Abstract:

Measurements of mechanical properties of tissue can be used in many applications ranging from disease diagnosis to treatment planning and monitoring. In this paper, we present a technique to measure mechanical properties of the tissue undergoing laser surgery during which the cavitation bubble is introduced. Utilizing the laser‐induced microbubble, the mechanical properties of the tissue were assessed by measuring displacement and oscillations of the bubble under applied acoustic radiation force. The bubbles were produced using a nanosecond pulsed laser operating at 532 nm. Using the lens (0.92 numerical aperture, 11.5‐mm focal length), the laser beam was focused inside the gelatin to create microbubbles ranging from 80‐ to 250‐cm diameter. The bubbles were then interrogated using acoustic pulses of different durations and amplitudes. First, the size of each laser‐induced microbubble was estimated by measuring the laser‐produced shock wave and pulse‐echo ultrasound signals. Then, a 1.5‐MHz transducer generated an acoustic radiation force to displace the microbubble while a 25‐MHz transducer probed the microbubble continuously to measure the resulting displacement. Finally, using theoretical model, viscoelastic properties of the medium were assessed from the measurements of the bubble dynamic behavior. The results were verified using optical methods.