Study On Quantitative Evaluation Of Lung Function With Low-dose CT In Connective Tissue Disease-associated Interstitial Lung Disease

Objective: To study the correlation between CT quantitative parameters and pulmonary function in connective tissue-associated interstitial pneumonia(CTD-ILD)by half-dose expiratory and inspiratory CT scanning,so as to explore the application value of half-dose CT scanning and CT quantitative technique in the evaluation of CTD-ILD lung injury.Methods: 34 patients diagnosed as connective tissue disease in clinical in Guangxi Medical University were collected,including 17 cases of systemic sclerosis,5 cases of dermatomyositis,3 cases of rheumatoid arthritis,2 cases of Sjogren’s syndrome,2 cases of mixed connective tissue disease and 5 cases of systemic lupus erythematosus.According to whether the lung diffusion capacity decrease or not,34 patients were divided into experimental group(n = 22)and control group(n = 12).All patients underwent end-inspiratory and end-expiratory CT scanning,then the images were analyzed by lung 3D imaging software in Siemens syngo.via workstation.After research,the CT quantitative parameters of the two phases were obtained,including lung volume(TLV),mean lung density(MIA),high density attenuation area(HAV%),low density attenuation area(LAV%),normal lung volume percentage(NL%),interstitial lung volume percentage(ILDV%).HRCT images were scored using the CT visual assessment scale.All patients accepted pulmonary function examination within one week after CT scanning mentioned above,and the pulmonary function parameters such as total lung function(TLC),vital capacity(VC),forced vital capacity(FVC),one second forced end-expiratory lung volume(FEV1)and carbon monoxide diffusing capacity(DLCO)were obtained for further analysis.On the basis that the quantitative parameters of CT were in accordance with normal distribution,its difference between the experimental group and the control group was analyzed by two independent samples t-test.The differences of MLD among different lung regions(upper lung,middle lung,lower lung area,inner zone and outer lung area)were compared.The correlation between pulmonary function indexes and both CT quantitative parameters and visual score was studied,and ROC curve was used to evaluate the value of CT quantitative parameters in predicting pulmonary diffusion dysfunction in patients with ILD.Results:(1)The quantitative parameters of inspiratory phase lung volume CT(TLVin),inspiratory phase mean lung density(MLDin),inspiratory phase high-density decay(HAVin%),high-density attenuation expiratory phase(HAVex%),inspiratory phase normal lung volume volume percentage(NLin%)in the experimental group(diffuse lung function decline)and control group(normal pulmonary diffusion function)between groups are statistically significant.(2)The difference in lung density between different lung regions was compared.The results showed that MLD of the lower lung was significantly higher than that of the upper lung and the middle lung(P < 0.05),and MLD of the outer lung was significantly higher than that of the inner lung(P < 0.05).(3)Correlation analysis of CT quantitative parameters of inspiratory phase and lung function parameters showed moderate positive correlation between TLV and TLC,VC,FVC,EFV1,which TLV was highly correlated with FVC(r=0.79)and EFV1(r=0.80).MLD had moderate negative correlation with VC,FVC,FEV1 and DLCO,and MLD was highest correlated with FEV1(r=-0.61).There was moderate positive correlation between LAV and TLC,FVC,FEV1.HAV was negatively correlated with VC,FVC,FEV1 and DLCO.NL% was positively correlated with VC,FVC,FEV1 and DLCO.ILDV% had moderate negative correlation with DLCO.(4)In the quantitative parameters of expiratory phase CT,only LAV was positively correlated with FEV1/FVC.(5)NL%showed the highest sensitivity and specificity in predicting pulmonary diffusion dysfunction,and the area under ROC curve was 0.962.Conclusion:(1)CT quantitative parameters can provide an objective index to evaluate the pulmonary function damage of CTD-ILD.(2)There is a good correlation between TLV and pulmonary function parameters,which can be used to predict the severity of pulmonary ventilation disorders.(3)NL% and ILDV% can be used to evaluate the reserve capacity and damage of lung diffusion function,and they are good indicators for predicting lung function.