JP3249247B2 - Ultrasound diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus and, more particularly, to an ultrasonic diagnostic apparatus having a function of displaying a tomographic image of a human body and a function of displaying blood flow information using the Doppler effect.

[0002]

2. Description of the Related Art An ultrasonic probe used in a medical diagnostic apparatus uses a piezoelectric element (vibrator) as an exchange element between ultrasonic waves and electric signals. The electromechanical coupling coefficient, which is a material constant of the piezoelectric ceramic used for the piezoelectric element, is one of the important parameters that determine the characteristics of the ultrasonic probe, and the larger the value, the more desirable. The electromechanical coupling coefficient has different values in various vibration modes of a vibrator having directionality, and the vibration mode is determined by the polarization direction and the vibrator shape. A general medical ultrasonic probe has a configuration called an array probe in which a large number of transducers are arranged, and the shape of each transducer is excited in a vibration mode having the electromechanical coupling coefficient k ₃₃ ′.

At present, the highest value of k ₃₃ ′ is 70% in a piezoelectric ceramic material developed and put to practical use. An ultrasonic probe is formed by forming a back load material (backing material) on the back surface of the vibrator and an acoustic matching layer on the ultrasonic radiation surface. The probe characteristics vary depending on the structure of each of the members, their characteristics, and the like.

[0004] One of the probe characteristics is a fractional bandwidth obtained by taking the ratio of the width of the occupied frequency band of transmission / reception sensitivity to the center frequency thereof. Sensitivity and bandwidth are in opposition, and the optimized bandwidth of the probe is 7
It is about 0%. The nominal frequency of the ultrasonic probe is represented by the center frequency of the fractional band. In general, a probe having a higher frequency improves the resolution of the tomographic image and obtains an image with higher resolution. However, since the biological attenuation increases as the frequency increases, it becomes difficult to obtain a deep image. The tomographic image is driven by a pulse adjusted to the center frequency, but the blood flow information uses a low-frequency region where the influence of biological attenuation is small because a weak reflected signal from blood is used. A burst signal is used for the drive signal, and the wave number is appropriately selected from 1 to a long wave that can be called a continuous wave depending on the purpose.

For example, when the specific bandwidth of an ultrasonic probe having a center frequency of 5 MHz is 70%, the frequency used for Doppler becomes 3.5 MHz or more, and only blood flow information in an extremely shallow region can be obtained. For this reason, two types of probes are selectively used, such as using a probe having a lower nominal frequency, which is inferior in resolution of a tomographic image, to obtain blood flow information, and using a probe having a higher frequency to obtain a tomographic image having a high resolution. That was being done. However, properly using such two types of probes causes a loss of diagnostic time.

In view of the above, the present applicant has disclosed an ultrasonic probe having a laminated structure of a vibrator and representing two frequency bands having a frequency ratio of about twice as disclosed in Japanese Patent Application Laid-Open Nos. 63-173954 and 4-1992. No. 211599 has already been filed. Such an ultrasonic probe makes it possible to obtain a high-resolution tomographic image in a high-frequency band and a high-sensitivity Doppler image in a low-frequency band. However, in order to utilize two frequency bands with one vibrator, each frequency bandwidth has the same center frequency, that is, 50 to 50 times compared to a conventional probe used in a single frequency band.
70% reduction. In the tomographic image, the higher the frequency, the higher the resolution, but the higher the frequency, the higher the attenuation due to the biological attenuation, so that it is difficult to obtain a signal from a deep region, and the depth of field becomes shallow. Therefore, when the frequency bandwidth becomes shallower, the lowest frequency in the band becomes higher, and the depth of field becomes shallower as compared with a wide bandwidth, so that a deep region cannot be observed. In this way, the probe having two frequency bands can achieve a Doppler signal more than twice as high in sensitivity as the conventional probe having the same center frequency of the tomographic image, but the tomographic image has an area with a deep field of view. It is limited to probes that cannot be observed and target relatively shallow regions.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic diagnostic apparatus provided with an oscillator having a frequency band for Doppler information at a lower frequency lower than the center frequency of a frequency band used for tomographic images. It is something to offer.

[0008]

SUMMARY OF THE INVENTION An ultrasonic diagnostic apparatus according to the present invention comprises an oscillator and has a function of displaying a tomographic image of a human body and a function of displaying blood flow information using the Doppler effect. In the diagnostic device, the vibrator has a structure in which a piezoelectric body composed of a solid solution single crystal of lead zinc niobate-lead titanate is laminated, and an even-order harmonic having a frequency ratio of 2 or almost 2 is generated. It is characterized by being excited.

