Positron Emission Tomography (PET)

Photo: PET scan of horse

The photo on the left shows the portable PET scanner used for equine PET imaging. On the right, the left foot of a horse is being imaged with the system.

In May of 2016, the UC Davis veterinary hospital acquired a positron emission tomography (PET) scanner, becoming the first veterinary facility in the world to utilize the imaging technology for equine patients. In association with the UC Davis School of Veterinary Medicine’s Center for Equine Health (CEH), the hospital will launch use of the PET scanner in the summer of 2016. The unit has been acquired for research and clinical studies on lameness diagnosis in horses.

In 2015, veterinary radiologists from UC Davis were the first to ever image a horse using a prototype of the newly acquired scanner. This presented a major breakthrough in equine imaging, as PET imaging of horses had not been previously possible due to positioning restrictions of equine patients inside the standard PET instruments. With the new portable design, PET can now be applied to improve management of cases of equine lameness. The scanner weighs only 50 pounds, and was specifically designed for animal imaging.

Although PET is mostly used in human medicine for the detection of cancer metastasis and for functional assessment of the brain, last year’s UC Davis study demonstrated promising applications for assessing the musculoskeletal systems of horses.

Photo: PET image of horse hoof

PET images (left column) of an equine foot with corresponding CT images (center). On the right, the PET and CT images have been fused. This demonstrates that the active lesion identified with the PET is a fragment at the distal border of the navicular bone (top row). On the bottom row, the PET identifies an area of osseous remodeling at a ligament attachment that could not be detected on the CT images.

The idea of attempting to use PET imaging in horses came from a 2014 discussion between Dr. Mathieu Spriet, a UC Davis veterinary radiologist, and Dr. Ramsey Badawi, a PET physicist from the UC Davis School of Medicine (SOM). Dr. Badawi had recently designed a PET scanner for human breast imaging, demonstrating that the PET technology had matured to create smaller scanners dedicated to specific body area imaging, compared with the classic scanners designed to image larger body areas. The two imaging specialists worked with a private company (that had recently designed a portable PET scanner for imaging of the human brain) to create a portable unit for veterinary purposes.

With financial support from CEH, Dr. Spriet designed a pilot study to image six horses with the veterinary prototype. PET images of the feet, fetlocks, carpi and tarsi were obtained, and two different radiomarkers were tested. Data was then compared with other advanced imaging modalities (computed tomography [CT], magnetic resonance imaging [MRI] and scintigraphy) obtained on the same horses. Depending on the radiomarker used, information regarding both the soft tissue and the bone could be obtained. The strength of PET, when compared with CT or MRI, is that it provides information at a molecular level, regarding the activity of lesions.

Dr. Spriet’s research demonstrated that PET could distinguish between active and inactive tendon lesions. PET was also useful to demonstrate regional difference in metabolic activity in the feet of a horse with chronic laminitis. The use of a bone marker led to the detection of lesions at the attachment of ligaments or below the articular cartilage, which could not be identified with any other imaging modalities.

Patients likely to benefit from this novel imaging technique include cases for which other imaging modalities could not identify a lesion to explain the lameness, or patients where multiple lesions are identified and it is unclear which one is causing the lameness. PET will also likely be an important tool in assessing healing of known lesions, helping to optimize the rehabilitation program. UC Davis is now the first institution to offer PET scans to clinical equine patients.

Beyond large animal applications, this system will also provide opportunities for PET research in small animals at UC Davis. Projects regarding the extension of tumors and the detection of metastases in dogs have been submitted to the SVM’s Center for Companion Animal Health annual grant call.

The PET scanner acquisition was funded by the Grayson-Jockey Club Research Foundation and private donors through CEH. A series of research projects during the summer will help refine imaging protocols and acquire further reference data on the PET scanner. In the fall, a clinical trial regarding the use of PET to detect bone lesions in horses will commence. Additional clinical studies will likely begin in 2017, as further information becomes available from continued use of the PET scanner.

The hospital’s Diagnostic Imaging Service is proud to be leading this groundbreaking research in equine imaging. This program—as many other SVM success stories—succeeded because of strong collaborations with the SOM and the UC Davis Department of Biomedical Engineering. It is yet another example of how CEH research funded by private donors can translate into cutting-edge clinical application at the UC Davis veterinary hospital.