Ultrasonic imaging system

Abstract

The present invention discloses an ultrasonic imaging system, which belongs to the field of ultrasonic imaging technology and includes a multi-frequency imaging probe and a multi-frequency imaging probe. Based on the difference in acoustic reflection characteristics between an acoustic reflective film and biological tissue, the present invention transmits ultrasonic signals of multiple frequencies to a tissue to be imaged with an acoustic reflective film attached to its surface through the multi-frequency imaging probe. The transmitted ultrasonic signal frequency includes two frequency types, and the frequency of the first frequency type is less than the cutoff frequency f of the acoustic reflective film. th , the frequency of the second frequency type is greater than or equal to f th ;f th The invention relates to a frequency region in which the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal decreases in a stepwise manner; the ultrasonic imaging results under the first frequency type and the second frequency type are differentially calculated by the imaging processing module to obtain the ultrasonic imaging results of the tissue to be imaged; when imaging soft tissue, the contrast of the soft tissue ultrasonic image can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic imaging, and more particularly, relates to an ultrasonic imaging system. Background Art

[0002] In recent years, advances in imaging technology have significantly enhanced our ability to visualize and understand the complex biological structures and functions within the human body. Imaging techniques such as CT and MRI can provide high-contrast images of in vivo tissues, but due to radiation hazards and equipment costs, they cannot provide long-term continuous monitoring of patients. Ultrasound imaging, however, offers inherent advantages in long-term continuous monitoring due to its non-invasiveness, ease of use, low cost, and ability to provide real-time continuous monitoring. Therefore, the development of an ultrasound imaging system is of great significance.

[0003] However, traditional ultrasound imaging systems often use a single-frequency ultrasound probe to directly image the tissue being imaged. This makes it difficult to accurately distinguish between tissues with similar acoustic properties, making it challenging to monitor soft, complex tissues such as the intestines. For example, these tissues are susceptible to interference from factors such as food debris and air bubbles within the intestines. Therefore, there is an urgent need for an ultrasound imaging system that can generate enhanced ultrasound images to improve the contrast of soft tissues such as the intestines. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides an ultrasonic imaging system for solving the technical problem that the contrast of soft tissue ultrasonic images obtained by the existing ultrasonic imaging system is low.

[0005] In order to achieve the above object, the present invention provides an ultrasonic imaging system, comprising:

[0006] The multi-frequency imaging probe is used to transmit ultrasonic signals of multiple frequencies to the tissue to be imaged and receive corresponding reflected signals reflected by the acoustic reflective film attached to the surface of the tissue to be imaged; wherein the cutoff frequency f of the acoustic reflective film is th The value range of is [f1, f2], where f1 and f2 are the frequencies corresponding to the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal, respectively. The ultrasonic signal frequency emitted by the multi-frequency imaging probe includes two frequency types. The frequency of the first frequency type is less than f th , the frequency belonging to the second frequency type is greater than or equal to f th ;

[0007] The imaging processing module is used to perform ultrasonic imaging on the reflected signals corresponding to each frequency respectively, and after obtaining the ultrasonic imaging results under the first frequency type and the second frequency type, perform differential operation to obtain the ultrasonic imaging results of the tissue to be imaged.

[0008] Further preferably, the cutoff frequency f th It is the frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal.

[0009] Further preferably, the ratio of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2.

[0010] Further preferably, the acoustic reflective film comprises: a substrate and filling units; the filling units are distributed inside the substrate and are periodically arranged along a distribution plane; the sound velocities of the materials of the substrate and the filling units are different, and the larger sound velocity is at least twice the smaller sound velocity; the substrate is made of a flexible and deformable material;

[0011] The parameter q of the acoustic reflective film satisfies: the ratio p of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2;

[0012] Among them, the smaller the parameter q, the larger the ratio p; is the filling rate of the filling unit in the acoustic reflective film; n is the total number of filling units in the acoustic reflective film; A is the area of ​​a filling unit; S is the area of ​​the substrate.

[0013] Further preferably, the parameter a of the acoustic reflective film satisfies: f1∈[1MHz,10MHz], and f2∈[1MHz,10MHz];

[0014] Among them, the smaller the parameter a is, the smaller f1 and f2 are; a is the distance between the geometric centers of two adjacent filling units.

[0015] Further preferably, the material of the filling unit is air, and correspondingly, the filling unit is an air hole.

[0016] Further preferably, the multi-frequency imaging probe includes: an ultrasonic transducer array; in the ultrasonic transducer array, the frequencies of ultrasonic signals emitted by ultrasonic transducer elements in the same row are the same, and the frequencies of ultrasonic signals emitted by ultrasonic transducer elements in different rows are different.

[0017] Further preferably, each row of ultrasonic transducer elements of the ultrasonic transducer array sequentially transmits ultrasonic signals of corresponding frequencies to the tissue to be imaged, so as to perform scanning imaging of the tissue to be imaged at multiple frequencies;

[0018] The time interval between two adjacent rows of ultrasonic transducer array elements scanning and imaging the tissue to be imaged is less than a preset time interval.

