Ultrasonic diagnosis device and beam forming method

Abstract

To improve spatial resolution by calculating a delay time used in beam forming in a simple manner with higher accuracy than in conventional techniques even when a matching layer or an acoustic lens is interposed between each ultrasonic transducer and human tissue.SOLUTION: An ultrasonic diagnosis device according to one embodiment includes an ultrasonic probe and a bean forming circuit. The ultrasonic probe is provided with a second medium layer containing an ultrasonic lens between a contact surface of the ultrasonic transducer and a human body serving as a first medium that transmits ultrasonic signals. A beam forming circuit conducts beam forming by delaying reception signals of the ultrasonic transducers by different delay times and by adding the delayed reception signals. On an assumption that the plurality of ultrasonic transducers are provided at positions of a plurality of virtual transducers which are different from actual positions, the beam forming circuit conducts the beam forming using the delay time between a focal point in the first medium and the position of each of the virtual transducers.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to an ultrasound diagnostic apparatus and a beam forming method. [Background technology]

[0002] An ultrasound diagnostic device is a medical imaging diagnostic device that collects information from inside a subject non-invasively by emitting ultrasonic pulses or continuous ultrasonic waves generated from an ultrasonic transducer built into an ultrasound probe into the subject, and converting ultrasonic reflections caused by differences in acoustic impedance of the subject's tissue into electrical signals by the ultrasonic transducer. Medical examinations using ultrasound diagnostic devices are widely used for morphological and functional diagnosis of organs, since medical images such as cross-sectional images and three-dimensional images of the inside of a subject can be easily generated and collected by simply touching the ultrasound probe to the body surface.

[0003] In electronic scanning performed by an ultrasound diagnostic device, for example, a transmission beam having a focus at a predetermined depth in a predetermined direction can be formed by transmitting signals with different delay times from each ultrasound transducer arranged in a one-dimensional array.

[0004] On the other hand, in reception by electronic scanning, a delay is applied to the signal received by each ultrasonic transducer so that the signals generated from the focal point at a specified depth in a specified direction are in phase. Then, the received signals delayed in this way are added together to form a receive beam. The process of forming a receive beam is also called beamforming.

[0005] The delay time to be applied to each ultrasonic transducer in forming a receive beam can be calculated based on the distance from the focal point to each ultrasonic transducer and the propagation speed of the ultrasonic signal propagating through the medium between the focal point and each ultrasonic transducer.

[0006] Conventionally, each delay time was calculated assuming that only human tissue was the medium between each ultrasonic transducer and the focal point, and that the ultrasonic signal propagated in a straight line from the focal point to each ultrasonic transducer without refraction.

[0007] However, in an actual ultrasonic probe, a matching layer or an acoustic lens of the ultrasonic probe is interposed between each ultrasonic transducer and the human tissue, and the propagation speed of the ultrasonic signal is different between the matching layer or the acoustic lens and the human tissue. In addition, due to the difference in propagation speed, refraction according to Snell's law occurs in the path from the focal point to each ultrasonic transducer, and the assumption that the ultrasonic signal propagates linearly from the focal point to each ultrasonic transducer is no longer valid.

[0008] Therefore, the delay time calculated by the conventional method based on the assumption that there is no matching layer or acoustic lens between each ultrasonic transducer and the human tissue is different from the actual delay time. As a result, the beamforming process is performed using a delay time with an error, which is one of the causes of the deterioration of the spatial resolution of the generated ultrasonic image. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2001 / 26555 Summary of the Invention [Problem to be solved by the invention]

[0010] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to enable a delay time used for beamforming to be calculated with higher accuracy than conventional methods even when a matching layer or an acoustic lens is interposed between each ultrasonic transducer and human tissue, thereby improving spatial resolution. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described later can also be positioned as other problems. [Means for solving the problem]

