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Chronic degenerative Achilles tendinopathy (tendonitis) is a common clinical problem and its aetiology remains in part unexplained. For the treatment of Achilles tendinopathy, there were a lot of modalities including medication, physical agents, physiotherapy, and exercise. However, how to evaluate the effects of current therapeutic modalities and study the therapeutic mechanism in vivo remains a crucial problem. In this study, we show the potential of high-frequency ultrasound Doppler imaging for observation of Achilles tendon microcirculation of mice pre- and post-treatment and for exploration of the therapeutic mechanism with small animal models in vivo. A collagenase-induced Achilles tendinitis model of mice was also adopted here. Mice with collagenase-induced Achilles tendinitis were given a 45-kHz low-frequency ultrasound treatment, and then the morphology and microcirculation changes of Achilles tendons pre- and post-treatment were observed with B-scan, power Doppler, and color Doppler of a 25- MHz high frequency ultrasonic imaging system. Mouse Achilles tendon was about 4 to 5 mm in length and 0.5 mm in diameter. There were no focal hypoechogenic regions in normal Achilles tendons. Because of the immediate vascular dilatation resulting from the treatment of low frequency ultrasound, increase in microcirculation was observed within a shot period of time after treatment. In our future work, we will focus on imaging microcirculation changes of tendinosis pre- and post-treatment with long term time course study and expect to obtain more physiological information for future human study.