By Lauren Horton, MSc.

What is an Ultrasound Scan?

Ultrasound scanning is a medical imaging test which uses high frequency sound waves to produce diagnostic scans. It is one of several radiological methods used for diagnosing and treating illness and injury. Most people associate the use of ultrasound with pregnancy scans, but this is only one of many applications of the modality.

How Does it work?

Very simply, the sound waves are transmitted into the body using a transducer, or probe, held and controlled by a sonographer. The probe is attached to the ultrasound machine by a cable and plug.

Once the sound waves are in the body, most of them bounce off the internal structures and organs and return to the probe face. The rest of the soundwaves are absorbed into the tissue. Because the internal organs are made of different types of tissue, they can either quickly reflect the strong sound waves, or they can soak up some of the sound wave energy, and return them to the probe in a much weaker state.

The returned soundwaves are then processed in the ultrasound machine, and a visual representation of all the different energy soundwaves is produced. The result is a grayscale image of the inside of the body. The different shades of grey are an indicator of the strength of the returning soundwave. Bright areas on the scan are very strong reflected waves, while dark or black areas are very weak waves.

How Have Ultrasound Scans Evolved?

Pregnancy scans were first introduced in 1958 by Dr Ian Donald, in Glasgow, UK. The technology quickly became more sophisticated, with the development and addition of Doppler technology to study blood flow characteristics of normal anatomy as well as tumours. By the 1990’s, 3D and 4D scanning was becoming commonplace for scanning fetuses, hearts and performing biopsies.

New ultrasound uses and applications are being developed all the time. There are now laptop ultrasound machines, as well as hand-held devices which can be plugged into an iPhone so that people can be assessed anywhere.

There are even ultrasound scans being carried out at remote places such as Antarctic stations and International Space Station crews.

Veterinary Ultrasound Scans

First introduced in 1966, veterinary clinics without ultrasound machines are now rare. The information available from an ultrasound scan to diagnose animal illness means that pets can be treated much more quickly, and correctly. The amount of exploratory surgery is much less now, because the diagnosis can often be made with an ultrasound scan.  This means that, just like humans, animals have a much better chance of surviving trauma, disease, being in less pain and having a long and healthy life.

There are almost as many animal issues that can be detected with ultrasound, as there are in humans. The organ anatomy in many animals is very similar to those in humans.


How Vets Categorize Animals

Generally, there are two ways in which animals are described. They may be referred to as small or large, companion or production, pets or livestock. There is a grey area, whereby some animals are designated as neither of these classifications.

It is estimated that $99.0 billion was spent on pets in the US in 2020, $30.2 billion being on veterinary care and products.

The price for an abdominal ultrasound for a dog or a cat is up to $600.

Ultrasonography in Animals

The range of ultrasound examinations performed on pets is likely to be vastly wider than those of livestock.

Food production animals are more likely to have pregnancy scans. The number and sex of the fetuses is important for future planning of dairy and beef herds. Portable ultrasound machines have revolutionized the way in which farm animals can be scanned and monitored during pregnancy.

Horses are also high-users of ultrasound scans. As well as the many abdominal, lung and bowel scans performed on horses, tendons, ligaments and joints are often assessed in horses with racing injuries.

Pets, on the other hand, are much more likely to have regular veterinary care, including diagnostic tests and treatment. The American Animal Hospital Association (AAHA) reports that some pet owners spend more on their pet’s health than they do on their own.

Scans for Pets

The reasons for scanning pet animals are remarkably similar to the indications given by medics for human scans.

Ultrasound can detect many animal health problems.

  • Whether an animal is pregnant, and the number of fetuses
  • Foreign body, either in the gut, in the eyes and ears or under the skin
  • Heart efficiency
  • Organ disease or enlargement
  • Tumours
  • Blood clots
  • Fluid in the abdomen
  • Blocked kidneys
  • Tendon and ligament strains and tears
  • Bowel obstruction

One of the major issues for veterinarians is that animals cannot say where it hurts, and for how long it’s been a problem. Generally, animals are very stoic so will often have a late diagnosis. It is usually not until their behavior changes that owners realize something is wrong.

Initially, the veterinary surgeon will usually examine the animal by palpation. This means feeling round the body and belly, pressing in and detecting any irregularities or masses. It is also useful for them to see how the animal reacts when they touch a tender area.

Ultrasound scanning is then invaluable in providing a swift diagnosis, with little or no discomfort to the patient. They may have to have some hair shaved off. This is important for transmission of the ultrasound beam through the gel that is applied to the body. Sound waves get trapped in hair and don’t enter the body effectively.

Benefits of Ultrasound

One of the main advantages of ultrasound is that it provides a ‘real-time’ look at soft-tissue structures. This means that unlike any other diagnostic imaging tool, animals don’t have to be sedated or severely restrained.

The heartbeats and movements of puppies and kittens can be assessed, and other moving structures such as blood flow and tendons can be watched over a period of time.

Just as with human ultrasounds, animal scans are:

  • Non-invasive
  • Relatively affordable
  • No sedation required
  • Able to be repeated many times if necessary, without harm
  • No radiation, as there is with X-rays
  • Excellent visualisation of internal organs
  • Can be used to assist surgical, interventional and biopsy procedures
  • Greatly reduces need for exploratory surgery


How Do Animal and Human Ultrasound’s Differ?

There is little difference between how animals and humans are scanned with ultrasound. The preparation for an abdominal scan is exactly the same. Nothing to eat for 6 hours prior to the scan. This means that the sonographer has a clear view of the organs without having to try and see through stomach contents and bowel gas.

Similarly, it is important to have some fluid in the bladder to successfully visualize the uterus and ovaries. The reason for this, is that the urine allows swift and unobstructed transmission of the sound waves, both ways. The bladder also literally pushes surrounding bowel out of the way of the other organs so they can be seen clearly.

Human sonographers are thoroughly trained in anatomy and physiology. This means that high-quality, diagnostic scans are performed with confidence, influencing patient management and improving outcomes for people.

In the same way, veterinary sonographers must learn the anatomy and pathologies of many types and breeds of animals. The diagnostic abilities of the sonographer are crucial, and this is an extremely challenging field for vets. There is no doubt that animal care has significantly improved with the addition of ultrasound scans, and will continue to do so as technology improves. The benefits to our beloved animals are exactly the same as those to our human families.


Guest article by Laura Horton, MSc. is founder of, a website which helps you to be your dog’s best friend. She is also a registered health professional with many years’ experience in diagnostic imaging, teaching and health research.