Compared with the 120-kV group , effective dose and amount of contrast agent in the 80-kV group were decreased by 57.8 % and 30.5 % ( effective dose :2.7 0.5 vs. 6.4 1.3 mSv ; amount of contrast agent :57.1 3.2 vs. 82.1 6.1 mL ; both p < 0.0001 ) , respectively .