Topic: Windshield perforation angles

[Brandon Bertolli]

Okay, here is the radiograph:



That is a classic core-jacket separation. This was an FMJ of unknown calibre that entered on the right lateral aspect of the pelvis. No bones were hit, there were no fractures.
The core is a completely radio-opaque white shadow (double white arrows) while the jacket has lower density (it is more grey): enough to see the femur bone behind it. If the core was overlying the femur, you would not be able to see any part of the femur bone behind or in front of it.

[Michael Haag]

Even if these are not the best X rays, I would suggest not making judgements about impact angle from these...
Even an actual exam of the projectile must be done cautiously...
Doesn't look like enough info to me from these images to make good impact angle judgement.
Make 'em cut it out...  Hehe.
mgh

[Brandon Bertolli]

I wish they would cut more of them out (but that's just me trying to get a complete documentation of the projectile and the damage it caused). There were two cases where I really wanted the projectile but in each case it was not clinically possible. Scott Doyle and a gentleman by the name of Emil Hamza helped me ID one of the projectiles radiologically and in the other case, the projectile remains unknown.

[Michael Ward]

Brandon,

When you say "ID one of the projectiles radiologically", what do you mean?

[Brandon Bertolli]

Michael, it was a case that had baffling appearances to me, because there were multiple lead fragments and a fully intact symmetrical high density 'thing' embedded in the tibia.

We don't see many cases like that in the civilian setting, and that is the only one I have seen, period. To cut a long story short I wanted to know what ammunition this could have been, and it was at that point that the fine members of this board advised via Scott Doyle that the strange item was most likely a steel insert. It then remained for the ammunition to be identified by the unusual contour of the insert. Emil Hamza suggested a possible match: 7.62 x 25 Tombak-plated steel jacket steel core Tokarev of the Czech variety. His photographs were very similar to my radiograph in terms of the contour of the insert (which could not be removed from the patient and was not seen at surgery).

I managed to source some of those bullets here in the UK, extract the insert and X-ray it here at an equivalent angle as the one lodged in the patient. The contours were an exact match and no other insert that I have investigated so far has those same contours. So I am quite confident that this was a Tokarev insert.
It took a while to arrive at that conclusion: the guy was shot in Johannesburg in 2002 and I only came up with the answer towards the beginning of 2005 here in London. It is one of 150 cases I documented in four months in Johannesburg. These are the cases I will reference in my book (which is on ice at the moment because of work commitments).

[Bob Kennington]

Okay, here is the radiograph:



That is a classic core-jacket separation. This was an FMJ of unknown calibre that entered on the right lateral aspect of the pelvis. No bones were hit, there were no fractures.
The core is a completely radio-opaque white shadow (double white arrows) while the jacket has lower density (it is more grey): enough to see the femur bone behind it. If the core was overlying the femur, you would not be able to see any part of the femur bone behind or in front of it.

That is a good example.

A few observations from my prior caliber x-ray determinations:

1) When I've put known caliber fired bullets on the x-ray platen for scale, often I've seen the jacket surrounding the core like a halo. (Requires a very favorable exposure).

2) As to "unknown caliber": an x-rayed bullet can only appear larger than is measured directly from the x-ray. IOW, one can assert that the fired bullet's actual caliber is no greater than what can be directly measured on the x-ray itself. In the above x-ray, that would be a difficult determination without additional x-rays to align the core axis (if available) to the platen.

3) A bullet's caliber can be determined using the "Peter's Method", previously described in the AFTE Journal. It requires several x-rays of the victim to help orient the evidence bullet, "coning down"—and the use of a "tomographic phantom". (Which should be amongst the x-ray lab's equipment.)

The topic can be argued endlessly, but I find x-ray bullet caliber determinations fascinating. 

Once, a prosecutor asked me to make a caliber determination in the hallway outside of courtroom!

The victim—who was to testify—was in a wheelchair due to the first shooting, and had just suffered a subsequent shooting ( ). The bullet was caught just under the skin. It was quite the experience to palpate a bullet caught in a living shooting victim. 

To the prosecutor's question, "Was it consistent with 38 caliber?", I could say "Yes".

The judge threw out my testimony because there had been no "Discovery". (Although the defense attorney was standing beside me at the time of the examination.)   

[Brandon Bertolli]

1) When I've put known caliber fired bullets on the x-ray platen for scale, often I've seen the jacket surrounding the core like a halo. (Requires a very favorable exposure).

I've seen this also, usually at the base of bullets that have an exposed lead core. Beware, there is a false halo that can be caused by movement artefact (bullet is alongside a pulsatile vessel or organ) or also geometric penumbra from a large focal spot on the X-ray anode (older equipment, particularly mobile units).

