"WHITE DOT" Artifacts on X-RAYS

EXHAUSTED INTENSIFYING SCREEN

Small "white" (really lack of black) dots distributed diffusely across the surface of x-ray films suggest aging intensifying screens inside your cassettes. While some owners of x-ray equipment bought cassettes and intensifying screens with the expectation that it was a one-time purchase, the usual life of intensifying screens in a private office setting is only five years or so.

After five years or so, the fluorescent crystals on the intensifying screens begin to lose their ability to fluoresce, leaving small areas of non-exposure (lack of black) which we see as "white" dots. The aging of the screens is use-dependent, and the screens wear out faster if they are heavily used, less rapidly if they have a low rate of use. Busy hospitals and radiology labs turn over their screens about every year because of the high rate of use and consequent rapid exhaustion.

If aging of the intensifying screens is the cause of the “white” artifacts, a slight and gradual increase over time will have been noted in the exposure technique factors needed to maintain adequate darkness of films. When this gradual increase of exposure technique begins to be noticeable, there is nothing to do but to buy new intensifying screens.

It is possible to put new screens in old cassettes, but it is not recommended. Cassettes are very inexpensive compared to the high cost of intensifying screens, and old cassettes may no longer close tightly.

	When cassettes do not close tightly, light leaks can occur at the three free edges of the cassette, exposing the edges of the film to ambient light.
	Also the film is not held tightly against the intensifying screens, producing poor radiographic definition.

In the case of intensifying screens that are fairly new, and in which there has been no gradual necessity over time to increase exposure technique factors, “white” dots may also result from the use of some of the less expensive generic brands of film, which have insufficient silver distributed across the surface of the film, thus leaving random “blank” areas on the film. You definitely get what you pay for in film, with the better films costing about double the amount for which generic brands can be obtained. Not only does less expensive film contain less silver, but it tends to have greater base fog and less sophisticated technology in application of the silver crystals, resulting in poorer radiographic definition.

There is also a possibility of incompatibility between the brand of film and brand of screen and also between the brand of film and the brand of developing chemistry, but these incompatibilities usually produce a much worse and more obvious looking problem on the finished films. In a few cases (fortunately not common!) incompatible film has been known to permanently ruin the intensifying screens - a very expensive consequence arising from an attempt to save money!