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 kV, 100 mAs) (n = 40) ; 50 mAs group (low-dose protocol 120 kV, 50 mAs) (n = 40) ; and 25 mAs group (lower dose protocol 120 kV, 25 mAs) (n = 40). Images from control group were reconstructed by FBP, and low-dose 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 mAs (1.30 ± 0.17) mSv and 25 mAs (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 mAs 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 mAs 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 mAs with AIR was reduced compared with control group (100 mAs FBP) (28.43 ± 9.33) (P < 0.01), CNR and SNR were improved [CNR and SNR in control 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. (authors)