[0011] An ultrasonic diagnostic device according to an embodiment includes an ultrasonic probe and a beam forming circuit. The ultrasonic probe has a plurality of ultrasonic transducers arranged in an array, and a layer of a second medium including an ultrasonic lens is provided between the ultrasonic transducers and a contact surface with a human body, which is a first medium for propagating ultrasonic signals. The beam forming circuit delays the reception signals of the plurality of ultrasonic transducers by different delay times and adds the delayed reception signals to perform beam forming. The propagation speed of the ultrasonic signal differs between the first medium and the second medium. The beam forming circuit assumes that the plurality of ultrasonic transducers are respectively arranged at the positions of a plurality of virtual transducers different from the actual positions, and performs the beam forming using the delay times between the focal points in the first medium and the positions of the plurality of virtual transducers. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing an example of the appearance of an ultrasonic diagnostic apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing an example of a typical ultrasonic probe included in an ultrasonic diagnostic device. [Diagram 3] 1 is a schematic diagram for explaining a problem regarding a decrease in focus accuracy in a conventional beam forming process. [Figure 4] 1 is a block diagram showing an example of the arrangement of an ultrasound diagnostic apparatus according to a first embodiment. [Diagram 5]11 is a flowchart showing an example of a delay time calculation process for beamforming. [Figure 6] FIG. 1 is a diagram showing a concept of a calculation process of a delay time for beamforming. [Figure 7] 11 is a flowchart showing an example of a calculation process for the position of a virtual vibrator. [Figure 8] FIG. 4 is a conceptual explanatory diagram of a process for calculating a true propagation time from an actual ultrasonic transducer to a focal position. [Figure 9] FIG. 13 is a conceptual explanatory diagram of a process for provisionally setting the position of a virtual vibrator. [Figure 10] 11A and 11B are diagrams for comparing the accuracy of delay times obtained by the ultrasonic diagnostic apparatus of the embodiment with the accuracy of delay times obtained by a conventional simplified method. [Figure 11] 1 is a block diagram showing an example of the arrangement of an ultrasound diagnostic apparatus according to a first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] (First embodiment) Fig. 1 is a perspective view showing an example of the appearance of an ultrasonic diagnostic device 1 according to the first embodiment. As shown in Fig. 1, the ultrasonic diagnostic device 1 includes a device main body 10 and an ultrasonic probe 20. The device main body 10 includes various circuits (see Fig. 4) housed in a main body case with casters, as well as a display 110 and a user interface 120.

[0015] The display 110 displays ultrasonic images and various data generated by various circuits in the device main body 10. The display 110 is configured to include, for example, a liquid crystal display panel or an organic EL (Electro Luminescence) panel.

[0016] The user interface 120 is a device that allows the user to input various data and information to the device main body 10 through user operation, or to set various operation modes to the device main body 10. The user interface 120 is configured to include, for example, two devices, an operation panel and a touch panel.

[0017] The operation panel has operation devices such as a trackball, various switches, dials, etc., arranged thereon, and the user can input various data and information into the apparatus main body 10 by operating these operation devices.

[0018] On the other hand, a touch panel is a display and input device that is configured by overlaying a touch screen on a display panel such as a liquid crystal panel. By touching or pressing the touch screen according to the display on the display panel, various data and information can be input into the device body 10.

[0019] Fig. 2 is a diagram showing an example of a typical ultrasonic probe 20 provided in the ultrasonic diagnostic device 1. Fig. 2(a) shows an ultrasonic probe 20 called a convex probe, and Fig. 2(b) shows an ultrasonic probe 20 called a linear probe.

[0020] In a convex probe, the longitudinal shape of the contact surface at the tip of the probe with the human body is an outwardly convex arc. Ultrasonic transducers are arranged in an array on the inside of the contact surface, and the shape of this array surface is also an arc. Convex probes have a large contact surface with the human body, making it possible to observe a wide, fan-shaped field of view (wide angle).

[0021] On the other hand, the linear probe has a straight line (linear) shape in the longitudinal direction of the contact surface. The array surface of the ultrasonic transducers inside the contact surface is also linear. Since the ultrasonic beam travels in a straight line with the linear probe, resolution is maintained from shallow to deep areas within the range that can be imaged.

[0022] In addition, a sector probe is also included as the ultrasound probe 20 provided in the ultrasound diagnostic device 1. The sector probe has a small contact surface with the human body and is often used to observe the heart from the body surface.

[0023] 3 is a schematic diagram for explaining a problem related to a decrease in focal accuracy in a conventional beam forming process. The problem explained below is common to a convex probe, a linear probe, and a sector probe, but since the decrease in focal accuracy is most noticeable in a convex probe, the following explanation will be given taking a convex probe as an example.

[0024] FIG. 3(a) is a diagram explaining a method for calculating a delay time for obtaining an ideal focus, and FIG. 3(b) is a diagram explaining a conventional method for calculating a delay time (hereinafter, sometimes referred to as a conventional simplified method).

