Acoustic reflective film for ultrasound imaging of organs or tissues in vivo

Abstract

The present invention belongs to the fields of acoustics, medicine, and metamaterials, and discloses an acoustic reflective film for ultrasonic imaging of internal organs or tissues. The film comprises a first material and a second material having different sound velocities. The first material is flexible, and the second material is distributed within the first material in a periodic arrangement. The periodic arrangement of the second material enhances ultrasonic reflection based on the multiple scattering effect, thereby providing an imaging effect. This invention breaks away from the inherent concept of traditional oral contrast agents by utilizing two materials with different sound velocities and a periodic structure to produce an acoustic reflective film. The film can be attached to the outer wall of an internal organ or tissue through surgical implantation or other means, and can be used for long-term ultrasonic imaging of internal organs or tissues. This effectively addresses the problems of existing ultrasonic imaging equipment being unable to clearly image internal organs and tissues, and existing oral liquid contrast agents being unable to remain in the body for a long time and having limited available locations.

Description

Technical Field

[0001] The present invention belongs to the fields of acoustics, medicine and metamaterials, and more specifically, relates to an acoustic reflective film for ultrasonic imaging of organs or tissues in the body, which can enhance acoustic reflection and can be used for ultrasonic imaging of organs or tissues in the body in medicine. Background Art

[0002] Many organs in the human body exhibit periodic peristalsis, such as the cyclic peristalsis of the gastrointestinal tract during digestion, the filling and contraction of the bladder, the powerful heartbeat, and the micropulsations of blood vessels. The peristaltic state of these organs reflects various health parameters, such as the antral cycle, urination, heart rate, and pulse. Monitoring organ peristalsis (especially long-term monitoring) is a critical issue in medicine and health that needs to be addressed.

[0003] Current methods of monitoring heart beats include directly implanting electronic sensors in the heart to monitor heart beats and promptly intervening to perform cardiac pacing when the heart beats abnormally; or indirectly monitoring the electrocardiogram (ECG) waveform to obtain the heart rate cycle and pulsation status, and provide early warning for low heart rate, atrial fibrillation, etc.

[0004] Currently, there are three main methods for monitoring vascular pulsation: invasive puncture of deep blood vessels, non-invasive cuff pressurization of upper limb blood vessels, and traditional Chinese medicine pulse diagnosis of wrist blood vessels based on experience. Vascular pulsation monitoring can be used to monitor health parameters such as pulse cycle and blood pressure.

[0005] Gastrointestinal dysfunction caused by abnormal gastrointestinal motility is one of the most common digestive system diseases. Particularly for patients who have undergone partial gastrointestinal resection surgery, more than half experience short-term or long-term symptoms of abnormal gastrointestinal motility after surgery. These symptoms require prompt medication and treatment upon detection to maintain normal digestive function. Commonly used methods for monitoring gastrointestinal motility include intubation, X-ray barium swallows, capsule endoscopy, and radioactive element scintigraphy. Ultrasound, a harmless and painless diagnostic method, is also increasingly being used for gastrointestinal motility assessment. However, due to the weak reflectivity of the gastric wall and gastric fluid, clear echoes cannot be obtained during in-hospital ultrasound imaging. Therefore, prior to ultrasound diagnosis of gastrointestinal motility, patients must first take orally or inject a diluted liquid contrast agent (typically prepared by mixing a large number of approximately 10 μm bubbles in a liquid). Ultrasound imaging is then used to observe gastric motility. Taking oral contrast agents as an example, liquid contrast agents will be emptied from the stomach within 1 to 2 hours, so the contrast agent needs to be taken again before each examination, which is not suitable for long-term monitoring of patients with chronic gastrointestinal diseases. Summary of the Invention

[0006] In response to the problems that existing ultrasonic imaging equipment cannot clearly image tissues and organs in the body, and existing oral liquid contrast agents cannot exist in the body for a long time and have limited available locations, the purpose of the present invention is to provide an acoustic reflective film for ultrasonic contrast imaging of organs or tissues in the body. Breaking away from the inherent idea of ​​traditional oral contrast agents, the acoustic reflective film is obtained by utilizing two materials with different sound velocities and based on a periodic structure to form an ultrasonic contrast imaging film designed based on a flexible acoustic metasurface. The ultrasonic contrast imaging film is attached to the outer wall of an organ or tissue in the body through surgical implantation or other means for use in ultrasonic imaging of the organ, and is particularly suitable for long-term ultrasonic contrast imaging of organs in the body.

