Abstract
Objective: This paper evaluates the influence of the specific 133Xe ventilation images used to calculate differential function in quantitative ventilation-perfusion lung scans.
Methods: Whole-lung differentials were determined on 43 133Xe ventilation/99mTc-macroaggregated albumin perfusion studies. Ventilation calculations were performed for the first-breath, up to three equilibrium and the composite of all equilibrium images, and perfusion calculations were performed for the anterior and posterior images and their geometric mean. Differences of ≥5% between comparable images were considered significant.
Results: The first-breath ventilation differential differed from at least one equilibrium view in 13 patients (30%) and from the composite of all equilibrium images in seven patients (16%), while the posterior perfusion differential differed from the anterior differential in 15 patients (35%) and from the geometric mean differential in six patients (14%). By comparison, the posterior or geometric mean perfusion differential differed from either the first-breath or composite ventilation differential in 31 patients (72%). Nine patients (21 %) had ventilation/perfusion discrepancies ≥10%, with ventilation differentials more symmetric in seven patients.
Conclusion: The choice of 133Xe ventilation image has only a limited effect on differential calculations. Discrepancies are more frequent between ventilation and perfusion differentials, making it important to determine both, particularly in patients with asymmetric lung disease.
