Ultrasonic diagnostic apparatus, signal processing method, and

Abstract

To improve image quality.SOLUTION: An ultrasonic diagnostic apparatus includes a transmission / reception part, a first analysis part, a second analysis part, and a reconstruction part. The transmission / reception part transmits ultrasonic waves to the inside of a subject on the basis of transmission conditions, and receives echoes from the inside of the subject. The first analysis part obtains a transmission wave field by forward propagating ultrasonic waves transmitted on the basis of the transmission condition. The second analysis part obtains a reception wave field by back-propagating a signal based on the echo by applying a weight function depending on a wave front incident angle. A reconstructor performs a correlation analysis between the transmitted wavefield and the received wavefield to generate an echo component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to an ultrasound diagnostic apparatus, a signal processing method, and a program. [Background technology]

[0002] Seismic interferometry (also known as SPM (Shot-Profile Migration) or wavefield correlation method) is a well-known technique in the field of seismic wave measurement. Seismic interferometry is a method for reconstructing the location of underground earthquakes and reflecting surfaces, and estimates the location of earthquakes by performing correlation processing between the transmitted wavefield, which is simulated as forward propagation, and the received wavefield, which is simulated as backward propagation.

[0003] Here, since seismic waves and ultrasound waves are both elastic waves, it is conceivable to use seismic interferometry for image reconstruction in an ultrasound diagnostic device to reconstruct ultrasound images.

[0004] The receiving sensor in an ultrasound diagnostic device is generally composed of multiple piezoelectric elements. Because the frequencies used in ultrasound diagnostic devices are on the order of several MHz to several tens of MHz, tissues within a living body can be said to be located in a complex near-field. Under these conditions, image reconstruction using a partial restriction of the reflected wavefront from the point of interest can sometimes suppress unwanted artifacts caused by signals from spaces other than the point of interest. Considering a shallow point of interest, the amplitude of the ultrasound waves themselves is sufficient. Therefore, to prevent overlooking a tumor on the body surface, for example, it is desirable to reconstruct the image using only the component of the reflected wavefront from the tumor that faces the sensor, and suppress components in other directions that contain many unwanted signals from outside the tumor. On the other hand, when the point of interest is deep, the amplitude of the ultrasound waves decreases due to signal attenuation. Therefore, to ensure a high S / N ratio, it is desirable to reconstruct the image using all signals received by the sensor.

[0005] However, with conventional seismic interferometry, images were reconstructed using signals received by the sensor from all directions with equal weighting, which made it difficult to maintain a high signal-to-noise ratio while suppressing unwanted wave components. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] “Distributed Aberration Correction Techniques Based on Tomographic Sound Speed ​​Estimates”, R. Ali et al., IEEE T-UFFC, Vol. 69, No. 5, p1714, May 2022 Summary of the Invention [Problem to be solved by the invention]

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve image quality. 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 the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0008] An ultrasound diagnostic apparatus according to an embodiment includes a transmitting / receiving unit, a first analysis unit, a second analysis unit, and a reconstruction unit. The transmitting / receiving unit transmits ultrasound waves into a subject based on transmission conditions and receives echoes from within the subject. The first analysis unit obtains a transmitted wave field by forward propagating the ultrasound waves transmitted based on the transmission conditions. The second analysis unit obtains a received wave field by backpropagating a signal based on the echoes by applying a weighting function dependent on the wavefront incident angle. The reconstruction unit generates echo components by performing correlation analysis between the transmitted wave field and the received wave field. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an ultrasound device according to an embodiment. [Figure 2] FIG. 2 is a flowchart showing an example of the flow of processing performed by the ultrasound diagnostic apparatus according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of processing performed by the ultrasound diagnostic apparatus according to the first embodiment. [Figure 4] FIG. 4 is a flowchart illustrating the process in step S300A of FIG. 2 in more detail. [Figure 5] FIG. 5 is a diagram illustrating the processing performed by the ultrasound diagnostic apparatus according to the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating the processing performed by the ultrasound diagnostic apparatus according to the first embodiment. [Figure 7] FIG. 7 is a diagram illustrating the processing performed by the ultrasound diagnostic apparatus according to the first embodiment. [Figure 8] FIG. 8 is a flowchart illustrating the flow of processing performed by the ultrasound diagnostic apparatus according to the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating the processing performed by the ultrasound diagnostic apparatus according to the second embodiment. [Figure 10] FIG. 10 is a diagram illustrating the processing performed by the ultrasound diagnostic apparatus according to the second embodiment. [Figure 11] FIG. 11 is a flowchart illustrating the processing performed by the ultrasound diagnostic apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of an ultrasound diagnostic apparatus, a signal processing method, and a program will be described in detail with reference to the drawings.

[0011] (First embodiment) First, the configuration of an ultrasonic diagnostic apparatus according to the first embodiment will be described. Fig. 1 is a block diagram showing an example of the configuration of an ultrasonic diagnostic apparatus according to the first embodiment. As shown in Fig. 1, the ultrasonic diagnostic apparatus according to the first embodiment includes an ultrasonic probe 15 and an ultrasonic diagnostic apparatus 10. The ultrasonic diagnostic apparatus 10 includes a transmission circuit 19, a reception circuit 11, and a medical image processing apparatus 100.

