| A malignant tumor is a kind of disease directly threatening human's life., so how to treat it earlier is the aim of many experts. Focused ultrasound has some unique advantages to treat tumors when compared to the other therapies; therapeutic use of ultrasound has been much more studied and become a hot-point problem.At Present, many treatments have been invented in order to antitumor. These methods include an application of ultrasound: a high intensity focused ultrasonic surgery, ultrasound thermal treatment and sonodynamic therapy (SDT). IN these three main methods, there are some deficiencies and difficulties to apply the first two to clinic, but the sonodynamic therapy has been proved be effective. In which ultrasound activate certain porphyrins such as hematoporphyrin (Hp) and thereby induce significant antitumor effects. Hp is a kind of photo-sensitizer, which can accumulate in malignant tissue and can produce special fluorescence when illuminated with ultrasound. And also, ultrasound has a low enough tissue attenuation coefficient to penetrate intervening tissues and deliver its energy to no superficial objects while maintaining the ability to focus the energy into small volumes. Because of these, SDT is viewed as a new modality for noninvasive and selective treatment of no superficial tumors.Now days, many scholars at home and abroad, especially Japanese scholars S.Umemura and N.Yumita, have done many researches on this and have got some primary results, but those studies are limited in certain animal's transplanted tumors. So there is still a long way to go to apply SDT to clinic. In order to apply this method to clinic and treat tumors in human's body effectively and conveniently based on the internal and external studies; in this paper, we have designed a bi-frequency ultrasonic transducer, which can focus two different sound waves in the point. Use this transducer we want to study whether or not SDT can cause cancer cells be antitumor more effectively than using one single frequency; also we want to find out the optimum hematoporphyrin concentration, the optimum timing of the irradiation and the optimum ultrasonic intensity under firmed ultrasonic frequency with the help of MTT, a reliable-in-way to study the activity of cells.A new kind of focused bi-frequency ultrasonic transducer is designed, which can make two kinds of ultrasounds produced and converged in one point. Because of the nonlinear interference, there are more ultrasounds whose frequencies are not only fl and f2, but also fl+_f2, 2fl, 2f2 and more. So, more bubbles are activated by these ultrasounds. Based on these, the new transducer is used in vitro to activate the hematoporphyrin derivatives and to kill the cells. From all the work, we can draw such a conclusion: bi-frequency focal ultrasounds can increase the cell-killing effect in homodynamic therapy. And the longer the irradiation time, the better the cell-killing effect.Zhu Xu-Ning (Major Acoustics) Directed by Prof. Shang Zhi-Yuan... |
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