A blind, comparative clinical study was performed prospectively to examine the correlation between image quality of CT scan in terms of contrast enhancement effect and amount of intravenous contrast media. A total of 357 patients were randomized into two groups Ionic high-osmolality contrast media (68% meglumine ioglicate)was administered intravenously as 100ml bolus in one group and as 50ml bolus in the other group. Statistically significant differences of image quality were found in CT scans of the brain, head and neck, chest and abdomen (p<0.05). However in the pelvis, difference was not statistically significant. (p>0.05) We suggest that amount of contrast media may be r educed in pelvis CT without significant degradation of image quality.