18F-sodium fluoride positron emission tomography of the equine distal limb: Exploratory study in three horses

BackgroundPositron emission tomography (PET) is a cross-sectional, functional imaging modality that has recently become available to the horse. The use of F-18-sodium fluoride (F-18-NaF), a PET bone tracer, has not previously been reported in this species. ObjectivesTo assess the feasibility of F-18-NaF PET in the equine distal limb and explore possible applications in the horse in comparison with other imaging modalities. Study designExploratory descriptive study involving three research horses. MethodsHorses were placed under general anaesthesia prior to intravenous (i.v.) administration of 1.5 MBq/kg of F-18-NaF. Positron emission tomography imaging of both front feet and fetlocks was performed using a portable scanner. Computed tomography (CT) of the distal limb was performed under a separate anaesthetic episode. Bone scintigraphy and magnetic resonance imaging (MRI) were subsequently performed under standing sedation. Images obtained from PET and other imaging modalities were independently assessed and the results correlated. ResultsPositron emission tomography images were obtained without complication. The radiation exposure rate was similar to equine bone scintigraphy. Positron emission tomography detected focal F-18-NaF uptake in areas where other imaging modalities did not identify any abnormalities. This included sites of ligamentous attachment, subchondral compact bone plate and the flexor cortex of the navicular bone. F-18-NaF uptake was identified in some, but not all, osseous fragments and areas of osseous formation, suggesting a distinction between active and inactive lesions. Main limitationsA small number of horses were included and histopathology was not available. Conclusions(18)F-NaF PET imaging of the equine distal limb provides useful additional information when compared with CT, MRI and scintigraphy and has the potential for both research and clinical applications in the horse. The Summary is available in Chinese - see Supporting information.