JP6132337B2 - Ultrasonic diagnostic apparatus and ultrasonic image construction method - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus and an ultrasonic image construction method, and more particularly to an ultrasonic diagnostic apparatus and an ultrasonic image construction method that can obtain an ultrasonic image of an object to be measured without contact.

  Medical ultrasonic diagnostic imaging is widely used because high-resolution images can be obtained, the convenience of movement has been improved by downsizing the apparatus, and there has been no radiation exposure. In the future, there is a lot of room for further reduction in power consumption and ultra-miniaturization, and it is possible to integrate a transducer and signal processing circuit and connect wirelessly to a host device for image construction. The possibility of deployment to ubiquitous devices that anyone can use and receive medical examinations anytime, anywhere by adopting an implantable type is the MRI (Magnetic Magnetic Resonance Imaging) device and CT (Computerized Tomography, Compared to Computed Tomography), it is overwhelmingly large.

  By the way, at present, portable devices are beginning to be marketed, and remote diagnosis using a network is becoming possible, but there are still cables connecting the device and an ultrasonic diagnostic probe. In addition, the size of the ultrasonic diagnostic probe is not so different from that of the conventional stationary apparatus although it is portable. In particular, the style of ultrasonic diagnosis by pressing an ultrasonic diagnostic probe against the body surface of a subject via an acoustic coupler has not changed. Therefore, it is not a preferable diagnostic method for patients who have a wound on the body surface or who want to avoid pressing the body surface, and non-contact diagnosis such as MRI or CT is desired. However, due to the basic characteristic that ultrasound does not easily propagate in the air, it has been impossible to perform an ultrasound diagnosis by separating the ultrasound diagnostic probe from the body surface.

JP 2009-276319 A

  Patent Document 1 discloses an air ultrasonic diagnostic system that detects and evaluates material surface properties, internal defects, or abnormal portions in a non-contact manner using ultrasonic waves that propagate in the air. In the system of Patent Document 1, the phase of an ultrasonic beam is controlled (phased array scanning) by focusing the propagating ultrasonic wave in a measurement target object in a non-contact manner using an aerial array type ultrasonic transducer. As a result, focusing and steering are performed to construct an ultrasonic diagnostic image.

By the way, Snell's law is established between the incident angle θ ₁ and the refraction angle θ ₂ of the ultrasonic beam, and there is the following relationship when the sound speed v _{1 in} the air and the sound speed v ₂ in the living body.

sin θ ₁ / sin θ ₂ = v ₁ / v ₂ (1)

Here, when the sound speed in the air v ₁ = 340 m / s and the sound speed of the living body v ₂ = 1500 m / s, when the incident angle θ ₁ exceeds about 13 °, θ ₂ becomes 90 ° or more, and the ultrasonic wave in the air Will not propagate inside the living body.

  On the other hand, paying attention to the reflectance of ultrasonic waves at the boundary between different media, the reflectance R is expressed as follows.

R = (v ₂ ρ ₂ −v ₁ ρ ₁ ) / (v ₂ ρ ₂ + v ₁ ρ ₁ )
= (Z ₂ −z ₁ ) / (z ₂ + z ₁ ) (2)

Here, ρ ₁ is the density of air, 1.293 kg / m ³ , and ρ ₂ is the density of water, which is approximately equal to the density in the living body and is 1000 kg / m ³ . Further, specific acoustic impedance _{z 1} = _v 1 _ρ 1 of air, a specific acoustic impedance _z 2 = _{v 2} [rho ₂ of _{water, z} 1 _{«z 2} So, the R ≒ 1 from (2). In other words, even if ultrasonic waves are incident vertically from the air toward the living body, almost all of them are reflected. Therefore, even if the method of Patent Document 1 is used and internal evaluation is possible for a material whose intrinsic acoustic impedance is not significantly different, even if an ultrasonic wave is transmitted from the air to the living body, the in-vivo ultrasonic image There is a problem that ultrasonic propagation for construction cannot be realized.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic diagnostic apparatus and an ultrasonic image construction method capable of constructing an ultrasonic image by forming an ultrasonic beam that can propagate in a living tissue without contact.

In order to solve the above-described problem, an ultrasonic diagnostic apparatus according to an embodiment of the present invention is arranged at a position separated from the surface of a medium to be measured, and generates a focused ultrasonic wave as a primary sound source. A plurality of focused ultrasound controls each including an ultrasound generation means and a focusing point alignment means for controlling the focused ultrasound irradiated by the focused ultrasound generation means so as to have a focusing point on the surface of the medium to be measured or directly below it A plurality of focused ultrasonic control circuit units for focusing ultrasonic waves on the surface of the medium to be measured to form a plurality of secondary sound sources, and the inside of the medium to be measured based on the secondary sound sources. Transmission beam forming means for controlling a synthetic wavefront formed by the secondary transmission ultrasonic wave propagating through the beam .

  An ultrasonic diagnostic apparatus according to another embodiment of the present invention includes a focused ultrasonic wave generating unit that generates a focused ultrasonic wave, and a focused ultrasonic wave irradiated by the focused ultrasonic wave generating unit directly below the surface of the measured medium. And a secondary transmission ultrasonic pulse propagating through the inside of the measured medium based on a secondary sound source formed immediately below the surface of the measured medium by the focusing point aligning means. Is scanned in one or two dimensions with respect to the region of interest inside the medium to be measured, and the transmitted ultrasonic wave to the back surface of the secondary transmission ultrasonic pulse in the region of interest or the pulse echo signal reflected at the acoustic impedance boundary Image forming means for forming an image on the basis of the feature value.

  In addition, the ultrasonic diagnostic apparatus according to another embodiment of the present invention includes a focused ultrasonic wave generating means for forming a secondary point sound source from an aerial position separated from the surface of the object, directly below the surface of the object, A means for generating a secondary transmission ultrasonic pulse from the secondary point sound source toward the deep part of the object, and a transmission ultrasonic pulse transmitted through the object and reaching the back surface of the object. Means for receiving a pulse echo signal reflected on the back side of the object or at an acoustic impedance boundary inside the object on the surface side of the object and converting it to an electric signal; and storing means for storing a characteristic value of the electric signal And mechanical movement means for mechanically moving the focal point of the secondary point sound source in the region of interest on the surface of the object in a direction orthogonal to the plane while storing the in-plane coordinates of the focal point in the storage means, The characteristic value of the electrical signal stored in the storage means and And an image construction means for constructing an ultrasonic image by taking the correlation between the in-plane coordinates of runner-up sound.

An ultrasonic image construction method according to an embodiment of the present invention outputs an ultrasonic wave from a first sound source separated from the surface of a medium to be measured by a focused ultrasonic wave generation unit, and is focused by a focusing point alignment unit. A second sound source is formed so as to connect the acoustic focal point of the first sound source to the surface of the measurement medium, and a propagating ultrasonic wave propagating through the medium to be measured is generated by the second sound source. An ultrasonic diagnostic image is constructed by receiving propagating ultrasonic waves and performing signal processing for image formation.
In an ultrasonic image construction method according to another embodiment of the present invention, ultrasonic waves are output from a first sound source separated from the surface of a medium to be measured by focused ultrasonic wave generation means, and focused point alignment means A step of forming a second sound source so as to connect the acoustic focus of the first sound source to the surface of the medium to be measured and storing the surface shape of the medium to be measured, and a medium to be measured stored by the focusing point alignment means A second sound source is formed again along the surface of the substrate, a propagation ultrasonic wave propagating through the medium to be measured is generated by the second sound source, the propagation ultrasonic wave is received, and signal processing for image formation is performed. Constructing an ultrasound diagnostic image by performing.

