64层CT低剂量扫描在胸主动脉CTA中的临床应用研究

目的 探讨64层CT低剂量扫描在胸主动脉CT血管造影（CTA）成像中的临床应用研究。方法 应用64层CT对100例胸厚为22～23cm疑似胸主动脉疾病的患者分成5组进行胸主动脉CTA扫描,扫描范围为250～300mm,扫描条件为机器默认的120kV、350mAs,然后固定120kV,用300mAs、250mAs、200mAs及150mAs对其它四组患者进行扫描,记录不同mAs的CTDIvol及DLP,并转换为有效剂量ED。2位影像学家对上述图像进行SNR、CNR及主观评价。结果 将120kV、350mAs及300mAs、250mAs、200mAs及150mAs扫描产生的图像传至机器工作站进行SNR及CNR计算,其值分别为：4.81、4.02、2.59、1.73、1.57和3.81、3.27、1.86、0.92、0.94。2位影像学家对120kV下350～150mAs主观评价分值分别为：4.61±0.72,4.48±0.30,4.52±0.28,4.28±0.36,3.65±0.38;其CTDIvol、DLP分别为：10.08mGy、8.73mGy、7.14mGy、5.68mGy、4.21mGy和352.8mGy、309.32mGy、255.46mGy、203.8mGy、171.08mGy,将DLP转换为ED为5.29mSv、4.64mSv、3.83mSv、3.06mSv、2.57mSv。对上述数据进行单因素方差分析,200mAs和350mAs、300mAs、250mAs产生的影像质量没有明显差异,但200mAs的CTDIvol、DLP及ED较350mAs分别低43.7%、42.2%及43.7%。结论 胸厚为22～23cm的患者进行胸主动脉CTA扫描推荐mAs为200mAs。对于体型较小（肌肉较少）或有肺气肿等疾病可以选用150mAs及以下条件进行扫描。

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

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 ram, the scan factors were 120 kV, 350 mAs, which were the acquiescent parameters of the CT scanner. Then, the patients of other 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 independent radiologists with different mAs. The images of different were read by 2 independent radiologists with 5-pointscale. 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 4±0.72, 4.48±0.30, 4.52±0.28, 4. 284±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. TheEDwereS. 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 43.7G, 42.2G 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.