Vet MRI: When Do Cats and Dogs Need One and How Is It Done?

If you have been told your pet "may need an MRI", you probably have many questions: why is it needed, how is it done, will your pet be put under, and where can it be done? This guide explains veterinary MRI and how it differs from other imaging methods, in plain language.

In short: A veterinary MRI shows soft tissue such as the brain, spinal cord, nerves and ligaments in detail, without using radiation. Cats and dogs most often need one for seizures, paralysis, loss of balance and disc problems. Because the animal must stay completely still, it is done under general anaesthesia and usually takes half an hour to an hour.

What is a veterinary MRI?

MRI (magnetic resonance imaging) uses a strong magnetic field and radio waves to create detailed cross-sectional images of the inside of the body. Unlike X-rays and CT, it uses no radiation.

MRI's real strength is soft tissue: the brain, spinal cord, nerves, ligaments and muscles show up far more clearly than with other methods.

When is an MRI recommended?

Your vet usually recommends MRI when an examination, blood tests, X-rays or ultrasound cannot find the cause, or when something needs a closer look:

• Seizures: examining the brain, especially after a first seizure or when seizures do not respond to treatment
• Weak back legs, paralysis or difficulty walking: spinal cord and disc problems (similar to a slipped disc). These are more common in breeds such as Dachshunds and French Bulldogs.
• Head tilt, loss of balance, flickering eyes: assessing the inner ear and brainstem
• Behaviour changes or loss of sight: suspected brain tumour or inflammation
• Masses in the nasal cavity, inner ear or around the eyes
• Joint and ligament injuries
• Surgical planning: seeing the edges of a mass and how it relates to surrounding tissue

How is an MRI done?

• General anaesthesia is needed. For sharp images the animal must stay completely still for the whole scan, which is only possible under anaesthesia.
• Scan time depends on the area examined; it usually takes from half an hour to an hour, sometimes longer.
• Contrast: for some scans a contrast agent is given into a vein and the images are repeated.
• Results: a veterinary radiologist or neurologist reviews the images and sends a report to your vet.

Before the scan

• Examination and blood tests: needed to check fitness for anaesthesia; older pets may need further tests.
• Fasting: food is withheld for a while before anaesthesia. Ask the clinic how long.
• Metal and implants: tell the clinic in advance about any metal implant, screw or plate. A microchip usually causes no problem but can distort the image in the area where it sits.
• Previous results: bring any X-ray, ultrasound and blood test results.

Where can an MRI be done?

MRI machines are expensive and need special facilities, so not every vet clinic has one. They are mostly found at animal hospitals in large cities and at university veterinary faculty hospitals. The process usually starts with an examination by your own vet; if an MRI is needed, your vet will refer you to a suitable centre and you plan treatment together based on the result.

MRI, CT, X-ray and ultrasound: what is the difference?

Method	Best for	Anaesthesia	Radiation
MRI	Brain, spinal cord, nerves, ligaments	Needed	None
CT scan	Bones, lungs, nasal cavity, tumour spread	Usually needed	Yes
X-ray	Bones and fractures, chest, swallowed objects	Often not needed	Yes (low)
Ultrasound	Abdominal organs, pregnancy, heart	Usually not needed	None
Endoscopy	Inside of the oesophagus, stomach and gut, removing foreign objects	Needed	None

In many cases diagnosis starts with more widely available methods such as X-ray and ultrasound; MRI and CT are the next step when needed.

What affects the cost?

MRI is usually the most expensive imaging method. The price mostly depends on the number of areas examined, whether contrast is used, anaesthesia and monitoring, the animal's weight and reporting. Ask the centre you are referred to for the total price and what it includes.