JP2014180362A - Ultrasonic probe and ultrasonic image diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic probe, and an ultrasonic image diagnostic apparatus, of better sensitivity.SOLUTION: An ultrasonic probe 2 includes: a piezoelectric material 22 for transmitting/receiving ultrasonic waves; an acoustic lens 25 provided to converge ultrasonic waves transmitted from the piezoelectric material 22 onto an analyte; an acoustic matching layer 23 provided to be positioned between the piezoelectric material 22 and the acoustic lens 25; and a rear surface layer 21 provided on the opposite side of the acoustic matching layer 23 relative to the piezoelectric material 22. Assuming any position in a stacking direction of a rear surface reflection material 21b which is a member having a largest acoustic impedance present on a rear surface layer side beyond an interface between the piezoelectric material 22 and the acoustic matching layer 23 as a start point, and a position of an interface between the acoustic lens 25 and the acoustic matching layer 23 as an end point, the acoustic impedance of the acoustic matching layer 23 is set so that the acoustic impedance gradually decreases from the acoustic impedance at the start point to the acoustic impedance at the end point.

Description

  The present invention relates to an ultrasonic probe and an ultrasonic diagnostic imaging apparatus.

  As an apparatus for nondestructive inspection, there is known an ultrasonic diagnostic imaging apparatus that obtains an image showing the inside of an object to be inspected by ultrasonic waves. The ultrasonic diagnostic imaging apparatus obtains an image by bringing an ultrasonic probe that transmits and receives ultrasonic waves into contact with an object to be inspected. The ultrasonic probe is a piezoelectric material that generates ultrasonic waves in response to input of drive signals, an acoustic lens that converges ultrasonic waves on the object to be inspected, and an acoustic matching to adjust the acoustic impedance from the piezoelectric material to the acoustic lens. It has a layer etc. (for example, patent documents 1). The acoustic matching layer of Patent Document 1 is designed to eliminate the acoustic impedance gap between the piezoelectric material and the acoustic matching layer in order to widen the frequency of the ultrasonic wave, so that the acoustic matching layer at the portion in contact with the piezoelectric material has an acoustic property. The impedance is the same as the acoustic impedance of the piezoelectric material.

JP 2007-129554 A

  However, the conventional ultrasonic probe as disclosed in Patent Document 1 has a problem that the change in decrease of the acoustic impedance from the piezoelectric material to the acoustic lens in the acoustic matching layer becomes abrupt and the sensitivity decreases due to attenuation of the ultrasonic wave. Had a point. In addition, ultrasonic waves transmitted and received from the piezoelectric material are transmitted through the piezoelectric material, but the acoustic impedance of the conventional acoustic matching layer is the ultrasonic wave existing on the piezoelectric material side of the acoustic matching layer, such as a piezoelectric material. Therefore, there is a problem in that the sensitivity is lowered due to attenuation of ultrasonic waves in the transmission path.

  An object of the present invention is to provide a more sensitive ultrasonic probe and ultrasonic diagnostic imaging apparatus.

  The ultrasonic probe according to the first aspect of the present invention includes a piezoelectric material that transmits and receives ultrasonic waves, and an acoustic lens that is provided so as to converge ultrasonic waves transmitted from the piezoelectric materials to a transmission target of the ultrasonic waves. And an acoustic matching layer provided between the piezoelectric material and the acoustic lens, and a back layer provided on the opposite side of the acoustic matching layer with respect to the piezoelectric material. The position of the interface between the acoustic lens and the acoustic matching layer starts from any position in the stacking direction of the member having the largest acoustic impedance existing on the back layer side relative to the interface between the material and the acoustic matching layer. The acoustic impedance of the acoustic matching layer is set so that the acoustic impedance gradually decreases from the acoustic impedance at the start point to the acoustic impedance at the end point. It is characterized in.

  The invention according to claim 2 is the ultrasonic probe according to claim 1, wherein the starting point is located at a position of the opposite surface of the member having the largest acoustic impedance. .

  The invention according to claim 3 is the ultrasonic probe according to claim 1 or 2, wherein the back layer includes a back reflector having an acoustic impedance higher than that of the piezoelectric material. And

  The invention according to claim 4 is the ultrasonic probe according to any one of claims 1 to 3, wherein the acoustic impedance is from the start point to the start point to the end point. It is characterized by decreasing exponentially.

  The invention according to claim 5 is the ultrasonic probe according to any one of claims 1 to 4, wherein the acoustic matching layer includes a plurality of layers having different acoustic impedances, and the plurality The thickness of each layer is less than a quarter wavelength in wavelength units corresponding to the sound velocity of each layer and the center frequency of the ultrasonic wave.

  A sixth aspect of the present invention is the ultrasonic probe according to any one of the first to fifth aspects, wherein the acoustic matching layer is composed of a plurality of layers having different acoustic impedances. Each of these layers is laminated by applying a material constituting each layer.

  The ultrasonic diagnostic imaging apparatus according to the seventh aspect of the invention outputs ultrasonic waves that are transmitted toward the subject by a drive signal and outputs a reception signal by receiving reflected ultrasonic waves from the subject. An ultrasonic wave for displaying an ultrasonic image based on the probe, a transmitter for generating the drive signal for driving the ultrasonic probe, and the received signal output by the ultrasonic probe; An ultrasonic diagnostic imaging apparatus including an image generation unit that generates image data, wherein the ultrasonic probe is the ultrasonic probe according to any one of claims 1 to 6. Features.

  According to the present invention, it is possible to provide a more sensitive ultrasonic probe and ultrasonic diagnostic imaging apparatus.

