If your pet falls ill, your vet is likely to suggest a sequence of investigations to find out what is going on, just as doctors do when humans are unwell.
After the initial discussion of a pet’s problems (so-called history gathering), and then a thorough physical examination, further investigations are often needed to make a diagnosis of the cause of the problem. It’s common to carry out laboratory tests (usually blood and urine tests), and then sometimes to move on to so-called “diagnostic imaging”. In the past, this nearly always meant taking x-rays, but these days, a new tool has become widely available in vet clinics across Ireland: ultrasound scans.
Most people have heard of ultrasound, but the details of what’s involved are rarely discussed. It’s a technology that uses high levels of computer power, and it has advanced dramatically in the past twenty years. Most companion animal vet clinics now use ultrasound scans as a routine procedure.
Ultrasound uses echoes from high-frequency sound waves (“ultrasonic” waves) to create detailed moving images of parts of the inside of the body.
The word ultrasound is derived from the Latin word “ultra” which means “beyond”, and the word “sound” which means “something that can be heard”. Ultrasound machines use sound waves that are too high a frequency for humans to hear, which is why they are “beyond sound”.
This sound for ultrasonography is generated by a small handheld probe with a smooth, dome-like tip which is pressed against the skin during the procedure. When it’s used in animals, some fur usually needs to be clipped off the pet’s body over the skin where the probe will be placed. A type of transparent gel is placed between the probe and the skin, to maximise the contact point that the ultrasonic sound waves need to cross over.
These ultrasonic waves bounce off different parts of the inside of the body, creating ultrasonic echoes that bounce back to the probe, which detects them and translates them into electronic data. This data travels through a connecting wire to the ultrasound machine, which may be as small as a laptop or as big as a large desktop computer. The ultrasound machine then uses computerised calculations to turn the data from the bounced-back sounds waves into a moving image.
This is a similar process to the way that bats navigate the world: bats produce ultrasonic sounds themselves, and pick up the echoes with their ears. Their brain then does the computing to create images of the environment around them.
With ultrasound scans, the image is displayed on the monitor of the ultrasound machine (like a computer screen) in real time, while the scan is carried out. A video recording of the scan is stored, and still images of particular features can be saved and analysed. Measurements are taken, allowing a detailed analysis of many internal structures.
An ultrasound scan is different to radiology (x-rays) because it provides a moving image, and it is able to discern more of the internal structure of the body, rather than just a static silhouette-type outline as in x-rays.
Ultrasound is different to CT and MRI scans: it’s much less expensive and it’s far more widely available. However it does not provide as much detail, especially for inaccessible areas such as the inside of the skull, or joints.
There are different levels of expertise in ultrasound, relating to training, qualifications and experience. And there are different types of ultrasound machine, from the cheapest and most basic to the most expensive with the latest top end technology. It’s important for pet owners to understand that one ultrasound scan is not necessarily the same as another: a vet in general practice may be able to identify whether or not a dog is pregnant, but they may struggle to identify small nodules on a dog’s liver. It’s important to choose the right scan for the right situation: your own vet should be able to advise you on what’s needed.
The main indication for ultrasound scans in pets is to make a specific diagnosis about what is wrong with a pet, while also ruling out other diagnoses. Sometimes ultrasound can be used to guide a vet when carrying out procedures such as taking biopsies from parts of the body that cannot be seen (e.g. liver).
One of the advantages of ultrasound over x-rays is that there is no risk of exposure to personnel from radiation, so that animals can be held during the procedure (in contrast, animals need to be sedated or anaesthetised when x-rays are taken, so that personnel can leave the x-ray room to minimise any risk of radiation exposure).
An ultrasound scan takes up to half an hour: sometimes owners stay with their pets, or the pet may be left in to the vet clinic for the day. The vet carrying out the scan may or may not comment on what they are seeing at the time. The images are reviewed in more detail later.
Once the scan is finished, the results may be explained to you at the time, or you may need to wait until you see the veterinarian who is dealing with your case.
Ultrasound scans are an exceptionally useful diagnostic tool.