[0012] The ultrasonic probe 15 has a plurality of piezoelectric vibrators, which generate ultrasonic waves based on drive signals supplied from a transmission circuit 19 included in the ultrasonic diagnostic device 10, which will be described later. The plurality of piezoelectric vibrators included in the ultrasonic probe 15 also receive reflected waves from the subject P and convert them into electrical signals (reflected wave signals). The ultrasonic probe 15 also has matching layers provided on the piezoelectric vibrators, and a backing material that prevents ultrasonic waves from propagating backward from the piezoelectric vibrators. The ultrasonic probe 15 is detachably connected to the ultrasonic diagnostic device 10.

[0013] When ultrasonic waves are transmitted from the ultrasonic probe 15 to the subject P, the transmitted ultrasonic waves are reflected successively by discontinuous surfaces of acoustic impedance in the tissues of the subject P, and are received as reflected waves by the multiple piezoelectric transducers of the ultrasonic probe 15 and converted into reflected wave signals. The amplitude of the reflected wave signal depends on the difference in acoustic impedance at the discontinuous surfaces from which the ultrasonic waves are reflected. When the transmitted ultrasonic pulse is reflected by the surface of a moving blood flow or heart wall, the reflected wave signal undergoes a frequency shift due to the Doppler effect, depending on the velocity component of the moving object relative to the direction of ultrasonic transmission.

[0014] The embodiment is applicable whether the ultrasonic probe 15 is a 1D array probe that scans the subject P two-dimensionally, or a mechanical 4D probe or 2D array probe that scans the subject P three-dimensionally.

[0015] The ultrasound diagnostic device 10 is a device that generates ultrasound image data based on reflected wave signals received from an ultrasound probe 15. The ultrasound diagnostic device 10 shown in Fig. 1 is a device that can generate two-dimensional ultrasound image data based on two-dimensional reflected wave signals and three-dimensional ultrasound image data based on three-dimensional reflected wave signals. However, the embodiment is also applicable to cases where the ultrasound diagnostic device 10 is a device dedicated to two-dimensional data.

[0016] As shown in FIG. 1, the ultrasound diagnostic apparatus 10 includes a transmission circuit 19, a reception circuit 11, and a medical image processing device 100.

[0017] The transmission circuit 19 and the reception circuit 11 control the transmission and reception of ultrasound waves by the ultrasonic probe 15 based on instructions from a processing circuit 150 having a control function 150f (described later). The transmission circuit 19 includes a pulse generator, a transmission delay unit, a pulser, and the like, and supplies a drive signal to the ultrasonic probe 15. The pulse generator repeatedly generates rate pulses for forming transmission ultrasound waves at a predetermined pulse repetition frequency (PRF). The transmission delay unit focuses the ultrasound waves generated from the ultrasonic probe 15 into a beam shape and provides a delay time for each piezoelectric vibrator required to determine the transmission directivity to each rate pulse generated by the pulse generator. The pulser also applies a drive signal (drive pulse) to the ultrasonic probe 15 at a timing based on the rate pulse.

[0018] That is, the transmission delay unit arbitrarily adjusts the transmission direction of the ultrasonic waves transmitted from the piezoelectric transducer surface by changing the delay time given to each rate pulse. Also, the transmission delay unit controls the position of the focal point (transmission focus) in the depth direction of the ultrasonic transmission by changing the delay time given to each rate pulse.

[0019] The transmission circuit 19 has a function of being able to instantaneously change the transmission frequency, transmission drive voltage, etc. in order to execute a predetermined scan sequence based on instructions from the processing circuit 150, which will be described later. In particular, the change in transmission drive voltage is realized by a linear amplifier type oscillation circuit that can instantaneously switch its value, or a mechanism that electrically switches between multiple power supply units.

[0020] The receiving circuit 11 also includes an amplifier circuit, an A / D (Analog / Digital) converter, a reception delay circuit, an adder, a quadrature detection circuit, etc., and performs various processes on the reflected wave signal received from the ultrasound probe 15 to generate a received signal (reflected wave data). The amplifier circuit amplifies the reflected wave signal for each channel and performs gain correction processing. The A / D converter A / D converts the gain-corrected reflected wave signal. The reception delay circuit provides the digital data with a reception delay time required to determine the reception directivity. The adder performs addition processing on the reflected wave signal to which the reception delay time has been applied by the reception delay circuit. The addition processing by the adder emphasizes the reflected wave signal from a direction corresponding to the reception directivity of the reflected wave signal. The quadrature detection circuit then converts the output signal of the adder into an in-phase signal (I signal, I: In-phase) and a quadrature signal (Q signal, Q: Quadrature-phase) in the baseband. The quadrature detection circuit then transmits the I signal and Q signal (hereinafter referred to as IQ signal) to the processing circuit 150 as a received signal (reflected wave data). The quadrature detection circuit may convert the output signal of the adder into an RF (Radio Frequency) signal and then transmit it to the processing circuit 150. The IQ signal and the RF signal are received signals having phase information.

