Effects of lung motion and tracer kinetics corrections on PET imaging of pulmonary function

A method to assess the three-dimensional distribution of alveolar ventilation-perfusion ratio (VA/Q) by imaging the lungs with positron emission tomography (PET) during a constant-rate intravenous infusion of 13NN-labeled saline solution was developed by C. G. Rhodes, S. O. Valind, L. H. Brudin, P. E. Wollmer, T. Jones, P. D. Buckingham, and J. M. B. Hughes (J. Appl. Physiol. 66: 1896-1904 and 1905-1913, 1989). We have modified this methodology to obtain high-resolution, low-noise PET images of local VA/Q where lung motion artifact was eliminated by respiratory gating of image collection. In addition, we have refined and implemented the methods to assess local alveolar ventilation by imaging the washout of equilibrated 13NN and local perfusion by imaging the distribution of an intravenous bolus of 13NN-labeled saline solution during apnea. This paper experimentally evaluates the effect of the implemented modifications in mechanically ventilated and anesthetized dogs. We found that the lack of gating had no significant effect on the average recovered VA/Q, but the spatial heterogeneity [pixel-by-pixel coefficient of variation squared (CV2) = SD2/mean2] was underestimated by 14%. The lack of gating during the washout underestimated the average specific ventilation by 11% and decreased the corresponding CV2 by 50%.