VQ Scan

A VQ scan, or ventilation-perfusion scan, is a nuclear medicine imaging test that helps doctors evaluate how well air and blood are flowing through your lungs. If you see a “VQ scan” mentioned on your radiology report, you might be wondering what exactly this test shows and why your doctor ordered it. This article explains what VQ scans are, how they work, and what the results might mean.

What Is a VQ Scan?

A VQ scan is actually two separate imaging procedures performed together to create a complete picture of lung function. The “V” stands for ventilation, which measures airflow into your lungs, while the “Q” represents perfusion, which measures blood flow through your lungs. By comparing these two images, doctors can identify areas where there might be a mismatch between air and blood flow.

The test is primarily used to diagnose pulmonary embolism (blood clots in the lungs), but it can also help evaluate other lung conditions like chronic obstructive pulmonary disease (COPD) or prepare patients for lung surgery.

How VQ Scan Imaging Works

The VQ scan procedure involves two phases that use different radioactive tracers to capture different aspects of lung function:

Ventilation Phase

During the ventilation phase, you’ll breathe in a small amount of radioactive gas or aerosol through a mask or mouthpiece. This harmless tracer moves through your airways and into the tiny air sacs (alveoli) in your lungs. A special camera called a gamma camera detects the radiation and creates images showing where air is flowing properly and where it might be blocked.

Perfusion Phase

For the perfusion phase, a different radioactive tracer is injected into a vein in your arm. This tracer travels through your bloodstream to your lungs. The gamma camera then takes pictures showing blood flow patterns throughout your lungs.

What to Expect During a VQ Scan

If your doctor has ordered a VQ scan, knowing what to expect can help ease any anxiety:

1. You’ll likely be asked to wear a hospital gown and remove any metal objects or jewelry.
2. The ventilation part comes first, where you’ll breathe in the radioactive gas.
3. For the perfusion part, you’ll lie on an examination table while the technologist injects the radioactive tracer.
4. The gamma camera will take pictures for both parts of the test, which requires lying still.
5. The entire procedure typically takes about 45-60 minutes.

The amount of radiation used is very small and considered safe for most patients. The tracers leave your body within a few days, primarily through urine.

Understanding VQ Scan Results

VQ scan results are interpreted by comparing the ventilation and perfusion images. The radiologist looks for “mismatches” between air and blood flow:

Normal Results

When both ventilation and perfusion are normal, the radioactive tracers distribute evenly throughout both lungs. This means air and blood are flowing properly.

Abnormal Results

The most significant finding radiologists look for is an area with normal ventilation but reduced perfusion (a “V/Q mismatch”). This pattern suggests a pulmonary embolism—a blood clot blocking an artery in the lung.  The test if often reported as low, intermediate and high probability for pulmonary embolism.

Other Findings

VQ scans can also show:

• Balanced reduction in both ventilation and perfusion (often seen in COPD)
• Areas with reduced ventilation but normal perfusion (may indicate airway obstruction)

Advantages of VQ Scans

VQ scans offer several benefits compared to other lung imaging tests:

Lower Radiation Than CT Scans

While CT pulmonary angiography (CTPA) is another common test for diagnosing pulmonary embolism, VQ scans typically deliver less radiation. This makes them preferable for certain patients, especially:

• Young patients
• Pregnant women
• Those who need repeated scans

No Contrast Dye Required

Unlike CTPA, VQ scans don’t require iodinated contrast dye, which makes them suitable for patients with:

• Kidney problems
• Contrast allergies
• Diabetes with kidney complications

High Diagnostic Accuracy

When performed and interpreted properly, VQ scans have excellent diagnostic accuracy for pulmonary embolism, particularly when the scan is either clearly normal or shows a high-probability pattern.

When Is a VQ Scan Recommended?

Your doctor might order a VQ scan if:

• You have symptoms of a pulmonary embolism (sudden shortness of breath, chest pain, rapid heart rate)
• You have risk factors for blood clots but can’t have a CT scan
• You need evaluation before lung surgery
• You’re being assessed for chronic lung disease or pulmonary hypertension

Radiologists typically note this study when other imaging methods are contraindicated or when a more detailed assessment of lung function is needed. While CT scans show anatomical details, VQ scans provide valuable functional information about how well your lungs are actually working.

Conclusion

A VQ scan provides important information about lung function by evaluating both airflow and blood flow. This nuclear medicine imaging test is particularly valuable for diagnosing pulmonary embolism when CT scans aren’t suitable. Although the procedure involves exposure to radiation, the benefits far outweigh the minimal risks for patients with suspected lung problems. If you see “VQ scan” on your radiology report, it means your doctor ordered a comprehensive evaluation of your lung function to help determine the cause of your symptoms.

References

 

1. https://my.clevelandclinic.org/health/treatments/17627-vq-scan
2. https://www.ncbi.nlm.nih.gov/books/NBK564428/
3. https://www.webmd.com/lung/what-to-know-vq-scan