A reproducible method to image the rat Achilles tendon anatomy by 7 Tesla Magnetic Resonance Imaging (MRI) - a feasibility technical note.

BACKGROUND: Achilles tendon rupture is the most common tendon injury, yet current methods to monitor healing remain largely qualitative and observer dependent. Magnetic Resonance Imaging (MRI) offers a non-invasive, quantitative alternative with translational potential from bench to bedside. Here we establish a standardized preclinical MRI protocol that could be used for longitudinal assessment of rat Achilles tendon healing in the future, with emphasis on reproducible anatomical positioning and visualization of subtendon anatomy. METHODS: Imaging was performed at 7T using a custom positioning mold to stabilize the hind limb and flatten the posterior tendons against a surface coil. RESULTS: 3D T1-weighted morphological scans enabled high-resolution visualization of the tripartite subtendon organization - soleus, medial gastrocnemius, and lateral gastrocnemius - which were visually delineated using multi-planar reformatting in 3D Slicer. Intra- and inter-observer variability yielded moderately good dice similarity coefficients. CONCLUSIONS: The rat Achilles tendon recapitulates human subtendon architecture, supporting its validity as a translatable model. The described setup enables reproducible delineation of subtendon anatomy and is well suited for future investigations into acute tendon injuries, treatment response, and healing.