Quantitative evaluation of regional pulmonary ventilation using PET and nitrogen-13 gas

A new quantitative method, "Simultaneous Exponential Equation method" (SEE), has been developed for the analysis of pulmonary ventilation studies using 13N-labeled nitrogen gas and positron emission computed tomography. This method uses Kety's model assuming insolubility of nitrogen gas in blood or tissues. Activity in poorly ventilated regions does not reach the equilibrium in the so-called equilibrium scan (EQ) performed following 3 or 4 min of washin. Therefore EQ images do not represent lung volume images nor do they provide the initial value of washout phase. Our method corrects for these transient phenomena observed during EQ scan and yields idealistic equilibrium state images (lung volume images) as well as more accurate regional ventilatory time constants than a modified Stewart-Hamilton (A/H) method and tomograms of high resolution.