The ups and downs of equine MRI in veterinary medicine
A look at the pros and cons of standing vs. recumbent magnetic resonance imaging systems.
Sep 01, 2013
Magnetic resonance imaging (MRI) was first performed on live horses at Washington State University's College of Veterinary Medicine in the late 1990s. Available for almost 15 years, this diagnostic modality has seen a steep increase in clinical use during the past five years. MRI images have expanded our thinking on many types of equine lameness and greatly improved veterinary diagnostic ability.
A look at your optionsBigger is generally better, and in the case of MRI, bigger is measured in teslas. MRI machines come in three different sizes based on the magnet's strength, which is measured in tesla units or Ts; 1 T is nearly 30,000 times stronger than the earth's gravitational pull. High tesla values can be obtained by placing a magnetic field in a confined or enclosed space.
Equine MRI evaluations are generally done with one of three types of systems. There are two high-field systems, which have 3-T and 1.5-T magnets, and a low-field system with a 0.27-T magnet. To get stronger magnetic fields and higher teslas, MRI units have been designed in a tubular shape with a core space that decreases as magnetic field increases. The 3-T and 1.5-T units are generally known as "down" magnet systems because the horse must be anesthetized to have its distal limbs or head and neck safely placed as deeply as possible into the machine's tubular core. Horses do not like the somewhat claustrophobic aspect of the magnetic coil or the recumbent positioning, so anesthesia is required.
The 0.27-T MRI is referred to as an "up" or "standing" MRI. This low-field system features a more open C- or U-shaped clam shell design, and a sedated horse is kept standing as the magnetic coil is placed around its leg, foot or other affected area. Each system has distinct strengths and weaknesses, and these MRI units have been in use long enough now to make an interesting and informative comparison.