MRI

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 tomographic 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. This is especially true for soft tissue injuries around joints, and in the areas difficult to palpate or image by other means such as radiographs or ultrasound. MRI is the only method presently available that can assess all tissues during a single examination.

Northwest Equine Performance will be installing the standing open MRI system, which allows the patients to stand under mild sedation, so distal extremities can be scanned in a weight-bearing state. This enables us to more precisely pinpoint your horse's source of pain. In order to obtain images, a receiving coil is placed closely along the horse's anatomic region of interest to collect emitted signal. The patient's legs are positioned within the center of a strong magnetic field generated by the MRI system. The sequences are selected, 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.

The standing MRI examination requires sedation only, not general anesthesia with its associated risk particularly during the recovery period. Eventually Northwest Equine Performance will offer the choice of standing or anesthetized MRI examinations in order allow imaging of regions higher up the limbs, as well as the neck and head. The standing MRI has limitations due to motion in imaging these regions that are not an issue when the patient is placed under general anesthesia.

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.

MRIs Are Changing The Face of Equine Diagnostics. Reprinted by permission of The Chronicle of the Horse. Visit www.chronofhorse.com to subscribe