Acoustic coupler, ultrasonic image processing method, and ultrasonic imaging device

Abstract

To provide an acoustic coupler for ultrasonic imaging which can detect the attitude of an ultrasonic probe from an image.SOLUTION: An acoustic coupler 10 comprises: a first layer 11 which contacts with an ultrasonic probe of an ultrasonic imaging device; a second layer 12 which contacts with an imaging object; and an intermediate layer 13 which is between the first layer and the second layer and made of a material with the high elastic modulus. The intermediate layer 13 includes a plurality of markers made of a material reflecting the ultrasonic wave in the vicinity of a boundary of, for example, adjacent two layers at different positions in the travel direction of the ultrasonic wave. The ultrasonic imaging device detects the attitude of the ultrasonic probe from the image of the markers included in the ultrasonic image.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic coupler that is interposed between an ultrasound probe and an object to be examined in an ultrasound imaging device such as a medical ultrasound diagnostic device. [Background technology]

[0002] In modern medicine, imaging diagnostics that can obtain information about the inside of the body non-invasively are an essential technology and are widely used. Among imaging diagnostic modalities, there are high expectations for ultrasound diagnostic devices that can provide a compact and inexpensive solution.

[0003] In particular, there is a high need for simple ultrasound diagnostic devices for screening tests for pneumonia, etc. However, because there are body hairs and pores on the surface of the subject's body, the quality of the image depends on the angle at which the ultrasound probe (hereinafter referred to as the probe) is pressed against the body surface, the method of scanning, and the thickness of the jelly applied to the subject's body surface, and there is a problem of operator dependency in that only experienced operators can obtain high image quality. Acoustic couplers using highly deformable gel instead of jelly have also been developed, and by using highly deformable gel, the operator-dependency problem of jelly application can be reduced, and the work involved in application and removal can be reduced.

[0004] When using an acoustic coupler, it is necessary to optimize the acoustic impedance in order to reduce the attenuation of ultrasound between the subject and an acoustic lens or the like arranged on the contact surface side of the probe. Patent Document 1 proposes constructing an acoustic coupler by stacking materials with different acoustic impedances.

[0005] However, when used in ultrasound diagnostic equipment, acoustic couplers are required to be able to deform to follow the irregularities on the surface of the object to be examined and to have excellent acoustic matching with the test subject. Conventional acoustic couplers have difficulty satisfying both of these requirements, and are therefore rarely used in clinical settings.

[0006] In response to this problem, the present applicant has developed and proposed a resin for acoustic couplers that has excellent acoustic properties and high deformability (Patent Document 2, etc.). By using such a highly deformable resin, it is possible to capture images by following the uneven shape of the object surface without distorting it. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 05-27784 [Patent Document 2] JP 2021-10571 A Summary of the Invention [Problem to be solved by the invention]

[0008] When performing ultrasound imaging for screening purposes, it is important to image the target area without missing anything. However, because the body surface is uneven, for example, when scanning while moving the probe, the direction of the ultrasound beam changes, and there is a possibility that the target area cannot be covered. It is difficult to check such gaps that occur between scans by comparing the images of each scan. Therefore, even if there is a gap that cannot be scanned between adjacent imaging planes, it cannot be checked, and as a result, there is a possibility that the target area will not be imaged.

[0009] An object of the present invention is to provide a means for imaging a target area without omission, specifically, to provide an acoustic coupler that makes it possible to grasp the positional relationship between multiple images obtained by ultrasonic imaging. [Means for solving the problem]

[0010] The present invention solves the above problems by embedding markers made of a material that reflects ultrasonic waves in the resin (gel) that constitutes the acoustic coupler. By arranging the markers at two or more different positions in the ultrasonic propagation direction, the imaging plane determined by the ultrasonic propagation direction can be reliably specified.

[0011] That is, the acoustic coupler of the present invention has a first layer that contacts an ultrasonic probe (hereinafter also simply referred to as a probe) of an ultrasonic imaging device, and a second layer that contacts an imaging target, and is characterized in that it includes a plurality of markers at different positions between the first layer and the second layer with respect to the ultrasonic wave traveling direction. For example, an intermediate layer with a high elastic modulus is disposed between the first layer and the second layer, and markers are disposed above and below this intermediate layer.

[0012] The ultrasonic image processing method of the present invention is an ultrasonic image processing method in which an acoustic coupler is placed between an object to be examined and an ultrasonic probe, ultrasonic waves are transmitted to and received from the object to be examined via the ultrasonic probe, and an ultrasonic image of the object to be examined generated is processed, and includes a step of using the acoustic coupler of the present invention as the acoustic coupler and identifying multiple markers of the acoustic coupler in the ultrasonic image, and a step of calculating position information of the ultrasonic probe using the positional relationship of the identified multiple markers.