It is a figure which shows the external appearance structure of an ultrasonic image diagnostic apparatus. It is a block diagram which shows schematic structure of an ultrasonic image diagnostic apparatus. It is a block diagram which shows schematic structure of a transmission part. It is a figure explaining the drive waveform of a pulse signal. It is a figure explaining the waveform of the pulse signal to transmit. It is sectional drawing which shows schematic structure of an ultrasound probe. It is sectional drawing which shows an example of dicing. It is the schematic which shows the decreasing curve of the acoustic impedance in an Example. It is the schematic which shows the decreasing curve of the acoustic impedance in a 1st comparative example. It is a graph which shows the measurement result of the sensitivity of an Example and a 1st comparative example. It is sectional drawing which shows schematic structure of the ultrasound probe in a modification. It is the schematic which shows the decreasing curve of the acoustic impedance in a modification. It is a graph which shows the measurement result of the sensitivity of a modification and a 2nd comparative example.

  Embodiments of the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  The ultrasonic diagnostic imaging apparatus S according to the present embodiment includes an ultrasonic diagnostic imaging apparatus main body 1 and an ultrasonic probe 2 as shown in FIGS. 1 and 2. The ultrasonic probe 2 transmits an ultrasonic wave (transmission ultrasonic wave) to a subject such as a living body (not shown) as an inspection object for the ultrasonic diagnostic imaging apparatus S, and an ultrasonic wave reflected by the subject. A reflected wave of a sound wave (reflected ultrasonic wave: echo) is received. The ultrasonic diagnostic imaging apparatus main body 1 is connected to the ultrasonic probe 2 via a cable 3, and transmits an electric signal drive signal to the ultrasonic probe 2, thereby providing an object to the ultrasonic probe 2. Based on a received signal that is an electrical signal generated by the ultrasonic probe 2 in response to the reflected ultrasonic wave from within the subject received by the ultrasonic probe 2. The internal state in the subject is imaged as an ultrasonic image.

  The ultrasonic probe 2 includes a transducer 2a made of a piezoelectric element, and a plurality of the transducers 2a are arranged in a one-dimensional array in the azimuth direction, for example. In the present embodiment, for example, the ultrasonic probe 2 including 192 transducers 2a is used. Note that the vibrators 2a may be arranged in a two-dimensional array. The number of vibrators 2a can be set arbitrarily. In the present embodiment, a linear scanning electronic scanning probe is used for the ultrasound probe 2, but either an electronic scanning method or a mechanical scanning method may be used, and a linear scanning method, Either the sector scanning method or the convex scanning method can be adopted. The bandwidth in the ultrasonic probe 2 can be set arbitrarily.

  For example, as shown in FIG. 2, the ultrasonic diagnostic imaging apparatus main body 1 includes an operation input unit 11, a transmission unit 12, a reception unit 13, an image generation unit 14, a memory unit 15, a DSC (Digital Scan Converter). ) 16, a display unit 17, and a control unit 18.

  The operation input unit 11 includes, for example, various switches, buttons, a trackball, a mouse, a keyboard, and the like for inputting data such as a command for starting diagnosis and personal information of a subject, and the like. Output to the control unit 18.

  The transmission unit 12 is a circuit that supplies a drive signal, which is an electrical signal, to the ultrasonic probe 2 via the cable 3 under the control of the control unit 18 to generate transmission ultrasonic waves in the ultrasonic probe 2. . More specifically, the transmission unit 12 includes, for example, a clock generation circuit 121, a pulse generation circuit 122, a pulse width setting unit 123, and a delay circuit 124, as shown in FIG.

The clock generation circuit 121 is a circuit that generates a clock signal that determines the transmission timing and transmission frequency of the drive signal.
The pulse generation circuit 122 is a circuit for generating a pulse signal as a drive signal at a predetermined cycle. For example, as shown in FIG. 4, the pulse generation circuit 122 can generate a pulse signal by a rectangular wave by switching and outputting three-value voltages. At this time, the amplitude of the pulse signal is the same for the positive polarity and the negative polarity, but is not limited thereto. Note that a pulse signal may be generated by switching between two or four or more voltages.
The pulse width setting unit 123 sets the pulse width of the pulse signal output from the pulse generation circuit 122. That is, the pulse generation circuit 122 outputs a pulse signal having a pulse waveform according to the pulse width set by the pulse width setting unit 123. For example, the pulse width can be changed by an input operation by the operation input unit 11. Further, the pulse width corresponding to the identified ultrasonic probe 2 may be set by identifying the ultrasonic probe 2 connected to the ultrasonic diagnostic imaging apparatus main body 1.
The shape of the drive signal is not particularly limited, and can be appropriately selected from sine waves, cosine waves, rectangular waves, and the like. Further, a signal obtained by synthesizing these plural signals may be used. From the viewpoint of being able to be configured with a simple and small circuit, the drive signal is preferably a rectangular wave having a plurality of pulses. At this time, it is preferable that at least one of the plurality of pulses has a pulse width (duty) different from that of the other pulses. Thereby, since the frequency bandwidth of the drive signal is increased, the frequency bandwidth of the transmitted ultrasonic wave can be further increased, and the time resolution, that is, the distance resolution in the depth direction can be further improved. An example of the shape of such a drive signal is shown in FIG. The drive signal shown in FIG. 5 includes a first pulse signal, a second pulse signal having a different polarity from the first pulse signal, and a third pulse signal having the same polarity as the first pulse signal. It is a provided square wave. The pulse width (T1) of the first pulse signal, the pulse width (T2) of the second pulse signal, and the pulse width (T3) of the third pulse signal are set to 16 ns, 56 ns, and 104 ns, respectively. The pulse width of each pulse signal is not limited to that described above, and can be set arbitrarily. For example, in the present embodiment, the pulse width is set to gradually increase, but the pulse width may be set to gradually decrease. Thus, the frequency bandwidth of the drive signal can be further increased by making the pulse widths of the first to third pulses all different. Note that the pulse widths of all the pulse signals among the plurality of pulse signals may be set to be the same.

