This page is about your lung ventilation-perfusion (VQ) scan at Royal Brompton Hospital. It tells you about the scan, what will happen at your appointment and what to expect on the day. 

A lung ventilation–perfusion (VQ) scan looks at two things:

• ventilation (V): how air moves in and out of your lungs
• perfusion (Q): how blood flows through the small blood vessels in your lungs

Looking at both together helps your specialist understand how well your lungs are working.

We know that having a scan can feel worrying. This page explains what will happen, how to prepare, and what to expect on the day. Our team will support you throughout your visit.

What the scan involves

A VQ scan has two parts: a ventilation scan and a perfusion scan. An experienced technologist will carry out the scan by positioning gamma camera detectors in a circle around your chest. The gamma camera detectors move around your chest taking pictures to create 3D images of your lungs. 

You will need to lie still for two scans. The ventilation scan and the perfusion scan are then combined to give detailed information about how your lungs are working.

You will also have a low‑dose CT scan to help improve the quality of the images.

Ventilation scan (V)

• You will lie on the scanning bed.
• You will breathe room air mixed with a very small amount of radioactive 81m‑Krypton gas.
• The gas is tasteless and odourless.
• You will breathe normally through a face mask.
• The scan takes about 8 minutes.

The tracer does not cause any side effects.

Perfusion scan (Q)

• You will receive a small amount of radioactive tracer called 99mTc‑MAA through a vein in your arm.
• This tracer travels to the smallest blood vessels in your lungs.
• You may be asked to take deep breaths during the injection.
• After the injection, we will take another scan lasting about 8 minutes.

Low‑dose CT scan

• We will also take a low‑dose CT scan of your lungs.
• This helps improve the quality of the ventilation and perfusion images.
• The CT scan takes around 10 seconds.

During the scans

• The gamma camera detectors will move around your chest to take 3D images.
• You will need to lie still for both scans.
• You will need to raise your arms above your shoulders so the camera can get close to your chest. We will support you to raise your arms if you have difficulty or have limited shoulder mobility.

What will happen on the day

When you arrive

• A technologist will explain the procedure and answer any questions.
• You will be helped into a comfortable position on the scanning bed.

Waiting period

• There is a short waiting period between the injection and the perfusion scan.
• You may eat and drink normally during this time.
• We recommend drinking plenty of fluids and emptying your bladder regularly. This helps your body clear any excess tracer.

During the scan

• You will need to lie still, but you can breathe normally.
• The gamma camera is similar in size to a CT scanner and quieter than an MRI scanner.
• If your clothing has metal fastenings that cannot be removed, we may ask you to change into a gown.

How to prepare

• No special preparation is needed for this scan.
• You can eat and drink normally before your appointment.
• You can continue taking your usual medicines unless your doctor has advised otherwise.

Risks of radiation during a lung ventilation-perfusion (VQ) scan

The amount of radiation used during a lung ventilation-perfusion (VQ) scan is small and kept to a minimum. We believe that the benefits of having the scan far outweigh any risks.

The risk of a person getting cancer because of this radiation is low, 1 in 10,000 to 1 in 1,000 people. This level of risk is very small compared with the overall lifetime chance of getting cancer. The overall lifetime chance of getting cancer is around 1 in 2 people. 

After the scan

• A doctor will check the images while you wait.
• Once the images are confirmed, you can go home.
• The radiation dose from this scan is very small.
• You do not need to change your routine, but you should keep a small distance (around 2 meters) from children under 2 years of age for 24 hours 
• The tracer will not make you sleepy.
• You can drive and return to normal activities.

Your results

A nuclear medicine consultant will review your scan and send the report to your referring specialist. The results will also be available on the hospital’s electronic system.

Your specialist doctor will discuss the results with you and explain any next steps.