[0013] The ultrasound imaging device of the present invention comprises a transmission / reception unit to which an ultrasound probe is connected and which transmits and receives ultrasound via the ultrasound probe, and an image generation unit which generates an ultrasound image using ultrasound, which is a reflected wave received from an object to be examined, wherein the ultrasound image is an image captured by interposing the acoustic coupler of the present invention between the object to be examined and the ultrasound probe, and further comprises an imaging position calculation unit which calculates position information of the ultrasound probe based on the position of an image of a marker included in the ultrasound image. Effect of the Invention

[0014] According to the present invention, by embedding a marker in the acoustic coupler, the position and scanning direction of the probe can be confirmed from the position of the marker included in the ultrasound image captured through the acoustic coupler, thereby making it possible to confirm the position of the surface scanned by the probe (i.e., the imaging surface). [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing an embodiment of an acoustic coupler of the present invention. [Diagram 2] 13(a) and (b) are diagrams showing examples of marker types and their arrangements, respectively. [Diagram 3] 3A to 3C are diagrams showing an example of a method for manufacturing an acoustic coupler according to the present invention. [Figure 4] 5A to 5C are diagrams showing another example of a manufacturing method for an acoustic coupler according to the present invention. [Diagram 5] FIG. 2 is a diagram showing an example of a usage state of the acoustic coupler of the present invention. [Figure 6] FIG. 14 is a diagram for explaining the case where the long axis direction of the ultrasound probe is parallel to the arrangement of the markers on the acoustic coupler; (a) is a diagram showing the relationship between the markers and the long axis direction, and (b) is a diagram showing the image (point image) of the marker in an ultrasound image when the ultrasound probe is in the position shown in (a). [Figure 7] 13A and 13B are diagrams for explaining an image in which a marker exists on only one surface. [Figure 8] 13A and 13B are diagrams for explaining images in which markers exist on two surfaces. [Figure 9] FIG. 14 shows a case where the long axis direction of the ultrasound probe is tilted at an angle θ with respect to the marker of the acoustic coupler, where (a) shows the relationship between the marker and the long axis direction, and (b) shows the image (point image) of the marker in an ultrasound image when the ultrasound probe is in the position shown in (a). [Figure 10] 13A and 13B are diagrams for explaining a method for identifying warp and weft threads for a mesh-shaped marker. [Figure 11] FIG. 14 is a diagram explaining the detection method when the ultrasound probe is moved along the longitudinal axis direction; (a) is a diagram showing the relationship between the marker and the longitudinal axis direction, and (b) is a diagram showing the change in the image (point image) of the marker before and after the ultrasound probe is moved. [Figure 12] FIG. 14 is a diagram explaining the detection method when the ultrasound probe is moved along the short axis direction; (a) is a diagram showing the relationship between the marker and the short axis direction, and (b) is a diagram showing the change in the image (point image) of the marker before and after the ultrasound probe is moved. [Figure 13] 1A and 1B are diagrams for explaining a detection method when the imaging surface is inclined with respect to a reference surface, in which (a) shows a case where the imaging surface is perpendicular to the reference surface, and (b) shows a case where the imaging surface is inclined with respect to the reference surface. [Figure 14] 1 is an overall view showing an embodiment of an ultrasonic imaging apparatus of the present invention; [Figure 15] FIG. 11 is a flowchart showing an example of an operation of an imaging position calculation unit. [Figure 16] 6A and 6B are diagrams showing examples of display of position information calculated by an imaging position calculation unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of an acoustic coupler and an ultrasonic imaging method using the same of the present invention will be described.

[0017] First, an embodiment of an acoustic coupler will be described with reference to FIGS. The acoustic coupler 10 of this embodiment is composed of multiple layers each made of polymer gel, and markers identifiable in an ultrasonic image are disposed between or inside the layers. For example, as shown in Fig. 1, the coupler includes a layer (first layer) 11 that is interposed between an ultrasonic imaging device (ultrasonic probe), a layer (second layer) 12 that is interposed between an imaging target, and an intermediate layer 13 that is interposed between the first layer 11 and the second layer 12. In the example shown in Fig. 1, multiple markers 15 are held and fixed at two locations of the intermediate layer 13, near the boundary with the first layer 11 and near the boundary with the second layer 12.

[0018] Although FIG. 1 shows an acoustic coupler consisting of three layers, it may have a multi-layer structure in which an additional layer is inserted between or within these layers, and the marker 15 may be disposed between the first layer 11 and the second layer 12.

[0019] It is desirable that the polymer gel, which is the material of each layer of the acoustic coupler 10, is capable of achieving both the acoustic properties and mechanical properties required for ultrasonic imaging. Regarding the acoustic properties, for example, it is desirable that the sound velocity is equivalent to that of water (within a deviation of 5%) and that the ultrasonic attenuation rate is 0.1 dB / MHz / cm or less. The mechanical properties differ depending on the function of the layer, and it is desirable that the layer (second layer) 12, which is interposed between the imaging target 30, is highly deformable, and that the intermediate layer holding the marker 15 has a high elastic modulus.

[0020] As the material of the polymer gel, specifically, a hydrogel consisting of a crosslinked polymer such as agarose (agar), acrylamide, polysaccharide, or a mixture of acrylamide and polysaccharide, and water, or a non-hydrogel containing an organic solvent such as alcohol can be used. In particular, hydrogels using acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-propyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, diacetoneacrylamide, N-hydroxydiethylacrylamide, N-(3-methoxypropyl)acrylamide, and N-isopropylacrylamide as polymerizable monomers are preferable because they have acoustic properties close to those of water and can allow ultrasound to reach deep areas without attenuation. When acrylamide is used as the polymerizable monomer, it is preferable to use (bis)acrylamide such as N,N'-methylene(bis)acrylamide and N,N'-ethylene(bis)acrylamide as the crosslinking agent.

