Why are xrays printed on a clear piece of plastic and held up to a light box, instead of just black ink on white paper?


Why are xrays printed on a clear piece of plastic and held up to a light box, instead of just black ink on white paper?

In: Technology

They aren’t “printed” they are a photographic exposure with the “film” reacting to the X-rays to produce a negative as happened with cameras before digital cameras existed.

They’re not just printed on paper, they’re analog photographs. The x-rays go through your body and turn the chemicals on the film black–unless they’re absorbed by something dense like your bones, that part of the image stays white.

The plastic is actually film like an old school camera. X-rays show up on x-ray film just like visible light shows up on visible light film.

Former radiographer/x-ray tech here. In the film days, the cassette in which the film was loaded was more than a light-tight box to hold the film flat. While photographic film is sensitive to x-rays, long ago they started lining the inside of cassettes with radio-luminescent plastic, which converted the x-ray energy into photons (light), providing a much lower dose of x-rays’ ionizing radiation during the medical procedure. No idea if this trick is still used in the digital realm.

Good responses here. Part of it is that a transparent image, lit from behind, can reproduce a *much* finer range of detail, and wider range of brightness, than an opaque image lit from in front…that’s why slide projection is popular in color photography.

Med students spend a *lot* of time learning how to tell one object from another in an X-ray…every faint, subtle line means something.

Definitely digital in Canada for at least 13yrs. Great thing is being able too zoom and change brightness levels on the fly.

The clear plastic has a layer of tiny silver halide (commonly bromide) crystals. When you take an xray exposure, you flood the object with xrays, and most of them pass through the object. Some of them get scattered by the object. Dense things, like bones, scatter more than soft things, like fleshy bits, so fewer xrays make it all the way through to the film behind the object. The places where the xrays strike the silver halide crystals on the film, a chemical reaction takes place that activates the crystal (it gets charged). This leaves it susceptible to a process called chemical reduction (you get a bit of black metalic silver) at that spot when it’s placed in the developer. In the places where the xrays didn’t make it through the object, you have less black metalic silver formed, and so it is more transparent to light.

No printing, there’s just less of a blackening chemical reaction in the places where fewer xrays hit the film.