Microwave methods of measuring changes in lung water

Two microwave methods for measuring changes in lung water content have been investigated. The first is based on measuring changes in the phase of an active microwave signal transmitted through the thorax, while the other is based on measuring the natural microwave radiation emitted by the body with a radiometer. The feasibility of using the active microwave method is investigated by making measurements on phantoms, on anesthetized dogs with induced pulmonary edema, and on isolated dog lungs. The obtained results clearly illustrated that the method is sensitive enough to measure small changes in lung water content. In the radiometer method, on the other hand, both calculations and preliminary measurements in phantoms indicate that the natural microwave emission changes with lung water content and that conventional radiometry systems should be able to detect as little as three to four percent change in lung water content. Initial results from both methods, therefore, indicate the soundness of the basic ideas and justify further development of these methods for clinical use.