Application of delayed lung imaging following radioaerosol inhalation.

Lung scintigraphy following radioaerosol inhalation reveals evidence of airway disease and regions of decreased ventilation. In obstructive pulmonary diseases, aerosol deposition can be so excessive that lung parenchyma is not visualized immediately after radioaerosol administration. Most of the tracer which is deposited is cleared within hours, but the aerosol reaching the alveoli is retained with a half-life in excess of 2 weeks. If imaging is repeated 8-24 hours after inhalation, abnormal bronchi will usually be cleared of tracer, and regional ventilation defects can be visualized.