Scatter radiation and film fogging

[Asmaa Mohammad]

Hello,

During the procedure of radiography using x-rays, scatter radiation occurs, due to the difference in densities of the object being radiographed.

That scatter radiation causes fogging (noise) of the film, i.e. the contrast of the film is reduced due to extra darkening of some areas of the film (increase in the overall density of the image).

What I have difficulty to imagine is how could these scattered photons increase the density of the radiographic image. Do they hit the object again or do they hit the film in a way that causes fogging (so what is that way?).

All in all, hope someone will clarify it for me!

thanks!

 

[gleem]

What I have difficulty to imagine is how could these scattered photons increase the density of the radiographic image.

The same way as any x-ray. The problem with scatter is that the source of scatter is extended resulting in the more or less uniform additional exposure across the whole film. The contrast you observe on the film is due both to the characteristics of the film and the variation of the exposure of the film due to the variation of the transmitted radiation through the object. The film produces an optical density depending on the exposure; the larger the ranging of exposures the more optical densities that will be registered. With no scatter you may have a large range variation of exposure from the object. This may result in the visualization of the who range of optical densities that can be appreciated by the eye. As the scatter is increase the range of exposures across the whole film decreases. This leaves a smaller range in optical densities to be registered on the film. Thus the contrast is reduced.