JP2011050471A - Ultrasonic probe and ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a transducer made of piezoelectric single crystal with low-voltage bipolar pulses without depolarization, and to achieve high penetration. <P>SOLUTION: A plurality of transducers 15 made of piezoelectric single crystal are arranged within a distal end of the ultrasonic probe 11, and preamplifiers 23 are connected to the respective transducers 15. The respective transducers 15 are driven with low-voltage bipolar pulses fed from a pulser 34 of an ultrasonic observation device 12 and generate ultrasonic waves without depolarization. Echo signals outputted from the transducers 15 upon receipt of reflection waves are amplified by the preamplifiers 23 to be transmitted to the ultrasonic observing device 12. As a result, penetration is improved without being affected by the electric capacity of a cable 29. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic probe including a transducer that transmits and receives ultrasonic waves, and an ultrasonic diagnostic apparatus including an ultrasonic observation device that causes an ultrasonic probe to transmit and receive ultrasonic waves.

  An ultrasonic diagnostic apparatus is known as a medical device using an ultrasonic pulse reflection method that receives an ultrasonic reflected wave transmitted to a subject and converts the intensity of the reflected wave into luminance to generate an image. . The ultrasonic diagnostic apparatus is composed of an ultrasonic probe having a transducer in the tip, and an ultrasonic observer that generates ultrasonic waves in the transducer and images the ultrasonic waves received by the transducer.

  The ultrasonic observer inputs a drive signal to the transducer of the ultrasonic probe connected via a cable. The vibrator generates ultrasonic waves based on the drive signal input from the ultrasonic observer. The ultrasonic wave generated by the vibrator is transmitted toward the body of the subject, reflected at the boundary of acoustic impedance, and the reflected wave is received by the vibrator. The vibrator generates an echo signal corresponding to the strength of the received reflected wave. The ultrasonic observer generates an image by converting the strength of the echo signal into luminance.

  The vibrator is made of, for example, a piezoelectric ceramic or the like in which a ferroelectric material such as lead zirconate titanate (hereinafter referred to as PZT) is subjected to polarization treatment to impart piezoelectricity. The polarization process is a process in which a high electric field is applied to the ferroelectric material to align the direction of spontaneous polarization and to give residual polarization. The PZT after the polarization process has hysteresis characteristics as shown in FIG. Yes. When an electric field in the direction opposite to the polarization direction of the ferroelectric is applied with a certain magnitude or more, the spontaneous polarization is weakened (referred to as depolarization or depolarization), and a reverse electric field greater than the coercive electric field Ec is applied. It is completely depolarized, spontaneous polarization disappears, and displacement ability and reception ability are lost. Therefore, the voltage of the drive signal supplied to the vibrator from the ultrasonic observer is set so that the electric field applied to the vibrator does not exceed the coercive electric field in the direction opposite to the spontaneous polarization of the vibrator.

  Ultrasonic diagnostic devices are desired to have high resolution and high sensitivity because of the demand for reliable diagnosis of deeper parts of the body with high-definition images. An invention has been made. For example, in order to obtain high resolution, an ultrasonic diagnostic apparatus using a bipolar pulse (see FIG. 2) instead of a general unipolar pulse (see FIG. 6) as a driving signal for a vibrator is known (for example, Patent Document 1).

  The bipolar pulse is applied so that the vibration of the vibrator caused by the first pulse is canceled by the next pulse having the opposite polarity. For this reason, the ultrasonic wave based on the bipolar pulse has an oscillation time shorter than that of the unipolar pulse, and the redundant portion in the case of the unipolar pulse is cut. An ultrasonic wave based on a bipolar pulse has a wider band than that of a unipolar when a spectrum diagram is drawn through frequency analysis. Therefore, the resolution of the image can be improved.

  In addition, in order to improve sensitivity and obtain high penetration (also called depth of penetration), an ultrasonic transducer using a piezoelectric single crystal with a high electromechanical coupling coefficient and excellent ultrasonic wave and reflected wave transmission / reception capability is used. An ultrasonic diagnostic apparatus is also known (see, for example, Patent Document 2).

JP 2000-005180 A JP 2000-014672 A

  In order to achieve both high resolution and high sensitivity, it is considered to drive a vibrator made of a piezoelectric single crystal with a bipolar pulse. However, as shown in FIG. 3, the piezoelectric single crystal has a narrow coercive electric field Ec, -Ec range compared to the piezoelectric ceramics such as PZT, so that a depolarization occurs more in the case of a bipolar pulse having a wide voltage range. It becomes easy to do. In order to prevent depolarization, the voltage of the drive signal must be lowered so as not to exceed the coercive electric field, but the power of the ultrasonic wave transmitted from the vibrator becomes weak and the penetration is lowered.

