Positron emission tomography (PET) is a medical imaging procedure that provides unique information about how an organ or system in the body is working. PET scans are mainly used to assess cancers, neurological (brain) diseases and cardiovascular (heart-related) disease.
The PET scanner has a ring of detectors that surround the person. It looks similar to a CT scanner. The scan is performed by a healthcare professional called a nuclear medicine scientist, who works with a nuclear medicine specialist (doctor).
A PET scan involves the painless injection of a small amount of a ‘positron-emitting’ radioactive material (called a radiopharmaceutical). Images of the body are then taken using a PET scanner. The camera detects emissions coming from the injected radiopharmaceutical, and the computer attached to the camera creates two and three-dimensional images of the area being examined.
Areas where the injected radiopharmaceutical gathers (for example, fast-growing cancer cells) appear ‘brighter’ than normal tissues on the images.Almost all PET scanners today are combined with a CT scanner so that the PET images can be combined or fused with the CT images. This allows the nuclear medicine specialist to combine the structural information from the CT scan with the PET’s functional information and improve the accuracy of the test. In these scanners, the person passes through both scanners on the one bed and in the same position.
Some of the uses of the PET scan include detection and monitoring of conditions such as cancer, neurological disease and cardiovascular disease.
PET scans can reveal changes in metabolism and how organs and tissues are working. Many cancers can be detected using PET before they can be ‘seen’ using other medical imaging techniques. PET scans can create an image of the entire body. This means that, for some cancers, they can show if (and where) cancer is spreading to other parts of the body.PET might also be used to see if tumours are malignant (cancerous) and to tell the difference between an active tumour and scar tissue.
PET imaging can provide information about the biochemical function of the brain. For example, epilepsy that can’t be treated with medications is sometimes treated by surgical removal of the part of the brain that causes the seizures. PET scans can assist this surgery because it can show the exact part of the brain responsible for the person’s epilepsy.PET imaging has also been used to assess people with other neurological diseases, including Alzheimer’s disease and Parkinson’s disease, because the images can show areas of the brain that are functioning differently to normal.
PET scans are used to assess both the blood flow to the heart and how the heart is working. This means that areas of the heart that have been permanently damaged by reduced blood flow (for example, after a heart attack) can be distinguished from those that are still working. The damaged areas may respond to surgical treatments such as angioplasty or coronary bypass surgery.
Medical considerations prior to the PET scan include:
Before the scan, you will be given a small injection of radioactive material. The injection is painless and it does not make you feel any different at all. The PET scanner then takes a series of images. For some tests, the procedure begins as soon as you have the injection. In other cases, you may have to wait at least 60 minutes after the injection before the scan is taken.
In most cases, you will need to rest before and after the injection of the radioactive material. For example, if you are having a brain PET scan, you will lie quietly in a darkened room before and after the injection to make sure your brain remains relaxed and is not stimulated by light, noise or reading.
Once the appropriate amount of time has passed, you will be asked to lie on the imaging bed. This bed has special rests for your legs, arms and head to help keep them still and comfortable.
You must lie quietly and still as the scanning table moves through the scanner ‘ring’. The scanner detects the gamma rays released by the radioactive material that has localised in the area of your body being investigated, and uses it to create images of your internal body structures.
Imaging generally takes around 30 minutes. The nuclear medicine scientist who performs the test will tell you exactly how long your procedure will take. They will be there to look after you during the procedure. A PET scan is completely painless and you will not feel any different after the injection, during imaging or after the scan.
After your PET scan, you can go on with your normal activities straight away. The injection of the radioactive material does not make you feel any different or drowsy. There are no sedative drugs or anaesthesia used during this procedure.
Your scan results will not be available immediately. Before you leave, the nuclear medicine scientist will tell you when your doctor will have the results. You will need to make a follow-up appointment with your doctor to discuss the results of your PET scan.
A PET scan is considered to be a safe procedure. It exposes you to around the same amount of radiation that you would receive from the general environment over about three years. The injected radioactive chemicals have a very short lifespan and are removed from the body fairly quickly.
Sometimes, you will be advised to avoid close contact with babies or pregnant women in the few hours after your scan. The nuclear medicine scientist will tell you if this is necessary, after your scan.
A lot of research has been done to check the safety and long-term side effects of nuclear medicine examinations. Up to now, there are no known issues – the radiation dose you receive from a PET examination is considered to be safe and justified.
Alternatives to the PET scan depend on the condition under investigation, but could include:
•Your GP (doctor)
A positron emission tomography (PET) scan is an imaging test that produces images of your organs and tissues at work. The test uses a safe, injectable radioactive chemical called a radiotracer and a device called a PET scanner.
The scanner detects diseased cells that absorb large amounts of the radiotracer, which indicates a potential health problem.
Healthcare providers frequently use PET scans to help diagnose cancer and assess cancer treatment. They can also assess certain heart and brain issues with the scan.
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Computed tomography (CT) scans use X-rays. Magnetic resonance imaging (MRI) scans use magnets and radio waves. Both produce still images of organs and body structures.
PET scans use a radioactive tracer to show how an organ is functioning in real time. PET scan images can detect cellular changes in organs and tissues earlier than CT and MRI scans. Your healthcare provider may perform a PET scan and CT scan at the same time (PET-CT). This combination test produces 3D images that allow for a more accurate diagnosis.
Some hospitals now use a hybrid PET/MRI scan. This new technology creates extremely high-contrast images. Providers mainly use this type of scan for diagnosing and monitoring cancers of the soft tissues (brain, head and neck, liver and pelvis).
Your healthcare provider may order a PET scan to check for signs of:
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In general, a PET scan can measure vital functions, such as blood flow, oxygen use and blood sugar (glucose) metabolism. It can also identify organs and tissues that aren’t working as they should.
If your healthcare provider suspects you may have cancer, they’ll likely recommend a PET scan, which can detect cancer and/or make a diagnosis.
If you’ve already been diagnosed with cancer, your provider may recommend more than one PET scan throughout your treatment to:
If you’re having heart issues, your provider may recommend a PET scan to:
If you’re experiencing neurological symptoms, your provider may recommend a PET scan to evaluate possible brain abnormalities, such as tumors, seizures and other central nervous system conditions.