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Lung Perfusion Scintigraphy – Explanation and Procedure

Lung perfusion scintigraphy is a nuclear medicine imaging technique used to assess blood flow through the lungs. It is primarily performed to diagnose pulmonary embolism.

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Things worth knowing about "Lung Perfusion Scintigraphy"

Lung perfusion scintigraphy is a nuclear medicine imaging technique used to assess blood flow through the lungs. It is primarily performed to diagnose pulmonary embolism.

What is Lung Perfusion Scintigraphy?

Lung perfusion scintigraphy is a nuclear medicine imaging procedure that visualizes the distribution of blood flow (perfusion) within the lung tissue. A mildly radioactive substance -- known as a radiopharmaceutical -- is injected into the bloodstream and accumulates in the small blood vessels (capillaries) of the lungs. A special detection device called a gamma camera then records the emitted radiation and converts it into a detailed image.

The procedure shows which areas of the lungs are receiving adequate blood flow and where perfusion deficits exist. Lung perfusion scintigraphy is frequently combined with lung ventilation scintigraphy, which assesses airflow through the lungs. This combined approach is known as V/Q scintigraphy (ventilation-perfusion scintigraphy).

When is the Procedure Used?

Lung perfusion scintigraphy is indicated in the following clinical situations:

Pulmonary embolism: A blood clot (thrombus) blocks a blood vessel in the lungs, interrupting blood flow to a segment of lung tissue.
Pre- and post-operative evaluation of lung function, particularly before lung resection surgery, to assess the functional distribution between both lungs.
Follow-up monitoring in patients with known pulmonary embolism or other pulmonary vascular disorders.
Chronic thromboembolic pulmonary hypertension (CTEPH): Elevated blood pressure in the pulmonary vessels as a result of unresolved or recurrent blood clots.

How is the Procedure Performed?

No special preparation is generally required before the examination. The patient receives an intravenous injection of a solution containing tiny radioactively labeled protein particles called macroaggregated albumin (MAA). These particles are large enough to temporarily lodge in the pulmonary capillaries but small enough to pose no risk to the body.

The patient is then positioned beneath the gamma camera, which detects the emitted gamma rays and captures images of the lungs from multiple angles. The actual scan typically takes only a few minutes. In the combined V/Q scintigraphy, the patient also inhales a radioactively labeled gas or aerosol to visualize ventilation.

How are the Results Interpreted?

A nuclear medicine specialist analyzes the resulting images. Common findings include:

Normal scan: Even and homogeneous distribution of the radiopharmaceutical throughout both lungs without any gaps or defects.
Perfusion defect: Areas of reduced or absent uptake indicate impaired blood flow. In pulmonary embolism, wedge-shaped perfusion defects are typically found alongside normal ventilation -- a pattern called a ventilation-perfusion mismatch.

Interpretation is often guided by standardized criteria such as the PIOPED criteria (Prospective Investigation of Pulmonary Embolism Diagnosis), which categorize the probability of pulmonary embolism based on scan findings.

Radiation Exposure and Safety

The radioactive substances used in lung perfusion scintigraphy have a very short half-life and are rapidly eliminated from the body. The effective radiation dose is relatively low and comparable to other diagnostic imaging procedures such as computed tomography (CT). Pregnant women should only undergo this procedure after careful consideration of the risks and benefits, as radiation exposure affects both the mother and the unborn child. However, in urgent cases, the procedure may still be performed during pregnancy, since untreated pulmonary embolism carries a high risk of serious complications.

Advantages and Limitations

Lung perfusion scintigraphy offers the following advantages:

Good tolerability, as no iodine-based contrast agents are required -- particularly relevant for patients with kidney disease or contrast media allergies.
Functional imaging of pulmonary blood flow, which complements structural imaging methods such as CT.
Minimally invasive and well-tolerated by most patients.

The main limitation is that the procedure does not provide the same level of anatomical detail as CT pulmonary angiography (CTPA), which is currently the preferred method for diagnosing pulmonary embolism in many clinical settings. Nevertheless, V/Q scintigraphy remains a valuable alternative, particularly for specific patient groups.

References

Konstantinides SV et al. - 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. European Heart Journal, 2020; 41(4): 543-603.
Bajc M et al. - EANM guidelines for ventilation/perfusion scintigraphy. European Journal of Nuclear Medicine and Molecular Imaging, 2009; 36(8): 1356-1370.
Miniati M et al. - Value of perfusion lung scan in the diagnosis of pulmonary embolism: results of the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED). American Journal of Respiratory and Critical Care Medicine, 1996; 154(5): 1387-1393.

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