[0021] Furthermore, for the second layer 12 that is interposed between the imaging subject, it is preferable to use a hydrogel having a structure that contains polyacrylamide and alginic acid in a mesh structure, with alginic acid held within the mesh of the polyacrylamide network structure, as disclosed in Patent Document 2. This gel combines a small elastic modulus (10 kPa or less) and high deformability (100% or more), both of which are required for ultrasound measurement, and can deform to follow the irregularities on the surface of the subject.

[0022] The first layer 11, the intermediate layer 13, and the second layer 12 may be made of different materials, but by using the same type of gel material, the bonding between the layers can be improved. Even when the same type of gel material is used, the acoustic impedance of each layer may be adjusted by varying the gelation or water ratio of the gel constituting each layer, adding additives such as fine particles to the layer, or adjusting the amount of additives, in order to provide a gradient in the acoustic impedance or to meet other purposes. By adjusting the composition of the layers, not only the acoustic impedance but also physical properties can be adjusted, for example, the side that contacts the probe is slippery and the side that contacts the living body is more sticky.

[0023] The intermediate layer 13 is a layer for fixing the marker 15 so that it does not move within the gel, and preferably has a higher elastic modulus than the first layer 11 and the second layer 12. Specifically, the Young's modulus is preferably about 10 kPa or more, and may be appropriately adjusted depending on whether the probe is operated by a robot (for robot) or manually, for example, to 10 kPa or more for robot use and about 10 kPa for manual use. In either case, by making the elastic modulus of the intermediate layer 13 relatively high, for example, deformation of the intermediate layer 13 is suppressed even when the probe is pressed, and the marker held in the intermediate layer 13 does not move and can function as an indicator of the position in the ultrasound scanning direction.

[0024] Although the intermediate layer 13 having such an elastic modulus can be made of a gel made of a different material from the first layer 11 and the second layer 12, it is preferable to make them of the same material in order to increase the bonding between the layers, and in that case, the elastic modulus can be adjusted by adjusting the concentration of the polymerizable monomer, the ratio of the polymerizable monomer to the crosslinking agent, the additives added during gelation, etc. For example, in the case of a gel using acrylamide as the polymerizable monomer and (bis)acrylamide as the crosslinking agent described above, the elastic modulus (Young's modulus) can be increased by increasing the concentration of either or both of acrylamide and (bis)acrylamide.

[0025] The marker 15 can be made of a material that reflects ultrasonic waves, such as a filament (wire), particles, or bubbles. Specifically, the material that reflects ultrasonic waves may be any material whose acoustic impedance is significantly different from that of the imaging target, and may include metals, metal oxides, glass or ceramics, and gases such as air, and may be appropriately selected according to the form of the marker 15. By arranging the material that reflects ultrasonic waves at a position closer to the ultrasonic probe than the imaging target, the ultrasonic imaging device receives the ultrasonic waves as a reflected signal that is stronger than the ultrasonic waves reflected from the imaging target, and the position of the marker can be grasped on the ultrasonic image. By detecting the position of the marker, the angle and inclination of the ultrasonic probe can be detected, and the imaging surface can be specified. A method for detecting the position of the ultrasonic probe will be described later.

[0026] As shown in Figs. 2(a) and 2(b), the markers 15 are arranged in two-dimensional directions with respect to the planar direction of the acoustic coupler. Fig. 2(a) shows an example of a wire, and Fig. 2(b) shows an example of a particle or bubble. Fig. 2 shows an arrangement on one plane, but as shown in Fig. 1, the markers 15 are arranged at different positions (different faces) in the direction of ultrasonic irradiation. The arrangement of the markers 15 may be the same on different faces, but may also be different depending on the face, which makes it possible to detect the amount of movement of the ultrasonic probe regardless of the angle of the ultrasonic probe with respect to the arrangement direction of the markers in the position detection of the ultrasonic probe described later. Note that Fig. 2 shows a case where the top surface shape of the acoustic coupler 10 is rectangular or square, but the shape of the acoustic coupler 10 is not limited to this and may be any shape such as a circle or an ellipse.

[0027] The surface (layer) on which the marker 15 is arranged may be inside the intermediate layer 13 as shown in Fig. 1, or may be the boundary surface between the intermediate layer 13 and the first layer 11 and the boundary surface between the intermediate layer 13 and the second layer 12. In either case, however, the marker is arranged so that its position relative to the intermediate layer 13 is fixed even if the first layer 11 and the second layer 12 are deformed. This allows the positional relationship between the probe and the marker to be maintained even if the first layer 11 or the second layer 12 is deformed.

[0028] Although there are no particular limitations on the thickness of each layer constituting acoustic coupler 10 or the size of the marker, in order to absorb the unevenness of the subject with second layer 12, minimize the attenuation of ultrasonic waves by the acoustic coupler, and ensure as large an imaging area of ​​the subject as possible, it is preferable that acoustic coupler 10 has a thickness of about 5 mm to 20 mm as a whole. When performing automatic measurement using a robot or the like, the optimum value changes depending on the configuration of the measurement system. The thickness of each layer may be the same or different, but it is preferable that the second layer has a thickness that can at least absorb the unevenness of the subject.

