Understanding ultrasound results

Understanding your Dog’s Ultrasound

Words: Dr Joanna Woodnutt

Ultrasound provides vets with a non-invasive imaging technique that is commonly used in practice and human medicine. Most dogs tolerate it consciously, making it an excellent way to view some of your dog's organs in real-time. But what is your vet actually looking at?

What is an ultrasound?

Like a bat's echo, an ultrasound machine paints a picture by sending out noises and listening to how they sound when they bounce back. The 'transducer probe' is the bit that your vet holds in contact with your dog. Quartz crystals in this probe send out high-frequency sounds beyond the range of human (and canine!) hearing. At the same time, the crystals also react to sounds being returned to them, and these reactions can be measured and turned into an image by a computer.

The computer then provides an image of the types of echo it’s getting. Solid objects, like bones or metal, reflect all the sound, so the image appears as a bright white line of reflected sound, followed by a shadow where the noise doesn’t reach. The same happens with air, whether in the lungs or guts. But what ultrasound really excels at is differentiating soft tissues ­— whilst on an x-ray, the internal organs are a blurry mess; on an ultrasound, they can be easily distinguished from one another and their internal structure investigated.

Because a transducer probe sends out sound waves, an ultrasound machine produces a 2D image. Unlike an x-ray, which is a silhouette image, ultrasound images produce an image that's a 'slice' through the body. It shows a lot of detail in that one slice for as deep as the machine can manage, but it won't show anything, even an inch to either side, until you move the probe. This means care must be taken when interpreting an image – the slice isn't even a millimetre thick, so it can be easy to miss things sitting on either side of the current image.

How are ultrasounds done in practice?

Unlike x-rays, ultrasounds are considered harmless, both to the animal receiving them and to others in the room. This, along with the fact the ultrasound is non-painful, means that most animals can have their ultrasounds done without sedation. Despite this, ultrasounds are often still booked as a day procedure, meaning you'll drop your dog off in the morning and collect them in the afternoon. This allows the vet to do your dog's ultrasound conveniently and repeat it later if needed to get a better image.

First, your dog’s fur will be clipped from the area and their skin cleaned to reduce interference with the picture. Ultrasound gel is also applied to improve the image. Once it’s time for the scan, your dog will be taken to a darkened room and held in the correct position by a nurse. Depending on the type of ultrasound being done, this may be standing, lying on their side, or lying on their back.

The vet doing the ultrasound will slowly move the transducer probe over the skin whilst looking at the live image on the screen. They may change the settings, freeze and save the images, or get extra information by using Doppler to look at the movement of blood through a vessel. In sedated animals, the vet may also get an ultrasound-guided biopsy. A needle is inserted through the skin, and the ultrasound machine is used to view the needle in real-time to check the right organ is being sampled.

Waiting for the results

Ultrasounds are usually interpreted live by the vet undertaking the assessment. Because so much ultrasound interpretation comes from where the probe is on the animal and which direction it's facing, it's tough for somebody to assess an ultrasound without being present. Therefore, you should receive the ultrasound results on the day of the procedure or within a couple of days if there's no urgency and the vet is busy. Having said this, vets will sometimes record short clips of ultrasound video to send to specialists if they’re unsure about the diagnosis, and you can expect to wait 2-5 days for this. Results from a biopsy may take longer – up to about a week.

What do the results mean?

The results depend on the area of the body being scanned and why your vet is looking there. Common areas and diseases seen during an ultrasound scan include:

Uterus

The uterus is commonly scanned, as ultrasound gives a much better image than x-ray when it comes to this organ. Pregnancy, pyometra, and uterine tumours can all be diagnosed by ultrasound scanning.

Bladder

The bladder is full of liquid, making it an easy object to find on an ultrasound. Tumours and bladder stones often show up well on ultrasound as they contrast nicely with this liquid.

Heart

Cardiologists get a lot of information about your pet's heart from ultrasound – correctly called an 'echocardiogram'. They can assess the size of the chambers and the thickness of chamber walls and check that blood is moving the correct way, and no valves are leaking.

Guts

Ultrasound is helpful when assessing your dog's guts for inflammation. Because we're looking at a live image, we're also able to watch and evaluate your dog’s gut movements. Foreign bodies can sometimes be investigated with ultrasound but will usually be combined with an x-ray.

Liver, spleen, pancreas, and other internal organs

The shape, density, structure, and size of internal organs can be measured using ultrasound. Many early-stage tumours are spotted with ultrasound, allowing vets and owners to make a plan before the tumour grows too large.

Free Fluid

If your dog has been in a car accident, vets can use ultrasound to quickly assess whether there is any fluid in the abdomen or chest, usually caused by bleeding or bladder rupture. By placing the probe in certain areas, they can quickly assess for internal bleeding, which can help decide on a treatment plan.

So, what does my dog’s ultrasound tell my vet?

Depending on what your dog is being assessed for, their ultrasound results can be beneficial for planning further diagnostic tests and treatments. Anything from minor inflammation of the guts through to severe internal bleeding can be assessed in most dogs without the need for sedation. It's a safe procedure with very few risks in most dogs but can't be used to determine everything – bones and lungs, for instance, are not easily viewed with an ultrasound.