[0021] When scanning a two-dimensional region within the subject P, the transmission circuitry 19 causes the ultrasonic probe 15 to transmit ultrasonic beams for scanning the two-dimensional region. Then, the reception circuitry 11 generates two-dimensional reception signals from the two-dimensional reflected wave signals received from the ultrasonic probe 15. When scanning a three-dimensional region within the subject P, the transmission circuitry 19 causes the ultrasonic probe 15 to transmit ultrasonic beams for scanning the three-dimensional region. Then, the reception circuitry 11 generates three-dimensional reception signals from the three-dimensional reflected wave signals received from the ultrasonic probe 15. The reception circuitry 11 generates reception signals based on the reflected wave signals and transmits the generated reception signals to the processing circuitry 150.

[0022] The transmission circuit 19 causes the ultrasonic probe 15 to transmit an ultrasonic beam from a predetermined transmission position (transmission scanning line). The reception circuit 11 receives, from the ultrasonic probe 15, a signal due to a reflected wave of the ultrasonic beam transmitted by the transmission circuit 19 at a predetermined reception position (reception scanning line). When parallel simultaneous reception is not performed, the transmission scanning line and the reception scanning line are the same scanning line. On the other hand, when parallel simultaneous reception is performed, when the transmission circuit 19 causes the ultrasonic probe 15 to transmit one ultrasonic beam at one transmission scanning line, the reception circuit 11 receives, as multiple reception beams, signals due to the reflected waves originating from the ultrasonic beam transmitted by the transmission circuit 19 to the ultrasonic probe 15 at multiple predetermined reception positions (reception scanning lines) through the ultrasonic probe 15 simultaneously.

[0023] The medical image processing device 100 is connected to the transmission circuitry 19 and the reception circuitry 11, and processes signals received from the reception circuitry 11 and controls the transmission circuitry 19. The medical image processing device 100 includes a processing circuitry 150, a memory 132, an input device 134, and a display 135. The processing circuitry 150 includes a B-mode processing function 150a, a Doppler processing function 150b, a generation function 150c, a display control function 150d, a reception function 150e, a control function 150f, a reconstruction function 150g, a selection function 150h, a first analysis function 150i, and a second analysis function 150j.

[0024] In this embodiment, the processing functions performed by the B-mode processing function 150a, Doppler processing function 150b, generation function 150c, display control function 150d, reception function 150e, control function 150f, reconstruction function 150g, selection function 150h, first analysis function 150i, and second analysis function 150j are stored in the memory 132 in the form of computer-executable programs. The processing circuitry 150 is a processor that reads and executes the programs from the memory 132 to realize the functions corresponding to the programs. In other words, the processing circuitry 150 in a state in which the programs have been read has the functions shown in the processing circuitry 150 of FIG. 1. Note that, although FIG. 1 illustrates the functions of the processing circuitry 150 being realized by a single processing circuit, the processing circuitry 150 may be configured by combining multiple independent processors, and each processor may execute a program to realize the function. In other words, each of the above functions may be configured as a program, and a single processing circuit may execute each program. Also, a single processing circuit may implement two or more of the functions of the processing circuit 150. As another example, a specific function may be implemented in a dedicated, independent program execution circuit.

[0025] 1, the processing circuitry 150, the B-mode processing function 150a, the Doppler processing function 150b, the generation function 150c, the display control function 150d, the reception function 150e, the control function 150f, the reconstruction function 150g, the selection function 150h, the first analysis function 150i, and the second analysis function 150j are examples of a B-mode processing unit, a Doppler processing unit, a generation unit, a display control unit, a reception unit, a control unit, a reconstruction unit, a selection unit, a first analysis unit, and a second analysis unit, respectively. Also, the transmission circuitry 9 and the reception circuitry 11 are examples of a transmission / reception unit.

[0026] The term "processor" used in the above description refers to circuits such as a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). The processor realizes its functions by reading and executing programs stored in memory 132.

[0027] Furthermore, instead of storing the program in memory 132, the program may be directly embedded in the circuitry of the processor. In this case, the processor realizes its functions by reading and executing the program embedded in the circuitry. The transmission circuitry 9, reception circuitry 11, etc. built into ultrasound diagnostic device 10 may be configured as hardware such as integrated circuits, or may be modularized software programs.

[0028] The processing circuitry 150 is a processing unit that performs various signal processing on the received signals received from the receiving circuitry 11. The processing circuitry 150 has a B-mode processing function 150a, a Doppler processing function 150b, a generation function 150c, a display control function 150d, a reception function 150e, a control function 150f, a reconstruction function 150g, a selection function 150h, a first analysis function 150i, and a second analysis function 150j.

[0029] The processing circuit 150 receives data from the receiving circuit 11 using the B-mode processing function 150a, and performs logarithmic amplification processing, envelope detection processing, logarithmic compression processing, etc. to generate data (B-mode data) in which the signal strength is expressed as brightness.

[0030] In addition, the processing circuit 150 uses the Doppler processing function 150b to frequency-analyze velocity information from the received signal (reflected wave data) received from the receiving circuit 11, and generates data (Doppler data) extracted from multiple points of moving object information such as velocity, dispersion, and power due to the Doppler effect.

[0031] The B-mode processing function 150a and the Doppler processing function 150b illustrated in FIG. 1 are capable of processing both two-dimensional reflected wave data and three-dimensional reflected wave data.

