The main differences between positron emission tomography (PET) and computed tomography (CT) lie in their working principles, applications, and safety profiles.
The main differences between positron emission tomography (PET) and computed tomography (CT) lie in their working principles, applications, and safety profiles.
Working Principle:
CT scans use X-rays to create detailed cross-sectional images of the body. X-rays are a form of electromagnetic radiation that, as they pass through the body, are absorbed differently by tissues of varying densities, creating contrast on the detector. PET scans, however, rely on positron-emitting isotopes labeled to substances (typically a glucose analog) distributed in the body. This substance is absorbed by cells, especially those with high metabolic activity like cancer cells. When positrons meet electrons and annihilate, gamma rays are produced, which are then detected and used to construct images14.
Applications:
CT scans primarily detect structural changes in the body, such as fractures, internal organ injuries, or the presence of tumors. They provide detailed anatomical images crucial for diagnosing many diseases. In contrast, PET scans are more commonly used to evaluate bodily functions and metabolic activities. They are particularly useful in cancer diagnosis, staging, and treatment monitoring, as the high metabolic rate of cancer cells makes them appear brightly on PET images. Additionally, PET scans are applied in neuroscience to study brain activity and metabolic changes14.
Safety:
While both CT and PET scans involve radiation exposure, their radiation sources and risks differ. Radiation in CT scans comes from external X-ray sources, and excessive exposure may cause skin burns or increase cancer risk. To mitigate this, CT scans typically adopt measures to minimize radiation dosage. PET scans, conversely, derive radiation from radioactive isotopes injected into the patient. These isotopes gradually decay and leave the body, but shortly after injection, patients pose a radiation risk to others. Thus, individuals undergoing PET scans must follow specific protective measures to reduce radiation exposure to others.
