(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: When ultrasound propagates through different layers of tissue, the focus on the transducer is distorted. In this study, the aberration effect on a low f-number histotripsy transducer array has been modeled computationally and validated experimentally to quantify aberration and improve the efficiency of histotripsy treatments.
Methods: A computational simulation of a 500kHz, 112-element array propagating to the focus through water coupled with various thickness of tissue was generated to predict the focal shift and pressure loss. The experimental arrangement to validate the simulation was set up in a water bath with the transducer and a calibrated needle hydrophone at the geometric focus of the transducer to measure the pressure output. Pressure output was measured with 2”, 1” and 0” rectangular box between the transducer and the hydrophone. A solution containing 84.5% water and 15.5% glycerin matching the speed of sound in the skin/muscle (1560m/s) was used to mimic the tissue. An acoustically transparent box with depths of 1” and 2” and filled with the above solution was placed between the transducer and the focus to mimic the computational conditions. The reduction in focal pressure was measured and compared to the predictions of the simulation.
Results: The K-wave simulation showed that overlying 1” and 2” thick uniform tissue with water coupling resulted in a focal location shift of 4mm and 6mm, respectively. The pressure loss that was predicted by simulation and measured experimentally was 47.2% and 53.3%, respectively, relative to the free field.
Conclusion: There was reasonable agreement in ultrasound pressure loss between the experiment and the k-wave output, confirming the validity of the simulations. Water coupling resulted in substantial aberration for the low f-number histotripsy transducer suggesting exploring options of changing the coupling media from water to a media that matches the speed of sound in the skin.
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