Radiology

Re: Radiology

Thomas Johnson — Fri, 19 Jun 2015 09:00:53 GMT

[quote user="Evelyn Barbour-Hill"]

[quote user="Evelyn Barbour-Hill"]I've never understood why textbook DV radiographs of the chest always have the right side of the chest on the left side of the page. It's only convention, and it seems an odd one.[/quote]

On consideration I think it's a human medical convention and comes from the days of the fluoroscope, where the patient stood facing the doctors. Behind him was the Xray generator firing away, and in front of him was the fluorescent screen at which the doctors gazed, pointed and grunted while cheerfully soaking up the radiation

[/quote]

I also suspect that it seemed like a good idea to position the xray film so that when you looked at it it was in the same orientation as if the patient was stood in front of you.

Re: Radiology

Evelyn Barbour-Hill — Wed, 17 Jun 2015 22:11:15 GMT

Re: Radiology

John Flynn — Wed, 17 Jun 2015 21:37:45 GMT

What utlenigur said took me a long time to get my head round as well - the bit about why it would matter what way round you put the dog given that you just got a 2-d shadow picture anyway.

Eventually, I clicked that the difference was just the effects of gravity on the bits inside a dog causing them to move about depending on how you positioned the dog and the reason you got a different looking picture on a right lateral chest from a left lateral chest was because the bits inside the dog had moved when repositioned and the insides of a dog aren't symmetrical.

The point on having the bit you're interested in near the plate for most things can be best understood by shining a torch at your thumb and looking at the shadow on the wall - the shadow will get smaller and clearer the nearer your thumb is to the wall giving a sharper picture - same applies to getting the bit you are interested in as near the plate as possible. The lungs are the main exception because it is the top lung that tends to fill with air when dog lying on side and it is the air around something unusual that will let you see it.

www.veterinaryradiology.net is great (free) site for practising looking at xrays, though many of cases are quite complicated compared to what generally will see.

Re: Radiology

Sammy82 — Wed, 17 Jun 2015 21:32:59 GMT

There is a way to tell if a lateral abdominal view is left or right by looking at the pillars of the diaphram. This was considered an important skill for my finals, never found a use for it since.

Re: Radiology

Danny cazabon — Wed, 17 Jun 2015 21:29:05 GMT

Hello again,

Thank you all for the explanations and also for the tips. I am relatively new to small animal practice and have always had some confusion in this area.

It definitely seems clearer now. Thanks again, much appreciated.

Re: Radiology

Evelyn Barbour-Hill — Wed, 17 Jun 2015 21:17:29 GMT

I'm not a diagnostic imaging specialist but.......

[quote user="An On MRCVS"] Is it like someone is taking a picture from the perspective of the cassette[/quote]

No. What you see on the digital screen is the shadow of what you are radiographing. Only a shadow with shadesof grey, instead of just black and white.

In other words: suppose you wrote HELP! on some thin paper, then shone a bright light on it, with a white screen behind it. What you see on the screen is the equivalent of the radiograph, and it would say HELP! the right way round. If you shone the light through the paper and looked at it from the side where you put the screen, the word would be in mirror writing but that would not be the same as a radiograph conventiionally viewed..

Come to think of it, if you go to the cinema, there's a bright light shining through the film and on to the silver screen. What you see from your luxury fauteil in the auditorium.... or even from the one-and-nine seats.... is the equivalent of a radiograph as conventionally viewed. If you are in the space at the back of your screen, like the Beatles in their squalid lodging while engaged for the Star Club in Hamburg, what you see as you wake at 3 o'clock in the afternoon is a mirror image.

Of course if your radiograph is on old-fashioned film, you can have it either way because you have to look through the film and you can do that from either side. Whereas a digital apparatus will always display the image the "right way round': so that, for instance any lead letters will read correctly and not in mirror writing, unless you deliberately flip it horizontally.

The important thing to remember, though, is that it doesn't matter, as long as you have a left and right marker on the image if you are going to need to know which is which.

I've never understood why textbook DV radiographs of the chest always have the right side of the chest on the left side of the page. It's only convention, and it seems an odd one.

As far as I know, the convention is that a "left lateral" means the left side is against the cassette, a "right lateral" means the right side is against the cassette. In a textbook they ought, in my opinion, to be appropriately placed, so that the liver is on the left of the page for a right lateral abdomen and the right of the page for a left lateral. But they may not be. It doesn't matter. However, if your textbook has a radiograph with, say, the pylorus against the cassette, and it's labelled "left lateral", the label is wrong.