  The delay circuit 124 sets a delay time for each individual path corresponding to each transducer corresponding to the transmission timing of the drive signal, delays the transmission of the drive signal by the set delay time, and is a transmission beam configured by transmission ultrasonic waves. This is a circuit for performing focusing.

  The transmission unit 12 configured as described above sequentially switches the plurality of transducers 2a that supply the drive signal while shifting a predetermined number for each transmission / reception of the ultrasonic wave under the control of the control unit 18, and the plurality of the output selected. Scanning is performed by supplying a drive signal to the vibrator 2a.

  As illustrated in FIG. 2, the reception unit 13 is a circuit that receives a reception signal of an electrical signal from the ultrasonic probe 2 via the cable 3 under the control of the control unit 18. The receiving unit 13 includes, for example, an amplifier, an A / D conversion circuit, and a phasing addition circuit. The amplifier is a circuit for amplifying the received signal with a predetermined amplification factor set in advance for each individual path corresponding to each transducer 2a. The A / D conversion circuit is a circuit for analog-digital conversion (A / D conversion) of the amplified received signal. The phasing addition circuit adjusts the time phase by giving a delay time to each individual path corresponding to each transducer 2a with respect to the A / D converted received signal, and adds these (phasing addition) to generate a sound. It is a circuit for generating line data.

  The image generation unit 14 generates B-mode image data by performing envelope detection processing, logarithmic amplification, and the like on the sound ray data from the reception unit 13 and performing luminance adjustment by performing gain adjustment and the like. In other words, the B-mode image data represents the intensity of the received signal by luminance. The B-mode image data generated by the image generation unit 14 is transmitted to the memory unit 15.

  The memory unit 15 is configured by a semiconductor memory such as a DRAM (Dynamic Random Access Memory), for example, and stores the B-mode image data transmitted from the image generation unit 14 in units of frames. That is, the memory unit 15 can store ultrasonic diagnostic image data configured in units of frames. The ultrasonic diagnostic image data stored in the memory unit 15 is read according to the control of the control unit 18 and transmitted to the DSC 16.

  The DSC 16 converts the ultrasonic diagnostic image data received from the memory unit 15 into an image signal based on a television signal scanning method, and outputs the image signal to the display unit 17.

As the display unit 17, a display device such as an LCD (Liquid Crystal Display), a CRT (Cathode-Ray Tube) display, an organic EL (Electronic Luminescence) display, an inorganic EL display, or a plasma display is applicable. The display unit 17 displays an ultrasonic diagnostic image on the display screen according to the image signal output from the DSC 16. Note that a printing device such as a printer may be applied instead of the display device.

The control unit 18 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and reads various processing programs such as a system program stored in the ROM to read the RAM. The operation of each part of the ultrasonic diagnostic imaging apparatus S is centrally controlled according to the developed program.
The ROM is configured by a nonvolatile memory such as a semiconductor, and stores a system program corresponding to the ultrasonic image diagnostic apparatus S, various processing programs executable on the system program, various data, and the like. These programs are stored in the form of computer-readable program code, and the CPU sequentially executes operations according to the program code.
The RAM forms a work area for temporarily storing various programs executed by the CPU and data related to these programs.

  Next, the ultrasonic probe 2 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 6, the ultrasonic probe 2 is stacked on the back surface layer 21, the piezoelectric material 22 stacked on the back surface layer 21, and the piezoelectric material 22, for example, from below in the front view. An acoustic matching layer 23 and an acoustic lens 25 laminated on the acoustic matching layer 23 are provided.

  The back layer 21 includes, for example, a backing material 21a and a back reflecting material 21b laminated on the backing material 21a. The piezoelectric material 22 is laminated on the back reflecting material 21b. That is, the back surface layer 21 is the opposite side to the side where the acoustic matching layer 23 is provided with respect to the piezoelectric material 22 in the stacking direction of each member constituting the ultrasonic probe (hereinafter simply referred to as “the opposite side”). Is provided). Further, when viewed from the opposite side, the backing material 21a and the back reflecting material 21b are provided in this order.

  The backing material 21a is an ultrasonic absorber that is formed of a material having an acoustic impedance lower than that of the piezoelectric material 22 and can absorb unnecessary ultrasonic waves. That is, the backing material 21 a absorbs ultrasonic waves generated from the opposite side of the piezoelectric material 22.

  The backing material 21a constituting the backing material 21a includes natural rubber, ferrite rubber, epoxy resin, and rubber-based composite material and epoxy resin composite material that are press-molded with powders such as tungsten oxide, titanium oxide, and ferrite in these materials. Material, vinyl chloride, polyvinyl butyral (PVB), ABS resin, polyurethane (PUR), polyvinyl alcohol (PVAL), polyethylene (PE), polypropylene (PP), polyacetal (POM), polyethylene terephthalate (PETP), fluororesin (PTFE) ) Thermoplastic resins such as polyethylene glycol and polyethylene terephthalate-polyethylene glycol copolymer are applicable.

  The preferable backing material 21a is made of a rubber-based composite material and / or an epoxy resin composite material, and the shape thereof is appropriately determined according to the shape of the back reflector 21b, the piezoelectric material 22, and the probe head including these. You can choose.

  The back reflecting material 21 b is made of a material having an acoustic impedance higher than that of the piezoelectric material 22, and reflects the ultrasonic wave output to the opposite side of the piezoelectric material 22. As described above, since the back surface reflecting material 21b is provided, the ultrasonic wave generated from the piezoelectric material 22 can be transmitted to the subject side more efficiently. Therefore, the sensitivity of the piezoelectric material 22 to the transmission and reception of the ultrasonic wave is further improved. Can be made.

  As the material constituting the back reflector 21b, tungsten carbide (WC, tungsten carbide), cemented carbide obtained by mixing cobalt (CO), which is a binder (binder), and sintered, and further carbonized thereto. A material to which an additive such as titanium (TiC) or tantalum carbide (TaC) is added can be used.