[0025] 3(a) and 3(b) show an example in which the ultrasonic transducers of a convex probe are arranged on a transducer array surface ES, which is a part of a circle (i.e., a circular arc) whose center is AC and whose radius is R. A large number of ultrasonic transducers are arranged in a row on the transducer array surface ES.

[0026] In Figures 3(a) and 3(b), the central ultrasonic transducer is denoted as E0, and any ultrasonic transducer located away from the central ultrasonic transducer E0 is denoted as En. In Figures 3(a) and 3(b), the two-dimensional coordinates (x, y) are set so that the central ultrasonic transducer E0 is located at the origin (0, 0) of the coordinates.

[0027] As described above, a matching layer and an acoustic lens are provided in this order on the transducer array surface ES of the ultrasonic probe 20 (convex probe). The outer peripheral surface of the acoustic lens is a contact surface CS that comes into contact with a subject (e.g., a human body or a patient) when imaging the subject.

[0028] The propagation speed of ultrasonic waves differs between the human body, the matching layer, and the acoustic lens. The human body is the first medium, and its propagation speed (sound speed in the first medium) is denoted as C. Although the propagation speeds of the matching layer and the acoustic lens are different in the strict sense, the acoustic lens is dominant in terms of thickness and propagation speed. Therefore, the matching layer and the acoustic lens are the second medium, and their propagation speed (sound speed in the second medium) is denoted as CL.

[0029] 3(a) and 3(b), it is assumed that a focal point Fm is formed at a position (0, F) at a predetermined depth in the front direction (y-axis direction) of the ultrasonic probe 20.

[0030] As is well known, the focal point of the ultrasonic probe 20 is formed by matching the propagation time from each ultrasonic transducer to the focal point. Specifically, the central ultrasonic transducer E0 is used as a reference, and the difference between the propagation time from the focal point to the central ultrasonic transducer E0 and the propagation time from the focal point to the ultrasonic transducers En other than the central ultrasonic transducer E0 is calculated, and this is set as the delay time τ. The delay time τ differs depending on the position of each ultrasonic transducer En, and also differs depending on the position of the focal point Fm. During transmission, the calculated delay time τ is applied to the transmission pulse applied to each ultrasonic transducer and transmitted, thereby forming the focal point Fm at a predetermined position.

[0031] On the other hand, during reception, the calculated delay time τ is applied to the received signal, and then each received signal is added together to form a reception beam that is focused (i.e., in-focus) at the position (depth) and direction of the specified focal point Fm.

[0032] As described above, a second medium, such as an acoustic lens, having a sound speed CL different from the sound speed C in the human body is interposed between the transducer array surface ES and the contact surface CS of the human body. Therefore, as shown in Fig. 3(a), refraction due to the difference in sound speed (i.e., refraction according to Snell's law) occurs at the contact surface CS in the path between the focal point Fm and the ultrasonic transducer En.

[0033] Therefore, the true delay time τ' must be calculated using the following (Equation 1).

[0034] τ'=(dn'-d0') / CL+(dn”-d0”) / C (Equation 1) Here, d0' is the distance from the contact surface CS to the ultrasonic transducer E0 on the path from the focal point Fm to the central ultrasonic transducer E0, and d0" is the distance from the focal point Fm to the contact surface CS. Also, dn' is the distance from the contact surface CS to the ultrasonic transducer En on the path from the focal point Fm to the ultrasonic transducer En, and dn" is the distance from the focal point Fm to the contact surface CS.

[0035] In order to calculate the true delay time τ' according to (Equation 1), it is necessary to determine the path of the sound wave based on Snell's law for each position of the focal point Fm (the position here includes the depth and direction of the focal point Fm) and calculate the distances dn' and dn" on this path, which is a fairly complicated process. Moreover, this process needs to be performed in real time according to the beam scanning.

[0036] Therefore, in the conventional simplified method, as shown in Fig. 3(b), the ultrasonic signal propagates linearly from the focal point Fm to each ultrasonic transducer En without refraction, and the ultrasonic signal propagates from the focal point Fm to each ultrasonic transducer En at a single sound speed C (i.e., the sound speed C of the human body), and the delay time τ is calculated. Specifically, in the conventional simplified method, the delay time τ is calculated according to the following (Equation 2).

[0037] τ=(dn-d0) / C (Equation 2) Here, d0 is the linear distance from the focal point Fm to the ultrasonic transducer E0, and dn is the linear distance from the focal point Fm to the ultrasonic transducer En.

