What is PET-CT?

Positron Emission Tomography (PET) demonstrates biochemical activity of various tissues within the body. An administered radioactive substance tagged to a natural compound accumulates in areas of altered metabolism (such as cancerous areas). As the radioactive substance decays emitted positrons produce gamma rays which are detected by special sensors. Images are constructed using complex computer processing.

Computed Tomography (CT) uses x-rays and complex computing to provide precise anatomical information in three planes about the size, shape and location of the organs of the body. 2 dimensional or 3 dimensional images of internal structures can be generated.

PET-CT combines the two state of the art imaging modalities of PET and CT. The functional information from PET is merged with the anatomical information from CT into a single image providing the most comprehensive diagnostic scan currently available to the cancer specialist.

What is the basis of PET scanning?

A cyclotron is used to produce a radioactive substance which is tagged to a normal body compound. The most commonly used radioactive compound is an analogue of glucose, called fluorodeoxyglucose (FDG); when this is injected into the body it is taken up by areas of high glucose metabolism. Cancer cells use more glucose than most normal healthy tissues thus the FDG accumulates in cancerous areas (and organs of normal high glucose metabolism such as the heart and the brain). Areas of high metabolism (which are emitting positrons) are detected by the scan sensors - in this way it is possible to demonstrate cancers and sites of cancer spread. 

When are PET-CT scans useful?

Cancer diagnosis and treatment planning are the main uses for PET-CT, which may:
• Identify cancer earlier than other imaging technologies
• Distinguish between malignant and benign tumours
• Determine the location and extent of cancer indicating spread to other areas of the body such as lymph nodes, liver or bones (metastatic disease)
• Identify recurrent cancer distinguishing it from scar tissue or fibrosis
• Demonstrate the response of cancer to treatment

PET-CT may also be used in non-cancer patients:
• Studying brain function in epilepsy
• Diagnosing Alzheimer’s Disease and other types of dementia
• Evaluating viability of heart muscle
• Studying coronary artery disease

How should I prepare for having a PET-CT scan?

We will send you detailed instructions at the time of your appointment. Wear comfortable loose fitting clothes. You should not eat for 4 hours prior to the scan, but drinking water is fine. We will give you advice regarding any medication you are taking.

What is it like?

When you arrive at our diagnostic imaging centre you will be registered at our front desk and we will review your clinical details. For the PET portion of the PET-CT scan you will receive an injection of the radiopharmaceutical. This contains a small dose of radioactive tracer. It is necessary to allow the radiopharmaceutical to distribute itself around the body before the scan is undertaken – this can take up to 1 hour when you will be asked to relax in a quiet, partly darkened room. You will be asked not to move too much and not to talk as this can affect the localisation of the radioactivity. You will then be transferred to the PET-CT scanner where you will lie down on the examination scan table.

The scanner looks like a large doughnut within which are multiple detectors that register and record the energy from the radiopharmaceutical – which by now has reached the area of interest. The total scan (CT and PET) usually takes 30-45 minutes. You may notice a quiet electrical hum but otherwise there are no affects.

Are there any side affects?
There is a small dose of radiation associated with both the CT and PET components of the test so you should let us know if you may be pregnant.

What happens after the scan?

After the examination you can go home and return to a normal diet and normal medication. The radioactive substance only lasts for a very short time so normal interactions with other people are possible. Drinking plenty of water helps to flush out the radioactivity from the system.

Who reads the scan?

The images are interpreted by a Consultant Radiologist who has a specialist training in Nuclear Medicine and PET-CT. The reports are sent back to your referring doctor usually within a few days.