Low-field versus high-field MRI and CT for imaging subchondral bone resorption in isolated equine fetlocks

Introduction/Purpose
Subchondral bone changes can be identified in the equine fetlock using standing low-field MRI (LF-MRI) in clinical conditions. However, a relatively low signal-to-noise ratio, contrast and spatial resolution may affect how well focal resorptive changes can be detected. This study aimed to compare the ability to detect and classify subchondral bone resorptive changes of LF-MRI, in comparison to high-field MRI (HF-MRI) and CT.

Methods
CT, HF-MRI and LF-MRI images were obtained from 20 isolated equine fetlocks. Subchondral bone resorptive changes were first assessed by 2 experienced radiologists on HF-MRI and CT images and classified as subchondral plate irregularity, resorption, or cyst-like lesion. Then, a blinded evaluation of LF-MRI images was performed. Imaging findings were compared, and lesions were confirmed post-mortem.

Results
Twelve fetlocks exhibited subchondral resorptive changes in the metacarpus or proximal phalanx, with a total of 24 lesions (17 irregularities, 4 resorptions, 3 cyst-like lesions). LF-MRI accurately identified 2/3 cyst-like lesions (and misclassified 1 as resorption), 3/4 resorptions, and 2/17 irregularities.

Discussion/Conclusion
Although ex-vivo acquisition does not reflect in-vivo conditions, results suggest that LF-MRI can successfully detect advanced subchondral resorptive changes, which are crucial for prognosis in clinical conditions. However, its ability to identify subchondral plate irregularities, potentially representing an earlier stage of resorption, is limited.