[0019] Further preferably, the multi-frequency imaging probe comprises: an ultrasonic transducer linear array; any two adjacent ultrasonic transducer array elements in the ultrasonic transducer linear array emit ultrasonic signals of different frequency types.

[0020] Further preferably, among the frequencies of the ultrasonic signals emitted by the multi-frequency imaging probe, when the number of frequencies belonging to a first frequency type is 1, the ultrasonic imaging result under the first frequency type is the ultrasonic imaging result under the frequency belonging to the first frequency type; when the number of frequencies belonging to the first frequency type is greater than or equal to 2, the ultrasonic imaging result under the first frequency type is the ultrasonic imaging result under any frequency belonging to the first frequency type, or the average result of the ultrasonic imaging results under the frequencies belonging to the first frequency type;

[0021] Among the ultrasonic signal frequencies emitted by the multi-frequency imaging probe, when the number of frequencies belonging to the second frequency type is 1, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under the frequency belonging to the second frequency type; when the number of frequencies belonging to the second frequency type is greater than or equal to 2, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under any frequency belonging to the second frequency type, or the average result of the ultrasonic imaging results under each frequency belonging to the second frequency type.

[0022] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0023] 1. The present invention provides an ultrasonic imaging system. Through research, it is found that the relationship curve between the reflectivity of an acoustic reflective film and the frequency of an ultrasonic signal has a step-down characteristic. The reflectivity of relatively hard biological tissues such as bones, connective tissues, food residues and bubbles in the digestive tract changes relatively smoothly with the change of the ultrasonic signal frequency and has high reflectivity. The reflectivity of soft tissues such as the intestines and stomach changes relatively smoothly with the change of the ultrasonic signal frequency and has low reflectivity. Based on the difference in acoustic reflection characteristics between the acoustic reflective film and biological tissues, the present invention designs an ultrasonic imaging system including a multi-frequency imaging probe and an imaging processing module. The multi-frequency imaging probe transmits ultrasonic signals of multiple frequencies to the tissue to be imaged with the acoustic reflective film attached to the surface. The frequency of the ultrasonic signal emitted by the multi-frequency imaging probe includes two frequency types. The frequency belonging to the first frequency type is less than the cutoff frequency f of the acoustic reflective film. th , the frequency belonging to the second frequency type is greater than or equal to the cutoff frequency f of the acoustic reflective membrane th ;f thThe invention relates to a frequency region in which a curve showing a relationship between the reflectivity of an acoustic reflective film and the frequency of an ultrasonic signal drops stepwise; the ultrasonic imaging results under the first frequency type and the second frequency type are differentially calculated by an imaging processing module to obtain an ultrasonic imaging result of the tissue to be imaged; when imaging soft tissue, the imaging interference of hard biological tissue can be eliminated, thereby solving the technical problem of low contrast of soft tissue ultrasonic images obtained by existing ultrasonic imaging systems.

[0024] 2. Furthermore, the ultrasonic imaging system provided by the present invention has a cutoff frequency f th The frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal can more accurately divide the ultrasonic signal frequency ranges of high reflectivity and low reflectivity, making it easier to select the ultrasonic probe used for differential imaging.

[0025] 3. Furthermore, in the ultrasonic imaging system provided by the present invention, the ratio of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the ultrasonic signal frequency is greater than or equal to 2. The larger the ratio of the highest reflectivity to the lowest reflectivity, the higher the differential image signal-to-noise ratio, so that the ultrasonic signal intensities of different frequencies have obvious differences, and better differential imaging can be achieved.

[0026] 4. Furthermore, the ultrasonic imaging system provided by the present invention adopts an acoustic reflective film comprising: a base and a filling unit; the filling unit is distributed inside the base and is periodically arranged along the distribution plane; the sound velocities of the materials of the base and the filling unit are different, and the larger sound velocity is at least twice the smaller sound velocity; the material of the base is a flexible deformable material; the smaller the parameter q of the acoustic reflective film, the larger the ratio p of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal; by adjusting the parameter q of the acoustic reflective film, the ratio p can be simply and conveniently controlled, so that the ratio p of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2.

[0027] 5. Furthermore, the ultrasonic imaging system provided by the present invention uses an acoustic reflective film including: a substrate and a filling unit; the smaller the parameter a of the acoustic reflective film, the smaller f1 and f2; by adjusting the parameter a of the acoustic reflective film, f1 and f2 can be made within the frequency range [1MHz, 10MHz] of commercial ultrasonic probes, and the applicability is relatively high.

[0028] 6. Furthermore, in the ultrasound imaging system provided by the present invention, the multi-frequency imaging probe includes an ultrasound transducer array. Within the ultrasound transducer array, ultrasound signals emitted by ultrasound transducer elements in the same row have the same frequency, while ultrasound signals emitted by ultrasound transducer elements in different rows have different frequencies. This design enables a single multi-frequency imaging probe to transmit ultrasound signals of different frequencies and receive corresponding reflected signals, simplifying operation.

