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How to Calculate Density in Radiography

Radiographic density refers to the level of darkness of an x-ray film. For most films, the ideal density is in between two and four. If the density is less than two, the film will appear too light. If the density is greater than four, the film will be too dark. An exception to this rule occurs when films are to be digitized. Digitization systems work best with film densities between four and six. In all cases, increasing density means greater contrast so a film with a higher density is preferable to a film with a lower density.

Things You'll Need

  • Lamp
  • Photometer
  • Pen or pencil
  • Paper
  • Calculator
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Instructions

    • 1

      Place the lamp on a stable, level surface. Position the x-ray film approximately 24 inches from the lamp. The film should be standing on its edge, facing the lamp, so light from the lamp shines through the film.

    • 2

      Measure the intensity of the incident light. This is the light that is shining on the film. Place the photometer in between the lamp and the film with the photometer's sensor directed towards the lamp (the photometer itself should be closer to the film). Read the value on the photometer and write it down.

    • 3

      Measure the intensity of the transmitted light. This is the light that is passing through the film. Place the photometer on the opposite side of the film, again with the sensor facing the lamp. Read the value displayed on the photometer and write it down.

    • 4

      Using the calculator, divide the value for the intensity of the incident light by the value for the intensity of the transmitted light. The log of this number is the radiographic density.


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