As the solid solution single crystal of lead zinc niobate-lead titanate, it is desirable to use one having a composition in which the molar fraction of lead titanate is 20% or less. By using such a solid solution-based single crystal piezoelectric body, the speed of sound can be reduced by 20% or more as compared with a piezoelectric body made of PZT ceramic, so that an ultrasonic probe with higher sensitivity can be obtained. Becomes possible.

In particular, the composition formula Pb _A [(Zn _1/3 Nb)
_{2/3) 1-x Ti x)} ] B O 3 ( here, x is 0.05 ≦
x ≦ 0.20, stoichiometric ratio A / B is 0.98 ≦ A / B <
It is preferable to use a solid solution single crystal of lead zinc niobate-lead titanate having a composition represented by 1.00). The reason for defining x in the above composition formula is as follows. When the value x is less than 0.05, the Curie temperature of the solid solution single crystal is low, and there is a possibility that depolarization may occur when soldering a flexible printed wiring board or an earth electrode plate or when cutting the solid solution single crystal. On the other hand, x is 0.2
If it exceeds 0, not only a large electromechanical coupling coefficient cannot be obtained, but also the dielectric constant is lowered, and it may be difficult to match the acoustic impedance of the transmitting and receiving circuit. More preferably, x is 0.06 to 1.2. If the ratio A / B of the composition formula deviates from the above range, the reliability of the obtained ultrasonic probe at the time of actual operation may be reduced.

[0011]

According to the present invention, the vibrator has a structure in which a piezoelectric material is laminated, so that even-order harmonics are disclosed as disclosed in JP-A-63-173954 and JP-A-4-212599. By using the fundamental frequency and the second harmonic, it is possible to realize an ultrasonic probe having two frequency bands whose frequency ratio is doubled or almost doubled. As a result, the frequency for Doppler information can be set lower by using the higher harmonic side for tomographic images and the lower frequency side for Doppler information. In the vibrator in which such piezoelectric members are stacked, the frequency ratio is reduced by forming the piezoelectric members from a solid solution single crystal of lead zinc niobate-lead titanate having an electromechanical coupling coefficient k ₃₃ ′ of about 83%. Can be further expanded. Further, since the ultrasonic probe including the vibrator in which the piezoelectric body made of the solid solution single crystal is laminated has a wider frequency bandwidth on the high frequency side than the conventional probe, the S / N of Doppler information is further improved and the The depth of field of the image is also increased, and the diagnosis area can be expanded.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. EXAMPLES First, PbO, ZnO, Nb ₂ O ₅ , T
After correcting the purity of these using iO ₂ , zinc niobate (PZN) and lead titanate (PT) were weighed so as to have a molar ratio of 91: 9, and the same amount of P was used as a flux.
bO was added. Pure water was added to this powder and mixed for 1 hour in a ball mill containing ZrO ₂ balls. After removing the water content of the obtained mixture, the mixture was sufficiently pulverized by a raikai machine, further placed in a rubber-type container, and subjected to rubber press at a pressure of 2 ton / cm ² . Solid 6 removed from rubber mold
00g was placed in a platinum container having a diameter of 50 mm and a capacity of 250 cc, and was heated to a temperature of 1250 ° C. in 5 hours and dissolved.
After slowly cooling to 800 ° C. at a rate of 0.8 ° C./hr, it was cooled to room temperature. Thereafter, nitric acid at a concentration of 20% was added to the platinum container, and the mixture was boiled for 8 hours to take out a solid solution single crystal. When a part of the single crystal was pulverized and subjected to X-ray diffraction, it was confirmed that the single crystal had a good crystal structure. Further, the (100) plane was taken out of the single crystal using a Laue camera, and cut with a cutter perpendicular to this plane. The crystal after cutting was attached to a platinum rod as a seed crystal.

