A PET (positron emission tomography) scan is a medical imaging test that measures how well your tissues and organs are working. It also helps detect signs of cancer.
A radioactive substance called a radiotracer is injected into your body. The tracer collects in areas of your body that use a lot of glucose, the kind of sugar your body needs to make energy.
What is a PET Scan?
A PET Scan is a type of imaging test that can help your doctor see how your organs and tissues are working. It is often used along with CT or MRI scans to create more detailed images of the body and help diagnose many diseases and conditions.
PET scanners work by detecting the radiation given off by a substance called a radiotracer as it collects in different parts of your body. In most cases, the radiotracer is tagged with a natural chemical like glucose so your body treats it in a similar way. When a group of cells needs energy, the radiotracer will build up in that area. This is reflected in the PET scan images that a computer reconstructs.
In most cases, a PET scan is carried out without any pain. However, a small injection of the radiotracer can be uncomfortable, and you may feel some pin pricks in your arm or hand. You will also need to remain still while the scan takes place, and you will be asked to hold your breath for a few seconds.
You will have to remove any jewellery that you want to keep on during the test, as it may affect the results. You should also wear loose, comfortable clothing that doesn’t have metal zippers or buttons.
Once you’ve changed into a gown, your blood sugar levels will be checked and you’ll have the radioactive tracer injected into a vein in the back of your hand or arm through an intravenous line. It is a very quick procedure and you should not feel any pain.
Your doctor will give you special instructions, such as fasting before the test and ensuring that you drink plenty of water after it to flush out the radioactive tracer from your body. Anyone who is pregnant or breastfeeding should tell their doctor before they have the test, as the radioactive material could harm the fetus.
After the PET scan, you’ll need to rest quietly in a room for 90 minutes. For some tests, you’ll also be asked to drink contrast material, which is a liquid that will help your doctor see better.
How does a PET Scan Work?
PET scans use a radioactive tracer to detect metabolic changes in the body that happen at the cellular level. They can also be used to check for cancer and heart disease.
The scans work by injecting a special radioactive material into the vein. The tracer travels through your blood and gathers in cells that are using lots of energy, such as cancer cells. These cells release tiny positively charged particles (positrons). A camera records the positrons and transforms them into images on a computer screen.
Your doctor may prescribe a medicine to make your heart pump harder before you have a PET scan. This medicine can help you feel more comfortable during the test and will make the scans take less time. It is very important that you keep still as much as possible, and don’t move too quickly while the test is being done.
When you go to the hospital or radiology centre for your scan, you’ll need to change into a gown and remove all metal objects. This includes hair clips, earrings and belts or clothes with snaps or zippers that could interfere with the scan.
A member of staff will insert an intravenous line into your vein and then inject the radioactive substance. You should not feel anything after the injection, and it will take 30 to 90 minutes for the tracer to reach your body parts that will be scanned.
You should drink plenty of liquid before and after your PET scan to flush out the tracer faster. This will help your doctor read the scan more clearly.
Some hospitals and radiology centres combine PET and CT scanning to create a more complete picture of the area under examination. They are called PET/CT or PET/MRI scans and provide even more information than a PET scan alone.
The test is safe and painless. However, some people do feel a bit claustrophobic in the scanner. If you are concerned about this, tell the staff at your appointment and they can help you find a quieter space.
Your doctor or nurse will give you instructions about the test and how to prepare for it. They may advise you not to eat or drink anything for several hours before the test, and they will tell you when it’s okay to resume drinking during the test.
What are the Benefits of a PET Scan?
A PET scan can help your doctor diagnose and treat many diseases. It also helps researchers find out how well certain parts of your body work and can show where they have gone wrong.
The most common type of PET scan involves injecting a small amount of a radioactive substance called a ‘tracer’ into your bloodstream and then scanning it. The tracers give off energy in the form of ‘gamma rays’, which can be detected by a PET scanner and converted into images.
During the scan, you will lie still on a narrow table that slides into a machine that looks like a large letter “O”. The detectors in the machine pick up the signal from the radioactive tracer and use this information to produce 3D images of your body.
A type of tracer that is commonly used for cancer imaging is 18F-fluorodeoxyglucose (FDG), which acts as a glucose analog and gets taken up by cells. The increased uptake of FDG in cancer cells gives a bright spot on the PET scan. This shows where cancer is growing and also helps identify the presence of metastases, which are places where cancer cells have spread throughout your body.
Another type of tracer can be used for brain imaging, which shows how your nerves are working and if you have problems with memory or thinking. It can also be used to check whether you have an infection or an inflammation in the brain.
When you arrive at the hospital, a nurse or nuclear medicine technologist will explain the procedure and take your blood to measure how much radioactive material is in your body. You’ll also need to provide information about any medications or supplements you’re taking and if you have diabetes.
Before the test, you’ll need to drink plenty of water or other liquids so that the tracers can be flushed from your body more quickly. Your blood sugar levels may also be tested, as high or low levels can affect how the images look on the PET scan.
The PET scan can last from 30 minutes to over an hour, depending on the area being scanned and how many tests are required. Sometimes, additional tests using other tracers or drugs can lengthen the time.
What is the Risk of a PET Scan?
PET scans are a type of nuclear medicine imaging test that can be used to diagnose a wide range of diseases. These include cancer, brain and heart conditions.
When a tracer (such as 18F-FDG) is injected into a vein in your arm, certain cells and organs in your body absorb the tracer, helping to show your doctor how well your health is. It also shows any areas where your organs and tissues are not working properly, which can help to pinpoint the location of the problem.
It can also find signs of cancer earlier than other diagnostic tests. Generally, this is because diseased cells in your body absorb more of the tracer than healthy ones do. These are called “hot spots” that show up on a PET scan, and can indicate whether the cancer is growing or spreading.
Your doctor will ask you to stop eating and drinking for about 6 hours before the test. This is because if you eat or drink, the tracer might not get to all your cells and might result in a suboptimal image.
During the test, you lie still in a narrow table that slides into a tunnel-shaped scanner. Your health care provider will then use a computer to change the signals from the tracer into 3D pictures that can be displayed on a monitor for your doctor to see.
A PET scan is a very safe procedure that uses radioactive material or a tracer that only stays in your body for a few hours. The radiation dose you receive is small – equivalent to the amount of natural background radiation you would normally be exposed to over years.
If you’re pregnant, or if you are breast-feeding, tell your doctor before the test. They will let you know if it is okay to have the test, and how long to wait before breastfeeding again after the test.
Your doctor can also ask you to avoid eating or drinking for 24 to 48 hours before the test. This is because a diet high in sugar or coffee could interfere with the distribution of the tracer and may lead to suboptimal images.