Facilities With MRI Technology
An equine MRI diagnostic test costs $700 to $1,500 or more. It's available at universities and private clinics across the country, including:
Virginia Equine Imaging, Middleburg, VA
Washington State, Pullman, WA
California Equine Orthopedics, San Marcos, CA
North Carolina State University, Raleigh, NC
Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA
Colorado State University, Ft. Collins, CO
University of Florida, Gainesville, FL
Rood & Riddle Equine Hospital, Lexington, KY
Univ. of Pennsylvania Veterinary School, Kennett Square, PA
Equine Specialty Hospital, Cleveland, OH
Randall Veterinary Hospital, Cleveland, OH
Fairfield Equine, Newtown, CT
South Shore Equine Clinic, Plympton, MA
How Does It Work?
MRI is short for magnetic resonance imaging. The "heart" of an MRI machine is an extremely strong magnet. MRI machines large enough to image the entire body could pull a heavy metal object from your hands at a distance of several feet from the machine, pull watches off wrists, make metal objects fly through the air, etc.
The other integral part of the machine is a radio-frequency-wave generator. Inside the magnetic field, most of the electrically charged ions in the body are lined up in a way that they cancel out. A small number will remain unpaired and can be stimulated. The radio waves are set at a frequency that will make hydrogen ions in the body vibrate/resonate (the resonance part of the image).
When the radio-wave stimulation is turned off, the hydrogen ions gradually return to their unstimulated state, giving off the extra energy in the process. The MRI machine detects the emitted energy and turns this into extremely detailed images. The machine can be set to focus on precise locations and depths within the body and can also be adjusted to focus on specific types of tissue, from bone to less-dense soft tissue like tendon, even joint fluid or blood. The result is images that have more detail and contrast than even a CAT scan.
MRI scanners range from huge machines that can hold the entire horse to smaller "tunnels" useful for the distal part of the leg. These require the horse be under general anesthesia and lying on a table. There are also small units that can be used with the horse standing.
Since problems with the various tissues in the foot come from different causes, have different rates of healing and call for different treatments, being able to distinguish among them is important to determining how the lameness should be handled.
For example, if the only finding is fluid in the navicular bone, attention may be paid to better cushioning for the bottom of the foot, with rest and possibly a course of anti-inflammatory agents until the fluid subsides. Navicular bursitis as an isolated finding that would often be treated by local injection of the bursa, with shoeing and the horse's activity changed to reduce stress on this area.
Problems in the various tendon and ligament structures may be the most critical to correctly identify, both because these structures are extremely slow to heal and also because inflammation and instability in them can easily result in damage to the bones and joints of the foot.
MRI studies of the feet are helping veterinarians to better interpret the results of local anesthetic blocks. Anesthetics injected into the navicular bursa will improve pain related to navicular-bone pathology and, sometimes, pain coming from deep digital flexor injury in the foot.
Blocks of the digital nerves below the fetlock ("heel" or "low" blocks) alleviate pain coming from the navicular bone itself but do not change or improve pain from other injuries. Injection of anesthetic into the coffin joint itself improves pain from arthritis/synovitis there, pain coming from the navicular bone and pain from deep digital flexor injuries, but not pain coming from inflammation of the collateral ligaments.
While radiographs, bone scans and ultrasounds may all pick up some types of problems, it's clear that only an MRI scan can reliably detect hoof problems coming from all types of injuries. While an MRI is uniquely suited to the foot, its usefulness doesn't stop there. Remarkably detailed images can be obtained of any joint, even the horse's brain.
The photos are courtesy of Virginia Equine Imaging, Middleburg, Va., www.vaequine.com, call 540-687-4663.
