In vitro sheep fetal lung tissue characterization with ultrasound

Ultrasound is a non-invasive diagnostic tool that could provide important information about pulmonary maturity. Quantitative ultrasound techniques that relate lung tissue acoustic properties, i.e. acoustic velocity, attenuation, and scattering, to its physical properties, such as, elastic and structural properties, have been reviewed. B-mode techniques were equipment dependent and produced conflicting results. A-mode techniques are less dependent on the measuring equipment and could provide more accurate information about lung development. A-node techniques were applied to the study of regional differences within the fetal lung. The accuracy of these techniques could be instrumental to the eventual determination of lung maturation. To pursue this possibility, the alveolar regions across the upper, middle, and lower lobes of physiologically mature normal preterm lamb lungs were scanned to determine their acoustic properties within the frequency range of 1-15 MHz. Average speed of sound, attenuation and size of backscatterers were found to be independent of lung regions. Comparison between the lung mean size of backscatterers and mean alveolar sac diameter, histologically measured from the whole lung, showed that these data were not statistically different. This suggested that the collagen rich alveolar sac septal walls were the principal sources of scattering. Histological measurements on the size of alveolar sacs across different regions of the lung were also independent of the lung regions. The results of this study on the fetal lamb lungs suggested that A-mode ultrasound is sensitive to lung developmental changes. The ability of A-mode ultrasound to determine lung maturity appears promising. Further experiments on regional lung development and lung maturation at the pre and post-surfactant synthesis stages of the gestational life may establish the basis for an accurate and risk-free ultrasound assessment of lung maturation that is reliable in a clinical settin