krypton-81m, or technetium-99m DTPA in an aerosol form is inhaled by the patient through a mouthpiece or mask that covers the nose and mouth. Ventilation imaging can also be performed using a Technegas machine which produces an aerosol of radioactive nanoparticles, specifically carbon nanoparticles containing technetium-99m. The perfusion phase of the test involves the intravenous injection of radioactive technetium macro aggregated albumin (Tc99m-MAA). A gamma camera acquires the images for both phases of the study. A SPECT image can also be taken following an injection of Technetium labelled MAA. SPECT is often skipped if the patient has pulmonary hypertension. It is also possible to perform the scan with positron emission tomography (PET) rather than conventional gamma camera scintigraphy. This has been performed with Gallium-68 labelled carbon nanoparticles (Galligas) using a conventional Technegas machine for ventilation images, and with Gallium-68 labelled MAA (Ga68-MAA) for perfusion images. PET has multiple potential advantages including superior resolution, speed and quantification. See also Ventilation/perfusion ratio References Respiratory system imaging Scintigraphy