PET Scan: A New Diagnostic Imaging Option for Horses

Last year, researchers from the University of California (UC), Davis, performed the first-ever positron emission tomography (PET) scan on a horse. In human medicine, physicians use this technology to diagnose conditions ranging from cancer to brain damage to heart and bone problems. It had never been applied to horses for logistical reasons, but a recently developed portable scanner is changing that.

Mathieu Spriet, DVM, MS, Dipl. ACVR, ECVDI, associate professor of surgical and radiological sciences at the UC Davis School of Veterinary Medicine, led a study to determine whether PET scans could be useful for diagnosing lower limb injuries in horses. He presented his team’s results at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.

How does this imaging modality work? Like with a scintigraphic scan, the veterinarian injects a small amount of radioactive tracer into the patient to obtain an image.

“But instead of getting a single (two-dimensional) image, we’re getting a series of images through the body, giving us much more information than the classic scintigraphic scan,” Spriet explained.

In their study, Spriet and his colleagues imaged six research horses with lameness localized to the lower limb. They took PET images of the front feet and fetlocks, knees, and hocks using soft tissue as well as bone markers to detect lesions. They also performed computed tomography, standing MRI, and scintigraphy for comparison.

On the PET scan results they detected early indications of lesions in areas such as the navicular bone, subchondral bone (located just under the cartilage surface within a joint), flexor tendons, suspensory ligament, and lamina. Several of these lesions, particularly on ligament attachments and subchondral bone, weren’t visible using the other imaging modalities.

“PET scan looks at the molecular level and can find some changes that we do not see yet with other modalities,” said Spriet. “It’s not going to be the first modality that you pick to assess a lameness, but it’s more of an option when we haven’t found the answer with other imaging modalities.

“The other advantage of PET scan is that you can tell whether the lesion is active or not,” he continued. “Sometimes we have old lesions that aren’t causing a problem anymore, and the PET scan helps you distinguish what’s an old lesion and what’s a more recent active lesion actually causing a problem.”

Spriet and his team concluded that PET images of horses’ lower limbs are easily obtained and might be particularly useful for tendinopathy and laminitis research.