Radiation exposure in spiral computed tomography -: Dose distribution and dose reduction

RATIONALE AND OBJECTIVES. The authors investigate the dose distribution of spiral and conventional computed tomography (CT) with film densitometry and to present a new method of evaluating the possibility of dose savings with spiral CT. METHODS. Films were exposed in a cuboid polymethylmethacrylate phantom in conventional and spiral scan technique. Axial density profiles were obtained by digitizing the films using a fluorescent light scanner. The ratio of the number of rotations in spiral CT to the number of slices in conventional CT was calculated, RESULTS In spiral CT with a pitch of 2, the densities in all points were lower than those in corresponding points in spiral CT with a pitch of 1 and in conventional CT with slice distance equal to slice thickness. A pitch of 1.5 in spiral CT led to a dose reduction of 14% to 30% compared with conventional CT. CONCLUSIONS. Increasing the pitch in spiral CT leads to a reduction of both integral dose and absorbed doses within the examined body region. The reduction of the integral dose can be significant, especially in cases where slice overlapping is diagnostically advantageous.