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I am a veterinary medicine student and I am trying to understand why x-rays are read in a laterally inverted fashion.

Example: Since this is a DV projection and the head is at the top of the image, it would lead one to believe the left side of the image is infact the left. Not the right.

EDIT: A lot of the answers provided talk about relative directions and taking a picture, this would make sense if it was a VD Projection. But how does this apply to DV?

When you click a picture of a person from behind, their sides are represented accurately.

example

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    This has been answered here. There will be usually the letter L (meaning left) in the upper right corner of the image, when the body is shown from the front. – Jan Jan 17 '18 at 15:25
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  • Take a picture with your camera. The left hand side of the subject is always on the image right side. – Graham Chiu Jan 19 '18 at 10:47
  • @GrahamChiu - not if you take a picture of their back. So why does this apply to DV? – ABCD312 Jan 19 '18 at 12:03
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    My intent was never to talk about conventions, but to understand the reason/ physics behind their existence. – ABCD312 Jan 19 '18 at 16:45
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When reading radiographs in human health, the x-rays are read as though facing the patient. So, when you have a PA chest x-ray ( or dorsoventral view for a dog ) the x-rays enter the posterior surface, exit the anterior surface to hit the imaging surface. This used to be x-ray film. So, the right side of the chest appears on the right of the film, and the left side on the left. But the sides are switched so you actually read the films as though looking from the anterior side of the patient i.e. facing the patient.

When taking an AP film, the patient is positioned so that the posterior surface is now closest to the film, and the patient's left is on the left of the film. And that's the way the film is read, from the front.

I've noticed some DV images of animals are not switched so that the R is on the left but apparently most are. But I'm guessing that vets also read DV and VD images of the thorax as though facing the ventral surface.

BTW, when taking horizontal or transverse CT slices through the human thorax, the view shown is that from caudal to cranial, i.e. looking upwards to the head.

https://www.radiologymasterclass.co.uk/tutorials/chest/chest_quality/chest_xray_quality_projection

And here's an example of a canine head using the DorsoVentral positioning

doggie head positioning

DV canine head

and you can see that the image is not reversed which I presume is because this is the normal way to read these type of images.

TL;DR - it's a convention used to reduce cognitive loading on radiologists.

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Think about it as a mirror. If I a-ray all the teeth for example. That means I mirror the mouth to the sheet. Now when I read the paper I need to invert the paper and look at it. The right side was ascribed on the right side and the left on the left of the paper. Once inverted the sides take a flip. I am gonna see the right side on the left and the left on the right. The key is to think about it as mirroring the picture and then you gotta switch it to view the picture.

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