X-ray settings


#1

I’ve just gotten the ‘green light’ from our local vet that he is willing to provide x-ray services. He has asked that when I come in that I provide some direction as to power level settings.

I’d really appreciate any advice.

Thanks,
Paul


#2

I’ll e-mail you the settings that my vet has used.

Dave


#3

Please provide the make and model of machine.
Does it have digital controls or dials?
What is the recording medium? (Digital or analogue).
If analogue (film) what cassettes are these (screen speed)?

Unfortunately you can’t just transfer exposure settings from one machine to another. Unless the setup is identical, there will be exposure differences. Also you need to advise us what cartridges you are X-raying, and what views you are doing. I assume you want side views mostly.


#4

Wow! That is awesome. I never even thought of something like that. I think a large picture like that as a poster would be incredible. It’s like abstract art that’s actually interesting!!
-Josh


#5

Here are a few of the x-rays generated by my vet. Unfortunately, I don’t have a suitable scanner so I’ve lost some resolution in photographing the images. There’s still more experimenting to do with settings but I’m very pleased with the results so far.
RICA Squeezebore

Project SALVO - duplex

US observation round

UK tracer

UK incendiary

RSA BUTTER - two variations -externally they are identical except for the hs

And just for variety, a 7.62x25

Thanks to Dr C for his time and use of x-ray equipment


#6

Odd Job et al,

I went back to the vet office to get information to answer some of your questions…

The machine is a InnoVet Select. It has dial controls and 2 primary settings of 100 or 300 mA with a max power of 125 KVp. I think that it is analogue. I don’t know the screen speed.

I brought in some rounds (a TRICAP which has a plastic case and a .44 QSPR which has a heavy steel case) and the x-ray images I have to show the differing nature of materials that I wanted to be able to x-ray.

The film size is 8x10". In order that I can have plastic, aluminum, steel and brass cases on a single film the x-ray tech thought we could shoot an image with a lead shield over the plastic/aluminum cases and then reshoot on the same film at a lower power setting and with the lead shield over the brass/steel cases.

I’m going to make a template so I can play with maximizing the number of rounds I can x-ray. Then I have the dilemma of selecting the first group of cartridges…

I’ll report back next week.

Paul


#7

I have taken quite a few with a 65KV fixed medical x-ray unit at my facility. Though I start with a baseline setting(s), I inevitably end up working up and down the settings as “who knows” when you will hit a projo “hard enough” to determine what lies within, especially true of tracer, incendiary and spotter components. Determining A/P cores, multi ball loadings, ball & shot loadings…I find easy, it’s when you do not know what lurks within (and in my case that is often)…so thus I see no way but “trial and error” (which does not help you if you are having someone else shoot the films. (PS


#8

Gents, will it be useful if I post a basic guide to X-ray exposures, and the pitfalls associated with X-raying cartridges?


#9

Hi Odd Job,

Yes, by all means!

It was an x-ray that Pepper took of the .44 QSPR that I brought into the vet. When I explained what the loading was and how it worked he was actually interested!


#10

Looks like everybody has gotten over their fears of X-ray explosion! Have a bunch of French CF .22’s. Took them to my dentist who is a competitive shooter, reloader and African Safari hunter. Took a lot of talking to convince him the X-Ray would not set the primers off!


#11

It’s x-rays, not Superman’s heat-vision!


#12

Somewhere between “Toast” and “Bake”. “Broil” is probably too high.


#13

Alright gents, here is a basic explanation of the X-ray exposure.

This may seem like too much detail, but bear with me and all will make sense soon.

An X-ray beam is nothing more than a bunch of photons that emerge from a machine and then pass through whatever is being X-rayed. These photons then hit a photon-sensitive detector. This detector will either emit light (which subsequently exposes a film) or it will store a surface charge (which is then read by a solid state reader). The former is an analogue setup and the latter is digital (expensive).
Now in most cases, you guys will be using a system that relies on film to capture the image, and the ‘detector’ is therefore a pair of intensifying screens within a light-tight cassette. The film that is to be exposed lies within this cassette also, sandwiched between the screens. The use of two screens means that a lower exposure can be used to produce the required amount of light that will expose the film.

