STAIR-STEP ARTIFACTS IN 3-DIMENSIONAL HELICAL CT - AN EXPERIMENTAL-STUDY

PURPOSE: Stair-step artifacts in helical computed tomography (CT) are associated with inclined surfaces in longitudinal sections. The authors investigated the origin and the characteristics of the artifacts. MATERIALS AND METHODS: A cone phantom and a skull were dry-scanned with a helical CT scanner, and images were reconstructed by using the half-scan interpolation algorithm with combinations of detector collimation (1 and 5 mm), table feed (1, 2, 5, and 10 mm), and reconstruction interval (1, 2, 5, and 10 mm). RESULTS: Stair-step artifacts were perceived in most instances. Stair-step artifacts arose from two sources: large reconstruction intervals and asymmetric helix interpolation, forming isoclosed curves and spirallike patterns in three-dimensional axial views, respectively. CONCLUSION: To eliminate the stair-step artifacts, both the collimation and the table feed should be less than the longitudinal dimension of the important feature on inclined surfaces, and the reconstruction interval should be less than the table feed. Adaptive interpolation may correct the artifacts.