2) As to "unknown caliber": an x-rayed bullet can only appear larger than is measured directly from the x-ray. IOW, one can assert that the fired bullet's actual caliber is no greater than what can be directly measured on the x-ray itself. In the above x-ray, that would be a difficult determination without additional x-rays to align the core axis (if available) to the platen.
 

One factor that will become increasingly influential is the digital age which is resulting in an increase in computed and digital radiography systems worldwide. Even the UK Forensic Radiography Response Team's equipment is almost entirely digital (screening and plain film): only the dentals are wet developed and solid state detectors attached to laptops are going to render dental films obsolete in a few years.

Anyway the problem with digital is the scale. You can now have an output image that is artificially smaller than the actual latent image on whatever detector is being used. If the calibration of that detector or the software that manipulates it is not right, you have a radiographic contour which cannot be described relative to the size of the bullet in situ. The same applies to images acquired on an image intensifier, because there is an intermediate step in the image chain where electrons are focused, and that means you've lost your relative size increase of the latent image.

3) A bullet's caliber can be determined using the "Peter's Method", previously described in the AFTE Journal. It requires several x-rays of the victim to help orient the evidence bullet, "coning down"—and the use of a "tomographic phantom". (Which should be amongst the x-ray lab's equipment.)

Measuring bullet calibres radiographically is kind of a sore point with me. I am aware that some members have techniques that they employ to make these determinations and I have also read up on the Peters method. These methods rely on the comparison of the bullet in situ to an approximate match or control bullet which is X-rayed under the same 'magnification' as the bullet in situ.

I have serious reservations about these methods.

In fact the only case I have read where I have any faith in the outcome of the calibre determination involves shotgun pellets where the suspect pellet lodged in the orbit was known to be one of only two or three possible sizes. I will have to find that paper for you, but the bottom line was that the pellet in situ was seen to be spherical on two projections and samples of the known sizes of pellets involved (two different hunters) when X-rayed at the same or similar magnification as the pellet in situ, revealed that only one size pellet was a possible match.

My beef with all the other methods is that there are technical factors and variables to do with deformity of the bullet that make it impossible to eliminate or compensate for differences between the radiological contour of the control bullet vs that of the one in situ. I find it unacceptable when the calibre determination is made in instances where there isn't a shortlist of suspected calibres with sufficient size differences between them to render such inaccuracies inconsequential.

Some of you may be interested to know (and some of you already do know) that I spent quite some time trying to develop a technique to determine the calibre of a retained bullet by radiological means. My method did not rely on a control bullet: it was an absolute measurement with all the variables leading to its magnification determined by CT scanning of the 'subject' in the same position as it was X-rayed.
Under the best conditions, using a very compliant and motionless deli sausage, I was able to get down to within 1mm of determining the size of the retained bullet, based on two sets of measurements in two planes at 90 degrees to one another. You might consider this to be accurate, but I found the accuracy of the measurement to be heavily influenced by where the person chose to physically or electronically determine that one edge of the bearing surface sits, as a starting or ending point for the measurement. When I factored in the variables associated with a live patient and the nature of the tissues involved and the fact that two views of the bearing surface at 90 degrees to one another might not be as easy to obtain in a patient as a sausage, I realised that despite my best efforts, my method would never be accurate enough to be used in as serious a matter as determining a man's innocence or guilt. I must add that these were bullets fired in a water tank at a ballistics lab and therefore represent bullets that are in very good condition as far as fired bullets go.
I really did try, people. I got medical physicists, equipment technical sheets, the cooperation of my colleagues and I even had a purpose-built jig for the X-ray cassettes and the sausage.

But I have no confidence in it. And my insight into the various pitfalls associated with X-ray imaging of this nature leaves me with no confidence in any technique I have read about thus far, with the exception of the one case I mentioned earlier (involving the shortlist of only two or three pellet sizes).

Anyway, I apologise for the ramble. I have issues with this calibre business, that's all.

[Bob Kennington]

"...Anyway the problem with digital is the scale. You can now have an output image that is artificially smaller than the actual latent image on whatever detector is being used...The same applies to images acquired on an image intensifier..."

I may be selling U.S. x-ray technology short, but a hospital x-ray of my ankle last summer seemed to require a wait of several minutes in order to view it.  If the day arrives that a "wet" x-ray becomes unavailable, then there will be issues if a bullet can be imaged as smaller.

"...My beef with all the other methods is that there are technical factors and variables to do with deformity of the bullet that make it impossible to eliminate or compensate for differences between the radiological contour of the control bullet vs that of the one in situ. I find it unacceptable when the calibre determination is made in instances where there isn't a shortlist of suspected calibres with sufficient size differences between them to render such inaccuracies inconsequential.

Bullet deformity will be a problem. Most cases presented to me involved a handgun. Handgun bullet x-ray profiles are more revealing as to caliber.

My very first case was a literal riot!

