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目的探讨使用低管电压行多层螺旋CT下肢静脉造影降低辐射剂量的可行性及图像质量的对比研究。方法前瞻性选择2011年8月至2012年5月疑似下肢静脉疾病的患者45例,分为Ⅰ组(常规剂量组120 kV、300mA)、Ⅱ组(100 kV、300 mA)、Ⅲ组(80 kV、300 mA)。分别对各组下肢静脉信噪比(SNR)、对比噪声比(CNR)及辐射剂量进行统计。由两名资深影像学医师以5分制对图像诊断的接受率及主观噪声进行评价,采用Kappa检验评价两名医师对图像质量评价的一致性。使用单因素方差检验(one-way ANOVA检验)对容积CT剂量指数(CTDIv-ol)、剂量长度乘积(DLP)、有效剂量(E)、SNR、CNR等主观评价行统计学分析。各组间数据使用LSD检验行统计学分析。结果Ⅰ、Ⅱ、Ⅲ组下肢静脉的SNR分别为355.97±11.68、314.37±20.88、283.93±10.71,3者间差异有统计学意义(F=57.12、P=0.00);CNR分别为328.86±10.67、292.47±19.41、270.27±10.42,3者间差异有统计学意义(F=43.8、P=0.00)。SNR与CNR各组间数据两两比较差异均有统计学意义(P=0.00,P<0.05)。Ⅰ、Ⅱ、Ⅲ组的图像主观评价平均分为4.89±0.31、4.83±0.38、4.77±0.42,3组间差异无统计学意义(Ⅰ与Ⅱ组P=0.357;Ⅱ与Ⅲ组P=0.347;Ⅰ与Ⅲ组P=0.063)。两名医师对Ⅰ、Ⅱ、Ⅲ组的图像主观评价结果经检验差异无统计学意义(F=1.74,P=0.178;F=0.653,P=0.526)(P>0.05)。两名医师对Ⅰ、Ⅱ、Ⅲ组的图像主观评价结果一致性较好(Kappa=0.872,P=0.00)。Ⅰ、Ⅱ、Ⅲ组的CTDIvol、DLP、E分别为20.13、12.48、6.24;2114.38±27.4、1447.78±16.7、646.28±16.12;31.72±0.39、21.72±0.24、9.70±0.23,差异均有统计学意义(P=0.00,P<0.05)。结论 80 kV组与常规组对比E降低了70%,而SNR、CNR分别仅下降20%和18%。同时图像的主观评价无统计学意义,均能达到诊断要求。所以推荐多层螺旋CT下肢静脉造影检查使用80 kV扫描。
Objective To explore the feasibility and the comparative study of the radiation dose reduction by low-voltage venography and multi-slice spiral CT venography. Methods Forty-five patients with suspected venous leg disease from August 2011 to May 2012 were prospectively selected. Patients in group Ⅰ (120 kV, 300 mA), group Ⅱ (100 kV, 300 mA), group Ⅲ kV, 300 mA). The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and radiation dose of the veins in each group were calculated. Two senior imaging physicians evaluated the rate of image diagnosis acceptance and subjective noise using a five-point scale. The Kappa test was used to evaluate the consistency of the two physicians in evaluating image quality. One-way ANOVA was used to statistically analyze subjective evaluation of volume CT dose-exponent (CTDIv-ol), dose length product (DLP), effective dose (E), SNR, CNR and so on. Data between groups were statistically analyzed using the LSD test line. Results The SNR of lower extremity veins in group Ⅰ, Ⅱ and Ⅲ were 355.97 ± 11.68, 314.37 ± 20.88 and 283.93 ± 10.71, respectively (F = 57.12, P = 0.00); CNR was 328.86 ± 10.67, 292.47 ± 19.41,270.27 ± 10.42, there was a significant difference between them (F = 43.8, P = 0.00). SNR and CNR data between the two groups were statistically significant differences (P = 0.00, P <0.05). There was no significant difference between subgroups in the subjective evaluation of Ⅰ, Ⅱ and Ⅲ subgroups (4.89 ± 0.31, 4.83 ± 0.38, 4.77 ± 0.42, P = 0.357 in group Ⅰ and Ⅱ; P = 0.347 in group Ⅱ and Ⅲ; Ⅰ and Ⅲ group P = 0.063). There was no significant difference between the two physicians in the subjective evaluation of Ⅰ, Ⅱ and Ⅲ images (F = 1.74, P = 0.178; F = 0.653, P = 0.526) (P> 0.05). The subjective evaluation results of the two physicians in group I, II and III were consistent (Kappa = 0.872, P = 0.00). The CTDIvol, DLP and E of group Ⅰ, Ⅱ and Ⅲ were 20.13,12.48,6.24, 2114.38 ± 27.4,1447.78 ± 16.7,646.28 ± 16.12, 31.72 ± 0.39,21.72 ± 0.24,9.70 ± 0.23, respectively, with statistical significance (P = 0.00, P <0.05). Conclusion Compared with the control group, the contrast E of the 80 kV group decreased by 70%, while the SNR and CNR decreased by only 20% and 18% respectively. At the same time subjective evaluation of the image was not statistically significant, can meet the diagnostic requirements. Therefore, multi-slice spiral CT venography is recommended to use 80 kV scan.