Standing MRI in Horses
Diagnosing problems within the foot has often been a challenge, since the hoof capsule makes it difficult to image internal structures via ultrasound, and radiographs are not always conclusive. The advent of MRI (magnetic resonance imaging) has greatly enhanced our ability to look inside the hoof.There are two types of MRI machines. One is a large cylinder or tube, similar to the human MRI system with high field magnets. This “closed” system requires the horse to be lying down and under general anesthesia, with his legs (front or hind) put into the machine. The other type, called an “open” machine, is U-shaped and uses a low field, smaller magnet and the horse can be standing—merely sedated. Sensors are placed in collars that can be put around the foot or limb of the standing horse.
Dr. Jairo Paucart, Littleton Large Animal Clinic (Littleton, Colo.) uses the standing unit with low-strength magnet. Strength of the magnet is measured in Tesla. “A big high field machine is probably a 1 or 3 Tesla, while ours is .27 Tesla. These low-field machines are designed to create images while the horse is standing. This gives the veterinarian and client the opportunity to get quick scans of the feet, and a quick diagnosis, in situations where the clinician is unable to see pathologies with x-ray or ultrasound,” says Paucart.
The standing MRI is quick, and clients appreciate the fact that the horse does not need to be anesthetized. “We cannot compare the quality of the images with those from high-field magnets—those are definitely better. Some lesions show up better with a high-field magnet, such as subchondral bone damage or articular damage,” he explains.
“Motion can be a problem when we are acquiring images, so the horses must be well sedated. If you have the perfect patient, and are doing the MRI on only one foot, you might be able to arrive at a diagnosis within the first 10 minutes. If you want to complete the full protocol, you might need at least 40 minutes,” he says.
With the standing MRI, you can scan the leg as high as the knee or hock. “Here at our clinic, the majority of cases involve the foot, but we also can check the pastern, fetlock joint and higher while the horses are standing. We rarely do higher scans (such as knee or hock) and the quality of those images are more inconsistent, especially in the hind leg,” he says.
“We can find many different pathologies in the foot. Some are related to ligaments or tendons or bones. The majority of our patients are horses that don’t have a high degree of lameness, but they still have a problem and we want better information—to be able to address the problem before the lameness becomes move evident,” says Paucart.
“Most of the time when we have a lame horse that needs an MRI, we find more than one lesion; the lameness is not related to just one area. There’s usually multiple damage. The opportunity to be able to obtain an accurate diagnosis, establish a logical treatment option and give the client a realistic prognosis on how the horse will do long-term, is probably the biggest advantage to using the MRI,” he says.
Heather Smith Thomas has raised and trained horses for 50 years and has been writing about them nearly as long, selling more than 9,000 stories and articles and publishing 20 books. She and her husband raise beef cattle and horses on their ranch near Salmon, Idaho.