Ventilation/perfusion scan

Medical imaging technique

A ventilation/perfusion scan (V/Q scan) is a type of medical imaging using scintigraphy and medical isotopes to evaluate the circulation of air and blood within a patient's lungs. It is primarily used to help diagnose or rule out a pulmonary embolism (PE).

Procedure

The V/Q scan involves two parts: the ventilation scan and the perfusion scan.

Ventilation scan

In the ventilation scan, a patient inhales a radioactive gas or aerosol, such as xenon or technetium-labeled aerosol, which allows for imaging of the airways and distribution of air in the lungs. This part of the scan helps to assess the airflow within the lungs.

Perfusion scan

The perfusion scan involves the intravenous injection of a radioactive tracer, typically technetium-99m-labeled macroaggregated albumin. This tracer travels through the bloodstream and into the pulmonary circulation, allowing for imaging of blood flow in the lungs. Areas of the lung that receive less blood flow will appear as "cold spots" on the scan.

Interpretation

The results of the V/Q scan are interpreted by comparing the ventilation and perfusion images. A mismatch between the two, where areas of the lung are ventilated but not perfused, may indicate a pulmonary embolism.

Indications

The V/Q scan is most commonly used to diagnose or exclude pulmonary embolism, especially in patients who cannot undergo computed tomography pulmonary angiography (CTPA) due to allergies to contrast media or renal impairment. It may also be used to assess regional lung function in patients undergoing lung surgery.

Limitations

While the V/Q scan is useful, it has limitations. It may not be as definitive as CTPA, and its accuracy can be affected by underlying lung conditions such as chronic obstructive pulmonary disease (COPD) or asthma.

Images

A typical ventilation/perfusion scan showing normal distribution of air and blood in the lungs.

A V/Q scan showing a mismatch indicative of a pulmonary embolism.

Related pages

• Pulmonary embolism
• Scintigraphy
• Nuclear medicine

References

• "Ventilation/Perfusion Scan." RadiologyInfo.org. Accessed October 2023.
• "Pulmonary Embolism: Diagnosis and Management." American Family Physician, 2023.