[0032] The processing circuitry 150 uses the generation function 150c to generate ultrasound image data from the data generated by the B-mode processing function 150a and the Doppler processing function 150b. The processing circuitry 150 uses the generation function 150c to generate two-dimensional B-mode image data that represents the intensity of the reflected wave as brightness from the two-dimensional B-mode data generated by the B-mode processing function 150a. The processing circuitry 150 also uses the generation function 150c to generate two-dimensional Doppler image data that represents moving object information from the two-dimensional Doppler data generated by the Doppler processing function 150b. The two-dimensional Doppler image data is velocity image data, variance image data, power image data, or image data that combines these.

[0033] Furthermore, the processing circuitry 150 uses the generation function 150c to convert (scan convert) the scan line signal sequence of the ultrasound scan into a scan line signal sequence in a video format such as that of a television, and generates ultrasound image data for display. Furthermore, the processing circuitry 150 uses the generation function 150c to perform various image processing other than scan conversion, such as image processing (smoothing processing) for regenerating an average brightness image using multiple image frames after scan conversion, and image processing (edge ​​enhancement processing) using a differential filter within the image. Furthermore, the processing circuitry 150 uses the generation function 150c to perform various rendering processes on the volume data in order to generate two-dimensional image data for displaying the volume data on the display 135.

[0034] The processing circuitry 150 controls the display 135 to display the ultrasound image data for display stored in the memory 132 using the display control function 150d.

[0035] The processing circuit 150 receives various operations from the user via the input device 134 using the reception function 150e.

[0036] The processing circuitry 150 controls the overall processing of the ultrasound diagnostic apparatus using a control function 150f. Specifically, the processing circuitry 150 controls the processing of the transmission circuitry 9, the reception circuitry 11, and the processing circuitry 150 using the control function 150f based on various setting requests input by the operator via the input device 134 and various control programs and various data read from the memory 132.

[0037] The processing circuitry 150 also has a reconstruction function 150g, a selection function 150h, a first analysis function 150i, and a second analysis function 150j, which will be described later.

[0038] The memory 132 is composed of a semiconductor memory element such as a RAM (Random Access Memory), a flash memory, a hard disk, an optical disk, etc. The memory 132 is a memory that stores data such as image data for display generated by the processing circuitry 150. The memory 132 can also store data generated by the B-mode processing function 150a and the Doppler processing function 150b. The B-mode data and Doppler data stored in the memory 132 can be called up by the operator after diagnosis, for example, and becomes ultrasound image data for display via the processing circuitry 150. The memory 132 can also store received signals (reflected wave data) output by the receiving circuitry 11.

[0039] In addition, the memory 132 stores, as needed, control programs for transmitting and receiving ultrasound, image processing, and display processing, as well as various data such as diagnostic information (e.g., patient ID, doctor's findings, etc.), diagnostic protocols, and various body marks.

[0040] The input device 134 receives various instructions and information input from an operator. The input device 134 is, for example, a pointing device such as a mouse or a trackball, a selection device such as a mode change switch, or an input device such as a keyboard.

[0041] The display 135 displays a GUI (Graphical User Interface) for receiving input of imaging conditions, images generated by the generation function 150c, etc. under the control of the control function 150f, etc. The display 135 is, for example, a display device such as a liquid crystal display. The display 135 is an example of a display unit. The display 135 has a mouse, a keyboard, buttons, a panel switch, a touch command screen, a foot switch, a trackball, a joystick, etc.

[0042] Next, the background of the embodiment will be described.

[0043] Seismic interferometry (also known as SPM (Shot-Profile Migration) or wavefield correlation method) is a well-known technique in the field of seismic wave measurement. Seismic interferometry is a method for reconstructing the location of underground earthquakes and reflecting surfaces, and estimates the location of earthquakes by performing correlation processing between the transmitted wavefield, which is simulated as forward propagation, and the received wavefield, which is simulated as backward propagation.

[0044] Here, since both seismic waves and ultrasound waves are elastic waves, it is conceivable that seismic wave interferometry could be used for image reconstruction in an ultrasound diagnostic device to reconstruct ultrasound images, as described in Non-Patent Document 1, for example.

[0045] Here, when the point to be imaged is shallow and close to the body surface, the amplitude of the ultrasound itself is sufficiently strong. Therefore, to prevent overlooking, for example, a tumor on the body surface, it is desirable to reconstruct the image using only the component of the reflected wavefront from the tumor that is facing the sensor, and suppress the components in other directions, which contain many unnecessary wave signals from outside the tumor. On the other hand, when the point to be imaged is deep and far from the body surface, the amplitude of the ultrasound decreases due to signal attenuation. Therefore, to ensure a high S / N ratio, it is desirable to reconstruct the image using all signals received by the sensor, even if signals from outside the imaging point are included.

[0046] However, with conventional seismic interferometry, images were reconstructed using signals received by the sensor from all directions with equal weighting, which made it difficult to maintain a high signal-to-noise ratio while suppressing unwanted wave components.

[0047] The ultrasound diagnostic apparatus according to the embodiment is based on this background and includes a transmission circuitry 19 and a reception circuitry 11 as a transmission / reception unit, and a processing circuitry 150. The transmission circuitry 19 and the reception circuitry 11 as a transmission / reception unit transmit ultrasound waves into a subject based on transmission conditions and receive echoes from the subject. The processing circuitry 150 forward-propagates the ultrasound waves transmitted based on the transmission conditions using a first analysis function 150i to obtain a transmission wave field. The processing circuitry 150 back-propagates the echo-based signal using a second analysis function 150j to obtain a reception wave field. The processing circuitry 150 performs correlation analysis between the transmission wave field and the reception wave field using a reconstruction function 105g to generate echo components.

