The gantry is a ring-shaped structure, containing the x-ray tube, collimators, filters, data acquisition system (DAS), associated electronics such as gantry angulation motors, rotational components including slip ring systems and the detector array in a CT or radiation therapy system. The table control, to regulate the gantry tilt and laser (or high intensity) lights are included within, or mounted on the gantry serving as anatomical positioning guides. To scan the patient, the patient table is moved through the gantry aperture.
The rotating arm on which an accelerator head is mounted is also called gantry. This gantry can rotate 360 degrees around its axis.

Image quality is an important value of all radiographic imaging procedures. Accurate measures of both image quality and patient radiation risk are needed for effective optimization of diagnostic imaging. Images are acquired for specific purposes, and the result depends on how well this task is performed. The imaging performance is mainly influenced by the imaging procedure, examined object, contrast agents, imaging system, electronic data processing, display, maintenance and the operator. Spatial resolution (sharpness), contrast resolution and sensitivity, artifacts and noise are indicators of image quality.
A high image contrast provides the discrimination between tissues of different densities.
The image resolution states the distinct visibility of linear structures, masses and calcifications.
Noise and artifacts degrade the image quality. In computed tomography (CT), high spatial resolution improves the visibility of small details, but results in increased noise. Increased noise reduces the low contrast detectability. Noise can be reduced by the use of large voxels, increased radiation dose, or an additional smoothing filter, but this type of filter increases blurring.
An image acquisition technique taking these facts into account maximizes the received information content and minimizes the radiation risk or keeps it at a low level.

See also As Low As Reasonably Achievable.

Ionization is the process of converting an atom or molecule with no electrical charge into an ion by adding or removing charged particles such as electrons or other ions, through high temperatures, electrical discharges, radiation etc.

See also Ion.

If a nucleus still has excess energy after attempts of stabilization, it can emit energy without changing the number of protons or neutrons. This process is named isomeric transition. One way of isomeric transition is the emission of a gamma rays, the other competing way is internal conversion, where the excess energy of the nucleus must exceed the binding energy of an electron, which then will be ejected from the atom.

See also Decay, Gamma Radiation and Internal Conversion.

Isotopes of a given element have the same number of protons but a different number of neutrons in the core. Isotopes have the same electronic structure as the given element and thus have a nearly identical chemical behavior. Larger elements tend to have more stable isotopes than smaller ones.
For example, I123, I125 and I131 are isotopes of iodine; they have a different mass number.