JP2014094147A - Ultrasonic diagnostic device, and ultrasonic diagnostic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic diagnostic device which satisfies the need for improving a propagation direction resolution when a parametric ultrasonic signal is used.SOLUTION: An ultrasonic diagnostic device 101A comprises: a signal generating circuit 3 for generating ultrasonic waves; a sending ring-shaped piezoelectric vibrator 2; a receiving disc-shaped piezoelectric vibrator 7; a receiving circuit 9 for processing an ultrasonic wave signal received; a signal processing circuit 12 for eliminating the fundamental wave component of the ultrasonic wave signal received; a multiplication circuit 10 for taking a cross correlation between a reference signal generated by a reference signal generating circuit 11 and a signal outputted from the signal processing circuit 12; a position location sensor 30 for locating the position of an ultrasonic transducer 1 to generate a position location signal; and an image processing circuit 13 for generating an image signal by processing the position information data of the position location sensor 30 and the arithmetic result data of the multiplication circuit 10.

Description

  The present invention relates to an ultrasonic diagnostic apparatus and method, and more particularly to an ultrasonic diagnostic apparatus and method using parametric ultrasonic waves.

In recent years, the use of non-linear ultrasonic waves has become popular, and image forming technology using harmonics in particular has already been applied to medical image diagnostic apparatuses as harmonic imaging for echocardiographic diagnosis. A subharmonic signal, which is a kind of nonlinear ultrasound, is used as contrast ultrasound. The harmonic used for harmonic imaging is a signal having a frequency component of 2 · f ₀ or 3 · f ₀ with respect to the fundamental frequency f ₀ , and usually f ₀ is 1 MHz to 5 MHz. The subharmonic signal used for contrast-enhanced ultrasound has a frequency (1 / n) · f ₀ (n is an integer of 2 or more) of an integer of the fundamental frequency f ₀ , and usually f ₀ Is 1 to 10 MHz and n = 2.

  Since these harmonics and subharmonics are all non-linear signals, the signal level is about 20 dB lower than the fundamental wave. Although the signal level is so small that the side lobe involved in the contrast resolution is conspicuous, the attenuation beyond the focal point can be made smaller than that of the fundamental wave of the same frequency, so that the depth of the signal can be taken. In addition, harmonics and subharmonics are characterized by small fluctuations in sound pressure at short distances and are less prone to artifacts due to multiple reflections. Formation is possible.

On the other hand, parametric ultrasound, which is a kind of nonlinear ultrasound, has been put into practical use as a super-directional speaker (parametric speaker). In a parametric speaker, when two ultrasonic waves having a fundamental wave component having a frequency f _{1 and} a fundamental wave component having a frequency f ₂ are mixed and an ultrasonic signal modulated with an audio signal is transmitted into the air, the difference frequency | f ₁ − Parametric ultrasound with f ₂ | is generated and propagates. As the parametric ultrasonic wave propagates through the air, the voice signal portion of the modulated signal is demodulated and recognized as voice. Parametric ultrasonic waves have a smaller beam width of the ultrasonic beam than a fundamental wave having the same frequency, so that a super-directional speaker is realized.

  Patent Documents 1 to 3 describe techniques related to ultrasonic image processing.

JP-A-8-080300 JP 2003-116848 A US Patent Application Publication No. 2011/0160582

In Patent Document 1, a transmission unit that transmits an amplitude-modulated wave (or an ultrasonic wave having two frequency components) obtained by applying an amplitude modulation of a constant frequency to a center frequency, and an echo from a subject are received. An ultrasonic probe including a receiving unit, a signal processing unit for receiving an echo including at least a difference frequency component generated in the subject and obtaining an ultrasonic image, and a display unit for displaying an output of the signal processing unit Is described. In Patent Document 1, the upper limit of the transmission frequency is preferably about ½ of the transmission ultrasonic frequency f _0. For example, if the repetition frequency is 4 kHz and f ₀ is 2 MHz, the frequency band is 40 Hz. ~ 1MHz. Practically, the relationship between the transmission frequency and the frequency of the parametric ultrasonic signal is illustrated as being sufficient to observe an A mode (Amplitude Mode) image even at about 100 Hz to 500 kHz. However, what is required as an ultrasound image is a B-mode (Brightness Mode) image, and the resolution in the ultrasound propagation direction necessary for diagnosis is approximately 100 Hz to 500 kHz used in the ultrasound diagnostic apparatus described in Patent Document 1. There is a problem that a highly reliable ultrasonic diagnostic image cannot be obtained.

  Patent Document 1 discloses an ultrasonic probe that is divided into two concentric circles, transmits an ultrasonic wave using an inner portion as a transmitting portion, and receives an echo using an outer portion as a receiving portion. There is a description that the reception efficiency can be improved when it is used. Here, for example, consider the case where the frequency of the parametric reception signal is set to 100 kHz optimum for B-mode image formation and general PZT ceramics is used as a reception piezoelectric vibrator. In this case, the PZT ceramic requires a thickness of about 15 mm in order to respond to the 100 kHz frequency signal with high efficiency by the resonance response. Furthermore, the damping layer also requires a thickness of 15 mm or more, and there is a problem that it is not suitable for applications that require miniaturization such as an ultrasonic endoscope.

  In Patent Document 2, in an ultrasonic diagnostic apparatus that sequentially receives ultrasonic waves emitted from one or more ultrasonic transducers and displays them on a display device, the shape of the affected area cannot be clearly displayed, and the outline is blurred. A technique for improving the fact that only the obtained image is obtained is described. That is, the ultrasonic wave of the first frequency is irradiated toward the affected part of the human body, and the second ultrasonic transducer has the second frequency at a desired angle with respect to the irradiation direction from the first ultrasonic transducer. Irradiate with ultrasonic waves. And the reflected wave containing the 1st and 2nd frequency reflected from the affected part with the 1st ultrasonic transducer is received, The difference frequency signal, the sum frequency signal, and those harmonics or a partial frequency are piled up. Receive. These are displayed on one display device, and the position and contour of the affected area can be clearly displayed. However, since the difference frequency and the split frequency ultrasonic waves have a low frequency, there is a problem that the spatial resolution in the ultrasonic wave propagation direction is lowered. Furthermore, since the ultrasonic transmission / reception sensor is not integrated, there is a problem that it cannot be applied to normal extracorporeal echo diagnosis and ultrasonic endoscopic diagnosis.

  Patent Document 3 describes a technique for applying a wireless communication system to an ultrasonic diagnostic apparatus. This ultrasonic diagnostic apparatus is a wireless ultrasonic scanner including an ultrasonic sensor, a motor, an ultrasonic transceiver, a high-speed data sampling module, a motor controller, and a master control module. An ultrasonic reception signal acquired by the ultrasonic sensor is amplified by an ultrasonic transducer, converted into an RF signal by a high-speed data sampling module, and wirelessly transmitted to the master control module. The master control module sets the scanning mode and wirelessly transmits control signals and the like to the high-speed data sampling module. In addition, it is described that the high-speed data sampling module is a digital signal processing circuit including an A / D converter and the wireless communication interface is Bluetooth (registered trademark) and the like. However, Patent Document 3 does not clearly indicate the frequency band used for wireless communication, and it is assumed that an ultrasonic wave having a frequency of 1 to 10 MHz, which is often used in the medical field, assumes a load on the wireless communication interface. There is a problem that is too big.

  Accordingly, an object of the present invention is to provide an ultrasonic diagnostic apparatus that can be miniaturized while realizing high resolution in the ultrasonic propagation direction.

  An ultrasonic diagnostic apparatus according to the present invention forms an addition drive signal of a first drive signal having a first frequency characteristic and a second drive signal having a second frequency characteristic, and superimposes the addition drive signal. An ultrasonic wave transmitting means for converting the ultrasonic wave signal into the medium to be measured, a first ultrasonic signal generated by the first drive signal component of the addition drive signal, and the addition drive signal An ultrasonic receiving means for receiving and propagating a parametric ultrasonic signal generated and propagated in the medium to be measured along with the propagation of the second ultrasonic signal generated by the second drive signal component; and parametric reception Fundamental wave component removing means for removing the fundamental wave component from the signal, spatial resolution improving means for improving the spatial resolution in the ultrasonic propagation direction of the parametric reception signal from which the fundamental wave component has been removed, And a signal processing means for resolution to form an ultrasound image based on improved parametric received signal.

