| Objective(s):To investigate the application value of 120-row volumetric scanning mode,64-row helical scanning mode and 16-row spiral-scanning-mode of 320-row CT in low-dose scan of porcine orbit,and to compare the image quality and radiation dose of 320-row CT volumetric scanning mode and helical scanning mode;The application value of reducing tube voltage,applying iterative reconstruction(AIDR)and automatic tube current Modulation(ATCM)technology in low-dose CT examination of orbit,and Providing the best CT examination method for clinical applicationMethods:From January 2017 to February 2018,ten porcines from the Kunming Medical University Animal Experiment Center are selected for orbit CT scan.The examinations are performed in the Department of Radiology,the Fourth Affiliated Hospital of Kunming Medical University.The scanning method is divided into three groups according to the number of detectors used and the scanning mode.The A group is 120-row CT volume scanning mode,the B group is 64-row spiral scanning mode,and the C group is 16-row spiral scanning mode.The three groups are divided into five groups according to the selected tube voltage,standard deviation,and reconstruction method.Groups A1.B1.C1:tube voltage 120 kV,fixed tube current 200 mAs,FBP reconstruction.Groups A2?B2?C2:tube voltage 100 kV,AEC standard deviation(layer thickness 2 mm,SD value 3.5),AIDR II level reconstruction;Groups A3?B3?C3:tube voltage 100 kV,AEC standard deviation(layer thickness 2 mm,SD value 4.5),AIDR II level reconstruction;Groups A4?B4?C4:tube voltage 80 kV,AEC standard deviation(layer thickness 2mm,SD value 3.5),AIDR II level reconstruction;Groups A5?B5?C5:tube voltage 80 kV,AEC standard deviation(layer thickness 2mm,SD value 4.5),AIDR ? level reconstruction.Scan layer thickness 0.5mm and reconstruction layer thickness 2mm,layer interval 2mm,reconstruction of soft tissue function.In the axial images of the optic nerve Lens plane,the CT values of the ROI of the bilateral medial rectus muscle abdominal,the bilateral vitreous body and the bilateral adipose body of orbit in the range of 3?5mm2 are measured respectively.The CT value of the adipose body of orbit is used as the background control CT value,and the standard deviation of the CT values of the air in the region of interest 3?5 mm2 outside the orbit of the same layer was selected as the background noise.The image signal-to-noise ratio is the mean value of the tissue CT value/SD value.The contrast-to-noise ratio is the mean value of the tissue CT value minus the adipose body of orbit CT value/background air SD value.The image quality and radiation dose in 3 groups of 15 groups are statistically analyzed;the measurement data are expressed as mean±standard deviation(x±s).CT value,noise,signal-to-noise ratio,contrast-to-noise ratio,volumetric CT dose index,and dose length product between groups are compared by one-way analysis of variance(ANOVA)or Kruskal-Wallis H rank sum test,and the pairwise comparison is performed by LSD test Or Wilcoxon Mann-Whitney U rank-sum test.Image subjective quality scores are rating count data using the Kruskal-Wallis H rank sum test.Image quality assessor consistency is based on the Weight Kappa Tests(kappa test),and kappa coefficients are expressed in five groups to indicate different levels of consistency.The data measurer's consistency is measured using the ICC.Statistical test level a=0.05,the difference is statistically significant with P<0.05.Results:1.Group A:(1)The volumetric CT dose index(mGy)of five groups in group A are:40.6±0,27.96±0.72,22.39±0.76,16.14±0.67,and 15.71±0.59.There are statistically significant difference between groups A2-A5 and group Al.(2)The dose length product(mGy.cm)are:243.7±0,167.75±4.3,133.75±5.46,96.85±4.04,94.24±3.54,and there are statistically significant difference between groups A2-A5 and group Al.(3)The medial rectus muscle noise are:8.3±2.6,9.6±3.1,12.1.±4.3,18.0±4.7,19.9±5.8,There are statistically significant difference between groups A4,A5 and group Al.(4)The vitreous body noise are:4.2±1.3,6.2+1.9,7.7±2.8,12.3±3.4,and 14.7±4.6.Groups A4,A5 are statistically different from group Al.(5)The background air noise are:5.7±1.6,6.3±2.4,7.9±2.8,11.8±4.7,12.3±5.2.There are statistically significant difference between groups A4,A5 and group Al.