[0048] In addition, the ultrasound diagnostic method according to the embodiment involves forward propagating a transmission signal to obtain a transmission wave field, backpropagating a reception signal by applying a weighting function dependent on a wavefront incidence angle that represents the incident direction of the wavefront when a backpropagation simulation is performed on the reception signal to obtain a reception wave field, and performing correlation analysis between the transmission wave field and the reception wave field to generate a signal.

[0049] In addition, the program of the embodiment causes a computer to perform a process of forward propagating a transmitted signal to obtain a transmitted wave field, backpropagating a received signal by applying a weighting function dependent on the wavefront incident angle that represents the incident direction of the wavefront when a backpropagation simulation is performed on the received signal to obtain a received wave field, and performing a correlation analysis between the transmitted wave field and the received wave field to generate a signal.

[0050] In this way, by changing the incident angle corresponding to the received signals used for reconstruction using seismic interferometry for each depth, highly reliable images can be obtained at shallower depths by using more reliable received signals for reconstruction, and the S / N ratio can be improved at deeper depths by using all received signals for reconstruction.

[0051] First, the processing performed by the ultrasound diagnostic apparatus 10 according to the first embodiment will be described with reference to Figures 2 and 3. Figure 2 is a flowchart illustrating the flow of processing performed by the ultrasound diagnostic apparatus 10 according to the embodiment. Also, Figure 3 is a diagram illustrating the processing of image reconstruction using seismic interferometry performed by the ultrasound diagnostic apparatus 10 according to the embodiment.

[0052] First, in step S100, the transmission circuitry 9 and reception circuitry 11, which function as a transceiver, transmit ultrasonic waves into the subject based on transmission conditions and receive echoes from within the subject. Ultrasound diagnostic apparatus 10 typically transmits multiple ultrasonic waves in different directions using transmission circuitry 9, and reception circuitry 11 receives echoes from the subject for each of the multiple ultrasonic waves. For example, as shown in FIG. 3, transmission circuitry 9 transmits multiple ultrasonic waves 20a, 20b, and 20c. Furthermore, reception circuitry 11 receives echoes from the subject for each of the multiple ultrasonic waves 20a, 20b, and 20c (echo receptions 40a, 40b, and 40c), and acquires reception signals r1(x,t), r2(x,t), and r3(x,t) as reception signals 50, where x is the position coordinate in the direction of propagation of the ultrasonic beam and t is the time.

[0053] Here, the transmission conditions typically refer to transmission conditions such as the amplitude, phase, frequency, transmission aperture, or transmission apodization of the ultrasonic waves to be transmitted.

[0054] Next, in step S200, the processing circuit 150 calculates the transmission wave field 30 by forward propagation simulation of the ultrasonic waves transmitted based on the transmission conditions in step S100 using the first analysis function 150i. As an example, as shown in FIG. 3, the processing circuit 150 calculates the transmission wave fields f1(x, y, t), f2(x, y, t), and f3(x, y, t) by forward propagation simulation of the ultrasonic waves 20a, 20b, and 20c transmitted under transmission conditions #1, #2, and #3 using the first analysis function 150i. Here, x represents the position coordinate in the direction perpendicular to the propagation direction of the ultrasonic beam, y represents the position coordinate in the propagation direction of the ultrasonic beam, and t represents time. The processing circuit 150 obtains the transmission wave field 30 by numerical analysis based on the wave equation using the first analysis function 150i, for example, by simulating the time evolution of the wave equation. As one example, the processing circuit 150 uses the first analysis function 150i to calculate the transmission wave field 30 based on the transmission conditions in step S100, for example, by using the finite difference time domain (FDTD) method. As another example, the processing circuit 150 uses the first analysis function 150i to calculate the transmission wave field 30 based on the transmission conditions in step S100, for example, by using a simulation method using the angular spectrum method. Note that although a focused sound field is depicted as the transmission wave field in FIG. 3, the present embodiment is not limited to this, and for example, a plane wave sound field or a diffuse sound field may be used as the transmission sound field.

[0055] Next, in step S300, the processing circuit 150 uses the second analysis function 150j to backpropagate the echo-based signal by applying a weighting function dependent on the wavefront incidence angle, thereby obtaining a received wave field 51. Details of the wavefront incidence angle and the weighting function dependent on the wavefront incidence angle will be described in detail after the overall description of the flowchart in FIG. 2. As shown in FIG. 3, the processing circuit 150 calculates the received wave field 51 by backpropagating the echo-based received signal 50 acquired in step S100. As an example, the processing circuit 150 uses the second analysis function 150j to obtain the received wave field 51 by numerical analysis based on the wave equation. For example, the processing circuit 150 uses the second analysis function 150j to simulate the time evolution of the wave equation using the FDTD method, thereby calculating received wave fields b1(x,y,t), b2(x,y,t), and b3(x,y,t) from the received signals r1(x), r2(x), and r3(x), respectively.

[0056] Next, in step S400, the processing circuitry 150 uses the reconstruction function 150g to perform correlation analysis between the transmitted wave field 30 and the received wave field 51 to generate echo components and generate an image 52. Specifically, an image I is generated by the following equation (1).

