Breathing and lung function tests

Imaging scans

If you have symptoms that might be due to a lung problem, a chest X-ray or a scan of your lungs can sometimes be helpful.

Imaging tests can be done:

  • to find out why you get breathless,
  • why you have a cough or chest pain
  • to see if a specific treatment is suitable for your lung condition
  • to see if your condition has responded to treatment
  • as a screening test in people who may be at risk of lung problems
  • to monitor a lung condition

There are different types of imaging scan that can show a picture of your lungs and airways:

Test using X-rays

These are usually done in a radiology department.

Nuclear medicine tests

These usually involve an injection or breathing in a substance that shows up on a scanner.


Chest X-ray

What is a chest X-ray?

A chest X-ray is a procedure that uses X-rays to take a 2-dimensional, flat picture of the inside of your chest.

X-ray is a type of radiation that can pass through the body and is used to take a picture. Harder parts of the body like bone show up white on the picture. Solid tissues like the heart or liver also show up white. The lungs let more X-rays through and look black.

Although X-rays are a kind of radiation, the amount delivered in a chest X-ray is very small – about the same as a couple of days of normal background exposure – and is not harmful.

What is a chest X-ray used for?

Health professionals will use a chest X-ray to see inside your chest, looking at your lungs, ribs, heart or diaphragm. It’s often the first test used in people with symptoms like breathlessness, coughing up blood or chest pain. An X-ray is often used along with a CT scan and other tests.

How can I prepare for a chest X-ray?

You’ll usually receive an appointment letter. Read this carefully in case there is anything special you need to do to prepare. The main thing you need to do is to take off anything metal, such as jewellery, zips or belt buckles.

If you could be pregnant, it’s important to tell the radiographer, so that they can reduce any exposure of your unborn baby to X-rays.

What happens during a chest X-ray?

You may have a chest X-ray as an outpatient, or during a stay in hospital.

During a chest X-ray, you’ll be in one room while a health care professional, called a radiographer, stays next door or behind a screen. You’ll need to take off any clothes on your top half, including shirts, vests and bras, and wear a hospital gown.

It’s usually done standing up, though chest X-rays can be taken sitting or lying down if necessary. The X-ray machine will be pointed at your chest to take pictures. You need to hold your breath for a few seconds while the picture is taken. This makes sure that the image isn’t blurred.

When will I get the results?

You won’t usually get the results straight away, unless you are acutely unwell in A&E. You’ll be given an appointment with your doctor to discuss the results, and what happens next.


CT scan

What is a CT scan?

CT stands for computed tomography. It uses X-rays to build a 3-dimensional picture of the inside of your body. This gives a detailed picture of your lungs, blood vessels and other organs.

You may be given an injection of material that shows up on the scan and can help to outline blood vessels. This is called contrast.

What’s it used for?

Health care professionals will use a CT scan to understand what’s going on inside your lungs. It can be used to see if your lungs appear normal and to help diagnose lung conditions.

It might also be used to decide what type of treatment is needed, or if you’re a suitable candidate for treatment.

Sometimes a CT scan might be used to monitor a lung abnormality or response to treatment, for example in people with lung cancer.

How can I prepare for a CT scan?

You should receive a letter telling you how to prepare for your CT scan. Read this carefully to see if there are any special instructions, for example about eating and drinking.

You won’t be able to wear anything made of metal during the scan, so you’ll need to remove any metal jewellery, belts or clothing.

Tell hospital staff if you are allergic to iodine, as the contrast material injected as part of some scans may contain this. They will also ask if there is any possibility that you might be pregnant.

What happens during a CT scan?

You lie on a flat bed, which passes through the doughnut-shaped CT scanner as you hold your breath. Usually the scan itself only takes about 10 seconds. A health care professional called a radiographer will stay in the next room and operate the scanner.

You might be given an injection of contrast dye into a vein in your hand or arm.

Some people are anxious about having a CT scan and worry that they might get claustrophobic. In fact, even though you go through the scanner it is actually a doughnut shape rather than a tunnel so only a small part of you is actually inside and the scan itself takes only a few seconds. If you are worried, do let the people doing the scan know. They’ll be able to answer any questions you have.

The scan itself is usually done while you hold a single breath and only takes about 10 seconds. You’ll be able to go home the same day.

