What is the dominant type of interaction at 511 keV in positron emission tomography?

In positron emission tomography (PET) imaging, the dominant type of interaction at 511 keV photon energy is Compton scatter. At this energy level, when high-energy photons emitted from the annihilation of a positron and an electron collide with electrons in tissue, they predominantly undergo Compton scattering rather than being completely absorbed or interacting in other ways.

During Compton scattering, the incident photon transfers a portion of its energy to an electron, causing the electron to be ejected from the atom and the photon to be deflected at an angle with reduced energy. This scattering can lead to the photon being detected in a different part of the imaging system, which can provide valuable information about the location of positron annihilation events in the body.

Understanding the dominance of Compton scattering at this energy is crucial for interpreting PET scans and for optimizing imaging techniques. While other interactions like photoelectric effect, pair production, and Rayleigh scatter do occur, they are less significant at the 511 keV range and in the context of typical biological tissues encountered in PET imaging.