Application of Contrast-Enhanced Sonography With Time-Intensity Curve Analysis to Explore Hypervascularity in Achilles Tendinopathy by Using a Rabbit Model

OBJECTIVES: The purpose of this study was to investigate the ability of contrast-enhanced sonography in staging and grading hypervascularity in tendinopathic tissues by using a rabbit model. METHODS: Fourteen rabbits were injected with 100 and 50 μL of collagenase in their left and right Achilles tendons, respectively. The vascularity was assessed by non-contrast-enhanced and contrast-enhanced power Doppler sonography on day 0 (baseline) and days 1, 7, and 14 after collagenase injections. Color pixels within targeted areas were plotted according to time and analyzed by a curve-fitting method. RESULTS: Non-contrast-enhanced power Doppler sonography failed to differentiate vascularity at various stages or between bilateral tendons, whereas contrast-enhanced sonography showed that the peak color pixel amount reached its maximum on day 1 and declined over time in tendons treated with 100 μL of collagenase. A similar trend was observed in tendons receiving 50 μL of collagenase. For comparisons between bilateral tendons, higher vascularity was detected in those treated with more collagenase on day 1 or 7. Time-intensity curve analysis revealed rapid microbubble replenishment in both tendons during their initial phase after collagenase injections. CONCLUSIONS: Contrast-enhanced sonography discriminated the vascularity of various injury grades at different time points after collagenase injections. Time-intensity curve analysis detailed the hemodynamics in tendinopathic tissues, which helped differentiate vascularity in acute inflammatory from later degenerative phases.