Measurement of human lung lobar volume using X-ray CT

This study was conducted to measure the lobar volumes of human lung using CT under physiological conditions and to define its changes during respiration. Chest CT scans were obtained in 16 healthy volunteers from the apex to the base of the lung at four respiratory levels; maximal inspiratory level, half inspiratory capacity level, resting expiratory level and maximal expiratory level. The outlines of the lung lobes were traced with a digitizer on CT film and the area of the lung lobes in the cross-sectional plane was calculated using a personal computer. The total area of each lobe-right upper lobe (RUL), right middle lobe (RML), right lower lobe (RLL), left upper lobe (LUL) and left lower lobe (LLL)-multiplied by the thickness of the scan space gave the lung lobar volume. We calculated the sum total of five lobar volumes at three respiratory levels in order to obtain total lung volumes (total lung capacity (TCLCT), functional residual capacity (FRCCT) and residual volume (RVCT). Vital capacity (VCCT) was determined by subtracting RVCT from TLCCT. A good correlation was found between the lung volumes (TCL, FRC, RV and VC) measured by this method and those from spirometry in the supine position. The ratio of LUL to total lung volume at the resting expiratory level, which was independent of respiratory effort, was greatest, followed by those of RLL, RUL, LLL and RML. As the respiratory level was up from the resting expiratory level to the maximal inspiratory level, the ratios of RUL, RML and LUL to total lung volume decreased, while those of LLL and RLL increased. The ratio of LLL to vital capacity was greatest, 27.7%, followed by that of RLL, 27.2%; LUL, 21.6%; RUL, 16.6%; and RML, 6.9%. This method of using CT is expected to greatly contribute to clinical practice, e.g., diagnosis of diffuse lung disease which shows local volume change and determination of lobar resection operability for patients with poor pulmonary function. (author)