Lung Scintigraphy – Procedure, Uses & Results
Lung scintigraphy is a nuclear medicine imaging technique used to assess blood flow and air distribution in the lungs. It is primarily used to diagnose pulmonary embolism.
Things worth knowing about "Lung Scintigraphy"
Lung scintigraphy is a nuclear medicine imaging technique used to assess blood flow and air distribution in the lungs. It is primarily used to diagnose pulmonary embolism.
What is Lung Scintigraphy?
Lung scintigraphy is a diagnostic imaging procedure in nuclear medicine that visualizes the distribution of blood flow (perfusion) and/or airflow (ventilation) within the lungs. A small amount of a weakly radioactive substance called a radiopharmaceutical is introduced into the body. It distributes through the lungs according to blood flow or air movement and emits low-level radiation that is detected by a special camera known as a gamma camera, which converts the signals into detailed images.
The procedure is most commonly performed as a ventilation-perfusion scintigraphy (V/Q scan), in which both ventilation and perfusion are assessed together. This allows physicians to identify areas of the lung that are ventilated but not perfused – a hallmark finding of pulmonary embolism.
Indications
Lung scintigraphy is used in the following clinical situations:
- Suspected pulmonary embolism: This is the most common indication. A blood clot in the pulmonary vessels interrupts perfusion in an area of the lung while ventilation remains intact.
- Preoperative planning: Before lung surgery, such as resection for lung cancer, scintigraphy helps estimate the remaining functional lung capacity after the procedure.
- Follow-up after pulmonary embolism: To confirm restoration of normal perfusion following treatment.
- Chronic obstructive pulmonary disease (COPD): Assessment of regional lung function distribution.
- Pulmonary hypertension: Evaluation of elevated pressure in the pulmonary circulation.
How the Procedure Works
Perfusion Scintigraphy
To visualize pulmonary blood flow, radioactively labeled albumin particles (MAA – macroaggregated albumin) are injected into a vein in the arm. These particles are sized to temporarily lodge in the smallest blood vessels of the lungs (capillaries). The gamma camera records their distribution, revealing which areas of the lung are well perfused.
Ventilation Scintigraphy
To assess airflow, the patient inhales a radioactively labeled gas or aerosol, such as Technetium-99m DTPA aerosol or the noble gas Krypton-81m. The camera then shows which areas of the lung are reached by air.
Procedure Overview
The examination is painless and typically takes between 30 and 60 minutes, depending on the clinical question. The radiation dose is low and comparable to other standard nuclear medicine procedures. After the scan, it is recommended to drink plenty of fluids to help the kidneys excrete the radiopharmaceutical more quickly.
Interpretation of Results
The images are interpreted by a specialist in nuclear medicine. Perfusion and ventilation images are compared side by side. A so-called mismatch – an area that is ventilated but not perfused – is a characteristic sign of pulmonary embolism. Findings are often classified using standardized scoring systems such as the PIOPED criteria to guide clinical decision-making.
Advantages and Limitations
Lung scintigraphy offers several advantages:
- Lower radiation exposure compared to CT pulmonary angiography (CTPA)
- No iodine-based contrast agent required – suitable for patients with contrast allergies or impaired kidney function
- Can be used in pregnancy when the clinical benefit outweighs the risk
Limitations include:
- Pre-existing lung conditions (e.g., COPD, pneumonia) may complicate image interpretation
- Lower spatial resolution compared to CT imaging
- Limited availability at smaller medical facilities
Safety and Radiation Dose
The radiopharmaceuticals used have very short half-lives and are rapidly eliminated from the body. The effective radiation dose for a combined V/Q scan is typically around 1–2 millisieverts (mSv), roughly equivalent to about six months of natural background radiation. Serious side effects are very rare. Allergic reactions to the radiopharmaceutical are possible but uncommon.
References
- Mettler FA, Guiberteau MJ. Essentials of Nuclear Medicine and Molecular Imaging. 7th edition. Elsevier, 2019.
- Konstantinides SV et al. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. European Heart Journal. 2020;41(4):543–603.
- Value of the Ventilation/Perfusion Scan in Acute Pulmonary Embolism – Results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA. 1990;263(20):2753–2759.
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