[0057]

number

[0058] where n is an index that distinguishes each ultrasound wave 20a, 20b, 20c, etc., and N represents the total number of ultrasound waves included in the series of ultrasound waves, and "*" represents the complex conjugate.

[0059] Next, the details of the processing of step S300 will be described using FIGS. 4 to 7. FIG. 4 is a flowchart illustrating an example of the processing of step S300 in more detail. In step S300, first, in step S350A, the processing circuitry 150 uses the second analysis function 150j to design and apply a weighting function that changes depending on the position in the depth direction. As an example, the processing circuitry 150 uses the second analysis function 150j to apply a weighting function that changes in the depth direction so that the shallower the position of the object to be imaged, the greater the weight of the component corresponding to a smaller incident angle. In other words, the processing circuitry 150 uses the second analysis function 150j to apply a weighting function that changes in the depth direction so that the contribution of the weight of the component with a small wavefront incident angle becomes relatively greater the shallower the depth. Next, in step S360A, the processing circuitry 150 uses the second analysis function 150j to weight each incident angle at each spatial point based on the weighting function and perform a back propagation simulation of the received signal.

[0060] This point will be explained using Figures 5 to 7. Figure 5 is a diagram explaining the design of a weighting function when the position of point 2a at which an image is obtained is shallow, Figure 6 is a diagram explaining the design of a weighting function when the position of point 2b at which an image is obtained is deep, and Figure 7 is a diagram showing an example of the shape of a weighting function.

[0061] Referring to FIG. 5, consider the case where point 2a, where an image is obtained, is shallow. Ultrasonic waves transmitted by ultrasonic transmitter 20 are reflected at point 2a, and receiver circuit 11 receives echoes 40a, 40b, and 40c at different positions. Lines 91a, 91b, and 91c represent the direction of propagation of the ultrasonic wave wavefront when the transmitted ultrasonic waves transmitted by ultrasonic transmitter 20 are reflected at point 2a and the echoes are received at positions corresponding to echo receivers 40a, 40b, and 40c, respectively. Lines 91a, 91b, and 91c also represent the direction of incidence of the wavefront obtained by performing a backpropagation simulation on the signals received at positions corresponding to echo receivers 40a, 40b, and 40c, respectively. The direction of incidence of the wavefront obtained by performing the backpropagation simulation is opposite to the direction of propagation of the reflected transmitted ultrasonic waves.

[0062] Furthermore, wavefront incident angle 71a is an incident angle that represents the incident direction of a wavefront when a back propagation simulation is performed on a signal based on an echo corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted. Wavefront incident angle 71a is defined as the angle formed by line 91a and the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmission 20. Wavefront incident angle 71a corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted, is larger than wavefront incident angle 71b corresponding to echo reception 40b, which is located close to the frontal position where the ultrasonic wave was transmitted.

[0063] Furthermore, wavefront incident angle 71b is an incident angle that represents the incident direction of a wavefront when a back propagation simulation is performed on a signal based on an echo corresponding to echo reception 40b, which is located near the frontal position where the ultrasonic wave was transmitted. Wavefront incident angle 71b is defined as the angle formed by line 91b and the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmission 20. Wavefront incident angle 71b corresponding to echo reception 40b, which is located near the frontal position where the ultrasonic wave was transmitted, is smaller than wavefront incident angle 71a corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted.

[0064] Furthermore, for the signal based on the echo corresponding to echo receiver 40c, which is the front position where the ultrasonic wave was transmitted, the incident direction of the back-propagated wavefront is approximately 180 degrees opposite to the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmitter 20, so in this case the wavefront incident angle is approximately 0.

[0065] Also, consider the case in Figure 6 where point 2b, where an image is obtained, is located deep. Ultrasound transmitted by ultrasonic transmitter 20 is reflected at point 2b, and receiver circuit 11 receives echoes 40a, 40b, and 40c at different locations. Lines 93a, 93b, and 93c represent the direction of propagation of the ultrasonic wave wavefront when the transmitted ultrasound transmitted by ultrasonic transmitter 20 is reflected at point 2b and the echoes are received at locations corresponding to echo receivers 40a, 40b, and 40c. Lines 93a, 93b, and 93c also represent the direction of incidence of the wavefront obtained by performing a backpropagation simulation on the signals received at locations corresponding to echo receivers 40a, 40b, and 40c, respectively. The direction of incidence of the wavefront obtained by performing the backpropagation simulation is opposite to the direction of propagation of the reflected transmitted ultrasound.

[0066] Furthermore, wavefront incident angle 73a is an incident angle that represents the incident direction of a wavefront when a back propagation simulation is performed on a signal based on an echo corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted. Wavefront incident angle 73a is defined as the angle formed by straight line 93a and the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmission 20. Wavefront incident angle 73a corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted, is larger than wavefront incident angle 73b corresponding to echo reception 40b, which is located close to the frontal position where the ultrasonic wave was transmitted.