  A preferable back reflector 21b is made of tungsten carbide, and the shape thereof can be appropriately selected according to the shape of the piezoelectric material 22 and the probe head including the same.

  It is a preferable aspect that the back reflecting material 21b and the backing material 21a and the back reflecting material 21b and the piezoelectric material 22 are laminated via an adhesive layer. As an adhesive for forming the adhesive layer, an epoxy-based adhesive can be used. In addition, it is more preferable that the adhesive layer is thinner, and when an electrical connection between the members is necessary, the adhesive layer is provided so as not to prevent contact for the electrical connection.

  The piezoelectric material 22 includes an electrode and a piezoelectric material, and is an element (piezoelectric element) capable of converting an electrical signal into mechanical vibration, converting mechanical vibration into an electrical signal, and transmitting and receiving ultrasonic waves.

  The piezoelectric material is a material containing a piezoelectric body capable of converting an electrical signal into mechanical vibration and converting mechanical vibration into an electrical signal. Piezoelectric ceramics such as lead zirconate titanate (PZT) ceramics, lead titanate, lead metaniobate, etc., lithium niobate, lead zinc niobate and lead titanate, lead magnesium niobate and lead titanate, etc. Piezoelectric single crystal, crystal, Rochelle salt, polyvinylidene fluoride (PVDF), or VDF and a copolymer of, for example, ethylene trifluoride (TrFE), made of a solid solution single crystal of PVDF copolymer such as (P (VDF-TrFE)), polyvinylidene cyanide (PVDCN) which is a polymer of vinylidene cyanide (VDCN), vinylidene cyanide copolymer, nylon 9, nylon 11, etc. Odd nylon, aromatic nylon, alicyclic nylon, polylactic acid, poly Mud carboxylate butyrate polyhydroxycarboxylic acids, can be used cellulosic derivatives, organic polymer piezoelectric materials such as polyurea or the like.

  The thickness of the piezoelectric material is, for example, in the range of 100 to 500 μm. The piezoelectric material is used as the vibrator 2a in a state where electrodes are attached to both surfaces thereof.

  Materials used for electrodes applied to piezoelectric materials include gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu), aluminum (Al), nickel (Ni), tin (Sn) etc. are mentioned.

  As a method for attaching an electrode to a piezoelectric material, for example, a base metal such as titanium (Ti) or chromium (Cr) is formed to a thickness of 0.02 to 1.0 μm by sputtering, and then the above metal element is mainly used. Examples thereof include a method of forming a metal material made of a metal to be used and an alloy thereof, and further forming a partially insulating material to a thickness of 1 to 10 μm by a sputtering method or other appropriate methods as necessary.

  Electrodes can be formed by screen printing, dipping, or thermal spraying using a conductive paste in which fine metal powder and low-melting glass are mixed, as well as sputtering. The electrodes are provided on the entire piezoelectric material surface or a part of the piezoelectric material surface on the piezoelectric material in accordance with the shape of the ultrasonic probe 2.

  In addition, the electrode of the piezoelectric material 22 is in contact with the FPC 22a through the back reflecting material 21b, and the FPC 22a is electrically connected to the cable 3. Therefore, the drive signal output from the ultrasonic diagnostic imaging apparatus main body 1 is input to the piezoelectric material 22 via the FPC 22a, and the reception signal generated by the piezoelectric material 22 is output to the ultrasonic diagnostic imaging apparatus main body 1.

  The acoustic matching layer 23 matches the acoustic impedance between the piezoelectric material 22 and the acoustic lens 25, and suppresses reflection at the boundary surfaces of the piezoelectric material 22, the acoustic matching layer 23, and the acoustic lens 25. It is. The acoustic matching layer 23 is attached to the subject side with respect to the piezoelectric material 22.

  The acoustic matching layer 23 is configured by laminating a plurality of layers, for example, a lowermost layer 23a, an intermediate layer 23b, and an uppermost layer (frontmost layer) 23c. The layer thickness of the acoustic matching layer 23, which is the sum of the thicknesses of the plurality of layers, is determined to be ½λ or more when the wavelength of the center frequency (for example, 10 MHz) of the ultrasonic wave transmitted from the piezoelectric material 22 is λ. It is done. More preferably, the layer thickness of the acoustic matching layer 23 is determined to be λ or more. By determining the layer thickness of the acoustic matching layer 23 in this way, attenuation by the acoustic matching layer 23 on the low frequency side with respect to the center frequency of the ultrasonic wave generated from the piezoelectric material 22 can be reduced. That is, the transmission blocking characteristic on the low frequency side of the acoustic matching layer 23 can be further improved.

The acoustic impedance of the acoustic matching layer 23 is set so as to gradually decrease from the lowermost layer 23 a to the uppermost layer 23 c and the acoustic impedance of the lowermost layer 23 a is less than the acoustic impedance of the piezoelectric material 22. Further, in order to match the acoustic impedance of the acoustic lens 25 described later, it is preferable to reduce the difference between the acoustic impedance of the uppermost layer 23c and the acoustic impedance of the acoustic lens 25, more preferably, the uppermost layer 23c and the acoustic lens 25. The acoustic matching layer 23 is provided so that the acoustic impedance of the uppermost layer 23c at the interface with the acoustic lens 25 is substantially equal to the acoustic impedance of the acoustic lens 25.
In addition, the thickness of each of the plurality of layers constituting the acoustic matching layer 23 is a unit of wavelength (for example, λ) corresponding to the sound velocity determined by the composition of each layer and the center frequency of the ultrasonic wave transmitted from the piezoelectric material 22. It is preferable that it is less than 1 / 4λ. By determining the thickness of each of the plurality of layers in this way, attenuation by the acoustic matching layer 23 on the low frequency side with respect to the center frequency of the ultrasonic wave generated from the piezoelectric material 22 can be reduced. That is, the transmission blocking characteristic on the low frequency side of the acoustic matching layer 23 can be further improved. In addition, when the layer thickness of the acoustic matching layer 23 is determined to be λ or more and the thickness of each layer is less than ¼λ, the acoustic matching layer 23 has a structure of five or more layers having different acoustic impedances. Have.

