Radiography is based on the use of x rays.
These rays were discovered in the 19th century . They are electromagnetic waves, just like the microwaves used in portable telephones, or the light that we perceive with our eyes.
The apparatus is made up of an x ray tube (an emitter of x rays) , an examination table and a receptacle that contains the radiographic film.
For a chest x ray, the patient stands upright with his or her chest pressed against the examination table, which is in a vertical position.
The x ray tube is placed to the rear of the patient.
One asks the patient to inhale so as to fill his/her lungs, then submits him/her to x rays so as to make a record on the radiographic film.
The film cassette is then removed and the film is developed in the same way that traditional photographic film is developed. Current technology tends to replace radiographic film with digital recording plates.