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What’s the use of MRI for pets?

Although for many parts of the body, we can image them adequately using X-rays or ultrasound, there are some situations where the gold standard is the use of MRI. This gives us fantastically detailed views of the inside of an animal, including both bone and soft tissues, and has genuinely revolutionised the care we are able to give.

What is MRI?

MRI stands for “Magnetic Resonance Imaging”, and works in a completely different way to X-rays, CAT scans or ultrasound (which all work by sending a beam of energy, either as X-rays or sound waves, into the body, and then monitoring how that beam is changed by the tissues is passes through).

An MRI machine consists primarily of a very large, very powerful magnet and a radio antenna, connected to an ultra-powerful computer.

When activated, the magnet alters the spin of all the hydrogen atoms in the patient’s body, so they align themselves with the magnetic field. The antenna then sends a strong radio pulse into their body, which causes the atoms to revert to their normal state (or “ground state”), and in the process, release the energy as billions of incredibly weak radio signals. The antenna then detects these and the computer plots the position of the atoms, giving a really detailed view the tissues.

Because every tissue in the body is full of water, each molecule of which contains two hydrogen atoms, every tissue can be imaged in exquisite detail. Essentially, the machine changes the quantum state of the animal, then returns them to their original one, having generated an image of their internal organs and structures.

That doesn’t sound very safe!

Actually, MRI is in most respects the safest imaging technique there is.

Unlike X-rays and CT scans, there is no dangerous radiation involved (also known as “ionising radiation”, X-rays can cause radiation damage, deformities in unborn puppies, kittens etc, and cancer).

Also, there is no tissue heating effect - while a single ultrasound scan is very safe, in theory it is possible to “overdo it” and cause tissue damage. This is not the case with MRI, where no heating effect has been recorded.

As far as anyone knows, there is absolutely NO harm to an animal from the MRI itself.

So it’s perfectly safe with no risks?

Almost - however, there are two caveats.

A scan with an MRI takes a long time - perhaps as much as an hour, and if the patient moves during that time, it can ruin the image. As a result, a dog, cat, rabbit (or indeed any animal) that needs an MRI usually needs to be anaesthetised (or at least very heavily sedated). Although anaesthesia is pretty safe nowadays, there is always a very small risk.

The other thing is that the MRI generates an incredibly powerful magnetic field - we can’t have any metallic objects in the MRI room or they’ll be sucked into the magnet at high speed! In addition, animals with any metallic implants or electronic devices (e.g. pacemakers) near vital organs cannot be scanned, in case the implant moves during the scan. Likewise, metal plates in bones can distort the image near them, so we would normally avoid scanning animals with any metalwork in them; however, ID microchips are fortunately unaffected. 


So, what is it used for?

Because it is so good at seeing soft tissue structures, we mainly use MRI for the following cases, where X-rays and even CT won’t give us the information we need:

  • Neurological disorders where damage to the brain is suspected.
  • Suspected spinal injuries - unlike X-rays or CT, MRI allows us to directly see the spinal cord itself, as well as the bones of the spine and the discs.
  • Some joint injuries and diseases which allow us to look inside the joints and examine the cartilage, tendons and ligaments without needing surgery.
  • Sinus and nasal diseases where we can see the sinuses and the fine bone structures (e.g. the turbinates) in the nose.
  • Soft tissue tumours are also much easier to find and assess with MRI than with ultrasound or X-rays.

If you think MRI may be useful to your pet, have a chat with your vet - we can accept referrals from other practices; or, of course, any of our vets can book a patient in for a scan if needed.

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