PET Scan (Positron Emission Tomography)
What is a PET scan?
A positron emission tomography (PET) scan is a type of radiological study which uses radiation to reveal and track activity or disease in the body down to the cells.
If combined with a computerized tomography (CT) scan or a magnetic imaging resonance (MRI), a PET scan would produce multidimensional coloured images of the minutest activity in almost all organs of the body.
How is a PET scan performed?
A PET scan is an outpatient procedure which lasts for about 2 hours. You would be advised to avoid food intake for a minimum of 4 to 6 hours before having the procedure. You would also be advised to take a lot of water and avoid caffeinated drinks for at least 24 hours prior to the procedure.
The procedure would begin with injection of a radiotracer into your veins. The tracer could also be inhaled, swallowed or injected directly into the organ to be visualized.
After the tracer has been administered, you would be told to stay calmly for about 30 minutes for the tracer to reach the target organ, before you are taken to the scan room.
At the scan room, you would lie on a motorized table which slides into a giant O-shaped PET scan machine which takes images of the organ to be visualized. During the scanning process, you are expected to hold as still as possible and may be instructed to hold your breaths occasionally.
After the necessary images have been taken, the motorized table slides out of the scanner and the test is complete. You would be told to drink plenty of water at the end of the procedure to flush the radiotracer out of your body more quickly.
How does the PET scan work?
The radiotracer administered to the patient emits radiation which is detected by a PET scan machine. A radiotracer is a radioactive material tagged to a natural chemical such as glucose. When the radiotracer is injected into the body, it moves to cells which use glucose as their source of energy. The more the energy needs of an organ, the more the radiotracer builds up in that organ.
Activities on the PET scan are described as “hot spots” or “cold spots”. Areas with dense radiotracer volume appear bright and are referred to as hot spots. Areas where the radiotracer is less dense are less bright and are referred to as cold spots.
Compared with normal cells of the body, cancer cells use up glucose more actively hence the pivotal role PET scan plays in diagnosis of cancer.
When is a PET scan used?
Because of the special way it works, a PET scan is vital in revealing how an organ or a tissue is functioning, not just how it looks. Doctors use PET scan to diagnose and monitor brain tumours, heart disease, Alzheimer’s disease, and epilepsy.
What risks are involved with PET scan?
A PET scan uses radiation, so pregnant women should avoid it. In addition, after you have had a PET scan, you should avoid contact with pregnant women, infants, and newborns for a few hours until the radiotracer is completely flushed out.