[0038] In the conventional simplified method, since there is no need to determine the refraction path, the processing is simple. However, as is clear from Fig. 3(a) and Fig. 3(b) or (Equation 1) and (Equation 2), the true delay time τ' is different from the delay time τ calculated by the conventional simplified method. Therefore, if beamforming is performed using the delay time τ calculated by the conventional simplified method, a signal with low focus accuracy, in other words, a defocused signal, is generated, and as a result, the spatial resolution is reduced.

[0039] Therefore, in the ultrasonic diagnostic device 1 of the embodiment, beamforming with improved focus accuracy compared to the conventional method is realized by a simple method substantially similar to the conventional method. The configuration and operation of the ultrasonic diagnostic device 1 thus configured will be described below.

[0040] 4 is a block diagram showing an example of the configuration of an ultrasonic diagnostic device 1 according to the first embodiment. The ultrasonic diagnostic device 1 includes a device main body 10 and at least one ultrasonic probe 20 connected to the device main body 10.

[0041] The device main body 10 is configured to include a beam forming circuit 310, a B-mode processing circuit 320, a Doppler processing circuit 330, an image generating circuit 340, a frame memory 350, and a control circuit 360, as well as the display 110 and user interface 120 shown in Fig. 1. The device main body 10 also includes a scanning control circuit 400, a reception delay time calculation circuit 410, a virtual transducer position storage circuit 420, a transmission delay time calculation circuit 430, and a transmission signal generation circuit 440.

[0042] The virtual transducer position storage circuit 420 is a storage circuit that stores the position of the virtual transducer calculated in advance. The position of the virtual transducer is calculated as a position different from the position of the actual ultrasonic transducer. A specific method for calculating the position of the virtual transducer will be described later.

[0043] The scanning control circuit 400 is configured to set scanning parameters such as the focal positions and beam directions of the receiving beam and the transmitting beam in the receiving delay time calculation circuit 410 and the transmitting delay time calculation circuit 430, respectively, under the control of the control circuit 360, in accordance with, for example, the operating mode and processing parameters set via the user interface 120.

[0044] The reception delay time calculation circuit 410 is configured to calculate a reception delay time for forming a reception beam, using scanning parameters such as the reception focal position and reception beam direction output from the scanning control circuit 400, and the virtual transducer position read from the virtual transducer position storage circuit 420. A specific method for calculating the delay time will be described later.

[0045] Similarly, the transmission delay time calculation circuit 430 is configured to calculate a transmission delay time for forming a transmission beam for each ultrasonic transducer, using scanning parameters such as the transmission focal position and transmission beam direction output from the scanning control circuit 400 and the virtual transducer position read out from the virtual transducer position memory circuit 420.

[0046] The transmission signal generating circuit 440 is configured to generate a transmission pulse as an electrical signal by delaying a rate pulse having a predetermined repetition period (PRI: Pulse Repetition Interval) by a calculated transmission delay time, and to supply the generated transmission pulse to each ultrasonic transducer of the ultrasonic probe 20.

[0047] Each ultrasonic transducer of the ultrasonic probe 20 converts the supplied transmission pulse of the electrical signal into an ultrasonic pulse and transmits it toward the body of the subject.

[0048] The ultrasonic signals reflected from inside the body of the subject are converted into electrical signals in each ultrasonic transducer of the ultrasonic probe 20 and supplied to the beam forming circuit 310 as received signals.

[0049] The beam forming circuit 310 converts the reception signals output from each ultrasonic transducer into digital signals, and further delays each digitized reception signal by the reception delay time calculated by the reception delay time calculation circuit 410, and then adds up each reception signal to form a reception beam.

[0050] The B-mode processing circuit 320 performs logarithmic detection processing and the like on the beamformed received signals, and generates a B-mode image using information on the scanning direction.

[0051] The Doppler processing circuit 330 performs signal processing such as correlation processing and Fourier transform on the beamformed received signals, and generates a color Doppler mode image or a pulse Doppler mode signal based on the information on the scanning direction.

[0052] The image generating circuitry 340 converts the B-mode image or color Doppler mode image into a display image to be displayed on the display 110, and also performs processing to add various auxiliary information to the display image.

[0053] The frame memory 350 is a recording medium for sequentially recording the above-mentioned display images generated at a predetermined frame rate as frame images.

[0054] The control circuit 360 controls the entire ultrasonic diagnostic apparatus 1 .

