Principles of PET Technology

Positron Emission Tomography (PET) is a safe, non-invasive molecular imaging procedure used to detect change in metabolic activity, which is an early sign of disease. PET is used to help diagnose and plan and assess the treatment of cancer, heart disease and brain disorders. Additionally, it differentiates between benign and malignant tumors. While CT and MRI help detect anatomical abnormalities, PET detects changes in metabolic activities, which take place before any change in anatomical structure occurs.

PET works in the following way: a substance (e.g., glucose) is labeled with a positron-emitting radioactive material and injected into the patient. The labeled substance travels throughout the patient’s body and accumulates in highly active tissues, such as cancerous tissues. Positrons emitted by the radioactive material, after travelling a short distance, interact with electrons in tissue and annihilate. This process produces gamma rays that are sensed by the detectors. Using these gamma rays, a computer generates an image depicting metabolic activity inside the patient. In particular, cancerous tissues will appear as regions of higher intensity.

The left-hand image above depicts the annihilation of a positron, emitted by the radioactively labeled substance, and an electron to generate two gamma rays that are sensed by the detectors. The magenta and pink area in the image at right represents the patient or patient's organ, and the blue circle shows the location of the detectors in relation to the patient.