PURPOSE: To evaluate the effect of reduced volume of contrast media on vascular opacification and image quality in spiral CT of the chest. MATERIALS AND METHODS: Sixty patients referred for chest CT were examined withspiral CT with 60ml(n=30) or 90ml(n=30) of 30% ionic contrast media(Rayvist 300 , Schering, Germany) alternately.Injection rate of each group was as follows : 2.0 ml/sec for 20 seconds followed by 1.0 ml/sec for 20 seconds in 60ml group and 2.0ml/sec for 45 seconds in 90ml group. Twenty-five seconds scanning delay was employed. For the objective comparison of vascular opacification, CT numbers were measured at superior vena cava, ascending and descending aorta, right and left pulmonary artery, left atrium, and inferior vena cava. For the subjective comparison three radiologists scored the grade of vascular opacification and image quality blindly and independently. All data were analyzed statistically. RESULTS: The mean values of measured CT numbers in 90ml group were higher than those in 60ml group(p <.05) at the same level. The overall mean score of vascular opacification in 90ml group was 2.86, and 2.31 in 60ml group(p <.0001). In the overall mean score of imagequality, there was no statistically significant difference between 90ml group(2.46) and 60ml group(2.40). CONCLUSION: Althought there is some degradation of vascular opacification in 60ml group, overall image quality is not degraded. Therefore, 60 ml of contrast media can be used in spiral CT of the chest without degradation ofoverall image quality except in spiral CT angiography.