Densitometry is a method to image the density of for example, the bones to measure the mineral content or lung tissue to quantify emphysema.
Densitometry is also used to control the optical density of x-ray films by shining light on the film and measuring the transmission with a densitometer.

See also Bone Densitometry and Osteo CT.

A developing agent is a chemical, usually phenidone, hydroquinone or metole, which reduces exposed silver ions to atomic silver to visualize an image on a film.

See also X-Ray Film, Film Processor, Activator, Clearing Agent, Developer and Fixer.

The dipping method is a contact autoradiography of tissue using emulsion coated coverslips or x-ray films.

A film consists of a thin, transparent sheet of polyester or similar material. Films are coated on one or both sides with an emulsion sensitive to radiation, light or heat. Films are relatively radiolucent due to their relatively low atomic number (that of silver halide).

See also X-Ray Film, Direct Exposure Film and Intensifying Screen.

An intensifying screen is used to intensify the x-ray effect during radiation exposure of the x-ray film. Approximately 5% of the x-ray photons will be absorbed by the film only. Intensifying screens consist of a sheet of inorganic salts that emits fluorescent light when stroked by x-rays. The fluorescent input and output screens of the image intensifier are very similar to intensifying screens.
Calcium tungstate and rare earths are two common salts (also called phosphors) used for intensifying screens. For example, a calcium tungstate (CaWo4) screen can absorb around 40% of the x-ray photons and convert the radiation into light photons. A basic feature of this screen types is related to the position of the k-edge on the energy axis. Tungsten (W) is a heavy element has a k-edge at 69.5 keV, while that for rare earth elements is in around 50 keV.
The fraction of x-rays absorbed by a screen is depending on the speed. Factors affecting the speed of a screen: Mammography cassettes contain usually one intensifying screen, but most others use two screens per film cassette. The intensifying screen as part of a film screen system has been an important component in radiology to reduce the radiation dose of the patient. Today, the conventional film cassette is being replaced by an imaging plate used in digital systems.

See also Actinides, Cinefluorography and Added Filtration.