Vets have had X-ray machines for many years, and X-rays are very useful – we can take a snapshot of the insides of our patients and look at bone and even (on a good day!) some of the soft-tissue structures, e.g. the size of the heart, or the lungs.

However, it has significant disadvantages. X-rays use ionising radiation, so although a one-off exposure of a cat or dog is fine, our vets and nurses dare not be in the room at the time except in the direst emergency, or we risk radiation injury (usually in the form of cancer developing). If we do have to be in there, we’ll be wrapped up in hot (and very, very heavy) lead gowns. Yes, of course we’ll do it if the patient needs it – but we’d much rather avoid it!

Finally, X-rays cannot distinguish between fluid and solid tissue. As a result, we cannot measure the internal diameter of the heart chambers, or look at the gut wall to see if it is thickened, or turned inside out (an intussusception). We cannot easily assess a tendon to see if it’s just stretched or if it’s torn all the way through and other reasons.

Ultrasound changes all that..

So, what is an ultrasound machine?

Essentially, it is a high-tech dolphin. Yes, that is what I mean, it isn’t some weird glitch on the webpage – it’s an electronic whale.

Ultrasound is sonar – like the whales squeak out high pitched sound and listens for the echo, the ultrasound machine emits ultra-high frequency sound waves (way, way higher than a dog, whale, or even a bat, can hear) which can pass harmlessly through the body. The patient won’t feel a thing and there is no detectable risk to them either. When these sound waves pass from one type of tissue into another, some of the wave is reflected back – and the ultrasound probe detects the echoes as they come in. A clever computer then puts them all together as an image on the screen, in real time.

There is just one major disadvantage to ultrasound – the sound is so high pitched, it doesn’t carry through air (or even through bone). As a result, the probe has to be exactly on the skin, and we use an “acoustic coupling gel” to get good contact with the skin and therefore a good quality image. However, this means that it is almost impossible to scan through a fur coat! That’s why we will often have to shave a small patch to scan through – the fur traps bubbles of air and even if we wet the area with spirit, we can’t always get a good enough look inside.

So, what do we use it for?

Well, there are four main uses for ultrasound in veterinary medicine.

Firstly, just like in humans, we can use it to look at the uterus – for example, at the puppies and kittens living there. This allows us to see whether a bitch or a queen is pregnant at a very early stage, and assess how healthy the babies are (by looking at their little hearts beating!). Even more importantly, we can examine the uterus in a sick bitch to determine whether or not she has a pyo (a potentially fatal womb infection). Here, we’re looking for two black circles (sometimes called “shotgun barrels!) which are the two horns of the uterus when they’re filled with fluid.

Secondly, we can examine other abdominal organs – the intestines, the kidneys, the bladder, the spleen and the liver. This way, we can check for tumours, twists, and other injuries, without having to open up the patient in surgery. We can even use the scanner to see if there is free blood or fluid inside the abdomen that might indicate internal bleeding; or guide a biopsy needle to a suspicious lump, without needing surgery.

Thirdly, we can examine tendons and ligaments. This is occasionally useful in dogs and cats (for example, in Achilles tendon injuries), but is usually more an equine vet thing!

Finally, and becoming increasingly important, we can look at the beating heart of a dog or cat. We can measure the amount of blood backing up in the atria (a marker of heart failure), see how thickened or thinned the walls of the heart are, measure the speed of blood passing through a narrowed vessel, or see blood leaking through a damaged valve. This has genuinely revolutionised cardiology for dogs and cats, and with more and better scanners always coming onto the market, it’s going to be more and more important.

So, why do we still have our X-ray machines?

Well, as we said, the ultrasound machine can’t look through air (so it’s useless for lungs) or bone (so it’s fairly rubbish for looking at fractures). It also can’t be used to count how many puppies or kittens there are in a patient – we still need X-rays to count them (and yes, it is safe for them as long as it’s only a single exposure).

Put together, though, the two machines can diagnose over 99% of the lesions, injuries and diseases we need to look at in practice – not bad!