A Quick Guide on Various Radiographic Film
Types of Radiographic Film
- Screen Film – the most widely used IR in radiology.
Characteristics of Screen Film:
- Contrast – most manufactures offer screen-film with multiple contrast levels. High contrast produces a very black and white image, where as a low-contrast image is more gray.
- The difference of the density of the radiograph.
Latitude – the range of exposure techniques that produced an acceptable image.
• Bigger Grains – low contrast.
• Smaller Grains – high contrast. - Speed – is the sensitivity of the screen film combination to X-rays and light large grain emulsions are more sensitive than small-grain emulsions.
- Crossover- is the exposure of an emulsion by light from the opposite side of radiographic intensifying screen (IS).
- causes increase blur in image Three Characteristic of Cross-Over Control Layer:
a) It absorbs most of the cross-over light.
b) Does not diffuse in the emulsion but remains as separate layer.
c) It can completely be removed during processing. “Use IS which emits short wavelength light (e.g. blue or UVR)”. - Spectral Matching – use of rare-earth screens only in conjunction with film emulsions that have light absorption characteristics matched to the light emission of the screen.
Rare Earth Screen – are made with rare earth, those with atomic numbers of 57 to71. Calcium Tungstate Screen – emit blue and blue-violet light.
Orthochromatic Film – green-sensitive film.
Panchromatic Film – which is used in photography and is sensitive to the entire visible light spectrum (sensitive to all colors of light).
Monochromatic – sensitive to all blue light.
“When the Spectral Matching is improper, IR speed is reduced and patient dose increased”.
“The proper Spectral Matching result from correct screen film combination”. - Reciprocity Law – true for film exposed to X-ray and important when exposure times are long (as in mammography) or short (as in angiography).
Exposure = Intensity x Time
= Contrast Optical Density Safelight – most are incandescent lamps with a color filter.
- Provide enough light to illuminate the darkroom white ensuring that the film remains unexposed.
15 W & below – required wattage of the bulb.
Amber Filter – blue sensitive film.
Red Filter – is suitable for both green and blue-sensitive film.
- Direct-Exposure Film - emulsion is thicker than that of screen-film and it contains higher concentration of silver halide crystals to improve direct X-ray interaction.
- Is less sensitive to light and therefore should not be used with screens. - Mammography Film – a single-emulsion film designed to be exposed with a single radiographic intensifying screen.
Halation – the surface of the base opposite the screen is coated with a special light-absorbing dye to reduce reflection of screen light, which is transmitted through the emulsion and base. - Laser Film – silver halide film sensitized to the red light emitted by the laser in much the same way blue and green-sensitive screen-film is sensitized.
Modulation – the intensity of the laser beam is varied in direct proportion to the strength of the image signal. - Specialty Film
• Duplicating Film – designed for same-size, the size of the duplicating film is equal to the size of the film being duplicated.
- A single-emulsion film that is exposed to ultraviolet light or blue light through the existing radiograph to produce a copy.
Cine film – used by radiologic technologist who becomes involve in such procedures.
• Spot Film – 70 to 105 mm in width are used in a number of different types of spot cameras.
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