[0055] Each of the above-mentioned circuits can be configured as a circuit including, for example, a CPU or a dedicated or general-purpose processor. In this case, the CPU or processor can realize the above-mentioned functions by executing various programs stored in a storage circuit (not shown).

[0056] Furthermore, each of the above-mentioned circuits may be configured with hardware such as one or more FPGAs (field programmable gate arrays) or ASICs (application specific integrated circuits). The above-mentioned various functions can also be realized by such hardware. Furthermore, each of the above-mentioned circuits can realize various functions by combining software processing by a processor and a program with hardware processing.

[0057] Fig. 5 is a flow chart showing an example of calculation processing of delay times for beamforming in the ultrasound diagnostic device 1. Fig. 6 is a diagram showing the concept of calculation processing of delay times for beamforming in the ultrasound diagnostic device 1.

[0058] In step ST100 of FIG. 5, the reception delay time calculation circuit 410 calculates the virtual oscillator En from the virtual oscillator position storage circuit 420. * Get the position of (n=0~N). Virtual oscillator En * A method for calculating the position (i.e., coordinates) will be described later with reference to FIGS.

[0059] In step ST101, the delay calculation target element En * The coordinates of the focal position Fm are set as initial values ​​in step ST102.

[0060] Then, in the next step ST103, the central virtual oscillator E0 * and the nth virtual oscillator En * From the position of, the focal position Fm, and the sound speed, the delay time τ * (En * , Fm) is calculated based on the following (Equation 3). * (En * , Fm) is calculated.

[0061] τ * =(dn * -d0 * ) / C (Equation 3) Here, as shown in Figure 6, * is the nth virtual oscillator En * and the linear distance between the focal position Fm, d0 * is the virtual oscillator E0 at the center * and the focal position Fm, and C is the propagation speed of the ultrasound in the first medium (i.e., the human body).

[0062] In step ST104, the focal position Fm is changed to Fm+1. That is, the focal position is updated. In step ST105, the process of step ST103, that is, the delay time τ * The focal position to be calculated is given by the scanning control circuit 400 as, for example, a beam scanning direction and a focal depth.

[0063] Next, in step ST106, the delay calculation target element is set to En+1 * In step ST107, the process of step ST103 is performed for all delay calculation target elements, that is, the delay time τ * It is determined whether the calculation of is completed.

[0064] For all focal positions and all delay calculation target elements, the delay time τ * When the calculation of the delay time τ * (En * , Fm) is used to perform beamforming.

[0065] The delay time τ calculated using the flowchart shown in Figure 5 * can be used for forming a receiving beam as well as for forming a transmitting beam. In the case of forming a receiving beam, the delay time τ * That is, the beam forming process is performed by applying the calculated reception delay time τ * After delaying them by a factor of 1, the received beam is formed by adding them together.

[0066] On the other hand, in transmission, the calculated transmission delay time τ * The ultrasonic probe 20 generates a transmission pulse as an electrical signal delayed by a delay, and transmits the generated transmission pulse from each ultrasonic transducer of the ultrasonic probe 20 toward the subject, thereby forming a transmission beam within the subject.

[0067] Next, the virtual oscillator En * The method of calculating the position of the virtual oscillator En will be described with reference to FIG. 7 to FIG. * 10 is a flowchart showing an example of a calculation process of a position.

[0068] 8 is a diagram for explaining the concept of the process of calculating the true propagation time T1 from the actual ultrasonic transducer En to the focal position Fm. In the path from the actual ultrasonic transducer En to the focal position Fm (i.e., the first path), the true propagation time T1 is calculated assuming that refraction occurs according to Snell's law at the contact surface CS between the ultrasonic probe 20 and the human body. * 11 is a diagram for explaining the concept of a process for provisionally setting the position of a target object.

[0069] Hereinafter, referring to FIG. 8 and FIG. 9, the virtual oscillator En * A method for calculating the position will be described.

[0070] First, in step ST200, the focal position Fm to be calculated is set as an initial value. In the next step ST201, the position of the ultrasonic transducer En to be calculated (the actual position of the ultrasonic transducer En) is set as an initial value.

[0071] In step ST202, a first path from the target focal position Fm to the target element En is determined according to Snell's law. In step ST203, a first propagation time T1 of the first path is calculated using the sound speed C in the first medium and the sound speed CL in the second medium.

