Objective To assess the image quality (IQ) of an iterative reconstruction (IR) technique(sinogram affirmed iterative reconstruction,SAFIRE) for upper limb intravascular fistula CT angiography on a second generation dual-source CT scanner and determine the optimal dose level using IR with IQ comparable to filtered back projection(FBP).Methods The experiment was a prospective study.A total of 150 patients were averagely divided into 5 groups to perform upper limb intravascular fistula CT angiography.The control group was scanned with conventional tube output (120 kV,110 mAs) and images were reconstructed with FBP.The tube current of the other 4 groups (reconstructed with SAFIRE) was successively reduced to 70％,60％,50％ and 40％ of that of control group.Quantitative measurements of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were obtained in two regions of interest (ROI) in each group.The ROIs were placed at the subclavian artery near shoulder joint,and the stoma of radial artery and cephalic vein.Analysis of variance (ANOVA) was used for comparisons of objective evaluation parameters (SNR,CNR) and radiation dose (CTDIvol,DLP,E) among 5 groups.Two radiologists graded IQ in a blinded fashion on a 4-point scale (4-excellent,3-good,2-fair and 1-poor).The Kruskal-Wallis nonparametric test was performed for detection of differences in subjective evaluation of IQ among groups.Results The radiation doses of groups 77,66,55 and 44 mAs were 70％,55％,40％ and 25％ of the control group respectively.The differences of SNR and CNR among groups 77,66,44 mAs and the control group were statistically significant in ROI1 (F =24.018,20.386,P ＜ 0.05),SNR and CNR of group 77 and 66 mAs were higher than the control group while group 44 mAs was lower.The difference of SNR and CNR among group 55 mAs and the control group was not statistically significant in ROI1 (P ＞ 0.05).The differences of SNR and CNR among groups 77,66,55 mAs and the control group were statistically significant in ROI2 (F =15.934,13.818,P ＜ 0.05),and groups 77,66 and 55 mAs had higher SNR and CNR.The difference of SNR and CNR between group 44 mAs and the control group was not statistically significant in ROI2 (P ＞ 0.05).Groups 77,66,55 mAs and the control group had higher scores of the subjective IQ (≥ 3) which was descended in group 44 mAs.The differences of contrast,sharpness,noise and general impression of images among the 5 groups were statistically significant by Kruskal-Wallis nonparametric test(H =10.268,14.542,15.840,11.014,P ＜ 0.05).Using the criterion of excellent IQ(score 4),the ROC curve of dose levels and IQ acceptability established a reduction of 60％ of effective dose [Group 55 mAs:(3.545 ± 1.396) mSv] as an optimum cutoff point (AUC:0.844,95％ CI:0.705-0.982).Conclusions Iterative reconstruction technique could provide a dose reduction to 40％ (3.545 mSv) compared with the filtered back projection in upper limb intravascular fistula CT angiography without reducing equivalent image quality.

Objective: To analyze associated factors of HIV infection among college students who are young men and have sex with men (YMSM) in Tianjin, providing reference for HIV prevention and control among YMSM college students. Methods: During Aug. 1st, 2018 to Dec. 31st, 2018, SHENLAN recruited college students who were YMSM aged 18-24 years from gay baths, gay bars, QQ, WeChat and gay dating app BLUED. HIV infection status and associated factors (general demographic characteristics, unsafe sexual behaviors, addictive substance using, basic knowledge of HIV) was collected and analyzed. Results: A total of 470 college students, including 21 HIV infected (4.47%), were enrolled in this study. Univariate Logistic regression analyses indicated that age, age at first sex behavior, HIV related knowledge, tobacco use, recreational drug usage, syphilis infection was associated with HIV infection among YMSM students (P<0.05). Multivariate analysis found age of first sex (OR=21.20，95%CI=3.09-145.43), recreational drug use (OR=5.07，95%CI=1.77-14.48), lack of HIV related knowledge (OR=3.38，95%CI=1.33-8.63)were associated with HIV infection (P<0.05). Conclusion College students who are YMSM in Tianjin have a high rate of HIV infection, who deserves further attention. Targeted campus HIV/AIDS prevention program should be developed combined with specific characteristics of this population.