According to a first aspect of the present application, a focused ultrasonic wave generation unit that generates a focused ultrasonic wave as a primary sound source that is disposed at a position separated from the surface of the medium to be measured, and the focused ultrasonic wave generation unit emits light. And a focusing point alignment unit that controls the focused ultrasound so as to have a focusing point immediately below the surface of the medium to be measured.
A second invention according to the present application includes a plurality of focused ultrasound control circuit units each including the focused ultrasound generation means and the focus point alignment means, and the plurality of focused ultrasound control circuit units includes the plurality of focused ultrasound control circuit units. A synthetic wavefront formed by secondary transmission ultrasonic waves that are propagated in the medium to be measured based on the secondary sound source is formed by focusing ultrasonic waves on the surface of the medium to be measured. The ultrasonic diagnostic apparatus according to the first aspect, further comprising transmission beam forming means for controlling.
Furthermore, the third invention according to the present application is characterized in that the focusing point positioning means includes focusing point position varying means for varying the position of the focusing point along the propagation direction of the focused ultrasound. The ultrasonic diagnostic apparatus according to the first invention.
According to a fourth aspect of the present invention, the focusing point position varying unit includes a phase difference control unit that gives a phase difference for each signal that drives a plurality of ultrasonic transducer elements constituting the ultrasonic transducer array. An ultrasonic diagnostic apparatus according to the third aspect of the invention.
Further, according to a fifth aspect of the present application, the ultrasonic transducer array includes a curved composite piezoelectric vibrator having a two-dimensional array structure, and a curved and bonded arrangement with the same curvature on the ultrasonic transmission / reception side of the composite piezoelectric vibrator. The surface of the acoustic matching layer and the surface opposite to the ultrasonic transmission / reception side of the composite piezoelectric vibrator have a concave curved surface having the same radius of curvature, and the surface opposite to the ultrasonic transmission / reception side of the composite piezoelectric vibrator The ultrasonic diagnostic apparatus according to the fourth aspect, further comprising a backing layer bonded to the substrate.
According to a sixth invention of the present application, the ultrasonic transducer array is a linear array, a sector array, an annular array, or a structure capable of performing beam scanning combining these. 4 is an ultrasonic diagnostic apparatus according to the invention.
Further, according to a seventh aspect of the present application, the focusing point alignment unit further includes a separation distance measuring unit that measures a distance between the ultrasonic transducer array and the surface of the medium to be measured. The distance measuring means is the ultrasonic diagnostic apparatus according to the fourth invention, wherein the distance is measured by feeding back the distance information to the phase difference control means.
Further, an eighth invention according to the present application is directed to a synthetic ultrasonic beam composed of a synthetic wavefront of the secondary transmission ultrasonic wave transmitted through the measured medium, on a surface opposite to the surface of the measured medium, The ultrasonic diagnostic apparatus according to the second aspect, further comprising non-contact detection means for detecting non-contact as transmitted ultrasonic waves.
Furthermore, a ninth invention according to the present application detects, in a non-contact manner, a pulse echo signal obtained by reflecting a synthetic ultrasonic beam propagating through the measured medium at an acoustic impedance boundary on the surface side of the measured medium. The ultrasonic diagnostic apparatus according to the second aspect of the present invention, further comprising non-contact detection means.
The tenth invention according to the present application is characterized in that the focused ultrasonic wave generating means includes an ultrasonic transducer and drive control means for applying an amplitude modulation voltage signal to the ultrasonic transducer. An ultrasonic diagnostic apparatus according to the first aspect of the invention.
Furthermore, an eleventh invention according to the present application is directed to a focused ultrasonic wave generating means for generating a focused ultrasonic wave and the focused ultrasonic wave irradiated by the focused ultrasonic wave generating means so that the focused ultrasonic wave is located immediately below the surface of the measured medium. Focusing point alignment means for controlling, and a secondary transmission ultrasonic pulse propagating in the measured medium based on a secondary sound source formed immediately below the surface of the measured medium by the focusing point alignment means, A one-dimensional or two-dimensional scan with respect to a region of interest inside the measured medium, and a transmitted ultrasonic pulse to the back surface of the secondary transmission ultrasonic pulse in the region of interest, or a pulse reflected at an acoustic impedance boundary An ultrasonic diagnostic apparatus includes an image forming unit that forms an image based on a feature value of an echo signal.
According to a twelfth aspect of the present invention, in the ultrasonic diagnostic apparatus according to the eleventh aspect, the characteristic value includes a maximum amplitude value of the transmitted ultrasonic pulse or the pulse echo signal. It is.
Furthermore, in a thirteenth aspect of the present application, the feature value includes a maximum amplitude value of a harmonic component of the transmitted ultrasonic pulse or the pulse echo signal. This is an ultrasonic diagnostic apparatus.
According to a fourteenth aspect of the present invention, in the eleventh aspect, the feature value includes a phase detection value of a fundamental component of the transmitted ultrasonic pulse or the pulse echo signal. This is an ultrasonic diagnostic apparatus.
Furthermore, a fifteenth aspect of the present invention is the fifteenth aspect according to the eleventh aspect, wherein the characteristic value includes a phase detection value of a harmonic component of the transmitted ultrasonic pulse or the pulse echo signal. This is an ultrasonic diagnostic apparatus.
According to a sixteenth aspect of the present application, the focused ultrasonic wave generating means for forming a secondary point sound source directly below the surface of the object from an aerial position separated from the surface of the object, and the secondary point sound source described above. Means for generating a secondary transmission ultrasonic pulse toward a deep part of the object, and a transmitted ultrasonic pulse transmitted through the object and reaching the back surface of the object by the secondary transmission ultrasonic pulse. Means for receiving a pulse echo signal reflected at an acoustic impedance boundary inside the object or on the surface side of the object and converting it to an electric signal, and storing a characteristic value of the electric signal And a relative movement mechanically while the in-plane coordinates of the focal point are stored in the storage means in the orthogonal direction in the plane within the region of interest on the surface of the object. And mechanical storage means for storing the storage means Feature value of the stored electrical signals and by taking the correlation between the in-plane coordinates of secondary point source is an ultrasonic diagnostic apparatus characterized by comprising an image construction means for constructing an ultrasonic image.
Furthermore, in a seventeenth aspect of the present application, ultrasonic waves are transmitted from the first sound source spaced from the surface of the medium to be measured by the focused ultrasonic wave generating means, and the measurement medium is measured by the focusing point alignment means. A second sound source is formed so that the acoustic focal point of the first sound source is connected to the surface, and a transmitted or reflected ultrasonic pulse propagating through the measured medium is generated by the second sound source and received. An ultrasonic image construction method for constructing an ultrasonic diagnostic image by receiving transmitted or reflected ultrasonic pulses by means and performing signal processing for image formation.
The eighteenth invention according to the present application is characterized in that the generated secondary transmission ultrasonic wave is scanned one-dimensionally or two-dimensionally with respect to a region of interest inside the measured medium. An ultrasonic image construction method according to the seventeenth invention.
Further, according to a nineteenth aspect of the present application, the second sound source is based on an acoustic radiation pressure using a focused ultrasonic wave generated by the first sound source. This is a sound image construction method.
According to a twentieth aspect of the present application, ultrasonic waves are transmitted from the first sound source spaced from the surface of the medium to be measured by the focused ultrasonic wave generation means, and the measurement medium is measured by the focusing point alignment means. Forming a second sound source so as to connect the acoustic focus of the first sound source to the surface and storing the surface shape of the measured medium; and storing the measured medium by the focusing point alignment means A second sound source is formed again along the surface of the substrate, an ultrasonic wave propagating through the medium to be measured is generated by the second sound source, a transmitted or reflected ultrasonic pulse is received, and an image is formed. And constructing an ultrasound diagnostic image by performing the signal processing.

