JP2011010793A - Ultrasonography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the distance resolution and azimuth resolution of an ultrasonography.SOLUTION: In a circuit 14 for processing received ultrasonic signals, a component of the same basic frequency f1 as the transmission pulse is extracted with a correlation part F1 composed of a matched filter, and components of harmonic waves f2, f3, ... generated from non-linear distortion of a subject are extracted by one or a plurality of band pass filters F2, F3, .... The extracted components are added after multiplying prescribed coefficients k1, k2, ... by coefficient multipliers K1, K2, ... to be used for the image processing. Accordingly, the signal-to-noise ratio can be improved by subjecting the basic frequency component to the correlation process, and the capability of detecting signals can be improved by the pulse compression effect. At the same time, the penetration (the distance resolution in the depth) can be improved and the contrast to noise can be also improved. Only the basic frequency component permitting use of the transmission signal itself as a reference signal is subjected to the correlation processing, while conventional band pass filters which can be easily prepared are used for harmonic waves, so that the azimuth resolution can be also improved.

Description

  The present invention transmits a first ultrasonic signal from a transmitter into a subject, receives a second ultrasonic signal coming from within the subject such as a reflected wave by the receiver, and receives the received ultrasonic signal from the received signal. The present invention relates to an ultrasonic diagnostic imaging apparatus in which an image processing unit creates a tomographic image in the subject and displays the tomographic image on a display unit, and particularly relates to an apparatus that extracts a higher-order harmonic component from a second ultrasonic signal.

  Ultrasound generally refers to sound waves of 16000 Hz or higher and can be examined non-destructively, harmlessly and in real time, and thus is applied to various fields such as defect inspection and disease diagnosis. For example, an ultrasound that scans the inside of the subject with ultrasound and images the internal state of the subject based on a reception signal generated from a reflected wave (echo) of the ultrasound coming from inside the subject. There is a diagnostic imaging device. This ultrasonic diagnostic imaging apparatus is smaller and less expensive for medical use than other medical imaging apparatuses, has no radiation exposure such as X-rays, is highly safe, and has a blood effect using the Doppler effect. It has various features such as the ability to display flow. For this reason, ultrasonic diagnostic imaging devices are used in the circulatory system (such as the coronary arteries of the heart), the digestive system (such as the gastrointestinal tract), the internal medicine system (such as the liver, pancreas, and spleen), the urinary system (such as the kidney and bladder), and the maternity Widely used in departments.

  In particular, in recent years, not the signal component (fundamental frequency component) of the frequency (fundamental frequency) of the first ultrasound signal transmitted from the ultrasound probe into the subject, but a frequency that is an integral multiple of the fundamental frequency ( Harmonic imaging technology that forms an image of the internal state of a subject using signal components (high-order harmonic components) of higher-order harmonic frequencies has been researched and developed. In this harmonic imaging technology, the side lobe level is small compared to the level of the fundamental frequency component, the S / N ratio (signal to noise ratio) is improved, the contrast resolution is improved, and the beam width is increased by increasing the frequency. The azimuth resolution is improved by narrowing, the sound pressure is small and the fluctuation of sound pressure is small at a short distance, so that multiple reflections are suppressed, and attenuation beyond the focal point is the same as the fundamental wave. Compared with the case where the frequency of the harmonic itself is used as a fundamental wave, it has various advantages such as a greater depth speed.

  However, the generated higher-order harmonics have a problem that the attenuation until the return to the ultrasonic probe is severe and the searchable depth is shallow. Therefore, in Patent Document 1, a fundamental frequency component is used for diagnosis together with a high-order harmonic component. A schematic configuration of the prior art is shown in FIG. As shown in FIG. 14, signals received by the ultrasound probe 101 are transmitted from the bandpass filters B1, B2, B3,..., Bm connected in parallel to the amplifiers A1, A2, A3, and Bm. .., Am are combined by the image combining unit 102 and used for image formation. The center frequency f1 of the bandpass filter B1 is set to the fundamental frequency, and the center frequencies f2, f3,..., Fm of the remaining bandpass filters B2, B3,. Harmonic, 3rd harmonic, 4th harmonic, etc. are set. The fundamental frequency components and the higher-order harmonic components extracted in this way are amplified by the amplifiers A1, A2, A3,..., Am with the respective gains a1, a2, a3,. Is added. By configuring in this way and creating a diagnostic image with a fundamental frequency component in the deep portion and a higher-order harmonic component in the shallow portion, it is possible to form a highly accurate image from the deep portion to the shallow portion.

JP 2004-208918 A

  On the other hand, using a pulse as the first ultrasonic signal for transmission may increase S / N and distance resolution. However, when a broadband signal including the higher-order harmonics is input to the bandpass filter, as shown in FIG. 15, pre-ringing and post-ringing occur in addition to the extracted signal, which hinders improvement in distance resolution. That is, FIG. 15A shows a waveform obtained by passing a fundamental wave pulse through a fundamental band-pass filter B1, and FIG. 15B shows a waveform obtained by passing a third-order harmonic through a band-pass filter B3 of a third-order harmonic. Represents. From these, it is understood that high-order harmonics that are originally high in frequency and expected to improve the distance resolution do not improve the distance resolution with respect to the fundamental wave. Therefore, by passing the higher-order harmonics through the bandpass filters B2, B3,..., Bm, an improvement in azimuth resolution can be expected, but an improvement in distance resolution cannot be expected. Further, since the band-pass filter only outputs the input signal after band limiting, it cannot be expected to improve the S / N.

