Radiation dose reduction with chest CT using iterative reconstruction technique

Objective To evaluate the image quality and dosage reduction of chest low dose CT (LDCT) using advanced iterative reconstruction (AIR) technique and filtered back projection (FBP). Methods One hundred and twenty patients underwent non-contrast chest CT examinations,they were randomly assigned into three groups:control group (standard dose protocol 120 k V,100 m As) (n=40) ; 50 m As group (low-dose protocol 120 k V,50 m As) (n=40) ; and 25 m As group (lower dose protocol 120 k V,25 m As) (n=40).Images from control group were reconstructed by FBP,and lowdose groups were reconstructed by FBP and AIR.Quantitative noise,signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured,image quality was scored subjectively by three experienced radiologists.The radiation dose,image noise and the image quality of the 3 groups were compared and analyzed statistically.Differences of radiation dose and noise among groups were determined with t test,image quality with Mann-Whitney test and the consistency of diagnosis with Kappa test. Results The mean effective radiation dose in low dose groups 50 m As (1.30±0.17) mSv and 25 m As (0.66±0.08) mSv was reduced by 52.4% and 75.8% respectively compared with control group (2.73±0.27) mSv.Image noise (MSD) in 50 m As group with AIR compared with FBP was reduced[ (21.33±6.44) and (31.01±7.51),P<0.01].CNR was improved[ (41.73±9.94) and (28.02±10.23),P<0.01],and SNR was improved[ (44.09±10.34) and (29.61±9.34),P<0.01],MSD in 25 m As group with AIR compared with FBP was reduced[ (30.28±10.68) and (45.89±18.66),P<0.01].CNR was improved[ (31.68±11.23) and (22.83±10.24),P<0.01],and SNR was improved[ (32.91±14.25) and (21.60±10.21),P<0.01].MSD in 50 m As with AIR was reduced compared with control group (100 m As FBP) (28.43±9.33) (P<0.01),CNR and SNR were improved[CNR and SNR in contrd group was (33.54±10.21) and (34.44±12.01) ] (P<0.01).Kappa value of the two reviewers were 0.56. Conclusion Compared with FBP,50 and 25 mAs groups with AIR technique (iDose4) could maintain or improve image quality on pulmonary CT while reducing radiation dose by 52.4% and 75.8% respectively. Key words: Lung; Tomography,X-ray computed; Radiation dosage