What is a Ventilation-Perfusion (V/Q) scan?

From the Guidelines

A VQ scan, or ventilation-perfusion scan, is a nuclear medicine imaging test that evaluates the flow of air and blood in your lungs, consisting of two parts: the ventilation scan and the perfusion scan, to diagnose pulmonary embolism by identifying areas with normal ventilation but reduced blood flow, creating a "mismatch" pattern. This test is primarily used to diagnose pulmonary embolism (blood clots in the lungs) and is particularly valuable for patients who cannot receive contrast dye used in CT pulmonary angiograms, such as those with kidney problems or contrast allergies, and for pregnant women due to lower radiation exposure 1.

The procedure is non-invasive, takes about 30-60 minutes, and requires minimal preparation. Results are interpreted by comparing the ventilation and perfusion images to identify any abnormal patterns that might indicate pulmonary embolism or other lung conditions. The ventilation scan measures air distribution using inhaled radioactive gas or aerosol, while the perfusion scan assesses blood flow using intravenous radioactive particles 1.

Some key points to consider when using VQ scans include:

• The test is safe and few allergic reactions have been described 1
• The radiation exposure from a lung scan with 100 MBq of Tc-99m macroaggregated albumin particles is 1.1 mSv for an average sized adult, significantly lower than that of CT angiography (2–6 mSv) 1
• Lung scan results are frequently classified according to the criteria established in the PIOPED study: normal or near-normal, low, intermediate (non-diagnostic), and high probability of PE 1
• Prospective clinical outcome studies suggested that it is safe to withhold anticoagulant therapy in patients with a normal perfusion scan 1

Overall, the VQ scan is a useful diagnostic tool for pulmonary embolism, especially in patients who cannot undergo CT pulmonary angiography, and its results should be interpreted in the context of clinical probability and other diagnostic tests 1.

From the Research

Definition of Ventilation-Perfusion (V/Q) Scan

• A Ventilation-Perfusion (V/Q) scan is a medical imaging test that evaluates lung function by assessing ventilation (airflow) and perfusion (blood flow) in the lungs 2, 3, 4, 5.
• The test is used to diagnose and manage various lung conditions, including pulmonary embolism, congenital heart disease, and chronic obstructive pulmonary disease (COPD) 2, 3, 4, 5.

How V/Q Scan Works

• The test involves two parts: ventilation scanning and perfusion scanning 2, 4.
• Ventilation scanning uses a small amount of radioactive material to visualize airflow in the lungs 4, 5.
• Perfusion scanning uses a small amount of radioactive material to visualize blood flow in the lungs 4, 5.
• The results of the two scans are compared to identify areas of mismatch between ventilation and perfusion, which can indicate lung disease or damage 2, 3, 4, 5.

Clinical Applications of V/Q Scan

• V/Q scans are commonly used to diagnose and manage pulmonary embolism, a potentially life-threatening condition that occurs when a blood clot blocks blood flow in the lungs 3, 4, 5, 6.
• The test is also used to evaluate lung function in patients with COPD, cystic fibrosis, and other chronic lung diseases 2, 3.
• V/Q scans can help identify areas of lung damage or disease, which can inform treatment decisions and improve patient outcomes 2, 3, 4, 5.