[0029] 7. Furthermore, in the ultrasonic imaging system provided by the present invention, each row of ultrasonic transducer elements of the ultrasonic transducer array sequentially transmits ultrasonic signals of corresponding frequencies to the tissue to be imaged, so as to perform scanning imaging of the tissue to be imaged at multiple frequencies; the time interval between two adjacent rows of ultrasonic transducer elements scanning and imaging the tissue to be imaged is less than a preset time interval, thereby ensuring that when the tissue to be imaged is dynamic, the morphology of the tissue to be imaged remains approximately unchanged during the imaging process, thereby achieving accurate imaging.

[0030] 8. Furthermore, in the ultrasound imaging system provided by the present invention, the multi-frequency imaging probe includes: an ultrasonic transducer linear array; the frequency types of the ultrasound signals emitted by any two adjacent ultrasonic transducer array elements in the ultrasonic transducer linear array are different; in addition to being able to transmit ultrasound signals of different frequencies and receive corresponding reflected signals by using only one multi-frequency imaging probe, the operation is simple, and the ultrasound transducer array elements of different frequencies can also image tissues in exactly the same position, avoiding artifacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of an ultrasonic imaging system provided by an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of a multi-frequency imaging probe provided in Example 1 of the present invention;

[0033] Figure 3 Schematic diagram of a multi-frequency imaging probe provided in Example 2 of the present invention;

[0034] Figure 4 Schematic diagram of a multi-frequency imaging probe provided in Example 3 of the present invention;

[0035] Figure 5 A top view of an acoustic reflective film provided in an embodiment of the present invention;

[0036] Figure 6 A side structural diagram of an acoustic reflective film provided by an embodiment of the present invention;

[0037] Figure 7 Schematic diagram of an acoustic reflective film with a single-layer periodic air hole structure provided by an embodiment of the present invention;

[0038] Figure 8 A schematic diagram of a cutoff frequency variation curve of an acoustic reflective film under different parameters a when the parameter q remains unchanged, provided in an embodiment of the present invention;

[0039] Figure 9 A schematic diagram of a curve showing a change in cutoff frequency of an acoustic reflective film under different parameters q when the parameter a remains unchanged, provided by an embodiment of the present invention;

[0040] Figure 10 A schematic diagram showing a comparison of the relationship between the reflectivity of the acoustic reflective film and biological tissue and the frequency of the ultrasonic signal provided in Example 11 of the present invention;

[0041] Figure 11 A schematic diagram of the imaging process of the ultrasound imaging system provided in Example 11 of the present invention;

[0042] Figure 12 The imaging flow chart of the ultrasonic imaging system provided in embodiment 11 of the present invention when continuously imaging the tissue to be imaged. DETAILED DESCRIPTION

[0043] 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.

[0044] In order to achieve the above object, the present invention provides an ultrasonic imaging system, such as Figure 1 As shown, it includes: a multi-frequency imaging probe and an imaging processing module;

[0045] The multi-frequency imaging probe is used to transmit ultrasonic signals of multiple frequencies to the tissue to be imaged, and transmits them in multiple times, each time transmitting an ultrasonic signal of one frequency, and receives the corresponding reflected signals reflected by the acoustic reflective film attached to the surface of the tissue to be imaged; the cutoff frequency f of the acoustic reflective film is th ∈[f1,f2], f1 and f2 are the frequencies corresponding to the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal, respectively; the ultrasonic signal frequency emitted by the multi-frequency imaging probe includes two frequency types, and the frequency belonging to the first frequency type is less than f th , the frequency belonging to the second frequency type is greater than or equal to f th Preferably, in an optional embodiment, the cutoff frequency f thIt is the frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal.

[0046] The imaging processing module is used to perform ultrasonic imaging on the reflected signals corresponding to each frequency respectively, and after obtaining the ultrasonic imaging results under the first frequency type and the second frequency type, perform differential operation to obtain the ultrasonic imaging results of the tissue to be imaged.

[0047] It should be noted that the tissue to be imaged in the present invention can be soft tissue or hard tissue, and is particularly suitable for soft tissue. When imaging soft tissue, it can eliminate the imaging interference of hard biological tissue, thereby solving the technical problem of low contrast of soft tissue ultrasound images obtained by existing ultrasound imaging systems.

[0048] For multi-frequency imaging probes:

[0049] In an optional embodiment, the multi-frequency imaging probe includes: an ultrasonic transducer array; in the ultrasonic transducer array, the frequencies of ultrasonic signals emitted by ultrasonic transducer elements in the same row are the same, and the frequencies of ultrasonic signals emitted by ultrasonic transducer elements in different rows are different.

[0050] At this time, each row of ultrasonic transducer array elements sequentially transmits ultrasonic signals of corresponding frequencies to the tissue to be imaged, so as to perform scanning imaging of the tissue to be imaged at multiple frequencies;

[0051] Preferably, for dynamic tissue to be imaged, to ensure that the morphology of the tissue to be imaged remains approximately unchanged during the imaging process, the time interval between two adjacent rows of ultrasonic transducer elements scanning the tissue to be imaged is less than a preset time interval. The preset time interval is determined based on the velocity of the tissue to be imaged. Specifically, the preset time interval satisfies the requirement that the distance the tissue to be imaged moves within the preset time interval is less than the wavelength of the ultrasound wave (i.e., the longitudinal resolution of the ultrasound wave).