  An object of the present invention is to provide an ultrasonic diagnostic imaging apparatus that can improve distance resolution, azimuth resolution, and S / N.

  An ultrasonic diagnostic imaging apparatus according to the present invention receives a first ultrasonic signal into a subject and a second ultrasonic signal in which the first ultrasonic signal is reflected in the subject. Generating a tomographic image in the subject from the extraction result of the signal processing unit, a signal processing unit that extracts a desired signal component by performing predetermined signal processing on a reception signal at the receiving unit In the ultrasonic diagnostic imaging apparatus configured to include an image processing unit that performs and a display unit that displays the generated tomographic image, the transmission unit transmits a first ultrasonic signal in pulses, and the signal When the frequency of the first ultrasonic signal is a fundamental frequency, the processing unit performs correlation processing between the output of the receiving unit and a preset reference signal, so that the first output is output from the output of the receiving unit. 2 Components of the fundamental frequency included in the ultrasonic signal A predetermined weight for each of a correlation unit to be detected, a filter for extracting one or more preset higher-order harmonic components from the output of the reception unit, and the output from the correlation unit and the one or more filters And an addition unit for performing addition.

  According to the above configuration, the first ultrasonic signal is transmitted from the transmission unit into the subject, the second ultrasonic signal coming from the subject such as a reflected wave is received by the reception unit, and the signal processing is performed. The image processing unit creates a tomographic image in the subject from the extracted result by performing predetermined signal processing on the received signal by the unit, and an ultrasonic image diagnosis for causing the display unit to display the tomographic image In the apparatus, it should be noted that the first ultrasonic signal transmitted from the transmitting unit is used as a pulse, and the same basic as the transmitted first ultrasonic signal among the second ultrasonic signals received thereby. While the frequency component is extracted by the correlator, the higher-order harmonic component generated by the nonlinear distortion of the subject is extracted by one or more filters that limit the pass band such as a band pass filter. Then, the outputs from the correlation unit and the one or more filters are added with predetermined weights added by the adding unit, and given to the image processing unit.

  Therefore, when a band limiting filter is used for the fundamental frequency component, pre-ringing or post-ringing occurs in addition to the extracted signal, and the S / N is reduced, and correlation processing is performed. Thus, such an extra signal is not generated, and the S / N can be improved, and the return timing can be accurately detected. Furthermore, the signal compression capability can be increased by the pulse compression effect, and the distance resolution can be improved more than the distance resolution determined by the wavelength of the physical frequency, and the S / N and the timing accuracy are improved. In addition, the penetration (distance resolution in the depth direction) can be improved, the contrast with noise becomes clear, and the contrast can also be improved. Also, in the correlation processing, for the fundamental frequency component that can use the transmission signal itself as a reference signal, an appropriate correlation calculator (matched filter) can be realized, but at what level it is generated For high-order harmonics that are difficult to predict, it is difficult to implement such an appropriate correlation calculator (matched filter), so the traditional bandpass filter is used to reliably limit unrelated bands, Use only to improve azimuth resolution. Thus, distance resolution, azimuth resolution, and S / N can be improved.

  The ultrasonic diagnostic imaging apparatus according to the present invention further includes a weight setting unit that sets the weight in the adding unit according to at least one of a diagnostic region and a diagnostic depth in the subject.

  According to the above configuration, the fundamental frequency component and one or more higher-order harmonic components are weighted and used so that a high-resolution higher-order harmonic component that is severely attenuated is a shallow part (short-distance part). The fundamental frequency component, which is suitable for viewing and has a low resolution but reaches far, is suitable for viewing a deep part (far-distance part). Thus, from a shallow part to a deep part, and by weight, it is diagnosed. A suitable and more accurate ultrasonic image can be formed. Here, the diagnostic part and the diagnostic depth of the subject can be represented by an elapsed time with the focal point of the first and second ultrasonic signals and the transmission time of the first ultrasonic signal as the time origin, for example, The weight is set according to the focal point and elapsed time.

  Furthermore, in the ultrasonic diagnostic imaging apparatus of the present invention, the transmission unit uses a chirp wave as the pulse.

  According to the above configuration, a range side rope (time) is obtained by using a chirp wave whose frequency increases or decreases with the passage of time, instead of a simple Gaussian envelope waveform, as a pulse as the first ultrasonic signal. (A side rope) can be suppressed.

  Preferably, the correlation unit includes an analog product-sum operation device based on a CCD principle.

  According to the above configuration, it is possible to perform correlation processing more appropriately even with a weak signal level.

  In the ultrasonic diagnostic imaging apparatus of the present invention, the ultrasonic transducers in the transmission unit and the reception unit are formed by laminating an organic piezoelectric element for reception on an inorganic piezoelectric element for transmission. .