[0007] To achieve the above objectives, according to one aspect of the present invention, there is provided an acoustic reflective film for ultrasound imaging of organs or tissues in vivo, characterized in that it comprises a first material and a second material having different sound velocities, wherein the first material is a flexible and deformable material, and the second material is distributed within the first material and arranged periodically along a distribution plane; the sound velocity of the material with the higher sound velocity of the first material and the second material is at least twice that of the material with the lower sound velocity;

[0008] The acoustic reflective film is used to be fixed on the surface of the internal organ or tissue to be imaged by ultrasound; the ultrasonic wave is used to be incident along an incident direction with an angle of no more than 60° with respect to the normal direction of the distribution plane. In this way, the periodically arranged second material can enhance the reflection of the ultrasound based on the multiple scattering effect, thereby playing a role in imaging.

[0009] As a further preferred embodiment of the present invention, the second material is air. Accordingly, the acoustic reflection film comprises a sheet-like flexible material matrix and periodically arranged air holes (102) sealed in the matrix.

[0010] As a further preferred embodiment of the present invention, the air hole (102) is a cylindrical hole, a polygonal prism hole or an elliptical cylinder hole; preferably a cylindrical hole.

[0011] As a further preferred embodiment of the present invention, an adhesive layer (103) is further provided on the bottom surface of the acoustic reflective film; the adhesive layer (103) is preferably a chitosan adhesive layer.

[0012] As a further preferred embodiment of the present invention, the second material is arranged in a two-dimensional periodic manner inside the first material. For the periodically arranged second material, the center distance a between two adjacent second material areas does not exceed 10 mm; the cross-sectional size d of a single second material area is smaller than the center distance a, and the height h does not exceed 10 mm.

[0013] As a further preferred embodiment of the present invention, the second material is arranged in a one-dimensional periodic pattern inside the first material. For the periodically arranged second material, the center-to-center distance a between two adjacent second material regions does not exceed 10 mm; the cross-sectional dimension d of a single second material region along the periodic arrangement direction does not exceed 10 mm, and the height h of a single second material region does not exceed 10 mm.

[0014] Furthermore, compared to the plane where both the periodic arrangement direction and the normal direction of the distribution plane are located, the ultrasonic wave incident direction is also parallel to the plane.

[0015] As a further preferred embodiment of the present invention, the height h is less than 1 mm.

[0016] As a further preferred embodiment of the present invention, the ultrasonic wave is used to be incident along an incident direction parallel to the normal direction of the distribution plane.

[0017] According to another aspect of the present invention, the present invention provides the use of the above-mentioned acoustic reflective film in the preparation of an implantable ultrasound contrast agent for internal organs or tissues.

[0018] Through the above technical solution conceived by the present invention, compared with the existing technology, the present invention utilizes at least two materials with different sound velocities, based on a periodic structure, to obtain an ultrasound contrast imaging film designed based on a flexible acoustic metasurface, which is attached to the wall of an organ or the outer wall of a tissue in the body, and can effectively enhance the reflection of ultrasound and play a contrast imaging role.

[0019] The principle of ultrasound imaging is to obtain acoustic reflection information at different depths by measuring the phase and intensity of different reflected signals. The different strengths of acoustic reflection at different depths will cause different tissues to appear different shadows in ultrasound imaging, which can be used to detect the distribution of tissues at a certain depth in the human body. However, for most organ walls in the human body, since their modulus and density are not much different from muscles, fat, etc. in other tissues, the reflected echo of ultrasound is small, and no obvious outline can be shown in ultrasound imaging. Most ultrasound waves will penetrate the organs and continue to propagate forward (as described later). Figure 3 By attaching the ultrasound contrast film of the present invention to the surface of the organ, the reflectivity of the ultrasound wave can be enhanced, and the ultrasound wave will be reflected on the film to form a significant echo (as shown later). Figure 3 (as shown in the figure attached in the figure), the significant outline and dynamic changes of the organ can be obtained in ultrasound imaging, thereby improving the imaging effect and achieving contrast imaging.

