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Prediction of anatomical lung volume using planimetric measurements on chest radiographs

Background The anatomical lung volume is conventionally measured by computed tomography (CT). However, chest radiographs could be considered as an alternative method with low cost and low radiation. Purpose To predict the anatomical lung volume using planimetric measurements of chest radiographs. Material and Methods In total, 119 participants (M:F ratio = 66:53; age, 53.7 ± 9.6 years) who underwent chest CT for lung cancer screening were enrolled. The lung volume on CT was measured as a reference for the anatomical lung volume. To eliminate the bias from the degree of inspiration, virtual chest radiographs (posterior–anterior view and lateral view) were generated from the CT images using the thick multiplanar technique, and the lung area (cm2) was measured in the right (P), left (Q), and lateral (R) lungs according to the planimetric method. A regression equation predicting the anatomical lung volume from the planimetric measurements was generated. The correlation between the measured and estimated lung volumes was evaluated. The percentage error rate (%) was calculated and the equation was validated internally and externally. Results The equation predicting the anatomical lung volume (mL) was 9.6*S–1367, where the summed lung area (S) was defined as (P + Q + R). The measured and estimated lung volumes were highly correlated (R = 0.941, P < 0.001). The absolute error rate was 5.7 ± 4.9%. The root mean square error of the equation was 290.2. The root mean square errors on internal and external validation were 300.4 and 267.0. Conclusion The anatomical lung volume may be feasibly and accurately predicted from planimetric measurements of chest radiographs.