[0052] In another alternative embodiment, the multi-frequency imaging probe includes an ultrasonic transducer array; any two adjacent ultrasonic transducer elements in the array emit ultrasonic signals of different frequencies. Compared to the previous alternative embodiment, this embodiment enables ultrasonic transducer elements of different frequencies to image tissue at the exact same location, thus avoiding artifacts.

[0053] To further illustrate the multi-frequency imaging probe, several specific embodiments are described below in detail:

[0054] Example 1:

[0055] like Figure 2As shown, the multi-frequency imaging probe in this embodiment is a dual-frequency imaging probe, specifically a two-row ultrasonic transducer array. The ultrasonic signals emitted by the ultrasonic transducer elements in the first row are all 3 MHz in frequency, while those emitted by the ultrasonic transducer elements in the second row are 7 MHz in frequency, with a 3dB bandwidth of less than 1 MHz. The probe cross-section has a length (s) and width (h) of 10 cm and 3 cm, respectively. The ultrasonic transducer elements are square, with a side length (d') of 4 mm. The spacing (a') between two adjacent ultrasonic transducer elements in the same row is 5 mm, and the spacing (b') between two adjacent ultrasonic transducer elements in the same column is 6 mm.

[0056] When capturing dynamic tissue, each row of ultrasonic transducer elements of the ultrasonic transducer array sequentially transmits ultrasonic signals of corresponding frequencies to the tissue to be imaged, so as to perform multiple-frequency scanning imaging of the tissue to be imaged. Specifically, the ultrasonic transducer linear array formed by the first row of ultrasonic transducer elements and the ultrasonic transducer linear array formed by the second row of ultrasonic transducer elements of the dual-frequency imaging probe are rapidly switched for imaging to ensure that the organ morphology is approximately unchanged during the imaging process of the two-frequency ultrasonic transducer linear array. The faster the switching speed, the smaller the impact on differential imaging. Considering the need for stable differential imaging of fast-moving tissue (such as a beating heart), the time interval between the probe completing the two-frequency scanning imaging is preferably less than 50ms.

[0057] Example 2

[0058] like Figure 3 As shown, the multi-frequency imaging probe in this embodiment is a quad-frequency imaging probe, specifically a four-row ultrasonic transducer array. The first row of ultrasonic transducer elements emits an ultrasonic signal at a frequency of 2 MHz, the second row of ultrasonic transducer elements emits an ultrasonic signal at a frequency of 4 MHz, the third row of ultrasonic transducer elements emits an ultrasonic signal at a frequency of 6 MHz, and the fourth row of ultrasonic transducer elements emits an ultrasonic signal at a frequency of 8 MHz. Increasing the number of probe frequencies can further improve the contrast of differential imaging, thereby enhancing applicability.

[0059] In this embodiment, the length s and width h of the probe cross section are 10 cm and 4 cm respectively; the ultrasonic transducer array element is a square with a side length d' of 4 mm; the spacing a' between two adjacent ultrasonic transducer array elements in the same row is 5 mm, and the spacing b' between two adjacent ultrasonic transducer array elements in the same column is 6 mm.

[0060] The process of scanning and imaging the tissue to be imaged by the quad-frequency imaging probe is basically the same as the basic process of scanning and imaging the tissue to be imaged by the dual-frequency imaging probe in Example 1, and will not be described in detail here.

[0061] It should be noted that the probe design can be extended to an n-frequency probe, which is composed of n groups of probe linear arrays with different center frequencies, and the linear arrays with different center frequencies are arranged in sequence in space; n is greater than or equal to 2.

[0062] Example 3

[0063] like Figure 4 As shown, the multi-frequency imaging probe in this embodiment includes an ultrasonic transducer linear array, specifically a transducer array with one row and twenty columns. Any two adjacent ultrasonic transducer elements in the linear array emit ultrasonic signals of different frequencies, with high- and low-frequency ultrasonic transducer elements alternating. The ultrasonic transducer elements are square, with side lengths b' = d' = 4 mm. The spacing a' between adjacent ultrasonic transducer elements is 5 mm.

[0064] It should be noted that the parameters of the multi-frequency imaging probe in the above embodiments are only one embodiment and not the only design.

[0065] For acoustic reflective films:

[0066] Cutoff frequency f of acoustic reflective film th ∈[f1,f2], f1 and f2 are the frequencies corresponding to the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal, respectively; the ultrasonic signal frequency emitted by the multi-frequency imaging probe includes two frequency types, and the frequency belonging to the first frequency type is less than f th , the frequency belonging to the second frequency type is greater than or equal to f th Preferably, in an optional embodiment, the cutoff frequency f th It is the frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal.

[0067] Preferably, in an optional embodiment, the ratio of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2.

