Optimization of low-dose protocol in thoracic aorta CTA : weighting of adaptive statistical iterative reconstruction (ASIR) algorithm and scanning parameters

Abstract

Objective To investigate the best weighting of adaptive statistical iterative reconstruction (ASIR) algorithm and optimized low-dose scanning parameters in thoracic aorta CT angiography(CTA).Methods Totally 120 patients with the body mass index (BMI) of 19-24 were randomly divided into 6 groups.All patients underwent thoracic aorta CTA with a GE Discovery CT 750 HD scanner (ranging from 290-330 mm).The default parameters (100 kV,240 mAs) were applied in Group 1.Reconstructions were performed with different weightings of ASIR (10％-100％ with 10％),and the signal to noise ratio (S/N) and contrast to noise ratio (C/N) of images were calculated.The images of series were evaluated by 2 independent radiologists with 5-point-scale and lastly the best weighting were revealed.Then the mAs in Group 2-6 were defined as 210,180,150,120 and 90 with the kilovoltage 100.The CTDIvoland DLP in every scan series were recorded and the effective dose (E) was calculated.The S/N and C/N were calculated and the image quality was assessed by two radiologists.Results The best weighing of ASIR was 60％ at the 100 kV,240 mAs.Under 60％ of ASIR and 100 kV,the scores of image quality from 240 mAs to 90 mAs were(4.78 ±0.30)-(3.15 ±0.23).The CTDIvol and DLP were 12.64-4.41 mGy and 331.81-128.27 mGy,and the E was 4.98-1.92 mSv.The image qualities among Group 1-5 were nor significantly different (F =5.365,P ＞ 0.05),but the CTDIvol and DLP of Group 5 were reduced by 37.0％ and 36.9％,respectively compared with Group 1.Conclusions In thoracic aorta CT Angiography,the best weighting of ASIR is 60％,and 120 mAs is the best mAs with 100 kV in patients with BMI 19-24. Key words: Adaptive statistical iterative reconstruction; Radiation dose; Image quality; Thoracic aorta CTA