So which system to pick?
Still there is the question of low-field image vs. high-field image since MRI is, at the core, a diagnostic tool, and the
image produced must be diagnostic.
In the study that compared 3-T, 1.5-T and 0.27-T systems, it was certainly shown that bigger units produced significantly
"better" images. And "better" generally means clearer and more distinct images with a more pronounced differentiation to object
edges and sharper contrast. Sometimes, however, "better" is in the eye of the beholder since different clinicians prefer radiographic
or ultrasonographic images produced by certain machines, while other clinicians may prefer images from other machines. But
these researchers also stated, "The images from all of the examinations (3T, 1.5T and 0.27T) were considered to be of diagnostic
value."1 Exceptions were made for the dorsal/distal aspect of the hoof capsule, which did not image clearly in the low-field system.
These findings suggest that standing MRI may in fact be a reasonable diagnostic choice for a number of clinical cases. Standing
MRI eliminates the need for general anesthesia, and this reduces not only the cost but the risk of complication or death.
Some anatomical areas and particular lesions such as the dorsal/distal aspect of the hoof capsule referenced above and articular
cartilage defects in areas of joints where this tissue is very thin (the thinner the structure, the more difficult it is to
scan, and larger units will generally give a more useful image) will always require a high-field system MRI scan for accurate
and complete diagnosis. Subtle cartilage damage may be beyond the diagnostic capabilities of low-field systems, but navicular
bone degeneration, deep digital flexor tendinitis, collateral ligament desmitis, phalangeal bone bruises, navicular collateral
desmitis, corns, fractures and other issues of the foot along with similar problems of appropriate structures in the pastern,
fetlock and now even the hock and carpas can be noted on the newer, improved up-MRI unit. These advantages may make standing
MRI even more popular, and emerging technological advances will only continue to improve image quality to a point where "up"
or "down" may no longer be a debate.
Dr. Kenneth Marcella is an equine practitioner in Canton, Ga.
1. Bolen G, Audigie F, Spriet M et al. Qualitative comparison of 0.27T, 1.5T, and 3T magnetic resonance images of the normal
equine foot. J Equine Vet Sci 2010;30(1):9-20.
2. Johnston GM, Taylor PM, Holmes MA, et al. Confidential enquiry of perioperative equine fatalities (CEPEF-1): preliminary
results. Equine Vet J 1995;27(3):193-200.
3. McKnight AL, Manduca A, Felmlee JP, et al. Motion-correction techniques for standing equine MRI. Vet Radiol Ultrasound 2004;45(6):513-519.