[0029] The size of the marker may be any size that can be detected as a point or line image on an image, and if it is a line, the line width is preferably about 0.1 mm to 5 mm. As for bubbles or particles, the particle diameter is preferably about 0.01 mm to 0.1 mm.

[0030] An acoustic coupler configured in this manner can be manufactured, for example, by the following manufacturing method.

[0031] When placing a marker 15 in the intermediate layer 13, as shown in Figure 3, first, a marker (e.g., a wire mesh) is placed in a mold 40 for molding the intermediate layer, and the gel or resin composition that constitutes the intermediate layer is poured into the mold and hardened by chemical or physical operations to produce an intermediate layer sheet 131 with markers 15 placed in two places (two layers) inside.

[0032] The intermediate layer sheet 131 is placed vertically in another molding die 41, and the gel or resin composition for the first layer and the gel or resin composition for the second layer are poured into both sides of it, and both compositions are hardened and gelled by chemical or physical operations to produce acoustic coupler 10 in which the first layer 11 is formed on one side of the intermediate layer 13 and the second layer 12 is formed on the other side. With this method, an acoustic coupler in which a marker is disposed inside the intermediate layer can be manufactured.

[0033] As another manufacturing method, as shown in FIG. 4, first, the gel or resin composition constituting the first layer (or the second layer) is hardened by chemical or physical operation to prepare a gel sheet 111, and then the gel sheet 111 is placed in a mold 42 and a marker 15 is placed on its upper surface. Next, the resin composition constituting the intermediate layer is injected into the mold 42 and gelled to form the intermediate layer 13. The marker 15 is placed on the upper surface of the intermediate layer 13, and the resin composition constituting the second layer (or the first layer) is injected from above and hardened. The timing for placing the marker 15 on the upper surface of the intermediate layer 13 is preferably before the resin constituting the intermediate layer is completely gelled. With this method, an acoustic coupler can be manufactured in which the marker 15 is placed between (at the boundary between) the intermediate layer 13 and the layers 11 and 12 on both sides of the intermediate layer 13.

[0034] The method in Fig. 3 is suitable when the marker is a wire, and since the marker is held inside the intermediate layer, the marker does not move even when the gel constituting the second layer is deformed, making it highly reliable as a position indicator. The method in Fig. 4 places the marker on a flat surface, so there is a high degree of freedom in the shape of the marker, and the manufacturing method is easy because it is a method of sequentially laminating layers of gel.

[0035] However, Fig. 3 and Fig. 4 are merely examples of the method for manufacturing an acoustic coupler, and the method for manufacturing the acoustic coupler of the present invention is not limited to these manufacturing methods. In Fig. 3 and Fig. 4, the first layer 11 and the second layer 12 are both shown to have flat surfaces, but the shape of the surface does not necessarily have to be flat, and may be a curved surface such as a spherical surface.

[0036] When the acoustic coupler of this embodiment is used to bring the ultrasonic probe into contact with the surface of the subject to perform imaging, as shown in Fig. 5, the second layer 12 of the acoustic coupler 10 is placed on the subject 30 so that it is in contact with the body surface of the subject 30, and the ultrasonic probe 20 is pressed against the first layer 11 side to perform imaging. At this time, since the first layer 11 is made of a highly deformable gel, the acoustic coupler can be brought into contact without any gaps with the body surface of the subject, which may be uneven or curved due to the deformation of the gel.

[0037] In addition, since the intermediate layer 13 is made of a highly elastic hard gel, even if the ultrasonic probe 20 is pressed against the acoustic coupler 10, the pressing force is absorbed by the deformation of the first layer 11 and the second layer 12, and the flat shape of the intermediate layer 13 is maintained. Therefore, the arrangement of the markers 15 held in the intermediate layer 13 is prevented from being distorted, and the relationship between the positions of the ultrasonic probe and the markers is maintained. When ultrasonic imaging is performed in this state, the ultrasonic imaging device receives the reflected waves from the markers 15, and the image of the markers 15 is superimposed on the ultrasonic image, and the posture of the ultrasonic probe, i.e., the position (angle in a plane) and inclination (angle relative to the plane) of the ultrasonic probe can be confirmed from the image of the markers 15.

[0038] Next, a method for detecting the position (posture) of the ultrasonic probe using the marker 15 in ultrasonic imaging using the acoustic coupler 10 having the above configuration will be described. Here, a case where the marker 15 is a lattice-like wire (mesh) will be described as an example.

[0039] In an ultrasonic image, the irradiation range of ultrasonic waves is the imaging area, and the imaging surface is determined by the direction and spread of ultrasonic waves irradiated from the ultrasonic probe. The spread of ultrasonic waves is determined by the arrangement of transducers in the ultrasonic probe and the beamformer of the ultrasonic imaging device, and the irradiation direction is determined by the posture of the ultrasonic probe. Therefore, if the posture of the ultrasonic probe is known, the position of the imaging surface obtained at that time can be known. In other words, when the surface of the subject on which the ultrasonic probe is abutted is set as a reference plane as the posture of the ultrasonic probe, the irradiation area is determined by detecting the position and angle of the ultrasonic probe within the reference plane and the inclination of the ultrasonic probe relative to the reference plane. When imaging is performed through an acoustic coupler, the reference plane is defined by the main plane of the acoustic coupler.

