Standardized uptake values and attenuation correction in 18 F-sodium fluoride PET of the equine foot and fetlock.
Authors: Kimberley Sannajust, M. Spriet, S. Anishchenko, D. Beylin
Journal: Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Summary
# Editorial Summary Standardised uptake values (SUVmax) derived from 18F-sodium fluoride PET imaging are increasingly used to quantify bone metabolic activity in equine limbs, yet reference ranges for the distal extremity have been poorly characterised in the literature. Sannajust and colleagues conducted a retrospective analysis of 19 feet and 19 fetlocks, defining 20 and 22 regions of interest respectively, to establish baseline SUVmax values with and without CT-based attenuation correction. Overall corrected SUVmax values were substantially higher than uncorrected measurements (5.0 ± 1.8 versus 3.6 ± 1.5 for feet; 3.8 ± 1.4 versus 2.9 ± 1.1 for fetlocks), with attenuation effects varying dramatically by anatomical region—the navicular bone and distal phalanx flexor surfaces showed corrections exceeding 74–83%, whilst dorsal proximal phalanx uptake was minimally affected at 5.2%. Notably, the distal phalanx, particularly the toe and dorsal regions, demonstrated significantly higher metabolic activity (SUVmax 7.7 and 7.5 respectively) compared with other structures, reflecting normal physiological loading patterns. These reference values and attenuation correction data are essential for accurate interpretation of equine PET studies and refine clinical decision-making regarding lameness investigations, though the authors appropriately note that uncorrected images retain diagnostic value when CT-based correction is unavailable.
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Practical Takeaways
- •Reference SUVmax values provided can help standardize interpretation of 18F-NaF PET scans in equine distal limbs and aid diagnosis of navicular syndrome and other foot pathology
- •Attenuation correction should be applied when CT data are available, but absence of correction does not invalidate clinical assessment in routine practice
- •High uptake in distal phalanx and navicular regions is normal; clinicians should compare contralateral limbs and serial imaging rather than relying on absolute values alone
Key Findings
- •Overall SUVmax in equine feet was 3.6±1.5 (NAC) and 5.0±1.8 (CTAC); fetlocks were 2.9±1.1 (NAC) and 3.8±1.4 (CTAC)
- •Navicular center showed highest attenuation correction at 83.4%, followed by distal phalanx flexor surface at 81.3%
- •Distal phalanx regions (toe, dorsal, central) demonstrated significantly higher SUVmax (6.1–7.7) compared to other foot areas
- •Attenuation correction increased signal intensity by less than doubling, suggesting non-corrected images remain clinically useful for interpretation