The optimal dose reduction level in chest CT with CT volume scan mode using iterative reconstruction in piglet model

Objective To determine the feasibility and the optimal dose reduction of AIDR 3D on piglet chest CT which can provide image quality (IQ) comparable to filtered back projection (FBP).Methods Twenty-nine normal pigs with the weight of 3-12kg underwent 640-slice MDCT chest CT (Aquilion one,Toshiba) for 5 times with 80 kvp and various mAs.SureExposure3D technique were used and the index of noise were set to SD 10.0,12.5,15.0,17.5,20.0(Group A,B,C,D,E) to reduce dose successively.Group A were reconstructed with FBP,Group B,C,D,E were reconstructed using AIDR 3D (strong level).Quantitative image noise and signal to noise ratio(SNR) were measured in each group.Two radiologists graded subject image quality on both lung images (artifacts,central airway,lung tissue) and mediastinal images (mediastinal structure) and overall image quality using a 5-point scale in a blinded manner.Analysis of variance (ANOVA) and LSD test were used for comparisons of objective evaluation indices (CT value,noise,SNR)and radiation dose(CTDIvo1,DLP,ED) among the five groups.The Friedman test and Wilcoxon test were used for comparisons of demographic data and for detection of differences in subjective evaluation of IQ among groups.A receiver-operating characteristic (ROC) analysis was performed to establish a radiation reduction threshold up to which comparable IQ(score≥4) was maintained.Results Compared with Group A[noise(15.25 ± 3.14)HU,SNR 3.23 ± 1.07],Group B,C had significant lower noise and higher SNR [noise (12.11 ± 2.75),(13.18 ± 3.16)HU; SNR 4.13 ± 1.38,3.80 ± 1.20;F =7.38,3.11,P ＜0.05].Group D,E showed no significantly different noise and SNR with Group A[noise (15.14±4.51),(15.79 ±4.17)HU;SNR 3.40± 1.56,3.45 ± 1.70;P＞0.05].Group B,C had significant better subject image quality compared with Group A (P ＜0.01).Group D had no significantly different subject image quality compared with Group A (P ＞ 0.05).Group E had 5 pigs with overall image scores of ＜ 3.The ROC curve of IQ established SD 17.5 (Group D) as optimal cut-off point (AUC 0.75,95％ CI 0.58-0.92).Group D provided equivalent subjective image score and objective IQ measurements compared with FBP images in Group A.The ED of group D was 59％ lower than that of group A[CTDIvol (1.14±0.27) mGy vs (0.47 ±0.16)mGy,F=183.83,P＜0.01].Conclusion Using AIDR 3D technique,80 kvp with SureExposure3D (SD 17.5) can provide comparable IQ compared with routine dose with FBP reconstruction,and reduce 59％ dose in piglet model. Key words: Radiation dosage ;  Tomography, X-ray computed ;  Animal experimentation