Magnetic resonance imaging provides images with unmatched tissue contrast and anatomic definition, thus offering numerous diagnostic advantages over other imaging technologies. MRI displays anatomic and physiologic detail in both bony and soft tissue structures through a series of slices using magnetic properties of the horse' tissues. The MRI has provided the diagnosis in many cases when other imaging modalities failed to clearly identify the lameness. MRI is the only method presently available that can assess all tissues during a single examination.
Northwest Equine Performance has a standing open MRI system, which allows the patients to stand under sedation, so distal extremities can be scanned in a weight-bearing state. In order to obtain images, a receiving coil is placed around the horse's anatomic region of interest to collect emitted signal. The patient's legs are positioned within the center of the strong magnetic field generated by the MRI system. The sequences are selected by a veterinarian, and a radiofrequency signal is collected to create the image. The typical MR exam of an equine patient yields 300-500 high-detailed images to review.
NWEP currently offers the only standing MRI in Oregon or Washington. The standing MRI examination requires sedation only, not general anesthesia with its associated risk particularly during the recovery period.
MRI should be considered as a diagnostic tool when the site of pain or injury can be localized, but the problem cannot be distinguished by other forms of imaging such as radiographs, nuclear scintigraphy, or ultrasound. For instance, if your horse has been diagnosed with navicular disease, but has been unresponsive to therapy, the MRI may be the next logical approach. The MR exam because it can more precisely evaluate soft tissue and bone within the hoof capsule provides a more concise diagnosis such as navicular bursitis, impar ligament desmitis, or suspensory ligament desmitis of the navicular bone. It is particularly useful for lameness localized to the foot. Importantly, MRI is capable of demonstrating cortical erosions along the flexor surface of the navicular bone, and adhesions to the adjacent deep digital flexor tendon. The use of MRI in equine veterinary medicine allows more timely intervention, and an improved prognosis and long-term outcome for equine athletes. MRI has become one of the most important diagnostic tools in equine lameness.
Standing MR images of a horse with a moderate - severe injury to the deep digital flexor tendon (red arrows).
The standing MRI can go up as high as the carpus (knee) region in the front end and as high as the hock region in the hind end in a well behaved horse that will stand still for the scans. The images above show MR images of a moderate suspensory ligament injury with associated cannon bone involvement (pink arrow), compared to the normal transverse image in the middle. The image on the far right shows us the level at which the injury is present on another plane.