[0020] The acoustic reflective film of the present invention enhances ultrasonic reflection primarily through the multiple scattering effect of the periodically distributed second material (e.g., periodically distributed air pores) within the film. Taking the xy plane as an example, and constructing a spatial rectangular coordinate system, the periodically distributed second material comprises m×n elements (m ≥ 3 and n ≥ 1, with m and n both being positive integers; when n = 1, it corresponds to a one-dimensional periodic array) on the xy plane, and is distributed as a single layer. When ultrasonic waves are incident perpendicularly (in this case, the ultrasonic incident direction is parallel to the Z-axis), the multiple scattering effect enhances ultrasonic reflection, providing a contrast agent. Similarly, when the ultrasonic incident direction is at a certain angle (i.e., at a certain angle to the Z-axis), the periodically distributed second material can still enhance ultrasonic reflection due to the multiple scattering effect (considering the reflection angle, the angle should not exceed 60° to ensure broadband reflection).

[0021] Since the enhanced reflection of ultrasound by the ultrasound contrast imaging surface in the present invention is based on the multiple scattering effect of the acoustic metasurface structure, taking air holes as an example, the periodically arranged air holes produce strong reflection of high-frequency ultrasound waves incident on the metasurface, and the reflectivity formula is shown in Formula 1.

[0022]

[0023] Where k is the wave number of the sound wave in the hydrogel, k = ω / c, ω = 2πf is the angular frequency, and c is the speed of sound in the flexible material. n is the nth-order scattering coefficient, which is related to the structural design parameters of the metasurface.

[0024] Taking cylindrical air holes as an example, the two shape parameters of the air hole diameter d (i.e., the cross-sectional dimension d of a single second material region along the periodic arrangement direction) and the period spacing a will comprehensively influence the imaging effect of the flexible acoustic metasurface obtained by the acoustic reflective film of the present invention. Similar to existing acoustic multiple scattering theory, when the air hole diameter d remains constant, the smaller the air hole period spacing a (i.e., the higher the air hole duty cycle), the stronger the metasurface's reflectivity to ultrasound waves and the more pronounced the imaging effect. When the air hole duty cycle is fixed, the proportional decrease in the air hole period spacing a and diameter d leads to a higher reflection frequency range for the metasurface of the present invention.

[0025] In addition, the first material used in the present invention is a flexible material. Compared to rigid materials such as metal, flexible materials have lower modulus and better deformability. Therefore, they have better conformability and biocompatibility when attached to complex surfaces. They can meet the requirements of conformal attachment to complex surfaces of internal organs (such as curved and wrinkled surface morphologies), achieving stable attachment. Taking the use of hydrogel as the raw material for the ultrasound reflective film of the present invention as an example, hydrogel is a commonly used flexible material for in vivo implantation. It has good biocompatibility, a Young's modulus close to that of human tissue, low cost and easy processing. Accordingly, the ultrasound reflective film of the present invention can achieve good biocompatibility and good practicality. In addition, different hydrogel materials have different in vivo degradation times. The type and ratio of hydrogel materials can be selected and adjusted according to specific needs to achieve stable monitoring over long-term or medium-term periods. (Of course, if the ultrasound contrast imaging film needs to be semi-permanently present in the body to prevent degradation, the hydrogel material can be replaced with other non-degradable bio-flexible materials known in the prior art, such as silicone-based elastomers and other flexible polymer materials.) BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a top view of the acoustic metasurface design in Example 1 of the present invention.

[0027] Figure 2 This is a side structural diagram of the ultrasound contrast imaging film in Example 1 of the present invention.

[0028] Figure 3 The figure shows the comparison of the ultrasonic path diagrams before and after the ultrasonic contrast imaging film of the present invention is attached.

[0029] Figure 4 It is a comparison of the reflectivity of pure hydrogel (i.e., pure hydrogel without structure) and metasurfaces of different sizes (i.e., periodic air holes with different size parameters inserted into the hydrogel).

[0030] Figure 5 Schematic diagram of other feasible air hole cross sections.

[0031] Figure 6 1 and 2 are top views and side structural views of the ultrasound contrast imaging film structure in Example 11 of the present invention.

[0032] In the figure, the meanings of the various reference numerals are as follows: 101 is the flexible base material, 102 is the inserted periodic air holes, 103 is the adhesive layer at the bottom of the film, 1 is the ultrasound probe, 2 is the human epidermis, 3 is the ultrasound wave emitted by the ultrasound probe, 4 is the organ (or tissue) to be measured, 5 is the transmitted wave that penetrates the organ and continues to propagate inward, 6 is the flexible metasurface attached to the organ surface, and 7 is the ultrasound echo reflected by the acoustic metasurface attached to the organ surface. d represents the diameter of the air holes; a represents the periodic interval between the air holes (i.e., the center-to-center distance between two adjacent air holes); and h represents the height of the air holes. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] Taking air as the second material as an example, the present invention can produce an ultrasound contrast film by inserting air holes into a flexible material. The flexible material can be a hydrogel, a silicone-based elastomer material represented by polydimethylsiloxane, a gel material, or other flexible polymer materials. The periodic air holes can be produced by demolding methods, laser cutting, 3D printing, and other methods.

