XRAY Film As A Copy Film?

[Craig]

Why would X Ray film have emulsion on both sides? Shouldn't single side work fine for X Rays?

 

[Alan Townsend]

People who have used most xray films would get this. It's got nothing to do with DOF. This is double-sided film. It has emulsion on both sides. The side facing the lens during the exposure is sharp. The emulsion on the other side is unsharp. There is no way around this unless you strip the unsharp side after processing... But this technique literally cuts the density range in half. I tested this 'til the cows came home. An easier way around this issue, is to use single-sided xray...

I would think removing the back side emulsion before exposing the film would work much better than after since this would also greatly reduce the halation. This could be done just using fixer after masking the front. Or, the back side could be turned black by appropriate agent to act as anti halation later, then removed after processing. That would make it hard to judge density while developing. However, since the max density of hru xray film is around 3.5 (what I measured on hru 2 years ago), a single side would give only 1.75, which is close to what I get with my "bad film".

 

[koraks]

Why would X Ray film have emulsion on both sides? Shouldn't single side work fine for X Rays?

First, keep in mind x-ray film doesn't really record x-rays. It can And it would, but in a typical medical setting the flux is way too small to generate an image. Instead, the x-rays hit a phosphor screen which emits visible light, and that is what creates the image.

As to the double sided nature: I suspect it's because it's basically "free" additional density for the same number of photons and thus the same x-ray dose. Which means less exposure to the patient for the same image density, do less risk of tissue/dna damage. Ease of use might also have something to do with it as there's no risk of loading the film in the wrong orientation in the exposure unit.

Apparently applications like mammography require higher resolving power or better/higher fidelity rendering of very fine structures. For this purpose a single-sided film is apparently preferable because it can better deal with scatter, halation etc. which would erode this fine detail.

 

[Alan Townsend]

I watched your video this AM. Contact printing xray to xray doesn't work great as you found, but reversal processing would also be difficult for several reasons. Two years ago, I found that using a piece of ortho litho film along with a piece of xray can work together fairly well. The ortho litho raises the contrast enough to get good dmax on the xray without using print developer, and the xray negative can be as sharp as one done in camera. The ortho litho should be the interpostive, then the xray internegative. I was also contact printing xray onto ortho litho in 4x5 with topside down, then enlarging the ortho litho onto xray. Doesn't work as well, but kindof OK.

 

[Alan Townsend]

As to the double sided nature: I suspect it's because it's basically "free" additional density for the same number of photons and thus the same x-ray dose. Which means less exposure to the patient for the same image density, do less risk of tissue/dna damage. Ease of use might also have something to do with it as there's no risk of loading the film in the wrong orientation in the exposure unit.

My understanding is that in the xray film packs, there are phosphor screens on both sides of the film acting somewhat independently, but for the same reasons you mention, to reduce patient xray exposue. Also read that if a single exposure on xray film is correct, the patient is exposed to less xrays than with the newer digital systems.