An anion is a negative charged ion; the atom has more electrons than protons. Anions are attracted from the positively charged anode. This is a basic part for producing radiation in the x-ray tube.

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.

A tomographic imaging direction, frontwards relative to a short axis of the human body from the back to the front.

See also Anterior Posterior, Left Anterior Oblique, Right Anterior Oblique, Annotation, Antegrade.

A tomographic imaging direction, backwards relative to a short axis of the human body from the front to the back.

An antiparticle is a subatomic particle similar in mass but with opposite electromagnetic properties. Most particles have their antiparticles, electron - positron, etc. Antimatter is composed of antiparticles. Colliding of a particle with its respective antiparticle leads in case of low-energy particles mostly to photon production, in case of high-energy particles to exotic heavy particles.