Owner FAQ
- How safe is MRI for the horse ?
- What is the difference between high field and low field scanners ?
- Isn't high field always the better way to image?
- What is the difference between standing and anesthetised ('down') scanners ?
- Doesn’t the horse move?
- How safe is it to operate the scanner ?
How safe is MRI for the horse ?
Hallmarq equine MRI systems have been used for almost 17,000 standing sedated horse examinations on 44 sites in 11 countries. During this time there have been no fatalities. Had general anesthesia been necessary over 170 of these would have died as a result of the normal approximately 1% mortality rate following general anesthesia. Hallmarq firmly believes that the standing MRI product has revolutionised the diagnosis and treatment of lameness by making MRI safe, affordable, and widely accessible to veterinarians and horse owners and has made a significant contribution to equine health and welfare.
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What is the difference between high field and low field scanners ?
High field scanners operate at a stronger magnetic field than low field scanners. The stronger field produces a stronger signal, so high field scanners can produce higher resolution pictures in a shorter time than low field scanners. Both high field and low field scanners have been used in human clinical medicine for many years. Low field scanners have been used for "Open MRI" because they are less claustrophobic. Both have a niche in clincal imaging. High field scanners:
- are tubular in shape, whereas low field scanners are 'C' or 'U' shaped. Getting the horse into the tube requires general anesthesia, with the associated costs and risks.
- require a larger room and more specialist equipment as the stray magnetic field covers a larger area
- are much more expensive to purchase, and need regular refills with costly liquid helium, so they tend to be installed only in universities and a very few clinics, and cost more for the scan
Isn't high field always the better way to image?
Images from high field scanners include a lot of detail and can cover a larger region in a single scan. However this does not necessarily make for a better diagnosis, in much the same way as a veterinarian may choose to use a smaller x-ray or ultrasound machine in circumstances where it is diagnostically appropriate, even if a more powerful machine would give a higher quality image. The resolution of the Hallmarq scanner is typically 0.8mm x 0.8mm in-plane for most scans which allows for the visualisation of fine structures, and many horse owners prefer the lower cost and the ability to scan the horse without general anesthesia. However if an even higher resolution image should be required one can be obtained by increasing the time taken to collect the signal, under general anesthesia if the veterinarian should consider it necessary.
Low field scanners, including the Hallmarq system, require continuous air conditioning with close temperature control to maintain a stable environment. High field scanners require no more than normal office air conditioning, though other special room design features are required for safe operation in the presence of liquid helium.
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What is the difference between standing and anesthetised ('down') scanners ?
All high field scanners require anaesthesia. There are two types of low field scanner, one uses a large magnet and also requires anaesthesia, the other (the Hallmarq system) uses a small magnet which fits around the leg and is normally used with the horse standing and sedated but not anesthetised.
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Doesn’t the horse move?
In a high field scanner the heartbeat and breathing of the horse can produce motion of the leg in the scanner, which is normally reduced with padding and careful positioning. In the Hallmarq scanner the standing horse is supported by a chest rail, but it may sway during the scan which particularly affects parts of the leg above the foot. Special software corrects the effect of the motion to produce diagnostic scans.
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How safe is it to operate the scanner ?
There are no known biological hazards of static magnetic fields, and MRI does not use any ionising radiation nor toxic chemicals. There are international safety standards for MRI operators relating to the RF and gradient fields generated during the imaging process, but the low field Hallmarq system falls well within all relevant safety standards. The most significant safety concerns are from magnetic metal objects (eg tools, horse shoes) and the normal hazards of working around horses.
