Positronemissiotomografia

Positronemissiotomografia (PET) is a nuclear medicine imaging technique that produces three-dimensional images of functional processes in the body. It detects pairs of gamma photons emitted indirectly by a positron-emitting radiotracer introduced into the body, allowing visualization and measurement of metabolic activity, blood flow, receptor binding, and other physiological functions.

The procedure involves administration of a radiopharmaceutical—commonly fluorine-18 labeled fluorodeoxyglucose (F-18 FDG)—followed by uptake time and scanning in a PET detector ring. When a positron from the tracer annihilates with an electron, two photons are emitted in opposite directions; coincident detection of these photons enables reconstruction of tracer distribution.

Clinical applications include oncology (tumor detection, staging, treatment response), neurology (dementia evaluation, epilepsy focus localization), and cardiology (myocardial viability and perfusion assessment). PET is frequently combined with computed tomography (PET/CT) or magnetic resonance imaging (PET/MRI) to provide complementary anatomical detail.

Advantages of PET include high sensitivity to biochemical changes and the ability to quantify physiological processes. Limitations include relatively lower spatial resolution than some modalities, exposure to ionizing radiation, dependence on availability of short-lived radiotracers and specialized equipment, and potential for false positives from inflammatory processes.

Safety considerations focus on minimizing radiation dose and ensuring appropriate clinical indications; use is typically avoided or modified in pregnancy. Ongoing developments include new tracers targeting specific molecular pathways and expanded hybrid imaging platforms.