Study On HIFU Transcranial Tumor Treatment Phase Controlled Transducer And Its Phase Controlled Drive System

High-Intensity Focused Ultrasound(HIFU)has attracted increasing attention from researchers due to its non-invasive,non-toxic side effects and reproducible treatment.It has been applied to the clinical treatment of solid soft tissue tumors such as breast cancer,uterine fibroids,prostate cancer and pancreatic cancer.However,in HIFU transcranial treatment of brain tumors,due to the strong acoustic attenuation and heterogeneous structure of the skull,it is easy to cause focus shift,focal depth deformation,low focal temperature and burns on the skull.The solution of these problems requires the development of drive control circuits for phase-controlled transducers and phase-controlled transducer elements,phase-controlled transducer control methods and their software systems.The sound pressure field and temperature field formed by HIFU brain tumor treatment were simulated by Westervelt acoustic wave propagation equation and Pennes biothermal conduction equation.The influence and regulation of partial and all array element excitation of hemispherical phase-controlled transducer on the formation of focal region were studied and designed.The corresponding phase,power amplifier and other hardware circuits and user interface software.ObjectiveIn the transcranial treatment of HIFU phase-controlled transducers,due to the strong attenuating and heterogeneous structure of the skull,the degree of attenuation of the ultrasound transcranial focus emitted by each array element is inconsistent,the focus position is shifted,the thermal injury of the skull and the energy of the focal region do not reach the therapeutic effect.The large-opening hemispherical phase-controlled transducers that have emerged in recent years have attracted the attention of researchers with their ability to maximize the coverage of the skull and the maximum energy of ultrasound to reach the target area through the skull,thereby reducing the risk of burns in the skull and treating deep brain tumors.However,the hemispherical transducer has problems such as small regulation range and difficulty in focusing on the shallow surface;the spherical crown transducer with relatively small opening diameter has the characteristics of being able to treat a large range of focal length and can treat a shallow brain tumor.However,there are problems that may cause thermal damage to the skull.Whether it is possible to take advantage of the advantages of these two transducers while avoiding the deficiencies of these two transducers is the focus of many researchers.The purpose of this study is to study the array element selection and phase control method for the focusing of the spherical coronal phase-controlled transducer on the basis of the hemispherical phase-controlled transducer,and to achieve the spherical crown on the same hemispherical transducer.The focus of the transducer and the hemispherical transducer expands the controllable range of the focal region;at the same time,the hardware circuit and user interface software for phase control and power amplification of the phase-controlled transducer array element are designed and fabricated,and the HIFU is transcranial application of brain tumor therapy in clinical provision of technical methods and theoretical references.MethodsIn this paper,a numerical simulation model with a small diameter of 125mm and a small opening randomized hemispherical phase-controlled transducer with a diameter of 125mm is used as an example.A numerical simulation model of craniotomy HIFU is established with brain tissue,and different positions are selected according to different tumor lesion locations.Partial array element excitation or full array element excitation,on the GPU parallel computing platform(OMNISKY SCS4450)using CUDA C language FDTD numerical analysis Westervelt acoustic wave nonlinear propagation equation and Pennes biothermal conduction equation,numerical simulation based on time reversal numerical fitting method the phase information of each array element excitation signal is simulated by using the array element excitation signal numerical simulation HIFU cranial focusing to form the sound pressure field and temperature field,and the partial array element excitation and all array element excitation are formed to form the focal region,and the same hemispherical transduction is performed.The focusing characteristics and array element selection characteristics of the spherical crown transducer and the hemispherical transducer are realized on the device.On the basis of this numerical simulation,the variation characteristics of the 176-element small-cavity transducer craniotomy numerical simulation model are applied to the numerical simulation model of transcranial treatment of 256-element hemispherical transducer with opening diameter of 300mm.The energy device forms the focal region characteristic,and then designs and builds a high output power,high precision array element phase control and driving hardware circuit and user interface control software system.Results1.Craniotomy numerical simulation model of a small opening 176 array element hemispherical phased transducer(1)When the excitation element area is selected at the transducer base,the focal point forming the highest sound pressure is moved forward toward the transducer side when the excitation area is less than 22%;focusing at the set position when the excitation area ratio is 23%or more.(2)In the transducer,the regular/random selection of different array regions with an excitation area ratio of 23%forms a concentrated therapeutic focus field at the geometric focus.(3)Only the region of the array with excitation area ratio of 23%is selected at the transducer base,and the focus is deviated from the geometric focus distance.Part of the excitation is defocused,and the concentrated therapeutic focal region cannot be formed.(4)According to the position of the tumor,the cross-section method and the distance method are used to select the excitation element to form the spherical coronal transducer,which is higher than the sound pressure at the full excitation focus.2.Transcranial numerical simulation model of a large opening 256 array element hemispherical phased transducer(1)When the array element with the excitation area less than 22%is selected in the 256-element transducer,there is also the case where the focus moves forward toward the transducer side;focusing at the set position when the excitation area ratio is 23%or more.(2)Randomly select different array elements with excitation area ratio of 23%in the phase-controlled transducer to focus at the geometric focus,and form a concentrated therapeutic focal region without obvious temperature rise in the skull.(3)Under the same irradiation conditions,the transducer element is selected by the section selection method and the distance selection method,and the partial excitation of the excitation area ratio of 23%is focused at a deviation from the geometric focus to form a new spherical coronal transducer.The full excitation can achieve a higher focusing effect of the focal temperature in the case where the temperature at the skull does not change much.By discussing the three-dimensional deviation from the geometric focus of 3mm-15mm(interval 3mm)and the three-dimensional deviation of the geometrical focus from the geometric focus of the three vertices,the three-dimensional deviation from the geometric focus of 9mm,6mm,it is determined that the partial excitation can achieve three-dimensional deviation according to the tumor position of different patients.The geometric focus of6mm can increase the therapeutic volume of the therapeutic focal zone.3.Design and implementation of phase control and drive system for 256-element phased transducer(1)The 10-channel phase control module based on the FPGA main control chip can realize the coarse phase control delay of 5ns and the fine phase control delay of1ns under different frequencies and different duty cycles.(2)The power amplifier module based on the class E power amplifier circuit can stably output the sine wave signal of the two-channel voltage peak-to-peak value of20.9V.(3)Based on the HIFU user control interface designed by Visual Studio,real-time import/export of delay and amplitude information of each array element can be realized,and the excitation mode of superimposition of two excitation signals can be realized.(4)The impedance of the 256-element random-distributed phase-controlled transducer element based on PZT-8 piezoelectric ceramics fluctuates between150?-500?,and the array element resonance frequency is stable at the set frequency of 700kHz±1%.Conclusions1.When the hemispherical phase-controlled transducer selects 23%or more of the excitation area for phase-controlled focusing,it can be focused at the set focus.2.Using the section selection or distance selection element method,a new spherical crown transducer can be formed on the hemispherical phased transducer,so that the tumor is located in the new sound axis direction,and the spherical crown transducer is focused,and the craniotomy model can be increased.The large 3774mm~3 can treat the focal volume,and the transcranial model can increase the treatable focal volume of 4701 mm~3.3.Built 256-element phase-controlled transducer phase control and drive system,delay accuracy,output power and excitation mode can meet the needs of HIFU transcranial tumor clinical treatment.