Dose reduction in spiral CT: Detection of pulmonary nodules with and without anatomic adaptation of tube current.

Purpose: To investigate the potential of projection angle-dependent anatomi cal adaptation of tube current to reduce dose in spiral CT examinations of the thorax without loss in detectability of pulmonary nodules and image qua lity. Patients and Methods: Dose can be reduced for non-circular patient cr oss-sections without an increase in noise if the tube current is reduced at those angular positions where the patient diameter and, consequently, atte nuation are small. The examinations were dose with a SOMATOM Plus 4 (Siemen s AG). CT projection data were analysed to determine the optimum tube curre nt for each projection angle in real time. We compared image quality, done. and detection rates of pulmonary nodules for thoracic spiral CT examinatio ns with and without online anatomically adapted tube current control in a g roup of 38 patients. Three radiologists counted all intrapulmonary nodules in consensus separated in three different groups (< 5mm, 5-10 mm, > 10 mm). Image quality was evaluated in a scale from 1-3 (1=very good, 2=good, 3=wo rse). Results: On average, the dose was reduced by 21% (15-34%). With a con stant tube current, 704 pulmonary nodules were detected, with tube current modulation 707 pulmonary modules. For three patients we saw more pulmonary nodules (five) with tube current modulation, for two patients we saw less p ulmonary nodules (two). In a direct comparison, the missed intrapulmonary n odules were also detected in the respective method. Thus, the detection rat e of intrapulmonary nodules was uninfluenced. In general, no deterioration of image quality was observed. Conclusion: On average, 21% dose reduction w as achieved by an anatomically adapted tube current modulation in spiral CT examinations of the thorax without a loss in detectability of pulmonary no dules and image quality. This method is an important contribution to dose r eduction in spiral CT.