[0068] In an alternative embodiment, Figure 5 As shown, the acoustic reflective film includes: a substrate 101 and a filling unit 102; the filling units are distributed inside the substrate and are periodically arranged along the distribution plane; the sound speeds of the materials of the substrate and the filling units are different, and the larger sound speed is at least twice the smaller sound speed; the material of the substrate is a flexible deformable material; the angle between the emission direction of the ultrasonic signal and the normal direction of the distribution plane does not exceed 60°; preferably, the emission direction of the ultrasonic signal is parallel to the normal direction of the distribution plane.

[0069] The parameter q of the acoustic reflective film satisfies: the ratio p of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2;

[0070] Among them, the smaller the parameter q, the larger the ratio p; is the filling rate of the filling unit in the acoustic reflective film; n is the total number of filling units in the acoustic reflective film; A is the area of ​​a filling unit; S is the area of ​​the substrate.

[0071] Preferably, in an optional implementation manner, the distances between any two adjacent filling units in the x and y directions are the same.

[0072] In an optional embodiment, after the parameter q of the acoustic reflective film meets the above requirements, the parameter a of the acoustic reflective film satisfies: f1∈[1MHz,10MHz], and f2∈[1MHz,10MHz];

[0073] Among them, the smaller the parameter a is, the smaller f1 and f2 are; a is the distance between the geometric centers of two adjacent filling units.

[0074] Preferably, if Figure 6 As shown, in an optional embodiment, an adhesive layer 103 is further provided on the bottom surface of the acoustic reflective film; the adhesive layer is preferably a chitosan adhesive layer.

[0075] In an alternative embodiment, Figure 7 As shown, the filling unit is made of air, and accordingly, the filling unit is an air hole. The acoustic reflective film comprises a sheet-like flexible material substrate and periodically arranged air holes sealed within the substrate. The air holes can be cylindrical, polygonal prism, or elliptical, with cylindrical holes being preferred.

[0076] The filling units are arranged in a two-dimensional periodic arrangement or a one-dimensional periodic arrangement inside the substrate. Specifically, in an optional embodiment, the filling units are arranged in a two-dimensional periodic arrangement inside the substrate. For a periodically arranged substrate, the center spacing a between two adjacent filling units does not exceed 10 mm; the cross-sectional dimension d of a single filling unit along the periodic arrangement direction (when the filling unit is a cylindrical hole, d is the cross-sectional diameter of the cylindrical hole along the periodic arrangement direction) is less than the center spacing a, and the height h does not exceed 10 mm; preferably, the height h is less than 1 mm. In another optional embodiment, the filling units are arranged in a one-dimensional periodic arrangement inside the substrate. For a periodic arrangement of filling units, the center spacing a between two adjacent filling units does not exceed 10 mm; the cross-sectional dimension d of a single filling unit along the periodic arrangement direction (when the filling unit is a cylindrical hole, d is the cross-sectional diameter of the cylindrical hole along the periodic arrangement direction) does not exceed 10 mm, and the height h of a single filling unit does not exceed 10 mm; preferably, the height h is less than 1 mm; and the emission direction of the ultrasonic signal is parallel to plane A; plane A is the plane where the periodic arrangement direction and the normal direction of the distribution plane are located.

[0077] The acoustic reflective film includes a sheet-like flexible material substrate and periodically arranged air holes sealed in the substrate, and the air holes are cylindrical holes. This is described in detail below. In this case, the filling units are air columns.

[0078] In order to obtain different cutoff frequencies f th , the preparation examples are as follows:

[0079] Example 4

[0080] For example, an acoustic reflective film with a cutoff frequency of 4 MHz, made from a double-crosslinked hydrogel of polyvinyl alcohol and carboxymethyl chitosan, has a periodic column structure with a parameter a (the distance between the geometric centers of two adjacent filling units) of 0.36 mm and a parameter q (the filling ratio of the filling units in the acoustic reflective film) of 0.55 (corresponding to an air column diameter d of 0.2 mm). This periodic air column structure has no fewer than three periods in the x and y directions.

[0081] The preparation process can be:

[0082] First, 10 ml of a 4 wt% carboxymethyl chitosan aqueous solution and 10 ml of a 20 wt% polyvinyl alcohol were dissolved in deionized water at 90°C. After complete dissolution, 1.5 ml of a 4 wt% aluminum chloride hexahydrate solution was added. The mixture was then mixed evenly by magnetic stirring and degassed. The mixture was poured into a 3D-printed mold with a designed periodic column structure with parameters a of 0.36 mm and q of 0.55, and cyclically frozen and thawed at -20°C. After demolding, the air holes were sealed with hydrogel to prevent water ingress, thereby obtaining the target acoustic metamaterial, namely the acoustic reflective film.

[0083] In addition, by varying the ratio of raw materials in the hydrogel, the modulus parameters of the hydrogel material can be adjusted within a certain range, enabling better mechanical adaptation for different fitting locations. The periodic air column structure can be designed with five or more layers in the y-direction.

[0084] Example 5

[0085] This example and Example 4 both utilize a polyvinyl alcohol and carboxymethyl chitosan dual-crosslinked hydrogel. The parameter q is 0.55 in both cases. The difference lies in the acoustic reflective film in this example having a parameter a of 0.72 mm and a periodic column structure with a diameter of 0.4 mm. The corresponding acoustic reflective film has a cutoff frequency of 2 MHz.