Sergeant Fred Pelny of the Metro-Dade Police Department was wounded during a riot, and the firearm presented was a 44 Spl Charter Arms revolver. I was also presented with his ample x-ray with the question, "Can you determine what caliber this is?"

I could see a large caliber bullet—in profile—with a large, flat, meplat. 

Determining the "largeness" of the caliber using the Peters Method, I positioned comparable caliber "knowns" and included other calibers known for their meplats.

Whilst a very slight difference in profile diameter could be determined by overlapping the Pelny x-ray with the knowns*, only the defense attorney was annoyed at the sight of an obvious 44 Spl bullet in Sergeant Pelny's x-ray. The judge allowed the methodology and the jury subsequently concurred with my findings.

*taken at the same determined height from the platen.

I'm an advocate of the Peters Method, but wouldn't attempt a caliber determination of deformed bullets in general and would be averse to strictly-rifle calibers.

"...Under the best conditions, using a very compliant and motionless deli sausage, I was able to get down to within 1mm of determining the size of the retained bullet, based on two sets of measurements in two planes at 90 degrees to one another. You might consider this to be accurate...Anyway, I apologise for the ramble. I have issues with this calibre business, that's all.

One millimeter isn't good enough, but combined with the bullet profile, I would consider handgun bullet caliber determination in "wet" x-rays to be a valuable endeavour.

Since several x-rays are needed for positioning the unknown bullet profile ever closer to the platen in the Peters Method, a pulsatile image should be detectable and rejected from consideration.

(A handy piece of information, though. I've developed a small pulsatile condition in the vision of one eye this year —and was advised that it was harmless  ) .

[Brandon Bertolli]

I'm an advocate of the Peters Method, but wouldn't attempt a caliber determination of deformed bullets in general

And that is one of the problems: how do you determine radiologically that a bullet is not deformed?
More than 90% of the ballistic injuries I have seen have been from handguns, and the imaging has been on wet films. My test with the sausage was also on wet films with CT used to measure the bullet-to-film distance in two planes. I assert that no claim can be made that the bullet is not deformed, because such deformity may be of the type that puts the bullet 'out-of-round' and it will only be apparent if an X-ray is done with the beam aimed exactly parallel and central to the long axis of the bullet. I haven't seen this done in any verifiable way (even by an accidental shot) and I can tell you that I have seen one or two gunshot wounds in my time (young though I am).

Have a look at this one, from my files:



This was an adult male struck in the head by a bullet. According to his statement, he didn't see the shooter and didn't know where the bullet came from.
The bullet looks like it isn't deformed, on both views which were taken at 90 degrees to one another. The main difference between the two views is magnification of the bullet, because the area of interest has a different bullet-to-film distance from one radiographic view to the next.

Yet here is the bullet, recovered by the trauma surgeon under local anaesthetic:



Black arrow indicates the surface that was influenced by an intermediate target (highest probability) or skull bone (very low probability). My guess is that it was a masonry ricochet.
This is one of many cases that causes me to be concerned about calibre measurements in general. Clearly it has a minimum and maximum calibre measurement depending on the orientation of the bullet towards the beam at the time. So which profile are we seeing in each radiograph?

We don't know! It could be a profile that I don't even have an equivalent photographic representation of.

Then there are variables that we haven't factored in:

1) The difference between the radiographic outline of the bullet in situ vs the control bullet, in terms of edge degradation from scattered radiation within the body and also composite edging from the anatomy itself.

2) Variables to do with jacket thicknesses and metallic composition and the effect of this on the attenuation of the X-ray beam at the bearing surface.

3) (This one is most serious): the means by which one pair of edge intervals is measured and/or compared to the other. If you are doing it with a digital caliper, you are just eyeballing it. I can produce a radiograph with multiple exposures of the same bullet with all the conditions constant except the radiographic exposure itself, and it is my claim that in a controlled experiment you would all come up with different measurements of those bullets. When I say different, I mean not just from one exposure to the next, but also amongst different viewers measuring the same radiographic exposure. The reason for this is that unlike an actual bullet, the radiographic shadow has no physical 'stop' against which you can adjust the calipers. You have to apply a three dimensional tool to measure a purely two-dimensional interval. I have tried it also and didn't get consistent results.
Even if you employ software to do the measuring, you can be confounded by a bearing surface edge that has a grey scale that drifts from white to the black or grey of the surrounding anatomy. Sounds simple to measure, but just you try it! I have a high resolution transparency scanner here and it is very difficult to determine where the bearing surface ends and the surrounding anatomy begins. I tried the calipers and the scanner in the sausage experiment and although the scanner is good for eliminating dexterity and 3D vs 2D measuring, it is still no picnic to measure those intervals consistently. The difference between the resolution of two bearing surfaces may even be appreciated in a single exposure. All it takes is a difference in composite anatomical density to render that difference radiographically.