  In the ultrasonic diagnostic apparatus of the present invention, preferably, the ultrasonic transmission means includes a piezoelectric vibrator formed of an annular composite piezoelectric body, and the ultrasonic reception means is arranged on an annular inner diameter portion of the ultrasonic transmission means. The piezoelectric vibrator and the film-shaped piezoelectric vibrator are ultrasonic transducers that are integrally formed, including a film-shaped piezoelectric vibrator formed of porous polypropylene. Furthermore, the ultrasonic wave receiving means has charge amplifier means for converting a charge signal from the film-like piezoelectric vibrator into a voltage signal, and filter means for removing noise from the voltage signal from the charge amplifier means. Are preferably formed integrally.

  In addition, the ultrasonic diagnostic apparatus according to the present invention forms an addition drive signal of the first drive signal having the first frequency characteristic and the second drive signal having the second frequency characteristic, and the addition drive signal Is converted into an ultrasonic signal, and the ultrasonic transmission means for transmitting the ultrasonic signal toward the medium to be measured, the first ultrasonic signal generated by the first drive signal component of the addition drive signal, and the addition signal Ultrasonic wave receiving means for receiving and propagating a parametric ultrasonic signal generated in the medium to be measured along with the propagation of the second ultrasonic signal generated by the second drive signal component of A wireless transmission interface means for converting the received parametric reception signal into a wireless signal and transmitting it, and a wireless reception communication interface means for receiving the transmitted wireless signal and converting it into a wired reception signal Wireless communication interface means, fundamental wave component removing means for removing the fundamental wave component from the converted parametric reception signal, and spatial resolution improvement for improving the spatial resolution in the ultrasonic propagation direction of the parametric reception signal from which the fundamental wave component has been removed Means and signal processing means for forming an ultrasound image based on the parametric received signal with improved spatial resolution.

  In the ultrasonic diagnostic method according to the present invention, an addition drive signal of the first drive signal having the first frequency and the second drive signal having the second frequency is formed by the ultrasonic transmission means. The step of converting the addition drive signal into an ultrasonic signal and transmitting the ultrasonic signal toward the medium to be measured, and the first receiving signal component generated by the first drive signal component of the addition drive signal by the ultrasonic receiving means A parametric reception signal generated and propagated in the medium to be measured along with the propagation of the ultrasonic signal and the second ultrasonic signal generated by the second drive signal component of the addition drive signal is received and converted into a parametric reception signal. A step of removing the fundamental wave component from the parametric received signal by the fundamental wave component removing means, and a parameter of which the fundamental wave component has been removed by the spatial resolution improving means. Tsu has a step to improve the spatial resolution of the ultrasonic wave propagation direction of the click received signal, by signal processing means, and forming an ultrasonic image based on a parametric received signal spatial resolution is improved.

  According to the present invention, the fundamental wave component removing means for removing the fundamental wave component from the parametric received signal, and the spatial resolution improving means for improving the spatial resolution in the ultrasonic propagation direction of the parametric received signal from which the fundamental wave component has been removed. By providing, the spatial resolution in the ultrasonic propagation axis direction can be improved.

  Further, the ultrasonic transducer is formed by integrating the piezoelectric vibrator and the film-like piezoelectric vibrator, and further, the charge amplifier means and the filter means are configured integrally with the ultrasonic transducer, thereby reducing the size and weight of the ultrasonic transducer. It is also possible to realize an ultrasonic probe including an acoustic transducer.

  In addition, since the ultrasonic diagnostic apparatus of the present invention performs signal processing using relatively low-frequency parametric ultrasonic waves, a wireless communication interface can be used with a small burden, and an ultrasonic image with high resolution can be generated. Can do.

1 is a block diagram showing a basic configuration of an ultrasonic diagnostic apparatus according to a first embodiment to which the present invention is applied. It is a figure which shows the structure of the ultrasonic transducer which comprises the ultrasonic diagnosing device to which this invention was applied. (A) is a sectional side view of an ultrasonic transducer. (B) is a front view of a whole surface common ground electrode type ultrasonic transducer. (C) is a front view of a ground electrode split type ultrasonic transducer. It is a cross-sectional schematic diagram which shows the outline of the internal structure of a porous polypropylene piezoelectric vibrator. (A) is an overall cross-sectional view, (B) is an enlarged view of a portion A in a broken line in FIG. (A), and (C) is an enlarged view of a cell portion. It is a figure which consists of a table | surface which put together the performance parameter of the porous polypropylene piezoelectric vibrator and another piezoelectric vibrator. FIG. 2 is a block diagram illustrating a configuration example of a receiving circuit in the configuration of FIG. 1. FIG. 2 is a block diagram illustrating a configuration example of a signal processing circuit in the configuration of FIG. 1. 2 is a signal processing procedure showing a method of removing a fundamental wave component in the signal processing circuit having the configuration of FIG. It is the graph by the simulation which shows the change of the sound pressure level with respect to the distance of the propagation direction of a fundamental wave ultrasonic wave and a parametric ultrasonic wave in water, and the distance of a beam width direction. (A) shows the change in the sound pressure level with respect to the propagation axis direction distance in the fundamental wave, and (B) shows the change in the sound pressure level with respect to the propagation axis direction distance in the parametric ultrasonic wave. (C) shows the change in the sound pressure level with respect to the beam width direction distance in the fundamental wave, and (D) shows the change in the sound pressure level with respect to the beam width direction distance in the parametric ultrasonic wave. It is an operation | movement waveform diagram for demonstrating the operation | movement which improves the spatial resolution of the ultrasonic propagation direction of the ultrasonic diagnosing device of this invention. (A) and (B) are waveforms of ultrasonic signals S ₁ and S ₂ to be transmitted. (C) is a waveform of the received parametric reception signal R _para . (D) is a waveform of the reference signal S _ref . (E) is a waveform of a pulse compressed signal R _comp that has been subjected to cross-correlation between R _para and S _ref and pulse compressed. It is a block diagram which shows the basic composition of the ultrasonic diagnosing device of 2nd Embodiment to which this invention was applied. FIG. 11 is a block diagram illustrating a configuration example of first and second signal processing circuits in the configuration of FIG. 10. 11 is a signal flowchart showing a method for extracting phase information in the configuration of FIG. 10. It is a block diagram which shows the basic composition of the ultrasonic diagnosing device of 3rd Embodiment to which this invention was applied. It is a block diagram which shows the basic composition of the ultrasonic diagnosing device of 4th Embodiment to which this invention was applied.

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

1. 1. Configuration example of ultrasonic diagnostic apparatus according to first embodiment 1-1. Configuration example of ultrasonic diagnostic apparatus 1-2. Configuration example of ultrasonic transducer 1-3. Piezoelectric vibrator for ultrasonic reception 1-4. Configuration example of receiving circuit 1-5. 1. Configuration example of signal processing circuit 2. Operation principle and operation of ultrasonic diagnostic apparatus 2-1. Features of parametric ultrasonic signals 2-2. Operation of ultrasonic diagnostic apparatus 2-3. 2. Pulse compression technology 3. Configuration example of ultrasonic diagnostic apparatus according to second embodiment 4. Configuration example of ultrasonic diagnostic apparatus according to third embodiment Configuration example of ultrasonic diagnostic apparatus according to fourth embodiment

1. 1. Configuration example of ultrasonic diagnostic apparatus according to first embodiment 1-1. Configuration Example of Ultrasonic Diagnostic Device An ultrasonic diagnostic device 101A to which the present invention is applied, as shown in FIG. 1, transmits a signal generation circuit 3 that generates ultrasonic waves and generated ultrasonic waves into a living tissue 5. A ring-shaped piezoelectric vibrator 2 and a disk-shaped piezoelectric vibrator 7 that receives reflection of ultrasonic waves from an abnormal tissue 6 or the like in the living tissue 5. The ultrasonic diagnostic apparatus 101 </ b> A removes the fundamental wave component of the ultrasonic signal received by the reception circuit 9 and the reception circuit 9 that receives the ultrasonic signal received by the disk-shaped piezoelectric vibrator 7. The signal processing circuit 12 includes a multiplication circuit 10 that performs cross-correlation processing between the reference signal generated by the reference signal generation circuit 11 and the signal output from the signal processing circuit 12. Further, the ultrasonic diagnostic apparatus 101A specifies the position of the ultrasonic transducer 1 and specifies the position specifying sensor 30 for generating the position specifying signal in order to specify the position of the ultrasonic wave to be transmitted into the living tissue 5. And an image processing circuit 13 that processes the position information data of the specific sensor 30 and the calculation result data of the multiplication circuit 10 to generate an image signal constituting an ultrasonic image. Preferably, a display 14 for displaying image by inputting image signal data of the image processing circuit 13 is provided.