[0072] 8 is a diagram for explaining the processing of steps ST202 and ST203 in more detail. As described in the right column of FIG. 8, the first propagation time T1 of the first path is calculated by steps (1) to (4).

[0073] First, in step (1) of FIG. 8, a condition is defined regarding the position where refraction occurs on the first path. Specifically, a condition is defined that, on the first path from the focal point Fm to the actual ultrasonic transducer En, refraction according to Snell's law occurs at some position on the arc from P1 to P2 on the contact surface CS. Here, position P1 is the intersection of the contact surface CS (arc with AC as the center) and a straight line connecting the focal point Fm and the actual ultrasonic transducer En. Position P2 is the intersection of the contact surface CS and a straight line connecting the center AC and the actual ultrasonic transducer En. Position P2 can also be said to be the intersection of the normal of the transducer array surface ES (i.e., the curved surface convex toward the outside on which the actual ultrasonic transducer En is arrayed) that passes through the position of the ultrasonic transducer En and the contact surface CS.

[0074] Next, in step (2) of FIG. 8, the position of one point on the arc from P1 to P2 is determined as the inflection point P according to Snell's law shown in the following (Equation 4). L The position is calculated as:

[0075] sinθ A / sinθ B =V A / V B =C / CL (Equation 4) Here, θ A and θ B are the refraction points P of the ultrasonic signal emitted from the focal point Fm, respectively. L The angles of incidence and emergence are V A (=C) and V B (=CL) are the propagation velocities of the ultrasonic signal in the first medium and the second medium, respectively. V A (=C) and V B (=CL) is a known value, and the ratio of the two is sinθ A / sinθ BThat is, the ratio between the incident angle and the exit angle can be calculated. From the ratio between the incident angle and the exit angle, the inflection point P on the arc from P1 to P2 can be calculated. L The location of the object can be identified.

[0076] Next, in step (3) of FIG. 8, the focal point Fm is moved to the refraction point P L Distance dn” to the inflection point P L 8, the distance dn' to the actual ultrasonic transducer En is calculated. Then, in step (4) of Fig. 8, the true propagation time T1 in the first path (true path) is calculated by the following (Equation 5).

[0077] T1=dn” / C+dn' / CL (Equation 5) In this manner, in step ST203 of the flowchart in FIG. 7, the true propagation time T1 on the first path (true path) is calculated.

[0078] In step ST204 of FIG. 7, a virtual transducer En corresponding to an actual ultrasonic transducer En is * The position of the virtual transducer En is provisionally set in the second medium on the normal line of the array surface ES of the actual ultrasonic transducer En. Then, in the next step ST205, the provisionally set virtual transducer En * A second propagation time T2 of the second path is calculated assuming that the ultrasonic signal travels in a straight line at the sound speed C in the first medium to the position.

[0079] 9 is a diagram for more specifically explaining the processing of steps ST204 and ST205. As described in the right column of FIG. 9, the second propagation time T2 of the second path is calculated by steps (1) and (2).

[0080] In step (1) of FIG. 9, a virtual transducer En corresponding to a target element En (actual ultrasonic transducer En) is * The position of the virtual transducer En is provisionally set in the second medium on the normal line of the array surface ES of the target element En. Then, in step (2) of FIG. 9, the provisionally set virtual transducer En is *The distance dn of the second path, assuming that the ultrasonic signal travels in a straight line with a propagation speed C in the first medium, is * Then, the propagation time T2 is calculated using the following (Equation 6).

[0081] T2=dn * / C (Formula 6) Returning to FIG. 7, in step ST206, the virtual oscillator En is adjusted so that the difference between the first propagation time T1 calculated in step ST203 and the second propagation time T2 calculated in step ST205 is minimized, or so that the first propagation time T1 and the second propagation time T2 are equal to each other. * Determine the location of.

[0082] Then, in step ST207, for all target elements En (actual ultrasonic transducers En), virtual transducers En * If not, the processes in steps ST202 to ST206 are repeated. * When the positions of the virtual transducers En are determined, in step ST208, all the virtual transducers En are also determined for all the planned target focal positions Fm. * Then, for all the planned target focal positions Fm, it is determined whether the positions of all the virtual transducers En * If it is determined that the position has been determined, the process proceeds to step ST209.

[0083] In step ST209, a set of virtual transducers En corresponding to the specified focal position is * The position is stored in the virtual transducer position storage circuit 420.