  Specifically, the material used for the acoustic matching layer 23 is aluminum, aluminum alloy (for example, AL-Mg alloy), magnesium alloy, macor glass, glass, fused quartz, copper graphite, PE (polyethylene) or PP (polypropylene). , PC (polycarbonate), ABC resin, ABS resin, AAS resin, AES resin, nylon (PA6, PA6-6), PPO (polyphenylene oxide), PPS (polyphenylene sulfide: glass fiber can be included), PPE (polyphenylene ether) PEEK (polyetheretherketone), PAI (polyamideimide), PETP (polyethylene terephthalate), epoxy resin, urethane resin and the like. Preferably, a thermosetting resin such as an epoxy resin is molded with tungsten, zinc white, titanium oxide, silica, alumina, bengara, ferrite, tungsten oxide, yttrium oxide, barium sulfate, molybdenum, etc. as a filler. Applicable. Here, by making the type, amount, distribution, and the like of the filler different in each layer, the acoustic impedance of each layer can be different even for the same type of resin.

  The acoustic lens 25 is arranged to focus the ultrasonic beam using refraction and improve the resolution. In other words, the acoustic lens 25 is provided on the ultrasonic probe 2 on the side in contact with the subject, and efficiently causes the ultrasonic waves generated by the piezoelectric material 22 to enter the subject. The acoustic lens 25 is a portion in contact with the subject and has a convex or concave lens shape according to the internal sound velocity, and the ultrasonic wave incident on the subject is subjected to a thickness direction (elevation) perpendicular to the imaging section. Direction).

The acoustic impedance of the acoustic lens 25 is appropriately set so that the attenuation and reflection of ultrasonic waves between the acoustic lens 25 and the subject are smaller than the acoustic impedance of the subject. Here, since the subject is a human body or the like, generally, the acoustic impedance of the acoustic lens 25 is set to be extremely low compared to a hard substance such as a piezoelectric body. Accordingly, the acoustic lens 25 is formed of a material (for example, a soft polymer material) corresponding to the set acoustic impedance.
In order to further reduce the attenuation and reflection of ultrasonic waves between the acoustic lens 25 and the acoustic matching layer 23, the acoustic impedance of the acoustic matching layer 23 that is in contact with the acoustic lens 25 (the uppermost layer 23c) is The acoustic lens 25 is preferably substantially the same.

  Examples of the material constituting the acoustic lens 25 include conventionally known homopolymers such as silicone rubber, butadiene rubber, polyurethane rubber, epichlorohydrin rubber, and ethylene-propylene copolymer rubber obtained by copolymerizing ethylene and propylene. Copolymer rubber or the like is applicable. Of these, silicone rubber and butadiene rubber are preferably used.

The acoustic matching layer 23, the piezoelectric material 22, and the FPC are diced. For example, as shown in FIG. 7, the acoustic matching layer 23, the piezoelectric material 22 and the FPC are diced from the acoustic matching layer 23 to the FPC at a pitch of 0.20 mm with a dicer having a thickness of 0.02 mm. . Each channel diced at a pitch of 0.20 mm is further diced into three equal parts.
Although not shown, a die groove formed by dicing is filled with a resin such as a silicone adhesive.
Further, as shown in FIG. 7, a protective layer 24 may be provided in a die groove generated by dicing. The protective layer 24 prevents the cleaning liquid from passing through the acoustic lens 25 and entering the adhesive layer between the component parts inside the acoustic lens 25 when the ultrasonic probe 2 is cleaned before and after the measurement. However, it is made of a material having a gas barrier property that enables highly accurate measurement.
The description of the embodiment related to the dicing and filling of the die groove is merely an example, and can be changed as appropriate. Moreover, the example of FIG. 7 is schematic and does not limit the thickness of each layer.

Next, the acoustic impedance of each of the piezoelectric material 22, the back reflecting material 21b, and the backing material 21a and the reflection of ultrasonic waves between the members will be described.
When the back reflector 21b is not provided and a member having a lower acoustic impedance than the piezoelectric material 22 such as the backing material 21a is bonded to the opposite side of the piezoelectric material 22, the opposite side of the ultrasonic waves generated from the piezoelectric material 22 The reflectance R indicating the rate at which the ultrasonic waves transmitted to the subject are reflected to the subject side is calculated by the following equation (1). Here, Zpzt represents the acoustic impedance of the piezoelectric material 22. Z represents the acoustic impedance of a member bonded to the opposite side of the piezoelectric material 22.
R = (Z−Zpzt) / (Zpzt + Z) (1)

  For example, as shown in Table 1 below, when a backing material 21a having an acoustic impedance of 5.8 Mrays is bonded to the opposite side of the piezoelectric material 22 having an acoustic impedance of 33 Mrays, transmission is performed from the piezoelectric material 22 to the opposite side. The reflectance R of the ultrasonic wave reflected by the backing material 21a among the ultrasonic waves thus obtained is about 0.7 based on the formula (1). Here, the polarity inversion of the reflected wave accompanying the reflection is omitted. That is, as shown in Table 2 below, the reflectance of the ultrasonic wave transmitted from the piezoelectric material 22 to the opposite side at the interface between the piezoelectric material 22 and the backing material 21a is about 70%. Examples of the backing material 21a exhibiting such reflectance include a backing material 21a made of a material in which tungsten fine particles having a 10% volume fraction are dispersed in an epoxy resin. However, the backing material 21a is an example and is not limited thereto. .

