PET

PET Scans:

1)      What is a PET scan?

  1. A positron emission tomography (PET) scan is a molecular imaging procedure that reveals unique information about how an organ or tissues are functioning.  It involves the painless injection of a small amount of “positron emitting” radioactive materials called radiopharmaceuticals. Then, the PET scanner takes images of the body. The camera detects emissions coming from the injected radiopharmaceutical, while the computer attached to the camera creates two- and three-dimensional images of the examined area. At the same tie in the same machine, modern PET machines often use a CT X-ray scan. Simply put, it uses radiation, or nuclear medicine imaging, to produce 3-D color images of the functional processes within the human body.
  2. PET scans are mainly used to assess cancers, neurological (brain) diseases and cardiovascular (heart-related) diseases.
  3. Basic process:

i.      Radiopharmaceutical (radiotracer) - Before undergoing a PET scan, a cyclotron (a type of machine) produces a radioactive medicine, which is then tagged to a natural chemical (glucose, water, ammonia, etc.). This tagged natural chemical—radiotracer—is then inserted into the human body.

  1. Once inserted, the radiotracer goes to areas inside the body that uses the specific natural chemicals tagged. For example, FDG (fluorodeoxyglucose—a radioactive drug) is a radiotracer tagged to glucose. This glucose tagged radiotracer goes into those parts of the body that use glucose for energy. For example, cancers—because they use glucose differently from normal tissues—can be shown using FDG.

ii.      Detecting positrons- Once the radiotracer accumulates in the body’s tissues and organs, its natural decay includes emission of tiny positively-charged particles—positrons—that react with electrons in the body. A PET scanner detects this energy emitted by positrons and creates three-dimensional images that show how the radiotracers are distributed in the areas of the body being examined.

iii.      The image - The image displays how parts of the patient’s body function by the way they break down the radiotracer. A PET image will show different levels of positrons according to brightness and color.  As with the FDG example, images may show ‘hot spots’—areas where a large amount of FDG accumulates. These spots indicate that a high level of chemical activity/metabolism is occurring there. On the other hand, there are also ‘cold spots’—areas of low metabolic activity that appears less intense than surrounding tissues.  Using these images and the information they produce, physicians are able to evaluate how well organs and tissues are working and to detect abnormalities.
What happens during a PET scan?

  1. A PET scan procedure begins with an intravenous (IV) injection of a radiotracer that usually takes between 30-60 minutes to distribute throughout the body. During this time, you will be asked to stay still and not talk. Some patients may also be given medication to relax. Then, the patient will lie down on a cushioned PET examination table that slides into the PET scanner. The PET scan beds will have special rests for your legs, arms, and head to help keep them still and comfortable.
  2. In most cases, a patient will need to rest before and after the injection of these radioactive materials. For example, when taking a brain PET scan, you will lie quietly in a darkened room before and after the injection to ensure that your brain remains relaxed and is not stimulated by light, noise, or reading.
  3. During the scanning, you must lie quietly and still as the scanner detects the gamma rays released by the radiotracers.  In many centers, you will be able to listen to music during the scan.
  4. Throughout the entire process, the staff watches the patient. Additionally, if you feel unwell, you can press a buzzer that alerts the staff.
  5. This process is not painful.
  6. After the scan, most patients can go home and can assume normal activities straight away as the radiotracers do not make them feel any different or drowsy. Doctors may advise to consume lots of liquids to quickly flush the radiotracers out of your system. However, your scan results will not be available immediately. Thus, before leaving, nuclear medicine scientist will inform you when your doctor will have the results. Note: after the scan, remember to make a follow-up appointment with your doctor to discuss the results of your PET scans.

 

2)      What should I do to prepare for a PET scan?

  1. Usually, a PET scan is taken on an outpatient basis. Before the scan, your doctor will inform you of detailed instructions to prepare for your scan.
  2. Before the actual scan, be sure to notify your doctor about any prescription and over-the-counter medications you’re taking (including vitamins and herbal supplements). Special instructions will be given to those taking certain medications or with certain diseases, like diabetes.
  3. Also, if you are a pregnant woman or are breastfeeding, you should not take the PET scan for risk towards the baby. Likewise, anyone just undergone a PET scan should stay away from pregnant women, babies, and young children for a few hours after the examination.
  4. Generally, before the scan, a patient should not eat anything for several hours. At the time of the scan, please wear comfortable clothes. At some imaging centers, you will be asked to change into a hospital gown. Additionally, if you are examining an area near your bladder, physicians may insert a soft tube (catheter) into your urethra to keep urine drained from your bladder in the course of the scan.

 

3)      What are the risks?

  1. A PET scan is considered a safe procedure. It is also painless and non-invasive, not requiring any recovery time. Possible risks may derive from the radioactive substances used during a PET scan. Thus, pregnant women should not take PET scans as the radioactive material may harm the fetus. However, the amount of radiation exposed to is too low to actually affect the normal functioning of your body. The radioactive chemicals have short life spans and are flushed away from the body fairly quickly (consume a lot of liquid).
  2. On the other hand, PET is highly effective at identifying cancer, brain disorders, heart conditions, and other diseases. A PET scan eliminates the need for surgical biopsy and can detect whether diseases are benign or malignant. It is a great tool that assists physicians in evaluating treatment options and in assessing the process of those treatments.

 

4)      What happens with the scan results?

  1. After the scan, most patients can go home and can assume normal activities straight away as the radiotracers do not make them feel any different or drowsy. Doctors may advise to consume lots of liquids to quickly flush the radiotracers out of your system. However, your scan results will not be available immediately. Thus, before leaving, nuclear medicine scientist will inform you when your doctor will have the results. Note: after the scan, remember to make a follow-up appointment with your doctor to discuss the results of your PET scans.

 

 

http://www.petscaninfo.com/zportal/portals/pat/petct_basics

http://www.mayoclinic.com/health/pet-scan/MY00238

http://interactive.snm.org/index.cfm?PageID=11123

http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/PET_scan

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