  According to the present invention, since the secondary sound source generates propagating ultrasonic waves that propagate through the medium to be measured by focused ultrasonic waves having a focusing point at or just below the surface, an ultrasonic diagnostic image can be constructed without contact. .

It is a conceptual diagram for demonstrating the method of the ultrasonic diagnosis using the ultrasonic diagnostic apparatus with which this invention was applied. It is a block diagram which shows the principal part of the structural example of the ultrasonic diagnosing device to which this invention was applied. It is a block diagram which shows the part of image construction among the structural examples of the ultrasound diagnosing device to which this invention was applied. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows notionally the structural example of the focusing-type ultrasonic transducer used for the ultrasound diagnosing device with which this invention was applied, (A) is a front view, (B) is a perspective view which shows the wiring of each transducer element. is there. It is a figure which shows the other structural example of the focusing-type ultrasonic transducer array used for the ultrasonic diagnosing device to which this invention was applied, (A) is a top view, (B) is the cross section in the AA 'line of (A) figure. FIG. 4C is a cross-sectional view taken along line BB ′ in FIG. It is a schematic diagram for demonstrating the acoustic radiation pressure which is an operation principle of the ultrasonic diagnostic apparatus of this invention. It is a schematic diagram for demonstrating the propagation ultrasonic wave generation by the secondary sound source using the acoustic radiation pressure which is the operation principle of the ultrasonic diagnostic apparatus of this invention. (A) The figure shows the state which transmits a propagation ultrasonic wave, (B) The figure shows the state which receives the ultrasonic echo reflected by the to-be-measured object. It is a figure which shows the waveform of the amplitude modulation wave of a sine wave for producing | generating an acoustic radiation pressure. It is a conceptual diagram which shows the example of the waveform of the propagation ultrasonic wave which propagates in the biological body in the ultrasonic diagnostic apparatus of this invention. It is a waveform of the propagation ultrasonic wave when a viscoelastic characteristic becomes large in order of (A) figure, (B) figure, and (C) figure. In the ultrasonic diagnostic apparatus of this invention, it is a conceptual diagram for demonstrating the process which produces | generates a secondary sound source on a body surface. The focal position on the body surface is searched by measuring the size of the output signal pattern reflected and received by the body surface by changing the delay time pattern of the signal transmitted from the focused ultrasonic transducer array. It is a figure for demonstrating a procedure. (A) The figure and (B) figure are figures which show the transmission signal waveform from which a delay time pattern differs. (C) is a figure which shows the output signal pattern of the received signal corresponding to (A) figure, (D) figure is a figure which shows the output signal pattern of the received signal corresponding to (B) figure. It is a conceptual diagram for demonstrating that the secondary sound source formed by the focusing type ultrasonic transducer array propagates through the body to form a composite wavefront. It is the schematic of the environment for experiment which shows that an ultrasonic image construction is possible by a propagation ultrasonic wave. (A) is the measurement value of the ultrasonic image measured using the propagation ultrasonic wave of 40 kHz in the configuration of FIG. (B) is a computer simulation value of an ultrasonic image using 40 kHz propagation ultrasonic waves. (C) is a computer simulation value of an ultrasonic image using 400 kHz propagating ultrasonic waves.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The description will be made in the following order.

1. 1. Configuration example of ultrasonic diagnostic system Configuration example of ultrasonic diagnostic apparatus 2-1. Circuit configuration example of ultrasonic diagnostic apparatus 2-2. 2. Configuration example of ultrasonic transducer Operation principle and operation 3-1. Formation of secondary sound source 3-2. Focusing point control 3-3. Ultrasonic beam forming 3-4. Receive beamforming 4. Mock experiment

1. Configuration Example of Ultrasonic Diagnostic System As shown in FIG. 1, an ultrasonic diagnostic system 40 using the ultrasonic diagnostic apparatus 1 to which the present invention is applied includes, for example, an ultrasonic diagnostic apparatus main body 1a installed on the back of a ceiling. And an ultrasonic probe 50a having a focused ultrasonic transducer array 50 to which a wiring 2a extending from the ultrasonic diagnostic apparatus main body 1a is connected through the multi-joint manipulators 7a, 7b, 7c, and 7d. The ultrasound diagnostic system 40 performs signal processing on the data for constructing an ultrasound image acquired by the ultrasound probe 50a and displays it on the monitor 32 connected via the wiring 2b.

  The articulated manipulator includes a fixed arm 7d fixed to the ceiling, a first arm 7c connected to the fixed arm 7d by a first joint 8c so as to be freely rotatable, and a first arm 7c freely connected by a second joint. It has the 2nd arm 7b couple | bonded so that rotation was possible, and the 3 axis | shaft displacement arm 7a connected to the 2nd arm so that free rotation was possible by the 3rd joint 8a. An ultrasonic probe 50a having a focusing ultrasonic transducer array 50 is connected to the tip of the triaxial displacement arm 7a. The ultrasonic probe 50 a is held away from the body surface of the subject 6 lying on the bed 9 by the operator 3 holding the triaxial displacement arm 7 a with one hand. Since the triaxial displacement arm 7a is arranged so as to always maintain the vertical direction with respect to the horizontal plane, the measurement surface of the ultrasonic probe 50a is always maintained in the horizontal direction with respect to the horizontal plane. By the joints 8a, 8b, 8c of the multi-joint manipulators 7a, 7b, 7c, 7d, the operator 3 can freely move the ultrasonic probe 50a in the horizontal direction and the vertical direction along the body surface of the subject 6. it can. Each joint 8a, 8b, 8c incorporates an encoder, and the position of the ultrasonic probe 50a can be accurately identified based on the encoder output information.

  The operator 3 can confirm the observation location while moving the ultrasonic probe 50a and watching the monitor 32. Further, the remote controller 5 held in the other hand can transmit an instruction to the ultrasonic diagnostic apparatus main body 1a while looking at the monitor 32 to control the image drawing mode and the like.

