A ventilation–perfusion (VQ) scan is a nuclear medicine scan that uses a radiopharmaceutical to image airflow (ventilation) and blood flow (perfusion) in the lungs.

The aim of the scan is to look for evidence of any blood clot in the lungs, called pulmonary embolism (PE).

A VQ scan consists of two parts. In the first part, radioactive material is breathed in and pictures or images are taken to look at the airflow in the lungs. In the second part, a different radioactive material is injected into a vein in the arm, and more images taken to see the blood flow in the lungs.

Why would I need a VQ scan?

You may need a VQ scan if your doctor thinks you might have a blood clot in your lung. A blood clot in the lung can sometimes be fatal, particularly if left untreated. The most common early symptoms are shortness of breath and a sharp pain when you breathe in. Sometimes blood clots can occur over a long period of time (chronic pulmonary embolus) and the symptoms can be more difficult to diagnose. A VQ scan can be useful in identifying small chronic pulmonary emboli, even when other scans are negative.

Occasionally VQ scans are used to quantify blood flow and ventilation in the lungs when surgery is being considered.

How do I prepare for a VQ Scan?

If you are or think you might be pregnant, and/or breast-feeding, you must inform the doctor who is referring you for the VQ scan and also the staff at Trinity Medical Imaging.

Women who are breast-feeding need to make special preparations for after the scan. This will involve stopping breast-feeding for approximately 24 hours. This is due to the radioactivity in your breast milk after the scan injection. You should discuss this with your referring doctor or with the nuclear medicine practice where you will be having the test. You might need to have bottles of formula or previously expressed breast milk available.

VQ scans can be carried out if you are pregnant, and the radiation dose patients receive is roughly half that from a CT pulmonary angiogram, which is the other common scan used to diagnose pulmonary embolus.

What’s special about Trinity Medical Imaging?

At Trinity Medical Imaging, we perform our VQ scans using a technique called SPECT. When we take pictures of both the ventilation and perfusion parts of the scan, the gamma camera rotates around the patient and creates a three-dimensional view. This technique improves detection of small blood clots and reduces errors in interpretation.

In some cases, we will combine this VQ SPECT scan with a CT (or CAT) scan which combines the information about blood flow and ventilation with the structure of the lung to improve the accuracy of the test.