Objective To investigate the effectiveness of new-generation snapshot freeze(NG SSF)technology for improving image quality of coronary CT angiography(CCTA)in patients with different heart rate(HR).Methods CCTA data of 164 patients obtained with a 256-row CT scanner and voltages of 80,100 and 120 kV,respectively,in one cardiac cycle were retrospectively analyzed.Smart electrocardiogram(ECG)gating technology was used to calculate patient's HR and choose automatic exposure phase.For these with HR≤65 beats/min(low HR group),the exposure time window was set between 70%—80%R-R interval,for 65 beats/min＜HR≤85 beats/min(medium HR group)was set between 40%—80%R-R interval,while for those HR＞85 beats/min(high HR group)was set between 40%—60%R-R interval.Standard reconstruction(STD),the first-generation snapshot freeze(SSF1)and NG SSF were performed to reconstruct CCTA images,respectively.Subjective scoring of each segment of right coronary artery(RCA),left anterior descending(LAD)and left circumflex artery(LCX)shown on CCTA were performed based on Likert scale.Results In low HR group,the scores of middle and distal segments of LAD and all segments of RCA and LCX on NG SSF CCTA were significantly higher than on STD,and of middle segment of RCA and distal segment of LAD were both higher than on SSF1(all P＜0.05).In medium HR group,the scores of all branches on NG SSF CCTA were significantly higher than on STD or SSF1 CCTA(all P＜0.05).In high HR group,the scores of coronary branches showed on NG SSF CCTA were all significantly higher than on STD CCTA,while of the proximal and distal segments of RCA,middle and distal segments of LAD and all segments of LCX were significantly higher than on SSF1 CCTA(all P＜0.05).Conclusion NG SSF could effectively enhance image quality of prospective ECG-gated CCTA in patients with varying HR.

Objective To investigate the effectiveness of new-generation snapshot freeze(NG SSF)technology for improving image quality of coronary CT angiography(CCTA)in patients with different heart rate(HR).Methods CCTA data of 164 patients obtained with a 256-row CT scanner and voltages of 80,100 and 120 kV,respectively,in one cardiac cycle were retrospectively analyzed.Smart electrocardiogram(ECG)gating technology was used to calculate patient's HR and choose automatic exposure phase.For these with HR≤65 beats/min(low HR group),the exposure time window was set between 70%—80%R-R interval,for 65 beats/min＜HR≤85 beats/min(medium HR group)was set between 40%—80%R-R interval,while for those HR＞85 beats/min(high HR group)was set between 40%—60%R-R interval.Standard reconstruction(STD),the first-generation snapshot freeze(SSF1)and NG SSF were performed to reconstruct CCTA images,respectively.Subjective scoring of each segment of right coronary artery(RCA),left anterior descending(LAD)and left circumflex artery(LCX)shown on CCTA were performed based on Likert scale.Results In low HR group,the scores of middle and distal segments of LAD and all segments of RCA and LCX on NG SSF CCTA were significantly higher than on STD,and of middle segment of RCA and distal segment of LAD were both higher than on SSF1(all P＜0.05).In medium HR group,the scores of all branches on NG SSF CCTA were significantly higher than on STD or SSF1 CCTA(all P＜0.05).In high HR group,the scores of coronary branches showed on NG SSF CCTA were all significantly higher than on STD CCTA,while of the proximal and distal segments of RCA,middle and distal segments of LAD and all segments of LCX were significantly higher than on SSF1 CCTA(all P＜0.05).Conclusion NG SSF could effectively enhance image quality of prospective ECG-gated CCTA in patients with varying HR.

Objective To investigate the impact of parameters setting on image quality and radiation dose of low-dose chest CT scanning when iCT tube current was set as 17 mAs.Methods Two hundred volunteers who accepted low-dose chest CT screening with tube current was set as 17 mAs were randomly divided into four groups according to the tube voltage and automatic exposure control (DoseRight) settings (group A:120 kV,DoseRight;group B:100 kV,DoseRight;group C:120 kV,fixed tube current;group D:100 kV,fixed tube current).Then hybrid iterative reconstruction (HIR:iDose4) and iterative model reconstruction (IMR) were performed on all scanned images of lung and mediastinal window algorithm,respectively.The effective dose and image quality of 4 groups were compared.Results There were significant differences of image quality score and effective dose among 4 groups.The image quality of group A and B were better than that of group C (P＜0.05),and of group D was the worst compared with the other three groups (P＜0.05).Image quality scores of the mediastinal window of group C and D and the lung window of group D at iDose4 reconstruction were lower.SNR value of group A,B,C,D decreased in order (P＜0.01).Group A had the highest effective dose (P＜0.01),while the effective dose of group B and group C had no significant difference (P=0.055),and group D had the lowest effective dose (P＜ 0.01).Conclusion When tube current was set as 17mAs at iCT,selecting 100 kV tube voltage,DoseRight and IMR reconstruction arithmetic can obtain satisfactory image quality and low radiation dose.