| Objective: To explore the application of iterative reconstruction technique(ASIR-V) for reducing radiation dose of chest revolution CT scan.Methods: We randomly collected 120 patients who underwent chest revolution CT scan and randomly divided them into four groups. Each group contained 30 cases and was scanned in the weight of 0%, 20%, 40%, 60% ASIR-V, respectively(afterhere marked as A, B, C, D group). Scanning conditions were set as follows: the noise index was set to 9, 120 KV tube voltage, tube current automatic milliampere(Smart m A 80-350), X-ray tube rotation speed 0.5s, pitch 0.992:1. We measured the height and weight of patients before the examination, and calculated the body mass index(BMI). Then we recorded the volume computed tomography dose index(CTDIvol), dose length product(DLP) which were displayed automatically in machine for each patient scan. In addition, according to the formula of the effective dose(ED)(MSV) = K(m Sv, m Gy-1 of / cm x DLP(m Gy cm), we calculated the value of ED(k=0.019) to made an evaluation on four groups of CT images. We also measured noise(SDn), noise ratio between pulmonary artery and erector spinae contrast(CNRp), noise ratio of pulmonary artery(SNp). We made a subjective quality score for four groups of lung window and mediastinum window images. And then we used the single factor variance analysis to deal with the differences between all groups.Results:(1) With the increase of ASIR-V weight, the effective dose of the patients decreased gradually where a negative correlation existed between them. There was statistics significant difference between four groups of data(P<0.05). The effective dose of A group was maximal which was 5.13±0.48 m Sv. The effective dose of D group was minimum which was 1.97±0.50 m Sv and dose reduction was about 61.6% of A group.(2) For different ASIR-V weight, there were statistics significant differences between the four groups(P<0.05). The noise values of A, B and C groups(SDa) decreased gradually with the increase of ASIR-V weight. C group was 7.23±1.78, and the fourth group, the largest group of four noise, was 8.81±1.91.(3) For different ASIR-V weight, the noise ratio of the contrast of the pulmonary artery and vertical spinal musculare for four group(CNRp) was significant difference(P<0.05). For the four groups, there were statistical differences(P<0.05) in the pulmonary artery signal to noise ratio(SNp) in different ASIR-V weights. CNRp was maximum in 40% ASIR-V weight, which was 1.54±1.01, while in 20% ASIR-V weight CNRp was the smallest, which was 0.998±1.07.(4) For four groups, there were significant differences(P<0.05) for the SNp in different ASIR-V weights. SNp in the first three groups showed an increasing trend. The D group was the lowest whose value was 4.84±1.60 while C group was the maximum whose value was 6.10±1.90.(5) In terms of the evaluation for image quality, there were significant differences among the four groups(P<0.05). The scores of four groups showed a decreasing trend and the former three groups of decreasing trend is relatively weak which was significantly lower. Group A scored the highest value(14.2±1.03), and group D scored the lowest value(8.7±1.12).Conclusion: Considering the effective radiation dose and subjective evaluation index of image quality, the application of 40% weight of ASIR-V can effectively decrease the ED values and also can guarantee the image quality in CT revolution chest plain scan. |
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