Another step forward in equine diagnostic imaging has been taken with the successful use of positron emission tomography (PET) on a standing horse.
The use of Equine PET was pioneered at UC Davis. The first horse was imaged in 2015, and until now, the equipment available has required horses to be under general anaesthesia for the examination to be performed.
PET shows the activity of bone or soft tissue lesions at the molecular level. A πPET scanner from Brain Biosciences, Inc. (Rockville, Maryland), was used to produce the first equine PET images. The device was originally designed to image the human brain, for research into conditions such as Alzheimer’s disease, Parkinson’s disease, Traumatic Brain Injury, Brain Cancer, and other neurological and psychiatric disorders.
A clinical program launched in August 2016 with support from the UC Davis Center for Equine Health (CEH) resulted in PET images of more than 100 horses. Reports on the research has been published*.
PET is particularly useful for detecting bone lesions that are not recognized using other imaging techniques, and for differentiating active and inactive injuries in bone or soft tissue. Movement of the subject could disrupt the image, so the early studies were carried out with the horse under general anaesthesia. Anaesthesia adds to the cost of the procedure, requires additional staff and equipment, and although rare, patients can have adverse reactions to anaesthetic drugs.
In order to develop a PET scanner specifically designed to address the unique needs of equine imaging, the PET research group at UC Davis, led by Dr. Mathieu Spriet, worked with the engineering team from Brain Biosciences, led by David Beylin and Pavel Stepanov.
PET images are captured using detectors arranged in a ring. The current research was performed on a prototype that used the ring of detectors present in the πPET scanner but placed horizontally on the ground. The detector unit was encased in a low protective shell. This permits imaging of the foot but keeps the ring low enough for the horse to step out of the scanner safely.
Two horses from the CEH research herd were imaged using the standing equine PET prototype for the first time on January 16, 2019 under the supervision of Spriet, with assistance from UC Davis equine surgery residents Drs. Jannah Pye and Bridget Nottle, and technical support from Rich Larson.
The clinicians positioned the front feet of the sedated horse in the centre of the ring of the scanner, one at a time.
High quality PET images, presenting 3-dimensional information, were captured within five minutes for each foot. Images were obtained on two consecutive days using the two most common PET tracers for equine imaging, the 18F-Sodium Fluoride (bone tracer) and the 18F-Fluorodeoxyglucose (soft tissue tracer). The entire procedure went smoothly, and the data collected confirmed the ability to acquire PET images of the equine forelimb in standing patients without motion artifacts compromising image quality.
Another important goal of this initial imaging session was to measure the radiation exposure to staff. Radiation measurements showed that the dose received by the staff was like that for scintigraphic bone scans, which are commonly performed in horses, thereby confirming the safety of the procedure.
“This is a major milestone in the development of clinical equine PET imaging,” said Spriet. “The ability to perform PET on standing horses will open many new clinical applications, such as following up on injury healing and screening for lesions at risk for catastrophic breakdown in racehorses.”
In order to image the standing horse limb from the foot to the knee, the ring of detectors needs to open freely to allow the horse to remove its leg from the instrument without getting hurt. Belin and Stepanov have validated a mechanical design for such a scanner, and effort is currently underway to build it.
For more details, see:
Positron emission tomography of the equine distal limb: exploratory study.
Mathieu Spriet, Pablo Espinosa, Andre Z. Kyme, Pavel Stepanov, Val Zavarzin, Stephen Schaeffer, Scott A. Katzman, Larry D. Galuppo, David Beylin,
Veterinary Radiology (2016) 57, p 630-638
18 F-sodium fluoride positron emission tomography of the equine distal limb: Exploratory study in three horses.
Spriet M, Espinosa P, Kyme AZ, Phillips KL, Katzman SA, Galuppo LD, Stepanov P, Beylin D.
Equine Vet J. (2018) 50, p125-132.