Ultrasonic Absorption and Reflection by Lung Tissue Free

The acoustic reflection and absorption coefficients of both normal and diseased (pneumonitis) excised lung tissue (dog) were experimentally determined at a frequency of 0.98 Mc/sec. It is found that the physiological saline‐lung interface reflects 50% of the sound energy impinging at normal incidence. The acoustic amplitude absorption coefficient per unit path length of lung tissue is 4.7 cm⁻⁴. The very high absorption exhibited can be explained as the result of radiation of acoustic energy by the pulsating gaseous structures of the lung tissue. The theory indicates that the absorption coefficient of lung tissue should approach a minimum as the frequency is increased above 1 Mc/sec and should then increase at still higher frequencies. The diseased lung exhibited an acoustic absorption coefficient approximately 25% less than that of normal lung specimens. (This work was aided by a grant from the American Thoracic Society.)