  The ring-shaped piezoelectric vibrator 2 and the disk-shaped piezoelectric vibrator 7 are preferably integrated in the same housing to constitute the ultrasonic transducer 1, and the ultrasonic transducer 1 is more preferably connected to the receiving circuit 9. It is integrated and forms the main part of the probe.

Signal generating circuit 3, a first ultrasonic signal generator 3A and the second ultrasonic signal of the second frequency f ₂ S ₂ for generating a first ultrasonic signals S ₁ of the first frequency f ₁ The second ultrasonic signal generating unit 3B that generates the signal, and the adder 3C that generates the addition signal of the first and second ultrasonic signals S ₁ and S ₂ . As will be described later, the first and second ultrasonic signals S ₁ and S ₂ are preferably chirp signals having a predetermined interval period and having different frequencies from the start frequency and the end frequency. Further, the signal generation circuit 3 adds the first and second ultrasonic waves S ₁ and S ₂ by the adder 3C in the drive circuit to generate an addition signal S ₊ = S ₁ + S ₂ , and the addition signal S _An inversion signal S ₋ = − (S ₁ + S ₂ ), which is 180 ° different in phase from ₊ , is generated and subjected to predetermined voltage amplification by the drive circuit 3D, respectively, and then a ring-shaped piezoelectric transducer for transmission. The piezoelectric vibrator 2 is driven.

  The receiving circuit 9 impedance-transforms and amplifies the piezoelectric signal converted by the disk-shaped piezoelectric vibrator 7 that receives the parametric ultrasonic signal propagating in the living tissue, and passes the amplified signal to the subsequent circuit.

  The signal processing circuit 12 removes the fundamental wave component from the parametric ultrasonic signal received and processed by the receiving circuit 9 and extracts only the difference frequency component.

  The multiplication circuit 10 performs pulse compression by performing cross-correlation processing of the parametric ultrasonic signal from which the fundamental wave component is removed together with the reference signal generation circuit 11 to improve the resolution in the ultrasonic propagation direction.

  The position specifying sensor 30 is disposed in a probe including the ultrasonic transducer 1, acquires information for specifying the position of the ultrasonic transducer 1 on the living tissue 5, and sends position specifying information data to the image processing circuit 13. . The position specifying sensor 30 is configured using, for example, a magnetic sensor.

  The image processing circuit 13 receives the ultrasonic signal data with improved spatial resolution in the propagation direction and the position information signal data generated by the position specifying sensor 30, and generates an image signal for image display. Ultrasonic image data is generated according to this image signal. The image processing circuit 13 is realized by, for example, a scan converter. Note that the ultrasonic image data output from the image processing circuit 13 may be displayed as a moving image or a still image on the display 14 as described above. However, the data may be processed or may be processed as it is on another medium such as an external storage. Needless to say, it may be stored in the apparatus, printed out by a printer, or converted into a signal appealing to the five senses of sound and vibration and presented to a person.

1-2. Ultrasonic transducer configuration example An ultrasonic transducer may be configured by separately preparing an ultrasonic transmission transducer and an ultrasonic reception transducer. However, these are integrated as one unit for ease of use and improved performance. It is preferable to configure.

  As shown in FIG. 2, the ultrasonic transducer 1 is integrally provided with a ring-shaped piezoelectric vibrator 2 as a transmitting transducer and a disk-shaped piezoelectric vibrator 7 as a receiving transducer. 2A is a side cross-sectional view of an integrated ultrasonic transducer, and FIG. 2B shows a case where the ground electrode 17 is formed so as to cover almost the entire surface of the ultrasonic transducer 1 (entire electrode common type). 2C is a front view of the ring-shaped piezoelectric vibrator 2 and the ground electrode 28 of the disc-shaped piezoelectric vibrator 7 formed separately from each other. It is a front view in the case of being connected by connection conductive wirings 4A, 4B, 4C at the time of assembling the acoustic wave transducer (electrode split type).

  As shown in FIG. 2A, the ultrasonic transducer 1 includes a ring-shaped piezoelectric vibrator 2 and a disk-shaped piezoelectric vibrator 7, and a gap 29 is formed inside the ring of the ring-shaped piezoelectric vibrator 2. A disc-shaped piezoelectric vibrator 7 is provided. One surface of each of the ring-shaped piezoelectric vibrator 2 and the disk-shaped piezoelectric vibrator 7 is connected to the ground electrode 17, and the circuit ground is connected to the metal housing 15 via the internal ground wiring 23 and the external ground wiring 26. Connected to potential.

  As will be described later, the disk-shaped piezoelectric vibrator 7 is made of porous polypropylene (hereinafter also referred to as “cellular PP”) that can be reduced in thickness and weight even in a relatively low frequency range of about 100 kHz. Although the cellular PP has a remarkably lower elastic modulus than a piezoelectric vibrator such as PZT, it is preferable to use a metal as the backing layer. Therefore, the metal backing plate 16 is provided with a gap 29 on the surface opposite to the surface connected to the ground electrode 17 of the disk-shaped piezoelectric vibrator 7. The metal backing plate 16 also serves as a pressing member that stably fixes the disc-shaped piezoelectric vibrator 7 at a predetermined position.

  The disk-shaped piezoelectric vibrator 7 is connected to the external circuit from the surface of the metal backing plate 16 opposite to the surface to which the disk-shaped piezoelectric vibrator 7 is connected via the connection internal wiring 25 and the connector 20 for external circuit connection. Connected to. The ring-shaped piezoelectric vibrator 2 has a connection electrode 18 connected to a surface opposite to the surface to which the ground electrode 17 of the ring-shaped piezoelectric vibrator 2 is connected, and an external circuit via a connection internal wiring 24 and a connector 19. Connected to.

  The piezoelectric vibrator configured as described above is housed in the housing 15 for protection from the external environment. By such an integrated ultrasonic transducer 1, a small and light probe can be realized. As shown in FIGS. 2B and 2C, the front shape of the ultrasonic transducer 1 is preferably a circular shape from the viewpoint of the radiation efficiency of ultrasonic waves, but is not limited to a circular shape. Instead, an elliptical shape, a rectangular shape, or other shapes may be used.

1-3. Piezoelectric vibrator for ultrasonic reception The frequency of the parametric ultrasonic wave used in the ultrasonic diagnostic apparatus to which the present invention is applied is about 100 kHz. Therefore, even if a composite type piezoelectric body is used for the disk-like piezoelectric vibrator 7, The thickness becomes very large, and it is difficult to reduce the size and weight. Therefore, a piezoelectric vibrator that can be thinned even at a low frequency is required. As a piezoelectric material that can be thinned, there is porous polypropylene (cellular PP).

  As shown in FIG. 3A, the cellular PP is a foaming resin material having a polypropylene resin 34 as a base material. A large number of cells 35 (bubbles and pores) are formed inside the polypropylene resin 34. When the metal electrodes 32 and 33 are formed on both surfaces of the film-like or thin plate-like polypropylene resin 34 having such a thickness t and vibration is applied in a direction perpendicular to the electrode surface, FIG. 3 (B) and FIG. As shown in C), a charge is induced on the surface of the cell. By connecting an external circuit to the metal electrodes 32 and 33, a potential fluctuation corresponding to the displacement due to vibration occurs, so that the cellular PP can function as a piezoelectric vibrator.

