X-rays, Ultrasound and CT Scans for Pets Explained

If your vet has suggested an x-ray, ultrasound or CT scan for your dog or cat, you're probably wondering what it will show and whether your pet will need to be sedated or put under. The three work in different ways, and each suits some jobs better than others.

Why vets use imaging

Imaging lets your vet see inside your pet's body, and it helps diagnose many conditions. Taking the images doesn't itself mean cutting the skin, which is what "noninvasive" means, but some scans might involve an injection of contrast dye, and pets may be sedated or anaesthetised. Some of the equipment is large and costly, so certain scans are only available at specialised facilities. A scan is one piece of the picture, and your vet is the person to explain what the results mean for your own pet.

What an x-ray can show

X-ray imaging, also called radiography, is the most common imaging method in veterinary clinics. It's painless, though pets may be sedated to decrease stress and help them stay still. The exposure is very brief and uses low doses of radiation.

The images, called radiographs, show bones, some foreign objects such as rubber or metal, and large body cavities, and they're good for detecting fractures, tumours, injuries and deformities. Soft tissues don't show up well on standard x-rays, so your vet might use a contrast procedure, where a dye that blocks x-rays is given intravenously or by mouth to outline organs such as the kidneys, heart or digestive tract. Modern x-rays are usually made and stored digitally, so they're easy to share with specialists for a second opinion.

What ultrasound is used for

Ultrasound uses sound waves to create images from the echoes that bounce off tissues. It's better than x-rays for showing soft tissues, but it can't image bone well.

The operator presses a probe against the body, usually the abdomen, and moves it to scan the organs, and modern ultrasound gives real-time images that move as the probe moves. It's painless, noninvasive and safe, and it's commonly used to examine the abdomen. Ultrasound of the heart is called echocardiography.

What a CT scan adds

CT is a computer-enhanced x-ray that takes multiple cross-sectional images, known as slices, of the body. Your pet lies on a motorised bed that moves through the scanner while x-rays are taken from different angles, and a contrast dye might be injected to make some structures easier to see.

CT gives detailed images of tissue density, which helps detect deep tumours and infections, blood vessel changes and fractures.

Sedation and anaesthesia

What your pet needs depends on the scan. For x-rays, pets may be sedated to decrease stress and help them stay still. CT scans take time and need the animal to stay perfectly still, so animals are usually anaesthetised.

Your vet knows your pet's health and temperament, so they're the right person to tell you what's planned. If you're unsure what your pet will need, ask the practice before the appointment, including how to prepare.