Perfusion images after injection of Tc99m MAA demonstrate heterogeneously decreased perfusion in the lower lungs. Dynamic perfusion images with inhalation of Xenon 133 show decreased single-breath ventilation in both lower lungs, with gradual filling in and retention on delayed images. The upper lungs demonstrate more normal initial ventilation with normal washout on later images.
The next step in interpretation of the VQ scan is to examine a recent chest radiograph:
There is evidence of air trapping with flattened diaphragms and elevation of the minor fissure on radiograph. CT shows emphysema predominantly in the lower lungs with cystic changes.
This patient has alpha-1 antitrypsin deficiency. This condition is associated with panlobular emphysema with basal predominance. A variable percentage of patient will have upper lobe emphysema and bronchial wall thickening/bronchiectasis.
Emphysematous portions of the lungs demonstrate matched decrease in perfusion and ventilation, similar to patients with severe COPD. Dynamic Xenon imaging shows gradual filling in within emphysematous areas, with prolonged retention on delayed images.
