Technical improvement of the HIFU transducer

(1) About planar annular array transducer. A concentric small circular area is dug in the center of the circular piston source to form an annular planar sound source.The sound pressure generated by the annular planar sound source at any point in space can be regarded as the sound pressure generated by the positive circular planar surrounded by the outer diameter of HIFU piezo ceramic and the negative circular planar piston source surrounded by the inner diameter of a ring. When multiple piezo rings are excited at the same time, the sound pressure generated by each circle at a certain point on the sound axis will have a phase difference. According to the phase of the sound pressure generated by a ring at a certain point on the acoustic axis, it is required for the energized excitation signal on each ring can be calculated, so that the sound pressure is generated by each ring at that point is in phase, This point achieves high intensity focused piezo. Qian Shengyou introduced the negative sound source to calculate the sound field characteristics of the concave spherical annular array transducer, and studied the focusing of the multi-ring combination and multi-ring phase control. Studies have shown that a single narrow ring is used for the treatment of smaller tumors, and multi-point heating therapy can be achieved by a multi-ring combination for a wide range of treatment areas. This transducer can be designed fully to combine self-focusing and phase-controlled focusing, which is suitable for high temperature usage, and has a simple structure, which is an ideal sound source for high-intensity ultrasonic heating treatment.

(2) About concave spherical annular array transducer. Since the 250Khz hifu piezo ceramics transducer of the spherical-deficient structure has good high temperature resistance and focusing performance, people have mainly studied the phase control problem of this type of architecture in recent years. The concave spherical piezoelectric ceramic piece is divided into a plurality of independent rings, and the energization  signals of the respective rings are adjusted so that the sound pressure at a certain point in the sound field is in phase to achieve ultrasonic focusing. Qian Shengyou et al.'s research on the concave spherical surface-shaped toroidal ultrasonic focusing transducer for hyperthermia shows that under the self-focusing effect of the concave spherical transducer, the sound field is generated by the single concave spherical ring still has a focusing effect. However, the focus position is related to the width of the ring, the aperture, etc., and is not at the geometric focus. After multi-ring combination, the focusing transducer in the sound field does not correspond to the focus point of single-ring radiation. When the concave spherical ring has the combination mode and the amplitude or frequency of each ring excitation signal are changed, the distribution of the sound field will change and be obtained. When phase-controlled focusing piezo is performed on multiple loops, the position of the focusing transducer is adjustable within a certain range, but attention should be paid to the choice of the radius of curvature of the concave surface, otherwise it may not be possible to focus, and the influence of the near-field region should be fully considered. When it is treating a large area of the tumor, multi-point heating can be achieved by a multi-ring combination to obtain a better therapeutic effect. This focusing transducer combines characteristics of self-focusing and phase-controlled focusing, which has a simple structure and high temperature resistance, and is an ideal sound source for high-intensity ultrasonic heating treatment.

(3) Concave spherical array transducer. It is shown that in the case of constant frequency and tissue absorption coefficient, the greater is the sound intensity, the longer is irradiation time, the more heat is the tissue absorbs, the faster temperature rises, and the more is susceptible, the tissue is to damage. Therefore, the amount of exposure to healthy tissue should be minimized during treatment. Sun Junxia et al. designed a concave spherical sector array transducer from the aspects of reducing the sound.it is the intensity of the source and reducing the exposure time of healthy tissue. The HIFU piezo ceramics transducer is a transducer group surrounded by several concave sector transducers of equal area and shape, FIG. it is a three-dimensional model of the transducer, it is a transducer at Projection in a plane perpendicular to the axial direction of the concave spherical surface. during the treatment, the transducer is operated in turn, and only two opposite transducers work at a time, and the area irradiated by the healthy tissue at the same time will be reduced.

The results show that the relative change in the focusing position is very small, the focusing effect is ideal, and it is very beneficial to reduce the amount of exposure to healthy tissue. However, the use of this HIFU ultrasound piezo reduces the amount of radiation in the healthy tissue, and the amount of radiation is received by the diseased tissue, and the effect of ultrasound focusing piezo is weakened, which affects the therapeutic effect in turn .