Structural design of HIFU array element treatment

The designing parameters of the HIFU piezo ceramic directly affect the performance and production cost of the system. This paper is based on the existing hardware foundation of the laboratory, based on the spherical crown ultrasonic array model, the basic design of the probe parameters is proposed. (1) When is designing the probe, we need to consider the performance parameters of the launch system. The number of channels that the transmitter module of the HIFU treatment system used is 128. Therefore, when designing the Hifu piezoelectric ceramic transducer , combined with the structural characteristics of the ultrasonic array model designed this time, the resonance frequency of the array element is a very important design parameter. In the design of HIFU probe , the operation frequency of the probe is generally between 0.5MHz and 4MHz. We chose 2MHz as the resonant frequency of this probe.

(1) The radius curvature R of the crown spherical HIFU array is selected to be 60 mm in this design.

(2) Determining the range edge length of the array element according to the size of the clinical treatment area. The beam width at each depth of focus in the Hifu piezoelectric crystal probe is defined as the FLHM full ROI, where ROI is the size of the treatment region of in the cross section of the acoustic beam. According to the clinical requirements, the size of the sputum area is treated by the probe in this design is set to ROI>10mm, so FLHM>10 is combined with the above formula can obtain a<3.2mm.

(3) Determining the range of parameters Dcenter and PzTEdgeL in the spherical crown of ultrasonic array model to ensure that the array model ,which does not cause array element overlap in these ranges. For the spherical crown ultrasonic array model, when the R is 60, in order to ensure the array elements do not overlap, and the parameters of the ultrasonic high focusing piezo are all 1. 7PZTEdgeL.

(4) After determining the N, R, F values, pZTEdgeL<3.2, Dcenter/pZTEdgeL starts from the minimum value of 1.7, and calculates the sound field characteristics (maximum deflection range, focal length) of the array in all cases of 1.7, pZTEdgeL<3.2. Looking for the fill rate, The spherical crown surface is the highest, the focal length is the smallest, and the deflection range is the largest. The DCenter/PzTEdgeL is increased by 0.1, and the above calculation continued. The same excellent solution of ultrasonic high focus piezo is found in the current calculation results, and the two excellent solutions  performed twice. For comparison, the solution with the highest filling rate is the smallest focal region and the largest deflection range is selected. Continuing the iterative process until the optimal solution is found.In this design, we calculated the sound field characteristics of 64 array structures with different array design parameters, which the parameter information are 64 arrays. Finally, by comparing the sound field information of 64 arrays, one of the most effective array structures is obtained as the array model manufactured by this probe. The specific analysis method is expressed as follows:

First, setting the number of focal points in the single-point focus mode and the spatial position is corresponding to the focus within the specific sound field calculation range; then calculate the maximum deflection range of the array structure and the focal length of each focus, respectively; The principle of large deflection range and small focal length has chosen a reasonable set of array structures. Its geometric structure of Hifu piezo transducer impedance is expressed as shown,it is array structure characteristic parameters.Through theoretical calculations, the array is at the geometric focus point when the excitation signal is a continuous sinusoidal signal with a frequency of 2MHz in the case of single-point focusing. The focal length A is 1.5 7.5 mm3. For the array under different deflection conditions,respectively, the peak time of sound pressure distribution in the focal planes XOY and xoz .

As can be seen from the figure, the array does not change much in the deflection process, but the deflection grating strength will occur at 6mm. The normalized sound field distribution of the array at different deflection distances is deflected along the X axis by 0 mm (a), 2 mm (b), 4 mm (c), and 6 mm (d) by the following table in a single point focusing mode , when the excitation signal is a continuous sinusoidal signal of frequency 2MHz, the maximum deflection range of the probe RFD,=12mmRFDz along the X, Y, and Z axes is RFD=12Inln=7mm.A quality evaluation table of the sound pressure of the array in the case of single point focusing. Among them, 1, 2, 4, and 5 respectively indicate the Grade 1, Grade2, Grade 4, and Grades levels of the sound field quantization standard in the table. Where (a) is a single point focus of different deflection distances achieved in the focal plane y = 0' (2), and (b) is a single point of different deflection distances achieved in the focal plane z = 0' (3) focus.