[0084] As can be seen from the above-mentioned processing of steps ST200 to ST208, for one focal position Fm, all virtual transducers En * A set of virtual transducer positions is determined, which is composed of positions (n=0 to N). Therefore, a plurality of sets of virtual transducer positions are determined for a plurality of focal positions Fm.

[0085] On the other hand, in order to avoid complicating the beamforming process (the process of step ST108 in FIG. 5) performed in real time, a set of virtual transducers En * It is preferable to use the position of

[0086] In the above-mentioned conventional simplified method (see FIG. 3(b)), the beamforming process is performed using the positions En of a set of actual ultrasonic transducers. Therefore, in the present embodiment, the beamforming process is performed using the positions En of a set of virtual transducers regardless of the actual focal position. * By using the position, it is possible to utilize the hardware and software configurations of the beamforming process by the conventional simplified method. As a result, it is possible to reduce the development cost and development risk of the ultrasound diagnostic device 1 of the embodiment.

[0087] As a method for determining one set of virtual vibrator positions from a plurality of sets of virtual vibrator positions, for example, a method in which a user specifies one focal position is considered. Alternatively, for example, a user may specify a plurality of focal positions, and a set of virtual vibrator positions may be determined by averaging the plurality of positions for each of the positions of the plurality of sets of virtual vibrators corresponding to the specified plurality of focal positions.

[0088] FIG. 10 shows the delay time τ obtained by the ultrasonic diagnostic apparatus 1 of the first embodiment described above. * This figure compares the accuracy of the delay time τ calculated by the conventional simplified method with that of the delay time τ calculated by the conventional simplified method. Figure 10(a) is a graph in which the delay time τ calculated by the conventional simplified method that does not use a virtual oscillator (see Figure 3(b)) is shown by a dashed line, and the true value τ' of the delay time in the actual path with bending (see Figure 3(a)) is shown by a solid line. The horizontal axis of the graph is the angle corresponding to the oscillator position, and the vertical axis of the graph is the delay time.

[0089] FIG. 10B shows the delay time τ calculated by the delay time calculation method of the first embodiment using a virtual oscillator. * (See FIG. 6) is shown by a dashed line, and the true value τ of the delay time in an actual path with bending is shown by a solid line.

[0090] As can be easily seen from a comparison between FIG. 10(a) and FIG. 10(b), the delay time τ calculated by the delay time calculation method of the first embodiment is * The difference between the delay time τ and the true delay time τ' is smaller than the difference between the delay time τ calculated by the conventional simplified delay time calculation method and the true delay time τ'.

[0091] In this way, the delay time τ calculated by the delay time calculation method of the first embodiment * The accuracy of is higher than the accuracy of the delay time τ calculated by the conventional simplified method, and as a result, the focus accuracy is improved, and the spatial resolution of the generated ultrasound image can be increased.

[0092] Second embodiment 11 is a block diagram showing an example of the configuration of an ultrasound diagnostic device 1 according to the second embodiment. The difference from the first embodiment (see FIG. 4) is that the second embodiment includes a transmission virtual transducer position storage circuit 450. The ultrasound diagnostic device 1 according to the second embodiment is configured to determine the transmission virtual transducer position used for forming a transmission beam independently as being different from the reception virtual transducer position used for forming a reception beam, and to store the determined independently.

[0093] It is known that in transmitting an ultrasonic signal, the geometric focus position and the maximum acoustic amplitude position are different. In the calculation of the virtual transducer position in the first embodiment, the focus position Fm shown in Figs. 8 and 9 is the geometric focus position. In contrast, in the second embodiment, the focus position used to calculate the virtual transducer position is replaced with the geometric focus position, and the maximum acoustic amplitude position is used to calculate the transmission delay time. The other processes are the same as those in the first embodiment, and the description will be omitted.

[0094] In the second embodiment, during transmission, a transmission beam is formed using a transmission delay time stored in the transmission virtual transducer position storage circuit 450, and during reception, a reception beam is formed using a reception delay time stored in the virtual transducer position storage circuit 420.

[0095] As described above, according to the ultrasound diagnostic device 1 of each embodiment, even if a matching layer or an acoustic lens is interposed between each ultrasound transducer and human tissue, it is possible to calculate the delay time to be used for beamforming with a simple method and with higher accuracy than conventional methods, thereby improving the spatial resolution.