  In the ultrasonic diagnostic system 40 shown in FIG. 1, the focused ultrasonic transducer array 50 constituting the ultrasonic probe 50a functions as a transducer that transmits and receives ultrasonic waves, and reflects reflected ultrasonic waves (echo waves). ) Is shown. In addition, an ultrasonic transducer that transmits ultrasonic waves is used for the ultrasonic probe, and an ultrasonic receiver installed on the opposite side of the subject is used (in the case of FIG. 1, the bed side). Needless to say, ultrasonic waves transmitted through the body of the subject may be measured.

2. 2. Configuration Example of Ultrasonic Diagnostic Device As shown in FIG. 2, an ultrasonic diagnostic device 1 to which the present invention constituting the above-described ultrasonic diagnostic system 40 is applied includes a focused ultrasonic transducer array 50 that transmits and receives ultrasonic waves. The control circuit unit 10 is connected to the focusing type ultrasonic transducer array 50 and inputs / outputs an ultrasonic signal converted into an electrical signal. The control circuit unit 10 is connected to the control circuit unit 10 to image a body tissue. And a transmission beamformer 17 for imaging an internal tissue that performs beamforming for transmission.

  As shown in FIG. 3, the ultrasonic diagnostic apparatus 1 inputs a signal from the control circuit unit 10 and forms a reception beamform for imaging a body tissue. And a signal processing unit 29 that performs signal processing such as pulse compression, phase detection, filtering, and the like on the signal from the reception beamformer 25 for imaging internal tissue, and an image signal that is signal-processed by the signal processing unit 29 A scan converter 30 that performs display image construction, an image processing unit 31 that performs predetermined image processing based on an output signal of the scan converter 30, and a monitor 32 that displays an image signal processed by the image processing unit 31 Prepare.

  The internal tissue imaging transmission beamformer 17 and the internal tissue imaging reception beamformer 25 set the operation of the ultrasonic diagnostic apparatus 1 and a processing unit (CPU, Central Processing Unit) 26 that manages the measurement procedure and the like, An instruction executed by the processing unit 26 is expanded and connected to a bus 28 together with a storage unit (memory) 27 for storing processing data, and the instruction from the processing unit 26 is executed and processed via the bus 28. The processing unit 26 is, for example, a microprocessor or a microcontroller, and the storage unit 27 is a volatile memory or a non-volatile memory built in the microprocessor. The storage unit 27 may be a volatile memory or a non-volatile memory externally attached to the microprocessor. The bus 28 may be a standard bus used in a microcomputer system, such as an ISA bus or a PCI bus, or may be a bus designed for exclusive use. Note that the processing unit 26 and the storage unit 27 may be configured to be connected separately via the bus 28, for example, a stand-alone personal computer or a workstation.

  The control circuit unit 10 is a unit that forms the core of the ultrasonic diagnostic apparatus 1 to which the present invention is applied. The control circuit unit 10 is prepared for each column array 60 in which a plurality of transducer elements 61 are arranged one-dimensionally, and is connected to the corresponding column array 60.

  As shown in the block diagram within the broken line in FIG. 2, the control circuit unit 10 includes a transmission beamformer 17 for imaging an internal tissue that sets the form of a propagating ultrasonic beam for performing ultrasonic image imaging of the internal tissue. Based on the signal to be generated, a beam steering delay time pattern generation unit 15 that generates a delay time pattern for transmission beam steering and / or transmission beam forming, and a secondary sound source is formed on the body surface of the subject 6 or immediately below it. And a delay time pattern generation unit 16 for forming a secondary sound source for generating a delay time pattern for controlling the focal point distance. The control circuit unit 10 includes a delay time addition unit 14 that delay-adds the delay time patterns generated by the beam steering delay time pattern generation unit 15 and the secondary sound source formation delay time pattern generation unit 16. Further, it has a transmission beamformer 13 for forming a secondary sound source that converts the output signal of the delay time adding unit 14 into an amplitude-modulated wave of a sine wave and forms a secondary sound source on the body surface of the subject 6. The amplitude-modulated wave output from the transmission beamformer 13 for forming the secondary sound source is sent to a pulser that amplifies the amplitude so that the transducer element 61 can be driven, and drives each transducer element 61. The control circuit unit 10 has a pulsar array 12 in which pulsars are arranged by the number of transducer elements 61 constituting the column array unit 60 for one column. The output of the pulsar array 12 is supplied via the multiplexer 11 to each transducer element 61 constituting the focused ultrasonic transducer array 50 by the wire bundle 70.

  Along with the path for generating and transmitting the above-described ultrasonic wave, the control circuit unit 10 has a path for receiving the ultrasonic wave and processing the signal. That is, the control circuit unit 10 includes a receiver array 18 to which an ultrasonic signal received by the transducer element 61 constituting the converging ultrasonic transducer array 50 and converted into an electric signal is input via the multiplexer 11, and a receiver array. 18 includes a reception beamformer 19 that receives the signal processed at 18 and performs delay addition processing on each signal. The output of the reception beamformer 19 is selectively connected via the SW 20 to the maximum value detection unit 21 that detects the maximum value of the reception signal or the Doppler shift detection unit 23 that detects the Doppler shift of the reception signal. In the case of the ultrasonic focusing mode in which the ultrasonic wave is focused on the body surface, the separation distance between the ultrasonic probe 50a having the focusing type ultrasonic transducer array 50 and the body surface of the subject 6 is measured. The 19 outputs are controlled via the SW 20 having the control signal input terminal 201 so as to be connected to the maximum value detection unit 21. In the case of an ultrasonic image construction mode in which ultrasonic waves are focused on the body surface of the subject 6 to form a secondary sound source and ultrasonic images are constructed by propagating ultrasonic waves propagating through the subject's body, the SW 20 Control is performed so that the output of the reception beamformer 19 is connected to the Doppler shift detector 23. The control of the SW 20 is preferably executed according to an instruction of the processing unit 26 via the sw 20 having the control signal input terminal 201.

  The maximum value detection unit 21 connected to the reception beamformer 19 detects the maximum value of the reception signal and inputs it to the secondary sound source formation delay time pattern generation unit 16, and based on the transmission signal pattern and the detected reception signal. Then, the separation distance calculation unit 24 measures the separation distance between the body surface of the subject 6 and the ultrasonic probe, and transmits the separation distance information to the processing unit 26 via the bus 28. In this specification, the secondary sound source does not indicate a substantial transducer or the like, but refers to a focusing point formed on the body surface by the focusing ultrasonic transducer array 50.

  The output of the Doppler shift detection unit 23 to which the reception beamformer 19 is connected is input to the FV conversion unit 24 that converts the Doppler shifted frequency into a voltage, and the received signal converted into the voltage signal is used for imaging a body tissue. An image construction process is performed by inputting to the reception beamformer 25.

2-2. Configuration Example of Ultrasonic Transducer As shown in FIG. 2, a focused ultrasonic transducer array 50 constituting an ultrasonic diagnostic apparatus 1 to which the present invention is applied is a transducer element arranged in a two-dimensional array of m rows and n columns. 61. Control is performed so that a secondary sound source is formed on the body surface of the subject for each column focusing type ultrasonic transducer array unit (hereinafter also referred to as a column array unit) 60 in which m transducer elements 61 are arranged one-dimensionally. The circuit unit 10 is preferably connected.