[0086] The preparation process is similar to that of Example 4, except that the size of the mold used for casting needs to be proportionally enlarged to twice its original size, that is, the parameter a of the periodic column is adjusted to 0.72 mm and the diameter is adjusted to 0.4 mm.

[0087] In addition to Example 5, the present invention also experiments with other methods of proportionally enlarging / reducing the parameter a and the diameter in Example 4, i.e., keeping the parameter q unchanged. The corresponding enlargement / reduction of the parameter a and the corresponding cutoff frequency of the acoustic reflective film are shown in Table 1 below. In this way, the parameters a and q can be flexibly adjusted according to the actual requirements of the cutoff frequency:

[0088] Table 1. Correspondence between parameter a of acoustic reflective film and cutoff frequency

[0089] Parameter a Parameter q <![CDATA[Cutoff frequency f th > 1.44mm 0.55 1MHz 0.72mm 0.55 2MHz 0.36mm 0.55 4MHz

[0090] More specifically, when the parameter q remains unchanged, the cutoff frequency of the acoustic reflective film under different parameters a changes as follows: Figure 8 shown.

[0091] Example 6

[0092] This example, like Examples 4 and 5, utilizes a polyvinyl alcohol and carboxymethyl chitosan dual-crosslinked hydrogel. However, the acoustic reflective film in this example has a periodic column structure with a parameter a of 0.36 mm and a parameter q of 0.25 (corresponding to a diameter of 0.7 mm). The corresponding cutoff frequency of the acoustic reflective film is 7 MHz.

[0093] The preparation process is similar to that of Example 4, except that the column portion of the mold used for casting needs to be enlarged to 0.25 mm, that is, the parameter a of the periodic column is 0.36 mm, and the diameter is adjusted to 0.25 mm.

[0094] In addition to this embodiment, the present invention also experiments with other methods in which the parameter q (diameter) in Example 4 is enlarged or reduced while the parameter a remains unchanged, and the corresponding cutoff frequencies of the acoustic reflective film are formed. The results are shown in Table 2 below. In this way, the parameters a and q can be flexibly adjusted according to the actual requirements of the cutoff frequency of the acoustic reflective film:

[0095] Table 2. Correspondence between the parameter q of the acoustic reflective film and the cutoff frequency

[0096] Parameter a Parameter q <![CDATA[Cutoff frequency f th > 0.36mm 0.25 3MHz 0.36mm 0.55 4MHz 0.36mm 0.7 7MHz

[0097] More specifically, when the parameter a is kept constant, the cutoff frequency of the acoustic reflective film under different parameters q changes as follows: Figure 9 shown.

[0098] Example 7

[0099] This embodiment, like Embodiments 4, 5, and 6, uses a double-crosslinked hydrogel of carboxymethyl chitosan and polyvinyl alcohol. The difference is that in this embodiment, the hydrogel material is poured into a structureless rectangular mold for solidification, and then a laser subtractive process is used to etch periodic air holes in the hydrogel. The air holes are then sealed with hydrogel to obtain an acoustic reflective film.

[0100] Example 8

[0101] By replacing the carboxymethyl chitosan and polyvinyl alcohol double cross-linked hydrogels in Examples 4, 5, and 6 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, etc.), the same process can be used to prepare acoustic reflection films, and the corresponding cutoff frequency remains basically unchanged.

[0102] Example 9

[0103] By replacing the hydrogel materials in Examples 4, 5, and 6 with other silicone-based elastomer materials with similar modulus and density, such as polydimethylsiloxane, Ecoflex flexible material, etc., the same process can be used to prepare acoustic reflective films, and the corresponding cutoff frequency remains basically unchanged.

[0104] Example 10

[0105] Although cylindrical air hole structures are more suitable for the air hole design of the present invention due to their isotropic geometric properties, acoustic metamaterials with narrowband reflection capabilities and strain-induced reflection band frequency shift can also be prepared by replacing the cylindrical air holes in Examples 4-8 with air columns of similar dimensions, such as polygonal prisms or elliptical cylinders. The present invention does not limit the air hole morphology; other air column structures can be used without affecting the characteristic reflection peak frequency shift of the acoustic reflective film when deformed.

[0106] For the imaging processing module:

[0107] In an optional embodiment, among the frequencies of the ultrasound signals emitted by the multi-frequency imaging probe, when the number of frequencies belonging to a first frequency type is 1, the ultrasound imaging result under the first frequency type is the ultrasound imaging result at the frequencies belonging to the first frequency type; when the number of frequencies belonging to the first frequency type is greater than or equal to 2, the ultrasound imaging result under the first frequency type is the ultrasound imaging result at any frequency belonging to the first frequency type, or the average result of the ultrasound imaging results at the frequencies belonging to the first frequency type;

[0108] Among the ultrasonic signal frequencies emitted by the multi-frequency imaging probe, when the number of frequencies belonging to the second frequency type is 1, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under the frequency belonging to the second frequency type; when the number of frequencies belonging to the second frequency type is greater than or equal to 2, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under any frequency belonging to the second frequency type, or the average result of the ultrasonic imaging results under each frequency belonging to the second frequency type.

