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Film-screen radiography is the traditional imaging technique in which an x-ray image is recorded on a radiographic film placed in contact with an intensifying screen inside a cassette. The screen converts x-ray photons into visible light photons, which then expose the film emulsion, creating a latent image that is developed chemically.
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| X-ray film | • Double emulsion coated on both sides of a polyester base. • Sensitive to visible light (blue/green depending on emulsion). • Requires darkroom processing with developer and fixer chemicals. | | --- | --- | | Intensifying screen | Phosphor layer that absorbs x-rays and re-emits energy as visible light. Backing: reflective layer to increase light emission.
Types of phosphors: • Calcium tungstate (blue light, older type). • Rare-earth phosphors (gadolinium oxysulfide, lanthanum oxybromide → emit green light, more efficient). | | Cassette | • Light-tight holder with film + screen combination. • Provides close contact between film and screen. |
Film-screen radiography system. (a) Scheme of an X-ray film cassette and profiles of intensifying screen and X-ray film. The lightweight film cassette made of metal materials features a carbon fiber protective shield, intensifying screens, X-ray film, and a back panel. (b) The comparison of X-ray film direct exposure to X-rays (left) with that of X-ray film in combination with a scintillators screen. (c) X-ray absorption spectra of gadolinium oxysulphide (GOS, red), calcium tungsten (CaWO4, orange), and X-ray emission spectra of 60 kV (sky blue) and 100 kV (dark blue) X-rays. The atomic number of rare-earth elements ranges from 57 to 70 with the -edge between 39 and 61 keV. (d) Upon X-ray irradiation, the free silver ions aggregate in negatively charged sensitivity centers to acquire an electron, forming the latent image region. (e) The latent image in the film was converted into the visible image through photochemical processing including development, fixation, washing, and drying. (f) The characteristic curve of the film-screen system in response to X-ray exposure, which can be divided into three parts including the toe region (blue), the straight-line region (yellow), and the shoulder region (red). Notably, base plus fog is the background intensity of the unexposed film produced by accident light irradiation. The optical intensity is a function of X-ray exposure plotted on a logarithmic scale.
Ou X, Chen X, Xu X, et al. Recent development in X-Ray imaging technology: future and challenges. Research. 2021;2021. doi:10.34133/2021/9892152