Quantification of regional extravascular lung water in dogs with positron emission tomography, using constant infusion of 15O-labeled water

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Abstract
Continuous infusion of 15O-labeled water allows a quantitative measurement of the total water pool in the chest region by positron emission tomography (PET). By subsequent inhalation of 11CO the intravascular space (blood pool) can be quantitated as well. After a suitable normalization of the intravascular activities the extravascular water can be determined by subtraction of the blood pool from the water pool. The regional extravascular lung water distribution can be visualized in tomographic slices. The method was validated in an animal experiment using five dogs. They were measured before and after induction of a lung edema by IV injection of oleic acid. The increase of extravascular lung water was monitored by the thermodye-dilution method (TDD). The correlation of extravascular lung water as measured by TDD with PET measurements is good (r=0.94). The PET values agree also with gravimetric lung water determinations. An absolute quantitation of regional extravascular lung water is possible after absorption correction of the PET data via transmission measurements and calibration of the camera system. The uncertainty in the absolute quantification is±20%. In the experiments described here the mean extravascular lung water was 0.13 g/cm3 before and 0.25 g/cm3 after induction of lung edema.