Like most major advancements in horse racing, there was an element of chance that came with the development of one of the most effective technologies for ensuring the safety of racehorses.
Although it likely won't be part of the same lore as the coin flip in 1969 that resulted in Penny Chenery receiving the rights to a foal that would be named Secretariat, a brainstorming exercise in 2013 at the UC Davis School of Veterinary Medicine would make a lasting impact on evaluating the soundness of racehorses.
“An engineer at Davis was working on developing a new scanner,” Dr. Mathieu Spriet, a professor in surgical and radiological sciences, recalls. “He came to me because he was writing a big grant, and he was looking for additional goals for his grant. He was like, 'Can we do PET on a horse?' I was like, 'Whoa!' And that's how it started, with a guy coming knocking on my door.”
What Spriet is referring to is positron emission tomography (PET), where a small amount of radioactive material is injected into the horse and then a sophisticated scanner detects how it has moved throughout the body. The image the scanner produces of the radioactive dye inside the body alerts to the discovery of an issue, similar to the theory behind other imaging technologies like X-ray, computed tomography (CT), or magnetic resonance imaging (MRI).
PET scans produce particularly detailed three-dimensional images. The technology was first developed for humans in 1974 by two professors of nuclear medicine and biophysics at UCLA. It is most commonly used to detect the presence and spread of cancer.
“If there's one good thing with horses, it's that there isn't much cancer,” Spriet said. “They get in trouble in many other ways.”
Spriet's intellectual curiosity extends as far as his world travels, with a veterinary degree from France, a subsequent master's of science from Canada, and now a professorship in the United States. So, he started to brainstorm.
“The truth is that, a lot of the time in vet medicine, we end up following what's happening in human medicine but, at least at the time, there was not much done looking at the bone [with PET scans] except looking at metastases,” he said. “But then I came across an early paper that was describing using [PET scans] in people for foot pain. And I thought, that's what we have in horses all the time. So, that's how I got excited.”
Spriet says he shared his ideas of how the advanced imaging technology could be used to detect indicators of lameness in horses with Dr. Sue Stover, director of the orthopedic research laboratory at UC Davis.
“I showed it to her, and she was like, 'Oh my god, you've found gold. You've found a mine of gold,'” Spiret recalled. “That's something that started out of an academic interest question of whether you can do PET on a horse.”
On April 15, 2015, a research horse named Fancy Piece of Candy, an 18-year-old Quarter Horse with a lesion in her left front foot, became the first horse to undergo a PET scan.
“Fancy Piece of Candy” would also be an appropriate nickname for a promising new piece of technology at a veterinary school. Four decades after the initial PET scan on a human, the first PET scan on a horse was deemed a success.
“It was actually a pretty good fit for the horse foot,” Spriet said. “That thing was never built to image a horse. It was built to image the human brain.
“At the end of the day, today's scanners look very different from that, but the detectors are pretty much the same.”
A number of factors contributed to making the application of this revolutionary idea in equine medicine more accelerated than the application of other academic innovations.
PET scan machines were subsequently built specifically for horses. As such, instead of horses having to be under general anesthesia and turned on their sides to position the foot inside the machine, the MILEPET scanner allows horses to stand while under sedation. The machine maneuvers on wheels to the horse. A ring of sensors is opened and positioned around the limb that will be scanned. Each image takes approximately four minutes to produce, meaning that multiple leg scans can be done in less than a half hour.
The application of PET to horses came at a time when racing was on high alert about equine safety. There were 144 fatalities during the 2018-19 season in California, according to a California Horse Racing Board annual report, including more than 20 in a three-month period at Santa Anita that caused the track to cease operations temporarily in March 2019.
Grants and funding from organizations like the Grayson Jockey Club Research Foundation accelerated the integration of PET scans into assessing equine welfare.
Perhaps most importantly, rather than collecting hundreds of thousands of points of data and then assessing what they all mean in the big picture, radiologists knew what to look for with a PET scan.
“The sesamoid bone is of high interest for us because the majority of breakdowns that happen are due to fracture of this little bone at the back of the ankle, the sesamoid bone,” Spriet said. “They've figured out that a lot of horses that break the sesamoid bone have on pathology this area that becomes abnormal. But the challenge is that it's not something you can see on an x-ray. It's something you cannot see on bone scan [scintigraphy]. It's something that's actually quite difficult to see on MRI. But, PET is really good at picking up that.”
What a PET scan will detect is “stress remodeling,” which represents abnormal bone trying to repair itself. This repairing process attracts increased blood flow to that area, which a PET scan can detect. Bone that is repairing is more fragile than established bone and less conducive to holding up to the high impact of racing or other equestrian sports. This is represented by bright coloring on the image produced by the scan.
