Noninvasive quantitative imaging of shape and volume of lungs

The Dynamic Spatial Reconstructor (DSR) can be used to determine detailed structure-to-function relationships or organ systems in vivo. A basic index of lung structure (shape and dimensions) is total lung volume. We checked the accuracy with which in vivo lung volumes can be measured by comparing lung volume (air plus tissue) determined by DSR scanning with that determined by excision and water displacement. Six dogs (2.5-26 kg) under morphine-pentobarbital anesthesia were scanned supine or prone at functional residual capacity and/or total lung capacity. With the trachea clamped at the lung volume scanned, a lethal dose of pentobarbital was administered, the lung excised, and its volume determined by water displacement. In vivo scan data were used to reconstruct adjacent 0.9-mm-thick transverse sections over the entire axial extent of the thorax. A three-dimensional surface-detection algorithm was used to generate shaded surface displays of the in situ lungs. The number of voxels (volume picture elements) of known dimensions contained within the three-dimensional image of the lung was summed to estimate total lung volume. Lung volumes calculated from the in vivo images ranged from -3.4 to +2.3% of the lung volume determined in vitro. The mean difference was 1.38 +/- 0.07% (SE). Regression analysis yielded an r value (correlation) of 1.00, a slope of 0.99, and an intercept of -4.35 ml. Multiple lung inflation steps scanned and analyzed in one dog showed similar accuracy. This technique is applicable to subjects with thorax dimensions up to 42 cm in cephalocaudal height and 39 cm in ventrodorsal and transverse diameters.