Okay, now here is the first variable/problem: not all screens are the same. They have different phosphors, and the phosphors may be embedded in the screens in a coarse or fine grain. This means that one screen may be more sensitive or will convert X-ray photons to light ‘faster’ than another screen even if they are both embedded with the same phosphor. The bottom line for you, is that there different ‘speed’ screens. Generally, when discussing screens of the same phosphor type, the finer the grain of the phosphors, the slower the screen but the more detail there is. You may have heard the terms ‘fast,’ ‘regular’ or ‘detail’ cassettes. The detail cassettes will have finer grain phosphors but will also require more x-ray photons to produce the required amount of light to expose the film inside. In medicine, we can’t just use detail cassettes for everything we do, because it results (indirectly) in an increased radiation dose to the patient, amongst other things. Obviously for cartridges it doesn’t matter, so our first decision about the X-ray settings is as follows:

Use detail cassettes if available

The next thing we need to look at, is the X-ray exposure itself. There are four variables associated with an X-ray beam:

  1. The penetrating ability of the photons in the beam. You can think of this as photon energy.
  2. The number of photons present in the beam.
  3. The duration of the exposure, in other words the interval in which these photons are going to be emitted.
  4. The distance between the source of the X-ray beam and the detector. In our case it is the focus-to-film distance (FFD) sometimes referred to as the source-to-image distance (SID).

The technical factor that affects the penetrating ability of the beam is the kV setting (kilovoltage). Without going into too much detail, the higher the kilovoltage setting within the X-ray machine, the greater the energy of the emerging photons, which results in them being able to penetrate materials of a greater density. Consequently, the optimal kV for X-raying brass cartridge cases is unlikely to be the optimal kV for X-raying steel projectiles, for example. Part of the reason for this is that brass is less dense than steel, and the other part of the reason is that the thickness of the brass is less than the thickness of the projectile, in general. Here are some rules about kV and cartridges:

If the kV is too low, then the item being X-rayed will appear white on the film. This is because the photons had insufficient energy to penetrate the cartridge component, which means the photons couldn’t get to the screens at all.
If the kV is too high, then the item being X-rayed will appear very dark or may even be invisible on the film. This is because the photons had so much energy that the cartridge component could not absorb them at all, and the photons arrive at the screens unattenuated, which means that it is as if there was nothing in between the X-ray machine and the screens.

The ideal kV setting is one which produces photons of an energy that is not too high and not too low. This is because we want the item being X-rayed to absorb some of the photons, but let some of them through to hit the screens. Unfortunately, each material being X-rayed has its own ‘sweet-spot’ in terms of optimal kV settings. Some materials are special because they exhibit extremes (either high or low) in terms of absorbing X-ray photons. For example, lead is a very dense metal and absorbs x-ray photons so well, that even small bullets will totally absorb even high kV X-ray beams. On the other end of the scale, you get aluminium (or ‘aluminum’ for my US/Canadian friends) which is very low density in terms of absorbing X-ray photons. In fact small quantities of aluminium as found in small arms cartridges and bullet jacketing may not be apparent on standard X-ray exposures. Brass, copper and steel lie somewhere in between aluminium and lead. Of course plastics are often low density and cannot be seen on standard X-ray views. To make matters worse, a piece of brass 2mm thick, will absorb more X-ray photons than a piece of brass 1mm thick. That 2mm piece of brass may be the equivalent of a 1mm piece of mild steel. Any items within a cartridge case will have their density added to the density of the case, such that you have to mentally estimate the combined density of that cartridge, in terms of how likely it is to absorb the X-ray photons. So you have variables to do with the type of material and its thickness.

I cannot provide a chart of KV values for different cartridges or even different metals, but I can tell you that the kV range of most medical X-ray units is from 40kV to 150kV. I X-ray small handgun and rifle cartridges and I have found a useful kV range to be from 55kV to 70kV. This is good for the contents of the cases, other than lead or tungsten projectiles. For mild steel projectiles you may have to increase to 80kV, but then you will start to lose detail because at high kVs you get a phenomenon called ‘scatter’ which results in degrading of the edges of the image. This is similar to turning on a high pressure hose and seeing it splash on concrete. When you are X-raying cartridges directly on cassettes, you have no mechanisms to reduce scatter. In the hospital we employ Bucky grids to reduce this, but for you to employ these on X-raying cartridges means you have to have some training from a radiographer (to be honest with you, when you start going into grid territory, you may as well pay a radiographer to X-ray your cartridges professionally). Be advised that you may be in the position where you can never X-ray a lead projectile to your satisfaction, simply because it is too dense. By the time you have cranked the kV up to penetrate the projectile, there is little else on the X-ray image to see, and the image of the projectile is degraded by scatter to such a degree that the small holes/cavities you were looking for may not be appreciated.