  On the other hand, when a member having higher acoustic impedance than the piezoelectric material 22 is provided between the piezoelectric material 22 and the backing material 21a, such as the back reflecting material 21b in the ultrasonic probe 2 described above, The reflectance of the sound wave is higher at the interface between the back reflector 21b and the backing material 21a.

  For example, when a back reflector 21b having an acoustic impedance of 107 Mrays is provided between the piezoelectric material 22 having an acoustic impedance of 33 Mrays and a backing material 21a having an acoustic impedance of 5.8 Mrayls, as shown in Table 2. The reflectance of the ultrasonic wave transmitted from the piezoelectric material 22 to the opposite side at the interface between the piezoelectric material 22 and the back reflecting material 21b is about 52%, and the back reflecting material 21b at the interface between the back reflecting material 21b and the backing material 21a. The reflectance of the ultrasonic wave transmitted through the inside is about 90%. Examples of the back reflecting material 21b showing the reflectance include the back reflecting material 21b made of WC. However, the back reflecting material 21b is an example and is not limited thereto.

In other words, 48% of the ultrasonic waves transmitted from the piezoelectric material 22 to the opposite side are transmitted through the back reflector 21b, and 90% of the transmitted ultrasonic waves are reflected at the interface between the back reflector 21b and the backing material 21a. Then, the light passes through the back reflecting material 21b again and is transmitted to the subject side through the piezoelectric material 22, the acoustic matching layer 23, and the acoustic lens 25.
In this way, when the back reflector 21b is provided, the ultrasonic wave transmitted from the piezoelectric material 22 to the opposite side is not only the interface between the piezoelectric material 22 and the back reflector 21b, but also the back reflector 21b and the backing. It is also reflected at the interface with the material 21a. From this, the sensitivity is further improved by further reducing the attenuation of the ultrasonic wave in the path until the ultrasonic wave reflected at the interface between the back reflector 21b and the backing material 21a is transmitted to the subject. Can do.

  Therefore, in the present invention, the back reflector 21b, which is the member having the largest acoustic impedance existing on the back layer 21 side relative to the interface between the piezoelectric material 22 and the acoustic matching layer 23, is set as the starting point P1, and the acoustic lens 25 and the acoustic matching. The acoustic impedance of the acoustic matching layer 23 is set so that the acoustic impedance gradually decreases from the acoustic impedance at the start point P1 to the acoustic impedance at the end point P2, with the position of the interface with the layer 23 as the end point P2. Thereby, since the attenuation of the ultrasonic wave in the path | route until the ultrasonic wave reflected by the interface of the back reflector 21b and the backing material 21a is transmitted to a subject can be reduced more, a sensitivity is improved more. be able to.

  As a specific example, a graph showing a decrease in acoustic impedance from the back layer 21 to the acoustic lens 25 is shown in FIG. In the example shown in FIG. 8, the position of the surface on the opposite side of the member having the largest acoustic impedance, that is, the position of the surface of the back reflecting material 21b on the side in contact with the backing material 21a is set as the starting point P1. The acoustic impedance of the acoustic matching layer 23 is set so that the acoustic impedance decreases exponentially from the acoustic impedance at the start point P1 to the acoustic impedance at the end point P2.

  In FIG. 8, the position of the surface of the back reflecting material 21b on the side in contact with the backing material 21a is the starting point P1, but the starting point P1 is strictly at the position of the surface of the back reflecting material 21b on the side in contact with the backing material 21a. Even if not, the acoustic impedance of the back reflector 21b is higher than that of the piezoelectric material 22, and the initial acoustic impedance of the acoustic matching layer 23 is lower than that of the piezoelectric material 22, so 22. If the acoustic impedance of the member that reaches the acoustic lens 25 through the acoustic matching layer 23 is gradually reduced, the attenuation of the ultrasonic wave reflected at the interface between the back reflector 21b and the backing material 21a is further reduced. Therefore, the sensitivity can be further improved. Specifically, in the case of the ultrasound probe 2, if the starting point P1 of the acoustic impedance is in the back reflector 21b, the member from the back reflector 21b to the acoustic lens 25 through the piezoelectric material 22 and the acoustic matching layer 23 The acoustic impedance can be gradually reduced.

Hereinafter, examples will be described based on more specific conditions and measurement results. Of course, the present invention is not limited to these numerical values.
For convenience, the center frequency of the ultrasonic wave generated from the piezoelectric material 22 is f0, the plate thickness of the piezoelectric material 22 is tpzt, the acoustic impedance of the back reflector 21b is Zdml, the plate thickness of the back reflector 21b is tdml, and the acoustic of the backing material 21a. The impedance is denoted as Zbk, and the acoustic impedance of the acoustic lens 25 is denoted as Za.
Further, the thickness of the acoustic matching layer 23 is described as tsgml, and the sound velocity of the ultrasonic wave having the center frequency transmitted through the acoustic matching layer 23 is described as Vsgml. In addition, among the acoustic impedances of the acoustic matching layer 23, the acoustic impedance (initial acoustic impedance) of a portion (for example, the lowermost layer 23a) in contact with the piezoelectric material 22 is described as Zslgml.

As shown in FIG. 8, the embodiment of the present invention under the conditions of f0 = 10 MHz, Zpzt = 32.76 MRayls, tpzt = 105 μm, Zdml = 107 MRayls, tdml = 80 μm, Zbk = 2.8 MMRayls, Za = 1.5 MRayls Comparison was made with a first comparative example based on a conventional ultrasonic probe. Here, Zdml> Zpzt. That is, the acoustic impedance of the back reflector 21 b is higher than the acoustic impedance of the piezoelectric material 22.
Further, as shown in FIG. 8, in the example, Zslgml = 25 MRayls and tsgml = 0.64 μm. In the first comparative example, Zslgml = 32.76 MRayls and tsgml = 0.7 μm. Here, an example is Zpzt> Zslgml. That is, in the embodiment, the initial acoustic impedance is less than the acoustic impedance of the piezoelectric material 22.
On the other hand, as shown in FIG. 9, in the first comparative example, Zpzt = Zslgml, and the initial acoustic impedance is equal to the acoustic impedance of the piezoelectric material 22.

