The low-field strength units run at 0.2 to 0.3 tesla, and the high-field strength units at 1.5 tesla. Newer units now have
field strengths that run at 3 tesla or higher. The advantage of a higher magnetic field is that you get more signal, so you
can get the same detail and resolution with a much shorter imaging time. The potential capability of those newer, higher-field,
3+ tesla systems is that it may be possible to get information with a much shorter scanning time for an anesthetized patient.
"It really hasn't worked out that way," Schramme says. "Because of the risk of tissue overheating, they need to lengthen the
sequences to let the tissue cool down."
The University of Minnesota College of Veterinary Medicine Leatherdale Equine Center has a 3-tesla magnet, the only such unit
for horses in the country. The unit's disadvantage is that you lose the ability to do some portions of the equine limb because
the bore gets smaller and smaller, and although you can still look at feet, and possibly ankles, it's hard to get up any higher
than that. "I haven't looked at 3-tesla MRIs of horses, but if you ask our counterparts on the human side if they can tell
the difference in their diagnostic abilities between a 1.5- and a 3-tesla unit, most of them will admit that they don't know
if they can see a difference."
MRI is proving to be a vital tool in veterinary diagnostic testing and is giving new hope to many equine athletes. Recently,
MRI was able to diagnose a problem in the famous racehorse Lava Man. Doug Herthel, DVM, Alamo Pintado Equine Medical Center,
treated the horse aggressively, which enabled it to get back to racing after previously being retired. "The MRI gave us an
idea of what we could do," Judy remarked. "We can be a lot more specific, more focused and a lot more directed with our therapies."
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine
with a background in horses, pets and livestock. Kane is based in Seattle.