How is a V/Q scan performed?

To evaluate ventilation: The patient inhales a radioactive gas (Xe-133) or Tc-99m–labeled DTPA until equilibrium is reached, and a gamma camera is used to evaluate the distribution of the isotope in the airways.

To evaluate perfusion: Tc-99m MAA particles, which are roughly the same size as the capillary diameter, are infused intravenously. A gamma camera is used to take images showing the distribution of the isotopes trapped in the pulmonary vasculature.