A PET scan works by annihilating antimatter inside your body
In a PET scan, a radioactive tracer releases positrons, the antimatter twins of electrons. Each one meets an ordinary electron almost at once, and the pair vanish in a flash of two gamma rays flying in opposite directions. Cameras catch those pairs and build a 3D map of what your cells are doing.
Positron emission tomography is a functional scan: rather than photographing structures, it tracks chemistry such as blood flow and metabolism. Because biochemical change usually comes before visible anatomical change, it can reveal disease earlier than scans that show only shape. Scanners are often paired with CT so that the activity map can be laid over a detailed picture of the body. Their main drawback is cost, both to buy and to run.
The workhorse tracer is FDG, a sugar molecule in which one hydroxyl group has been swapped for radioactive fluorine-18. Cells take it up like glucose, but the swap stops it being processed further, and most tissues cannot strip off the phosphate the cell adds, so the tracer is stuck inside until it decays. Tissues hungry for glucose glow brightly: the brain, liver, kidneys and most cancers, which burn sugar fast because of the Warburg effect. Scans searching for cancer spread make up about 90 percent of current PET work, and FDG is especially useful in lymphomas and lung cancer.
The brain is another major target. Alzheimer's disease lowers the brain's use of both glucose and oxygen, so FDG scans can help separate it from other dementias and catch it early, and newer tracers such as florbetapir, developed by Avid Radiopharmaceuticals, light up the amyloid plaques linked to the disease. Oxygen-15 scans measure blood flow, but with a half-life of two minutes the isotope has to be piped straight from a cyclotron. PET can also pinpoint the origin of epileptic seizures, which appear as dim, underactive patches between attacks.
In cardiology PET measures blood flow in heart muscle and gives sharper images than SPECT, though SPECT machines are cheaper and more widespread, and which is more cost-effective is debated. Researchers value PET because the same animal or person can be scanned repeatedly, acting as their own control, which cuts the number of laboratory animals a study needs.
Source: Positron emission tomography