[0035] The following are specific embodiments:

[0036] Example 1:

[0037] like Figure 1 As shown, the ultrasound contrast imaging film of the present invention is composed of a flexible base material 101 and air holes 102 embedded therein in a periodic two-dimensional array. The air holes of the actual prepared metamaterial are sealed at both ends by flexible materials to prevent water, tissue fluid and other liquids from entering the air holes during use.

[0038] like Figure 2 As shown, under the thin layer of flexible material, an adhesive layer 103 for adhering to the outer wall of the organ can be provided, which can be tightly adhered to the outer wall of the target organ to prevent it from falling off.

[0039] The preparation process is as follows:

[0040] A flexible metasurface composed of a double-crosslinked hydrogel of carboxymethyl chitosan and polyvinyl alcohol and air pores. First, 10 ml of a 4 wt% carboxymethyl chitosan aqueous solution and 10 ml of a 20 wt% polyvinyl alcohol are dissolved in deionized water at 90°C. After complete dissolution, 1.5 ml of a 4 wt% aluminum chloride hexahydrate solution is added. Then, the mixture is evenly mixed by magnetic stirring, degassed, and poured into a flexible metamaterial mold with a periodic pore structure having a designed periodic spacing a = 0.1 mm, a diameter d = 0.07 mm, and a height h = 0.1 mm. The mixture is cyclically frozen and thawed at -20°C, demolded, and the air pores are sealed again with the hydrogel to obtain the target flexible metasurface with broadband reflection capability. Then, an adhesive layer (such as Figure 2 For example, a chitosan adhesion layer can be used to form a strong adhesion with biological tissue; the chitosan adhesion layer can be formed by referring to relevant existing technologies using 1-3 wt% chitosan, an EDC coupling agent, and an NHS activator to adhere the metasurface to the surface of the organ to be tested.

[0041] Example 2: Periodic air pores are inserted into the hydrogel material using a laser cutting method instead of the mold method in Example 1. First, 10 ml of a 4 wt% carboxymethyl chitosan aqueous solution and 10 ml of a 20 wt% polyvinyl alcohol solution are dissolved in deionized water at 90°C. After complete dissolution, 1.5 ml of a 4 wt% aluminum chloride hexahydrate solution is added. The mixture is then mixed evenly by magnetic stirring, degassed, and added to a rectangular mold. The mixture is frozen and thawed at -20°C to solidify into a hydrogel film. A periodic air pore structure is cut out in the hydrogel material using a laser cutter, and the upper and lower surfaces are then sealed again with hydrogel to produce a metasurface.

[0042] Example 3: Using the additive manufacturing method of 3D printing, a hydrogel 3D printer is used to directly print the hydrogel structure with periodic air pores in the present invention (the shape parameters of the formed periodic structure are consistent with those in Example 1) to prepare the flexible metasurface described in the present invention.

[0043] Example 4: The dimensions of the metasurfaces manufactured in Examples 1-3 are proportionally enlarged to twice their original dimensions, i.e., the lattice constant of the periodic columns is adjusted to 0.2 mm, the diameter is adjusted to 0.14 mm, and the height is adjusted to 0.2 mm. This allows the manufacture of an acoustic metasurface having a strong reflection capability for ultrasonic signals within the 1-12 MHz range and a slightly weaker reflection capability for ultrasonic signals within the 12-20 MHz range. Figure 4 As shown ( Figure 4 This is obtained by controlling the incident ultrasonic wave to be incident along the z direction and performing a frequency sweep from 1 MHz through simulation).

[0044] Example 5: The dimensions of the metasurfaces manufactured in Examples 1-3 are enlarged five times proportionally, i.e., the lattice constant of the periodic columns is adjusted to 0.5 mm, the diameter is adjusted to 0.35 mm, and the height is adjusted to 0.5 mm. This allows the manufacture of an acoustic metasurface having a strong reflection capability for ultrasonic signals within the 1-5 MHz range and a slightly weaker reflection capability for ultrasonic signals within the 5-20 MHz range. Figure 4 As shown ( Figure 4 This is obtained by controlling the incident ultrasonic wave to be incident along the z direction and performing a frequency sweep from 1 MHz through simulation).