  The transducer element 61 is composed of an ultrasonic vibrator, and the material and configuration are not particularly limited, and any known element can be used without limitation. For example, it may be made of a ceramic material such as PZT (lead zirconate titanate), or a resin-based material such as porous polypropylene (cellular PP) or ferroelectric polymer PVDF (polyvinylidene fluoride). It may be a piezoelectric single crystal such as lithium niobate.

  As shown in FIG. 4A, the column array unit 60 has a concave curve shape with the focusing point axis 63 as a symmetric axis so as to form an ultrasonic focusing point at any position on the focusing point axis 63. The plurality of transducer elements 61 are arranged on the base material 62.

  As will be described later, each transducer element 61 constituting the column array unit 60 is driven by a signal having a phase difference so that the ultrasonic wave is focused on the focusing point axis 63. Here, by arranging the transducer elements 61 so as to be symmetrical with respect to the focusing point axis 63, the transducer elements 61 at the symmetrical positions can be driven in the same phase, and the number of connection wirings can be reduced. it can. That is, as shown in FIG. 4B, the transducer element 61a on the focusing point axis 63 has a connection wiring 71a, and the transducer elements 61b1 and 61b2 adjacent to the transducer element 61a are driven in the same phase. Therefore, the same connection wiring 71b is provided. Similarly, the transducer elements 61c1 and 61c2 that are adjacent to the transducer elements 61b1 and 61b2 and are symmetrical with respect to the focusing point axis 63 are driven with the same phase signal by the same connection wiring 71c. Similarly, the outermost transducer elements 61n1 and 61n2 are driven by the same connection wiring 71n. By using such wiring, the ultrasonic wave can be focused on the focusing axis 63.

  A large number of transducer elements 61 are arranged in a two-dimensional manner, and instead of constructing a focused ultrasonic transducer array 50, an ultrasonic transducer manufactured using a capacitive micromachined process (cMUT). ), A large number of transducer elements can be formed on a single substrate to achieve further miniaturization and weight reduction.

  The use of a composite piezoelectric body as a focusing type ultrasonic transducer in which a large number of transducer elements are formed on a single substrate facilitates the formation of a concave curved surface, which is preferable.

  As shown in FIG. 5A to FIG. 5C, the focused ultrasonic transducer array 80 using a composite piezoelectric material has a composite piezoelectric material 82. The composite piezoelectric body 82 can have a well-known configuration, for example, a piezoelectric pillar that is a large number of fine columnar piezoelectric elements formed on a piezoelectric layer, and a structure in which the periphery of the piezoelectric pillar is filled with a flexible resin. It has become. The composite piezoelectric body 82 has a common ground electrode 83 on one side, and the common ground electrode 83 is usually disposed on the ultrasonic transmission / reception surface side. The divided electrodes 81 arranged on the opposite surface, that is, the surface on the backing layer 85 side, are two-dimensionally arranged as shown in FIG. As the resin filling the piezoelectric pillar of the composite piezoelectric body 82, a flexible resin such as a polymer resin such as epoxy can be used. Since the composite piezoelectric body 82 is a plate-like piezoelectric vibrator in which the piezoelectric pillars, which are fine columnar piezoelectric elements, are connected by a flexible resin as described above, a curved structure can be easily realized. It is characterized by a large electromechanical conversion constant that cannot be realized with ceramic plates.

  An acoustic matching layer 84 is bonded on the common ground electrode 83 to reduce acoustic impedance mismatch between the composite piezoelectric body 82 and air so that efficient ultrasonic transmission / reception can be performed. However, as for the thickness of the acoustic matching layer 84, the wavelength λ calculated from the frequency f of the ultrasonic wave to be handled and the inherent sound velocity v of the material of the acoustic matching layer 84 is also optimally set to a thickness of 1/4. Thick plates are used. Therefore, even if acoustic matching is suitably realized using ultrasonic waves of frequency f at the time of transmission, if ultrasonic waves having a frequency deviating from f are handled at the time of reception, the efficiency of ultrasonic reception is reduced. In the ultrasonic diagnostic apparatus 1 of the present invention, using only the focusing type ultrasonic transducer array 80, an aerial ultrasonic wave having a frequency f is transmitted toward the body surface, a secondary sound source is formed immediately below the body surface, and the frequency f Since the ultrasonic wave with the frequency f ′ is received at the reception frequency, the ultrasonic wave with the frequency f ′ (= envelope frequency that is equal to or lower than (½) f) is handled. This will cause acoustic mismatch.

  As other conditions for the acoustic matching layer 84, the acoustic impedance of the acoustic matching layer 84 is optimized and the acoustic matching layer 84 is also curved so that flexibility is required. Used. By forming such an acoustic matching layer 84, a curved composite ultrasonic transducer having high ultrasonic transmission / reception efficiency can be formed.

  In the above description, in any of the focused ultrasonic transducer arrays, the case where the transducer elements are arranged in a two-dimensional matrix (lattice form) of m rows and n columns has been described. When an image is constructed by relatively scanning, a single annular array transducer structure in which transducer elements are arranged concentrically may be used, or a known transducer array structure may be used. Needless to say.

3. 3. Principle of Operation and Operation 3-1.2 Formation of Secondary Sound Source As described above, since it is difficult to propagate ultrasonic waves between air and a living body (substantially equivalent to water) having greatly different acoustic impedances, the ultrasonic wave according to the present invention. The diagnostic device 1 uses the principle that, when there is a medium having a large difference in acoustic impedance in the direction in which the ultrasonic wave with high intensity travels, that is, a strong ultrasonic wave, a direct current pressure is generated on the medium surface. Then, a secondary sound source formed directly under the subject's body surface is used.

As shown in FIG. 6, a case is considered where a nonlinear signal Asinω ₁ t × sinω ₂ t having an amplitude A is radiated toward the body surface 6 a of the subject 6 by a signal source. The nonlinear signal Asinω ₁ t × sinω ₂ t is expressed as follows by the addition theorem of trigonometric functions.

sin ω ₁ t × sin ω ₂ t = − (1/2) {cos (ω ₁ + ω ₂ ) t
−cos (ω ₁ −ω ₂ ) t} (3)

Here, when ω = ω ₁ = ω ₂ , the expression (3) includes only the second harmonic (2ω) and the DC component.

Asinω ₁ t × sinω ₂ t = − (1/2) {cos (2ω) t−1} (3 ′)

The body surface 6a is recessed by a distance d _DC considering the viscoelastic characteristics of the object in the amplitude of the signal by the acoustic radiation pressure composed of the DC component of the radiation pressure, which is a nonlinear ultrasonic phenomenon of the equation (3 ′).

  By applying amplitude modulation to such acoustic radiation pressure, the pressure for pressing the body surface 6a can be changed. The body surface 6a is vibrated by the pressure change of the body surface, and the propagation ultrasonic wave propagating in the living body by the longitudinal wave can be generated. In FIG. 6, for convenience, not the focused ultrasonic wave but a plane wave display, but as will be described later, the focused ultrasonic wave is actually used so that the maximum ultrasonic intensity is obtained at the acoustic focal point. Allow maximum nonlinearity at the acoustic focus.