Re: Radiology

Utlendigur — Wed, 17 Jun 2015 21:12:27 GMT

[quote user="An On MRCVS"]I understand that the lesion to be examined should be on the side closest to the cassette.[/quote]

Not quite sure what you are asking. For limbs, you want the limb being xrayed closest to the cassette for positioning so the limb is flat/parallel with the plate. For chests, sometimes things like lung tumours show up better when they are in the side furthest from the cassette as the uppermost lung lobes will be more air-filled (so more contrast with a soft tissue density) compared to the dependent lobes which will be more consolidated. For abdomens, it can depend what you are looking for/at eg pylorus vs fundus as to which view is more useful.

[quote user="An On MRCVS"]Once processed are we seeing that image inverted on our screens? Is it like someone is taking a picture from the perspective of the cassette and thats what we see as developed?[/quote]

Maybe think of it as if you were lying underneath the cassette looking up through it and what you are xraying to the xray machine - that is the view you get on the image. The xray machine produces a beam of xrays, so it would be more like a projector - and you would be standing behingd the screen it was projecting onto, rather than sitting in front of it, so the image would be reversed. Not sure if that helps or confuses

[quote user="An On MRCVS"]Also I have been through some textbooks and i'm very confused by the fact that for example; a right lateral abdominal radiograph seems to look like its on the same side as a left abdominal radiograph. The patient was lying on his right side, placed in lateral recumbency, and image taken, how can this be a left lateral radiograph?[/quote]

Probably just flipped the film over or used the image software if digital to digitally "flip" the image, maybe just to show for comparison although I have known some vets prefer to view images like that

Re: Radiology

John Flynn — Wed, 17 Jun 2015 21:03:05 GMT

I'm assuming you have a digital system. Furthermore, I think you have a CR system (with physical casettes that you take a picture on and then put in a machine to develop) rather than DR system where the sensor "plate" that the xrays hit creates a picture on the computer screen without you needing to lift it up and develop it or anything.

The software for your clinic's CR system may "flip" images itself if there is an alignment "dot" or similar on the cassettes that you are supposed to place cranially or laterally or some system. Alternatively, the software may simply put the image up as it finds it on the cassette and the orientation will depend on what you you had the dog on the table (assuming the cassettes can only be put into the developing machine one way round). Either way, the software probably allows you to manually "flip" the image to create a mirror image of what you are looking at on the screen to suit your preference.

Traditionally, folks tend to look at thoracic and abdominal radiographs with the right side of the patient on the left side of the screen as you are looking at it (i.e. as if the dog was a person and that person was standing in the computer screen and facing you like a mirror). For xrays of limbs folks usually view them with cranial to the left when relevant.

A further area for confusion is that while generally a view is talked about by naming the anatomical "direction" term that the xray beam hits first, followed by the surface that the beam exits on (such as ventro-dorsal=feet in the air, dorso-ventral=lying on sternum), when it comes to abdominal and thoracic radiographs when the patient is lying on its side these are named "right lateral" or "left lateral" depending on the side of the animal in contact with the plate! (So a right lateral thoracic radiograph has the animal lying with its right side on the plate and the xray beam will hit the left side of the patient frist). For limb views, the terms medio-lateral and latero-medial and commonly both abbreviated to "lateral view" as it generally doesn't matter and it is less of a mouthful.

More confusing terms:

Radiography = taking the pictures

Radiology = looking at them

If you are not sure if your processor is flipping images round on you - the surest way is to put a metal marker on one side of the patient and you will then know that the picture on the screen with the metal marker on that side is actually that side whether the computer has it to the right or left of the screen. For convention, I'd suggest then always lining the left side of the patient up with the right side of the screen so you're always looking at xrays the same way round (so for a DV or a VD, I'd still see the spleen on the right of the screen as I look at it), or with the head of the animal to the left of the screen if taking lateral views.

I'm sure someone else will find a simpler way to explain this clearly!

Re: Radiology

Sammy82 — Wed, 17 Jun 2015 20:59:59 GMT

Normally your the picture appears on the screen as if you were looking from the xray machines perspective. If you are unsure, just place one of the old fashioned R/L markers next to the animals side to easily identify which side is which. It is recommended to always look at xrays in the same orientation to be able to develope a routine, e.g. always look at lateral abdomen views dorsum up, ventrum down, head to the left and tail to the right. The right lateral automatically appears this way, the left lateral needs inverted to look at it this way. That's probably the reason why both views seem to be the same in the book, they have probably just inverted one picture to make it easier to compare the two.