[0040] First, referring to Fig. 6, a case where the long axis direction of the ultrasonic probe 20 is parallel to the warp threads 15A or weft threads 15B of the mesh will be described. Fig. 6(a) is a view of the reference plane from above, and the long axis direction of the ultrasonic probe is indicated by line L. Fig. 6(b) shows an image of the marker when the direction of ultrasonic irradiation is perpendicular to the reference plane. That is, in Fig. 6(a), the imaging plane (S) is a plane that includes line L and is perpendicular to the paper. In Figs. 9, 11, and 12 used in the description below, (a) shows a view of the marker (mesh) from above, and (b) shows the imaging plane, as in Fig. 6.

[0041] As shown in FIG. 6(a), for example, the ultrasonic probe is parallel to the warp threads 15A of the mesh. Weft If the marker 15 does not overlap with the weft 15B of the mesh arranged above and below, the imaging plane will intersect with the weft 15B of the mesh arranged above and below, and in the ultrasound image, it will appear as an image of the weft 15B arranged at equal intervals, as shown in Fig. 6(b). Here, as shown in Fig. 7, if the marker 15 exists only on one surface of the acoustic coupler, similar point images will appear in the image in both cases (a) when the imaging plane (ultrasound irradiation direction) is perpendicular to the reference plane and (b) when the imaging plane is tilted and receives reflected waves from an adjacent marker, making it impossible to distinguish between the two cases.

[0042] In contrast, when markers are placed on two planes, the marker farther from the ultrasound source has a greater distance between the point images on the first and second layers due to its greater depth, and as shown in Figure 8, the two can be distinguished from each other based on the difference between the distance d1 when the imaging plane is perpendicular to the reference plane (a) and the distance d2 when it is inclined (b).

[0043] Next, when the long axis direction L of the ultrasonic probe has a certain angle with respect to the vertical or horizontal direction of the mesh, as shown in Fig. 9(a), the imaging plane crosses the warp and weft of the mesh, and the intersections of the ultrasonic beam (imaging plane) with the warp and weft appear as point images of the warp and weft, respectively. Here, as shown in Fig. 9(b), when the angle θ of the imaging plane with respect to the warp is less than 90 degrees, the point images of the weft appear more than the point images of the warp, and in this example, the point images P1, P2, P3 of the warp and the point images Q1, Q2, Q3, Q4 of the weft appear as P1, Q1, Q2, P2, Q3, Q4, P3. When it exceeds 90 degrees, the relationship between the warp and weft is reversed, but the same is true.

[0044] Let the spacing between weft threads be α, the spacing between adjacent warp thread point images P1 and P2 be Δx, and the spacing between adjacent weft thread point images Q1 and Q2 be Δy. Δx=α / sinθ (1), Δy=α / cosθ (2) where α is a constant determined by the mesh and is constant if it is assumed that the mesh does not deform.

[0045] Therefore, by calculating Δx and Δy from the image, the following equation (3) is obtained. θ=tan -1 (Δy / Δx) (3) This makes it possible to know the angle θ of the ultrasonic probe in the longitudinal direction.

[0046] In order to obtain Δx and Δy from the image, it is necessary to distinguish between the point images of the weft and the point images of the warp. There are several methods for distinguishing between them, and one of them is to calculate the distance of each point image by brute-force calculation and use the frequency of appearance (histogram). In the example of FIG. 9, there are three point images P1, P2, and P3 of the warp and four point images Q1, Q2, Q3, and Q4 of the weft, totaling seven point images. The distance between P1 and the other six point images is calculated, and the distance between P2 and the other five point images is calculated, and so on in the same manner, totaling 21 distances. Among the calculated distances, the interval Δy between adjacent wefts and the interval Δx between adjacent warp and warp are constant and appear with a certain frequency, but the distance between the point images of the warp and the point images of the weft appears less frequently. Therefore, for example, the distance with the highest frequency is set as Δx (or Δy), the point image used to calculate that distance is removed, and the distance Δy (or Δx) is obtained from the remaining point image.Whether to use Δy or Δx can be determined, for example, by substituting the obtained distance into equation (1) or equation (2) to calculate θ, and then determining the validity of the value.

[0047] For example, when the angle θ is small, the frequency of the spacing Δy between adjacent weft threads increases, and the frequency of the spacing Δx between adjacent warp threads decreases. As the angle approaches 90 degrees, the relationship is reversed. If we use the spacing Δx between warp threads to calculate the angle θ using equation (1), and then substitute this angle and the spacing h between weft threads into equation (2) to calculate α, the value will deviate significantly from the actual α, and we can see that the distance with the highest frequency is Δy, not Δx.

[0048] As a different method, a method is conceivable in which auxiliary markers for distinction are placed only in either the vertical or horizontal directions, and the vertical and horizontal directions are distinguished by the difference in the display pattern of the markers when the part of the probe is changed after the markers are affixed to the measurement target. For example, as a preparation mode before measurement, the surgeon is made to move the probe in a specific direction, and when the auxiliary markers placed in the vertical direction are seen consecutively, it is possible to distinguish that the markers are placed in the vertical direction. Note that as the auxiliary markers, it is conceivable to use markers with different spacing from other markers, or an image generated by overlapping markers on an ultrasound image.

