Young's modulus estimation of bovine lens ex-vivo using a laser-induced microbubble under impulsive acoustic radiation force.
ABSTRACT According to the most widely accepted theory of presbyopia, the age-related loss of accommodation is attributed to Young's modulus changes in the lens. Previously, we have developed an approach to measure the mechanical properties of viscoelastic medium using microbubbles and acoustic radiation force. In this study, we tested this technique to assess the mechanical properties of bovine lenses ex-vivo. An impulsive acoustic radiation force was applied to laser-induced microbubbles created with nanosecond laser pulses at different locations in the lens. An acoustic radiation force with typical duration less than 150 μs was generated by a 3.5 MHz transducer. For accurate spatio-temporal measurements of the microbubble's displacement, a custom-made ultrasound system consisting of two 25 MHz transducers was built. The first transducer emitted a train of pulses and the other transducer received the train of echoes reflected from the microbubble. The developed system was operating at 400 kHz pulse repetition frequency. The results show good agreement between experimental measurements and the theoretical model of microbubble dynamics. Evaluation of the spatial distribution of elasticity demonstrates that the Young's modulus of the nucleus is higher than that of the cortex for bovine eye lenses of mature animals. [Work supported by NIH Grant EY018081.].