Aventilation/perfusion lung scan, also called aV/Q lung scan, orventilation/perfusion scintigraphy, is a type ofmedical imaging usingscintigraphy andmedical isotopes to evaluate the circulation of air and blood within a patient'slungs,[1][2] in order to determine theventilation/perfusion ratio. Theventilation part of the test looks at the ability of air to reach all parts of the lungs, while theperfusion part evaluates how well blood circulates within the lungs. In physiology,perfusion is described with the letter Q, hence the term V/Q scan.
Ventilation-perfusion scintigraphy in a woman taking oral contraceptives and valdecoxib with a pulmonary embolism. (A) After inhalation of 20 mCi of Xenon-133 gas, scintigraphic images were obtained in the posterior projection, showing uniform ventilation to lungs.. (B) After intravenous injection of 4.1 mCi of Technetium-99m-labeled macroaggregated albumin, scintigraphic images were obtained, shown here in the posterior projection. This and other views showed decreased activity in the following regions: apical segment of right upper lobe, anterior segment of right upper lobe, superior segment of right lower lobe, posterior basal segment of right lower lobe, anteromedial basal segment of left lower lobe, and lateral basal segment of left lower lobe.
V/Q Scan Interpretation
Result
Interpretation
Significance
Normal
No perfusion deficit
Excludes pulmonary thromboembolism
Low probability
Perfusion deficit with matched ventilation deficit
< 20% probability of PE
Intermediate probability
Perfusion deficit that corresponds to parenchymal abnormality on chest x-ray
20% - 80% probability of PE
High probability
Multiple segmental perfusion deficits with normal ventilation
> 80% probability of PE
Decreased uptake of the inhaled radioisotope may indicate an impaired ability to breathe, airway obstruction, or possible pneumonia.
Decreased circulation of the injected MAA indicates a problem with blood flow into or within the lungs. A localized area of decreased uptake, usually in a wedge shaped (or pie shaped) configuration with normal ventilation images (mismatched defect) suggests apulmonary embolus or blood clot in the lungs, which leads to reduced perfusion beyond the obstruction.
Although this test uses radioactive materials, the total amount of radiation exposure is low. Typicaleffective doses for a V/Q scan range from one to fivemSv.[7][8] In order to decrease the radiation exposure in pregnant patients, the total radioactivity administered may be decreased or the ventilation phase omitted. ACT pulmonary angiogram (CTPA) withradiocontrast can alternatively be performed, although this can result in a greater radiation dose to the patient.[9]
The ventilation and perfusion phases of a V/Q lung scan are performed together and may include achest X-ray for comparison or to look for other causes of lung disease. A defect in the perfusion images requires a mismatched ventilation defect to indicate pulmonary embolism.[8]
In the ventilation phase of the test, a gaseous radionuclides such asxenon-133,krypton-81m, ortechnetium-99mDTPA in an aerosol form is inhaled by the patient through a mouthpiece or mask that covers the nose and mouth.[10] Ventilation imaging can also be performed using a Technegas machine which produces an aerosol ofradioactive nanoparticles, specifically carbonnanoparticles containingtechnetium-99m.[11] The perfusion phase of the test involves the intravenous injection of radioactivetechnetium macro aggregated albumin (Tc99m-MAA). Agamma camera acquires the images for both phases of the study.[12] A SPECT image can also be taken following an injection of technetium labelled MAA. SPECT is often skipped if the patient haspulmonary hypertension.
It is also possible to perform the scan withpositron emission tomography (PET) rather than conventional gamma camera scintigraphy.[13] 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.[14][15]
^Lobov, Sergei A.; King, David W.; Knox, Karen J.; Senden, Tim J.; Stephens, Ross W. (February 2013). "Cationised radiolabelled nanoparticles for perfusion imaging of the lungs".Biomaterials.34 (6):1732–1738.doi:10.1016/j.biomaterials.2012.11.022.PMID23218595.
^Bailey, Dale L.; Eslick, Enid M.; Schembri, Geoffrey P.; Roach, Paul J. (September 2016). "68Ga PET Ventilation and Perfusion Lung Imaging—Current Status and Future Challenges".Seminars in Nuclear Medicine.46 (5):428–435.doi:10.1053/j.semnuclmed.2016.04.007.PMID27553468.
