MRI is unique from other imaging techniques in that there are different sequences to look at, and each sequence contains hundreds
of images. In the same tissue, fluid, for example, can look different on different sequences. In certain sequences fluid is
white, while in other sequences, fluid is black. Depending on the imaging sequence, the same tissue will have different signal
This gradient echo coronal section (left) through the right-hind fetlock joint shows subchondral bone damage to the medial
condyle of the third metacarpal bone, shown by increased signal intensity (white) indicative of inflammatory fluid just above
the joint (arrow).
Consequently, learning to use MRI effectively requires a crash course in the process, the technology and of course, practice
in interpreting the images.
"It is a matter of first learning the physics of MRI, understanding how MRI works," notes Natasha Werpy, DVM, who specializes
in equine imaging and runs the MRI center at the Equine Orthopaedic Research Center at Colorado State University.
Her colleagues concur.
"There is a learning curve as far as interpreting MRI images, though there are some veterinarians who have got quite a lot
of expertise at interpreting them, it's really a role for specialists," says Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, Dipl.
ACVS, director of the Equine Orthopaedic Research Center at Colorado State University.
This proton density sagittal section through the right front fetlock joint shows subchondral bone and cartilage damage to
the distal aspect of the third metacarpal bone, shown by increased signal intensity (white) indicating inflammatory fluid
surrounded by decreased signal intensity (black) indicating sclerosis (arrows).
Werpy works at a reading center that helps interpret the images the center produces. She says she can log onto a permissions-based
server to view images as quickly as she needs to.
This interpretive expertise enables practitioners of all skill levels to use the technology.
Veterinary MRI units are available to equine practitioners in many locations around the country, including many universities
and larger equine clinics.
This proton density transverse section through the left front proximal metacarpus shows desmitis of the dorsomedial aspect
of the proximal suspensory ligament, shown by increased signal intensity (grey/white instead of black) diffusely in this region
During the next few years, there will be more training courses offered to learn how to interpret the images, as well as a
driving force for more equine MRI radiologists, as they realize the benefits of the technology.
More units will come on line, too, making MRI a viable option in almost any part of the country.
"The thing about MRI that is so important to realize is that it really allows you to differentiate different types of lesions
at a level that we were never able to do before," Werpy says.
This proton density transverse section through the left front coffin joint of a horse with subchondral bone and cartilage
damage of the distal aspect of the second phalanx, as shown by an area of decreased signal intensity (arrows) in the medial
The many stages of injuries, from acute lesions with fluid to scar tissue and adhesions, will have better opportunity for
diagnosis with MRI, and those horses likely will get treated differently as equine practitioners will be developing treatments
for different stages of injuries that they were unable to do before. Thus, MRI is on the cutting edge of targeted treatment,
especially in performance horses.
"Over time we will be able to separate lesions by stages and types. They might be better treated with specific treatments
for a specific stage of injury," Werpy says. "We'll be able to hopefully develop treatments more specifically to give a better
prognosis. That is the way I look at it when I read these studies."