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Radiography: x-ray film

Jreptile

Radiographic film properties and storage

Introduction

  • An x-ray film consists of a polyester base and a gelatin-based coating of photosensitive silver halide crystals on both surfaces.
  • The silver halide is sensitive to x-rays.
  • Silver halide may also be sensitive to heat, pressure and some chemicals.
  • When exposed, these crystals undergo a physical change, which results in a black area on the finished radiograph. The unexposed crystals will leave a white area.
  • The silver halide are more sensitive to visible light than x-rays, hence the use of intensifying screens to convert x-rays photons to visible light within the x-ray cassette.
  • This also reduces the amount of x-rays used to obtain a radiograph, results in shorted exposure time and ultimately less exposure to patient and personnel.
  • Cassette-film systems may result in loss of image sharpness.

Film speed

  • The term "speed" can be applied to films as well as screens Radiography: cassette and intensifying screen.
  • A fast film will become blacker for a given exposure than a slow film.
  • The speed of films is determined by the size and number of halide grains.
  • Larger grains give faster speed but reduced resolution and detail.
  • Speed is a relative value and cannot be compared across different manufacturers.
  • Speed is often used to describe a film-screen combination rather than one or the other in isolation.
  • Because of the small size of most exotic patients, high and regular speed systems are of limited value in these species. Low-speed screens produce a sharper and better detailed image, but will require more exposure (either by raising mAs or time or both).
  • Film choice is limited by the type of screen used.
  • Mammography films (ultra-slow speed films) are very advantageous in exotic practice as they require longer exposure time than regular screen-film systems and are less affected by patient motion caused by fast breathing.

Storage of x-ray films

  • Radiographic film is a delicate material and requires careful handling .
  • Ideal storage facilities:
    • Cool conditions (10-18°C/50-64.4°F).
    • Dry conditions (no more than 50% humidity).
    • Away from sudden changes in temperature and humidity.
    • Protected from light.
    • Protected from processing chemicals and their fumes.
    • Protected from ionizing radiation.
    • Film stored on edge (not stacked on top of one another as this may result in pressure marks).
Even when stored in ideal conditions film gradually deteriorates with age so stock should be rotated.

Film identification

  • It is essential that radiographs be clearly, correctly and indelibly labeled.
  • Information on each film should include:
    • Owner and patient's name or identification number.
    • Date radiograph taken.
    • Hospital or practice name.
    • Anatomical marking, ie left or right.

Methods of marking film

  • "X-Rite" tape:
    • Self-adhesive, lead-impregnated tape on which information is written and then stuck to cassette before exposure.
    • Can be difficult to see on finished radiograph, especially if exposure has been high.
This problem can be overcome by the use of special holders for the tape.
  • Lead numbers and letters:
    • Commonly used for anatomical marking but can also be used for identification.
    • Words formed from required combinations of letters and stuck to cassette before exposure.
    • Metal holders, into which the letters slide, are also available and can be stamped with practice name.
  • Light marker:
    • Photograph the identification information, written on a special piece of paper, onto a corner of the film which has been shielded from the main exposure by a lead blocker.
    • This marking can be done by manual marking of the film in the dark room or if cassette is inserted into machine before film is removed the identification window in the cassette automatically slides back and exposure is made.
  • Writing on the film after exposure (not ideal).

Types of radiographic film

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Sensitometry

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Further Reading

Publications

Refereed Papers

Other sources of information

  • Jekl V (2013) Principles of radiography. In: Manual of Rabbit Surgery, Dentistry and Imaging. Eds: Harcourt-Brown F & Chitty J. BSAVA, UK. pp 39-55.
  • Capello V, Lennox A M & Widmer W R (2008) The Basics of Radiology. In: Clinical Radiology of Exotic Companion Mammals. Wiley-Blackwell, USA. pp 2-16.

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