Next, PbO, ZnO, Nb ₂ O ₅ , T
After correcting the purity of iO ₂ , zinc niobate (PZN) and lead titanate (PT) were weighed so as to have a molar ratio of 91: 9, and the flux was further PZN-PT: PbO = 25.
Molar%: 75 mol% was added and mixed with a ball mill. After removing the water content of the obtained mixture, the mixture was sufficiently pulverized by a raikai machine, further placed in a rubber-type container, and subjected to rubber press at a pressure of 2 ton / cm ² . The solid material removed from the rubber mold was placed in a platinum container having a diameter of 50 mm and a capacity of 250 cc, and the temperature was raised to 970 ° C. to completely dissolve the solid material. A single crystal was grown by immersing the seed crystal prepared by the above-described method in the melt and pulling the platinum rod with the seed crystal attached at a speed of 60 rpm and a pulling speed of 0.1 mm / hr. .

Next, the grown crystal was taken out of the (100) plane with a Laue camera and cut out perpendicular to this plane with a cutter. Subsequently, the cut surface was polished with a # 2000 abrasive until the thickness became 220 μm. Ti / Au electrodes were formed on both sides of the polished crystal piece (first piezoelectric body) by sputtering. Further, a crystal piece (second piezoelectric body) having substantially the same thickness as the piezoelectric body and having no electrode formed thereon was bonded to one electrode of the first piezoelectric body with an epoxy-based adhesive. At this time, the adhesive is selected such that the adhesive layer becomes thin, and the adhesive is applied by pressing. FIG. 1 shows a vibrator manufactured by such a method. In FIG. 1, 1 is a first piezoelectric body, 2 and 3 are electrodes formed on both surfaces of the first piezoelectric body 1, respectively.
Is a second piezoelectric member bonded to the electrode 3, and 5 is a lead drawn out from the electrode 2, 3. By applying a drive signal between the leads 5, 5, it is possible to transmit and receive ultrasonic signals in two frequency bands.

An array probe was manufactured using the transducer shown in FIG. That is, the second piezoelectric body on which the electrodes were not formed was bonded to a backing material using an epoxy adhesive. An acoustic matching layer was formed on an electrode on the surface side of the first piezoelectric body. The thickness of the acoustic matching layer was set such that the width of the frequency band on the high frequency side was widened. Thereafter, the acoustic probe was cut from the acoustic matching layer to the second piezoelectric body at a predetermined pitch by a dicing saw, thereby producing an array probe including a plurality of vibrators having strip-shaped laminated piezoelectric bodies.

As a comparative example, a piezoelectric ceramic (T-96, k ₃₃ ′ = 6, manufactured by Toshiba Ceramics Co., Ltd.) was used as the piezoelectric body.
8%), and an array probe having a similar structure was prepared.

The frequency characteristics of the array probes obtained in Examples and Comparative Examples were measured. As a result, the probe of the example had the characteristic diagram shown in FIG. 2, and the probe of the comparative example had the characteristic diagram shown in FIG.

[0018] PZN k ₃₃ 'of 83%, as shown in FIG. 2
-The array probe of the embodiment having the piezoelectric body made of a PT solid solution single crystal has a peak frequency fL on the low frequency side of 1.9M.
Hz, the center frequency fH of -6 dB on the high frequency side is 6.6M
Hz, -6 dB ratio band (Δf / fH) is 35%,
As shown in FIG. 3, the array probe of the comparative example having a piezoelectric body made of a piezoelectric ceramic with k ₃₃ ′ of 68% has a peak frequency fL on the low frequency side of 2.5 MHz and -6d on the high frequency side.
The center frequency fH of B is 6.6 MHz, and the -6 dB ratio band (Δf / fH) is 29%. In addition, the overall amplitude level of the probe of the example is several d higher than that of the probe of the comparative example.
B has increased, and the S / N has improved.

Therefore, the probe of the embodiment has the same center frequency on the high frequency side as the probe of the comparative example, but the peak frequency fL on the low frequency side can be reduced from 2.5 MHz (comparative example) to 1.9 MHZ. Moreover, the S / N of the Doppler signal
Can be improved, and the fractional band on the high frequency side can be increased, so that the depth of field of the tomographic image can be made deeper than the probe of the comparative example.

