New PET scanner for horses a world first

UC Davis' new portable PET scanner is the first of its kind to be used to image horses.
UC Davis’ new portable PET scanner is the first of its kind to be used to image horses.

The PET scanning of horses could be “the next big revolution in equine imaging since the development of MRI”, and the UC Davis veterinary hospital in California is at the forefront of the technology.

Davis will be the first veterinary facility in the world to use a positron emission tomography (PET) scanner for equine patients when the new tool is launched this summer.

The unit has been acquired in association with the UC Davis School of Veterinary Medicine’s Center for Equine Health (CEH) for research and clinical studies on lameness diagnosis in horses.

The image on the left is a transverse PET image through the pastern of the horse. The black area is the short pastern bone (middle phalanx). The arrows indicates focal increased signal in the soft tissue at the back of the pastern. The PET image can be fused to a CT image to confirm the anatomic location of the lesion. The fused imaged (right) confirms that the lesion is on the border of the deep digital flexor tendon (marked with arrow heads).
The image on the left is a transverse PET image through the pastern of the horse. The black area is the short pastern bone (middle phalanx). The arrows indicates focal increased signal in the soft tissue at the back of the pastern. The PET image can be fused to a CT image to confirm the anatomic location of the lesion. The fused imaged (right) confirms that the lesion is on the border of the deep digital flexor tendon (marked with arrow heads).

While most other imaging techniques provide “morphological” information (identifying changes in size, shape or density of structures), PET is a “functional” imaging technique, observing activity at the molecular level – detecting changes in the tissue before the size or shape is modified. Once morphological changes have occurred, PET can tell whether the changes are still active or not.

“In practicality, that means two things,” said Dr. Mathieu Spriet, a UC Davis veterinary radiologist. “One, PET can detect lesions that other advanced modalities do not identify, and two, it can tell us if a lesion — identified with another modality — is a significant injury or not.”

Initial data obtained last year at UC Davis during a research project using a prototype of the new scanner demonstrated great success for bone imaging.

“Preliminary data suggests that PET will be the next big revolution in equine imaging since the development of MRI,” said Spriet.

To confirm the findings, UC Davis will launch a clinical trial later this year, using horses for which other advanced imaging modalities (MRI, CT or nuclear scintigraphy) have failed to identify the cause of the lameness, and horses for which the results of other imaging modalities are confusing due to the presence of multiple abnormalities or equivocal findings.

PET has also shown great promises in evaluating soft tissue lesions, in particular regarding laminitis and tendon lesions. Research studies gathering further information in these specific areas will commence shortly at UC Davis. As more data becomes available, additional clinical trials will likely develop.

Combined PET and CT images of the foot of a 20-year-old Thoroughbred.
Combined PET and CT images of the foot of a 20-year-old Thoroughbred. The PET demonstrates an active lesion of the navicular bone (white arrows) as well as abnormal uptake in the bone adjacent to the pastern joint (black arrow). This second lesion was not seen on the CT, but suggests early degenerative changes that could lead to the development of a bone cyst.

Support for research projects and clinical trials involving PET, as well as the acquisition of the scanner, was provided by the Grayson-Jockey Club Research Foundation and private donations through CEH.

“We’re grateful that our donors can see the vision of what these new technologies can bring to equine health,” said Dr Claudia Sonder, director of CEH.

“We look forward to this PET research translating to cutting-edge clinical applications at the UC Davis veterinary hospital.”

First patient diagnosed with PET

A horse named “Fancy Piece of Candy” — an 18-year-old quarter horse mare known to have a lesion in her left front foot — was the first horse to be PET scanned at UC Davis during the research project last year.

The mare was placed under general anesthesia and injected with 35 mCi of 18F-FluoroDeoxyGlucose (F-FDG), the most common radionuclide used in PET imaging. Starting one hour after injection, the feet and fetlocks of both front limbs were imaged. Each site took 15 minutes to image. The mare recovered safely after the imaging procedure.

Images were created in three different planes, and the anatomy of the distal limb could easily be identified. An area of marked increased in radionuclide uptake was identified in the navicular bone of the left front foot, confirming the presence of an active lesion. Additionally, an area of increased uptake was present in the soft tissue at the back of the foot, in the area of one of the major tendons.

Sagittal PET images through the foot of the normal (left) and lame (right) limb of the horse. The arrow indicates increased signal in the area of the navicular bone of the lame limb due to the presence of a lesion.
Sagittal PET images through the foot of the normal (left) and lame (right) limb of the horse. The arrow indicates increased signal in the area of the navicular bone of the lame limb due to the presence of a lesion.

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