[0067] Furthermore, wavefront incident angle 73b is an incident angle that represents the incident direction of a wavefront when a back propagation simulation is performed on a signal based on an echo corresponding to echo reception 40b, which is located near the frontal position where the ultrasonic wave was transmitted. Wavefront incident angle 73b is defined as the angle formed by line 93b and the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmission 20. Wavefront incident angle 73b corresponding to echo reception 40b, which is located near the frontal position where the ultrasonic wave was transmitted, is smaller than wavefront incident angle 73a corresponding to echo reception 40a, which is located far from the frontal position where the ultrasonic wave was transmitted.

[0068] Furthermore, for the signal based on the echo corresponding to echo receiver 40c, which is the front position where the ultrasonic wave was transmitted, the incident direction of the back-propagated wavefront is approximately 180 degrees opposite to the transmission direction of the transmitted ultrasonic wave transmitted by ultrasonic transmitter 20, so in this case the wavefront incident angle is approximately 0.

[0069] In step S300, which calculates the received wave field 51 using seismic interferometry, an important issue is the range of wavefront incidence angles of the echo signals used for image reconstruction. Specifically, when the imaging point 2a is located near the sensor and shallow, as shown in Figure 5, the signal strength is sufficient at shallow positions. Therefore, image reconstruction using only the signal from echo receiver 40c at the front position, for example, will provide sufficient image quality. Conversely, if image reconstruction is performed using signals from echo receivers 40a and 40b that are far from the front position, noise and other factors may be visualized, potentially resulting in a degradation of the image quality of the reconstructed image.

[0070] Therefore, for example, when the position of the point 2a to be imaged is shallow as shown in Figure 5, a function is selected, such as weighting function 1a in Figure 7, in which the weighting value becomes large only when the wavefront incident angle θ is near 0, and the value of the weighting function rapidly decreases as the wavefront incident angle θ increases.

[0071] On the other hand, when the position of imaging point 2b is deep and close to the sensor as shown in Figure 6, the signal attenuates at deep positions, so it is desirable to pick up all signals from echo receivers 40a, 40b, and 40c and perform image reconstruction. Therefore, when the position of imaging point 2b is deep as shown in Figure 6, for example, a function is selected such that the value of the weighting function becomes relatively large up to the region where the wavefront incident angle θ is large, such as weighting function 1b in Figure 7.

[0072] To summarize the above, in the process of step S300, first, in step S350, the processing circuitry 150 uses the second analysis function 150j to design and apply a weighting function that changes depending on the position in the depth direction. As an example, the processing circuitry 150 uses the second analysis function 150j to apply a weighting function in which the contribution of the weight of components with small wavefront incident angles becomes relatively larger the shallower the depth. Next, in step S360A, the processing circuitry 150 uses the second analysis function 150j to weight each spatial point for each incident angle based on the weighting function and perform a backpropagation simulation of the received signal. In other words, the processing circuitry 150 uses the second analysis function 150j to backpropagate the echo-based signal based on a weighting function that depends on the positional relationship between the point where the image is obtained and the point where the echo is received, thereby obtaining a received wave field.

[0073] As described above, in the first embodiment, in ultrasound reconstruction using seismic interferometry, a received wave field is obtained by backpropagating echo-based signals while applying a weighting function that depends on the wavefront incident angle. This makes it possible to improve image quality by suppressing unnecessary signal components at shallow positions, and to ensure a high S / N ratio at deep positions, thereby obtaining high-quality images at both shallow and deep positions.

[0074] The embodiment is not limited to the above example. In the above embodiment, a continuous function is used as the weighting function employed in step S300, but the embodiment is not limited to this. For example, a discontinuous weighting function, such as a weighting function that sets the weight of a specific received signal to 1 and the weights of other received signals to 0, may be selected as the weighting function.

[0075] As an example, in step S300, the processing circuit 150 may use a selection function 150h to select the echo-based signals to be backpropagated in the process of generating the received wave field, and use a second analysis function 150j to backpropagate only the selected echo-based signals to generate the received wave field.

[0076] In the above-described embodiment, the case where ultrasonic reconstruction is performed using seismic interferometry has been described, but the embodiment can be extended to general model-based reconstruction. As a model-based reconstruction method in the embodiment, for example, there is a method in which a transmitted signal is forward propagated to obtain a transmitted wave field, a received signal is backward propagated by applying a weighting function to the wavefront incidence angle to obtain a received wave field, and a correlation analysis is performed between the transmitted wave field and the received wave field to generate a signal.

[0077] (Second embodiment) In the second embodiment, a case will be described in which a weighting function is determined based on a virtual receiving aperture determined for each position in the depth direction. In the second embodiment, the processes other than step S300 in FIG. 2 are the same as those in the first embodiment, and therefore a description of the processes other than step S300 will be omitted. In the second embodiment, the processing circuit 150 performs the process shown in FIG. 8 in step S300. FIG. 8 is a flowchart showing the flow of the process performed in step S300 in FIG. 2 in the second embodiment.

[0078] First, in step S310B, the processing circuit 150 sets a virtual receive aperture at each spatial point using the second analysis function 150j. Regarding the virtual receive aperture, in an ultrasound diagnostic device, ultrasonic transducers are directional and can only pick up sounds within a limited range. For example, in FIG. 9, the reflected wave from point 2a, which is shallow, can only be received by a group of transducers within a range of width 3a. Conversely, the reflected wave from point 2b, which is deep, can only be received by a group of transducers within a range of width 3b. Therefore, the effective aperture width of the transducer group can be considered for the point to be imaged, and this is called the virtual receive aperture. That is, width 3a is the virtual receive aperture for point 2a, and width 3b is the virtual receive aperture for point 2b. When the virtual receive aperture width is plotted as a function of depth, for example, it results in a shape similar to curve 4 shown in FIG. 10. In step S310B, the processing circuit 150 sets a virtual receiving aperture at each spatial point by using the second analysis function 150j to obtain data from the memory 132 indicating the shape of curve 4 obtained, for example, by performing measurements on a known group of transducers.

