Pioneering PET scanner helping horses stay on track to recovery


Above: 3D video of a PET scan of a front ankle showing multiple injuries in several bones. The yellow areas indicate precisely the sites of injury.

The equine Positron Emission Tomography (PET) scanner pioneered by the UC Davis School of Veterinary Medicine, in collaboration with Longmile Veterinary Imaging, is now in heavy use at Santa Anita Park in Southern California.

In just over six months since the installation in December 2019, with the financial support from the Stronach Group, more than 100 scans have been performed with the “Milepet” (Molecular Imaging of Limbs in Equids), the PET scanner specifically designed to acquire images on horses without the need to lay them down.

Overall, 65 horses were imaged with the scanner, with several horses imaged multiple times, several weeks apart. In total, images of 186 front fetlocks, 28 hind fetlocks, 16 knees, and 11 feet were acquired. The front fetlocks were the main area of interest, as these are the joints most commonly involved in severe injuries in racehorses.

The Milepet scanner positioned to image a hind ankle. Although front ankles are most commonly imaged, the Milepet also allows scanning the hind ankles.
The Milepet scanner positioned to image a hind ankle. Although front ankles are most commonly imaged, the Milepet also allows scanning the hind ankles. © UC Davis

The first objective after installation of the scanner at the racetrack was to complete a study, funded by the Grayson Jockey Club Research Foundation, aiming at assessing the value of PET for identification and follow-up of injuries. The study called for 24 horses with signs of fetlock injuries to be imaged three times with the PET scanner, with follow-up scans six and 12 weeks after the initial scans. All 24 horses have now been enrolled, and over half of these horses have completed all their three scans.

All scans were successful, providing very interesting preliminary results.

“The PET scans provide very precise information about the injury,” said Dr Mathieu Spriet, associate professor of diagnostic imaging at UC Davis and lead veterinarian on the study. “With a classic ‘bone scan,’ we usually can associate the injury with one of the bones of the ankle, but with the PET, we can really localize the abnormality to a specific area in a bone.”

This is of particular importance, as injuries to specific areas of the ankle bones are known to predispose horses to catastrophic breakdown.

Another benefit of the PET scan is the ability to see changes over time.

“As we have repeated scans six weeks apart, we have seen marked improvement on many of the injuries following treatment and rest, whereas other injuries remained active,” Spriet said.

The image on the left is the original scan (same as video). The image on the right was obtained 6 weeks later.
PET scan images from the same fetlock shown in the video. The image on the left is the original scan (same as video). The image on the right was obtained 6 weeks later. There has been improvement of most of the injuries with treatment and rest, but the persistence of yellow areas indicate that the horse is not ready yet to go back to training. © UC Davis

“Being able to assess the response of an injury is very helpful to decide the course of action: deciding whether a horse needs more time off, a different treatment, can go back to the track or should be retired from racing – these are very challenging decisions to make for the veterinarians at the track. The PET images have provided objective data to support these decisions.”

In addition to the 24 horses in the Grayson Jockey Club study, more than 40 horses have been scanned at the request of their veterinarians. Horses were sent in by 14 different veterinarians coming from 26 different trainers, demonstrating how broadly the technique has already been embraced by the Santa Anita racing community.

As a Magnetic Resonance Imaging (MRI) scanner was also installed at Santa Anita Park earlier this year, another on-going study, supported by the Oak Tree Foundation, aims at comparing PET and MRI findings in the fetlocks of racehorses. Twenty horses have been enrolled in this study with preliminary results demonstrating the complementarity of both techniques to provide the best assessment of various injuries.

The Milepet scanner at work at Santa Anita. © UC Davis

Another study, supported by the Dolly Green Research Foundation, has recently started. This study aims at monitoring horses who are resuming training after being laid-up following a fetlock injury. The goal is to assess the fetlock regularly to be able to adapt the training if early signs of injury were to recur.

“It is very impressive how much has been accomplished and how much we have learned in the last six months, thanks to the support of key partners and the hard work of the technical staff and the veterinarians at Santa Anita Park,” Spriet said. “We have been able to establish this new technology as a reliable, high-precision diagnostic tool for racehorses.”

It is likely that the knowledge about PET will keep growing quickly. In addition to the different on-going studies at Santa Anita Park, this technology is now available outside of California, as a Milepet scanner has just been installed at New Bolton Center, the equine veterinary hospital of the University of Pennsylvania. There are also on-going efforts to secure the funding to install another Milepet at the UC Davis Veterinary Medical Center, where it would be available for racehorses from Golden Gate Fields and for sport horses across Northern California.

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