Research And Implementation Of Ultrasonic Focusing System Guided By Magnetic Resonance

In recent years,tumor has become a fatal threat to people’s health.Traditional chemotherapy,radiotherapy,surgical resection and so on will cause irreversible damage to the body of patients.However,medical ultrasound(US)has been widely used in many fields of clinical medicine due to its non-invasive,high safety,low cost and noninvasive advantages.High intensity focus ultrasound(HIFU)guided by magnetic resonance(MR)has also become an advanced means of human tumor ablation.At present,the single point focusing technology is relatively mature,but it has defects such as small coverage area of focus area and small number of focus.Therefore,this paper has carried out the research of the ultrasonic focusing system guided by MR,and the main research contents are as follows:(1)According to the needs of the project,the ultrasonic focusing system guided by MRI is constructed,which mainly includes plane array ultrasonic transducer,MRI system and self-designed ultrasonic focusing system.(2)Research on ultrasonic focusing based on planar array ultrasonic transducer.Calculate the pressure formula of the plane array ultrasonic transducer,analyze the geometric characteristics of the focus and its influencing factors,establish the model in MATLAB software,optimize the parameter setting to improve the spatial resolution of the focus.In this paper,gerchberg Saxton(GS)ultrasonic focusing algorithm is studied,and its advantages and disadvantages are analyzed by simulation.A GS initial value optimization algorithm based on pseudo inverse matrix(PINV)is proposed,which improves the focus consistency and efficiency of multi-point focusing.Through MATLAB simulation,the effectiveness and superiority of the algorithm are verified.(3)An ultrasonic focusing system based on phased array technology is designed and developed.The ultrasonic focusing system has 256 signal channels.The direct digital synthesis(DDS)technology is used to design the signal generator.Each channel works independently and the frequency,phase and amplitude of the output signal are controllable.In order to reduce the reflection of the signal,the impedance matching design is carried out for each signal channel of the ultrasonic focusing system to improve the transmission efficiency of the circuit.(4)The output signal and ultrasonic focusing test of the developed ultrasonic focusing system verify the ultrasonic focusing function of the system,and design the magnetic resonance guided ultrasonic focusing heating test.The experimental data shows that the ultrasonic focusing system designed in this paper can output accurate signals and achieve After ultrasonic focusing,the tissue temperature at the single-point focus increased by 8.7 and the tissue temperature at the three-point focus increased by 4.5 ℃ under magnetic resonance detection,meeting the design requirements.