Understanding Equine MRI

By Paige Burkhardt Laing, BSRT(R)(MR)(ARRT), Owner/Operator of Equine MRI of MD, LLC

Photos courtesy Kimberly Dean Photography

Lame. What horse owner’s nightmares are made of. This word is quite possibly the single most anxiety-provoking word in the equine owner’s vocabulary. These feelings typically come from the undeniable likelihood that it may be difficult, or even impossible, to confidently diagnose the source. This is particularly true when lameness originates from a region not easily evaluated with traditional imaging techniques such as x-ray and ultrasound. In many cases it is imperative to consider advanced diagnostics, such as MRI.

Initially discovered in the 1930’s, MRI wasn’t put into use in human medicine until 1977. It wasn’t until the late 1990’s it was first utilized in the equine population. While the use of MRI in equine medicine continues to gain popularity, it remains a grossly undervalued and underutilized diagnostic imaging tool. It is estimated that of all horses that meet the clinical criteria to be referred for MRI, only 10-15% of them go on to receive the imaging they need. Whether due to cost, somewhat limited availability, or perhaps a general lack of knowledge among horse owners and clinicians alike, one thing is for certain: we must raise awareness of the endless clinical benefits that are made possible by utilizing MRI in the diagnostic process.

When I opened Equine MRI of MD, my decision was motivated by the fact that the equine population was being underserved when it came to advanced imaging. The more patients I saw, the more patients I realized were enduring prolonged periods of rest, ineffective testing, and failed “treatments” before turning to MRI. For whatever reason, it seemed to me that MRI in the equine industry was still too often viewed as the “Hail Mary” pass when in many cases it should be utilized much sooner in treatment planning.

Delaying an MRI can have many negative effects for both the owner and the horse. When used as a last resort, many owners are already frustrated and have begun to lose faith in the diagnostic process. Additionally, they are often out of financial resources having likely spent the cost of the MRI many times over. Worst of all, the clinical lesion has now become chronic. This means that potential interventions will have a decreased chance of success secondary to the chronicity of the problem. Studies show that early diagnosis yields the best chance for a positive treatment response while reducing the chance for secondary injuries that can occur if the horse is compensating for pain.

Horses are athletes. In human medicine, MRI is the “go-to” gold standard imaging modality to assess for pathology. I like to use the analogy of the star quarterback hobbling off the field clutching his knee after a sack. Typically, the next thing you see on the ESPN newsfeed is that said quarterback is undergoing an MRI. This is because in human medicine, when soft tissue injury or a combination of soft-tissue and bony injury are suspected, MRI is the next-step standard of care. It is the only modality with the ability to simultaneously distinguish both bony and soft tissue pathology. This is important to consider because it is not uncommon to have a soft-tissue component when there is a bony injury.

Say, for example, a horse undergoes a (non-MRI) bone scan following suspected injury. If present, a bone bruise could be identified. However, a tendon or ligament tear (typically the more troubling pathology) would go undetected. The possible result? The horse would be rested for the appropriate time for the bone to heal and be put back into work with a vulnerable soft-tissue injury. At best it would not heal, and at worst the horse could suffer catastrophic and irreversible damage. To use imaging tools that only have the capability to image one type of tissue is limiting and robs the horse of a thorough and accurate diagnosis while making it virtually impossible to develop the most appropriate treatment plan with the greatest chance to return to work. If we are to consider our horses athletes, MRI must be the standard of care in equines as it is in humans.

Lameness accounts for the greatest losses within the equine industry. Historically, it has consisted of a cycle of trial and review that relies on a slow process of elimination. If a conventional lameness exam yields inconclusive results, the standard approach is to establish a provisional diagnosis and treat the horse as such. This is successful in only 30% of cases. That means that 70% of the time a lame horse will cycle through this process time after time until there is an appropriate response to treatment. If and when the horse becomes sound during this process, the problem remains that there still is no definitive diagnosis. So how do you truly know the injury/pathology has been managed to the extent it requires?

With MRI, we no longer have to settle for a “trial” approach. The use of this modality provides an immediate and  definitive diagnosis in over 90% of cases. This early and definitive diagnosis will lead to a targeted treatment plan, decreased time off, and an improved chance for a favorable outcome. Dr. Kent Allen, owner of Virginia Equine Imaging in Middleburg, VA and Federation Equestre Internationale contact veterinarian for the US Equestrian Team maintains that an accurate diagnosis of any equine injury is paramount. He says, “I have a favorite quote that I have used in talks and papers that states, ‘Absent a diagnosis, surgery is trauma, medicine is poison, and alternative medicines are witchcraft.’ Without a diagnosis, all the treatments that can be devised are a waste of time.” I would add that taking into consideration the limitations of conventional imaging tools, such as x-ray and ultrasound, it is unrealistic to expect a conclusive diagnosis when employing these modalities alone.

