| Objective: 1. To confirm the hypothesis that reducing the tube voltage and tube current of computed tomographic pulmonary angiography(CTPA) by the use of Test-bolus(TB) for patients with different body mass index(BMI), and at the same time the quality of image is not affected. 2. To research the issue that which kind of scanning method between TB and Bolus-tracking(BT) method can make higher image quality with the same scanning parameters for CTPA examination process, for different BMI patientsMethods: We collected 60 cases of clinical suspected pulmonary embolism patients as the object of study from Tianjin Medical University second affiliated hospital range from September 2014 to September 2015,who were divided into 6 groups. In accordance with the pre-experimental design, patients were divided into the A to F experimental groups according to patients with different body mass index(BMI), each group of 10 patients. Group A :BMI < 25,scanning parameters : 80 k V,100 m A, TB method;Group B :BMI < 25,scanning parameters : 120 k V,automatic m A, TB method; Group C :BMI ? 25,scanning parameters : 80 k V,100 m A, TB method;Group D :BMI ? 25,scanning parameters : 120 k V,automatic m A, TB method; Group E:BMI < 25,scanning parameters : 80 k V,100 m A, BT method;Group F :BMI ? 25,scanning parameters : 120 k V,automatic m A, BT method. Objective evaluation: CT value on the main pulmonary artery, the difference between main pulmonary artery and superior vena cava, the difference between main pulmonary artery and left atrium, image signal- noise ratio(SNR), contrast to noise ratio(CNR), and radiation effective dose(ED) were measured, respectively. Subjective evaluation: evaluation by giving 1-5 score of the quantity of images by 2 physicians with more than ten years of experience of medical imaging diagnosis,by the way of double blind method.1. Comparison of group A and group B :Evaluated difference of image quality and effective radiation dose between using low tube voltage, automatic tube current modulation of TB method scanning and conventional tube voltage, automatic tube current modulation of TB scanning for patients with a BMI < 25. 2.Comparison of group C and group D :Evaluated difference of image quality and effective radiation dose between using low tube voltage, automatic tube current modulation of TB method scanning and conventional tube voltage, automatic tube current modulation of TB scanning for patients with a BMI ? 25. 3. Comparison of group A and group C :Evaluated difference of image quality and effective radiation dose between patients with a BMI<25 and ? 25 using same low tube voltage, automatic tube current modulation of TB method scanning. 4. Comparison of group A and group E :Evaluated difference of image quality and effective radiation dose between TB scanning and BT scanning using same low tube voltage, automatic tube current modulation for patients with a BMI < 25. 5. Comparison of group D and group F :Evaluated difference of image quality and effective radiation dose between TB scanning and BT scanning using same tube voltage, automatic tube current modulation for patients with a BMI ? 25. Statistical methods: the difference of the main pulmonary artery CT value between groups, CT value of main pulmonary artery and superior vena cava, CT value of main pulmonary artery and left atrium, SNR and CNR were counted by independent samples t test,SPSS 19.0 software, and the subjective evaluation used Nonparametric rank sum test, the consistency of the two radiologists image analysis used kappa test, kappa value of 0.8-1.0 suggests that the consistency of both was very good; 0.61-0.8 indicated good consistency; 0.41-0.6 showed general congruency; < 0.40 showed bad consistent. Selecting P<0.05 as an indication that the difference was statistically significant.Result: 1. No statistical difference of age, sex ratio between A-F groups(P=0.109), and the evaluation of the image from two physicians with a good consistency(P=0.769). 2. Compared Group A with Group B : CT value of pulmonary artery of group A is higher than that of group B, and the difference is statistically significant(P < 0.05); CT value difference between main pulmonary artery and left atrium in the group A was more significant than in group B, the difference is statistically significant(P < 0.05); SNR and CNR in group B higher than group A, and the difference is statistically significant(P < 0.05). The effective radiation dose in group A was significantly lower than that of group B(P < 0.05),but the difference of image score and the CT value difference of aorta and superior vena cava between the two groups had no statistical significance(P > 0.05). The results indicated that,used the TB method,scanned with a low dose group get higher pulmonary arterial CT value compared with the conventional scanning dose group for BMI < 25 patients, and more pronounced compared with the left atrium, lower effective radiation dose lead to decreased SNR and CNR, but the quality of the image unaffected. 3. Compared Group C with Group D : the CT value of main pulmonary artery of group C is higher than that of group D, the difference has statistical significance(P < 0.05). CT value difference between pulmonary artery and left atrium, main pulmonary artery and left atrium in group C was higher than that in group D, the difference is statistically significant(P < 0.05). SNR and CNR in group D were higher than group C, the difference was statistically significant(P < 0.05). The effective radiation dose of group C was significantly lower than that of group D(P < 0.05). The score of image in group D was significant higher than group C, the difference was statistically significant(P <0.05). Results indicated that, used the TB method, scanned with a low dose group get higher pulmonary arterial CT value compared with the conventional scanning dose group, for BMI ? 25 patients, and more pronounced compared with left atrium and vena venous, when the effective radiation dose is lower, the SNR and CNR decreased, and the image quality decreased. 4. Compared Group A with Group C : pulmonary artery CT value of group A is higher than that of C group, the difference has statistical significance(P < 0.05), the difference between main pulmonary artery and left atrium, pulmonary artery and superior vena cava in the CT value were not statistically significant(P > 0.05), and the SNR and CNR in group A were higher than group C, the difference was statistically significant(P<0.05); there was no statistical difference in effective radiation dose between group A and C(P > 0.05),but difference in image score was statistically significant(P < 0.05). This study Showed that by the TB method and low dose scanning, BMI<25 patients can obtain higher pulmonary arterial CT value, higher SNR and CNR than whose BMI?25,although effective radiation dose had no obvious difference, patients with BMI < 25 can get higher image quality. 5.Compared Group A with Group E: the difference of CT value of main pulmonary artery, the main pulmonary artery and superior vena cava, SNR, CNR and the effective radiation dose between group A and group E were no statistical significance(P > 0.05). the difference of CT value between pulmonary artery and left atrium, and image score difference between the groups have statistical significance(P < 0.05). The results showed that,scanned the BMI <25 patients with low dose and roughly equivalent effective radiation, and BT method were compared, TB method, the image quality from TB method is better than BT method due to the CT value difference with left atrium was larger. 6. Compared Group D with Group F: the difference of main pulmonary artery CT value, CT value difference between the main pulmonary artery and superior vena cava, SNR, CNR and the effective radiation dose between group D and group F with no statistical significance(P > 0.05), but the difference of CT value pulmonary artery and left atrium and image score between the groups have statistical significance(P < 0.05). Scanning BMI ?25 patients with conventional dose and roughly equivalent effective radiation, get better image quality by TB method than BT method due to the CT value difference with left atrium was larger.Conclusion: 1 For patients with BMI < 25, low dose CTPA scanning by TB method can ensure the image quality and reduce the effective radiation dose at the same time. 2. For patients with BMI ?25,in same effective radiation dose conditions, CTPA scanning by TB method with routine dose can get better image quality than BT method. |
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