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V/Q Scan
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

V/Q Scan

A V/Q scan uses two imaging tests—ventilation and perfusion—to evaluate how air and blood flow through your lungs, primarily to detect a pulmonary embolism.

What is a V/Q scan?

A V/Q scan combines two tests: a ventilation scan, which measures airflow, and a perfusion scan, which measures blood circulation. It uses a small amount of a radioactive tracer to create images of the lungs. It is most frequently used to diagnose a pulmonary embolism (PE), a life-threatening blood clot in the lungs often caused by deep vein thrombosis (DVT).

Why do I need a V/Q scan?

You may need this scan if you experience symptoms of a PE, such as sudden shortness of breath, chest pain, rapid breathing, or coughing up blood. Risk factors that may prompt a scan include:

  • Family history of blood clots
  • Recent surgery or long periods of inactivity
  • Obesity or older age
  • Smoking
  • Underlying conditions like COPD, cancer, or heart disease

What happens during a V/Q scan?

The scan is performed in a radiology clinic or hospital. During a ventilation scan, you breathe a tracer gas through a mask while the scanner captures images. During a perfusion scan, a tracer is injected into your vein to track blood flow. You may have one or both tests, which take between 30 and 60 minutes total.

Risks and Considerations

Radiation exposure is minimal and leaves the body within a few days. However, because radiation can be harmful to a developing baby, you must inform your provider if you are pregnant or breastfeeding. Allergic reactions to the tracer are rare.

What do the results mean?

Abnormal results indicate that air or blood is not moving through the lungs properly. If the ventilation and perfusion images do not match, it may confirm a pulmonary embolism, requiring immediate treatment. The scan may also reveal other conditions, such as pneumonia, heart failure, or COPD.

Frequently Asked Questions

Both tests are used to detect pulmonary embolisms, but they work differently. A V/Q scan uses a radioactive tracer to visualize airflow and blood flow separately, making it particularly useful for patients with kidney issues who cannot tolerate the iodine-based contrast dye used in a CTPA. A CTPA provides detailed anatomical images of the blood vessels and is often the first-line test because it is faster and can also show other lung abnormalities. Your doctor will choose the test based on your kidney function, allergy history, and clinical presentation.
Yes, you can typically drive yourself home and resume normal activities immediately after a V/Q scan, as the procedure is non-invasive and does not require sedation. The only restriction is related to the radioactive tracer; you should drink plenty of water after the test to help flush the tracer from your body through urine. If you are breastfeeding, you may need to pump and discard breast milk for a short period as directed by your radiology team to minimize radiation exposure to the infant.
"mismatch" occurs when the ventilation scan shows normal airflow to a part of the lung, but the perfusion scan shows reduced blood flow to that same area. This pattern is highly suggestive of a pulmonary embolism, as a clot blocks blood flow without blocking air. While a mismatch is strong evidence for a clot, it is not always 100% definitive on its own; doctors may correlate this with D-dimer blood tests, clinical symptoms, or a follow-up CTPA to confirm the diagnosis and rule out other causes of perfusion defects.
The radioactive tracer used in a V/Q scan has a short half-life and is eliminated from the body primarily through urine within a few days. The total radiation dose is generally low and comparable to or lower than that of a standard CT scan. For most adults, the radiation exposure is not considered a risk to future fertility. However, if you are planning to conceive or are currently pregnant, you must inform your provider, as the radiation, though minimal, is best avoided during pregnancy.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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