AUTOMATIC CALCULATION OF TOTAL LUNG CAPACITY FROM AUTOMATICALLY TRACED LUNG BOUNDARIES IN POSTERO-ANTERIOR AND LATERAL DIGITAL CHEST RADIOGRAPHS

Total lung capacity (TLC) is a very important parameter in the study o f pulmonary function. In the pulmonary function laboratory, it is norm ally obtained using plethysmography or helium dilution techniques. Sev eral authors have developed methods of calculating the TLC using poste ro-anterior (PA) and lateral chest radiographs. These methods have not been often used in clinical practice. In the present work, we have de veloped an automated computer-based method for the calculation of TLC, by determining the pulmonary contours from digital PA and lateral rad iographs of the thorax. The automatic tracing of the pulmonary borders is carried out using: (1) a group of reference lines is determined in each radiograph; (2) a family of rectangular regions of interest (ROI s) defined, which include the pulmonary borders, and in each of them t he pulmonary border is identified using edge enhancement and threshold ing techniques; (3) removing outlaying points from the preliminary bou ndary set; and (4) the pulmonary border is corrected and completed by means of interpolation, extrapolation, and are fitting. The TLC is cal culated using a computerized form of the radiographic ellipses method of Barnhard. The pulmonary borders were automatically traced in a tota l of 65 normal radiographs (65 PA and 65 lateral views of the same pat ients). Three radiologists carried out a subjective evaluation of the automatic tracing of the pulmonary borders, with a finding of no error or only one minor error in 67.7% of the PA evaluations, and in 75.9% of the laterals. Comparing the automatically traced borders with borde rs traced manually by an expert radiologist, we obtained a precision o f 0.990 +/- 0.001 for the PA view, and 0,985 +/- 0.002 for the lateral . The values of TLC obtained by the automatic calculation described he re showed a high correlation (r = 0.98) with those obtained by applyin g the manual Barnhard method. (C) 1998 American Association of Physici sts in Medicine.