  An object of the present invention is to drive a vibrator made of a piezoelectric single crystal by a low-voltage bipolar pulse without depolarization, thereby obtaining high penetration.

  The ultrasonic probe of the present invention is a vibrator made of a piezoelectric single crystal, generates ultrasonic waves by bipolar pulses supplied from a transmission circuit of an ultrasonic observation device, receives reflected waves, and outputs echo signals. And an amplifying means that is directly connected to the vibrator without passing through the capacitive transmission line and amplifies the echo signal.

The piezoelectric single crystal is a solid solution type piezoelectric single crystal containing at least lead titanate and represented by Pb [(B1, B2) _1-X Ti _X ] O ₃ , wherein X is 0.05-0. .55, B1 is any one of Zn, Mg, Ni, Sc, In, and Yb, and B2 is either Nb or Ta.

  The used electric field strength of the vibrator is preferably 250 V / mm or less.

  An ultrasonic diagnostic apparatus according to the present invention includes an ultrasonic probe described above, a transmission circuit that outputs a bipolar pulse to the ultrasonic probe, and a reception circuit that receives an echo signal amplified by the ultrasonic probe. And.

  According to the present invention, the vibrator made of a piezoelectric single crystal is driven with a bipolar pulse, and the amplification means and the vibrator are directly connected without using the capacitive transmission line. The attenuation of the signal is reduced, and the penetration can be improved even when the vibrator is driven at a low voltage so that depolarization does not occur in the vibrator.

  Since various types of piezoelectric single crystals including lead titanate can be used, an optimal piezoelectric single crystal can be selected in consideration of the use and cost of the ultrasonic probe.

  In addition, since the electric field strength used is defined in consideration of the coercive electric field of the piezoelectric single crystal, no depolarization occurs in the vibrator.

It is a block diagram which shows the structure of the ultrasonic diagnosing device of this invention. It is a graph which shows an example of a bipolar pulse. It is a graph which shows the hysteresis characteristic of a piezoelectric material single crystal. It is a table | surface which shows the use frequency of the ultrasonic wave according to a diagnostic region. It is a graph which shows the hysteresis characteristic of PZT. It is a graph which shows an example of a unipolar pulse.

  Hereinafter, embodiments of an ultrasonic diagnostic apparatus embodying the present invention will be described. As shown in FIG. 1, the ultrasonic diagnostic apparatus 10 includes an ultrasonic probe 11 and an ultrasonic observer 12. The ultrasonic probe 11 is, for example, an external type whose tip is in contact with the body surface of the subject, transmits ultrasonic waves from the body surface of the subject into the body, and has a boundary of acoustic impedance. The reflected wave reflected at is received. The ultrasonic observation device 12 causes the ultrasonic probe 11 to transmit an ultrasonic wave, and the ultrasonic probe 11 receives the reflected wave and images the echo signal output.

  A transducer array 14 is disposed at the tip of the ultrasonic probe 11. The transducer array 14 employs, for example, a convex electronic scanning method in which a plurality of transducers 15 are arranged in a one-dimensional or two-dimensional array on a support formed in a convex shape.

  The vibrator 15 is made of a piezoelectric single crystal that has been subjected to polarization processing to impart piezoelectricity, generates ultrasonic waves based on the drive signal supplied from the ultrasonic observation device 12, receives reflected waves, and receives echo signals. Is output. A piezoelectric single crystal has an extremely high electromechanical coupling coefficient compared to PZT, and is excellent in ultrasonic wave transmission / reception capability.

The piezoelectric single crystal used for the vibrator 15 is a solid solution type piezoelectric single crystal containing at least lead titanate represented by the general formula of Pb [(B1, B2) _1-X Ti _X ] O _3. It is used. X in the general formula is preferably 0.05 to 0.55, B1 is any one of Zn, Mg, Ni, Sc, In, and Yb, and B2 is either Nb or Ta. It is preferable that

As a solid solution type piezoelectric single crystal corresponding to the above conditions, for example, lead zinc niobate-lead titanate (Pb [(Zn _1/3 Nb _2/3 ) Ti] O ₃ ) (PZNT), or lead magnesium niobate A binary single crystal such as lead titanate (Pb [(Mg _1/3 Nb _2/3 ) Ti] O ₃ ) (PMNT) can be used. Note that the reason why X is defined in the range of 0.05 to 0.55 in the above general formula is to maintain the Curie temperature and the electromechanical coupling coefficient of the piezoelectric single crystal above a certain level. Alternatively, a single crystal of PZT may be used.