Such cellular PP has advantageous properties over existing piezoelectric materials. For example, as shown in FIG. 4, in a general piezoelectric vibrator PZT-5, the voltage output constant g ₃₃ is 0.011 Vm / N, and even in a ferroelectric polymer PVDF (PolyVinylidene DiFluoride), 0.2 Vm / In contrast to N, the cellular PP has an order of magnitude as large as 60 to 180 Vm / N. Further, the piezoelectric strain coefficient _{d 33} is also in PZT-5, 171pC / N, the PVDF, whereas a 20 pC / N, the cellular PP, much larger and 400~1200pC / N. Therefore, the cellular PP can generate the piezoelectric output more efficiently. Cellular PP is soft because it is a resin, and has a lower resonance frequency in the case of the same thickness as compared with other piezoelectric materials having a large elastic modulus. Therefore, it can be said that it is suitable for receiving relatively low frequency parametric ultrasonic waves used in the ultrasonic diagnostic apparatus of the present invention. Furthermore, a filter effect that excludes other frequency components can be expected by appropriately selecting the thickness so as to resonate in the vicinity of 100 kHz. Cellular PP are the foamable resin, the density is lower than that of other piezoelectric material ^{(ρ = 330kg / m 3,} PZT-5 in 7,500 kg / ^{m 3,} etc.), along with miniaturization, even lighter Can contribute. In the ultrasonic diagnostic apparatus of the present invention, it is needless to say that not only the piezoelectric vibrator as described above but also a bulk type piezoelectric element such as PZT or PVDF can be used.

1-4. Configuration of Reception Circuit Parametric ultrasonic waves received by the disk-shaped piezoelectric vibrator 7 are input to the reception circuit 9. Although not limited to the following, the reception circuit 9 is connected to the output of the charge amplifier circuit 9A and the charge amplifier circuit 9A electrically connected to the output of the disk-shaped piezoelectric vibrator 7 as shown in FIG. And a filter circuit 9B.

  The input of the charge amplifier circuit 9A is electrically connected to the disc-shaped piezoelectric vibrator 7 via the external connection wiring 22 and the connector 20. Since the output impedance of the piezoelectric vibrator is very high, it is necessary to perform impedance conversion using a high input impedance amplifier. Therefore, it is preferable to use a charge amplifier circuit 9A having an impedance conversion function for the front end of the receiving circuit 9. By using the charge amplifier circuit 9A, a parametric ultrasonic signal obtained by converting a charge signal into a voltage signal can be obtained. Here, unnecessary noise due to mechanical parasitic vibration of the piezoelectric vibrator is superimposed on the parametric ultrasonic signal, and it is preferable to use the filter circuit 9B for noise removal because it interferes with precise measurement. The parametric ultrasonic signal converted into the voltage signal from which unnecessary noise has been removed is amplified by the amplification function of the charge amplifier circuit 9A, and a stable signal can be sent to the signal processing circuit 12 at the subsequent stage.

  The receiving circuit 9 may be mounted as a circuit functional block in the same housing as other signal processing circuits and the like. However, as described above, the received and output ultrasonic signals are minute and external noise. Therefore, it is preferable that the probe is mounted on the housing of the ultrasonic transducer 1 and configured as an integral probe.

1-5. Configuration of Signal Processing Circuit Parametric ultrasonic waves received by the disk-shaped piezoelectric vibrator 7 are input to the signal processing circuit 12 after being subjected to the above reception processing in the receiving circuit 9. As will be described later, since the non-linear frequency component of the received parametric ultrasonic wave has a sound pressure level lower than 40 dB compared to the fundamental wave component, it is necessary to remove the fundamental wave component in order to extract the non-linear frequency component. is there. Therefore, the signal processing circuit 12 is used to remove the fundamental wave component and unnecessary high-order harmonic components of the received and processed parametric reception signal.

As shown in FIG. 6, the signal processing circuit 12 includes a storage circuit 12A connected to the output of the reception circuit 9, and a band-pass filter 12B connected to the output of the storage circuit 12A. A double pulse detection circuit 12C is connected to detect a pulse signal input to the memory circuit 12A. The double pulse detection circuit 12C detects a double pulse, generates a reset signal, and inputs the reset signal to the memory circuit 12A. To do. A reception sum signal _{R +} for the first and second ultrasonic signals _S 1, addition signal of _{S 2 S +,} the inverted signal S phase and _{S +} is generated with a predetermined delay time from 180 ° different _{S + The} reception inversion signal R _{− with} respect to ₋ is input to the memory circuit 12A. Following R _+, R _- is the input to the storage circuit 12A, the double pulse detection circuit 12C detects a double pulse, generates a reset signal.

For example, the double pulse detection circuit 12C has a function of detecting an envelope of a signal output from the receiving circuit 9 and input to the signal processing circuit 12, and a signal waveform obtained by this function is two envelope pulses. In the case of a double pulse consisting of: a reset signal is returned to the memory circuit 12A, and the memory information in the memory circuit 12A is reset. On the other hand, the memory circuit 12A has a function of A / D conversion, of the two received pulses, when inputting 1 claw received pulse R ₊ stores R ₊ waveform, second received pulse R _- enter the Sometimes the stored R ₊ is read and these phases are aligned and added.

FIG. 7 is a signal flow diagram showing a signal flow including a functional block of the signal processing circuit 12 for removing the fundamental wave component of the parametric reception signal. The signal processing circuit 12 includes the first ultrasonic signal S ₁ having the first frequency f ₁ (= ω ₁ / 2π) generated by the signal generation circuit 3 and the second frequency f ₂ (= ω ₂ / 2π) of the second ultrasonic signal S ₂ and the addition signal S ₊ = S ₁ + S ₂ and the inverted signal S ₋ = − (S ₁ + S ₂ ) of the addition signal propagate through the living tissue 5 and are abnormal. The ultrasonic signals reflected by the tissue 6 and the like are received, and parametric ultrasonic reception signals R ₊ and R ₋ received by the reception circuit 9 are input. Inverted signal S _- is from the addition signal S _+, is transmitted with a delay of a predetermined delay time. Therefore, R _{− is} also received with a delay of the same delay time t _DLY from R ₊ . Here, the received signal R based on the addition signal S _{+ +,} the inverted signal S _- received signal based on the R _- are respectively expressed as follows.

_{R + = S + + αS +} 2, R - = S - + αS - 2

Thus, the ultrasonic waves propagating in the biological tissue 5 is nonlinear components S _{+ ^2,} S _- include ^2. Therefore, as described above _{R +} and R _- When adding the + fundamental wave component _S, S _- is nonlinear terms [alpha] S ₊ ² is canceled, [alpha] S _- ² only can leave. Incidentally, S ₊ and S _- with a only signals are inverted phase each other, by squaring, S + ₂ ⁼ S _- is ^two relationships, by adding, to the amplitude twice Needless to say.

Parametric received signal output from the signal processing circuit 12 _{R =} R + + R _-, as shown in FIG. 7,

R ₊ + R ₋ = 2α + 2αCOS (ω ₁ −ω ₂ ) t ²
−α {cos (2ω ₁ ) t + cos (2ω ₂ ) t + ₂ cos (ω ₁ + ω ₂ ) t ²
+ ...}

Thus, signals having fundamental wave components ω ₁ (= 2π · f ₁ ) and ω ₂ (= 2π · f ₂ ) are removed.

The center frequency of the band pass filter 12B is set to a frequency at which the “difference” component 2αCOS (ω ₁ −ω ₂ ) t ² can be extracted. Accordingly, the ultrasonic signal that has passed through the band-pass filter 12B also removes harmonics of the fundamental wave component, harmonics of the nonlinear component, and the like, and a signal having only the frequency component of the “difference sound” can be extracted.

2. 2. Operation principle and operation of ultrasonic diagnostic apparatus 2-1. Features of Parametric Ultrasonic Signal FIGS. 8A and 8B show the relationship between the sound pressure level of ultrasonic waves propagating in water and the propagation distance along the propagation direction (hereinafter referred to as propagation axis direction distance). Is a graph calculated by simulation. The reason why the ultrasonic propagation medium is underwater is that the propagation characteristics are similar to those of the living tissue 5 to be measured in the ultrasonic diagnostic apparatus. FIG. 8A is a graph in which ultrasonic waves having fundamental frequencies of 0.95 MHz (black circles, solid lines) and 1.05 MHz (white circles, broken lines) are respectively calculated and plotted in water. This indicates that the sound pressure level attenuates as the propagation axis direction distance increases. FIG. 8B is a graph obtained by calculating and plotting a case where parametric ultrasonic waves having a frequency of 100 kHz are propagated in water. This indicates that the sound pressure level is hardly attenuated even when the propagation axis direction distance is increased.

