Examination of the Improvement of Longitudinal Resolution by Using Helical CT

Multiplanar reformation(MPR) images of helical CT suffer from poor longitudinal resolution and the "stair-step" artifact. We attempted to solve these problems by studying five scanning modes(1 mm collimation with 1 pitch; 1 mm collimation with 2 pitches; 3 mm collimation with 0.5 pitch; 3mm collimation with 1 pitch; and 5 mm collimation with 1 pitch). Longitudinal resolution was found to be affected more by slice collimation than table feed. The stair-step artifact consists of a rotation effect and aliasing effect. The rotation effect was a cyclic artifact, and the cycle was dependent on table feed. In order to solve these problems, we employed a restoration filter to improve longitudinal resolution and a band filter to remove the stair-step artifact. In the clinical images, we used three scanning modes(1 mm collimation with 1 pitch; 3 mm collimation with 0.5 pitch; 3 mm collimation with 1 pitch). In conclusion, these problems in scanning images were completely solved by using 1 mm collimation with 1 pitch. However, we were not able to solve the problems in scanning images using 3 mm collimation with 0.5 and 1 pitch.