[0049] As another method for identifying the warp and weft, it is possible to identify the warp and weft by utilizing the fact that the area of ​​the ultrasonic beam irradiated on the warp and weft varies depending on the angle. For example, as shown in FIG. 10(a), when the angle between the long axis direction of the ultrasonic probe and the warp is small, the ultrasonic beam that hits the warp is irradiated diagonally across the warp, so the point image has a large eccentricity and is close to an ellipse. On the other hand, the ultrasonic beam that hits the weft is irradiated at an angle close to perpendicular to the weft, so the shape is close to a circle. Based on this difference in shape, the warp and weft are identified on the image. In the example of FIG. 9, a point image of the deformed warp 15A appears as shown in FIG. 10(b), and the interval h between adjacent wefts and the interval w between adjacent warp and warp can be measured. Note that the center position of the elliptical point image is the position of the point image.

[0050] This method is effective when there is a relatively large difference in the irradiation angle of the ultrasonic beam between the warp and weft. The above two methods may be combined to identify the warp and weft.

[0051] Next, the case where the ultrasonic probe moves in parallel will be described. First, when the ultrasound probe is moved in the longitudinal direction, all the point images move in the same direction while maintaining their arrangement. Figures 11(a) and (b) show the state in which the ultrasound probe is moved from the state in Figure 9 and the change in the point images in that case. As shown in Figure 11(b), the point image moves to the left by a shift amount Δξ corresponding to the actual movement amount of the ultrasound probe, in this example. The movement amount of the ultrasound probe in the longitudinal direction can be known by calculating the shift amount Δξ of this point image using a method such as optical flow.

[0052] On the other hand, when the ultrasonic probe is moved in the short axis direction, the warp point image and the weft point image shift in opposite directions, as shown in Fig. 12(a) and (b). That is, the weft point images Q1, Q2, ... are shifted in the opposite directions on the image. Rightward The warp thread point images P1, P2, etc. are shifted to the left direction The shift amount Sp of the warp point image and the shift amount Sq of the weft point image are expressed by the following equations using the angle θ of the major axis direction with respect to the above-mentioned reference plane, where Δη is the movement amount in the minor axis direction.

[0053] Sp = Δη / tanθ Sq = Δη tan θ

[0054] Therefore, if the angle θ is known from equation (3), the shift amounts Sp and Sq of the warp and weft threads can be used to calculate the amount of movement Δη when the ultrasonic probe is moved in the minor axis direction at the angle θ. In this case, the warp and weft threads can be identified by the method using the distance histogram described above.

[0055] As can be seen from the above formula, the amount of movement Δη is calculated using "tan θ", so it cannot be calculated when θ is a multiple of 90 degrees, that is, when the long axis direction of the ultrasonic probe is parallel to the warp or weft direction. However, by positioning the mesh on the lower side of the acoustic coupler 10 (the deeper side in the direction of ultrasonic propagation) at a 45 degree offset from the upper mesh, it becomes possible to calculate it using the shift amount of the point image of the lower mesh (warp and weft).

[0056] Next, we will explain the detection of the tilt φ when the imaging surface S is tilted from a plane perpendicular to the reference surface S0. When the imaging surface S is perpendicular to the reference surface S0, the distance between the point images of the meshes arranged above and below (upper and lower layers in the line direction) is the shortest (Fig. 13(a)), but when the imaging surface S is tilted with respect to the reference surface S0, the distance between the first and second layers becomes longer, as shown in Fig. 13(b). In other words, if the distance between the layers when perpendicular is d1 and the distance between the layers when tilted is d2, then the tilt φ is: d2cosφ=d1 Since the distance d1 between the layers is determined by the structure of the acoustic coupler, the slope φ can be calculated if d2 is known.

[0057] As described above, by using an acoustic coupler in which markers are arranged in a two-dimensional direction in two layers with different thickness positions inside, it is possible to detect the rotation of the imaging surface within the reference plane (angle θ with respect to the reference direction), the amount of movement in the major and minor axis directions (Δξ, Δη), and the inclination (φ) with respect to the reference plane by analyzing the images of the markers (point images).

[0058] The above describes the case where the marker is a mesh consisting of warp and weft threads, but the posture of the ultrasonic probe can also be detected using a similar concept for particles or bubbles in which the markers are arranged two-dimensionally.

[0059] Next, the configuration of an ultrasonic imaging device compatible with the acoustic coupler of this embodiment will be described.

[0060] 14 is a diagram showing the overall configuration of an ultrasonic imaging device, and like known ultrasonic imaging devices, this ultrasonic imaging device 50 includes a transmitting unit 51 that transmits ultrasonic signals to the ultrasonic probe 20, a receiving unit 52 that receives echo signals from the imaging target detected by the ultrasonic probe 20, a signal processing unit 53 that processes the signals received by the receiving unit 52 and generates ultrasonic images, a transmitting / receiving control unit 54 that controls transmission and reception, and a display control unit 55 that generates a display image to be displayed on a display device using the ultrasonic images generated by the signal processing unit 53. In addition, as auxiliary devices of the ultrasonic imaging device 50, a display device 56 that displays ultrasonic images, etc., and a storage device 57 that stores the processing results of the signal processing unit 53, such as ultrasonic images, may be included.