[0109] This is described in detail by the following examples:

[0110] Example 11

[0111] Taking the acoustic reflective film obtained in Example 4 with a parameter a of 0.36 mm and an air column diameter d of 0.2 mm as an example, it was found through research that the acoustic reflective film has high reflection performance for sound waves with a frequency below 1-4 MHz and low reflection performance for sound waves with a frequency of 4-8 MHz. The harder biological tissues in the body (such as tendons and bones) have high reflection performance for ultrasonic waves in the range of 1-8 MHz. Figure 10 As shown. Specifically, by adjusting parameter a so that the ratio of the highest reflectivity to the lowest reflectivity in the curve of the relationship between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2, the acoustic reflective performance of the acoustic reflective film and biological tissue differs significantly. The present invention utilizes this difference in acoustic reflective performance between the acoustic reflective film and biological tissue to achieve differential imaging based on a multi-frequency imaging probe, enabling higher-contrast ultrasonic imaging.

[0112] Specifically, taking the acoustic reflective film obtained in Example 4 with a parameter a of 0.36 mm and an air column diameter d of 0.2 mm as an example, the reflection spectrum of the acoustic reflective film can be divided into three parts: below 4 MHz is a low-frequency strong reflection area, and the acoustic reflective film has a strong reflection ability for sound waves within this frequency range; 4 MHz to 4.5 MHz is a step-down area, and the reflectivity within this frequency range decreases rapidly with increasing frequency; above 4.5 MHz is a high-frequency weak reflection area, and the acoustic reflective film has a weak reflection ability for sound waves within this frequency range. Therefore, it is necessary to make the multi-frequency imaging probe emit two types of frequencies, the frequencies of the first frequency type are within the frequency range of the low-frequency strong reflection area, and the frequencies of the second frequency type are within the frequency range of the high-frequency weak reflection area.

[0113] Specifically, the frequency of the first frequency type is less than f th , the frequency of the second frequency type is greater than or equal to f th ; Cut-off frequency f of acoustic reflective film th ∈[f1,f2], f1 and f2 are the frequencies corresponding to the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal, respectively; preferably, the cutoff frequency f th It is the frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal.

[0114] The acoustic reflective film is attached to the surface of the tissue to be imaged, and ultrasonic signals of multiple frequencies are transmitted to the tissue to be imaged through a multi-frequency imaging probe, and the corresponding reflected signals are received; by performing a differential operation on the ultrasonic imaging results under the first frequency type and the ultrasonic imaging results under the second frequency type, a high-contrast ultrasonic image of the acoustic reflective film can be obtained. When biological tissue is imaged using the frequencies under the first frequency type and the frequencies under the second frequency type, there is no obvious difference in the echo images. Therefore, after the differential operation, the brightness of the ultrasonic image of the biological tissue will be significantly reduced. Specifically, Figure 11 As shown. Figure 12 As shown, when imaging tissue continuously, the original two-dimensional image matrix obtained by the multi-frequency imaging probe at different frequencies is normalized and standardized before being converted into corresponding grayscale images. The grayscale images at different frequencies are then differentially processed to obtain a single-frame differential image. By performing temporally continuous differential imaging, multiple temporally continuous differential images can be obtained.

[0115] Example 12

[0116] Taking the acoustic reflective film obtained in Example 4 with parameter a of 0.36 mm and air column diameter d of 0.2 mm as an example, frequencies of 4 MHz and 5 MHz can be selected for imaging respectively, and differential operations can be performed to obtain high-contrast ultrasonic images of the acoustic reflective film.

[0117] Example 13

[0118] This embodiment is modified based on Example 11. The 4 MHz and 5 MHz frequencies in Example 11 can also be selected as a combination of any frequency within the frequency range of a low-frequency strong reflection zone and any frequency within the frequency range of a high-frequency weak reflection zone. For example, 4 MHz can be replaced by an imaging probe with a frequency of 3 MHz, 2 MHz, or 1 MHz, and 5 MHz can be replaced by a frequency of 6 MHz, 7 MHz, 8 MHz, etc.

[0119] Example 14

[0120] When the geometric parameters of an acoustic reflective film change, the frequency ranges of the low-frequency strong reflection area and the high-frequency weak reflection area will change. This example uses the acoustic metamaterial obtained in Example 5, with a parameter a of 0.72 mm and an air column diameter d of 0.4 mm, as an example. The step-down region is around 2 MHz. Therefore, imaging at frequencies of 2 MHz and 4 MHz was performed separately, and a differential operation was performed to obtain a high-contrast ultrasound image of the acoustic reflective film.

[0121] Example 15

[0122] Taking the acoustic metamaterial obtained in Example 4, with a lattice constant a of 0.36 mm and an air column diameter d of 0.2 mm, as an example, n-frequency probe imaging was performed. m low-frequency probes were selected in the strong reflection area, and (nm) high-frequency probes were selected in the weak reflection area. The images from each low-frequency probe and each high-frequency probe were averaged and then differentially calculated to obtain a high-contrast multi-frequency differential ultrasound image of the acoustic reflective film. n and m are arbitrary positive integers, with n greater than m.