Alright, those of you still reading, I applaud your interest and move swiftly on to the second variable, which is the number of photons in the beam. This is governed by the mA control on the X-ray machine. This is the current in the X-ray machine at the time of the exposure, measured in milli-Amps. It basically equates to the number of electrons that were available to produce the photons in the beam. I’ll not explain how this happens, all you need to know is that a higher mA value means a larger number of photons in the beam. Too little mA means you get a ghostly image and the area around the cartridge, when seen on the X-ray film, is very light. It may be grey instead of black, or in severe cases you can see through the film. If the mA is too high, you promote scatter at a lower kV than would normally have occurred. This means you get the same degraded edges on the image, but you may still see the item being X-rayed (it does not disappear or become too dark such as occurs when the kV is to high). High mA results in general blackening of the film. I can’t suggest mA values right now, because mA is tied in to time (the third variable of the X-ray exposure).

In most modern X-ray machines, the exposure is given in mAs, which is mA multiplied by the time in seconds, or fractions thereof. This means that before you select the mA or the s, you must know what the final value is in mAs.
For example, let’s say I know that I want a final mAs of 20, combined with whatever kV I think is necessary for the cartridge I am X-raying. I could get 20mAs by having 200mA and 0.1s or 10 ms, because 200mA x 0.1S gives me 20mAs. Maybe the machine can only do steps of mA, for example it may not have a 200mA output, but it offers 150mA or 400mA. In this case you can choose 400mA and just reduce the time to 5ms. That will give you the same 20mAs, it just means the exposure was much quicker than with a 200mA selection.
So, what do I recommend?

Well if you are X-raying on a detail cassette you need more mAs than you do if you are X-raying on a regular cassette. This is why you have to know the speed of the screens you are using. It affects mAs selection. When I X-ray handgun cartridges on detail cassettes I use an mAs value in the range of 15 to 30. If I am X-raying on a regular cassette, I must use less mA, say about 8mAs to 18mAs. It all depends on the type of cassette (the screens within).

Now the last variable, FFD or SID is very important. All X-ray exposure charts are relevant to a particular FFD or SID. The reason for this is because the X-ray beam is not comprised of photons that travel parallel to one another. They diverge like light rays. The closer you are to an X-ray machine, the more photons can strike you during the exposure. To use an analogy, if you approach a sprinkler that is on a 40 degree arc, you will get wet by the sprinkler as it covers more of that 40 degree arc, the closer you step towards the sprinkler. This means that the further the cartridge is from the X-ray beam, the fewer photons in the beam will strike it. This means you have to turn up the mAs to make up for the ‘loss’ of photons and you also have to increase kV slightly because air causes some absorption of the beam. The photons have to travel through more air molecules and therefore you need a bit more kV. Here is the rule:

The standard FFD or SID for radiography of small items placed directly on cassettes, is 100cm. If you come closer, you drop the mAs and kV, and if you move away, you increase both. The increase and decrease is more noticeable in terms of mAs.

Whew, so what is a reasonable starting point, in terms of all these variables?
For small cartridges where you would want to see how many metallic projectiles are within, I would start with the following settings:

1) Detail cassettes are preferable.
2) Use 65kV to start with and work from there.
3) Use 20mAs for a detail cassette and about 7mAs for a regular cassette.
4) Keep the FFD/SID constant. 100cm is standard.

And that should do, gents. Now that you know what an X-ray exposure is, you should be able to work out for yourself how to adjust the exposure according to the appearances of the film you already produced.

Any questions, just ask!


#14

Thanks for the detailed explanation - I’m off to set up my next vet’s appointment.
Dave


#15

It’s my pleasure.
Just remember that I use top quality hospital machinery and cassettes. You might get variations in exposure if you are using old equipment. However the principles remain the same, and you can usually fine tune the settings. Get the kV right and the job is an easy one.
If you have access to digital equipment, you can do the job in half the time with a much more forgiving exposure latitude. Most vets don’t have that though.