[0061] The transmitting unit 51 and the receiving unit 52 include a beamformer that phases ultrasound waves to match the imaging target, and send ultrasound signals to the ultrasound probe 20 corresponding to the ultrasound image and Doppler information to be acquired under the control of the transmission / reception control unit 54, and send echo signals from the ultrasound probe to the signal processing unit 53, for example as signals for each frame.

[0062] The signal processing unit 53, like a normal ultrasonic imaging device, includes an image generation unit 531 that generates B-mode images, etc., a Doppler processing unit 533 that calculates blood flow information based on echo signals, and further includes an imaging position calculation unit 535 that calculates position information (movement amount, angle, inclination) of the ultrasonic probe 20 using the image (B-mode image) generated by the image generation unit 531.

[0063] When the imaging position calculation unit 535 receives the ultrasound image created by the image generation unit 531, it identifies the marker images (point images) included in the image and performs various calculations to determine the ultrasound imaging plane. Specifically, it calculates the distance between point images, creates a distance histogram, determines the shape of the point images, calculates the amount of movement of the point image group (calculate optical flow), etc.

[0064] Such a function of the imaging position calculation unit 535 may be realized by software using a computer equipped with a CPU, a GPU, and a memory as one function of the signal processing unit 53, or may be realized by hardware such as an ASIC or an FPGA. Also, it may be realized by a computer or hardware separate from the signal processing unit 53.

[0065] FIG. 15 shows an example of a procedure for calculating the position information of the ultrasonic probe 20 by the imaging position calculation unit 535.

[0066] When it is set that imaging is to be performed using the acoustic coupler of the present invention (S101), imaging position calculation unit 535 operates and starts capturing an image from image generation unit 531 (S102). Whether imaging is to be performed using the acoustic coupler of the present invention may be set, for example, by the user via an input device (not shown) or the like, or imaging using an acoustic coupler may be set as a default, and when a marker does not exist in the image, it may be automatically determined that the acoustic coupler of the present invention is not being used.

[0067] When the imaging position calculation unit 535 captures the first ultrasound image, it detects the position of the marker from the point image contained therein, detects the distance between the point images, and creates a histogram of the distance (S103). The imaging position calculation unit 535 calculates the angle θ of the long axis direction of the ultrasound probe from the histogram (S104). For example, when the point images are parallel or nearly parallel to the warp or weft of the mesh, the distance between the point images is constant, and only that distance appears as a peak in the histogram. Also, when multiple distances appear in the histogram, the distance between the point images of adjacent warp threads and the distance between the point images of adjacent weft threads are determined based on the frequency, and the angle θ is calculated. The position and angle calculated in step S104 are stored as the initial position of the first ultrasound image (S105, S106).

[0068] Next, every time an image is captured while moving the ultrasonic probe, the point image of the marker in the obtained image is detected and compared with the initial arrangement of the point images to determine whether the movement is in the long axis direction, the short axis direction, the change in angle, or the change in inclination (S107). That is, if the arrangement pattern of the point images does not change (S108), it is determined whether the interval between the point images in the first layer and the point images in the second layer has changed, or whether the pattern of the point images has shifted in the horizontal direction (azimuth direction) of the image (S1081). If the interval between the first layer and the second layer has changed (FIG. 13) by comparing it with the interval at the initial position, it is determined that the inclination φ of the ultrasonic probe has changed, and the inclination of the ultrasonic probe is calculated from the distance (S1082). After that, the inclination of the initial position is updated, and the process returns to step S102 (S109).

[0069] If the point images are shifted in the horizontal direction (azimuth direction) of the image while maintaining the arrangement pattern (S1082), it is determined that the point images have shifted in the long axis direction (FIG. 11), and the amount of movement in the long axis direction is calculated from the amount of shift Δη of the point images (S1083). After that, the initial position in the long axis direction is updated, and the process returns to step S102 (S109).

[0070] If it is determined in step S108 that the distance between the point images has changed, it is determined that a movement or rotation (change in angle) has occurred in the minor axis direction, and first, as in steps S103 and S104, the distance between each point image is calculated in a round-robin manner, a histogram is created, and the angle θ is calculated (S1084, S1085). If this angle θ is the same as the angle θ calculated in step S104 (S1086), it can be considered as a movement in the minor axis direction (FIG. 12), so the amount of movement in the minor axis direction is calculated using the shift amount of the warp point image and the shift amount of the weft point image (S1087). Thereafter, the initial position in the minor axis direction is updated, and the process returns to step S102 (S109).

[0071] If the angle calculated in step S1085 is different from the angle registered as the initial position (S1086), the initial position is updated with this angle, and the process returns to step S102 (S109).

[0072] In this way, the initial position is updated every time any change occurs in the initial position, and the above steps are repeated to obtain position information of the imaging surface for each image.

