Positrons Meet Tissue
Positron emission tomography detects pairs of 511 keV photons produced when a positron from a radioactive tracer annihilates with a tissue electron. By recording millions of coincidence events around a detector ring, the scanner reconstructs a 3D map of tracer concentration — revealing metabolism, receptor density, or blood flow depending on the tracer used. FDG, an analog of glucose labeled with fluorine-18, is the workhorse tracer for oncology.
Tracer Kinetics & Compartment Models
After intravenous injection, the tracer distributes through the bloodstream, crosses capillary walls into tissue, and may become metabolically trapped. The rate constants governing these transitions — K₁ (influx), k₂ (efflux), k₃ (trapping), k₄ (release) — determine how tissue activity rises and falls over time. For FDG, k₄ is effectively zero in most tissues, meaning phosphorylated FDG remains trapped.
Standardized Uptake Value
SUV provides a semi-quantitative measure of tracer uptake normalized to injected dose and body weight. An SUV of 1.0 indicates average whole-body distribution; malignant tumors typically show SUVs of 3-20 due to elevated glycolysis (the Warburg effect). This simulation models how injected dose, body mass, uptake kinetics, and isotope decay interact to produce the SUV measured at the standard 60-minute imaging time point.
Clinical Applications
FDG-PET is indispensable in oncology for staging, restaging, and treatment response assessment. Beyond cancer, PET with specialized tracers maps amyloid plaques in Alzheimer's disease (florbetapir), dopamine transporters in Parkinson's (FP-CIT), and myocardial perfusion (rubidium-82). Each tracer brings unique kinetics — this simulator helps you understand the fundamental time-activity curves underlying all PET imaging.