CN111261135A - Mie resonance-based double-negative-type acoustic metamaterial for transcranial ultrasonic imaging - Google Patents

Abstract

The invention discloses a double-negative-type acoustic metamaterial for transcranial ultrasonic imaging based on Mie resonance, which comprises an ultrasonic couplant used as a matrix and a scatterer dispersed in the matrix and used for generating the Mie resonance, wherein the scatterer is a porous polyethylene glycol diacrylate hydrogel microsphere; the volume fraction of the porous polyethylene glycol diacrylate hydrogel microspheres in the matrix is 15-25%. The double-negative acoustic metamaterial provided by the invention can effectively eliminate the dissipation and distortion effects of the skull on sound waves, so that transcranial ultrasonic imaging is hopefully realized without depending on the naturally existing or artificially manufactured sound window of the skull.

Description

A Double Negative Acoustic Metamaterial Based on Mie Resonance for Transcranial Ultrasound Imaging

technical field

The invention belongs to the field of acoustic metamaterials, in particular to a double negative acoustic metamaterial based on Mie resonance for transcranial ultrasound imaging.

Background technique

In the medical field, magnetic resonance imaging (MRI), computed tomography (CT) and brain ultrasound are the main imaging diagnostic methods for brain diseases. Although MRI is generally considered to be the most suitable method for brain examination, and CT also has its excellent diagnostic value, in some cases, brain ultrasound has an irreplaceable role. First, cranial ultrasound can provide hemodynamic information that cannot be obtained by MRI and CT; secondly, cranial ultrasound equipment is portable and suitable for bedside detection and long-term dynamic monitoring in emergency departments such as ambulances, emergency rooms, and intensive care units. In particular, bedside examinations can be performed for critically ill patients who cannot move; in addition, ultrasound detection has no radiation damage caused by CT and no discomfort caused by the strong magnetic field of MRI. Therefore, brain ultrasound imaging technology has important clinical application value. However, due to the huge acoustic impedance mismatch between the skull and the intracranial soft tissue, the ultrasound will be severely reflected at the interface between the inner and outer skulls, coupled with the strong absorption of the sound waves by the skull, the ultrasound signals that carry information about the intracranial tissue and blood flow Only about 1% of the energy is left when it reaches the receiving probe. Current cranial ultrasound imaging techniques strongly rely on naturally occurring or artificially created acoustic windows in the skull, such as the "temporal bone window" and "orbital acoustic window," which cannot directly pass through most of the thicker skull for tissue and blood flow imaging . And the study found that with the increase of age, the temporal bone will gradually thicken, and the failure rate of transcranial Doppler ultrasound in elderly women can reach more than 10%. In conclusion, the skull has strong attenuation and distortion effects on ultrasound, and it is difficult for ultrasound to effectively penetrate the skull to achieve intracranial tissue and blood flow imaging in a conventional manner.

In recent years, the rapid development of acoustic metamaterials has provided new ideas for solving the above problems. Acoustic metamaterials are currently one of the hotspots in the international academic and engineering circles. They are artificial periodic materials composed of subwavelength structural units with extraordinary physical properties. By ingeniously designing the structural units of metamaterials, the transmission direction of sound waves can be precisely controlled, so as to achieve unique functions that conventional materials do not have, such as negative refraction, negative reflection, acoustic stealth, etc., in military stealth, vibration and noise reduction, medical imaging It has a wide range of application value in other fields.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a double negative acoustic metamaterial for transcranial ultrasound imaging based on Mie resonance, which can effectively eliminate the dissipation and distortion effects of the skull on sound waves.

The present invention provides the following technical solutions:

An acoustic metamaterial based on Mie resonance for transcranial ultrasound imaging, the double negative acoustic metamaterial comprises an ultrasonic couplant as a matrix and a scatterer dispersed in the matrix for generating Mie resonance, so The scatterers are porous polyethylene glycol diacrylate hydrogel microspheres.

Preferably, the volume fraction of the porous polyethylene glycol diacrylate hydrogel microspheres in the matrix is 15-25%.

Preferably, the density of the ultrasonic coupling agent is 900-1100 kg/m ³ , and the sound speed is 1400-1600 m/s.

Preferably, the mass density of the porous polyethylene glycol diacrylate hydrogel microspheres is 500-700 kg/m ³ , and the sound velocity is 120-180 m/s.

Preferably, the radius of the porous polyethylene glycol diacrylate hydrogel microspheres is 50-70 μm.

The acoustic metamaterial simultaneously achieves negative equivalent mass density and negative equivalent elastic modulus in the frequency range of 0.63-0.73 MHz.

