Annihilation in general refers to the transition of a particle and its antiparticle by collision into something different, depending on their energies and based on the conservation of energy and momentum. The electromagnetic radiation emitted is the result of the annihilation (combination and disappearance) of an electron and a positron. Two gamma rays of 0.511 MeV energy, assuming very low-energy particles, are emitted perpendicular to each other.

Process of conversion of continuous (analog) signals, such as the detected radiation (voltage), into numbers. This is carried out with an analog to digital converter. There are two kinds of discretization involved: the voltage is only measured (sampled) at particular discrete times and only voltages within a particular range and separated by a particular minimum amount can be distinguished. Voltages beyond this range are said to exceed the dynamic range of the digitizer.

An embolization can occur by movement of a blood clot, piece of tissue, or pocket of air or gas through the bloodstream until it stops in place, cutting off the flow of blood.
An embolization during a medical procedure is the insertion of material such as gelatin sponge or metal coils through a catheter into a blood vessel to stop hemorrhaging, excessive bleeding or cut off blood flowing to a tumor or arteriovenous malformation.

Radionuclides are naturally occurring or artificially produced atoms with unstable nuclei. Therefore radionuclides undergo a radioactive decay, and emit gamma ray(s) and/or subatomic particles.
Radionuclides are used as agents in nuclear medicine and to destroy tumors in cancer therapy.

See Isotope and Radioactive Decay.

Fractionation is the delivery of a given total radiation dose as several smaller doses, separated by intervals of time to minimize side effects.