The functional microstructure of tendon collagen revealed by high-field MRI.

T2 was used in this study to assess tendon microstructure. Two unloaded digital extensor tendons were bent such that their long axes were imaged throughout 180° with respect to B0. T2-weighted images reveal periodic banding (∼200 μm) when tendons were oriented at ±55° with respect to B0. Five pairs of tendons were used to study the influence of load on T2W MRI: one tendon of each pair was loaded with a 7.8-N mass, and both tendons were fixed in formalin then imaged at 55° to B0. MRI banding was present in the unloaded, but not loaded, tendons. In unloaded tendons, polarized-light microscopy revealed collagen crimp with a periodicity similar to MRI. In loaded tendons, there was a strain-induced extinction of periodicity on both MRI and polarized-light microscopy. These studies confirm that crimp is detectable by high-field MRI and could serve as an in vivo index of physiological strains in collagenous tissues.