Study Of Acoustic Focal Region In Ultrasound Therapy

Ultrasound therapy is a new technology of non-invasive treatment ,it can cure the deep lesions of tissues without damaging the surface normal tissues. In recent years,the ultrasound treatment technologies develop rapidly,but there have many problems when these technologies widely used in clinical practice. For example: high-intensity focused ultrasound (HIFU) can not be focused when the ultrasound through the ribs;It will take much time when treat the large scale tumors with HIHU;Because don’t place enough emphasis on the development Of ultrasonic physiotherapy equipment, which results in slow development of ultrasound physiotherapy technology. These problems stand in the way of ultrasound treatment technologies development and seriously limit the progress. Improve the control of focused beam, resulting in the form of multi-mode acoustic focal region is the key to break through the bottleneck. Transducer is the core technology of ultrasound treatment,just start from it these issues above can be resolved. Traditional unit self-focusing transducer only have a single focus , and the shape of focal region can not be changed,so it substantially limits the application of this transducer in ultrasonic treatment.But , the focus way of Ultrasonic Phased Array is very flexible,it can depend on the lesions’ shape and location form the different focus intensity and distribution patterns.Through study the control method of ultrasound phased array elements’ phase and amplitude to realize the multi-focus mode of sound field has great significance to the development of ultrasound treatment technologies.The Diffractive Optical Elements (ODE) can make the light intensity distribution of certain output plane meet specific requirements through the modulation of incident light field amplitude and phase.Now ,this design has achieved satisfactory results in many areas such as beam shaping. And it is similar to ultrasonic phased array technology, which is through the control of each element’s phase and amplitude to obtain the desired sound field distribution.In this paper , the first chapter introduces the development and application of ultrasound treatment technologies,the performance of varieties of focused transducer ,and understanding the reaserch progress of ultrasound field variable-focus domain ,home and abroad; In the second chapter , we begin to learn the ultrasonic phased array transducer from it’s principle , introduces different types of phased array transducer in classification ,study the ultrasound field variable-focus domain through the use of two-dimensional plane phased array and concave spherical annular phased array ;In the third chapter, form multi-focus control mode through the use of matrix pseudo-inverse sound field synthesis algorithm in a 13×13 two-dimensional phased array, in order to maximize the concentration of sound intensity in the target volume we use genetic algorithm to optimize the sound field gain of multi-focus control mode ,base on the best optimized multi-focus control mode, through the merger of three and five focus we obtain "line" and "round" shape ultrasound focal region which suitable for the treatment of larger volume tumor on the focal plane. Finally, find the factors that affect the acoustic focal region by analysis and evaluation of the axial acoustic focal region,some method and approach that improve the property of the acoustic field were concluded.In chapter four ,we start from improving the sound field patterns of ultrasonic acupuncture and study how to achieve the needle-shaped sound field.A concave spherical surface piezoelectric ceramics is separated into six equal circular domain,and discretization the axial sound field generated by the six-ring domain. In order to achieve axial needle-shaped sound field and ensure uniform and concentration of sound field in needle-shaped region, it’s essential to make the sound field outside the needle region down as much as possible .So ,we use the Augmented Lagrange Algorithms to optimize the control of the six rings’ phase, and ultimately achieve the desired sound field distribution.The distribution of needle-shaped focused sound field is conducive to accurately stimulate acupuncture points,and make ultrasonic acupuncture become invisible " needle "acupuncture in a true sense.Finally,make the ultrasonic acupuncture achieve the aim of traditional acupuncture therapy or even rise superior to the traditional results.