Objective To construct a trajectory model for the changes in body roundness index(BRI)of elderly people in China from 2011 to 2018 based on the data derived from Chinese Longitudinal Healthy Longevity Survey(CLHLS),and analyze the influencing factors of different BRI trajectories.Methods Based on the longitudinal cohort data from the CLHLS platform,group-based trajectory model(GBTM)analysis was used to construct longitudinal change trajectories of 3 waves of BRI(2011,2014,and 2018)that meet our research criteria.Unordered multinomial logistic regression analysis was employed to identify the influencing factors of different BRI trajectories.Results A total of 2 512 valid samples were included in the analysis.The BRI trajectory of Chinese elderly people fitted by GBTM was optimally grouped into low-,medium-,and high-level growth trajectory models.There were statistically significant differences among different BRI trajectory groups in gender,length of education,resident place,living with spouse,retirement pension,sleep quality,smoking history,drinking history,continuous exercise,frequency of fruit consumption,frequency of salt-preserved vegetables consumption,and"fruit+protein"dietary patterns(P<0.05).Disordered multiclass logistic regression analysis found that,using the low-level growth trajectory model as a reference,males and those with a history of smoking were less likely to exhibit moderate to high growth levels of BRI trajectories;Elderly people with retirement pensions were more likely to exhibit a moderate to high growth level of BRI trajectory;People with a history of alcohol consumption were more likely to exhibit a moderate steady growth level of BRI trajectory;People with longer than 10 years of education were less likely to exhibit a high level of growth in the BRI trajectory,while urban residents and those who frequently consumed fruits and salted vegetables were more likely to exhibit a high level of growth in the BRI trajectory.Conclusion The trajectory of BRI changes among elderly people in China from 2011 to 2018 can be divided into 3 groups,which are influenced by multiple factors such as gender,resident place,and length of education.It is necessary to pay attention to and make measures in advance to improve the quality of life in the elderly.Countermeasures It is advisable to incorporate BRI as a core indicator in elderly health monitoring systems,establish a dynamic management mechanism for high-risk populations,and implement precision-targeted lifestyle interventions and health guidance.

Objective To discuss the feasibility of double-low technique applied in aortic MSCTA.Methods Totally 70 patients with BMI not more than 25 kg/m2 were divided into a routine group and an experimental group randomly and equally,and then went through aortic MSCTA.Iohexol (350 mgI/ml) was injected with the velocity of 4 ml/s.The routine group had the parameters as 120 kV,120 mAs and 1.5 ml/kg contrast agent,and the experimental group had the parameters as 90 kV,120 mAs and 1.0 ml/kg contrast agent,while the other scanning parameters were kept the same in the two groups.The radiation doses,contrast agent doses and iodine contents were recorded in the two groups,and the image quality was assessed with double-blind method objectively and subjectively.Results The experimental group had the CT dose index volumes (CTDIvol),dose length product (DLP) and effect dose (ED) significantly lower than those in the routine group (P＜0.05).The two groups had the consistency of subjective scores (Kappa＞0.6) and image quality scores (not lower than 2) meet the desired requirements,and there were no significant differences between the scores (P＞0.05).Objective evaluation showed that the signal values of aortic trunk and major branch vessels as well as image noise SD of the experimental group were obviously higher than those in the routine group (P＜0.05).There were no statistical differences between the signal noise ratios (SNR) and contrast to noises (CNR) in the two groups (P＞0.05),The iodine content in the contrast agent of the experimental group was significantly lower than that in the routine group (P＜0.05).Conclusion Double-low technique applied in aortic MSCTA of the patient with BMI not more than 25 kg/m2 reduces the radiation dose and iodine content in the contrast agent,has the image quality meet the desired requirements,and thus is of great value for clinical application.