the axial scanning mode with two different multi-detector row CT systems at the same institution.
Materials and methods: The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study and waived informed consent. The study involved two groups of consecutive patients, a group of 22 (nine men, 13 women; mean age, 56 years; age range, 27-85 years) examined with one multi-detector row CT system with four detector rows, and another group of 13 (seven men, six women; mean age, 69 years; age range, 53-81 years) examined with a different four-detector row CT system. Examinations in each group took place in a 4-week period. CT images were retrospectively evaluated by a neuroradiologist and a physicist for presence, appearance, location (within the image set and on individual images), and size of artifacts. Elimination of artifacts was verified by scanning a water phantom after scanner service and repair.
Results: A pseudolesion, or artifact, was identified in scans of four of 22 patients examined with the first scanner and eight of 13 patients examined with the second scanner. The artifact on images obtained on the first scanner, an approximately 2-cm-diameter faintly hyperattenuating and nonenhancing area with hypoattenuating collar, was found at gantry isocenter on every fourth image. A different pattern was found on images obtained on the second scanner: a 1.1-cm-diameter circular area of hypoattenuation with a faintly attenuating rim, that mimicked a cyst. This artifact was observed also at the CT scanner gantry isocenter on every fourth image. Artifacts disappeared after recalibration (first scanner) or collimator cleaning (second scanner).
Conclusion: CT scanning in the axial mode can produce a regularly repeating artifact when data from one detector row of a multi-detector row CT scanner are compromised. Because of the risk of misinterpreting such patterns, routine assessment of each detector element is recommended for multi-detector row CT scanners that are routinely used in the axial scanning mode.