Study of iterative reconstruction(iDose~4)for radiation dose reduction in chest CT scan:apilot study

Objective:To study the value of iterative reconstruction(iDose 4)in radiation dose reduction in chest CT scan.Methods:One hundred and twenty patients planning to have contrast-enhanced chest CT examination were randomly assigned to 3 groups,with 40 patients in each group.The scanning parameters in plain scan and pulmonary artery phase were similar(120Kv,automatic tube current regulation).In the aortic phase,the tube current was 40 mAs,30 mAs and 20 mAs respectively in these 3 groups.Filtered back projection(FBP)was used in plain and pulmonary artery phase for image reconstruction.Both filtered back projection(FBP)and iDose 4were used in aortic phase,the iDose 4 grade levels were 1 to 6.The effective radiation exposure was compared between pulmonary arterial phase and aorta phase.The differences of CT value of the air within tracheal lumen,the standard deviation(SD value)and signal-to-noise ratios(SNR)were compared and analyzed.Image quality was evaluated subjectively and using a 3-grade scale according to the pulmonary ministructure(subpleural small vessels within the area 2cm from the pleura)on pulmonary window.Taking the mean score2 as the acceptable image quality for clinical application,the mean score in different mAs-iDose 4 groups were evaluated. Results:The effective radiation exposure in routine dosage group for pulmonary arterial phase was(5.84±1.41)mSv.For aorta phase,the 40 mAs group was(1.49±0.70)mSv;the 30 mAs group was(1.04±0.19)mSv and the 20 mAs group was(0.71±0.05)mSv.The CT value of the intra-tracheal air revealed no significant difference between groups with different electric current and with different image reconstruction method(P0.05).The average SD value and SNR showed significant differences between groups with different electric current and with different reconstruction methods(P0.05).For the grading of intra-pulmonary mini-structure,the mean score for each group in pulmonary arterial phase was 3.The mean score deviation of aorta phase was more than 2 for the group of 40 mAs under reconstruction of iDose4-4、5、6,the group of 30 mAs under reconstruction of iDose4-5、6and the group of 20mAs under reconstruction of iDose4-6.Conclusion:The application of iterative reconstruction(iDose 4)was valuable in radiation dose reduction with image quality guarantee in Chest CT.Acceptable image quality can be obtained for chest CT images acquired at 40 mAs by using iDose4-4,30 mAs by using iDose4-5 and 20 mAs by using iDose4-6.