Technique to apply holographic interferometry to excised animal lungs

Frequency analysis of acoustic waves sent into, and reflected from, lung airways is being studied as a possible early indicator of lung disease. To help evaluate the acoustic impedance of the lung, a method has been developed to determine which parts of the surface of an excised lung are responding to the acoustic excitation via the trachea. Holographic interferometry, a very sensitive technique that can measure movements of a few μm, is being used to detect the lung-surface movement. Lungs from normal guinea pigs are being analyzed. Acoustic waves at selected frequencies are sent into the trachea and a double-exposure holograph is made of the lung. Each exposure is approximately 4 ms in duration with a separation of 2 ms. The laser pulse is obtained by interrupting the beam from a 0.5-w argon ion laser. Fringe patterns produced are an indication of lung movement. Work is continuing to distinguish normal and diseased lungs using a combination of acoustic excitation and holographic interferometric techniques