A modified method of lung tissue volume measurement using computed tomography numbers

Purpose The values of lung tissue volume obtained by computed tomography (CT)-based analyses tend to be larger than those obtained by other methods. Establishing accurate reference values for normal lung tissue volume is important for elucidating lung changes in various diseases and may also provide reference values for information on an individual’s potential lung function and lung growth. The present study established a method for accurately calculating the lung tissue volume using CT numbers. Materials and methods An equation for calculating lung tissue volume based on volume and composition ratio was established, and the lung tissue volume was calculated by substituting the defined CT numbers for air and lung tissue into the equation. The definition of CT number for lung tissue was determined by measuring 64 areas in 32 cases of atelectasis. The definition of CT number for air was determined by evaluating the air CT number measured in the trachea. The degree of measurement error using this method was evaluated in 12 normal cases in which CT was performed on multiple days during inspiratory and expiratory CT. The volume of lung tissue was calculated for 100 normal cases (50 consecutive males and 50 consecutive females). Results Lung tissue volume showed a moderate correlation with height (r = 0.65, p < 0.0001). The strongest correlation was observed with volume of the total lung (r = 0.75, p < 0.0001). The lung tissue volume was approximately 530 ml for a standard body size (height, 1.7 m). The variation in the values using this method was 1.7–17.4%. Conclusion Our study using CT numbers supports the findings of previous reports using non-image analysis. This measurement method has the potential to provide a large amount of new, noninvasive anatomical information regarding the lungs.