  As shown in FIGS. 7A and 7B, the ultrasonic wave travels toward the body surface 6a, and the body surface 6a elastically vibrates with the waveform of the envelope curve of the modulated ultrasonic signal. This elastic vibration becomes a secondary transmission ultrasonic wave from the secondary sound source and propagates toward the deep part of the body. When this secondary transmission ultrasonic wave reaches the boundary 6b with the abnormal tissue having different acoustic impedance (FIG. 7A), a part becomes a transmitted wave, reaches the back surface, and the rest is reflected as a pulse echo signal. It reaches the body surface 6a side (FIG. 7B).

  FIG. 8 shows an applied voltage signal waveform for driving one of the transducer elements 61 constituting the column array unit 60 which is a focused ultrasonic wave generation means.

As shown in FIG. 8, the voltage signal applied to the column array unit 60 excites the secondary transmission ultrasonic pulse signal V _{(body) trans} having the pulse width T _pulse 'of the propagating ultrasonic wave propagating in the _body to the body surface. A reception time T _rec for receiving a signal V _{(air) burst} having a pulse width T _pulse of an aerial ultrasonic wave and a pulse echo signal V _{(body) rec} arriving at the body surface from inside the living _body based on the Doppler effect It consists of a baseline signal V _{(air) base} that is not 0V. And it required the time course of time _{T rep} by airborne ultrasound pulse width _{T pulse} and the reception time _{T rec,} 1 set of required this time _{T rep} is repeated. The pulse signal V _{(air) burst} includes a first burst pulse V _b1 , a second burst pulse V _b2 , and a baseline time T _{base0 of} 0 V sandwiched between these burst pulses V _b1 and V _b2. It can be said that it is a pulse signal, specifically consisting of an amplitude modulated wave of a sine wave. By applying the applied voltage signal shown in the upper waveform diagram of FIG. 8, the focused ultrasound propagates from the column array unit 60 toward the body surface, and after a propagation time T _air , forms a secondary sound source on the body surface, This becomes a secondary transmission ultrasonic pulse V _{(body) trans} and propagates toward the deep part of the body. This ultrasonic signal V _{(body) trans} is the transfer function H (ω) of the column array unit 60, the ultrasonic loss AL (ω) during propagation in the air, the DC component conversion efficiency DC (ω) due to the acoustic radiation pressure, and the body The influence of the viscoelastic property TS (ω) of the surface tissue is integrated, and a pulse waveform _{V (body) trans} as shown in the lower diagram of FIG. 8 is obtained.

The ultrasonic wave V _{(body) trans} propagates to the deep part of the body, is reflected by the abnormal tissue 6b at a specific position in the deep part, and then is directed to the body surface as shown in the lower diagram of FIG. The amplitude of V _{(body) rec} attenuates and _returns to the body surface 6a, and the body surface 6a _undergoes elastic displacement vibration based on the pulse echo signal waveform V _{(body) rec} . At this time, since the ultrasonic wave of the frequency f is constantly irradiated on the body surface 6a in the reception period T _rec of the applied voltage, the pulse echo signal V _{(body) rec} that is the irradiation signal is subjected to Doppler shift, f Return to the column array unit 60 at a frequency of ± Δf.

In addition, although the waveform of the secondary transmission ultrasonic pulse V _{(body) trans} described above has been described for the case of a transmission ultrasonic pulse excitation signal composed of two burst pulses, the number of burst pulses may be three or four. Five may be sufficient. As shown in FIG. 9A to FIG. 9C, the waveform of longitudinal wave propagating ultrasonic waves propagating in the living body may change depending on the viscosity characteristics such as the viscoelastic characteristics in the living body. As shown in FIGS. 9B and 9C, the longitudinal wave propagating ultrasonic wave may have a gentle waveform as it progresses, and depending on the viscoelastic characteristics of the object, from the beginning of the propagation, FIG. In some cases, the waveform is as shown in FIG. 9B or FIG. (Viscoelastic properties are large in the order of FIGS. 9A, 9B, and 9C)

When the pulse echo signal of the ultrasonic wave reflected at the boundary 6b with the abnormal part reaches directly below the body surface of the subject 6, the body surface 6a has a vibration speed V _surface of f × Δx when the frequency is f. (Where f = 1 / (T _burst + T _base0 ).

  Returning to FIG. 8, the reception mode according to the present invention will be described below.

In the reception period T _rec , a sine wave V _{(air) base} having a relatively small frequency f follows. In this section, a DC subsidence displacement d _DC due to a relatively small acoustic radiation pressure corresponding to the frequency and amplitude is generated during T _rec , and a sine wave of the same frequency continues to be reflected. In this state, when the pulse echo signal V _{(body) rec} arrives at the body surface 6a, the body surface 6a is displaced at a vibration speed corresponding to the frequency f and the displacement amplitude. The ultrasonic wave undergoes a Doppler shift, and the reflected signal becomes a Doppler signal of f ± Δf and returns to the focused ultrasonic transducer array 50 for reception. In general, Δf is considerably smaller than f. Therefore, f ± Δf is not smaller than (1/2) f, and the acoustic matching effect at the time of reception can be utilized in the same acoustic matching layer, and reception sensitivity is increased. Can be made.

3-2. Focusing point control As described above, by irradiating the body surface with focused ultrasound, a secondary sound source is formed on the body surface, and a secondary transmission ultrasound wave that propagates to the deep part of the living body by vibrating the body surface is formed. Can do. Further, by focusing the ultrasonic wave directly below the body surface, the ultrasonic wave propagating into the body can be propagated as a spherical wave or a cylindrical wave. For the spherical wave and the cylindrical wave thus formed, n Each of the arrayed column array units 60 is further subjected to phase control to form a wavefront synthesized ultrasonic beam (beam forming), focus the formed ultrasonic beam (beam focusing), linear scanning or sector scanning (beam) Steering) can be performed, and an ultrasound diagnostic image of the region of interest can be reconstructed.

  In FIG. 10, in order to explain the vertical position control method of the focusing point for the secondary sound source, the control circuit unit 10 of FIG. 2, the column array unit 60 constituting the focusing type ultrasonic transducer array 50, The corresponding part of the body surface 6a is extracted and shown. In the vertical position control method of the focal point, the beam steering delay time pattern generation unit 15 out of the delay time pattern generation units 15 and 16 in the control circuit unit 10 outputs no signal in the initial state. Only the next sound source formation delay time pattern generation unit 16 operates.

  The separation distance X1 between the first first focused ultrasonic transducer array 60 and the body surface 6a in the n focused ultrasonic transducer arrays 50 arranged, and the nth column array focused ultrasonic transducer array 60, It is set as the separation distance Xn with the body surface 6a. In this case, generally, X1 ≠ Xn. The m transducer elements 61 constituting the first column array unit 60 generate the air-focused ultrasonic wave B1 by the delay time pattern generated by the secondary sound source formation delay time pattern generation unit 16. This air-focused ultrasonic wave B1 is located on the body surface 6a as the acoustic focus F1. Since X1 ≠ Xn, even if the secondary sound source formation delay time pattern generation unit 16 generates the same delay time pattern as the first column array unit 60 for the nth column array unit 60, the nth column array unit 60 The aerial ultrasonic wave Bn generated by the array unit 60 is focused on the body surface 6a and does not form an acoustic focus. Since the column array unit 60 has a curved shape with a predetermined radius of curvature and has a fixed acoustic focal point, the focusing point control amount is controlled to increase or decrease around the fixed focusing point. .