[0073] The position information of the ultrasonic probe 20 thus calculated by the imaging position calculation unit 535 is stored in the storage device 57 together with the ultrasonic image used for the calculation, or is passed to the display control unit 55, which then displays on the display device 56 the ultrasonic image and the position of the ultrasonic probe when the ultrasonic image was captured.

[0074] The display mode is not particularly limited, but for example, as shown in Fig. 16, an image 161 showing a three-dimensional imaging area may be displayed together with a two-dimensional ultrasound image 160, and an imaging plane 162 determined by the ultrasound probe may be displayed on this three-dimensional image. This allows the surgeon to check at a glance which part of the subject is being imaged by the displayed ultrasound image, and also to check whether any part has been missed in the scan or whether the order of the scans matches the preset procedure.

[0075] Such display may be performed in real time during imaging, or may be performed using ultrasound images stored in storage device 57.

[0076] According to the ultrasound imaging device of this embodiment, when imaging is performed using the acoustic coupler of this embodiment, position information can be calculated and displayed in response to changes in the position of the ultrasound probe. This allows the operator to screen the imaging range without omissions, and also allows the operator to re-image the confirmed area as necessary.

[0077] In the above embodiment, the acoustic coupler 10 and the ultrasonic probe 20 are separate bodies. However, the acoustic coupler 10 of the present invention can also be fixed to the ultrasonic probe 20 for use. [Explanation of symbols]

[0078] 10: acoustic coupler, 11: first layer, 12: second layer, 13: middle layer, 20: ultrasonic probe, 30: imaging target, 50: ultrasonic imaging device, 53: signal processing unit, 535: imaging position calculation unit.

Claims

1. An acoustic coupler having a first layer with which a probe of an ultrasonic imaging device comes into contact and a second layer with which an imaging target comes into contact, the acoustic coupler including markers disposed in a two-dimensional direction with respect to a plane direction of the acoustic coupler on a plurality of surfaces between the first layer and the second layer, the surfaces being at different distances from the probe with respect to a propagation direction of ultrasonic waves from the probe to the acoustic coupler, The acoustic coupler is characterized in that the marker is made of a lattice-shaped linear body, and the spacing between the lines that make up the linear body is constant.

2. 2. The acoustic coupler of claim 1, 1. An acoustic coupler comprising: an intermediate layer between said first layer and said second layer, said intermediate layer having a higher elastic modulus than said first layer and said second layer.

3. 3. The acoustic coupler of claim 2, The acoustic coupler, wherein the plurality of markers are disposed between the first layer and the intermediate layer and between the second layer and the intermediate layer, respectively.

4. 3. The acoustic coupler of claim 2, The acoustic coupler, wherein the plurality of markers are embedded in the intermediate layer.

5. An acoustic coupler having a first layer with which a probe of an ultrasonic imaging device contacts, a second layer with which an imaged subject is to be imaged, and an intermediate layer between the first and second layers and having a higher elastic modulus than the first and second layers, wherein the acoustic coupler includes markers arranged at predetermined intervals in a two-dimensional direction relative to the planar direction of the acoustic coupler between the first layer and the intermediate layer and between the second layer and the intermediate layer on a plurality of surfaces that are at different distances from the probe in the direction of propagation of ultrasound from the probe to the acoustic coupler.

6. 6. The acoustic coupler according to claim 2 or 5, 11. An acoustic coupler, wherein the intermediate layer has a Young's modulus of elasticity of 10 kPa or more.

7. 6. The acoustic coupler of claim 5, The acoustic coupler, wherein the plurality of markers are any one of filaments, particles, and bubbles.

8. 6. The acoustic coupler of claim 5, An acoustic coupler, wherein the marker is a lattice-shaped linear body.

9. 6. The acoustic coupler according to claim 1, wherein the acoustic coupler is in the form of a sheet.

10. An ultrasonic image processing method for processing an ultrasonic image of an object to be inspected, comprising: disposing an acoustic coupler between an object to be inspected and an ultrasonic probe; transmitting and receiving ultrasonic waves to and from the object to be inspected via the ultrasonic probe; and processing a generated ultrasonic image of the object to be inspected, The acoustic coupler according to claim 1 or 5 is used as the acoustic coupler, An ultrasound image processing method comprising: a step of identifying a plurality of markers of the acoustic coupler in the ultrasound image; and a step of calculating position information of the ultrasound probe using a positional relationship of the identified plurality of markers.

11. 11. The ultrasound image processing method of claim 10, Identifying a plurality of markers of the acoustic coupler in ultrasound images acquired at a first position and a second position of the ultrasound probe, respectively; and calculating a moving direction and a moving angle of the ultrasound probe using the position of the marker in the ultrasound image at the first position and the position of the marker in the ultrasound image at the second position.

12. a transmitting / receiving unit to which an ultrasonic probe is connected and which transmits and receives ultrasonic waves via the ultrasonic probe; and an image generating unit which generates an ultrasonic image using ultrasonic waves which are received as reflected waves from an object to be examined, The ultrasonic image is an image captured by interposing the acoustic coupler according to claim 1 or 5 between the object to be inspected and the ultrasonic probe, The ultrasonic imaging device further comprises an imaging position calculation unit that calculates position information of the ultrasonic probe based on the position of a marker image included in the ultrasonic image.

Images