The application of low radiation dose in thoracic aorta CTA with 64 slice CT

YA NG Wei-dong

Abstract：Objective To investigate low radiation dose in thoracic aorta CT angiography (CTA ) with 64 slice CT . Methods 100 patients whose body mass index (BMI) was 22~23 were randomly divided into 5 groups ,the patients of first group underwent thoracic aorta CTA with 64 slice CT scanner .The scanning range was from 250 cm to 300 mm ,the scan factors were 120 kV ,350 mAs ,which were the acquiescent parameters of the CT scanner .Then ,the patients of oth-er groups underwent thoracic aorta CTA by varying mAs (300 mAs ,250 mAs ,200 mAs ,150 mAs) ,the CTDIvol and DLP were recorded in different mAs and the DLP was put into effective dose .The SNR and CNR were calculated by 2 in-dependent radiologists with different mAs .The images of different were read by 2 independent radiologists with 5-point-scale .Results The values of SNR and CNR at the 120 kV ,350 mAs and 300 mAs ,250 mAs ,200 mAs ,150 mAs were 4 .81 ,4 .02 ,2 .59 ,1 .73 ,1 .57 and 3 .81 ,3 .27 ,1 .86 ,0 .92 ,0 .94 .The values by two independent radiologists were 4 .61 ± 0 .72 ,4 .48 ± 0 .30 ,4.52 ± 0 .28 ,4 .28 ± 0 .36 ,3 .65 ± 0 .38 .The CTDIvol and DLP with different mAs (350 mAs ,300 mAs ,250 mAs ,200 mAs ,150 mAs) were 10 .08 mGy ,8 .73 mGy ,7 .14 mGy ,5 .68 mGy ,4 .21 mGy and 352 .8 mGy , 309 .32 mGy ,255 .46 mGy ,203 .8 mGy ,171 .08 mGy .The ED were 5 .29 mSv ,4 .64 mSv ,3 .83 mSv ,3 .06 mSv ,2 .57 mSv .Statistical analysis was performed for analysis of variance ,and the date were not statistically significant ( P>0.05) at the exposure factors of 200 mAs ,250 mAs ,300 mAs than 350 mAs ,but the CTDIvol ,DLP and ED of 200 mAs were reduced by 43 .7% ,42 .2% and 43 .7% ,respectively than the 350 mAs .Conclusion The best mAs is 200 mAs for the average person whose chest thickness is from 22 to 23 in thoracic aorta CTA .For smaller (less muscle) or emphysema and other diseases ,150 mAs and less than 150 mAs can be chosen .