Further, by making the acoustic matching layer from a single layer to a multilayer, it is possible to realize an array probe in which the specific band on the high frequency side is further increased. The ultrasonic probe according to the present invention is not limited to the structure shown in FIG. For example, as shown in FIG. 4, a piezoelectric body 1 'having electrodes 2' and 3 'as well as a piezoelectric body 1 having electrodes 2 and 3 on both surfaces.
And a vibrator having a structure in which the polarization directions (arrow directions in the drawing) face each other with a thin epoxy-based adhesive may be used. Leads 5, 5 are connected to the electrodes 2, 3 'located on the outside, respectively, and a drive signal is applied between the leads 5, 5 to enable transmission and reception of ultrasonic signals in two frequency bands. However, the internal electrodes 3, 2 'in the resonator having the laminated structure shown in FIG. 4 are not used for driving. If the vibrator having such a configuration has the same center frequency on the high frequency side as the vibrator having the piezoelectric body made of the conventional piezoelectric ceramic, the peak frequency on the low frequency side is reduced as compared with the conventional vibrator. As a result, the fractional band on the high frequency side can be increased.

In the vibrator shown in FIG. 4 described above, two piezoelectric bodies having electrodes on both sides are bonded with a thin epoxy-based adhesive so that the polarization directions (arrow directions in the drawing) are opposite to each other. It can be produced without an adhesive layer by another method utilizing the characteristics of the solid solution single crystal. That is, it is known that a domain-inverted layer can be formed by heat-treating a lithium niobate single crystal at a temperature close to the Curie point, and the thickness of the inversion layer can be controlled by the heat treatment. The PZN-PT solid solution single crystal used in the present invention also has a 170 Curie point close to the Curie point.
By performing a heat treatment at about 180 ° C., an inversion layer can be formed. By utilizing such a phenomenon, as shown in FIG. 5A, electrodes 12 and 13 are respectively formed on both surfaces of a piezoelectric body 11 made of a PZN-PT solid solution single crystal, and then heat-treated under predetermined conditions. As shown in FIG. 5B, the piezoelectric bodies 11 and 11 'whose polarization directions (arrow directions in the figure) are opposed to each other.
Can be obtained. FIG.
14B is a lead. The vibrator having the structure shown in FIG. 5B has an ideal vibration since no electrode or adhesive layer is interposed at the facing interface, and is cut into strips by the dicing saw as described above. In this case, it is possible to realize an array probe with less variation in characteristics between array elements and less deterioration of characteristics than the bonding method. Therefore, the polarization inversion method is effective for manufacturing an ultrasonic probe having two frequency bands as in the present invention.

[0022]

As described above, according to the present invention, since the peak frequency on the low frequency side can be reduced and the fractional band on the high frequency side can be increased, the ultrasonic frequency for capturing blood flow information is set to a lower value. Attenuation of extremely weak reflected signals from blood cells by the living body can be reduced, a blood flow signal with a high S / N ratio can be obtained, and a deep region can be observed by widening the tomographic image. It is possible to provide an ultrasonic diagnostic apparatus having remarkable effects such as a remarkable improvement.

[Brief description of the drawings]

FIG. 1 is a front view showing a transducer used for an ultrasonic probe according to the present invention.

FIG. 2 is a diagram showing frequency characteristics of the ultrasonic probe according to the embodiment of the present invention.

FIG. 3 is a diagram showing frequency characteristics of an ultrasonic probe of a comparative example.

FIG. 4 is a front view of a vibrator showing another example of the present invention.

FIG. 5 is a front view showing a step of manufacturing a vibrator by the polarization inversion method in the present invention.

[Explanation of symbols]

1, 1 ', 4, 11, 11' ... piezoelectric body, 2, 3, 2 ',
3 ', 12, 13 ... electrodes.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaru Kawachi 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Takeshi Kobayashi Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa No. 1 Toshiba R & D Center Co., Ltd. (72) Inventor Yohachi Yamashita 70, Yanagicho, Kochi-ku, Kawasaki-shi, Kanagawa Prefecture In-house Toshiba Yanagimachi Plant (56) References JP-A-56-161035 (JP, A) JP-A-62-155000 (JP, A) JP-A-2-294199 (JP, A) JP-A-56-115582 (JP, A) JP-A-56-115586 (JP, A) (58) Int.Cl. ⁷ , DB name) A61B 8/00-8/15 H04R 17/00 330 G01N 29/00-29/28

Claims (1)

(57) [Claims] 1. An ultrasonic diagnostic apparatus comprising an ultrasonic probe having two frequency bands and having a function of displaying a tomographic image of a human body and a function of displaying blood flow information using a Doppler effect. An ultrasonic diagnostic apparatus, wherein the transducer constituting the probe has a piezoelectric body made of a solid solution single crystal of lead zinc niobate-lead titanate.