There was significant difference in the CT attenuation of RCA , LAD and CX among the 3 groups ( P < 0.05 ) , the CT attenuation was the highest in group B , the CT value of RCA , LAD and CX were 537 90 , 505 90 , 484 75 HU , respectively.the CT attenuation was the lowest in group C , the CT value of RCA , LAD and CX were 357 126 , 360 95 , 378 121 HU , respectively .