  The piezoelectric single crystal used for the vibrator 15 is preferably produced by, for example, a solid phase epitaxy method (SPE method). The solid phase epitaxy method is a method in which an amorphous layer formed on a substrate by ion implantation or vapor deposition is heat-treated at a relatively low temperature, and an epitaxial thin film is grown in a solid phase. Can be produced. In addition, the piezoelectric single crystal manufactured using the solid phase epitaxy method has a coercive electric field after polarization processing lower than that manufactured by other methods, but in this embodiment, the vibrator 15 is depolarized. Since it is driven at a low voltage that does not occur, there is no problem.

  The vibrator 15 sandwiches two opposing surfaces of the piezoelectric single crystal with a pair of electrodes 16. One electrode 16 is a common electrode of each vibrator 15 and is connected to the ground. A first common transmission line 17 is connected to the other electrode 16. The first common transmission path 17 transmits the drive signal supplied from the ultrasonic observer 12 and the echo signal generated by the transducer 15.

  One end of the first switch 19 is connected to the subsequent stage of the first common transmission line 17. First and second branch transmission lines 20 and 21 are connected to the other end of the first switch 19 which is branched into two branches. The first switch 19 selectively switches a branch transmission line connected to the first common transmission line 17 among the first and second branch transmission lines 20 and 21.

  The first and second branch transmission lines 20 and 21 transmit drive signals and echo signals, respectively. A preamplifier 23 for amplifying an echo signal is inserted in the second branch transmission line 21. The preamplifier 23 is composed of, for example, a transistor constituting an emitter follower circuit.

  The first and second branch transmission lines 20 and 21 are respectively connected to the two branch ends of the second switch 25 at the subsequent stage of the preamplifier 23. The other end of the second switch 25 is connected to a second common transmission path 26 that transmits a drive signal and an echo signal. In conjunction with the first switch 19, the second switch 25 selectively switches the branch transmission line connected to the second common transmission line 26 among the first and second branch transmission lines 20 and 21.

  The second common transmission line 26 becomes a shield wire 28 from the middle, and a plurality of wires are bundled to form a cable 29. The cable 29 has a length of about 1 to 2 m in a general extracorporeal type, and about 3.5 m in an ultrasonic endoscope in which a vibrator is built in the distal end of the endoscope. A connector portion (not shown) is provided at the rear end of the cable 29. By inserting this connector portion into a socket portion (not shown) of the ultrasonic observation device 12, the ultrasonic probe 11 and the ultrasonic wave are connected. The observation device 12 is electrically connected.

  The first common transmission line 17 and the second polarization transmission line 21 are extremely short as compared with the cable 29 having a length of several meters, and the amount of voltage drop due to the electric capacity and the line resistance is very small. Therefore, the preamplifier 23 is almost in the same state as being directly connected to the vibrator 15 without passing through the transmission line.

  The socket part of the ultrasonic observation device 12 is connected to a multiplexer (hereinafter referred to as MUX) 31. The MUX 31 selectively switches the transducer 15 to be driven from the transducer array 14.

  The MUX 31 is connected to one end of the third switch 33. A pulser 34 that outputs a drive signal for generating an ultrasonic wave and a receiver 35 that receives an echo signal are connected to the two branch ends of the third switch 33, respectively. The third switch 33 selectively operates a branch transmission line connected to the second common transmission line 26 among the branch transmission lines connected to the pulser 34 and the receiver 35 in conjunction with the first switch 19 and the second switch 25. Switch to.

  The first to third switches 19, 25, and 33 are electronic switches such as circulators that transmit power in a fixed direction without the need to input a switching control signal from the outside. When irradiating ultrasonic waves from the transducer 15 to the site to be observed, the first to third switches 19, 25 and 33 are connected to the first branch transmission path 20 and the pulser 34 as shown in the figure, and When receiving the reflected wave, the first to third switches 19, 25, 33 are connected to the second branch transmission line 21 and the receiver 35.

  The first to third switches 19, 25, 33 are actually connected to both the first and second branch transmission lines 20, 21, the pulsar 34, and the transmission line connected to the receiver 35. Starting from the second common transmission path 26 through the first branch transmission path 20 and the first common transmission path 17, the direction in which the drive signal is transmitted to the vibrator 15 and the first common transmission from the vibrator 15 as the starting point. Electric power is transmitted only in two predetermined directions of transmitting an echo signal from the path 17 to the receiver 35 through the second branch transmission path 21 and the second common transmission path 26.

