Hubei Hannas Tech Co.,Ltd-Professional Piezoceramic Elements Supplier
News
You are here: Home / News / Ultrasonic Transducer information / The position and shape of the sound focal range of the concave spherical HIFU transducer

The position and shape of the sound focal range of the concave spherical HIFU transducer

Views: 3     Author: Site Editor     Publish Time: 2021-05-12      Origin: Site

Inquire

facebook sharing button
twitter sharing button
line sharing button
wechat sharing button
linkedin sharing button
pinterest sharing button
whatsapp sharing button
sharethis sharing button

Objective To study the changes in the shape and geometrical position of the acoustic focal range of the concave spherical ultrasonic transducer when the sound intensity is high and the medium has a large attenuation. Methods From the perspective of physical acoustics, the effects of nonlinearity and media attenuation caused by high sound intensity on the sound focal range are analyzed, and the linear superposition algorithm of Rayleigh integral is used to perform numerical simulation calculations. Both theoretical analysis and numerical calculation show that with the increase of sound intensity and medium attenuation, the geometric position of the acoustic focal zone has a millimeter-level advance along the acoustic axis in the direction of the transducer; at the same time, the acoustic focal zone The shape gradually changed from a symmetrical long ellipsoid to a short ellipsoid with a "fat head and thin tail".

 

High sound intensity and medium attenuation have an important influence on the position and shape of the sound focal region of the concave spherical transducer. Full consideration should be given to the precise positioning and dose control of HIFU equipment, the formulation of inspection standards, and even the clinical application.

 

my country has made remarkable breakthroughs in the development and clinical application of high-intensity focused ultrasound (high-intensity focused ultrasound (HIFU) equipment). However, to truly achieve accurate positioning and treatment dose control on the equipment, so that clinical treatment can achieve the ideal effect of effectively killing the lesion without damaging the surrounding normal tissues, there are still many theoretical and technical issues that need to be studied and resolved in depth. Domestic and foreign experimental studies on the formation of damage of HIFU in biological tissues have shown that with the increase of sound intensity, the position of the focal zone moves forward and gradually changes from a long ellipsoid to a "tadpole shape" or a "cone shape". Although in recent years, foreign literature has made some qualitative explanations for the above phenomenon by numerically solving the nonlinear acoustic wave propagation equation (KZK equation), but the calculation procedure is complicated and the physical relationship in the calculation process is unclear. For this reason, this paper takes the concave spherical focusing transducer as an example, and discusses the problem by studying the influence of the medium attenuation and the nonlinear propagation characteristics under high sound intensity on the sound focal range.

 

In our previous work, based on the Kirchhoff diffraction integral, we have derived the expression of the sound pressure at any point in the single-frequency sound field under the condition of a linear sound field with a concave spherical focusing transducer with uniform radiation on the surface (also called For Rayleigh points).

 

From the analysis of nonlinear acoustics theory, when the sound pressure of the single-frequency sine wave radiated from the surface of the transducer into the medium is large enough, it is called a "finite amplitude wave", which propagates a certain distance in the medium (called the discontinuous distance). ), the waveform will be distorted into a sawtooth wave, which can also be regarded as a shock wave. In addition to the fundamental frequency of the original emission, the frequency spectrum of this wave also includes a series of higher harmonics. They are gradually generated by continuously absorbing energy from the fundamental wave during the propagation of sound waves, that is, the tissue harmonics in ultrasound medicine. The amplitude coefficient can be used to describe the propagation of high-order harmonics with the propagation distance and the relationship of energy changes during propagation.

 

The sawtooth wave forms a distance, so σ is a dimensionless quantity reflecting the propagation distance. Based on this, we have calculated the amplitude coefficient curve of the fundamental wave and the first 3 harmonics. When the sound wave propagates in the medium, the sound pressure decays exponentially with the distance, which can be expressed in a form. For general soft tissues, the attenuation coefficient T M is roughly proportional to the frequency. In order to simplify the calculation, this article expresses the attenuation coefficient of each harmonic component as where α is the sound attenuation system of the fundamental frequency sound wave in biological tissues per unit distance.

 

 Q2H)91HAK`VER)UJG2%SG



It should include the sound absorption and scattering of the tissue. After considering the above two factors (non-linearity and attenuation), the expression of the sound pressure in the focused sound field can be extended to the following form: is the wave number of each harmonic. This formula is what we call the linear superposition algorithm of Rayleigh integral.

