Skip Navigation
Menu Search
Johns Hopkins Medical Imaging

In This Section      

Positron Emission Tomography (PET scan)

Positron emission tomography (PET) scans create images to show how well organs or tissues in the body are functioning or look for the presence of disease.

PET scans are routinely used in combination with computerized tomography (CT). The study is commonly referred to as PET/CT scan.

PET scan is a nuclear medicine exam often used to help diagnose cancer, detect the spread of cancer to other parts of the body or measure the effectiveness of cancer treatment. PET imaging is also used to diagnose diseases of the brain and heart such as Alzheimer's disease, Parkinson's disease, Huntington's disease, epilepsy, stroke or coronary artery disease.

How do I prepare for a PET scan?

PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your doctor before scheduling the exam. Other options will be discussed with you and your doctor.

BREASTFEEDING: If you are breastfeeding, we recommend that you do not breastfeed your child for 24 hours following the injection of the radiotracer.

CLOTHING: Please dress comfortably. You may be asked to change into a patient gown that is provided for you. Please remove all piercings and leave all jewelry and valuables at home. Do not wear any lotions.

ACTIVITY: Avoid strenuous activity or exercise for 24 hours prior to the appointment. Physical therapy is allowed.

CONTRAST AGENTS: You will be required to drink a liquid called barium, which is a contrast agent. The more contrast you are able to drink, the better the images are for the radiologist to visualize your digestive tract. The barium may cause some abdominal discomfort. If you have a colostomy bag, you are advised to bring an extra bag and possibly a chance of clothes.

Iodinated intravenous (IV) contrast is only used when the requesting physician asks for CT scan with IV contrast in addition to the PET/CT. If your doctor requested additional CT scan with IV contrast and you have a history of allergic reaction to iodinated contrast, then you must be premedicated before the IV contrast portion of the scan.

Premedication is ordered by your physician and is usually taken 24, 12 and two hours prior to the scan. If you have a contrast allergy but have not completed premedication, the PET/CT scan (without IV contrast) can still be performed. You can then arrange to have the IV contrast CT scan at a later date. This will not compromise your PET/CT scan.

ALLERGY: Please inform the access center representative when you schedule your scan if you have had an allergic reaction to any contrast dye in the past.

EAT/DRINK: Eat nothing for four hours before the appointment time. No gum. No coffee or other drinks. You are encouraged to drink plain water (no flavors) as much as you like until the time of the scan, unless specified by your other providers. There may be different food and drink recommendations from your physician if you also have upcoming surgery.

DIABETICS: If you are having your PET scan with Johns Hopkins radiology, you will be given specific instructions before your examination.

CARDIAC STUDIES: If you are having a PET/CT cardiac scan with Johns Hopkins radiology, you will receive detailed information about the preparation for your specific exam. This may be different than listed above.

MEDICATION: You may take your medications as usual, with plain water only. Based on your medical condition, your doctor may request other specific preparation.

ANTI-ANXIETY MEDICATION: If you require anti-anxiety medication due to claustrophobia, contact your ordering physician for a prescription. Please note that you will need someone else to drive you home.

What happens during a PET scan?

Specific protocols may vary, but generally a PET scan follows this process:

  1. You will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.
  2. If you are asked to remove clothing, you will be given a gown to wear.
  3. You will be asked to empty your bladder prior to the start of the procedure.
  4. One or two intravenous (IV) lines will be started in the hand or arm for injection of the radiotracer.
  5. You will be positioned on a padded table inside the scanner.
  6. The radiotracer will be injected into your IV. The examination will start 30–60 minutes after the injection. You will remain in the facility during this time. You will not be hazardous to other people, as the radiotracer emits less radiation than a standard X-ray.
    • After the radiotracer has been absorbed for the appropriate length of time, the scan will begin. You will lie on a scan table that slides into a large, circular opening of the scanning machine. Pillows and straps may be used to prevent movement during the procedure.
    • The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will enable the technologist to communicate with and hear you. You can communicate with the technologist to let him/her know if you have any problems during the procedure.
    • The X-rays and gamma rays absorbed by the body will be detected by the scanner and transmitted to the computer. The computer will transform the information into an image to be interpreted by the radiologist.
  7. The scanner table will move slowly so that the body part being studied is scanned and the scan can take between 20 to 40 min. It will be important that you remain very still during the procedure. When the scan has been completed, the IV line will be
  8. After the radiotracer has been absorbed for the appropriate length of time, the scan will begin. The scanner table will move slowly so that the body part being studied is scanned.
  9. When the scan has been completed, the IV line will be removed. If a urinary catheter has been inserted, it will be removed.

While the PET scan itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

Learn more about what happens during a PET scan.

What happens after a PET scan?

  • You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
  • You will be instructed to drink plenty of fluids and empty your bladder frequently.
  • The IV site will be checked for any signs of redness or swelling. If you notice any pain, redness and/or swelling at the IV site after you return home following your procedure, you should notify your doctor as this may indicate an infection or other type of reaction.
  • You may resume your usual diet and activities, unless your doctor advises you differently.
  • Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.