  As shown in FIG. 2, the pulser 34 generates a bipolar bipolar pulse as a drive signal and applies it to the vibrator 15. Since the bipolar pulse is applied so that the vibration of the vibrator 15 caused by the first pulse is canceled by the next pulse having the opposite polarity, the ultrasonic wave based on the bipolar pulse has an oscillation time shorter than that of the unipolar pulse. The redundant part in the case of a pulse is cut. Ultrasonic waves based on bipolar pulses have a wider band than that of unipolar when a spectrum diagram is drawn through frequency analysis, so that the resolution of the image can be improved.

  As shown in FIG. 3, the vibrator 15 made of a piezoelectric single crystal has a property that depolarization is likely to occur because the range of the coercive electric fields Ec and −Ec is narrower than that of PZT shown in FIG. . For example, the coercive electric field | Ec | of the piezoelectric single crystal is 350 V / mm, and the coercive electric field | Ec | of PZT is 1 kV / mm. Therefore, the bipolar pulse output from the pulsar 34 has a lower voltage than that of a conventional PZT vibrator so that depolarization does not occur in the vibrator 15.

  In the present embodiment, for example, 256 transducers 15 and 48 transmission / reception circuits including the third switch 33, the pulser 34, and the receiver 35 are provided. The MUX 31 selects a transmission path connected to the pulsar 34 so that the adjacent 48 transducers 15 among the 256 transducers 15 are simultaneously driven as one block, and 1 of the drive signal and the echo signal is selected. One to several vibrators 15 to be driven are shifted every transmission / reception.

  A timing controller 37 is connected to the pulser 34 and a memory 38 is connected to the receiver 35. The timing controller 37 outputs a timing signal for generating a drive signal to the pulser 34 under the control of the CPU 39. The pulsar 34 transmits a drive signal to the vibrator 15 based on the timing signal. The memory 38 temporarily stores the echo signal received by the receiver 35.

  A phase matching calculation unit 40 is connected to the memory 38. Under the control of the CPU 39, the phase matching calculation unit 40 adds a delay corresponding to the time difference to each echo signal from the memory 38 and then adds each echo signal.

  The added echo signal output from the phase matching calculation unit 40 is input to the display image calculation unit 42 after detection and log compression. The display image calculation unit 42 performs various types of image processing on the signal from the phase matching calculation unit 40 and then converts the signal into a television signal scanning method (NTSC method). The signal converted into the NTSC system by the display image calculation unit 42 is converted into an analog signal and displayed on the monitor 43 as an ultrasonic image.

  Next, the operation of the above embodiment will be described. The tip of the ultrasonic probe 11 is brought into contact with the body surface of the subject. In the ultrasonic observation device 12, the second common transmission path 26 connected to the transducer 15 to be driven by the MUX 31 is selected under the control of the CPU 39, and a drive signal is generated from the pulser 34 by the timing signal from the timing controller 37. It is done.

  A drive signal composed of a bipolar pulse is transmitted to the vibrator 15 through the second common transmission path 26, the first branch transmission path 20, and the first common transmission path 17. The vibrator 15 is excited by a bipolar pulse, whereby ultrasonic waves are transmitted from the vibrator 15 toward the site to be observed.

  The ultrasonic wave transmitted to the site to be observed is reflected at the boundary of the acoustic impedance in the body of the subject. The transducer 15 receives the reflected wave and outputs an echo signal according to the intensity. The echo signal passes through the first common transmission path 17 and the second branch transmission path 21, is amplified by the preamplifier 23, and is received by the receiver 35 through the second common transmission path 26.

  The bipolar pulse of the drive signal has a lower voltage than that supplied to a conventional vibrator made of PZT in order to prevent depolarization of the vibrator 15. Therefore, the ultrasonic wave transmitted from the transducer 15 is weaker than the conventional diagnostic apparatus using the transducer made of PZT, and the echo signal is also small. However, in this embodiment, since the echo signal immediately after being output from the transducer 15 is amplified by the preamplifier 23 directly connected to the transducer 15, the sensitivity decreases correspondingly even if the transducer 15 is driven at a low voltage. Can be compensated by reducing the attenuation of the echo signal, and the penetration can be improved.

  If the preamplifier 23 is provided in the ultrasonic observer 12 and the echo signal is amplified after being transmitted to the ultrasonic observer 12 via the cable 29, the echo signal is attenuated by the electric capacity of the cable 29. The rate must be increased. When the signal amplification factor is increased, the noise also increases. Therefore, it is most effective to amplify the echo signal by the preamplifier 23 directly connected to the transducer 15 as in this embodiment.