[0079] Here, to explain the meaning of the virtual receive aperture, in seismic interferometry, all ultrasonic transducers actually receive signals. However, if image reconstruction is performed using signals from ultrasonic transducers far from the center, image degradation occurs. Therefore, signals from ultrasonic transducers far from the center are not backpropagated and are not included in image reconstruction. In other words, in this case, signals farther away than the virtual receive aperture are not reconstructed. In other words, the virtual receive aperture can be thought of as roughly indicating the cutoff position of the weighting function.

[0080] Next, in step S350B, the processing circuitry 150 uses the second analysis function 150j to design a weighting function for the wavefront incidence angle based on the virtual receive aperture set in step S350. As an example, the processing circuitry 150 uses the second analysis function 150j to set the weighting function by designing the half-width 5 of the weighting function so that the shape of the half-width 5 of the weighting function expressed as a function of the wavefront incidence angle at each depth matches the virtual aperture width at each depth. Next, in step S360B, the processing circuitry 150 uses the second analysis function 150j to weight each incident angle at each spatial point based on the weighting function, and performs a back-propagation simulation of the received signal.

[0081] 11, in step S350, the processing circuit 150 uses the second analysis function 150j to estimate the virtual sound source position on the aperture for each depth so that the F-number is uniform, and performs back propagation simulation on the received signal by weighting it based on the weighting function.

[0082] This allows, for example, image quality to be improved by suppressing unnecessary signal components at shallow positions, while ensuring a good S / N ratio at deep positions, making it possible to obtain high-quality images at both shallow and deep positions.

[0083] According to at least one of the embodiments described above, image quality can be improved.

[0084] Although several embodiments 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, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0085] 10 Ultrasound diagnostic equipment 15 Ultrasound probe 11 Receiving circuit 19 Transmitting circuit 100 Medical image processing device 132 memory 134 Input Device 135 Display 150 Processing Circuit 150a B-mode processing function 150b Doppler processing function 150c generation function 150d display control function 150e Reception Function 150f control function 150g reconfiguration function 150h selection function 150i 1st analysis function 150j 2nd analysis function

Claims

1. a transmitting / receiving unit that transmits ultrasonic waves into a subject based on transmission conditions and receives echoes from within the subject; a first analysis unit that obtains a transmission wave field by forward propagating the ultrasonic waves transmitted based on the transmission conditions; a second analysis unit that applies a weighting function that depends on a wavefront incident angle to a signal based on the echo and back-propagates the signal to obtain a received wave field; a reconstruction unit that performs correlation analysis between the transmitted wave field and the received wave field to generate echo components; An ultrasound diagnostic device comprising:

2. The ultrasonic diagnostic apparatus according to claim 1 , wherein the weighting function is a function that changes depending on a position in the depth direction.

3. The ultrasonic diagnostic apparatus according to claim 2 , wherein the weighting function is a function in which the contribution of the weight of the component with a small wavefront incident angle becomes relatively larger as the depth becomes shallower.

4. The ultrasonic diagnostic apparatus according to claim 3 , wherein the weighting function is determined based on a virtual receiving aperture determined for each position in the depth direction.

5. a selection unit for selecting a signal based on the echo to be back-propagated in the process of generating the received wave field; The ultrasonic diagnostic apparatus according to claim 1 , wherein the second analyzer generates the received wave field by backpropagating only signals based on the echoes selected by the selector.

6. the first analysis unit obtains the transmitted wave field by numerical analysis based on a wave equation; The ultrasonic diagnostic apparatus according to claim 1 , wherein the second analysis unit obtains the received wave field by numerical analysis based on a wave equation.

7. The ultrasonic diagnostic apparatus according to claim 1 , wherein the wavefront incident angle represents an incident direction of a wavefront when a back propagation simulation is performed on a signal based on the echo.

8. 2. The ultrasound diagnostic apparatus according to claim 1, wherein the second analysis unit obtains the received wave field by backpropagating a signal based on the echo based on the weighting function that depends on a positional relationship between a point at which an image is obtained and a point at which the echo is received.

9. Propagate the transmitted signal forward to obtain a transmitted wave field; a weighting function that depends on a wavefront incidence angle that represents an incidence direction of a wavefront when a back propagation simulation is performed on the received signal, and the weighting function is applied to the received signal to obtain a received wave field; A signal processing method that performs a correlation analysis between the transmitted wave field and the received wave field to generate a signal.

10. Propagate the transmitted signal forward to obtain a transmitted wave field; a weighting function that depends on a wavefront incidence angle that represents an incidence direction of a wavefront when a back propagation simulation is performed on the received signal, and the weighting function is applied to the received signal to obtain a received wave field; A program that causes a computer to execute a process of generating a signal by performing a correlation analysis between the transmitted wave field and the received wave field.

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