  FIG. 11A to FIG. 11D show transmission / reception waveforms for an example of the procedure of acoustic focal point alignment control. For the first column array unit 60 of FIG. 10 described above, voltage signals S1 (1), S2 (1)... Output from the pulsar array 12 as shown in FIG. . . Si (1). . . In the case of the delay time pattern 11 composed of Sm (1) (1 before 11 indicates the case with respect to the first column array unit 60, and 1 after indicates the first delay pattern) (see FIG. 11). A reception pulse signal after addition processing by the reception beamformer 19 as indicated by R1 (1) of C) is obtained. Similarly, for the first column array unit 60, the second transmission delay pattern 12 shown in FIG. 11B, that is, voltage signals S1 (2), S2 (2). . . Si (2). . . When the delay time pattern 12 composed of Sm (2) is set, the reception pulse after the addition processing by the reception beamformer 19 is R1 (2) in FIG. 11C. Further, for the i-th column array unit 60, an i-th transmission delay pattern 1i, ie, voltage signals S1 (i), S2 (i). . . Si (i). . . The reception pulse after the addition processing by the reception beamformer 19 when the delay time pattern 1i composed of Sm (i) is set is R1 (i) in FIG. Each received signal level is acquired by the maximum value detector 21. As described above, the received signal R1 (1) is a received pulse signal obtained by the transmitted delay time pattern 11, and R1 (2) is a received waveform obtained by the transmitted delay time pattern 2. R1 (3), R1 (4), and R1 (i) are the third, fourth, and i-th received pulse signals not shown in FIG. Among these received pulse signals, the time when the maximum amplitude value of the pulse becomes maximum is the case where the acoustic focus coincides with the body surface, that is, R1 (2) in FIG. The transmission delay time pattern that maximizes the maximum amplitude value is determined as follows. The maximum amplitude value Vpp of the reception pulse signal R1 (1) obtained corresponding to the transmission delay time pattern 11 is detected, and the separation between the body surface 6a and the column array unit 60 is detected by the separation distance calculation unit 22 based on the detection result. The distance is calculated. The calculated result is sent to the processing unit 26 via the bus 28, and the processing unit 26 instructs the secondary sound source formation delay time pattern generation unit 16 to generate a new delay signal pattern. The secondary sound source formation delay time pattern generation unit 16 transmits a new delay time pattern 12 by the pulsar array 12 (FIG. 11B). The reception signal R1 (2) shown in FIG. 8C for the new delay time pattern 12 is acquired, and the maximum value is acquired in the same manner as described above. Similarly, the transmission delay pattern is changed until a transmission delay pattern in which the maximum amplitude value of the reception signal is maximized is found, and when the transmission delay pattern is found, the transmission delay pattern is stored, and at the same time, the generation time of the reception pulse signal is evaluated. Thus, the distance from the column array unit 60 to the body surface 6a is determined. By fixing to the transmission delay time pattern 2 when the reception pulse R1 (2) is obtained, the acoustic focusing on the body surface 6a is completed for the first column array unit 60. The second, third,..., I,..., Nth column array unit 60 was also subjected to the same acoustic focusing and focusing on the body surface to construct a secondary sound source array. It will be.

  As described above, the delay time pattern (phase pattern) in which the level of the received signal is maximized by controlling the delay time of each transducer element 61 that transmits the aerial ultrasonic wave is adopted as the acquired focus point. In FIG. 2, in the focusing point control mode in which focusing point control is performed, the SW 20 is connected to the maximum value detection unit 21 side. The delay time pattern acquired for each column array unit 60 is stored in the storage unit 27, and the body surface position (distance) is controlled in the ultrasound image construction mode in which the propagation ultrasound is received and the ultrasound image is constructed. On the other hand, the switch 20 is switched to the Doppler shift detection unit 23 side, and the propagation ultrasonic signal, that is, the transmitted ultrasonic signal transmitted through the foreign matter having different acoustic impedance is reflected from the back side or at the boundary with the foreign matter, the pulse echo signal. Is obtained from the body surface side.

3-3. In the ultrasonic diagnostic apparatus 1 to which the present invention is applied, as described above, the secondary sound source is formed in a dot shape on the body surface 6a of the subject 6, and the formed secondary sound source is in the body. A secondary transmission ultrasonic wave propagating as a spherical wave or a cylindrical wave is propagated deep in the body. Here, the curvature and direction of the composite wavefront Sw formed by the propagating ultrasonic wave are arbitrarily set by further performing phase control on the secondary sound sources generated by the column array units 60 constituting the transducer array. Can do.

As shown in FIG. 12, the secondary sound source is obtained by adding the delay time pattern generated by the beam steering delay time pattern generating unit 15 to the delay time pattern generated by the secondary sound source forming delay time pattern generating unit 16. It is possible to carry out beam forming of propagating ultrasonic waves generated by the laser beam, that is, focus formation by beam focusing and to scan the beam steering, that is, beam steering. For example, the secondary sound source formed at the focal point F1 of the first column array unit 60 by the aerial ultrasonic wave B1 is a spherical wave or a cylindrical wave, and its wave front has a synthesized wavefront at a position Sw1 in the body of the subject 6 at a predetermined timing. Form. The phase of the secondary transmission ultrasonic wave generated by the secondary sound source formed at the focal point Fn by the aerial ultrasonic wave Bn of the n-th column array 60 is set by t _delay from that of the secondary sound source formed at F1. By driving the column array 60 with a delay, the propagation distance difference between the propagation ultrasonic wave generated by the secondary sound source generated by the first column array 60 and the propagation ultrasonic wave generated by the secondary sound source generated by the n-th column array 60 is different. X _delay = 1500 [m / s] × t _delay is generated. Since the velocity 1500 [m / s] of the ultrasonic wave propagating in the living body is constant, the wave front of the spherical wave generated by each secondary sound source is formed by setting t _delay for each secondary sound source, that is, by controlling the phase. The curvature and direction of the synthesized wavefront can be controlled. The formed synthetic wave Sw forms a propagating ultrasonic beam BB and propagates through the body to form a beam focal point FB. In addition, by dynamically controlling t _delay for each secondary sound source, the curvature and direction of the combined wavefront Sw can be dynamically changed, and sector scanning can be performed in the direction of the arrow locus _steer in FIG.

  Needless to say, a well-known method can be used as a method of performing beam forming and / or beam steering by controlling the phase by the beam steering delay time pattern generation unit 15.

3-4. Reception Beam Forming The received ultrasonic signal is subjected to predetermined signal processing at each receiver constituting the receiver array 18 and input to the reception beam former 19. In the reception beamformer 19, m reception signals (in the case of a focused ultrasonic transducer array of m rows and n columns) are subjected to delay addition processing to form one reception signal. A well-known configuration can be used for the reception beamformer 19.

