Basic Study on Surgical System for Non-Invasive Osteotomy using High Intensity Focused Ultrasound

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[Introduction]An experimental system for non-invasive ostetomy using high intensity focused ultrasound(HIFU) was developed and assessed in this study. [Materials and methods](1)HIFU was exposed from a transducer with a PZT element to the porcine bone fixed in a pool filled with degassed water. Conditions of wave form, frequency and intensity of the input signal were varied. (2)The energy exposed to the focal point was measured experimentally and compared with the one calculated by the developed simulation software using Finite Difference Time Domain Method (3)Voltage of square wave applied to a PZT element was composed of odd multiple resonant frequency wave currents to increase acoustic pressure. HIFU was exposed from 5 transducers while matching at the same focal point. [Results and discussions](1)The energy calculated at the focal point matched the one measured experimentally at a rate of approximately 90 percent. The simulation showed that a PZT element with larger curvature contributed to higher acoustic pressure as long as the size of the transducer opening was constant. (2)The measured acoustic pressure at the focal point was as 3 times in case of applied voltage of square wave as in case of sine wave. A circular cutting mark of 1 mm in diameter and 0.5 mm in depth was observed on the bone after the exposure of HIFU from 2 transducers. The measured acoustic pressure was as 1.65 times in case that HIFU exposed from 5 transducers each of which was applied with 30 W electricity as in case of only one transducer applied with 30 W electricity. The acoustic pressure was considered to be increased by improvement of impedance matching in the amplifier of the input signal. [Conclusion]An experimental system using HIFU suggested possible contribution of HIFU to the effective bone cutting.