  When the transmission / reception of the drive signal and the echo signal is completed once, the transducer 15 driven by the MUX 31 is switched, the same processing as described above is performed, and ultrasonic waves are scanned on the site to be observed.

  The echo signal received by the receiver 35 is temporarily stored in the memory 38. The echo signals stored in the memory 38 are added with a delay corresponding to the time difference by the phase matching calculation unit 40 under the control of the CPU 39. The echo signal added by the phase matching calculation unit 40 is detected and Log-compressed, converted to the NTSC system by the display image calculation unit 42, converted to an analog signal, and displayed on the monitor 43 as an ultrasonic image.

  As shown in FIG. 5, the frequency of the ultrasonic wave transmitted from the ultrasonic probe 11 to the subject differs depending on the diagnosis site. For example, in the diagnosis of the abdomen, 3.5 MHz ultrasonic waves are used, and the mammary gland or epidermis is Diagnosis uses 10 MHz ultrasound. Since the frequency is adjusted by the pulse width and repetition period of the bipolar pulse, the film thickness of the vibrator 15, etc., even if the voltage of the bipolar pulse is the same, the electric field strength applied to the vibrator 15 is the ultrasonic wave. The higher the frequency, the higher.

  For example, when the voltage of the bipolar pulse supplied to the vibrator 15 is 100 V, an electric field strength of 1000 V / mm is applied to the vibrator 15 in breast or epidermis diagnosis, and 660 V / mm is applied to the vibrator 15 in heart diagnosis. A field strength of mm is applied. In the diagnosis of the abdomen, there is no problem because the electric field strength applied to the transducer 15 is 300 V / mm. However, when diagnosing the mammary gland or the epidermis, the electric field strength applied to the transducer 15 is the coercive electric field | Ec | The voltage of the bipolar pulse must be set to be equal to or less than 350 V / mm.

  As shown at the bottom of the table in FIG. 5, if the voltage of the bipolar pulse is 25V, the electric field strength applied to the vibrator 15 at the time of diagnosis of the breast or heart is 250V / mm. Since the electric field strength is coercive electric field | Ec | = 350 V / mm or less of the piezoelectric single crystal, depolarization does not occur in the vibrator 15 and the electric field strength of the vibrator 15 made of the piezoelectric single crystal is used. As preferred.

  In the above embodiment, a binary single crystal is used as the piezoelectric single crystal. For example, lead indium niobate-lead magnesium niobate-lead titanate (PIMNT), scandium lead niobate-lead magnesium niobate-titanium. A ternary single crystal such as lead acid (PZMNT) may be used. In addition, although the solid phase epitaxy method is used for the production of the piezoelectric single crystal, the piezoelectric single crystal may be produced using another solid phase method, a gas phase method, or a liquid phase method.

  In the above embodiment, the external ultrasonic diagnostic apparatus using the ultrasonic pulse reflection method has been described as an example, but the present invention is also applicable to an ultrasonic diagnostic apparatus using the Doppler method and an internal ultrasonic diagnostic apparatus. . Further, the present invention can be applied to a mechanical scanning ultrasonic probe and a wireless probe that mechanically move one transducer instead of a transducer array including a plurality of transducers. Furthermore, even when the MUX, the pulser, and the receiver are built in the ultrasonic probe, the same effect as in the above embodiment can be obtained.

DESCRIPTION OF SYMBOLS 10 Ultrasonic diagnostic apparatus 11 Ultrasonic probe 12 Ultrasonic observer 15 Transducer 23 Preamplifier 29 Cable 34 Pulsar 35 Receiver

Claims (4)

A plurality of transducers that are composed of a piezoelectric single crystal, generate ultrasonic waves by bipolar pulses supplied from a transmission circuit of an ultrasonic observation device, receive reflected waves, and output echo signals;
An ultrasonic probe comprising: amplification means connected to the vibrator for amplifying the echo signal. The piezoelectric single crystal is a solid solution type piezoelectric single crystal containing at least lead titanate and represented by Pb [(B1, B2) _1-X Ti _X ] O ₃ , and the X is 0.05 to The B1 is 0.55, the B1 is any one of Zn, Mg, Ni, Sc, In, and Yb, and the B2 is either Nb or Ta. Ultrasonic probe.   The ultrasonic probe according to claim 1, wherein the electric field strength of the vibrator is 250 V / mm or less. The ultrasonic probe according to any one of claims 1 to 3,
An ultrasonic diagnostic apparatus comprising: a transmission circuit that outputs a bipolar pulse to the ultrasonic probe; and an ultrasonic observer having a reception circuit that receives an echo signal amplified by the ultrasonic probe.

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