Transducer Selection for In Vivo Ultrasonic Retinal Stimulation: A Porcine Eye Model Study

Jun Zhang, Yi Zhang, Juan-juan Gu, Yun Jing, Ruimi

Purpose: The aim of this study was to measure the frequency shift and attenuation of ultrasound propagation in the eye, in order to select an optimal frequency for ultrasonic retinal stimulation. Methods and Materials: Transducers of different frequencies (3.5-MHz, 20-MHz, and 40-MHz) were used to measure the intensity attenuation coefficient and center frequency shift in enucleated porcine eyes. Numerical modeling of acoustic fields in an intact eye was used to explain the center frequency shift. Three types of porcine eye samples were made for comparing attenuation coefficients in dissected and intact eyes. A comparison of focused and planar transducers was also provided. Result: 3.5-MHz ultrasound propagates through the eye with no significant frequency shift. At 20- and 40-MHz, however, the center frequency of the signal shifts to less than 15-MHz. The overall attenuation coefficients of the porcine eye are 0.13-dB/cm, 1.43-dB/cm, and 2.15-dB/cm at 3.5-MHz, 20-MHz, and 40-MHz respectively, which correspond to intensity losses of 51.25%, 96.31%, and 99.93% for an eye with a thickness of 24-mm. The attenuation coefficients of the dissected and intact eyes are within the same margin of error. There is no significant difference between the measurement results from the two types of transducers (focused and planar). Conclusion: This study revealed that significant central frequency shifts and attenuation occurs when high-frequency ultrasonic transducers are used for in vivo retinal stimulation.

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