 

Result:

 

1 The influence of medium attenuation on the sound focal range

The parameters of the unit concave spherical transducer used in this paper are: radius of curvature R = 15 cm, radius of aperture a = 42 cm, working frequency f = 1.7 MHz. Assuming that the medium is general soft tissue, its attenuation coefficient α is in the range of 01-30dB stew (cm·Mz). The sound velocity, density and other parameters of the medium are taken according to the relevant literature. In order to study the attenuation coefficient as a single influencing factor, only a single frequency, namely the fundamental frequency, needs to be calculated and analyzed for the change law of the sound focus domain with different α values. For this reason, in the formula (3), a series of numerical calculations were carried out by taking M=1. The results show that with the increase of attenuation, that is, when α = 0.3, 13 and 23dB stew (cm·Mhz), the shape of the -6dB acoustic focal region gradually changes from a long ellipsoid to a short ellipsoid, and its long axis1 and short axis

 

2

They are 111, 104, and 92 respectively. The position of the focal zone (position on the acoustic axis), the latter two are respectively 30mm and 65mm ahead of the former along the acoustic axis of the transducer. At the same time, the head of the focal zone (the end close to the transducer) is more "fat" than its tail (the end far from the transducer).

 

2 The effect of non-linearity caused by high sound intensity on the sound focus range is the same, the surface radiation sound pressure is considered as a single factor, and its values are respectively 44, 73, 4 MPa, and α = 3dB stew (cm·MHz). Considering that the attenuation of the medium increases rapidly with the increase of the harmonic frequency, the number of harmonics does not need to be too many. The calculation results show that: as the surface radiation sound pressure increases, the position and shape of the focal zone change unlike when the attenuation coefficient changes It's so big, but its changing law is similar. That is, the positions of the latter two focal areas are moved forward by 16mm and 21mm respectively; the ratio of the long and short axis of the 6dB focal area is 119, 116, and 113 respectively, and the head of the focal area also has a tendency to become "fat".

 

3 The combined effect of attenuation and nonlinearity on the sound focal range

The above two factors are simultaneously incorporated into formula (3) for calculation. Figure 3(a) and Figure 3(b) respectively show that α=3dB stew (cm·MHz), P′ 0=44MPa and α=2.3dB stew (cm·MHz), P′ 0=44MPa



Q2O26E4EP%`%23CRA0


When considering attenuation and nonlinear effects at the same time, the contour of the iso-sound pressure line in the focal zone is the calculation result in the figure. Compared with the two, the focal zone position has moved forward by 8.4mm, and the ratio of the focal zone's major and minor axes has changed from 11.9 to 8.5. It shows that the change trend of the focal zone caused by the attenuation coefficient and nonlinearity is the same, so the overall effect is strengthened.

 

 

in conclusion

The theoretical analysis and calculation results in this paper show that high sound intensity and medium attenuation have an important influence on the shape and position of the sound focal zone; the greater the attenuation coefficient of the medium, the higher the sound intensity (that is, the stronger the nonlinearity), and the sound focus The closer the field is to the transducer; the ratio of the long and short axes of the focal field also becomes smaller, that is, its shape gradually changes from a long ellipsoid to a short ellipsoid, and the head of the sound focus area becomes "fat" than the tail. Phenomenon, the shape tends to be "carrot". The above conclusions provide a basis for quantitatively analyzing the change law of the sound focus area of the HIFU piezo ceramics field, and further study the relationship between the sound focus area and the damage area.

 

 


Related Products

content is empty!

Feedback
Hubei Hannas Tech Co.,Ltd  is a professional piezoelectric ceramics and ultrasonic transducer manufacturer, dedicated to ultrasonic technology and industrial applications.                                    
 

RECOMMEND

CONTACT US

Add: No.302 Innovation Agglomeration Zone, Chibi Avenu ,Chibi City, Xianning, Hubei Province,China
E-mail: sales@piezohannas.com
Tel: +86 07155272177
Phone: +86 +18986196674         
QQ: 1553242848 
Skype: live:mary_14398
​        
Copyright 2017  Hubei Hannas Tech Co.,Ltd All rights reserved. 
Products