When will the results be available?

You won’t usually get the results straight away. The scans have to be reviewed by a specialist called a radiologist. You’ll usually be given an appointment with your doctor to discuss the results, and what happens next.


PET scan

What is a PET scan?

PET stands for positron emission tomography. This type of scan is used to measure the activity of cells in different parts of your body. The scan creates detailed 3-dimensional images of the inside of your body.

Parts of the body that use a lot of energy, such as areas of inflammation or infection, need a lot of sugar to provide this. Before a PET scan, a sugary substance is injected into the bloodstream. The PET scan measures how quickly the energy from this substance is used. The brighter the area on the scan, the more energy the cells are using. These brighter areas can be seen if there is inflammation or infection, or if there is a cancer present. 

Sometimes a PET scan is used with a CT scan, to create a more detailed image. This is called a PET-CT scan.

What’s it used for?

One of the most common uses of a PET scan is in people who have or might have cancer. The PET scan can help to show if an abnormal area such as a lung nodule is active (usually indicating cancer) or not. If a nodule does not light up on the PET scan it is less likely to be a cancer and more likely to be a scar.

The scan can also pick up if a cancer has spread to another part of the body or if it’s responding to medication. This is very important in planning the best treatment.

How can I prepare for a PET scan?

You’ll receive a letter from the hospital telling you how to prepare for your PET scan. Read it carefully. You'll usually be advised not to eat anything for 6 hours beforehand.

Drinking fluid is allowed, but you should ideally just drink water. You should also avoid strenuous exercise for 24 hours before your appointment.

It’s important to be on time for your PET scan. That’s because the radioactive substance used in the scan only has a short shelf life. Your scan may not work properly if it’s not done on time, and the test may be cancelled. If this happens, you’ll have to wait for another appointment.

You’ll be told to avoid babies and children for a few hours after a PET scan, because you will be slightly radioactive. If you have children, it’s important to organise childcare to cover this time.

What happens during a PET scan?

PET scanners have a flat bed with a large, circular scanner at one end. Before a scan, you’ll be injected with a slightly radioactive substance, which can be detected by the scanner. You will be asked to lie down on the table which will slide into the PET scanner. It’s important that you stay as still as you can while you are in the scanner. PET scans are painless and take around 30–60 minutes.

When will I get the results?

You won’t usually get the results straight away. The scans have to be reviewed by a specialist radiology doctor (a radiologist). You’ll usually be given an appointment with your doctor to discuss the results, and what happens next.


V/Q scan

What is a V/Q scan?

A V/Q scan is also called a ventilation-perfusion scan or a lung perfusion scan. It looks at the flow of air and blood in your lungs.

What’s it used for?

A V/Q scan is used to measure how different parts of the lung are functioning. It gives information about where air is going as you breathe in and out, and whether there are areas of the lung that are not getting a normal amount of blood flow.

The most common use is to see if there are blood clots in the lung. These show up as areas that air is going to but blood isn’t.

A V/Q scan can help health care professionals to decide which parts of your lungs need treatment or can be treated, if an operation is being considered. V/Q scans are used to help plan operations to remove lung cancer or to consider if someone is suitable for lung volume reduction if they have emphysema.

The V/Q scan is sometimes combined with a CT scan to get a more detailed picture.

How can I prepare for a V/Q scan?

You’ll receive a letter from your hospital telling you if there’s anything you need to do to prepare for your V/Q scan. Read this carefully. There is usually no special preparation required.

If you’re pregnant or breastfeeding, tell your health care professional and follow their advice.

What happens during a V/Q scan?

For the ventilation part of the scan you will be asked to breathe in a slightly radioactive gas called krypton for about 10 minutes. This is odourless and tasteless.

For lung perfusion you will be given an injection of slightly radioactive material. Sometimes only the perfusion part of the scan is needed.

The whole process usually takes up to an hour.

When will I get the results?

You won’t usually get the results straight away. The scans have to be reviewed by a specialist radiology doctor  called a radiologist. You’ll usually be given an appointment with your doctor to discuss the results.

If you have concerns or need advice, call our helpline on 03000 030 555 between 9am and 5pm on a weekday or email them.

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Last medically reviewed: January 2020. Due for review: January 2023

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.