Variation in the MRI signal intensity of naturally occurring equine superficial digital flexor tendinopathies over a 12-month period.

Background Signal intensity (SI) of equine tendinopathies in MRI differs between the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). In DDFT lesions, short tau inversion recovery (STIR) SI decreases earlier than T2-weighted (T2w) SI, while the latter decreases earlier in SDFT lesions, but long-term results using STIR sequences are lacking. Methods Standing MRI of eight horses with naturally occurring SDFT lesions was performed at the day of treatment as well as 2, 6 and 12 months after treatment. Results After 12 months, six horses were sound and showed complete resolution of increased SI in T2w fast spin echo (FSE) images, but increased SI was found in STIR images in three horses and persisted in T1w and T2*w gradient recall echo images of all horses. In contrast, hyperintense areas were still visible in the SDFT in T2w FSE images in two horses presenting with re-injury. In the six horses without re-injury, percentage of cross-sectional areas affected and SI decreased over time in all sequences. Conclusions This study suggests that SI in naturally occurring SDFT lesions decreases earlier in T2w FSE than in STIR images, in contrast to the DDFT.