  FIG. 8C and FIG. 8D simulate the ultrasonic sound pressure level with respect to the direction perpendicular to the ultrasonic propagation direction, that is, the distance in the width direction of the ultrasonic beam (hereinafter referred to as the beam width direction distance). It is the graph calculated by. As shown in FIG. 8C, when an ultrasonic fundamental wave having a fundamental frequency of 0.95 MHz and 1.05 MHz is propagated in water, a side lobe close to the center peak is generated, and the contrast is increased. It is suggested that speckle noise related to resolution increases. On the other hand, as shown in FIG. 8D, when parametric ultrasonic waves of 100 kHz are propagated in water, there is no generation of side lobes and the beam width contributing to the lateral resolution is as shown in FIG. 8 (D) shows that the fundamental wave ultrasonic wave of 100 kHz indicated by the one-dot chain line is much smaller than that in the case where the ultrasonic wave is propagated into water.

  In this way, by using parametric ultrasonic waves of about 100 kHz, it is possible to perform measurement by increasing the resolution of the ultrasonic signal along the ultrasonic propagation axis direction, that is, in the depth direction in the living tissue, At the same time, the side lobe level related to the contrast resolution is small, and the beam width that affects the lateral resolution is much better than the fundamental wave of the same frequency. As a result, ultrasound with excellent spatial resolution and contrast resolution. It is shown that an image is obtained.

2-2. Operation of Ultrasonic Diagnostic Device In order to generate parametric ultrasonic waves as described above, two ultrasonic signals S ₁ and S ₂ are generated by a signal generation circuit 3 as shown in FIGS. 9 (A) and 9 (B). Is generated. Two ultrasound signals _S 1, _{S 2} is the first frequency _{f 1} as the start frequency, a first chirp signal _{S 1,} a second start frequency frequency _{f 2} to the end frequency _{f 1} + Delta] f ₁ And a second chirp signal S ₂ having an end frequency of f ₂ + Δf ₂ . These chirp waves are repeated with a predetermined pulse width T and a specific period, as shown.

The first and second chirp signals S ₁ and S ₂ generated by the signal generation circuit 3 are added and amplified to drive the ring-shaped piezoelectric vibrator 2. The sum signal S ₊ of the first and second chirp signals S ₁ and S ₂ transmitted by the ring-shaped piezoelectric vibrator 2 propagates as parametric ultrasonic waves in the living tissue 5 and is reflected by the abnormal tissue 6 or the like. . Note that, for the fundamental wave component removal operation, as described above, it is necessary to generate an inverted signal S ₋ that is 180 ° out of phase with the added signal S ₊ and perform a process of adding it to S _+. For the sake of simplicity, in the following description, only the signal processing portion based on the addition signal S ₊ will be described.

FIG. 9C shows a schematic waveform of the parametric reception signal R _para from which the fundamental frequency component and the like are removed by the signal processing circuit 12 and the difference frequency component is extracted. As shown in FIG. 9C, the received and waveform-processed parametric reception signal R _para has a start frequency | f ₁ −f ₂ | and an end frequency | f ₁ −f ₂ | + | Δf ₁ −Δf _2. It has a frequency component of |. As shown schematically, the parametric received signal has improved sub-peak value, that is, time-axis sidelobe level relative to the main peak value, and low time resolution, that is, ultrasonic propagation axial resolution. It is necessary to let

FIG. 9D shows the waveform of the reference signal S _ref generated and output by the reference signal generation circuit 11. By performing a cross-correlation process between the parametric reception signal R _para and the reference signal S _ref , the main peak value V _m1 as shown in FIG. _9E has a sub peak value V _si (i is a positive integer). A pulse compression waveform having a Sinc function waveform shape is obtained. This pulse compression waveform is accompanied by a main peak V _m1 having a small half width and time axis side lobes V _s2 and V _{s3 on} both sides thereof. If the peak levels of the time axis side lobes V _s2 , V _s3, etc. are 1/10 or less of the peak value of the main peak V _m1 , the pulse width of this compressed pulse is the half width τ _{para of the} main peak V _m1. And the ultrasonic wave propagation axial resolution is improved by narrowing the half-value width τ _para . For more information about the pulse compression technique, as described later, taking the reference signal S _ref having a frequency that matches the frequency of the parametric received signal R _para, the cross-correlation by multiplying by the multiplier circuit 10 a parametric received signal R _para, Perform pulse compression. Due to the pulse compression, the waveform of the pulse compression signal R _comp has a sharp peak in the polarity on one side and the characteristic of the non-linear signal rounded in the polarity on the other side, as schematically shown in FIG. Presents a shape. Actually, in order to effectively extract a waveform corresponding to the main peak wave V _m1 , unnecessary frequency components are removed at the stage of receiving parametric ultrasonic waves or after cross-correlation is performed by the multiplication circuit 10. It is preferable to insert a circuit.

2-3. Pulse Compression Technology As shown in FIGS. 1 and 9, the pulse width (or half-value width) τ _comp (= τ _para ) is narrower by taking the cross-correlation between the parametric received signal R _para and the reference signal S _ref. Generating a signal waveform having a high peak voltage Vp is called a pulse compression technique. If a sufficiently pulse-compressed signal waveform is obtained, ultrasonic image signal data having higher resolution can be obtained.

  Hereinafter, the principle of the pulse compression technique will be described according to the configuration of FIG.

Drive signal output from the signal generating circuit _{3 D (t) (= A} t · V trans (t), A t is the drive circuit 3D is a high voltage output amplifier for driving the ring-type piezoelectric vibrator 2 (Voltage amplification factor), and the reference signal input to the multiplication circuit 10 is S _ref (t).

The pulse signal S _TX (t) of the transmission ultrasonic wave 4 propagating in the living tissue 5 is hereinafter referred to as T (t) for convenience, and its frequency characteristic is T (ω). Similarly, the received ultrasonic pulse The signal S _RX (t) is hereinafter expressed as R (t−τ), and its frequency characteristic is expressed as R (ω). The frequency characteristics T (ω) and R (ω) are assumed to have a relationship obtained by performing Fourier transform (FFT processing) on the time characteristics T (t) and R (t−τ), respectively.

In this case, the frequency characteristic R (ω) of the pulse signal S _RX (t) of the reception ultrasonic wave 8 is expressed by the following equation (1).

R (ω) = T (ω) · F (ω) · H _r (ω) (1)

Here, F (ω) is a transfer function of the living tissue 5, and H _r (ω) is a transfer function of the disk-shaped piezoelectric vibrator 7 for reception.

Further, the frequency characteristic T (ω) of the pulse signal S _TX (t) of the transmission ultrasonic wave 4 is expressed by the following equation (2).

T (ω) = D (ω) · H _t (ω) (2)

Here, D (ω) is a frequency characteristic of the drive signal D (t), and H _t (ω) is a transfer function of the ring-shaped piezoelectric vibrator 2 for transmission.

The reception pulse signal R _para (t−τ) obtained by the reception circuit 9 by receiving the pulse signal S _RX (t) of the reception ultrasonic wave 8 with the disc-shaped piezoelectric vibrator 7 is a circle for ultrasonic reception. The frequency characteristic R (ω) of the pulse signal S _RX (t−τ) of the received ultrasonic wave 8 received by the plate-like piezoelectric vibrator 7 can be expressed as the following equation (3).

R _para (ω) = R (ω) · A _r (ω) (3)

The reception pulse signal R _para (t−τ) output from the reception circuit 9 is supplied to the multiplication circuit 10, and between the drive signal D (t) and a reference signal S _ref (t) having the following relationship: Cross correlation processing is performed.

In addition, A _r (ω) in the expression (3) is a frequency characteristic of the voltage amplification factor of the receiving circuit 9 and is assumed to be constant in the frequency band including the harmonic component here. R _para (ω) is a frequency characteristic of R _para (t−τ).

  Further, D (ω) in the equation (2) is represented by the following equation (4).

D (ω) = S ₊ (ω) · A _t (ω) (4)

Here, A _t (ω) is a frequency characteristic of the voltage amplification factor of the drive circuit 3D provided in the signal generation circuit 3, and is generated from the first and second ultrasonic signal generators 3A and 3B here. It is assumed that the added signal S ₊ (t) is constant within the band of the frequency characteristic S ₊ (ω). From the above, the following expression (5) is obtained.

R _para (ω) = H _t (ω), D (ω), F (ω), H _r (ω), A _r (ω) (5)

Here, the frequency characteristic S ₊ (ω) of the addition signal S ₊ (t) can be expressed by the following equation (6).

S ₊ (ω) = D (ω) / A _t (6)

_{Here, A t,} A _r is a constant.

