Therefore, cancer cells and tumors collect more of the radiotracer and appear as a different color on the resulting images. The radiotracer 18F-FDG is frequently used because it is readily transported into cells. Once in cells, the chemical is phosphorylated into FDGphosphate.
The newly created molecule FDG-6 is trapped within the cell and will no longer participate in metabolism. As it breaks down it emits positrons, a positive electron, which break down further, releasing 2 equivalent photons in opposite directions. These photons are detected by a camera inside the PET unit, producing a high-resolution 3 dimensional image.
This may result in false positive test results, particularly in areas of inflammation and infection. Younger patients often give false negatives because of increased uptake in areas such as the brain, urinary system, thymus, and in smooth or striated muscle.
False negatives can also occur when tumors are slow growing and absorb less glucose. The energy pathway identified by FDG is used by all cells, making this radiotracer useful in many cancer types.
There are many different radiotracers used in PET scans that take advantage of other cellular processes. These are used to detect specific cancer types and to study other disease processes, like heart disease and Alzheimer's disease.
Information on other radiotracers and their use can be found in the Molecular Imaging and Contrast Agent Database. New tracers are under development and promise to be more specific and produce more effective images with increased specificity, sensitivity, and overall accuracy. Pet scans take advantage of the fact that cancer cells use lots of sugar to grow.
An altered form of sugar shown in the animation above as a candy bar is injected. PET scans detect when it collects in tumors. During A nurse will start an IV and the tracer compound will be injected into a vein. You will be moved to a quiet, dark room where you will lie still for a specified amount of time, usually about 1 hour. During this period your body will completely absorb and distribute the tracer compound. In many cases you will be asked not to speak to prevent the compound from collecting in your tongue and vocal chords.
Cancer cells are more metabolically active and may absorb glucose at a higher rate. This higher rate can be seen on PET scans. This allows your doctor to detect disease before it may be seen on other imaging tests.
FDG is just one of many radiotracers in use or in development. You will usually receive the radiotracer in an injection. Or you may swallow it or inhale it as a gas, depending on the exam. It accumulates in the area under examination.
A special camera detects gamma ray emissions from the radiotracer. The camera and a computer produce pictures and supply molecular information. Many imaging centers combine nuclear medicine images with computed tomography CT or magnetic resonance imaging MRI to produce special views. Doctors call this image fusion or co-registration.
Image fusion allows the doctor to connect and interpret information from two different exams on one image. This leads to more precise information and a more exact diagnosis. It is not currently available everywhere.
A PET scan measures important body functions, such as metabolism. It helps doctors evaluate how well organs and tissues are functioning. CT imaging uses special x-ray equipment, and in some cases a contrast material , to produce multiple images of the inside of the body. A radiologist views and interprets these images on a computer monitor.
CT imaging provides excellent anatomic information. These combined scans help pinpoint abnormal metabolic activity and may provide more accurate diagnoses than the two scans performed separately. Women should always tell their doctor and technologist if they are pregnant or breastfeeding. See the Safety in X-ray, Interventional Radiology and Nuclear Medicine Procedures page for more information about pregnancy and breastfeeding related to nuclear medicine imaging.
Tell the doctor and your exam technologist about any medications you are taking, including vitamins and herbal supplements. List any allergies, recent illnesses, and other medical conditions. You will receive specific instructions based on the type of your PET scan. Diabetic patients will receive special instructions to prepare for this exam.
If you are breastfeeding at the time of the exam, ask your radiologist or doctor how to proceed. It may help to pump breast milk ahead of time and keep it on hand for use until the PET radiotracer and CT contrast material are no longer in your body.
Leave metal objects including jewelry, eyeglasses, dentures and hairpins at home as they may affect the CT images. You may need to remove hearing aids and removable dental work. Eating may alter the distribution of the PET tracer in your body and can lead to a suboptimal scan. This could require you to repeat the scan on another day, so following instructions regarding eating is very important.
You should not drink any liquids containing sugars or calories for several hours before the scan. Instead, you are encouraged to drink water. If you are diabetic, your doctor may give you special instructions. Tell your doctor about all the medications you are taking.
List any allergies, especially to contrast materials or iodine. Your doctor will check for any conditions you may have that could increase the risk of receiving intravenous contrast material. A PET scanner is a large machine with a round, donut-shaped hole in the middle.
Multiple rings of detectors inside the machine record the energy emissions from the radiotracer in your body. The CT scanner is typically a large, donut-shaped machine with a short tunnel in the center. You will lie on a narrow table that slides in and out of this short tunnel.
Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is in a separate control room.
This is where the technologist operates the scanner and monitors your exam in direct visual contact. The technologist will be able to hear and talk to you using a speaker and microphone. Ordinary x-ray exams pass x-rays through the body to create an image. Nuclear medicine uses radioactive materials called radiopharmaceuticals or radiotracers.
Your doctor typically injects this material into your bloodstream. Or you may swallow it or inhale it as a gas. The material accumulates in the area under examination, where it gives off gamma rays. Special cameras detect this energy and, with the help of a computer, create pictures that detail how your organs and tissues look and function. Unlike other imaging techniques, nuclear medicine focuses on processes within the body.
These include rates of metabolism or levels of various other chemical activities. For more information on how a CT scan works, see Computed Tomography. You will lie on an exam table. If necessary, a nurse or technologist will insert an intravenous IV catheter into a vein in your hand or arm.
Positron emission tomography scan care at Mayo Clinic. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
This content does not have an English version. This content does not have an Arabic version. Overview Positron emission tomography Open pop-up dialog box Close. Positron emission tomography During a positron emission tomography PET scan, you lie on a narrow table that slides into a doughnut-shaped hole. PET scan of the heart Open pop-up dialog box Close. PET scan of the heart This PET image shows an area of reduced blood flow from one of the arteries that feeds the heart.
Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Radiological Society of North America. Accessed April 6, What is PET? Society of Nuclear Medicine and Molecular Imaging. Umterrainer M, et al. Recent advances of PET imaging in clinical radiation oncology.
Radiation Oncology. Adam A, et al. Adrenal imaging. In: Grainger and Allison's Diagnostic Radiology. Elsevier; American College of Radiology. Cervical cancer.
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