[0096] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0097] 1. Ultrasound diagnostic equipment 10. Device body 20 Ultrasound Probe 110 Display 120 User Interface 310 Beam forming network 400 Scanning control circuit 410 Receiving delay time calculation circuit 420 Virtual oscillator position memory circuit 430 Transmission Delay Time Calculation Circuit 440 Transmission signal generation circuit

Claims

1. An ultrasonic probe having a plurality of ultrasonic transducers arranged in an array, the ultrasonic probe having a layer of a second medium including an ultrasonic lens between the ultrasonic transducers and a contact surface with a human body, which is a first medium for propagating an ultrasonic signal; a beam forming circuit that delays the reception signals of the plurality of ultrasonic transducers by different delay times and adds up the delayed reception signals to perform beam forming; Equipped with a propagation velocity of the ultrasonic signal differs between the first medium and the second medium; The beam forming circuit assumes that the plurality of ultrasonic transducers are respectively arranged at positions of a plurality of virtual transducers different from actual positions, and performs the beam forming using the delay times between a focal point in the first medium and the positions of the plurality of virtual transducers. Ultrasound diagnostic equipment.

2. a propagation speed of the ultrasonic signal is slower in the second medium than in the first medium; The position of the virtual oscillator is set inside the second medium; The beam forming circuit performs the beam forming using the delay time calculated on the assumption that there is no refraction in a propagation path of the ultrasonic signal from the focal point to each of the positions of the virtual transducers, and that the ultrasonic signal propagates at a propagation speed in the first medium. The ultrasonic diagnostic apparatus according to claim 1 .

3. The ultrasonic probe is configured as a convex type probe in which the plurality of ultrasonic transducers are arranged along an outwardly convex curved surface, Each of the positions of the virtual oscillators is set on a normal line of the curved surface. The ultrasonic diagnostic apparatus according to claim 1 .

4. Each of the positions of the plurality of virtual oscillators is (a) calculating a first propagation time from the focal point to each ultrasonic transducer on an actual path where refraction occurs at an interface between the first medium and the second medium; (b) calculating a second propagation time from the focal point to each ultrasonic transducer in a virtual path assumed to proceed in a straight line from the focal point to the position of each ultrasonic transducer without bending; (c) minimizing a difference between the first propagation time and the second propagation time; To be determined, The ultrasonic diagnostic apparatus according to claim 1 .

5. the first propagation time is calculated assuming that refraction at the contact surface occurs in accordance with Snell's law; The second propagation time is calculated as a propagation time from the focal point to each ultrasonic transducer at a first propagation speed corresponding to the first medium. The ultrasonic diagnostic apparatus according to claim 4.

6. a memory circuit, the positions of the plurality of virtual vibrators are stored in advance in the storage circuit; The beam forming circuit performs the beam forming using the delay time calculated using the positions of the plurality of virtual transducers stored in the memory circuit. The ultrasonic diagnostic apparatus according to claim 1 .

7. a transmission delay time calculation circuit that calculates each transmission delay time between a transmission focal point in the first medium and the positions of the plurality of transmitting virtual oscillators by using the positions of the plurality of transmitting virtual oscillators; Further comprising: The ultrasonic diagnostic apparatus according to claim 1 .

8. The positions of the plurality of transmitting virtual oscillators used during transmission are different from the positions of the virtual oscillators used during reception. The ultrasonic diagnostic apparatus according to claim 7.

9. A beam forming method for performing beam forming using an ultrasonic probe having a plurality of ultrasonic transducers arranged in an array, the ultrasonic probe having a layer of a second medium including an ultrasonic lens between a contact surface with a human body, which is a first medium for propagating an ultrasonic signal, and the ultrasonic transducers, the method comprising: Assuming that the plurality of ultrasonic transducers are respectively arranged at a plurality of virtual transducer positions different from the actual positions, a delay time between a focus in the first medium and the positions of the plurality of virtual transducers is calculated; The received signals of the plurality of ultrasonic transducers are delayed by the calculated delay times, and the delayed received signals are added together to perform beamforming. Beamforming methods.

10. Each of the positions of the plurality of virtual oscillators is (a) calculating a first propagation time from the focal point to each ultrasonic transducer on an actual path where refraction occurs at an interface between the first medium and the second medium; (b) calculating a second propagation time from the focal point to each ultrasonic transducer in a virtual path assumed to proceed in a straight line from the focal point to the position of each ultrasonic transducer without bending; (c) minimizing a difference between the first propagation time and the second propagation time; To be determined, 10. The beamforming method of claim 9.

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