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Correlation of Positron Emission Tomography and Low-Field Standing Magnetic Resonance Imaging in Horses With Forelimb Lameness Localized to the Foot.
Abstract: Low-field magnetic resonance imaging (LF-MRI) and positron emission tomography (PET) imaging can be obtained in the standing horse. There is potential for increased diagnostic capacity combining PET with MRI, given that PET assesses the metabolic activity of injured tissues, whereas MRI provides structural and functional details on both bone and soft tissue anatomy. This study aimed to describe 18-fluorine-fluorodeoxyglucose (F-FDG)-PET and 18-sodium fluoride (F-NaF)-PET imaging of horses with forelimb lameness localized to the foot and compare PET with LF-MRI. Fourteen horses with lameness localized to the foot underwent standing MRI and PET with a dual-tracer protocol. MRI abnormalities and PET isotope uptake were subjectively graded. Weighted kappa statistics were used to compare the agreement between the ordinal grading of MRI and PET images. Maximum, minimum, and mean standard uptake values (SUV) were calculated at increased radiopharmaceutical uptake (IRU) regions. Metabolic volume (MV) within a cuboidal area of the IRU was calculated. No clinically significant kappa results were obtained comparing MRI to F-FDG-PET or F-NaF-PET. The mean SUV of background radiation was significantly lower than the mean SUV for subjectively mild and moderate-severe F-NaF-PET (p < 0.001). When comparing the SUV ratio for subjectively mild and moderate-severe groups, there was no significant difference between the two (p = 0.546). The major limitation of the study was the small population size. Low-field MRI may underrepresent bone remodeling and potentially misrepresent the source of lameness. We report various standardized uptake values and MVs for regions within the foot with IRU for F-FDG and F-NaF.
© 2026 The Author(s). Veterinary Radiology & Ultrasound published by Wiley Periodicals LLC on behalf of American College of Veterinary Radiology.
Publication Date: 2026-07-11 PubMed ID: 42433009DOI: 10.1111/vru.70211Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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Overview
- This study investigates how two imaging techniques, positron emission tomography (PET) and low-field magnetic resonance imaging (LF-MRI), compare in diagnosing foot-related forelimb lameness in horses.
- It specifically examines the correlation between PET scans using two tracers and LF-MRI to understand their diagnostic strengths and limitations.
Background and Rationale
- Both LF-MRI and PET can be performed on standing horses, making these imaging methods practical and less stressful for the animals.
- LF-MRI provides detailed structural and functional information about bone and soft tissue anatomy.
- PET imaging reflects metabolic activity in tissues, offering insights into physiological changes associated with injury.
- The study suggests combining PET with MRI could improve diagnostic accuracy because they offer complementary information: metabolic (PET) versus anatomical (MRI).
Objectives
- To describe and analyze PET imaging using two tracers—18-fluorine-fluorodeoxyglucose (F-FDG), which highlights metabolic activity, and 18-sodium fluoride (F-NaF), which detects areas of bone remodeling—in horses with forelimb lameness localized to the foot.
- To compare PET imaging results with those from LF-MRI to evaluate the concordance and explore potential diagnostic advantages or discrepancies between the modalities.
Methods
- Fourteen horses with forelimb lameness localized to the foot were included in the study.
- They underwent standing LF-MRI and PET scans using a dual-tracer protocol involving both F-FDG and F-NaF radiopharmaceuticals.
- Abnormalities observed on MRI and areas of increased uptake in PET were subjectively graded on an ordinal scale, indicating severity or intensity.
- Weighted kappa statistics were used to assess the agreement between MRI and PET grading systems, reflecting how similarly the two methods evaluated the same lesions.
- For PET images, standard uptake values (SUV) including maximum, minimum, and mean were calculated in regions showing increased radiopharmaceutical uptake (IRU).
- Metabolic volume (MV) within a defined cuboidal area around IRU sites was also measured to quantify the extent of metabolic activity.
Key Results and Findings
- No clinically significant agreement (kappa statistics) was found between MRI findings and either F-FDG-PET or F-NaF-PET, indicating that the two imaging modalities may identify different pathological features or interpret lesions differently.
- The mean SUV from background (normal tissue) was significantly lower than SUVs observed in mild or moderate-severe lesions on F-NaF-PET, confirming that F-NaF uptake accurately reflects pathological bone remodeling.
- There was no significant difference in SUV ratios between mild and moderately severe groups, suggesting SUV intensity alone may not reliably separate different severities of pathology as assessed by subjective grading.
Interpretation and Clinical Implications
- The poor agreement between MRI and PET imaging suggests that LF-MRI might underrepresent bone remodeling changes that PET, especially using F-NaF, can detect through metabolic activity.
- This discrepancy could lead to misidentification or underestimation of the source of lameness when relying on LF-MRI alone.
- Using PET alongside LF-MRI might improve diagnosis by identifying areas of active bone turnover or metabolic changes not evident on MRI images.
- The study provides standardized quantitative measures (SUVs and MV) from PET scans in the equine foot, potentially serving as reference values for future diagnostics and research.
Limitations
- The study’s major limitation is the small sample size of only fourteen horses, which may impact the generalizability and statistical power of results.
- Subjective grading of lesions introduces potential observer bias and variability in interpretation.
- The standing low-field MRI used may have lower spatial resolution compared to high-field MRI, restricting its sensitivity to certain pathological changes.
Conclusions
- PET imaging using F-FDG and F-NaF provides valuable metabolic information about bone and soft tissue lesions in horses with forelimb foot lameness that is not fully captured by LF-MRI.
- A combined imaging approach may enhance diagnostic accuracy by merging anatomical and functional/metabolic perspectives.
- The authors report quantitative metrics from PET that may assist future studies and clinical assessments focused on foot lameness in horses.
Cite This Article
APA
Kelleher ME, Aarsvold S, Anishchenko SI, Gokun Y, Beylin D, Zhu X.
(2026).
Correlation of Positron Emission Tomography and Low-Field Standing Magnetic Resonance Imaging in Horses With Forelimb Lameness Localized to the Foot.
Vet Radiol Ultrasound, 67(4), e70211.
https://doi.org/10.1111/vru.70211 Publication
Researcher Affiliations
- College of Veterinary Medicine, Veterinary Medical Center, The Ohio State University, Columbus, Ohio, USA.
- Puchalski Equine Imaging, Petaluma, California, USA.
- Alienbyte Scientific Software Inc., Rockville, Maryland, USA.
- Wexner Medical Center, Center for Biostatistics, The Ohio State University, Columbus, Ohio, USA.
- LONGMILE Veterinary Imaging, Brain Biosciences Inc., Rockville, Maryland, USA.
- Virginia-Maryland College of Veterinary Medicine, University of Maryland, College Park, Maryland, USA.
Grant Funding
- 6410 / Maryland Industrial Partnerships
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