(6)The signal-to-noise ratio of the medial rectus muscle are 4.2±2.1.,3.8±1.7,3.6±1.4,2.0±1.2,1.9±0.8,groups A4,A5 compared with group A1 statistically significant;(7)The vitreous body signal-to-noise ratio:2.8±1.3,2.3±1.0,1.9 ± 0.7,0.9±0.3,and 0.8 ± 0.1.Groups A4,A5 have statistically significant difference compared with group A1.(8)The medial rectus muscle contrast-to-noise ratio are:22.4±7.8,19.0±6.5,16.7±5.7,8.5±3.4,7.9 ± 4.2,groups A4,A5 compared with group Al statistically significant;(9)The vitreous body contrast-to-noise ratio are:17.7±5.6,15.1±4.7,13.5±4.1,8.0 ±3.6,7.2 ±3.2 There are statistically significant difference between groups A4,A5 and group A1.2.Group B:(1)The volumetric CT dose index(mGy)of five groups in group B are:52.6±0,29.46±0.79,20.08±0.83,20.79±1.07,17.06±0.52.There are statistically significant difference between groups B2-B5 and group B1.(2)The dose length product(mGy.cm)are:462.1±0,259.24±6.93,176.65±7.29,182.91±9.40,182.91±9.40.There are statistically significant difference between groups B2-B5 and group B1.(3)The medial rectus muscle noise are:8.7±2.7,9.2±3.2,10.5±3.9,12.3±4.2,18.6±6.4.There is a statistically significant difference between group B5 and group B1.(4)The vitreous body noise are:5.3±1.2,6.4±1.9,7.6±2.7,8.2±3.7,13.2 ± 4.3.There is a statistically significant difference between group B5 and group B1.(5)The background air noise are 5.3±1.4,6.2 ± 2.3,6.9±2.9,7.5±3.4,and 12.1± 5.8,respectively.There is a statistically significant difference between group B5 and group B1.(6)The signal-to-noise ratio of the medial rectus muscle are 4.3±2.2,3.9±1.9,3.6±1.5,3.3±1.2,2.1±0.9,group B5 and group B1 compared statistically significant;(7)The vitreous body signal-to-noise ratio are:2.6±1.2,2.1±1.0,1.8±0.8,1.6 ± 0.7,0.7±0.3,group B5 compared with group B1,there is a statistically significant difference;(8)The contrast-to-noise ratio of the medial rectus muscle are:22.6±7.4,19.3±6.7,18.5±6.2,16.1±5.3,9.7±4.5.There is a statistically significant difference between group B5 and group B1;(9)The vitreous body contrast-to-noise ratio are:17.4 ± 5.8,15.7±4.7,14.6±4.2,12.2±3.9,and 7.1 ±3.3.There is a statistically significant difference between group B5 and group B1.3.Group C:(1)The volumetric CT dose index(mGy)of the five groups in group C are:60±0,35.15±0.46,24.85±0.48,25.42±0.4,20.5±0.6.Groups C2-C5 compared with group Cl,the difference are statistically significant;(2)The dose length product(mGy.cm)are 419.8±0,242.85±3.31,171.69±3.39,175.65±2.96,and 141.69±4.2,respectively.Groups C2-C5 compared with group Cl,the difference are statistically significant;(3)The medial rectus muscle noise are:7.3 ± 2.1,8.5 ± 3.3,9.7 ± 3.8,11.6 ± 4.3,17.9 ± 6.7.There is a statistically significant difference between group C5 and group Cl.(4)The vitreous body noise are:4.7±1.3,5.7±2.0,6.3±2.4,7.7±3.6,12.9±4.5.There is a statistical difference between group C5 and group Cl.(5)The background air noise are 4.6±1.5,5.0±2.1,6.7±2.6,7.6 ± 3.3,and 12.6 ± 5.5.There is a statistically significant difference between group C5 and group Cl.(6)The signal-to-noise ratio of the medial rectus muscle are 4.5 ± 2.3,4.1 ± 2.0,3.7 ± 1.6,3.4±1.1,1.9±0.8.Group C5 is statistically different from group Cl;(7)The vitreous body signal-to-noise ratio are 2.7±1.3,2.3±1.1,1.9±0.8,1.5±0.7,and 0.8±0.2,respectively.There is a statistically significant difference between group C5 and group Cl.(8)The contrast-to-noise ratio of the medial rectus muscle are:21.5±7.3,18.2±6.2,17.3±5.9,15.2±5.1,8.6±3.7.and there is a statistically significant difference between group C5 and group Cl.(9)The vitreous body contrast-to-noise ratio are:16.7 ± 5.4,14.6±4.5,13.8 ± 3.9,12.9 ± 3.5,and 6.7 ± 3.1,and there is a statistically significant difference between group C5 and group Cl.4.Between groups A,B and C,the dose length product(mGy.cm)of group A3,group B4 and group C4 are 133.75±5.46,182.91±9.40,and 175.65±2.96,respectively.Groups B4,C4 compared with that of group A3,the difference in dose length product are statistically significant.Conclusion(s):1.Decrease the tube voltage,apply iterative reconstruction(AIDR)and increase the AEC noise SD value can significantly reduce the orbit radiation dose;As the AEC noise SD value increases,the tube current decreases,the noise increases,but still within the scope of the diagnosis;2.On the premise of obtaining images satisfying the diagnosis,the radiation dose of the 320-row CT orbit examination volume scanning mode is lower than that of the helical scanning mode. |
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