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Film Viewing Equipment ("Viewing Boxes") • The quality and characteristics of the viewing equipment play a decisive role in the recognition of diagnostic details in the radiological image. • The measurable, physical parameter for viewing equipment is the light stream (light quantity) which is emitted from the viewing surface of the equipment.
If the light stream L (lat. Lumen) is put in relation to the light emitting surface, you produce the measurement parameter Luminance L: L = Candela / Square meter (cd/m2).
LUMINANCE • A properly exposed X-Ray film has a mid-optical density of 1.2 • To be able to diagnose details in the lower density range of the density curve (D = 0.3 – 0.6), the luminance of the viewing device must be able to be reduced.
To view high density (Dopt > 2.2) areas of X-Ray films, a strong light source with an iris shutter (“hot light”) is needed. This light source must have a luminance of at least 5000 cd/m2. Due to their great importance in making diagnostic details of radiographs visible, all viewing devices must undergo an acceptance test and routine constancy tests.
Repeat tests for viewing devices, which are routinely used for diagnosis: