震波醫療機之設計與開發 Design and Development of Shock Wave Therapy

震波醫療機之設計與開發 Design and Development of Shock Wave Therapy 梁勝明遠東科技大學電腦應用工程系教授 馬亞尼義守大學生物醫學工程學系副教授 1 萬龍瑞 國立成功大學航空太空學系研究生 摘 要 本研究設計與開發了一套具電子式高壓放電系統之電水式體外震波醫療機以提供在震波碎石術 骨疾治療 消脂及其他醫療技術所需之震波產生源 本文所設計與開發之震波醫療機是由五個子系統所組成, 而此五個子系統分別為 :(1) 震波產生器 : 此設備為一橢圓反射體, 負責將第一焦點所產生的震波聚焦於第二焦點 ;(2) 雷射輔助定位系統 : 此系統利用光學以及幾何原理將光線投射於皮膚上以達到定位之目的 ;(3) 自動供水系統 : 此系統負責提供震波傳遞所需的介質並利用電磁閥以及伺服馬達以達到自動供水之目的 ;(4) 高壓放電系統 : 此系統負責提供於第一焦點利用一對電極棒間端瞬間放電進而產生震波所需之電壓 ;(5) 自動控制系統 : 此系統包含供水系統以及高壓放電系統之控制 本文所研發的高壓放電系統不僅適用於電水式體外震波產生器, 其亦可裝配於電磁式體外震波產生器做為其驅動能量釋放之來源 文中內容闡述所有系統之控制流程以及電路圖 此外, 高壓放電系統的每個控制訊號和其時序流程亦以由示波器所擷取之訊號來證明其正確性 特別值得一提的是高壓放電系統所產生的電磁波干擾訊號可以降低 99% 最後, 由系統所產生之聚焦震波其波形之正壓峰值 負壓峰值 上昇時間以及下降時間和震波能量密度 ( 強度 ) 亦透過 PVDF 壓力探針於水中完成量測 關鍵詞 : 電水式震波產生器 震波醫療機 震波聚焦 雷射輔助定位 1 現在為奇美電子公司主任工程師 51

Shen-Min Liang, Professor, Department of Computer Application & Engineering, Far East University Ioannis Manousakas, Associate Professor, Department of Biomedical Engineering, I-Shou University Long-Ray Wan, Graduate Student, Department of Aeronautics and Astronautics, National Cheng Kung University Abstract In this study, a therapy machine consisting of an electronic-type high-voltage system with an electrohydraulic shock wave generator was successfully developed for the purpose of noninvasive treatments such as lithotripsy, skeletovascular disorders, lipotripsy and other therapies. The designed and developed machine was divided into 5 subsystems: (1) a shock wave generator that consists of a pair of electrodes for current discharge and an ellipsoidal shock wave reflector; (2) an automatic water supply system which supplies the water as shock wave propagation medium. The water supply system uses electromagnetic valves and motor to achieve the need of the automatic water supply; (3) a laser-assisted positioning device that uses optics and a triangle geometry relation for projecting light onto a skin in order to localize a target; (4) a high-voltage discharge system which provides voltage needed by the two electrodes. The two electrodes produce shock waves at the first focus near the ellipsoidal shock wave reflector; (5) an automatic control system that includes the control of the water supply system and the high-voltage discharge device. The developed high-voltage discharge device can be used for other types of shock wave generator such as electromagnetic generators. It is noted that electromagnetic interferences associated with our developed high-voltage device have been reduced by 99%. The positive peak pressures, negative peak pressures, and shock wave intensities associated with focusing shock waves have been measured by using a PVDF membrane hydrophone (pressure sensor). Keywords: electrohydraulic shock wave generator, shock wave therapy, shock wave focusing, high-voltage discharge device 52

I. Introduction In past twenty years, shock wave has been applied as a non-invasive method for medical therapy such as extracorporeal shock wave lithotripsy (ESWL) and therapy of skeleton-vascular disorders. ESWL was a widely used therapy which replaced traditional surgery used for removing renal stones. There were three types of shock wave generator used in lithotripters-electrohydraulic, electromagnetic and piezoelectric types. The electro- hydraulic shock wave generator has a spark gap located at the first focus of a semi-ellipsoidal reflector. Shock waves generated at the first focus are reflected from the reflector to focus at the second focus of the semi-ellipsoidal reflector. A basic idea of shock wave lithotripsy is to focus produced shock waves outside of the body and to generate a high pressure at the target where a kidney stone locates for destroying the stone. The technique was introduced in 1980 and was so successful in clinics. Consequently in recent years more than 85% of patients with renal calculi were treated by ESWL. Very recently, ESWL was extended to treatment of musculoskeletal disorders [8-10] and was named as extracorporeal shock wave therapy (ESWT). Because of the imported machine of ESWL or ESWT was very expansive and the potential need in medical markets of Taiwan, we try to develop a home-made machine of ESWL or ESWT with some special features which are different from the existing commercial markets [11, 12]. The most difficult part for the ESWL/ESWT machine is to develop a high-voltage discharge system used for an electrohydraulic shock wave generator. Obviously, this high-voltage discharge system can also be applied to other types of shock wave generators [13]. Therefore, the first step is to develop an electrohydraulic extracorporeal shock wave generator with a high-voltage discharge system. Subsequently, other subsystems such as a laser-assisted positioning system and an electromagnetic valves-assisted water filling and draining system as well as their control systems will be developed. II. Materials and Design 2.1 Shock Wave Reflector A shock wave reflector of steel was designed and fabricated. The designed shock wave reflector has the dimensions of a semi-major axis, a = 85mm, a semi-minor axis, b = 60mm, the distance between two foci, 2c = 120.4mm, and the eccentricity of the ellipse, e = 0.71. The fabricated shock wave reflector with two electrodes is shown in Fig. 1. 2.2 Laser-Assisted Positioning System In past years, there was a difficulty for doctors and technicians to accurately estimate the depth of a nidus to be treated while operated an ESWT machine. To overcome this difficulty, a laser-assisted locating device of a nidus is designed, that is equipped to the shock wave reflector. The design concept is to design a regular pyramid with a regular base such that the side length of the regular base is equal to the height of the pyramid, as indicated in Fig. 2(a). The center and size of the regular triangular mark can indicate the location and the depth of the shockwave focus where the nidus locates under the skin. In order to form a regular triangle mark on a patient s skin, three laser-light planes are emitted from three laser beam heads respectively to form the regular triangle, as shown in Fig. 2(b). More detailed description can be found in Ref. [14]. 53

Fig. 1 A top view of our designed shock wave reflector with two electrodes. (a) inside the body. Reverse osmosis (RO) water supply tubing system was designed, which is better to be movable with the ESWL/ESWT machine. A RO water tank was built in our designed ESWL/ESWT machine. Figure 3 shows a schematic diagram of the RO water supply system. In this design, we used a minimum amount of pumps with electromagnetic valves. In particular, these pumps did not need to change the direction of motor s rotation while in water-filling or water-draining mode. 2.4 High-Voltage Discharge System The components of a high-voltage system include a power supply, high-voltage resistors and capacitors, a spark gap, a triggering module, and two electrodes. In order to assemble all the components into a high-voltage discharge system, a steel closet was designed with several small rooms in order to reduce electromagnetic radiation interferences. The designed steel closet is shown in Fig. 4. For a safety reason, all the small rooms were equipped with Bakelite to prevent the electric shock accident. (b) Fig. 2 (a) A schematic diagram of a regular pyramid. (b) A regular triangular mark formed by three laser-lights on a skin. Fig. 3 A sketch of a water supply system. 2.3 Electromagnetic Valves-Assisted Water System Since shock waves are generated at the first focus, it needs a liquid medium with sound impedance close to that of the body muscle for shock wave propagation from the first focus to the nidus 54

Fig. 5 A sketch of a control system. Fig. 4 The setup of a high-voltage discharge system. 2.5 Control System Figure 5 shows a sketch of a control system for the high-voltage discharge system and the water supply system, as shown in Fig. 5. Note that a computer was connected to a unit, designated as control circuit ( Ⅰ ). This circuit is basically an encoder for controlling signals. Because there were seven signals to be controlled and these signals were controlled without encoding. A wire is similar to an antenna. Connected wires can be interfered each other by receiving unnecessary electromagnetic disturbances. Control signals were better to be transmitted by encoding and decoding processes, resulting in more stability and safety. Furthermore, the encoded signals can be transmitted through a light transmitting unit without a wire connecting with another two units, designated as control circuit (Ⅱ) and control circuit (Ⅲ). The safety of avoiding electric shock (surge) was completely guaranteed by separating them. Moreover, due to the fact that signals transmitted to the high-voltage power supply should not be interfered by other signals, we separated the control circuit ( Ⅱ ) from the control circuit ( Ⅲ ) as an independent unit. (Refer to Fig. 5.) III. Results of output peak pressures The focused peak pressures from our developed ESWL/ESWT machine were measured by using a PVDF membrane hydrophone (pressure sensor). The operation voltage was set to range from 10kV to 15kV. A typical measured output pressure profile p( t) at 10kV at the second focus can be obtained from an oscilloscope and is shown in Fig. 6(a). The rise time associated with the pressure profile is estimated to be about 850ns and the falling time is about 500ns. Although the peak pressure is in terms of the unit of mv, it can be converted into the unit of bar by using the pressure sensor sensitivity. The measured output pressures with their standard deviations for different operation voltages are shown in Fig. 6(b), which were obtained by averaging five measured peak pressures. The average peak pressure at 10kV is 41.7bar and is increased to 132.5bar at 15kV. The corresponding energy flux density (I) (intensity) was calculated from the pressure profile by the integral defined by 1 2 2 I p ( t) dt (mj/mm ) c where is the medium density, and c the speed of sound in the medium. 55

IV. Discussions and Conclusions (a) (b) Fig. 6 The measured output pressures from 10kV to 15kV, (a) a measured pressure profile p( t) measured peak pressures. and (b) The corresponding average energy flux densities (intensities) of the peak pressures for different operation voltages are shown in Fig. 7. One can see that the average energy flux at 10kV is about 0.0075mJ/mm 2 and is largely increased to 0.0275mJ/ mm 2 at 15kV. Fig. 7 The distribution of shock wave intensities for different operation voltages of 10-15 kv. In this study, all software, control circuits and wiring components associated with the ESWL/ESWT machine have successfully designed and developed. The most difficult electromagnetic interference (EMI) problem due to the high-voltage discharge device has been solved. Some concluding remarks are noted below. (1) A shock wave reflector with a semi-major axis of a = 85mm, a semi-minor axis b = 60mm, the distance between two foci, 2c = 120.4mm, and eccentricity of 0.71, has been designed and proved to be efficient for producing satisfactory peak pressures at the second focus. (2) A laser-assisted positioning system for locating a nidus, the second focus, below the skin has been successfully developed in cooperation of the shock wave generator. In this way, the treatment process would be easier and more convenient. (3) An electromagnetic valves-assisted water supply system has been built for water filling/draining needed by the ESWL/ESWT machine. (4) A circuit of the high-voltage discharge system has been designed and wired with the aid of the manuals of high voltage power supply. Experiments were conducted to verify the designed high-voltage discharge circuit. The EMI effects of an independent power source shielded with metal covers and ferrite cores were assured to be eliminated through the observed results of captured pictures on an oscilloscope. The techniques of using an optical module, infrared, encoding and decoding were successfully applied in the control system. Circuits and software have been built to be able to completely communicate signals with the high-voltage discharge device. (5) The developed ESWL/ESWT machine has successfully operated from 10kV to 15kV. The input signals would not be interfered by the emitted EMI from the high-voltage discharge 56

system. All output signals were coincident with expected waveforms. Satisfactory results of output peak pressures and the corresponding energy flux densities measured by a PVDF pressure sensor at the second focus are reported. References [1]S. K.Shrivastava and Kailash, Shock Wave Treatment in Medicine, J. Biosci., Vol. 30, No. 2, pp. 269-75. Mar., 2005. [2]K. Kambe, M. Kuwahara, S. Kurosu, K. Takayama, O. Onodera and K. Itoh, Underwater Shock Wave Focusing - An Application to Extracorporeal Lithotripsy, Stanford Univ. Press, pp. 641-647, 1986. [3]P. Broyer, D. Cathignol, Y. Theillere and J. L. Mestas, High-Efficiency Shock-Wave Generator for Extracorporeal Lithotripsy, Medical & Biological Engineering & Computing, Vol. 34, No. 5, pp. 321-328, Sep., 1996. [4]J. McDermott, EMI Shielding and Protective Components, EDN, Vol. 24, No. 16, pp. 165-176, Sep., 1979. [5]T. Mitani, N. Shinohara, H. Matsumoto, M. Aiga, N. Kuwahara and T. Ishii, Noise-reduction Effects of over Magnetron with Cathode Shield on High-voltage Input Side, IEEE Transactions on Electron Devices, Vol. 53, No. 8, pp. 1929-1936, August, 2006. [6]C. Wang and Q. H. Zhang, EMI and Its Elimination in an Integrated High Voltage Pulse Generator IECON Proceedings of Industrial Electronics Conference, Vol. 2, pp. 1044-1049, 2000. [7]J. Etienne, L. Filipczynski, T. Kujawska and B. Zienkiewicz, Electromagnetic Hydrophone for Pressure Determination of Shock Wave Pulses, Ultrasound in Medicine and Biology, Vol. 23, No. 5, pp. 747-754, 1997. [8]C. J. Wang, An Overview of Shock Wave Therapy in Musculoskeletal Disorders, Chang Gung Med J., Vol. 26, No. 4, pp. 220-32, Apr., 2003. [9]C.-J. Wang, J.-Y. Ko and L.-M. Chen, Treatment of Lateral Epicondylitis of the Elbow with Shock Waves, Clinical Orthopaedics and Related Research, No. 387, pp. 60-67, 2001. [10]C.-J. Wang, H.-S.Chen, C.-E. Chen and K. D. Yang, Treatment of Nonunions of Long Bone Fractures with Shock Waves, Clinical Orthopaedics and Related Research, No. 387, pp. 95-101, 2001. [11]A. J. Coleman, J. E. Saunders and M. J. Choi, An Experimental Shock Wave Generator for Lithotripsy Studies, Physics in Medicine and Biology, Vol. 34, No. 11, pp.1733-1742, 1989. [12]R. O. Cleveland, M. R. Bailey, N. Fineberg, B. Hartenbaum, M. Lokhandwalla, J. A. McAteer and B. Sturtevant, Design and Characterization of a Research Electrohydraulic Lithotripter Patterned after the Dornier HM3, Review of Scientific Instruments, Vol. 71, No. 6, pp. 2514-2525, June, 2000. [13]Y. V. Andriyanov, O. N.Andriyanova, P. V. Kozodoy and V. P. Smirnov, The Electromagnetic Type Focusing Shock Wave Generators for Medical and Biology Application, IEEE Trans on Pulsed Power Conf., Vol. 2, No. 27-30, pp. 1410-1413, June, 1999. [14]L.-R. Wan, Design and Development of Shock-Wave Therapy Machine, Ph. D. dissertation, Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan, June, 2008. 57

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