Aiming at the problem that ultrasound is difficult to penetrate the skull, the present invention proposes a double negative acoustic metamaterial based on Mie resonance to precisely control the transmission path of the acoustic wave to improve its penetration rate. The acoustic metamaterial provided by the present invention is a composite material, the matrix of which is an ultrasonic coupling agent (density is 900-1100kg/m ³ , and the sound speed is 1400-1600m/s), and the scatterer that occurs Mie resonance is porous polyethylene Alcohol diacrylate (PEGDA) hydrogel microspheres. Due to the existence of a large number of air cavities, the porous hydrogel microspheres exhibit low sound velocity (120-180 m/s) and moderate mass density (500-700 kg/m ³ ), which can induce large unipolar Mie resonances, thereby yields a negative equivalent elastic modulus. At the same time, a large number of viscous particles exhibit a strong dipole Mie resonance, resulting in a negative equivalent mass density. By changing the density, sound velocity, radius and volume fraction of the porous hydrogel microspheres in the matrix, the frequency range (0.63-0.73 MHz) generated by the negative equivalent parameter can be regulated.

The double negative acoustic metamaterial provided by the invention can effectively eliminate the dissipation and distortion effects of the skull on acoustic waves. The double negative acoustic metamaterial provided by the invention is expected to realize transcranial ultrasound imaging independent of acoustic windows, and has great application value in the field of clinical imaging diagnosis.

Description of drawings

Figure 1 shows the finite element simulation of the focused ultrasound beam sound field: (a) only water exists; (b) water and skull; (c) water, skull and double negative acoustic metamaterial.

Figure 2 is a schematic diagram of the preparation of porous hydrogel microspheres by microfluidic technology.

Figure 3 shows (a) the real part of the equivalent density, (b) the imaginary part of the equivalent density, and (c) the equivalent elasticity of the porous hydrogel microspheres in Example 1 dispersed in the ultrasonic couplant calculated by the multiple scattering model The real part of modulus and the imaginary part of (d) equivalent elastic modulus; among them, the density of porous hydrogel microspheres is 500kg/m ³ , the speed of sound is 120m/s, the radius is 50μm, and the volume fraction is 15%; the density of ultrasonic couplant is 900kg/m ^3. The speed of sound is 1400m/s.

Figure 4 shows (a) the real part of the equivalent density, (b) the imaginary part of the equivalent density, and (c) the equivalent elasticity of the porous hydrogel microspheres in Example 2 dispersed in the ultrasonic couplant calculated by the multiple scattering model The real part of the modulus and the imaginary part of the (d) equivalent elastic modulus; the density of porous hydrogel microspheres is 600kg/m ³ , the speed of sound is 150m/s, the radius is 60 μm, and the volume fraction is 20%; the density of the ultrasonic couplant is 1000kg/m ³ , the speed of sound is 1500m/s.

Figure 5 shows (a) the real part of the equivalent density, (b) the imaginary part of the equivalent density, and (c) the equivalent elasticity of the porous hydrogel microspheres in Example 3 dispersed in the ultrasonic couplant calculated by the multiple scattering model The real part of modulus and the imaginary part of (d) equivalent elastic modulus; among them, the density of porous hydrogel microspheres is 700kg/m ³ , the speed of sound is 180m/s, the radius is 70μm, and the volume fraction is 25%; the density of ultrasonic couplant is 1100kg/m ³ , the speed of sound is 1600m/s.

Figure 6 shows (a) the real part of the equivalent density, (b) the imaginary part of the equivalent density, and (c) the real equivalent elastic modulus of the steel ball microspheres in Comparative Example 1 dispersed in the ultrasonic couplant calculated by the multiple scattering model. part and (d) the imaginary part of the equivalent elastic modulus; among them, the density of steel ball microspheres is 7900kg/m ³ , the speed of sound is 5955m/s, the radius is 60 μm, and the volume fraction is 20%; the density of ultrasonic couplant is 1000kg/m ³ , the speed of sound is 1500m/s .

Figure 7 shows the (a) real part of the equivalent density, (b) the imaginary part of the equivalent density, and (c) the equivalent elasticity of the hollow hydrogel microspheres in Comparative Example 2 dispersed in the ultrasonic couplant calculated by the multiple scattering model The real part of modulus and the imaginary part of (d) equivalent elastic modulus; among them, the density of hollow hydrogel microspheres is 200kg/m ³ , the speed of sound is 500m/s, the radius is 60μm, and the volume fraction is 20%; the density of ultrasonic couplant is 1000kg/m ³ , the speed of sound is 1500m/s.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings. Here, the embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

For the double negative acoustic metamaterial based on Mie resonance for transcranial ultrasound imaging proposed in the present invention, its scatterer porous polyethylene glycol diacrylate hydrogel microspheres (porous hydrogel microspheres) can be made of microscopic microspheres. The preparation was performed by fluidic technology (as shown in Figure 2).