Next, consider the cross-correlation function R _xy (j). The cross-correlation function R _xy (j) is obtained by _converting the discrete data of the signals x (t) and y (t) to x (i) (i = 0, 1, 2,..., N−1), y (i). If (i = 0, 1, 2,..., N−1), it is defined by the following equation (7).

Here, if x (i) = S _ref (t) and y (i + j) = R _para (t−τ), then R _xy (j) = R _xy (τ). S ₊ (t) and R _para (t−τ) are obtained by inverse Fourier transform of S ₊ (ω) and R _para (ω).

By referring to equation (7), R _xy (τ) becomes closer to 1 at the phase τ as the similarity between S _ref (t) and R _para (t−τ) increases. It shows that the half width Δt of the main peak at the phase τ becomes narrower. Therefore, the accuracy of the value of the phase τ is increased. The similarity between the waveforms of S _ref (t) and R (t) may be considered as the similarity between S _ref (ω) and R _para (ω), that is, the similarity of the frequency characteristics of the cross-correlation target signals. .

Further, the transmission pulse signal D (t) is a chirp wave. The chirp wave transmission pulse signal p (t) can be expressed by the following equation (8) as the amplitude P ₀ .

Here, ω _s (= 2πf _s) the initial angular frequency _{(f s} is the initial frequency), T is time sweep, the μ is the angular frequency sweep rate. Further, when _fe is the final frequency and 2πΔf is the sweep angular frequency, there is a relationship of μ = Δω / T = 2π (f _e −f _s ) / T. The pulse compression ratio of the chirp wave is given by TΔf, and the pulse width becomes narrower as Δf is increased, and the propagation axis direction resolution can be further increased.

  In addition to the chirp wave that is a frequency modulation signal, the effect of pulse compression is the same for a phase modulation signal, that is, a Barker sequence signal that is an encoded sequence signal, a complementary sequence signal, an M sequence signal, and the like. Although effective, when a chirp wave is used, the SN ratio can be maximized, which is preferable.

3. Configuration Example of Ultrasonic Diagnostic Apparatus in Second Embodiment Next, a second embodiment of an ultrasonic diagnostic apparatus to which the present invention is applied will be described. The ultrasonic diagnostic apparatus according to this embodiment obtains an ultrasonic diagnostic image using a phase shift amount which is another physical quantity for improving the spatial resolution of the parametric ultrasonic signal in the ultrasonic propagation direction. .

  FIG. 10 shows a block diagram of a configuration example of the ultrasonic diagnostic apparatus 101B. Constituent elements that are the same as those of the ultrasonic diagnostic apparatus (FIG. 1) of the first embodiment are given the same names and symbols.

As shown in FIG. 10, an ultrasonic diagnostic apparatus 101B to which the present invention is applied includes a signal generation circuit 3E that generates ultrasonic waves, and a ring-shaped piezoelectric vibrator 2 that transmits the generated ultrasonic waves into a living tissue 5. And a disk-shaped piezoelectric vibrator 7 that receives reflection of ultrasonic waves from the abnormal tissue 6 or the like in the living tissue 5. The ultrasonic diagnostic apparatus 101 </ b> B removes the fundamental circuit component of the ultrasonic signal received by the reception circuit 9 and the reception circuit 9 that performs signal processing of the ultrasonic signal received by the disk-shaped piezoelectric vibrator 7. A first signal processing circuit 12D, a multiplication circuit 10 for calculating a product of the reference signal S _ref generated by the reference signal generation circuit 11 and the signal r (t) output from the first signal processing circuit 12D; And a second signal processing circuit 12E for extracting phase information from the output of the multiplication circuit 10. Further, the ultrasonic diagnostic apparatus 101B specifies the position of the ultrasonic wave to be transmitted into the living tissue 5, generates a position specifying signal, position information data of the position specifying sensor 30, and calculation of the multiplication circuit 10. And an image processing circuit 13 for processing the result data to generate an image signal. Preferably, a display 14 for displaying image by inputting image signal data of the image processing circuit 13 is provided.

  As in the first embodiment, the ring-shaped piezoelectric vibrator 2 and the disk-shaped piezoelectric vibrator 7 are preferably integrated to form the ultrasonic transducer 1, and the ultrasonic transducer 1 is more preferable. Is integrated with the receiving circuit 9 and forms the main part of the probe.

Signal generating circuit. 3E, a second ultrasonic signal having a first signal generating portion 3F for generating a first ultrasonic signals S ₁ having a first center frequency f _1, the second center frequency f ₂ a second signal generating unit 3G for generating S _2, and first and second adder 3H adding the ultrasonic signal _S 1, _{S 2.} The first and second ultrasonic signals S ₁ and S ₂ each have the same phase δs. The signal generation circuit 3E adds the first and second ultrasonic signals S ₁ and S ₂ by the adder 3H to generate an addition signal S ₊ = S ₁ + S ₂ , and each performs predetermined voltage amplification Thereafter, the ring-shaped piezoelectric vibrator 2 which is a vibrator for transmission is driven. Further, the signal generation circuit 3E supplies the first and second ultrasonic signals S ₁ and S ₂ to the reference signal generation circuit 11. Based on the supplied signal, the reference signal generation circuit 11 generates a reference signal S _ref = sin {(ω ₁ −ω ₂ ) (t having a frequency component of the difference frequency | f ₁ −f ₂ | and a phase δ _S. −δs)}.

  The receiving circuit 9 impedance-transforms and amplifies the piezoelectric signal converted by the disk-shaped piezoelectric vibrator 7 that receives the ultrasonic signal propagating through the living tissue, and passes the amplified signal to the subsequent circuit. A preferred configuration is the same as that described in the section 1-4 of the first embodiment.

  The first signal processing circuit 12D removes the fundamental wave component from the received parametric ultrasonic signal and extracts only the difference frequency component. The configuration of the first signal processing circuit 12D is not limited to the following in addition to the memory circuit 12A and the like described in the first embodiment, but may be configured as shown in FIG. The first signal processing circuit 12D includes a band-pass filter 91 connected to the output of the receiving circuit 9 to remove signals other than parametric signals, and logarithmic amplification that compensates for attenuation of the sound pressure level due to the ultrasonic penetration distance. It is preferable that a circuit 92 and a STC (Sensitivity Time Control) circuit 94 for correcting the distance attenuation and adjusting the luminance in a specific distance range to be increased or decreased are connected in cascade.

  As shown in FIG. 11, the second signal processing circuit 12 </ b> E removes the phase detection circuit 63 that extracts the phase information of the output signal from the multiplication circuit 10 and the portion having the frequency characteristics from the output of the phase detection circuit 63. And a low-pass filter 64.

  The position specifying sensor 30 is configured using, for example, a magnetic sensor or an encoder, specifies the physical position of the ultrasonic transducer 1, generates position specifying information data, and sends it to the image processing circuit 13.

  The image processing circuit 13 receives the ultrasonic signal data with improved spatial resolution in the propagation direction and the position information signal data generated by the position specifying sensor 30, and generates an image signal for image display. Ultrasonic image data is generated according to this image signal. The image processing circuit 13 is realized by the scan converter 65, for example. Note that the ultrasonic image data output from the image processing circuit 13 may be displayed as a moving image or a still image on the display 14 as described above. However, the data may be processed or may be processed as it is on another medium such as an external storage. Similar to the first embodiment, it may be stored in the apparatus or printed out by a printer.

The operation of the ultrasonic diagnostic apparatus 101B according to the second embodiment will be described with reference to FIG. FIG. 12 is a signal flowchart showing the flow of signals generated and processed by each functional block of the ultrasonic diagnostic apparatus 101B. In order of the fundamental wave component removing operation, an addition signal S ₊ is different inverted signal S of 180 ° phase _- to generate, a process for the addition of the S ₊ using a first signal processing circuit 12D For the sake of simplicity, in the following description, only the signal processing portion based on the addition signal S ₊ will be extracted and described.