FIG. 10 is a graph showing the measurement results of the sensitivity of the example and the first comparative example. In FIG. 10, the measurement result according to the example is indicated by a solid line L1, and the measurement result according to the first comparative example is indicated by a broken line L2.
As shown in FIG. 10, the example of the present invention maintains the curve shape (band shape) of the graph drawn by the sensitivity (dB) value in the ultrasonic frequency band of 0 to 20 MHz with respect to the first comparative example. However, the sensitivity can be increased over the entire frequency band. In particular, it is possible to increase the sensitivity of the center frequency and the ultrasonic wave near the center frequency by about 5 dB.

  As described above, according to the ultrasonic diagnostic imaging apparatus S of the present embodiment, the member (for example, the back reflector 21b) having the largest acoustic impedance existing on the back layer 21 side than the interface between the piezoelectric material 22 and the acoustic matching layer 23. The acoustic matching layer is configured such that the acoustic impedance gradually decreases from the acoustic impedance at the starting point P1 to the acoustic impedance at the ending point P2 with the position as the starting point P1 and the position of the interface between the acoustic lens 25 and the acoustic matching layer 23 as the ending point P2. Since the acoustic impedance of 23 is set, the initial acoustic impedance is less than the acoustic impedance of the piezoelectric material 22, and the sensitivity can be increased as shown in FIG. That is, according to the present embodiment, it is possible to provide a more sensitive ultrasonic probe and ultrasonic diagnostic imaging apparatus.

  Further, the starting point P1 of the acoustic impedance is located on the surface on the opposite side of the member (for example, the back reflector 21b) having the largest acoustic impedance existing on the back layer 21 side than the interface between the piezoelectric material 22 and the acoustic matching layer 23. Therefore, the acoustic impedances of the back reflector 21b, the piezoelectric material 22, and the acoustic matching layer 23 in the reflected ultrasonic path can be gradually reduced. That is, since the attenuation of the ultrasonic wave reflected at the interface between the backing material 21a and the back reflecting material 21b can be further reduced, the sensitivity can be further increased.

  Further, the acoustic matching layer 23 is composed of a plurality of layers having different acoustic impedances, and the thickness of each of the plurality of layers is less than ¼ wavelength in wavelength units according to the sound speed and the center frequency of the ultrasonic wave that each layer has Therefore, since the attenuation of the ultrasonic wave can be further reduced by shortening the distance that the ultrasonic wave passes through each layer, the sensitivity can be further increased.

  Further, since the acoustic impedance of the piezoelectric material 22 and the acoustic matching layer 23 decreases exponentially from the starting point toward the acoustic lens 25, the distance required for the reduction of the acoustic impedance from the piezoelectric material 22 to the acoustic lens 25 can be easily set. Since it is possible to realize a decrease in acoustic impedance that can further reduce the attenuation of ultrasonic waves without increasing the length, sensitivity can be further increased.

(Modification)
Next, a modification of the present invention will be described with reference to FIGS.
The back layer 21 in the ultrasonic probe 200 according to the modified example does not include the back reflecting material 21b, includes only the backing material 21a, and the piezoelectric material 22 is laminated on the backing material 21a. Backing material 21a. The ultrasonic probe 200 has the same configuration as the ultrasonic probe 2 in the above embodiment except that the back layer 21 includes only the backing material 21a and the electrode of the piezoelectric material 22 and the FPC directly contact each other. Therefore, the same reference numerals are given in FIG. 11 and the detailed description is omitted.

As described above using the equation (1), the ultrasonic wave transmitted to the back side of the piezoelectric material 22 is also reflected at the interface between the piezoelectric material 22 and the backing material 21a. In this case, the reflected ultrasonic wave is transmitted to the subject side through the piezoelectric material 22, the acoustic matching layer 23, and the acoustic lens 25. Therefore, the sensitivity can be further improved by further reducing attenuation of the ultrasonic wave in the path until the ultrasonic wave reflected at the interface between the piezoelectric material 22 and the backing material 21a is transmitted to the subject.
Also in the modified example, the piezoelectric material 22, which is a member having the largest acoustic impedance existing on the back layer 21 side than the interface between the piezoelectric material 22 and the acoustic matching layer 23, is set as the starting point P 1, and the acoustic lens 25 and the acoustic matching layer 23 are also used. The acoustic impedance of the acoustic matching layer 23 is set so that the acoustic impedance gradually decreases from the acoustic impedance at the start point P1 to the acoustic impedance at the end point P2.
Further, as shown in FIG. 12, in the modification, the opposite surface of the member having the largest acoustic impedance, that is, the interface between the piezoelectric material 22 and the backing material 21a is set as the starting point P1. Thereby, since the attenuation | damping of the said ultrasonic wave in the path | route until the ultrasonic wave reflected by the interface of the piezoelectric material 22 and the backing material 21a is transmitted to a subject can be reduced more, sensitivity is improved more. Can do.

Hereinafter, the modified examples will be described with more specific conditions and measurement results, but of course, the modified examples of the present invention are not limited to these numerical values.
A modified example under the conditions of f0 = 10 MHz, Zpzt = 32.76 MRayls, tpzt = 105 μm, Zbk = 2.8 MMRayls, Za = 1.5 MRayls and a second comparative example based on a conventional ultrasonic probe were compared.
As shown in FIG. 12, in the modification, Zslgml = 25 MRayls and tsgml = 0.64 μm. In the second comparative example, Zslgml = 32.76 MRayls and tsgml = 0.7 μm. Here, the modified example is Zpzt> Zslgml. That is, in the modification, the initial acoustic impedance is less than the acoustic impedance of the piezoelectric material 22. On the other hand, in the second comparative example, Zpzt = Zslgml, and the initial acoustic impedance is equal to the acoustic impedance of the piezoelectric material 22.

