Magnetic resonance imaging (MRI) helps equine veterinarians understand all musculoskeletal problems better
Equine magnetic resonance imaging (MRI) has been rapidly adapted, and the resulting images have helped veterinarians identify and treat patients more precisely than ever before.
“It’s been revolutionary for us,” says Alison J. Morton, DVM, MSpVM, DACVS, DACVSMR, clinical associate professor large animal surgery at the University of Florida College of Veterinary Medicine. “MRI has helped us diagnose musculoskeletal problems we couldn’t prior. It’s helped us augment and improve our other diagnostics too.”
At the university, Morton uses a Toshiba Titan, high-field MRI with a 1.5 Tesla magnet. The machine was designed for human use originally. The equipment is important, but Morton says the software helps technicians get the most from the resulting images.
“We can get enhanced anatomic detail and see physiological things, like cardiovascular conditions and cartilage mapping – not just where the cartilage was injured but also components of the cartilage at a microscopic level,” Morton says. “The technology advances constantly. We are upgrading things all the time, not just the physical parts of the machinery, but the software too.”
Advancing the industry
The detail from an MRI has helped equine veterinarians interpret other diagnostic tools, like ultrasounds and X-rays.
“We’ve learned quite a lot from MRI on how to read and take radiographs better,” Morton says. “Especially for soft tissue injuries. There are things we never used to identify on ultrasonography, particularly imaging of tendons and ligaments. These were all done with horses bearing weight on the limb. MRI has shown us lesions we missed in these areas, and we have learned that a simple, non-weight- bearing ultrasound allows some lesions to open up and be better identified.”
Ultrasounds can be technically demanding, and MRIs have helped fine-tune techniques to get the best images. Morton cautions that not any one imaging technology can do it all. CT scans can be better for bony structures. In some cases, all the imaging modalities at a veterinarian’s disposal can be used on one case to get the most complete picture.
“An MRI is helpful because it tells us about the structure in a three-dimensional way,” she says. “It’s made us more critical of our skills and more demanding of our equipment.”
MRI can also be used to provide surgical guidance. For example, a recent case of Morton’s involved a chronic abscess in the foot that hadn’t resolved normally. It infected a whole tract that couldn’t be previously identified, and an MRI was performed to provide additional information on the exact location where surgery was needed.
“We’ve learned a lot about disease,” Morton says. “Tendon surgery has been revolutionized since we’ve been doing MRIs. We can realize other injuries that happen in these areas, especially in tendon sheaths and soft tissues of the foot.”
With additional information provided by MRI, veterinarians can outline the treatment plan and better define the prognosis. Morton notes the detail on MRI improved our understanding of injuries to the proximal suspensory ligament of the hindlimb and helps separate cases that can be improved with surgery or others that are degenerative and won’t recover at all.
Best bets for MRI
MRIs are very commonly used for any horse with lameness that localizes to the foot, although it is used for many other joints, too, Morton says. Typically, a horse may have been treated for something in the foot and hasn’t responded well. Or, a horse may be a valuable upper-level performance horse, in which case an MRI may be recommended immediately.
“A large majority of our cases are English sporthorses, but pleasure and pasture horses can be candidates too,” Morton says. “Our patients reflect our population of horses in this part of Florida. In different areas, people may see more Western performance or race horses.”
MRIs for every horse
The MRI at the University of Florida College of Veterinary Medicine is a traditional high-field MRI machine, meaning the horse must be anaesthetized and laid on its side. As with any human or horse that receives anesthesia, there are risks, Morton cautions.
“For horses, their large size and laying down for a long period of time can have complications from pressure on muscles and nerves,” she says. “We have a low complication rate, but there is still the potential for that.”
As an alternative to down MRI, standing low-field MRIs offer an option for horse owners and veterinarians that want to avoid anesthesia. With these machines, a light sedative is used and the horse walks into the machine on its own.
“A lot of times, we’ve had horses that already received a standing MRI and were referred for further screening,” Morton says. “It’s a very good diagnostic tool, but it doesn’t give you as much detail. When you get into the upper limbs, it can be difficult for the horse to remain still enough to get a good image.”
On the other hand, Morton has referred cases to standing MRI machines because the horse wasn’t a good fit for anesthesia, for example: late-term pregnant mares, horses with a history of reactions to anesthesia or cases where the pressure of being on one side for long could be risky.
Most MRIs are done on the lower part of the leg, says Dan Brown, BVSc ACIM, vice president, North America, for Hallmarq Veterinary Imaging, which manufacturers standing MRI machines for horses.
“If you know from nerve blocks that the lower leg is where the horse is lame, standing MRIs are a great option,” Brown says. “Ultrasound is difficult to use in the hoof wall, X-rays may not give you an answer.”
MRIs can image through the hoof wall, and, unlike X-rays, can image both bony and soft tissues. In most cases, MRI is an option where normal lameness work-ups have failed to provide an adequate answer. Fetlock injuries and navicular cases are commonly referred to MRIs for additional information.
While standing MRIs may offer a more convenient option, Brown says that horse
owners should expect any MRI machine to require that a horse’s shoes be removed, and even a light sedative may re- quire a withdrawal time for competitive horses.
“An MRI is a huge magnet, and metals and magnets don’t mix well,” he says. “There is no risk to the horse or the people using it from the magnet. There is no radiation, but the rooms will often be shielded simply to prevent interference from radio waves.”
Lameness in horses can have many causes, but MRI offers owners and veterinarians a robust diagnosis tool. The resulting information can then be paired with the right treatment plan to help the horse recover quickly, and without wasting money on interventions that may or may not work.
“MRI should be considered in any case of lameness where the veterinarian doesn’t have a clear answer,” Brown says. “It’s very hard to know how to proceed without knowing the cause.”