X-Ray vs Ultrasound vs CT Scan for Pets: What Each One Shows
Your vet says your pet needs a scan, and then asks whether it will be an X-ray, an ultrasound or a CT. They sound similar, but each one shows something different, and the right choice depends on what your vet needs to see.
Here is how the three compare, when each is used, and what to expect.
The three tests at a glance
X-ray | Ultrasound | CT scan | |
Shows best | Bones, joints, chest, large changes in organs | Soft tissue and the heart, in real time | Detailed 3D slices of any area |
Limits | Soft tissues look alike, so small changes can be missed | Sound does not pass well through bone or air-filled lungs | Needs your pet to stay very still |
Sedation | Not routine | Not routine | Often needed to keep still |
Time | Minutes | Usually a short visit | Under a minute for the scan |
X-ray: the first look
An X-ray gives a flat image of what is inside your pet. It is the fastest way to check bones and joints and to look at the chest and belly for changes in the size, shape, or position of organs.
Vets often use X-rays for suspected fractures, joint problems, dental concerns, coughing, breathing trouble, and when something swallowed may be causing a blockage. Our digital X-rays can be zoomed and adjusted, which helps catch even hairline fractures.
An X-ray cannot tell soft tissues apart. A liver and a spleen can look very similar, and small changes can hide behind other structures. That is when your vet may suggest a second test.
Ultrasound: soft tissue, live
An ultrasound uses sound waves to create a moving picture of your pet's soft tissues. It shows the structure inside organs, so your vet can tell the difference between tissue and fluid, and watch the heartbeat and blood flow.
It is the usual choice for the liver, kidneys, bladder, spleen, intestines and heart, and for checking a pregnancy. There is no radiation. Our portable ultrasound is battery-powered, so we bring it to your pet.
Ultrasound has its limits too. Sound waves do not travel well through bone or air, so it is not the test for the lungs or skeleton.
CT scan: the detailed 3D view
A CT scan takes thin cross-sectional slices of your pet and builds them into a detailed 3D picture. Nothing hides behind anything else, which helps when a flat X-ray doesn't give a clear answer.
Vets turn to CT for unclear or persistent symptoms, tumours, internal injuries, and the head, spine and chest. Vets also use it to plan surgery. Our Fidex scanner completes the scan in under 60 seconds, which means less time under anaesthesia. See our CT scan page for more.
CT needs your pet to stay completely still, so most pets receive mild sedation. Your vet decides this for each pet.
How your vet chooses
Your vet weighs up a few things:
What they need to see. Bones and the chest point to X-ray, soft organs and the heart to ultrasound, and unclear or complex cases to CT.
How urgent it is. An unwell pet may need an X-ray straight away, while a calmer case can wait for a more detailed test.
How stable your pet is. Sedation is a bigger consideration for pets who are weak or in pain.
The tests often work together. Many cases start with an X-ray and blood tests, then add an ultrasound or CT if more detail is needed. We run blood tests in our in-house laboratory, so imaging and results are usually ready the same day. You can read more on our diagnostic imaging page.
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