低剂量恒流控制CT扫描在初治继发性肺结核随访中的价值

Value of low-dose constant current control scanning in chest CT for the follow-up of secondary pulmonary tuberculosis in the primary therapy

目的探讨低剂量恒流控制CT扫描在初治继发性肺结核随访中对辐射剂量和图像质量的影响。方法对156例初治继发性肺结核患者首次CT检查行自动管电流调制扫描(120 kV,50~330 mA),在治疗期间的前3个月随访时行低剂量恒流控制扫描(120 kV,50 mA)。分别记录和计算两种扫描方式的辐射剂量指标:容积CT剂量指数、剂量长度乘积、有效剂量和体型特异性剂量估计值。客观图像质量评价包括分析主动脉弓和正常肺实质的信号强度、图像噪声、信噪比、对比噪声比和噪声的品质因数。采用5分制双盲法评价9种继发性肺结核CT基本病变的图像质量评分。结果与自动管电流调制CT扫描相比,低剂量恒流控制CT扫描的容积CT剂量指数、剂量长度乘积、有效剂量和体型特异性剂量估计值分别下降了68.2%(6.60/2.10 mGy)、69.9%(222.61/66.98 mGy×cm)、70.0%(3.23/0.97 mSv)和67.8%(8.66/2.79 mGy)(P<0.001),主动脉噪声增加了56.2%(40.52/92.46)(P<0.001)而信噪比降低了98.2%(1.04/0.44)(P<0.001),肺实质噪声增加了47.9%(48.84/93.82)(P<0.001),主动脉与肺实质的对比噪声比降低了95.0%(20.12/9.70)(P<0.001),噪声品质因数降低了94.2%(21.89/1.26)(P<0.001)。两种CT扫描方式的主动脉弓和肺实质CT值无统计学差异,对初治继发性肺结核患者9种CT基本病变的图像质量评分无统计学差异。结论低剂量恒流控制CT扫描比自动管电流调制更加显著地降低了辐射剂量,对主观图像质量评分无明显影响,推荐用于初治继发性肺结核的随访。

Objective To assess the effect of low-dose constant current control(LD-CCC)scanning on radiation dose and image quality in chest CT for the follow-up of secondary pulmonary tuberculosis in the primary therapy.Methods A total of 156 patients with secondary pulmonary tuberculosis in the primary therapy were received the automatic tube current modulation(ATCM)technique(120 kV,50~330 mA)at initial CT examinations,and the LD-CCC(120 kV,50 mA)scanning at the first 3 months of follow up CT examinations.The radiation dose indexes of each scanning mode were recorded and calculate respectively,including the volumetric CT dose index(CTDIvol),dose length product(DLP),effective dose(ED)and size-specific dose estimates(SSDE).Objective image quality measures including CT attenuation,image noise,signal-to-noise ratio(SNR),contrast-to-noise ratio(CNR)and figure of merit for the noise(FOMN)of aortic arch and normal lung parenchyma were assessed.Subjective image quality measures for nine forms of the basical lesions of secondary pulmonary tuberculosis were scored independently and blindingly on a five-point scale by two senior radiologists.The radiation dose and image quality indexes were compared by the paired Student t test.The consistency of CT image quality scores of two senior radiologists was evaluated by the Kappa test.Results Compared with the ATCM technique,CTDIvol,DLP,ED and SSDE of the LD-CCC scanning decreased by 68.2%(6.60/2.10 mGy),69.9%(222.61/66.98 mGy×cm),70.0%(3.23/0.97 mSv),and 67.8%(8.66/2.79 mGy),respectively(P<0.001);the image noises of of aortic arch were increased by 56.2%(40.52/92.46)(P<0.001)while SNRs were decreased by 98.2%(1.04/0.44)(P<0.001);the image noises of of aortic arch were increased by 47.9%(48.84/93.82)(P<0.001);and CNRs and FOMN of aortic arch and normal lung parenchyma were decreased by 95.0%(20.12/9.70)and 94.2%(21.89/1.26),respectively(P<0.001).There were no significant differences in CT attenuation values of aortic arch and normal lung parenchyma between ATCM and LD-CCC scanning(P>0.05).The consistency of CT image quality scores of two senior radiologists was excellent(Kappa=0.833,P<0.05).No statistically significant difference in subjective image quality scores for nine forms of the basical lesions of secondary pulmonary tuberculosis between ATCM and LD-CCC scanning was observed.Conclusions LD-CCC scanning should be recommended for the follow-up of secondary pulmonary tuberculosis in the primary therapy,because the radiation dose of the LD-CCC scanning are more significantly reduced than those of the ATCM technique,and subjective image quality scores have not been obviously changed.