“Coning down”: This refers to the narrowing of the beam to only expose that part of the body you are specifically interested in. When the beam exposes surrounding tissue, x-radiation is scattered by the surrounding tissue and fogs the portion of the film that you are specifically interested in. This is why the quality of films that expose large parts of the body is not nearly as good as a carefully “coned down” film exposing just the area of interest.
“Screens”: Screens are devices placed within the x-ray cassette, which actually fluoresce when exposed to x-radiation. This fluorescence also exposes the film to light photons, thus less radiation can still produce a satisfactory film exposure.
The problem is that the fluorescence of the screen slightly diffuses the image, making a poorer quality image. If you want an especially high quality film, you may need to use cassettes without screens and a more powerful x-ray beam.
Upright films: If the films are not marked, it is often possible to tell whether they are upright (if the abdomen is within the x-ray field) by the presence or absence of air fluid levels. You should know that the right and left markers used by many x-ray departments have three little lead beads within a circle.
These beads fall to the bottom side of the circle if the film is placed upright, but remain in the center if the film is flat.
Fluoroscopic radiation exposure: The image intensifier on a fluoroscopy unit allows the use of very low doses of radiation. This means that fluoroscopy units, in general, produce less radiation than obtaining ordinary films. During surgical procedures, the highest dose is to the hands, but Sanders et al. (JBJS 75A:326) calculated from their study that the average surgeon would need to perform 7,614 fluoroscopy assisted procedures per year to reach the limit recommended by the government for the hands. Nonetheless, one’s best protection is distance from the x-ray beam (and the tissue that is being radiated and scattering x-rays), as dose falls as the cube of the distance. A surgeon must not become cavalier.
“God is in the detail”: Visual acuity is high only at the fovea of the eye. This means that if you glance at an x-ray without actually making your fovea cross all the important parts, it is easy to miss minor flaws. A wise practice is to trace the surface of each bone with your eye to ensure that the fovea will pass close to all of the important parts of it.
Densities: There are only five different densities that can be seen on plain x-rays:
“The worst looking view is the one that speaks the truth”: When trying to determine whether union has occurred, if several views appear to show bridging bone, but one shows a clear defect then the “worst view tells the truth.” The apparent bridging is an artifact of the two bones overlying one another. The same is true with alignment. If