[0045] Example 6: The dimensions of the metasurface fabricated in Examples 1-3 are proportionally enlarged to 100 times the original dimensions, i.e., the lattice constant of the periodic columns is adjusted to 10 mm, the diameter is adjusted to 7 mm, and the height is adjusted to 10 mm. This allows the fabrication of an acoustic metasurface that has a strong reflection capability for ultrasonic signals below 250 kHz and a slightly weaker reflection capability for ultrasonic signals above 250 kHz.

[0046] Example 7: The hydrogel material is replaced with other hydrogel materials with similar modulus and density, such as polyacrylamide sodium alginate double network hydrogel, polyacrylic acid chitosan double network hydrogel, polyacrylic acid gelatin double network hydrogel, chitosan polyvinyl alcohol double network hydrogel, polyacrylamide / polyacrylic acid / polyvinyl pyrrolidone triple cross-linked hydrogel material and other single network, double network or multi-network cross-linked hydrogel materials. The difference in hydrogel matrix materials does not affect the broadband reflection characteristics of the metasurface.

[0047] Example 8: Replacing the hydrogel material with a flexible gel material such as gelatin or a silicon-based elastomer material represented by polydimethylsiloxane does not affect the broadband reflection characteristics of the metasurface.

[0048] Example 9: Replacing the hydrogel material with other flexible polymer materials can also achieve a similar broadband reflection effect.

[0049] Example 10: The periodically arranged circular hole-shaped cylinders are transformed into polygonal prisms with a cross section of a triangle, a quadrilateral, a pentagon, etc. (such as Figure 5 Of course, unlike the isotropic structure of the cylinder, other shapes are anisotropic structures, so the properties of the incident light in different directions may change.

[0050] Example 11: The periodic air holes in the y direction in Example 1-10 are connected to form a connected long rectangle, such as Figure 6As shown, the air holes are distributed in a periodic one-dimensional array; similarly, the film can also achieve a similar reflection enhancement effect for sound waves incident on the xz plane (of course, considering the reflection angle, in order to ensure the effect of broadband reflection, the angle between the incident direction and the Z-axis direction does not exceed 60°). Of course, for this periodic one-dimensional array corresponding to this embodiment, the center spacing a between two adjacent air holes, the cross-sectional size d of a single second material area along the periodic arrangement direction (such as Figure 6 (as shown), these two parameters can also be flexibly adjusted according to actual needs; the effect of changes in shape parameters on the reflection enhancement frequency of incident sound waves in the xz plane is similar to that of a two-dimensional periodic structure. However, in this embodiment, because the air hole structure is no longer periodic in the y direction, the reflection enhancement effect of this metasurface on the sound wave is greatly reduced if the sound wave is incident in the yz plane (excluding the special case of incident in the z direction, which can also be classified as within the xz plane).

[0051] Example 12: The air holes in Examples 1-3 are replaced with polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), polycaprolactone (PCL), liquid metal, other gases, and other degradable materials with a significant difference in sound velocity from the first material (the sound velocity of the material with a higher sound velocity is more than twice that of the other with a lower sound velocity, with a significant difference in sound velocity). Taking the solid material polylactic acid (PLA) as an example, unlike the air holes that need to be completely wrapped and sealed by the matrix material, the PLA column can be embedded in the matrix material (the first material is a flexible material and serves as the matrix), and the upper and lower surfaces do not need to be covered by the matrix material. Of course, non-solid materials such as liquid metal and gas still need to be completely wrapped and sealed by the matrix material.

[0052] Example 13: Replacing the air holes in Examples 1-3 with other non-degradable materials that have a significant difference in sound velocity from the first material, such as iron, aluminum, steel and other metal materials, and using the non-degradable flexible first material as the matrix can meet the needs of long-term monitoring.

[0053] Performance testing:

[0054] The ultrasound contrast film of the present invention can greatly improve the reflectivity of ultrasound through the periodic air hole structure to improve the ultrasound imaging effect. Figure 2 As shown, the light can be incident at a certain angle from the upper surface of the sheet-like metamaterial (the angle between the incident direction and the normal direction of the upper surface does not exceed 60°). Of course, vertical incidence is preferred (i.e., vertical incidence from the top surface of the cylindrical air hole).

