Evaluation of regional pulmonary function using short-lived radioactive gases

We investigated the application of short-lived radioactive gases for the assessment of regional pulmonary function, particularly diffusing capacity, in patients with chronic obstructive lung disease and interstitial lung disease. Short-lived radioactive gases including C15O-O, 11CO2, and 11CO were produced using a baby cyclotron for medical care. Using a γ camera, breath-holding images were taken serially after inhalation of the radioactive gases. The first exponential component of time-activity curve was analyzed to obtain clearance rate, which was expressed as exponential coefficient (λ). Moreover, we created a functional map which was calculated by the clearance rate of 11CO2 as a percentage. Regional clearance rates of each gas in normal volunteers revealed higher values in the lower lung field than in the upper lung field. Whole lung clearance rates (λ) of each gas in patients correlated well with DLCO/VA, which indicates diffusing capacity. The functional map showed decreased regional diffusion closely matched to the perfusion defects seen by 99mTc-MAA perfusion images. However, in certain interstitial lung diseases decreased clearance of 11CO2 was observed in regions having no evidence of perfusion defects. We concluded the functional map display of 11CO2 is useful indicator of the regional diffusing capacity of both the normal and diseased lung, and that it is beneficial to analyze the pathogenic physiology of diseased lungs by making a comparison between the functional map of 11CO2 and 99mTc-MAA perfusion images. (author)