SU‐E‐T‐289: Optimal Slow Scan Technique on a Single Slice CT Scanner

Abstract

Purpose: Adoption of slow scan CT (SSCT) for contouring targets affected by respiratory motion artifacts is an accepted practice. The goal of this study was to propose a CT technique which would yield a target shape that would most closely reproduce that of the ideal excursion volume traced by a moving target sphere. Methods: A single‐slice, large‐bore Marconi scanner was used to acquire axial and spiral scans of a moving plastic sphere. 1 cm movement in the superior‐inferior and anterior‐posterior directions was considered separately to isolate directional issues. Scan techniques such as 1 sec fast scan, 4 sec slow scan, over‐scanning and pitch variations were used to produce target volumes of different shapes due to the interplay between the movement of the target and the x‐ray tube. Shapes were compared to the true excursion volume by scoring them with the Paddick conformity index (CI) as well as by visual inspection. Results: For anterioposterior movement, the average CI was 0.777 (STDEV=0.05) and the largest CI occurred for the axial slow scan, yet visual interpretation showed best agreement with Axial SSCT with overscan. For inferior‐superior movement, the average CI was 0.83 (STDEV=0.05) and the largest CI of 0.872, occurred for the spiral scan with pitch 0.5, which did agree with visual inspection. Conclusions: Optimal scanning technique, depended on the direction of movement and the interpretation method. Furthermore, it required either a pitch of 0.5 or an axial overscan technique in order to reduce respiratory motion induced target artifacts.