When your pet is poorly, your vet may recommend advanced imaging modalities such as a CT or MRI. Both are incredibly powerful tools which allow greater detail compared to x-ray or ultrasound. They allow you vet to get a better understanding of what exactly is going on inside your pet’s body.
If your pet has ever been referred for advanced imaging, you may have noticed something curious: there seem to be more vet practices with CT scanners than MRI machines. So, why is that? Why is CT becoming increasingly common, but fewer practices have MRI?
Let’s take a look at what each of these machines do, how they’re used, and why CT has become more widespread in veterinary diagnostics.
What is advanced imaging?
Advanced diagnostic imaging is a term used to refer to more complicated imaging modalities such as magnetic resonance imaging (MRI) and computed tomography (CT), which give a more detailed picture of what may be going on in your pet’s body. They go beyond more common modalities such as x-ray and ultrasound.
CT and MRI: what exactly are they and what’s the difference?
Although both are considered advanced imaging, CT and MRI function very differently and are used to assess different structures in the body.
CT (computed tomography):
Simply put, CT is a 3D x-ray. Where basic x-rays produce a 2D image, CT produces 3D, cross sectional images and uses computer processing to highlight different parts within the image. This process isn’t dissimilar to how we cut a slice of bread from a loaf: we can slice in different directions (long wise or short) and create different thicknesses of slice. This is essentially how CT allows the vet to look at different parts of your pet’s body.
The patient lies on a table that slides into a large, doughnut-shaped machine. When inside, a tube, located within plastic housing, spins incredibly fast around the body. As it rotates, it emits x-rays which are detected at the opposite side. Different tissues within the body absorb x-rays different, thus creating contrast which is used to generate the image.
CT is extremely useful to assess many structures within the body, especially bones and lungs, so is often utilised for the following:
- Fractures and joint injuries.
- Nasal and skull issues.
- Lung and chest disease.
- Abdominal organ assessment, including tumours.
It is also relatively quick, so is often used in patients with multiple issues such as those incurred in road traffic accidents. As it is so quick, often the patient only requires sedation instead of a general anaesthesia.
MRI (magnetic resonance imaging):
MRI is a little more complicated and uses a powerful magnet to generate images, rather than x-rays.
Like CT, the patient lies on a table which slides into the doughnut-shaped machine. When inside, the machine instead of spinning remains static, but generates a powerful pulse which causes certain particles within the body to align. The pulse then stops, which causes these particles to flip back to their original position which generates energy which is detected. Different types of tissue within the body generate different signals, producing a contrast which is used to generate the image.
MRI is the modality of choice for neurological conditions and certain soft tissue problems, such as:
- Seizure disorders.
- Strokes.
- Brain and spinal cord tumours.
MRI provides better contrast in soft tissues than CT, but takes much longer, so requires a general anaesthesia.
CT vs MRI: logistics and practicalities.
CT scanners are common in referral centres and are now increasingly available in first-opinion practices. MRI scanners on the other hand are much less common in veterinary practices due to higher costs and operational complexities, so are predominantly only found in specialist referral hospitals.
So, why are CT scanners becoming more common?
1. Cost.
One of the main reasons CT is more widespread than MRI in veterinary practice is cost. A CT machine may cost between £150,000-£500,000 depending on a variety of factors such as spec and if it was refurbished from human use. MRI machines can cost anything up from £1 million, depending on its strength (measured in Tesla). And these costs are initial prices for the machines themselves, before the cost of installation and maintenance is added.
2. Building and safety.
CT machines are relatively easy to install. They require the same considerations as installing x-ray machines such as ensuring safe, protected distances for the imager. While additional shielding is often needed, it’s “more of the same”, rather than anything new. MRI machines require specially shielded rooms, ventilation and cooling systems and include extra levels of safety and training.
MRI magnets pose significant safety risks, especially with ferromagnetic materials (e.g. iron or steel). Strict safety protocols must be implemented along with in depth staff training. An extra consideration they require, as discussed above, relates to the fact that they are huge magnets, so nothing metal can be in close proximity or else risk the safety of humans, animals and machine alike. This includes larger items like patient trollies and anaesthetic monitoring equipment, but also smaller more forgettable things like collars and leads, jewellery and stethoscopes. This complexity makes MRI harder to integrate into busy first opinion practices, who weren’t purpose built for such imaging. CT in comparison is more affordable to purchase, operate and is easier to install.
3. Demand.
There needs to be enough demand for the modality to cover installation and maintenance costs. Many neurological conditions requiring MRI (such as seizures and spinal disease) are referred to hospitals to consult specialist veterinary neurologists or surgeons. Most first-opinion vets see relatively few cases that absolutely need MRI, so the demand doesn’t justify the investment for most clinics. In contrast, CT has broader utility and can be used in a large range of conditions including orthopaedics, oncology, and emergency care – areas that first opinion practices encounter regularly.
4. Time and staff demand.
As discussed above, MRI sequences take much longer than CT scans. So this needs to be factored into the day’s schedule. Additionally, as an MRI scan requires the patient to be under general anaesthesia there is further time required to accommodate this – and staff need to be available to closely monitor these patients.
What if my pet needs a CT or MRI?
If you vet recommends such advanced imaging, they will refer you to a practice or hospital with a CT or MRI machine. In the case of CT, this may be a nearby practice or can be done in house if your practice has one. As MRI is currently only available at referral hospitals, some travel with likely be required. However, there are mobile CT/MRI machines available which may travel to your practice or one close by.
What does this mean for you and your pet?
As a pet owner, the most important takeaways are:
- CT and MRI are both powerful modalities that provide detailed imaging and information, helping vets diagnose and treat complex problems.
- CT scans are fast, detailed, and increasingly available in first opinion practice.
- MRI scans are best for brain and spinal issues, but are only available at referral hospitals (/ mobile providers) and less available due to cost and complexity.
- Your vet will choose the most appropriate scan based on your pet’s condition. They will refer you to a specialised hospital if required or may be able to provide CT imaging in house.
If your pet needs one of these scans, don’t hesitate to ask your vet why they’re advising it, what it will help assess, and what to expect during the procedure. Understanding the “why” behind their advice can help you feel more at ease on the day of imaging.
Conclusion
Veterinary medicine continues to evolve rapidly, and the growth of advanced imaging is a testament to how much more we can now do for our pets. CT and MRI offer extraordinary detail into problems we couldn’t visualise even a decade or two ago. While CT has become a common tool thanks to its speed, cost, and broad utility, MRI remains an essential, complex modality in the diagnosis of complex neurological disease. With both modalities being available to our patients, we can offer increasingly advanced options to our beloved pets.
Further reading
What does advanced imaging for pets mean?
Why does my dog need a CT scan not a simple X-ray?
Why does my dog need an MRI scan, not something that can be done in practice?
Veterinary CT: Everything you need to know – IMV Imaging
Balancing Act: Justifying the expense of MRI for dogs and cats in veterinary care – Hallmarq
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