This is a low exposure test image taken with a CR cassette that was thought to contain scratches. If you squint at the image you can see the banding effect.įor more information on interference patterns see Jeremy Enfinger's excellent blog on this subject at For an interference pattern to occur, the lines must be at different spacings or frequencies. Imagine the longer parallel lines to be the grid lines and the shorter lines to be the laser reader path lines. This image is an example of an interference pattern. There is a special case of grid aliasing known as a " beat pattern" and I suspect that this is an example of a "beat pattern". The grid frequency is defined as the number of grid strips or lines per inch or per centimetre. The grid ratio is defined as the height of the grid strip divided by the thickness of the interspace material. To avoid this artifact, you could place the cassette in the bucky in a portrait orientation or you can change the grid to a different frequency that is compatible with the particular CR system that is being used (grid frequency higher than scan frequency). This artifact could be thought of as a form of diffraction grating artifact or interference pattern. This is likely to be caused by incompatibility of the CR system with the grid frequency of the wall bucky. If you examine this PA chest radiograph closely you will notice that it has a subtle vertical banding pattern, particularly in the right hemithorax. I couldn't find it on the WWW but should be available from Kodak if you ask nicely. This includes a very comprehensive explanation of the subject and is well worth the effort involved in finding it. For a very comprehensive discussion of the subject refer to the document titled "Stationary Grids for Kodak Computed Radiography" by Xiouhui Wang, Ph.D., andĭavid H. This is quite a complicated subject although the concept of an interference pattern is elegantly simple.
The frequency of static artifacts might also depend on floor coverings and your footwear. Grounding your hand on a metal object before you remove the film from the cassette would probably avoid the static discharge. Preventing static artifacts was at times difficult. Secondly, there is the discharge of static electricity forking out from the initial discharge point. This is simply the radiating light fog from the light associated with the initial spark from your finger to the film. Firstly, there is an amorphous graduated fog which can be seen radiating out from the black dot at the origin of the artifact. The artifact appears to have two components. Static artifact is caused by an electrical discharge, usually from your finger to the film. Its beauty belies its potential to spoil an otherwise successful radiograph. If there was to be a beauty competition for artifacts, here is your winner. I am not considering the "coins in the pocket" type artifacts here.ĭeveloper-fixer/film-screen (DFFS) radiography For more information on the spelling issue click hereĪrtifacts can usefully be divided into film artifacts associated with developer-fixer/film-screen (DFFS) radiography and digital artifacts associated with digital radiography (CR and DR). I am going to use the "i" version but for no particularly good reason. At least they have largely decided what to do- here in Australia we are just confused on the subject. The North Americans have traditionally called it an "Artifact" and the British have spelled it with an "e" as in "Artefact".
I have alluded to a transatlantic spelling issue in the title.
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