Lung VQ Scan (Ventilation-Perfusion Scintigraphy) is a specialized nuclear medicine test that detects airflow (ventilation) and blood flow (perfusion) in the lungs. It is most typically done to identify or to exclude pulmonary embolism (PE)- a potentially life-threatening scenario that results when blood clots clog the arteries in the lungs.

There are other clinical situations in which this scan is useful, but in which the evaluation of regional lung function is a crucial aspect, as in preoperative lung surgery, lung transplantation, or chronic lung conditions such as COPD or interstitial lung disease.

Lung VQ scan is non-invasive, fast, and safe, and is consequently particularly appropriate in the case of pregnant women, patients with contrast allergies, and those with kidney diseases who are unable to undergo the scans based on contrast-enhanced CT.

What is a Lung VQ Scan?

A Lung VQ scan is made up of two parts:

1. Ventilation Scan

This section determines the movement of air in the lungs.

Radioactive gas or aerosol is inhaled by the patient, spreading through the lungs. A gamma camera is used in order to measure the airflow patterns.

2. Perfusion Scan

This element determines the flow of blood in the lungs.

An injection of a radioactive tracer, usually Technetium-99m labeled macroaggregated albumin (99mTc-MAA), is injected into one of the veins. It is circulated by the pulmonary arteries, and the gamma camera captures the blood flow circulating in the body.

The successful completion of the two scans allows doctors to be able to identify ventilation-perfusion mismatches, which may signify pulmonary embolism or other abnormalities with the vascularity.

Why is the Lung VQ Scan Performed?

A Lung VQ scan is mostly done to detect or exclude pulmonary embolism (PE). Nevertheless, it is applicable in other clinical situations too.

Common Indications:

• Diagnosis or exclusion of pulmonary embolism (PE)
• Pre-surgical assessment:
  • Lung resection (e.g., lung cancer surgery)
  • Lung volume reduction procedures
  • Lung transplantation
• Evaluation of regional lung function in:
  • Chronic obstructive pulmonary disease (COPD)
  • Interstitial lung disease
  • Pulmonary hypertension
• Investigation of unexplained shortness of breath
• Post-operative monitoring after lung surgery or trauma
• Assessment of congenital lung or heart conditions (especially in children)

Understanding Pulmonary Embolism (PE)

Pulmonary embolism is a condition that results from the clotting of blood, mostly a leg/pelvic clot, but it travels to the lungs and blocks one of the pulmonary arteries.

The severity depends on:

• Size of the clot
• Number of clots
• Extent of lung involvement

PE may result in the lack of oxygen, damage to the lungs, or even death when left unattended.

The Lung VQ scan proves beneficial, especially when:

• CT Pulmonary Angiography (CTPA) is contraindicated.
• The patient suffers from contrast allergies or renal disease.
• The patient is pregnant
• The suspicion is that of recurrent or chronic embolism.

How is the Lung VQ Scan Performed?

The process is easy, pain-free, and, as a rule, is finished in the process of 45-60 minutes.

Ventilation Phase:

• The patient can inhale a radioactive gas (e.g., Xenon-133) or aerosol (e.g., 99mTc-DTPA).
• A gamma camera records the images of the airflow distribution pattern.
• Helps identify obstruction of the airway or a disease such as asthma or emphysema.

Perfusion Phase:

• Intravenous injection of 99mTc-MAA is done.
• The blood takes the tracer to the lungs.
• Blood flow patterns are documented at a variety of angles using the gamma camera.
• The two sets of images are compared with each other to detect abnormalities.

How Are the Results Interpreted?

The patient. The images are analysed by a specialist in nuclear medicine who compares ventilation and perfusion patterns.

Possible Findings:

• Normal Scan: A homogeneous airflow and blood flow.
• Mismatched Defect: Ventilatory perfusion is normal but limited - Suspended pulmonary embolism.
• Matched Defect Both ventilation and perfusion decreased: Signifies lung disease (e.g., COPD, fibrosis)
• Triple Matched Defect: Appearance VQ scan and chest X-ray - Low PE risk.

Advantages of Lung VQ Scan

• Non-invasive and painless
• Reduced radiation levels as opposed to CT scans.
• Iodinated contrast is not necessary.
• Precise when patients have kidney disease or a contrast allergy.
• Should be used in pregnant patients (with limited exposure of the fetus)
• Applicable in the pre-surgical planning.
• Offers pulmonary examination.
• Assistive when it comes to children and chronic lung disease.

Limitations

• Sometimes the results of the study by May are inconclusive.
• In severe lung disease, interpretation may prove challenging.
• Less anatomical detail is provided than in CT angiography.
• May miss very small emboli

Preparation & Safety

• No fasting required
• Report pregnancy and breast feeling.
• None of you has any significant drug limitations (consult with your physician)
• Radioactive tracers are safe and low-dose.
• Restart standard activities right after the scan.
• Consumption of additional fluids aids in emptying the bladder of the body.

Comparison with Other Imaging Modalities
The CT Pulmonary Angiography (CTPA) test is normally the initial test conducted to determine pulmonary embolism because of its anatomical imaging of the lung lesions.

A Lung VQ scan is, however, much better when:

• There is an indication of contraindication against the use of contrast.
• The patient is pregnant
• Functional lung examination is needed.

VQ scans can give superior functional information in chronic lung disease, particularly in the pre-operative period.

Conclusion

The Lung VQ Scan is a critical examination device that assesses the presence of efficiency in the circulation of air and blood within the lungs. Although it is mostly employed to diagnose pulmonary embolism, it is also important in pre-surgical planning and evaluation of chronic lung diseases.

The Lung VQ scan is safe, reliable, and non-invasive, and has been a pillar in the current imaging of the lungs, assisting clinicians in making sound and life-saving decisions.

Test Information

• Fasting: Not required
• Reporting Time: Within 2 hours