New technology will allow upright PET scanning of horse limbs

A research horse from the University of California, Davis, Center for Equine Health being imaged with the MILE-PET scanner at the university’s veterinary hospital.

The first PET scanner specifically designed to image the limbs of standing horses has passed the first important hurdle in an ongoing study.

The PET scanner, which stands for positron emission tomography, has been checked for safety, and protocols for scanning have been set up using research horses from the University of California, Davis, Center for Equine Health.

It will now be moved to the veterinary hospital at California’s iconic Santa Anita racecourse, where it is hoped the machine will play a part in reducing a worrying level of horse fatalities at the track.

PET scanners are used for imaging in nuclear medicine. The scan uses a special dye containing radioactive tracers.

The university’s School of Veterinary Medicine, in collaboration with Longmile Veterinary Imaging, announced the completion of the first phase of the validation of the MILE-PET scanner this week.

The advantage of the device is that it will allow PET scans to be carried out on the limbs of horses while standing using light sedation, eliminating the need for anesthesia.

This will allow many racehorses at Santa Anita to be imaged, in the hopes it will reveal early warning signs in horses that put them at risk of catastrophic breakdown.

Dr Mathieu Spriet, associate professor of veterinary radiology at the university, supervised the validation work.

Six horses were imaged twice with the standing scanner and once under general anesthesia. This allowed the researchers to confirm the repeatability of findings and to compare with results obtained with the technique previously developed on anesthetized horses.

The horses tolerated all of the procedures well. All imaging sessions were successful, and no complications were reported. The quality of images obtained on the standing horses was similar to the ones performed under general anesthesia.

A three-dimensional PET scan of the fetlock of a 2-year-old Thoroughbred recently retired from race training. It was acquired with a four-minute scan time. The yellow areas demonstrate regions of bone changes as an adaptation to race training.

“I am very excited to report that everything worked according to plan, if not better. I am very impressed with the quality of images we were able to obtain,” Spriet said.

Scan lengths ranging from 1 to 10 minutes were compared, and the team of experts concluded that a 4-minute scan is long enough to obtain images of high diagnostic quality.

The speed of acquisition is a great advantage for the horses, as multiple areas can be imaged with just a short sedation time.

The focus of the initial validation study was on the fetlock joint, as this is the area most commonly injured in racehorses. However, the researchers were also able to obtain high-quality images of the foot and carpus (horse knee).

The MILE-PET is now ready to image racehorses in training. This clinical trial will begin at the university before the scanner is moved to Santa Anita Park in mid-December.

The Stronach Group, owners of Santa Anita Park, and the Southern California Equine Foundation, which operates the veterinary hospital at Santa Anita, have been key partners in the project by supporting the scanner development costs.

Although the project has been in the works for more than a year, the recent highly publicized horse fatalities in Southern California have highlighted the need for improved safety in horse racing.

The availability of imaging techniques that are able to detect bone changes that might predispose to catastrophic breakdowns is one of the measures that has been proposed to reduce the track fatalities.

“PET has a very interesting role to play in racehorses, as it detects changes at the molecular level, before structural changes occur,” Spriet explains.

“In other words, PET provides warning signs that injuries might happen. There is still a lot of work ahead of us, as we need to learn to distinguish the PET changes that reflect normal adaptation to speed work from changes that are indicative of high risk for major injuries.”

The plan is to image as many horses as possible at Santa Anita over the coming year.

Once the researchers have established a large database representing the different patterns of PET findings in racehorses, patterns at risk for breakdown will be identified.

PET scanning will ultimately become an additional tool to help in the management of racehorses with gait abnormalities in order to prevent breakdown.

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