Mair concludes, "This system will allow the application of MRI technology in general equine practice, which would be unlikely
with higher-field closed magnets because of their inherently higher cost."
Eventually it will be possible to do high-quality MRI on standing horses, but the technology has yet to mature. The diagnostic
quality of these systems is not as good as the higher-filtering systems, such as the one at Washington State University.
"Without degrading that system, its just not yet mature enough that it comes close to what we're talking about when we anesthetize
a horse and use a high-filtering system," notes Dr. Russell Tucker, DVM, Washington State University (WSU) Teaching Hospital.
"The diagnostic quality and resolution are not the same."
At WSU, Tucker has worked extensively with MRI, as well as conventional imaging via ultrasound and radiography. MRI gives
a totally different look at the tissues than does conventional radiography or computed tomography (CT).
"When you look at an MRI compared with CT, it's night and day as far as all the structures you get to look at," Tucker says.
They are looking at soft tissue and the osseous damage as indicated by fluid accumulation and by changes of the magnetic properties
of the tissue. WSU's MRI, the first of its kind in the world, is designed for human use. Therefore, they have adapted the
device to allow horses to go into it while the horses are under general anesthesia.
"It is quite possible to do what we call magnetic resonance angiography, which gives you the same detail of vascularity that
CT angiography does," Tucker says.
For most of the vascular studies that WSU does, they don't have to inject contrast material, but solely use the fact that
under the magnetic influence flowing blood will have its own magnetic inherent contrast.
"I think it is important to note that with the anesthetized laterally recumbent horse, there is probably a lot of disruption
of the normal flow, some introduced flow deficits that may not be truly representative of true lesions," Tucker stresses.
"In time, with high-quality MR units, perhaps we will have a more-valid, physiologically true mapping of the vascularity as
opposed to horses lying down on their side."
Contrast enhanced MR or CT is not routinely used in the equine. The major advantage of contrast is that it changes a purely
morphologic assessment into a functional test.
The Basics of Computed Tomography Angiography
For human patients CT angiography (CTA) is a recently developed technique that uses X-rays to visualize blood flow in arterial
vessels throughout the body, from arteries serving the brain to those bringing blood to the lungs, kidneys and the arms and
legs. CTA combines the use of X-rays with computerized analysis of the images. Beams of X-rays are passed from a rotating
device through the area of interest in the patient's body from several different angles to create cross-sectional images,
which then are assembled by computer into a three-dimensional picture of the area being studied.
Dr. Sarah Puchalski, DVM, University of California-Davis, Veterinary Medical Teaching Hospital, and colleagues have developed
the CTA technique that allows equine veterinary practitioners to assess the subtleties of foot injury and lameness, to diagnose
with accuracy and to then be able to treat these injuries with greater proficiency. The major benefit is that it is a better
diagnostic tool for bony abnormalities, though previously no one was using it for soft-tissue injuries.