The specific preparation method of the porous polyethylene glycol diacrylate hydrogel microspheres is as follows: 1) Prepare a dispersed phase solution. In a brown glass bottle, add polyethylene glycol diacrylate (PEGDA), 2-hydroxy-2-methyl-1-phenyl-1-propanone (I-1173, photoinitiator), glacial acetic acid, magnetic stirring for 10 After a few minutes, deionized water was added, and finally, sodium bicarbonate (pore-forming agent) was weighed into the above solution, and a dispersed phase solution was obtained after stirring. 2) Prepare a continuous phase solution. Dimethicone oil and surfactant SPAN80 were added to the beaker and stirred until completely dissolved to obtain a continuous phase solution. 3) Assemble the microfluidic platform. Inhale the disperse phase and continuous phase solutions into 2mL syringes, respectively, fix the syringes on the syringe pump, and adjust the parameters of the syringe pump (the flow rate of the continuous phase is 0.5mL/h, and the flow rate of the disperse phase is 0.05mL/h); The flow control chip is installed on the fixture, the chip inlet is connected to the needle through a hose, the outlet hose leads to a collection bottle, and an ultraviolet lamp (7W-365nm) is installed above the collection bottle. 4) Turn on the syringe pump and UV lamp. After waiting for 2-3 hours, the solution of dispersed porous hydrogel microspheres was collected. 5) The porous hydrogel microspheres are separated. Centrifugal washing was repeated 3 times to obtain porous hydrogel microspheres.

Based on the multiple scattering model, the curves of the equivalent mass density and equivalent elastic modulus of the above acoustic metamaterials with frequency can be calculated. The specific calculation formulas are as follows:

where ρ is the dynamic equivalent mass density, ρ ₀ is the static mass density, η is the volume fraction of the scatterer porous hydrogel microspheres, k ₀ is the wavenumber, and f(0) is the forward scattering of a single scatterer function, f(π) is the backscattering function of a single scatterer, M is the dynamic equivalent elastic modulus, and M ₀ is the static elastic modulus. The calculation formula of the scattering function f(θ) is as follows:

where _{Sn is the scattering coefficient of a single scatterer, and P n (} cosθ) is the Legendre polynomial.

The present invention uses finite element simulation to simulate the sound field distribution of the focused ultrasound beam in three cases. The results are shown in Figure 1. In Figure 1, (a) only water exists, (b) water and skull, (c) water, Skull and double negative acoustic metamaterials. When the ultrasonic wave passes through the water medium with only the skull, the energy is greatly reduced (as shown in (b) in Figure 1), and the focused position of the focused ultrasonic beam after passing through the skull is very different from that when only the medium water exists alone, indicating that the skull is There is a serious distortion and attenuation of the ultrasonic beam, which is caused by the impedance mismatch between the skull and the water, which causes the sound waves to be reflected on the surface of the skull, and the dissipation of the sound energy by the skull. When a layer of the double negative acoustic metamaterial provided by the present invention (in Example 1 or Example 2 or Example 3) is added in front of the skull (as shown in (c) in FIG. 1 ), the focused ultrasound beam penetrates The energy after penetrating the skull is greatly increased compared to when the skull alone is present, and the focus is very close to that when only water alone is present. The above simulation results prove theoretically that the double negative acoustic metamaterial proposed by the present invention can effectively eliminate the dissipation and distortion effects of the skull on acoustic waves.

Example 1

The density of the porous hydrogel microspheres is 500kg/m ³ , the speed of sound is 120m/s, and the radius is 50 μm; the density of the ultrasonic coupling agent is 900kg/m ³ , the speed of sound is 1400m/s; the porous hydrogel microspheres are uniformly dispersed In the ultrasonic couplant matrix, the desired double negative acoustic metamaterial was obtained, in which the volume fraction of porous hydrogel microspheres was 15%. The variation curves of equivalent mass density and equivalent elastic modulus with frequency calculated based on the multiple scattering model are shown in Fig. 3. The acoustic metamaterial exhibits both negative equivalent mass density and negative equivalent mass density at frequencies from 0.63 to 0.67 MHz. Effective elastic modulus.