So, when might you consider an MRI for your horse? While there are various reasons a horse may be referred for MRI, the most common is the forelimb lameness. The horse may be the intermittent low grade lameness, he could be the horse that became acutely lame in work, or he could be the nagging, persistent lameness that is not responding to conservative treatment. The one thing all of these horses have in common? They are perfect candidates for MRI.

Specific indications for MRI referral are: negative or inconclusive x-rays, the region is not accessible by ultrasound, failed or unexpectedly poor response to treatment, evaluation for extent of injury after penetrating foot wounds, acute onset of lameness during exercise, soft tissue injury secondary to fracture, monitoring treatment and healing before returning to work, early detection of bone fracture in racehorses, and pre-purchase or post-purchase screening.

Before you start dialing your vet, there are some other things to consider. With MRI, we image a very small “field of view”, or region. It is crucial to the diagnostic process to have your vet perform a local anesthetic block to localize the region the lameness is originating from. Once this is done, it allows us to use that information in conjunction with the MRI to sort out the specific cause of lameness. Because MRI is so sensitive, we see all sorts of pathology. Many findings are insignificant in the grand scheme, so having the information from the block and lameness exam is extremely valuable to assist in identifying the significant findings from the insignificant findings.

The other consideration to take into account is the logistics of performing an MRI on a horse. Due to their size, it requires special accommodations. Generally speaking, MRI is reserved for distal limb imaging and there are two options to obtain a scan: high-field and low-field MRI. Each have perks and pitfalls.

The major pitfall to high-field magnets is the horse has to be put under general anesthesia. The perk is the higher magnetic field strength, with potentially faster scans and improved image quality. However, the parameter that controls image quality is actually something called the signal-to-noise ratio (SNR). Many people don’t realize that it is entirely possible to have a similar SNR from both a low-field and high-field magnet. While low field magnets innately have a lower magnetic field, their manufacturers make up for this by optimizing parameters within scan sequences and by utilizing high-quality coils that encompass only the region to be scanned. While a high-field magnet is potentially capable of producing higher quality images than a low-field magnet, the reality is that the difference is not great enough that it should control the decision of which type of MRI you choose.

The technology associated with low-field magnets used in equine distal limb imaging more than compensates for the low magnetic field strength. In fact, Hallmarq, a veterinary imaging company based out of the U.K., manufactures a low-field standing MRI unit that has incredible motion correction software with dedicated extremity coils that produce images that rival high-field magnets. The beauty of this type of magnet is the horse can remain safely standing, thus avoiding the risks associated with general anesthesia.

When choosing which kind of MRI your horse will get, the most important things to consider are the safety of your horse and the education of the staff operating the equipment. In regards to standing versus under general anesthesia, my professional opinion is that generally there is no reason to put a horse under for an elective imaging procedure. Especially when you can obtain the same information with them safely standing. But as with many things in medicine, it has to be weighed in a risk versus benefit manner. Does the benefit of a potential higher image quality outweigh the risk of putting your horse under anesthesia? Only you can answer that question. In regards to finding a facility with a proficient MRI operator, it is important to understand that MRI is user dependent and should never be reduced to “button-pushing.” A proficient MRI operator is of paramount importance as they are sitting at the scan console assessing image quality and making appropriate technical adjustments in real time. It is up to them to provide the radiologist with high quality images for interpretation. In most cases, the radiologist doesn’t see the images until after the horse has been discharged from the clinic,

making it imperative the operator is well-educated and competent. They can literally make-or-break the quality of an exam.

If you have decided to move forward with MRI, there are a few further things to consider. Typically we are easily able to image from and including the knee and distal in the front, and from and including the hock and distal in the hind. The foot is the most common region we image as MRI is the only modality capable of visualizing all of the soft tissue structures that exist within it. MRI has been particularly revolutionizing with navicular syndrome, allowing us to see structures in a way we haven’t been able to previously. If your horse comes in for a scan, the shoes will need to be removed in the front or hind (depending upon what region we are scanning). During the exam, your horse will receive small amounts of light sedation (similar to the sedation used for dentistry and farrier work). Reports are available within 24-48 hours, and include an assessment that takes the entire clinical scenario into consideration so that recommendations can be made based on MRI findings. At this point, you will be confident about the diagnosis and therefore able to move forward with realistic expectations of your horse’s future health.

MRI is certainly a very specialized and unique imaging tool with immense benefits. It allows us to make the most efficient use of the cutting edge treatments and therapies available in modern equine medicine. Now that we are starting to see increased availability in private practice settings, MRI should become the standard-of-care in distal limb lameness. This will help to reduce the financial strain due to loss-of-use and unnecessary treatments, but most importantly, it will improve the quality of life for our horses.

Paige Burkhardt Laing, BS (Medical Imaging), RT(R)(MR)(ARRT), is the owner and operator of Equine MRI of MD, LLC, currently the only MRI facility in the state of Maryland. For more information on obtaining an MRI for your horse in the Baltimore, Maryland region, or for medical imaging consulting services, contact Paige at 410.999.4060 or equinemriofmd@gmail.com. You can also follow her on Facebook and Instagram at “Equine MRI of MD, LLC”