Correlation of positron emission tomography ventilation-perfusion matching with CT densitometry in severe emphysema

Emphysema severity is frequently measured on CT via densitometry. Correlation with scintigraphic and spirometric functional measures of ventilation or perfusion varies widely, and no prior study has evaluated correlation between densitometry and lobar ventilation/perfusion in patients with severe emphysema. The aim of this study was to evaluate the utility and findings of gallium-68 (⁶⁸Ga) ventilation/perfusion positron emission tomography-CT (⁶⁸Ga-VQ/PET-CT) in severe emphysema assessment.

Fourteen consecutive patients undergoing evaluation for bronchoscopic lung volume reduction between March 2015 and March 2018 underwent ⁶⁸Ga-VQ/PET-CT assessment for lobar functional lung mapping, in addition to CT densitometry. Correlations between CT densitometry and ⁶⁸Ga-VQ/PET-CT parameters for individual lobar lung function were sought.

CT densitometry assessment of emphysema correlated only weakly (R² = 0.13) with lobar perfusion and was not correlated with ventilation (R² = 0.04). Densitometry was moderately (R² = 0.67) correlated with V/Q units in upper lobes, though poorly reflected physiological function in lower lobes (R² = 0.19). Emphysema severity, as measured by CT densitometry, was moderately correlated with proportion of normal V/Q units and matched V/Q defects in individual lobes.

Assessment of lobar pulmonary function by ⁶⁸Ga-VQ/PET-CT provides physiologic information not evident on CT densitometry such as ventilation and perfusion specifics and matched defects. Further research is needed to see if the discordant findings on ⁶⁸Ga-VQ/PET-CT provide prognostic information or can be used to modify patient management and improve outcomes.