Example 2

The density of the porous hydrogel microspheres is 600kg/m ³ , the speed of sound is 150m/s, and the radius is 60 μm; the density of the ultrasonic coupling agent is 1000kg/m ³ , the speed of sound is 1500m/s; the porous hydrogel microspheres are uniformly dispersed In the ultrasonic couplant matrix, the desired double negative acoustic metamaterial was obtained, in which the volume fraction of porous hydrogel microspheres was 20%. The variation curves of equivalent mass density and equivalent elastic modulus with frequency calculated based on the multiple scattering model are shown in Fig. 4. The acoustic metamaterial exhibits both negative equivalent mass density and negative equivalent mass density at frequencies from 0.67 to 0.70 MHz. Effective elastic modulus.

Example 3

The density of the porous hydrogel microspheres is 700kg/m ³ , the speed of sound is 180m/s, and the radius is 70 μm; the density of the ultrasonic coupling agent is 1100kg/m ³ , the speed of sound is 1600m/s; the porous hydrogel microspheres are uniformly dispersed In the ultrasonic couplant matrix, the desired double negative acoustic metamaterial was obtained, in which the volume fraction of porous hydrogel microspheres was 25%. The variation curves of equivalent mass density and equivalent elastic modulus with frequency calculated based on the multiple scattering model are shown in Fig. 5. The acoustic metamaterial exhibits both negative equivalent mass density and negative equivalent mass density at frequencies of 0.68-0.73 MHz. Effective elastic modulus.

Comparative Example 1

The density of the steel ball microspheres is 7900kg/m ³ , the sound speed is 5955m/s, and the radius is 60 μm; the density of the ultrasonic couplant is 1000kg/m ³ , and the sound speed is 1500m/s; the steel ball microspheres are uniformly dispersed in the matrix of the ultrasonic couplant , an acoustic composite material was obtained, in which the volume fraction of steel ball microspheres was 20%. The variation curves of equivalent mass density and equivalent elastic modulus with frequency calculated based on the multiple scattering model are shown in Fig. 6. The acoustic composite material exhibits positive equivalent mass density and positive equivalent elastic modulus within 0-1 MHz. .

Comparative Example 2

The density of the hollow hydrogel microspheres (hollow polyethylene glycol diacrylate hydrogel microspheres) is 200kg/m ³ , the sound speed is 500m/s, and the radius is 60 μm; the density of the ultrasonic couplant is 1000kg/m ³ , The speed of sound is 1500m/s; the hollow hydrogel microspheres are uniformly dispersed in the ultrasonic couplant matrix to obtain an acoustic composite material, wherein the volume fraction of the hollow hydrogel microspheres is 20%. The variation curves of equivalent mass density and equivalent elastic modulus with frequency calculated based on the multiple scattering model are shown in Fig. 7. The acoustic composite only exhibits a single negative equivalent elastic modulus within 0.82-1 MHz.

The above-mentioned specific embodiments describe in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above-mentioned embodiments are only the most preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, additions and equivalent substitutions made within the scope shall be included within the protection scope of the present invention.

Claims (6)

1. The double-negative-type acoustic metamaterial for transcranial ultrasonic imaging based on Mie resonance is characterized by comprising an ultrasonic couplant serving as a matrix and a scatterer dispersed in the matrix and used for generating the Mie resonance, wherein the scatterer is a porous polyethylene glycol diacrylate hydrogel microsphere.

2. The bipnegative-tone acoustic metamaterial for transcranial ultrasound imaging based on mie resonance according to claim 1, wherein the volume fraction of the porous polyethylene glycol diacrylate hydrogel microspheres in the matrix is 15-25%.

3. The dual-negative-tone acoustic metamaterial for trans-cranial ultrasound imaging based on Mie's resonance in claim 1 or 2, wherein the density of the ultrasonic couplant is 900-1100 kg/m³The sound velocity is 1400-1600 m/s.

4. The double-negative-tone acoustic metamaterial for transcranial ultrasonic imaging based on Mie's resonance in claim 1 or 2, wherein the mass density of the porous polyethylene glycol diacrylate hydrogel microspheres is 500-700 kg/m³The sound velocity is 120-180 m/s.

5. The double-negative-tone acoustic metamaterial for transcranial ultrasonic imaging based on Mie's resonance in claim 1 or 2, wherein the radius of the porous polyethylene glycol diacrylate hydrogel microsphere is 50-70 μm.

6. The biprimary negative acoustic metamaterial for transcranial ultrasound imaging based on mie resonance according to claim 1 or 2, wherein the acoustic metamaterial achieves both negative equivalent mass density and negative equivalent elastic modulus at a frequency range of 0.63-0.73 MHz.

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