  The output signal of the reception beamformer 19 is a signal affected by the Doppler effect. If the frequency of the transmission signal is f, it is composed of a frequency component of f ± Δf, and a foreign substance boundary is included in the Doppler shift ± Δf. The information that the pulse echo signal reflected on the body reaches the body surface and vibrates and displaces the body surface is included. In order to analyze the information, ± Δf is taken out by the Doppler shift detector 23 and further converted into a voltage signal by the FV converter 24. Since this FV conversion signal is output to each of the n control circuit units 10, they are subjected to delay addition processing by the imaging receive beamformer 25 for in vivo tissue, and the received signal after the addition processing is logarithmically amplified. Then, known signal processing 29 such as dynamic filtering and STC processing is performed, and the output signal is converted into an image signal by the scan converter 30, and image processing 31 such as edge enhancement, gamma correction, brightness, and contrast enhancement is performed on the monitor 32. indicate. In the ultrasonic diagnostic apparatus to which the present invention is applied, as described above, in the propagation ultrasonic wave based on the acoustic radiation pressure using the amplitude-modulated wave by the sine wave, in addition to the fundamental frequency f, the second harmonic component, etc. Therefore, an image can be constructed with higher spatial resolution by using this harmonic component.

4). Simulated experiment A water tank filled with a membrane (polyethylene film) corresponding to the body surface in part is considered to be a living body (density is almost equal and the propagation speed of ultrasonic waves is almost equal). An experiment was conducted in which a sound wave was applied to form a secondary sound source, and a propagating ultrasonic wave propagating in water was generated.

  FIG. 13 shows an outline of a measurement system for a propagation ultrasonic wave generation experiment using a secondary sound source. The focused ultrasonic transducer 100 that transmits focused ultrasonic waves is disposed so as to focus the ultrasonic waves 101 on the membrane 102 formed on a part of the wall surface of the water tank 105 separated by a predetermined separation distance. The water tank 105 is filled with water 107. In the water 107, three wooden rods 104a, 104b, 104c, which are like bones in a living body, are arranged at equal intervals. The distance between the wooden bars 104a and 104c was 4.8 cm.

  A nonlinear ultrasonic wave is transmitted from the focused ultrasonic transducer 100 to generate a propagating ultrasonic wave 106 that propagates in the water 107, and a microphone 108 is disposed on the opposite surface of the water tank 105. FIG. 14 shows an ultrasonic image obtained by setting the microphone 108 as a set and moving it in the X and Y directions with respect to the water tank and plotting the output voltage of the microphone 108 against the amount of movement.

  FIG. 14 shows the measurement results and the results of computer simulation performed for comparison. FIG. 14A shows the result of image processing and display of the ultrasonic signal measured by the measurement system of FIG. 13. The frequency of the ultrasonic wave transmitted from the focusing ultrasonic transducer 100 is 40 kHz. Yes.

  FIGS. 14B and 14C show the results of computer simulation performed for comparison with actual measurement values, and FIG. 14B uses ultrasonic waves having the same frequency as the actual measurement values. The result is shown. FIG. 14C shows a computer simulation result when the ultrasonic frequency is set to 400 kHz.

  From these results, it was verified that the positions of the three wooden bars were accurately indicated. 14B and 14C suggest that the resolution can be improved by further increasing the frequency of the ultrasonic waves.

  DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic apparatus, 10 Control circuit unit, 11 Multiplexer, 12 Pulsar array, 13 Transmission beam former for secondary sound source formation, 14 Delay time addition part, 15 Delay time pattern generation part for beam steering, 16 Delay for secondary sound source formation Time pattern generation unit, 17 Transmit beamformer for imaging of body tissue, 18 receiver array, 19 receive beamformer, 20 SW, 21 maximum value detection unit, 22 separation distance calculation unit, 23 Doppler shift detection unit, 24 FV conversion unit, 25 receiving beamformer for imaging of body tissue, 26 processing unit, 27 storage unit, 28 bus, 29 signal processing unit, 30 image processing unit, 32 monitor, 40 ultrasonic diagnostic system, 50 focusing type ultrasonic transducer array, 60 column Array unit, 61 G Nsu inducer element 70 wiring bundle, 71A～71n connection wiring, 80 a composite type of focused ultrasonic transducer array, 81 lower electrode, 82 a composite piezoelectric body, 83 a common ground electrode, 84 an acoustic matching layer, 85 backing layer

Claims (5)

A focused ultrasonic wave generating means arranged to be separated from the surface of the medium to be measured and generating a focused ultrasonic wave as a primary sound source;
A plurality of focused ultrasound control circuit units each including focused point alignment means for controlling the focused ultrasound irradiated by the focused ultrasound generating means so as to have a focused point directly under the surface of the medium to be measured ;
The plurality of focused ultrasonic control circuit units focus ultrasonic waves on the surface of the measured medium to form a plurality of secondary sound sources, and a secondary that propagates inside the measured medium based on the secondary sound sources. An ultrasonic diagnostic apparatus further comprising transmission beam forming means for controlling a synthetic wavefront formed by transmission ultrasonic waves .   The ultrasonic diagnostic apparatus according to claim 1, wherein the focusing point alignment unit includes a focusing point position varying unit that varies a position of the focusing point along a propagation direction of the focused ultrasound. Focused ultrasound generating means for generating focused ultrasound;
Focusing point alignment means for controlling the focused ultrasonic wave irradiated by the focused ultrasonic wave generating means to be positioned immediately below the surface of the medium to be measured;
A secondary transmission ultrasonic pulse propagating through the inside of the measurement medium based on a secondary sound source formed immediately below the surface of the measurement medium by the focusing point alignment means is used to generate a region of interest inside the measurement medium. Image based on the characteristic value of the transmitted ultrasonic pulse to the back surface of the secondary transmission ultrasonic pulse in the region of interest or the pulse echo signal reflected at the acoustic impedance boundary. An ultrasonic diagnostic apparatus comprising image forming means for forming. A focused ultrasonic wave generating means for forming a secondary sound source from an aerial position separated from the surface of the object directly below the surface of the object;
Means for generating a secondary transmission ultrasonic pulse from the secondary point sound source toward the deep part of the object;
The transmitted ultrasonic pulse transmitted through the object and reaching the back surface of the object is reflected on the back surface side of the object or at an acoustic impedance boundary inside the object. Means for receiving the converted pulse echo signal on the surface side of the object and converting it into an electrical signal;
Storage means for storing the characteristic value of the electric signal;
Mechanical moving means for mechanically moving the focal point of the secondary sound source in the region of interest on the surface of the object in a direction orthogonal to the plane while storing the in-plane coordinates of the focal point in the storage means When,
Ultrasonic diagnostic apparatus characterized by comprising an image construction means for constructing an ultrasonic image by taking the correlation between the in-plane coordinates of the characteristic values and secondary point source of electrical signals stored in the storage means. The ultrasonic wave is transmitted from the first sound source separated from the surface of the medium to be measured by the focused ultrasonic wave generating means,
A second sound source is formed by converging the focal point of the first sound source on the surface of the medium to be measured by the focusing point alignment means,
The second sound source generates a transmission or reflection ultrasonic pulse propagating through the measured medium,
An ultrasonic image construction method for constructing an ultrasonic diagnostic image by receiving a transmission or reflection ultrasonic pulse by a receiving means and performing signal processing for image formation.