Objective To investigate the feasibility of low-c oncentration iso_osmolar contrast agent together with low tube voltage and iterative reconstruction algorithm in rabbit liver computed tonography (CT) perfusion imaging.Methods A total of 15 bealthy New Zealand rabbits were scanned twice of liver CT perfusion scans each with 24 hours interval.The first scan (routine group) was acquired at 100 kV and 100 mAs with ultravist (370 mg/ml),while the second (double low group) was acquired at 80 kV and 100 mAs with iodixanol (270 mg/ml) at 24 hours after the first scan.The obtained images were reconstructed with filtered back projection (FBP) and adaptive iterative dose reduction (AIDR-3D)algorithms in the controlled and experimental groups,respectively.The perfusion parameters including hepatic artery perfusion(HAP),portal vein perfasion(PVP),hepatic perfusion index(HPI),and total liver perfusion(TLP) and image quality as image quality score,average CT value of abdomen aorta,signalto-noise ratio(SNR),carrier-to-noise ratio(CNR),and figure of merit(FOM) were compared used pair ttest or Mann-Whitney U-test between the two groups wherever appropriate.The effective radiation dose and iodine intake were also recorded and compared.Results The image quality and perfusion parameters had no significantly different between the two groups except for FOM.The effective radiation dose and iodine intake were 38.79％ and 27.03％ lower in the double low group.Conclusions Low concentration iso _osmolar contrast agent (iodixanol,270 mg/ml) together with low tube voltage (80 kV) helps to reduce radiation dose and iodine intake without compromising perfusion parameters and image quality in liver CT perfusion imaging.

BACKGROUND:Computer-assisted implant surgery can improve implantation accuracy,but the use of implant template in the posterior tooth area is limited for patients with small opening and small interocclusal distance.Therefore,the digital guide has been improved. OBJECTIVE:To study the effect of modified implant template on the accuracy of assisted implantation in missing second molars. METHODS:From July 2020 to July 2023,40 patients who received digital guide plate implantation or free hand implantation to repair missing second molars were selected from First Affiliated Hospital of Guangzhou Medical University.According to the coin toss method,patients were randomly divided into a trial group(n=22;modified digital guide assisted implantation)and a control group(n=18;free hand implantation).The data of neck deviation,tip deviation,depth deviation,and angle deviation were compared between groups for preoperative and postoperative cone beam CT overlap analysis.One week after the operation,the patients'satisfaction with the operation was assessed by visual analog scale score. RESULTS AND CONCLUSION:(1)The trial group included 25 implants(12 in the upper jaw and 13 in the lower jaw);the control group included 23 implants(8 in the upper jaw and 15 in the lower jaw).The neck deviation,tip deviation,depth deviation,and angle deviation of the trial group were all smaller than those of the control group(P<0.05,P<0.001).There was no significant difference in accuracy between the maxillary and mandibular implant site in the trial group(P>0.05).(2)There was no significant difference in satisfaction with the operation between the two groups(P>0.05).(3)The results showed that improving the digital guide plate for assisted implantation for missing second molar can improve surgical accuracy and is suitable for patients with small opening and small interocclusal distance in the posterior tooth area.