FIG. 13 is a graph showing the measurement results of the sensitivity of the modified example and the second comparative example. In FIG. 13, the measurement result according to the modification is indicated by a solid line L3, and the measurement result according to the second comparative example is indicated by a broken line L4.
As shown in FIG. 13, the modified example of the present invention increases the sensitivity in the ultrasonic of the center frequency by several dB while maintaining the band shape in the ultrasonic frequency band of 0 to 20 MHz compared to the second comparative example. be able to.

  The embodiment of the present invention should be considered that the embodiment disclosed this time is illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  For example, the acoustic matching layer 23 is not limited to the configuration of three layers, and the number of layers constituting the acoustic matching layer 23 and the method of forming the plurality of layers may be changed as appropriate. As an example, each of the plurality of layers constituting the acoustic matching layer 23 may be laminated by applying a material constituting each layer. In this case, specifically, among the materials that can be used as the acoustic matching layer 23 described above, a resin or the like that can be applied and has fluidity and viscosity by adjusting the temperature or the like is used as the material. In addition, a plurality of layers of materials having different acoustic impedances are prepared by adjusting the type and amount of the filler. Then, the acoustic matching layer 23 is formed so as to sequentially coat a plurality of materials such that a material having a relatively low acoustic impedance is on the acoustic lens 25 side and a material having a relatively high acoustic impedance is on the opposite side. .

  Each of the plurality of layers constituting the acoustic matching layer 23 is laminated by applying the material constituting each layer, so that the reduction of the acoustic impedance in the acoustic matching layer 23 corresponds to a more ideal reduction curve. Therefore, attenuation of ultrasonic waves in the acoustic matching layer 23 can be further reduced, and sensitivity can be further increased.

  Further, the acoustic matching layer 23 may be configured to gradually reduce the acoustic impedance from the start point P1 side to the end point P2 by a structure other than a multilayer structure including a plurality of layers. For example, the acoustic matching layer 23 of the single member is formed of the material of the acoustic matching layer 23 mentioned above, and the ratio of the filler in the single member formed of the material is changed from the start point P1 side to the end point P2 side. The acoustic impedance of the acoustic matching layer 23 may be gradually decreased from the start point P1 side to the end point P2 by gradually changing to the end point P2.

  In the above-described embodiments and modifications, the decrease in acoustic impedance from the opposite side of the interface between the piezoelectric material 22 and the acoustic matching layer 23 to the acoustic lens 25 shows an exponential decrease curve. Thus, the present invention is not limited to this, and can be set as appropriate. For example, the reduction in acoustic impedance from the opposite side of the interface between the piezoelectric material 22 and the acoustic matching layer 23 to the acoustic lens 25 may indicate a linear proportional reduction depending on the application of the ultrasonic diagnostic imaging apparatus. Other reduction curves may be shown.

  The description in the embodiment of the present invention is an example of the ultrasonic diagnostic imaging apparatus according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of each functional unit constituting the ultrasonic diagnostic imaging apparatus can be appropriately changed without departing from the characteristics of the present invention.

S Ultrasonic diagnostic imaging apparatus 2, 200 Ultrasonic probe 2a Transducer 12 Transmitter 13 Receiving unit 14 Image generating unit 15 Memory unit 17 Display unit 21 Back layer 21a Backing material 21b Back reflecting material 22 Piezoelectric material 23 Acoustic matching layer 23a Bottom layer 23b Middle layer 23c Top layer 24 Protective layer 25 Acoustic lens P1 Start point P2 End point

Claims (7)

A piezoelectric material that transmits and receives ultrasonic waves;
An acoustic lens provided to converge the ultrasonic wave transmitted from the piezoelectric material to the transmission target of the ultrasonic wave;
An acoustic matching layer provided to be positioned between the piezoelectric material and the acoustic lens;
A back layer provided on the opposite side of the acoustic matching layer with respect to the piezoelectric material,
Starting from any position in the stacking direction of the member having the largest acoustic impedance existing on the back layer side than the interface between the piezoelectric material and the acoustic matching layer, and the interface between the acoustic lens and the acoustic matching layer The ultrasonic probe is characterized in that the acoustic impedance of the acoustic matching layer is set so that the acoustic impedance gradually decreases from the acoustic impedance at the start point to the acoustic impedance at the end point, with the position of.   The ultrasonic probe according to claim 1, wherein the start point is located on the opposite surface of a member having the largest acoustic impedance.   The ultrasonic probe according to claim 1, wherein the back layer includes a back reflecting material having higher acoustic impedance than the piezoelectric material.   4. The ultrasonic probe according to claim 1, wherein an acoustic impedance decreases exponentially from an acoustic impedance at the start point to an acoustic impedance at the end point. 5. The acoustic matching layer is composed of a plurality of layers each having different acoustic impedances,
5. The thickness of each of the plurality of layers is less than ¼ wavelength in a wavelength unit corresponding to the sound speed of each layer and the center frequency of the ultrasonic wave. The described ultrasonic probe. The acoustic matching layer is composed of a plurality of layers each having different acoustic impedances,
The ultrasonic probe according to any one of claims 1 to 5, wherein each of the plurality of layers is laminated by application of a material constituting each layer. An ultrasonic probe that outputs a transmission ultrasonic wave toward a subject by a drive signal and outputs a reception signal by receiving a reflected ultrasonic wave from the subject; and
A transmitter for generating the drive signal for driving the ultrasonic probe;
An image generation unit that generates ultrasonic image data for displaying an ultrasonic image based on the reception signal output by the ultrasonic probe;
In an ultrasonic diagnostic imaging apparatus comprising:
The ultrasonic diagnostic imaging apparatus according to claim 1, wherein the ultrasonic probe is the ultrasonic probe according to claim 1.

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