The X-ray machine has become a staple of the modern veterinary practice, to a point where it’s hard to believe we used to be without it. So how does it work, and what can and cannot, be seen on an x-ray?
How does it work?
X-rays are a form of light wave, with a high frequency so they can penetrate solid material. Like any wave of light, they can be absorbed or scattered by different materials. This property is what we use to get our x-ray image, and this is why we recommend sedation of your pet before any x-rays are taken for a proper diagnostic image. A generator emits x-ray waves through our patient and onto a receiver plate below them. When the waves pass through a material in the body e.g. bone, they are affected by it in various degrees which is recorded on the plate. Using the magic of computer processing, we can convert the x-rays hitting the plate into the greyscale colours on our x-ray image.
There are 5 x-ray colours (and therefore material types) that we can differentiate on the image:
Metal – which is bright white
Bone
Soft tissue and fluid – such as liver, heart, urine or pus. This is all grey.
Fat
Air – as in the lungs. This is black.
As you can see from the above list, X-ray can be useful to tell apart various tissue types but is not a completely equivocal diagnostic tool due to the nuance in differentiating the various shades of grey soft tissue.
When is an X-ray useful?
– Orthopeadic conditions such as fractures.
– Helping diagnose gastrointestinal obstruction.
– Helping to diagnose constipation.
– Part of an assessment for heart disease.
– Bladder or kidney stones. Some stones show on an x-ray.
– Emergency cases for an overview of injuries.
– Part of an assessment for lung disease.
– Teeth roots and jaws
– Masses
– Foreign objects
– Anatomical abnormalities
Where does an X-ray have limits?
– Spinal problems. The spinal cord is a soft tissue structure that blends into the other soft tissues of the spine when seen on an x-ray.
– Differentiating benign from malignant masses. Because all soft tissue/fluid appears as grey, x-ray cannot tell us if a structure is something more sinister.
– The brain and skull. Due to the number of overlapping tissues, we cannot often see the brain clearly on an x-ray.
– Function of organs. The x-ray shows us size and shape but cannot give us an indication of how well an organ e.gs the liver is functioning.
I hope that you can see from this article that x-ray, though a powerful imaging tool, is just one part of the diagnostic process. Ther may be times where x-rays have to be repeated to check for progression, or when another imaging tool might be better such as ultrasound or CT scan. Your vet will be able to guide you through the best test for what needs to be checked on your pet.
