Spatial heterogeneity of lung perfusion assessed with ¹³N PET as a vascular biomarker in chronic obstructive pulmonary disease

Although it is known that structural and functional changes in the pulmonary vasculature and parenchyma occur in the progress of chronic obstructive pulmonary disease (COPD), information is limited on early regional perfusion (Q̇r) alterations. Methods: We studied 6 patients with mild or moderate COPD and 9 healthy subjects (6 young and 3 age-matched). The PET ¹³NN-labeled saline injection method was used to compute images of Q̇r and regional ventilation (V̇r). Transmission scans were used to assess regional density. We used the squared coefficient of variation to quantify Q̇r heterogeneity and length-scale analysis to quantify the contribution to total perfusion heterogeneity of regions ranging from less than 12 to more than 108 mm. Results: Perfusion distribution in COPD subjects showed larger Q̇r heterogeneity, higher contribution from large length scales and lower contribution from small length scales, and larger heterogeneity of Q̇r normalized by tissue density than did healthy subjects. Dorsoventral gradients of V̇r were present in healthy subjects, with larger ventilation in dependent regions, whereas no gradient was present in COPD. Heterogeneity of ventilation-perfusion ratios was larger in COPD. Conclusion: Q̇r is significantly redistributed in COPD. Q̇r heterogeneity in COPD patients is greater than in healthy subjects, mainly because of the contribution of large lung regions and not because of changes in tissue density or V̇r. The assessment of spatial heterogeneity of lung perfusion with ¹³NN- saline PET may serve as a vascular biomarker in COPD.