Assessing the Stiffness of the Achilles tendon using Laser Doppler Vibrometry

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There were approximately 232,000 Achilles tendon sports injuries in the United States for individuals six and over. The reasons for injuries are weak blood supply to the Achilles tendon and bowstring effect due to ankle pronation. Prior to tear of the Achilles tendon, the tendon may become thinner and not as stiff as normal. Achilles tendon surgery involves either a large incision in the back of the lower leg or several smaller incisions in the same area. Currently, doctors examine Achilles tendon injuries by using Magnetic Resonance Imaging (MRI) scan which can be expensive and time consuming. On the other hand, vibration-based methods can assess the stiffness of structures (such as beam, cables or human tendons) by measuring the propagation velocity of induced vibrations, in which faster propagation velocities indicate stiffer material or tissues. To determine the optima placement and positioning of the LDV and shaker along the Achilles tendon as well as optima frequency band for the shaker excitation to maximize the signal-to-noise ratio of the measured vibrations. The initial procedure included a vibration shaker to vibrate the Achilles tendon and a single Laser Doppler Vibrometer (LDV) to measure the guided vibrations propagating along the Achilles tendons a few cm away from the shaker. Data were recorded using Labview and analyzed with MATLAB. The data were collected multiple times to see the robustness of the setup. The vibration amplitude and frequency are extracted from the Doppler shift of the reflected laser beam frequency due to the motion of the surface. The target velocity component will be extracted as the output of LDV. At each collected data point the time domain of the delay of the response is shown. Repeated date collection at same position of the laser beam was assessed to see the robustness of the protocol. Table 1 shows the time delay of the response at the same point and their standard deviation. Our goal is to reduce the standard deviation between similar data collection sets. It can be concluded that assessing the stiffness of the Achilles tendon using Laser Doppler Vibrometry can ensure the safety and efficiency of diagnosing Achilles tendon injuries.