Positron emission tomography better known by its acronym PET - see PET Scan - is a scintigraphy method. It is a diagnostic investigation based on detecting positrons produced by a radio-active substance administered intravenously to the patient. PET provides an accurate image of cellular activity within the tissue examined. The investigation is always performed in a hospital.
Positron emission tomography (PET)
The process PET has various indications. In oncology it is used to diagnose some malignant tumours. It can also be used to assess the effectiveness of clinical trials. In cardiology, the investigation is used to analyse blood flow either in coronary arteries or in the cavities of the heart themselves. It is used to assess cerebral functions and the integrity of the brainin neurology. PET detect some abnormalities which cannot be seen by other imaging techniques.
The investigation procedure
Before the investigation begins, a substance called fluodeoxyglucose (FDG) is synthesised from fluor18, a radioactive molecule. As it has a relatively short half life (110 minutes), PET requires careful logistics. Patients are fasted from the day before and must rest for approximately 45 minutes before the investigation. The FDG is then injected intravenously into the patient. The substance is then metabolised by the most active tissues such as muscles. For this reason the patient must remain at rest for an hour, generally in semi-darkness. The patient then lies down in a machine similar to an X ray scanner, with a large ring. Different detectors positioned inside the instrument record the irradiation emitted by the organ being studied and images are then produced on a screen. Differences in colours or light levels are used to identify effective functioning of a tissue or organ. A cancer tissue, for example, uses more glucose than normal tissue. It is therefore brighter in appearance.
Possible risks of positron emission tomography (PET)
The amount of radioactive material administered is extremely small and has no effect on the normal functioning of the body. Generally, when the patient leaves the department he/she can return to normal everyday activities and is not any risk to people around them. Patients do however have to drink a lot of water to remove the radioactive substance. The investigation is not recommended in pregnant women. The radioactive substance may carry a risk - even if minimal - of exposing the foetus to irradiation. Patients who are breastfeeding must not do so for 24 hours after the investigation. During this period, the milk must be expressed and discarded.
Source: Interview with Sylvia Neuenschwander, president of the Société française de radiologie, 25 January 2011
PET provides an accurate image of cellular activity within the tissue examined. © Centre René Gauducheau