[0055] like Figure 4As shown, taking the metasurface with an air hole diameter of d = 0.07 mm, a period interval a = 0.1 mm, and a height of h = 0.1 mm obtained in Example 1 as an example, the incident ultrasonic wave is controlled to be incident along the z direction, and the frequency is swept from 1 MHz through simulation. The results show that the metasurface has a strong reflection enhancement function (reflectivity > 75%) for ultrasonic signals within a wider frequency band (1 MHz to 20 MHz), which can cover the frequencies of imaging ultrasound commonly used in hospitals.

[0056] When the size of the metasurface increases, it still shows a reflection enhancement effect (although the reflection of high-frequency sound waves will be weakened), for example Figure 4 As shown in , the metasurface with a periodic interval of a = 0.5mm, d = 0.35mm, and a height of h = 0.5mm still exhibits an acoustic reflection effect (although the reflection of high-frequency sound waves will be weakened). Based on this feature, according to the actual needs of the reflection enhancement band, the two shape parameters a and d can be adjusted independently and flexibly to meet different needs (of course, for the case where the periodic arrangement is a two-dimensional periodic arrangement, d needs to be smaller than a; in addition, whether it is a one-dimensional or two-dimensional periodic array, the parameter h can also be flexibly adjusted, and it has almost no effect on the acoustic properties of the film; of course, if h is smaller, the corresponding acoustic reflection film will have a thinner thickness and will be easier to conformally adhere to the surface of the target organ or tissue).

[0057] The above embodiments are merely examples. For example, according to actual needs, the diameter, height, and spacing of the air holes can be changed to other proportions. By adjusting the size design, a metasurface with a certain reflective effect can be obtained.

[0058] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An acoustic reflective film for ultrasound imaging of organs or tissues in vivo, characterized in that: The method comprises a first material and a second material having different material sound velocities, wherein the first material is a flexible and deformable material, and the second material is distributed within the first material and is periodically arranged along a distribution plane; and the material sound velocity of the first material and the second material is at least twice that of the material sound velocity of the second material. The acoustic reflective film is used to be fixed on the surface of the internal organ or tissue to be imaged by ultrasound; the ultrasonic wave is used to be incident along an incident direction with an angle of no more than 60° with respect to the normal direction of the distribution plane. In this way, the periodically arranged second material can enhance the reflection of the ultrasound based on the multiple scattering effect, thereby playing a role in imaging.

2. The acoustic reflective film according to claim 1, wherein: The second material is air. Accordingly, the acoustic reflection film comprises a sheet-like flexible material matrix and periodically arranged air holes (102) sealed in the matrix.

3. The acoustic reflective film according to claim 2, wherein: The air hole (102) is a cylindrical hole, a polygonal prism hole or an elliptical column hole.

4. The acoustic reflective film according to claim 3, wherein: The air hole (102) is a cylindrical hole.

5. The acoustic reflective film according to claim 2, wherein: An adhesive layer (103) is also provided on the bottom surface of the acoustic reflection film.

6. The acoustic reflective film according to claim 5, wherein: The adhesion layer (103) is a chitosan adhesion layer.

7. The acoustic reflective film according to claim 1, wherein: The second material is arranged in a two-dimensional periodic manner inside the first material. For the periodically arranged second material, the center distance a between two adjacent second material areas does not exceed 10 mm; the cross-sectional size d of a single second material area is smaller than the center distance a, and the height h does not exceed 10 mm.

8. The acoustic reflective film according to claim 1, wherein: The second material is arranged in a one-dimensional periodic pattern within the first material. For the periodically arranged second material, the center-to-center distance a between two adjacent second material regions does not exceed 10 mm; the cross-sectional dimension d of a single second material region along the periodic arrangement direction does not exceed 10 mm, and the height h of a single second material region does not exceed 10 mm. Furthermore, compared to the plane where both the periodic arrangement direction and the normal direction of the distribution plane are located, the ultrasonic wave incident direction is also parallel to the plane.

9. The acoustic reflective film according to claim 7 or 8, characterized in that: The height h is less than 1 mm.

10. The acoustic reflective film according to claim 1, wherein: The ultrasonic wave is used to be incident along an incident direction parallel to the normal direction of the distribution plane.

11. Use of the acoustic reflective film according to any one of claims 1 to 10 in the preparation of an implantable ultrasound contrast agent for internal organs or tissues.

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