Contribution of thorax computed tomography histogram analysis to clinical evaluation in chronic obstructive pulmonary disease

Background: Chronic obstructive pulmonary disease (COPD) is one of the leading causes of chronic diseases worldwide. Today, the diagnosis of COPD is made by detecting the fixed obstruction on the spirometer, but spirometry is insufficient in recognizing the disease in the early stages. Quantitative methods of thorax computed tomography (CT) can be an effective method to detect airway obstruction in the early stages; however, there is still insufficient evidence on this subject. Therefore, this study aims to evaluate the use of densitometric thorax CT histogram analysis findings of pre-COPD and COPD groups together with clinical data. Method: Patients aged 40-80 years who were coded as COPD as a preliminary diagnosis, whose thorax CT and spirometry data were available, were included in the study. Those with risk factors and/or symptoms with FEV₁/FVC (the ratio of forced expiratory volume to forced vital capacity in 1 second) less than 70% on their spirometry were considered as COPD while those with higher FEV₁/FVC were classified as pre-COPD. Quantitative densitometric analysis was performed on thorax CTs. Radiological definition of emphysema was used in analyse. Expiratory CT is required for the radiologic definition of air trapping. As in this retrospective study, the inspiratory CTs were present, transitional air zone was defined to be a possible alternative for air trapping. Findings (lung volume, minimum and mean attenuations, percent of transitional air zone, percent of emphysema) were compared with clinical data (smoking history, shortness of breath, number of exacerbations) functional (FEV₁ (forced expiratory volume in 1 second), %FEV₁, FVC (forced vital capacity), %FVC, FEV₁/FVC) data. Results: A total of 163 cases, including 106 COPD and 57 pre-COPD, were included in the study. In the COPD group, both the percentage of the total lung transitional air zone (51,4 ± 15,6 / 43,9 ± 23,3, p= 0,032 respectively) and the percentage of emphysema between COPD and pre-COPD groups were significantly higher than the pre-COPD group. In addition, the mean total lung attenuation in the COPD group (-830,0 [(-855,6) - (-803,3) HU)]) compared to pre-COPD (-808,2 [(-830,0) - (-768,5) HU) was found to be significantly lower (p<0,001). While the percentage of total lung emphysema was correlated with the severity of dyspnea in the COPD group (r=0.184, p=0.032), the histogram parameters that correlated with dyspnea in pre-COPD were the percentage of the total lung transitional air zone (r= -0,366, p=0,005), lung volume (r= -0,330, p=0,012) and mean attenuation (r= 0,280, p=0,035). When the correlation of densitometric analysis data with spirometric values was investigated, the percentage of total lung emphysema volume was found to be significantly correlated with all spirometric variables, while FEV₁/FVC was significantly correlated with all radiological variables evaluated. x Conclusion: The findings of the study show that in the transition from pre-COPD to COPD, lung density decreases and the percentage of the emphysematous volume and defined transitional air zone increases. While the percentage of emphysema was found to be important in the COPD clinic, the transitional air zone was found to be correlated with the clinic in the pre-COPD group. Thus, it was thought that CT could be a effective method in the clinical evaluation of patients with COPD and whose pre-diagnosis is COPD, and it was predicted that this efficiency would increase with the determination of the cut-off values for the extensity of the transitional air zone defined in our study and emphysema, with future prospective studies with a larger population. Keywords: Chronic obstructive pulmonary disease, pre-COPD, lung attenuation, histogram analysis, emphysema