Direct exposure films are highly sensitive to the direct effect of x-rays rather than in combination with an intensifying screen. However, a film is a relatively inefficient radiation detector and requires relatively high radiation exposure. The use of rectangular collimation and the highest speed films reduce radiation exposure.

See also Conventional Radiography.

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.

(CR) Computed radiography is an imaging technique that uses similar equipment to conventional radiography except that films are replaced by imaging plates. An imaging plate contains photostimulable storage phosphors, which store the radiation level received at each point in local electron energies. The imaging plate is placed under the patient in the same way as conventional film cassettes. After x-ray exposure, the imaging plate is run through a special scanner to read out the image. The digital image can then be processed to optimize contrast, brightness, and zoom. Computed Radiography can be seen as halfway between film-based conventional technology and current direct digital radiography.

An x-ray film is a photographic film used to generate a visual x-ray image. X-ray films are rarely used as the only radiation detector. Commonly they are used in conjunction with intensifying screens placed in the film cassette, because high resolution films have a poor sensitivity to x-rays. At direct film exposure, only a small amount of x-ray photons will be absorbed and react with the film emulsion. An intensifying screen contains scintillating materials to convert x-ray radiation into light or lows electromagnetic energies.
X-ray films provide very good spatial resolution and contrast, but need long exposures times and chemical processing.

See also Conventional Radiography and Digital Radiography.

Conventional (also called analog, plain-film or projectional) radiography is a fundamental diagnostic imaging tool in the detection and diagnosis of diseases. X-rays reveal differences in tissue structures using attenuation or absorption of x-ray photons by materials with high density (like calcium-rich bones).
Basically, a projection or conventional radiograph shows differences between bones, air and sometimes fat, which makes it particularly useful to asses bone conditions and chest pathologies. Low natural contrast between adjacent structures of similar radiographic density requires the use of contrast media to enhance the contrast.
In conventional radiography, the patient is placed between an x-ray tube and a film or detector, sensitive for x-rays. The choice of film and intensifying screen (which indirectly exposes the film) influence the contrast resolution and spatial resolution. Chemicals are needed to process the film and are often the source of errors and retakes. The result is a fixed image that is difficult to manipulate after radiation exposure. The images may be also visualized on fluoroscopic screens, movies or computer monitors.
X-rays emerge as a diverging conical beam from the focal spot of the x-ray tube. For this reason, the radiographic projection produces a variable degree of distortion. This effect decreases with increased source to object distance relative to the object to film distance, and by using a collimator, which let through parallel x-rays only.
Conventional radiography has the disadvantage of a lower contrast resolution. Compared with computed tomography (CT) and magnetic resonance imaging (MRI), it has the advantage of a higher spatial resolution, is inexpensive, easy to use, and widely available. Conventional radiography can give high quality results if the technique selected is proper and adequate. X-ray systems and radioactive isotopes such as Iridium-192 and Cobalt-60 for generating penetrating radiation, are also used in non-destructive testing.

See also Computed Radiography and Digital Radiography.