The Physics of PET Annihilation:
- Antimatter Positron ($e^+$) + Matter Electron ($e^-$) $\rightarrow$ Annihilation.
- This event produces exactly two $511\text{ keV}$ gamma rays that fly away from each other in opposite directions along a $180^\circ$ line.
- PET scanners use coincidence timing windows to detect these simultaneous, opposing photon hits, allowing the system to map metabolic activity inside the body.