A radiographic method for assessing lung area in neonates.

The aim of this study was to determine whether computer assisted analysis of lung area on the chest radiograph reliably predicted lung volume in neonates. Anteroposterior chest radiographs taken for clinical purposes were scanned and analysed using a Power Macintosh computer with a Wacom A5 Ultra Pad and NIH image software. The cardiac, mediastinal and thymic densities and areas of perihilar and lobar consolidation were subtracted from the thoracic area to give the lung area. This was compared with lung volume, assessed by measurement of functional residual capacity (FRC), within 1 h of the chest radiograph being performed. 50 infants, median gestational age 30 weeks (range 24-43) were studied. Their median lung area was 11.23 cm2 (range 0.82-28.53) and lung volume 28 ml (range 3-103). The intraobserver and interobserver coefficients of repeatability of lung area were 1.0 cm2 and 1.06 cm2, respectively. Lung area correlated significantly with FRC (r = 0.60, p < 0.0001). It is concluded that computer assisted analysis of the chest radiograph lung area is a reliable method of assessing lung volume in neonates.