Figure 3b. Transverse CT images obtained in the water phantom for quality assurance with scanner A (a–d) before and (e–h) after calibration. Each image represents data from one detector row. The quality of c is clearly compromised by an artifact (arrow). Images generated with data from the first and second detector rows (a, b) also contain the artifact, but it is subtle and would not affect the clinical quality of the image. No artifact is visible on images acquired after scanner calibration by the field service engineer.