The first ultrasonic signal S ₁ having the first center frequency f ₁ (= ω ₁ / 2π) is generated by the first signal generating circuit 3F in the signal generating circuit 3E, and the second signal generating circuit 3G , The second ultrasonic signal S ₂ having the second center frequency f ₂ (= ω ₂ / 2π) is generated and added by the adder 3H to generate the added signal S ₊ = S ₁ + S _2. . The addition signal S ₊ is applied to the ring-shaped piezoelectric vibrator 2 of the transmission / reception integrated ultrasonic transducer 1 as a transmission signal s (t) voltage-amplified to a predetermined voltage and transmitted into the living tissue 5.

s (t) = A _S · sin (ω _S t−δ _S )

Here, A _S represents the voltage amplitude in the frequency domain of the present embodiment is assumed to be a constant value. [delta] _S represents the first and second ultrasonic signals _S 1, an initial phase of _{S 2.}

  The parametric ultrasonic signal reflected at the boundary of the abnormal tissue 6 is received by the receiving disk-like piezoelectric vibrator 7 and converted into an electric signal, and the fundamental signal component is removed by the first signal processing circuit 12D or the like. Is done. The r (t) of the parametric ultrasonic wave subjected to the reception process is expressed as follows.

r (t) = A _r · sin {ω _S (t−τ) −δ _S }
= A _r · sin {ω _S t−δ _S −φ (z)},
ω _S = ω ₂ −ω ₁

Here, τ is the ultrasonic wave propagation time, and φ (z) is the phase at the position z. _Ar is the voltage amplification factor of the receiving circuit, and is assumed to be a constant value in the frequency band of the present embodiment. φ (z) changes every time it passes through tissues having different sound speeds. Therefore, an ultrasonic diagnostic image can be constructed by mapping based on the position information with the value of φ (z).

The received signal r (t) is multiplied by the reference signal S _ref = A ₁ · sin (ω _S t−δ _S ) by the multiplication circuit 10 to obtain a signal of the following format.

A _r A ₁ [sin {2 (ω _S t−δ _S ) −φ (t)} + sin φ (z)]

  Furthermore, by passing this signal through a low-pass filter, it is possible to extract a component of sin φ (z) that does not depend on the frequency. That is, image processing is performed by the image processing circuit 13 from sin φ (z) that is information on the living tissue 5 and position information of the ultrasonic transducer, and an image is displayed on the display 14 by the generated image signal, and an ultrasonic diagnostic image is displayed. Is obtained.

  As described above, the method of constructing an ultrasonic image using the phase information of the parametric reception signal is such that the phase in one cycle changes from 0 ° to 360 ° regardless of the frequency, and even at a low frequency of about 100 kHz, the MHz This is based on the idea that order resolution can be achieved. In the second embodiment, the spatial resolution in the ultrasonic propagation axis direction can be improved with a simpler configuration than the configuration example of the first embodiment.

4). Configuration Example of Ultrasonic Diagnostic Device in Third Embodiment An ultrasonic diagnostic device to which the present invention is applied transmits a parametric ultrasonic signal received as described above to a signal processing circuit or the like by wire to perform image signal processing. In addition, it is possible to perform wireless signal transmission with less burden on the wireless communication interface by taking advantage of the relatively low frequency of the parametric signal.

  FIG. 13 is a block diagram of a configuration example of the third embodiment of the ultrasonic diagnostic apparatus to which the present invention is applied. An ultrasonic reception signal can be transmitted wirelessly to a remote place, or a plurality of doctors can simultaneously construct an ultrasonic image according to the doctor's preference and perform ultrasonic diagnosis in a hospital.

  As shown in FIG. 13, an ultrasonic diagnostic apparatus 101C to which the present invention is applied includes an ultrasonic transducer 1 including a ring-shaped piezoelectric vibrator 2 and a disk-shaped piezoelectric vibrator 7 in the first embodiment described above. A signal generation circuit 3, a reception circuit 9, and a position specifying sensor 30. The difference from the first embodiment is that the first A / D converter 71 that converts the parametric reception signal received and processed by the reception circuit 9 into a digital signal, and the ultrasonic transducer generated by the position specifying sensor. The parametric reception signal is converted into a digital signal by the second A / D converter 72 that converts the position specifying information of one into a digital signal, and the first and second A / D converters 71 and 72, and the conversion is performed. A transmission wireless communication interface 73 that appropriately modulates, encodes, and wirelessly transmits a carrier signal with a signal, and a reception wireless communication interface 74 that wirelessly receives a digitally transmitted digital parametric signal and converts it into a wired signal. The wirelessly transmitted digital parametric reception signal is converted into ultrasonic image data by the signal processing circuit 12, the reference signal generation circuit 11, the multiplication circuit 10, and the image processing circuit 13 described in detail in the first embodiment. The ultrasonic image is displayed on the display 14.

  The parametric ultrasonic signal used in this embodiment is about 100 kHz, and the sampling frequency including oversampling is about 1 MHz. When one data is represented by 12 bits, it can be realized if the required wireless transmission rate is 12 Mbps. Wireless systems such as Bluetooth (registered trademark), Zigbee (registered trademark), and WiFi (WiFi), which have been practically used in recent years, satisfy these transmission speeds, and therefore can be used as a wireless communication interface in the ultrasonic diagnostic apparatus of the present invention. Thus, wireless communication with small size and low power consumption can be realized.

  In the above description, the example in which the wireless communication interface is applied to the configuration of the first embodiment, that is, the configuration of the ultrasonic wave propagation axial resolution improvement method using the pulse compression technique has been described. Of course, the wireless communication interface may be applied to an ultrasonic diagnostic apparatus using the configuration of this form, that is, the phase detection technique.

  Further, in the above description, in order to simplify the diagram, the case where only one receiving-side communication interface 74 is prepared has been described. However, by using a plurality of receiving-side communication interfaces, a plurality of doctors can each have a plurality of communication interfaces. Ultrasonic diagnosis can be performed while performing desired ultrasonic image processing using a display.

5. Configuration Example of Ultrasonic Diagnostic Device in Fourth Embodiment In the ultrasonic diagnostic device of the present invention, an analog wireless communication interface can be used as the above-described wireless communication interface, and this case will be described below. .

  In the fourth embodiment to which the present invention is applied, an ultrasonic reception signal is transmitted, received, and demodulated as an analog signal, for example, an FM signal, and an ultrasonic diagnostic image is finally constructed using the demodulated signal. be able to. In particular, as described in detail below, by using a capacitive type, for example, cMUT (Capacitive Micromachined Ultrasonic Transducer, an ultrasonic transducer manufactured using a capacitive micromachine process) as a receiving piezoelectric vibrator. The frequency modulation circuit can be configured with a very simple configuration by utilizing the fact that its own capacitance changes in capacitance corresponding to the signal intensity of the received ultrasound.

  As shown in FIG. 14, the ultrasonic diagnostic apparatus 101D of the present invention includes an oscillation circuit 75 having an oscillation unit 75A and a resonance coil 75B connected to the oscillation unit 75A, radio communication interfaces 76 and 78, a demodulation circuit 79, Is provided.

In the ultrasonic diagnostic apparatus 101D, when the disk-shaped piezoelectric vibrator 7 used for at least reception of the ultrasonic transducer 1 is a capacitive type, and there is no ultrasonic reception in the capacitive ultrasonic vibrator, It has a capacitance C _0. The capacitance C ₀ of the capacitive ultrasonic transducer constitutes an oscillation circuit 75 together with the resonance coil 75B connected to the oscillation unit 75A, and the oscillation circuit 75 has a frequency f ₀ = (1 / 2π). • Oscillates at (L · C ₀ ) ^-1/2 . This oscillation signal becomes the carrier signal of the FM signal.

Since the capacitance C ₀ changes to C ₀ ± ΔC ₀ at the time of ultrasonic reception, the oscillation circuit 75 oscillates at a frequency of f ₀ ± Δf ₀ in accordance with the change in the capacitance C ₀ . That is, Δf ₀ frequency modulation (FM) is applied to the carrier signal of frequency f ₀ .

In this manner, the FM signal can be wirelessly transmitted by the transmission and reception antenna circuits included in the wireless communication interfaces 76 and 78 as an analog signal. Further, the wirelessly transmitted signal is demodulated into a parametric reception signal by the demodulation circuit 79 and subjected to signal processing by the signal processing circuit 12 as described above, and the signal processed signal r (t) and the reference signal S _ref The cross-correlation processing is performed on the receiving side by the multiplier circuit 10 to generate a pulse compression signal. On the other hand, the position specifying signal of the ultrasonic transducer 1 is also modulated and demodulated by the above-described wireless communication interfaces 76 and 78, and image processing is performed using the pulse compression signal and the position specifying signal. Data transmission is performed by a wireless communication interface including an amplification circuit, a transmission antenna, a reception antenna, and an amplification circuit. Finally, an image is displayed on the display 14 or the like.