“That is what we know from all the necropsies that have been done on the horses breaking down on the track is that typically they don't break down out of nowhere,” Spriet said. “They break down because there are some underlying changes in the bone, which is what we call stress remodeling changes.”
The ability of PET scans to detect underlying indicators of lameness attracted the attention of the horse racing industry looking for solutions to the fatality crisis.
“We were basically very interested in looking for any type of imaging modality that could really move the needle in terms of safety,” Dr. Ryan Carpenter, a veterinarian practicing at racetracks in Southern California, said. “I think, for the typical Thoroughbred racetrack practitioner like myself, the injury that we struggle the most to identify are sesamoid bone fractures because we don't have a great imaging modality that can help us with that yet. They're the ones that, so to speak, will sneak up on you.”
By that, Carpenter means that horses do not present outward signs or symptoms of being at risk for a sesamoid fracture, which happens to be the major cause of breakdowns, like they would for other types of fractures.
“The cool thing we were seeing early on with the PET scan is that it was able to identify this lesion on the sesamoid bone that no other imaging modality was able to up until this point,” he said. “That was the real exciting thing for me as a racetrack practitioner because you look at the necropsy reports and you see where these things fracture repeatedly, but you're still left scratching your head saying how do I figure this out before the horse ends up on the necropsy floor.”
The Stronach Group invested $500,000 for the first ever MILEPET scanner that allows horses to be examined while standing and under sedation to be installed at Santa Anita Park in December 2019.
“We purchased the machine, which allows for a greatly reduced cost to the owner,” Dr. Dionne Benson, the chief veterinary officer for the Stronach Group, said. “You're talking about approximately, over a private facility, a 50 percent or more reduction in cost.”
It's one thing to show success in the laboratory and an entirely different undertaking for it to be applicable to the real world, especially one as fast-paced and unpredictable as horse racing.
“With any new imaging technology that comes on the market, there's always this big learning curve,” Carpenter said. “There's a learning curve of what's normal and what's abnormal, when do we react and when are we overreacting.”
However, the PET scan proved to be a front-runner capable of a sub-22-second opening quarter mile.
“The amazing thing about the PET technology,” Carpenter said, “is that from a new imaging modality that's been rolled out, I would say it's probably the smoothest and most seamless type of modality we've had that can be integrated into clinical practice. I don't think there was much of a time when we didn't fully understand what we're doing.”
The PET scan technology builds upon previous work done on the racetrack with other bone scanning modalities. Now, veterinarians like Carpenter and Spriet are looking to build upon the initial successes of the PET scan technology with research into how horses' PET scans evolve over time. One longitudinal study looks at horses returning from layoffs. Another examines horses that have won races to study what their PET scans look like. The total number of horses that have undergone PET scans is approaching 500. (“We're throwing a party for 500,” Spriet joked.)
Access to PET scans is part of the formula that has helped Santa Anita reduce its number of racing fatalities to three out of more than 4,800 starters during its 2021-22 meet. That represents a 74 percent reduction since the installation of the first MILEPET scanner at Santa Anita.
“I'm super grateful that the private veterinarians have embraced these technologies like they have,” Benson said. “As we continue down the road, I'm hopeful that the veterinarians and trainers will continue to embrace these technologies as tools, not as judgment and jury, and that way, we'll just be able to keep horses safe more effectively.”
As veterinarians are getting a handle on the promise that PET scans have shown in clinical practice, so are racehorse trainers. Trainer Doug O'Neill said he's found the technology helpful in determining whether a horse needs a layoff to prevent an injury – and when they don't.
“We have found the PET scan to be very useful from both the perspective of pinpointing the problem but also giving us a level of confidence to know the horse will not get hurt in a race,” he said. “When you have a clean PET scan, you know your horse is 100 percent safe to run and that's a good feeling.”
O'Neill said the 3-year-old bay filly It's Simple that he trains for Reddam Racing showed a change in her PET scans from before winning an allowance optional claiming race at Santa Anita on May 1 to after her fifth-place finish in the Melair Stakes at the track on May 28.
“We did it and gave confidence to press on but then it was clear when we needed to stop,” O'Neill said.
Spriet's initial idea of applying PET scans to horses is extending to other species of animals as well.
“There's a big concept right now in health research, the concept of 'One Health,'” Spriet said. “It's the concept that health involves the health of humans, animals, and the environment and combining that so you learn from one species to another.”
It's now coming full circle back to humans as well.
“The Santa Anita racehorses are the first population of athletes that have been followed up as much with PET because in the human field it has not been used that much,” Spriet said. “It's coming. There's more and more interest into that. I have presented some of the racehorse stuff at a human conference, and it's kind of fun because we vets are usually learning from the human doctors, but once in a while, we have animals that can inspire people like football players and track athletes.”
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