Abstract
The detection and quantitation of pulmonary oedema in man is difficult. The anatomical and physiological factors which control the distribution of long liquid were reviewed in order to assess the value of various physical processes upon which potential diagnostic systems might be based. From a consideration of the mechanisms of interaction, of gamma rays with matter, it was concluded that the process of incoherent gamma ray scattering would provide a basis for the measurement of fractional water content in lung tissue. A prototype scattering system was assembled so that the influence of various factors upon the accuracy of results could be explored. Once it was established that reliable results could be obtained, the factors of importance in the design of a clinical system were optimized. A device was constructed and used to explore, in vivo, the influence upon lung density of both gravity and the fractional air content of lung tissue. The division of excess lung water between the intravascular and interstitial compartments of the lung reflects the aetiology of the underlying disease. The differential diagnosis of pulmonary oedema might be possible if fractional lung blood volume could be measured. Therefore the possibility of developing a method for the measurement of the intercompartmental distribution of excess fluid was explored. It was shown that either the detection of coincident gamma rays emitted in cascade or the observation of photon induced characteristic x-rays could be used for this measurement provided suitable compounds can be developed which will be restricted to the vascular compartment.