  In the case where the modulation circuit is configured by an RC oscillation circuit, a DC resistance R may be used instead of the resonance coil 75B.

  In addition to using the above-described FM modulation, other analog radio transmission schemes such as AM modulation may be used, and it is needless to say that phase modulation schemes can also be used.

  Of course, the function of improving the spatial resolution is not limited to the pulse compression technique, but the phase detection technique described in the second embodiment may be used.

  DESCRIPTION OF SYMBOLS 1 Ultrasonic transducer, 2 ring-shaped piezoelectric vibrator, 3,3E signal generation circuit, 3A, 3B, 3F, 3G signal generation part, 3C, 3H adder, 3D drive circuit, 4 transmission ultrasonic wave, 4A, 4B, 4C Connection conduction wiring, 5 biological tissue, 5A ultrasonic propagation medium, 7 disc-shaped piezoelectric vibrator, 8 reception ultrasonic wave, 9 reception circuit, 9A charge amplifier circuit, 9B filter circuit, 10 multiplication circuit, 11 reference signal generation circuit, 12, 12D, 12E Signal processing circuit, 12A storage circuit, 12B band pass filter, 12C double pulse detection circuit, 13 image processing circuit, 14 display, 30 position specifying sensor, 15 housing, 16 metal backing plate, 17, 27, 28 Ground electrode, 18 connection electrode, 19, 20 connector, 21, 22 connection wiring, 23 inside Ground wiring, 24, 25 Internal connection wiring, 26 External ground wiring, 29 Gap, 32, 33 Metal electrode, 34 Polypropylene resin, 35 cells, 63 Phase detection circuit, 64 Low-pass filter, 71, 72 A / D converter 73, 74, 76, 78 Wireless communication interface, 75 oscillation circuit, 75A oscillation unit, 75B resonance coil, 79 demodulation circuit, 91 band pass filter, 92 logarithmic amplifier, 94 STC circuit, 101A to 101D ultrasonic diagnostic apparatus

Claims (15)

An addition drive signal of the first drive signal having the first frequency characteristic and the second drive signal having the second frequency characteristic is formed, the addition drive signal is converted into an ultrasonic signal, and the ultrasonic wave Ultrasonic transmission means for transmitting a signal toward the medium to be measured;
Along with the propagation of the first ultrasonic signal generated by the first drive signal component of the addition drive signal and the second ultrasonic signal generated by the second drive signal component of the addition drive signal, An ultrasonic receiving means for receiving and propagating the parametric ultrasonic signal generated and propagated to the parametric received signal;
Fundamental wave component removing means for removing a fundamental wave component from the parametric reception signal;
Spatial resolution improving means for improving the spatial resolution in the ultrasonic propagation direction of the parametric reception signal from which the fundamental wave component has been removed;
An ultrasonic diagnostic apparatus comprising: signal processing means for forming an ultrasonic image based on the parametric reception signal with improved spatial resolution. The ultrasonic transmission means includes an annular composite piezoelectric vibrator,
The ultrasonic receiving means includes a film-like piezoelectric vibrator formed of a porous polypropylene resin disposed on the annular inner diameter portion of the ultrasonic transmitting means,
The ultrasonic diagnostic apparatus according to claim 1, wherein the composite piezoelectric vibrator and the film-like piezoelectric vibrator are ultrasonic transducers formed integrally.   The ultrasonic wave receiving means includes charge amplifier means for converting a charge signal from the film-like piezoelectric vibrator into a voltage signal, and filter means for removing noise from the voltage signal from the charge amplifier means. The ultrasonic diagnostic apparatus according to claim 2.   3. The ultrasonic diagnosis according to claim 1, wherein the spatial resolution improving means includes a reference signal generating means for generating a reference signal, and a calculating means for calculating the parametric reception signal and the reference signal. apparatus.   5. The ultrasonic diagnostic apparatus according to claim 4, wherein the arithmetic means is a pulse compression means for performing a cross-correlation process between the reference signal and the parametric reception signal.   6. The ultrasonic diagnostic apparatus according to claim 5, wherein the first drive signal and the second drive signal are chirp signals.   5. The ultrasonic diagnostic apparatus according to claim 4, wherein the arithmetic means is phase detection means for detecting a phase of the parametric reception signal.   The phase detection means includes a multiplier for multiplying the parametric reception signal by a reference signal having the same frequency as the parametric reception signal, a phase detection means for detecting the phase of the multiplied signal, and the phase detection means. The ultrasonic diagnostic apparatus according to claim 7, further comprising a low-pass filter unit that processes the output signal.   The fundamental wave component removing unit includes a first addition drive signal formed by adding the first drive signal and the second drive signal, and a second obtained by inverting the phase of the first addition drive signal. The first parametric reception signal corresponding to the first addition drive signal, which is sequentially transmitted by the ultrasonic transmission means and sequentially received via the measured medium, and the second parametric reception signal. The ultrasonic diagnostic apparatus according to claim 1, wherein the fundamental wave component is removed by adding the second parametric reception signal corresponding to the addition drive signal in the same phase.   10. The ultrasonic diagnostic apparatus according to claim 9, wherein the fundamental wave component removing means includes a band pass filter having a predetermined frequency as a center frequency. An addition drive signal of the first drive signal having the first frequency characteristic and the second drive signal having the second frequency characteristic is formed, the addition drive signal is converted into an ultrasonic signal, and the ultrasonic wave Ultrasonic transmission means for transmitting a signal toward the medium to be measured;
Along with the propagation of the first ultrasonic signal generated by the first drive signal component of the addition drive signal and the second ultrasonic signal generated by the second drive signal component of the addition signal, Receiving and generating parametric ultrasonic signals and converting them into parametric received signals;
Wireless communication interface means comprising: a wireless transmission interface means for converting the received parametric reception signal into a wireless signal and transmitting; and a wireless reception communication interface means for receiving the transmitted wireless signal and converting it into a wired reception signal;
Fundamental wave component removing means for removing the fundamental wave component from the converted parametric reception signal;
Spatial resolution improving means for improving the spatial resolution in the ultrasonic propagation direction of the parametric reception signal from which the fundamental wave component has been removed;
An ultrasonic diagnostic apparatus comprising: signal processing means for forming an ultrasonic image based on the parametric reception signal with improved spatial resolution.   The wireless interface is connected to the ultrasonic receiving means, oscillates with a signal output from the ultrasonic receiving means at a predetermined frequency, a transmission antenna that transmits an output signal of the oscillation circuit, and the transmission 12. The receiving antenna for receiving a signal transmitted from the antenna, and a demodulating circuit for demodulating the received signal transmitted from the receiving antenna and supplying the demodulated signal to the spatial resolution improving circuit. Ultrasonic diagnostic equipment.   The ultrasonic wave receiving means is a capacitive ultrasonic transducer, and an oscillation circuit that generates an oscillation signal having a frequency determined by the electrostatic capacitance of the capacitive ultrasonic transducer and a DC resistance or a resonance coil The ultrasonic diagnostic apparatus according to claim 11, further comprising: an antenna circuit that transmits a signal generated by the oscillation circuit as a radio signal; and a power supply terminal that supplies power to the modulation circuit and the antenna circuit. .   The wireless communication interface includes an A / D conversion unit that performs analog-digital conversion on the parametric reception signal, a transmission antenna that wirelessly transmits the parametric reception signal digitized by the A / D conversion unit, and a transmission antenna. The ultrasonic wave according to claim 11, further comprising: a receiving antenna that receives a transmitted signal; and a decoding unit that converts the digitally encoded parametric received signal received by the receiving antenna into an analog signal. Diagnostic device. The ultrasonic wave transmitting means forms an addition drive signal of the first drive signal having the first frequency and the second drive signal having the second frequency, and converts the addition drive signal into an ultrasonic signal. Transmitting the ultrasonic signal into the measured medium;
Propagation of the first ultrasonic signal generated by the first drive signal component of the addition drive signal and the second ultrasonic signal generated by the second drive signal component of the addition drive signal by the ultrasonic receiving means And receiving a parametric reception signal generated and propagated in the measured medium and converting it to a parametric reception signal;
Removing fundamental wave components from the parametric reception signal by fundamental wave component removing means;
Improving the spatial resolution in the ultrasonic propagation direction of the parametric reception signal from which the fundamental wave component has been removed by the spatial resolution improving means;
Forming an ultrasonic image on the basis of the parametric reception signal with improved spatial resolution by a signal processing means.

Images