THORACIC SPIRAL CT - INFLUENCE OF SUBSECOND GANTRY ROTATION ON IMAGE QUALITY

PURPOSE: To determine if the lower milliampere second setting acid sho rter acquisition time of subsecond spiral computed tomography (CT) aff ects the image quality of thoracic CT scans. MATERIALS AND METHODS: In 92 consecutive outpatients, referred for thoracic CJ, spiral CT (120 kV, 292 mA) was performed with 1-second (n = 45) or 0.75-second (n=47) scanning time. An equal percentage of patients (70%) in each group re ceived intravenous contrast medium. At six mediastinal and six lung zo nes, degradation due to motion and noise, respectively, were graded in dependently on a tour-point scale by three blinded radiologists. Stati stically significant differences were determined with a two-tailed t t est. RESULTS: Mediastinal image quality was significant better on 0.75 -second scans than on 1-second scans (P<.001). Regions with the greate st improvement in image quality were around the aortic root, cardiac v entricles, and aortic arch. Lung image quality was also better on 0.75 -second scans than on 1-second scans (P =.04). On 0.75- and 1-second s cans, respectively, motion-related artifacts were found to degrade ima ge quality 6.2 and 8.7 times more than noise-related artifacts in the mediastinum and 2.6 and 3.9 times more in the lungs. CONCLUSION: Subse cond spiral CT is associated with improved clarity and diminished moti on artifacts on mediastinal and pulmonary images when compared with 1- second spiral CT.