关键词: 体层摄影术, 辐射剂量, 低对比剂浓度, 消化道, 活动性出血

Abstract: Background　Patients diagnosed with gastrointestinal bleeding by multislice-spiral CT（MSCT） received high doses of radiation and contrast agents.The CT value of iodine contrast agent was increased with the decrease of tube voltage.We tried to determine the optimal scanning scheme to reduce the radiation dose and contrast dose simultaneously on the premise of satisfying the diagnostic requirements.Objective　To explore the feasibility of low-concentration contrast medium of MSCT combined with low-dose scanning technology in the diagnosis of gastrointestinal bleeding model scanning，so as to obtain the optimal scanning scheme and provide research basis for clinical application.Methods　CT values of bleeding points of 30 patients with gastrointestinal bleeding diagnosed by MSCT enhanced examination and confirmed by surgery from May 2014 to October 2016 in North China University of Science and Technology Affiliated Hospital were measured.The average value was （212.1±64.5） HU.Taking the measured CT value of the bleeding point as the reference value，the nonionic contrast agent，ioversol（320 mgI/ ml ） was diluted with 0.9% sodium chloride solution and divided into 4 iodine solutions with different concentrations（6.4，5.76，5.12，and 4.48 mgI / ml，respectively）．The corresponding CT values of 120 kV were（214.7±1.6），（185.9±1.4），（162.2±1.4），and （140.5±2.5） HU，respectively.Different doses of CT enhancement scanning were performed on the bleeding model groups.The control group was 120 kV and 300 mAs.Experimental group：Group A：100 kV，300 mAs；Group B：100 kV，400 mAs；Group C：80 kV，400 mAs；Group D：80kV，465 mAs，and the concentration of contrast agent corresponds to the concentration of 4 iodine solutions.Each concentration was scanned 7 times.Two experienced radiologists used double blind method to read the film，recorded CT volume dose index（CTDIvol） and dose length product（DLP），and calculate effective dose （ED）．The objective noise of the image was measured，the signal-to-noise ratio of the image and subjective score of the image quality calculated，the detection of gastrointestinal bleeding in each group of MSCT recorded，and the CT value of bleeding points measured to evaluate the optimal scanning scheme.Results　CTDIvol was 19.6 mGy in control group，12.4 mGy in experimental group A，16.5 mgy in experimental group B，8.2 mGy in experimental group C，and 9.5 mGy in experimental group D.DLP and ED in experimental groups were lower than those in control group（P<0.05 ）．There was no statistically significant difference in image noise，signal-to-noise ratio and subjective score of image quality between experimental group B and control group（P>0.05）．The image noise of groups A，C and D in the experimental group was higher than that of control group，while the signal-to-noise ratio and subjective score of image quality were lower than those of control group（P<0.05）．The average CT values of the bleeding points in all experimental groups were higher than those of the control group at the same concentration of contrast agent（P<0.05）．Control group（6.4 mgI/ml） and experimental group B（6.4 and 5.76 mgI/ml） had the same detection rate of bleeding.There was no statistically significant difference between experimental group B（5.12 mgI/ml） and control group（6.4 mgI/ml） in detection rate（P>0.05），while experimental group B （4.48 mgI / ml） had lower detection rate than control group（P<0.05）．Conclusion　MSCT double low technique is feasible to diagnose hemorrhage in digestive tract hemorrhage model scanning.Experimental group B（100 kV，400 mAs ） is the optimal scanning parameter.Under the condition of simulated hemorrhage rate of 0.5 ml/min，the optimal contrast agent concentration at the bleeding point of the model under the scanning condition is 5.12 mgI/ml，and the corresponding CT value at the bleeding point is about
（99.4±10.1） HU.

Key words: Tomography, Radiation dosage, Low contrast concentration, Gastrointestinal, Active hemorrhage