[0123] Taking quad-frequency probe imaging as an example, two low-frequency probes (2MHz and 4MHz) were selected in the strong reflection area and two high-frequency probes were selected in the weak reflection area (5MHz and 8MHz). The images of each low-frequency probe and each high-frequency probe were averaged, and a differential operation was performed to obtain a high-contrast multi-frequency differential ultrasound image of the acoustic reflective film.

[0124] 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 ultrasonic imaging system, characterized in that: include: The multi-frequency imaging probe is used to transmit ultrasonic signals of multiple frequencies to the tissue to be imaged and receive corresponding reflected signals reflected by an acoustic reflective film attached to the surface of the tissue to be imaged; the cutoff frequency f of the acoustic reflective film is th The value range of is the interval [f1, f2], where f1 and f2 are the frequencies corresponding to the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal, respectively; the ultrasonic signal frequency emitted by the multi-frequency imaging probe includes two frequency types, and the frequency belonging to the first frequency type is less than f th , the frequency belonging to the second frequency type is greater than or equal to f th ; The imaging processing module is used to perform ultrasonic imaging on the reflected signals corresponding to each frequency respectively, and after obtaining the ultrasonic imaging results under the first frequency type and the second frequency type, perform differential operation to obtain the ultrasonic imaging results of the tissue to be imaged.

2. The ultrasonic imaging system according to claim 1, wherein: The cut-off frequency f th It is the frequency corresponding to the average value of the highest reflectivity and the lowest reflectivity on the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal.

3. The ultrasonic imaging system according to claim 1, wherein: The ratio of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2.

4. The ultrasonic imaging system according to claim 3, wherein: The acoustic reflective film comprises: a base and filling units; the filling units are distributed inside the base and are periodically arranged along a distribution plane; the sound velocities of the materials of the base and the filling units are different, and the larger sound velocity is at least twice the smaller sound velocity; the base is made of a flexible and deformable material; The filling rate q of the filling unit in the acoustic reflective film satisfies: the ratio p of the highest reflectivity to the lowest reflectivity in the relationship curve between the reflectivity of the acoustic reflective film and the frequency of the ultrasonic signal is greater than or equal to 2; The smaller the q is, the larger the ratio p is; n is the total number of the filling units in the acoustic reflective film; A is the area of ​​one of the filling units; and S is the area of ​​the substrate.

5. The ultrasonic imaging system according to claim 4, wherein: The geometric center distance a between two adjacent filling units in the acoustic reflective film satisfies: f1∈interval 1MHz, 10MHz], and f2∈interval [1MHz, 10MHz]; The smaller a is, the smaller f1 and f2 are.

6. The ultrasonic imaging system according to claim 4, wherein: The material of the filling unit is air, and accordingly, the filling unit is an air hole.

7. The ultrasonic imaging system according to any one of claims 1 to 6, characterized in that: The multi-frequency imaging probe includes: an ultrasonic transducer array; in the ultrasonic transducer array, the ultrasonic signals emitted by the ultrasonic transducer elements in the same row have the same frequency, and the ultrasonic signals emitted by the ultrasonic transducer elements in different rows have different frequencies.

8. The ultrasonic imaging system according to claim 7, wherein: The ultrasonic transducer array elements of each row of the ultrasonic transducer array sequentially transmit ultrasonic signals of corresponding frequencies to the tissue to be imaged, so as to perform scanning imaging of the tissue to be imaged at multiple frequencies; The time interval between two adjacent rows of ultrasonic transducer array elements scanning and imaging the tissue to be imaged is less than a preset time interval.

9. The ultrasonic imaging system according to any one of claims 1 to 6, characterized in that: The multi-frequency imaging probe comprises: an ultrasonic transducer linear array; two adjacent ultrasonic transducer array elements in the ultrasonic transducer linear array emit ultrasonic signals of different frequency types.

10. The ultrasonic imaging system according to any one of claims 1 to 6, characterized in that: Among the frequencies of the ultrasonic signals emitted by the multi-frequency imaging probe, when the number of frequencies belonging to a first frequency type is 1, the ultrasonic imaging result under the first frequency type is the ultrasonic imaging result under the frequencies belonging to the first frequency type; when the number of frequencies belonging to the first frequency type is greater than or equal to 2, the ultrasonic imaging result under the first frequency type is the ultrasonic imaging result under any frequency belonging to the first frequency type, or the average result of the ultrasonic imaging results under the frequencies belonging to the first frequency type; Among the ultrasonic signal frequencies emitted by the multi-frequency imaging probe, when the number of frequencies belonging to the second frequency type is 1, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under the frequency belonging to the second frequency type; when the number of frequencies belonging to the second frequency type is greater than or equal to 2, the ultrasonic imaging result under the second frequency type is the ultrasonic imaging result under any frequency belonging to the second frequency type, or the average result of the ultrasonic imaging results under each frequency belonging to the second frequency type.

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