Measurement of lung tissue mass in interstitial lung disease

A gamma camera and 99m Technetium were used to obtain transmission and emission scans of the thorax in order to estimate transthoracic tissue thickness, and volumes of blood and interstitial tissue in each pixel of the gamma camera image. This technique has been applied to six patients with stage 2/3 pulmonary sarcoidosis and eight with cryptogenic fibrosing alveolitis and age and sex-matched control groups without lung disease. In both conditions transthoracic tissue thickness was significantly increased: mean values (SD) were 14.6 (1.8) cm in cryptogenic fibrosing alveolitis and 12.3 (2.2) cm in stage 2/3 sarcoidosis. This was partially accounted for by an increase in the interstitial fluid compartment. Blood volume was unaffected. Measurement of transthoracic tissue thickness involves minimal radiation exposure and may be of value in monitoring these diseases; measurement of interstitial fluid volume may give information on disease activity.