Positron Emission Tomography (PET)

 
Sample image obtained using a combination of PET and CT imaging technology.
Positron emission tomography, also called PET imaging or a PET scan, is a safe and easy method of allowing your Doctor to see how the organs in the body are working. These are usually coupled with Computerised Tomography or CT, for a safe and easy scanning method.

PET/CT scans are performed to:

  • detect cancer
  • determine whether a cancer has spread in the body
  • assess the effectiveness of a treatment plan, such as cancer therapy
  • determine if a cancer has returned after treatment
  • determine blood flow to the heart muscle
  • determine the effects of a heart attack, or myocardial infarction, on areas of the heart
  • identify areas of the heart muscle that would benefit from a procedure such as angioplasty or coronary artery bypass surgery (in combination with a myocardial perfusion scan).
  • evaluate brain abnormalities, such as tumours, memory disorders and seizures and other central nervous system disorders
  • to map normal human brain and heart function

Preparing for the scan

Please tell your Doctor if you think you may be pregnant, are breastfeeding, if you are caring for small children or have diabetes. He will provide you with additional details. You will be asked not to eat before the scan but you will be able to drink water. Depending on the type of scan you may be in the department for 2-3 hours. You are encouraged to wear loose and comfortable clothing, however as part of the exam includes a CT scan it is important that you do not wear any metal. Metals create artefacts so jewellery and other accessories should be left at home if possible, or removed prior to your PET/CT scan. You should also inform your Radiographer or Radiologist of any medications you are taking and if you have any allergies, especially to contrast materials, iodine, or seafood. You will be asked and checked for any conditions that you may have that may increase the risk of using intravenous contrast material.

During the scan

Your radiologist will explain the type of scan to you when you arrive. Depending on the type of exam you are undergoing, a dose of slightly radioactive sugar called a radiotracer is then injected intravenously or swallowed. It will take approximately 30 to 60 minutes for the radiotracer to travel through your body and to be absorbed by the organ or tissue being studied. You will be asked to rest quietly, avoiding movement and talking. You will then be moved into the PET/CT scanner and the imaging will begin. You will need to remain still during imaging. The CT exam will be done first, followed by the PET scan. On occasion, a second CT scan with intravenous contrast will follow the PET scan. The actual CT scanning takes less than two minutes. The PET scan takes 20-30 minutes.

Total scanning time is approximately 30 minutes.

Depending on which organ or tissue is being examined, additional tests involving other tracers or drugs may be used, which could lengthen the procedure time to three hours. For example, if you are being examined for heart disease, you may undergo a PET scan both before and after exercising.

When the examination is completed, you may be asked to wait until the Radiologist checks the images in case additional images are needed. Occasionally, additional images are obtained for clarification or better visualization of certain areas or structures. The need for additional images does not necessarily mean there was a problem with the exam or that something abnormal was found, and should not be a cause of concern.

After the scan

The scan involves administering a very small amount of radioactive tracer which will only remain in your body for a few hours. This only gives you a very small amount of radiation and will not cause any problems.  However, occasionally, when performing heart or body scans we may need to give other drugs but the side effects of these will be discussed with you beforehand. Most nuclear medicine procedures are painless and are rarely associated with significant discomfort or side effects.

If the radiotracer is given intravenously, you will feel a slight pin prick when the needle is inserted into your vein for the intravenous line. When the radioactive material is injected into your arm, you may feel a cold sensation moving up your arm, but there are generally no other side effects.

When swallowed, the radiotracer has little or no taste.

With some procedures, a catheter may be placed into your bladder, which may cause temporary discomfort.

It is important that you remain still while the images are being recorded. Though nuclear imaging itself causes no pain, there may be some discomfort from having to remain still or to stay in one particular position during imaging.

Unless your Radiologist tells you otherwise, you may resume your normal activities after your nuclear medicine scan. If any special instructions are necessary, you will be informed by a Radiographer, Nurse or your physician before you leave the nuclear medicine department.

Through the natural process of radioactive decay, the small amount of radiotracer in your body will lose its radioactivity over time. It may pass out of your body through your urine or stool during the first few hours or days following the test. You may be instructed to take special precautions after urinating, to flush the toilet twice and to wash your hands thoroughly. You should also drink plenty of water to help flush the radioactive material out of your body.