  According to the above configuration, an organic piezoelectric element capable of receiving a relatively wide band for reception is used by using an inorganic piezoelectric element capable of transmitting high power for transmission for the ultrasonic transducers in the transmission unit and the reception unit. By using the piezoelectric element, it is possible to receive high-order harmonic components with high sensitivity.

  As described above, the ultrasonic diagnostic imaging apparatus of the present invention uses the first ultrasonic signal transmitted from the transmission unit as a pulse, and transmits the first ultrasonic signal transmitted among the received second ultrasonic signals. While the same fundamental frequency component as the ultrasonic signal is extracted by the correlation unit, the higher-order harmonic component generated by the nonlinear distortion of the subject is extracted by one or more filters that limit the pass band such as a band pass filter. The outputs from the correlation unit and the one or more filters are added with a predetermined weight in the adding unit, and used for image processing.

  Therefore, by performing correlation processing on the fundamental frequency component, the S / N can be improved and the timing of returning can be detected accurately. Furthermore, the signal compression capability can be increased by the pulse compression effect, and the distance resolution can be improved more than the distance resolution determined by the wavelength of the physical frequency, and the S / N and the timing accuracy are improved. In addition, the penetration (distance resolution in the depth direction) can be improved, the contrast with noise becomes clear, and the contrast can also be improved. Also, in the correlation processing, for the fundamental frequency component that can use the transmission signal itself as a reference signal, an appropriate correlation calculator (matched filter) can be realized, but at what level it is generated For high-order harmonics that are difficult to predict, it is difficult to implement such an appropriate correlation calculator (matched filter), so the traditional bandpass filter is used to reliably limit unrelated bands, Use only to improve azimuth resolution. Thus, distance resolution, azimuth resolution, and S / N can be improved.

It is a figure which shows the external appearance structure of the ultrasound diagnosing device in embodiment. It is a block diagram which shows the electrical structure of the ultrasonic diagnosing device in embodiment. It is a figure which shows the structure of the ultrasound probe in the ultrasound diagnosing device of embodiment. It is a block diagram of a signal processing circuit of an embodiment which processes a reception ultrasonic signal. In describing correlation processing and image processing, it is a diagram showing a more specific configuration of the ultrasonic diagnostic apparatus according to the embodiment. It is a figure for demonstrating the operation | movement which transfers an electric charge. It is a figure for demonstrating the operation | movement which divides one electric charge into 2 equal parts. It is a figure for demonstrating the operation | movement which integrates two electric charges. It is a wave form diagram for demonstrating correlation calculation. It is a figure for demonstrating typically the mode of the signal processing by this invention. It is a simulation image which shows the experimental result by this inventor. It is a figure for demonstrating typically the mode of improvement of penetration by the present invention. It is a figure for demonstrating the mode of the improvement of the contrast by this invention. 1 is a block diagram of a typical prior art signal processing circuit. FIG. It is a wave form diagram for demonstrating the ringing generate | occur | produced when a transmission signal is made into a pulse and a received signal is band-pass-filter-processed with the said signal processing circuit.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. Further, in this specification, as appropriate, a generic reference is used to indicate a reference numeral without a suffix, and an individual configuration is indicated by a reference numeral with a suffix.

  FIG. 1 is a diagram showing an external configuration of an ultrasound diagnostic imaging apparatus S in the embodiment, and FIG. 2 is a block diagram showing an electrical configuration of the ultrasound diagnostic imaging apparatus S in the embodiment. As shown in FIGS. 1 and 2, the ultrasonic diagnostic imaging apparatus S transmits ultrasonic waves (first ultrasonic signals) to a subject such as a living body (not shown), and the subject or contrast agent. The ultrasonic probe 2 that receives the reflected (echoed) or generated ultrasonic wave (second ultrasonic signal) at 2 and is connected to the ultrasonic probe 2 via the cable 3, and the ultrasonic probe. 2 transmits the first ultrasonic signal to the subject by transmitting the transmission signal of the electrical signal to the object 2 via the cable 3 and is received by the ultrasonic probe 2. Apparatus for imaging an internal state of a subject as an ultrasound image based on a received signal of an electrical signal generated by the ultrasound probe 2 in response to a second ultrasound signal coming from within the subject A main body 1 is provided.

  For example, as illustrated in FIG. 2, the diagnostic apparatus body 1 includes an operation input unit 11, a transmission unit 12, a reception unit 13, a signal processing unit 14, an image processing unit 15, a display unit 16, and a control unit. 17, a reference signal storage unit 18, and a timing generation unit 19.

  The operation input unit 11 is a device that accepts input of data such as a command for instructing start of diagnosis and personal information of a subject, for example, and is an operation panel or a keyboard provided with a plurality of input switches, for example.

  The transmission unit 12 is a circuit that supplies a transmission signal of an electrical signal to the ultrasonic probe 2 via the cable 3 under the control of the control unit 17 and generates a first ultrasonic signal in the ultrasonic probe 2. It is. The first ultrasonic signal is a pulse of a chirp wave that increases or decreases the frequency at a preset rate with the passage of time from the viewpoint of being easily detected by correlation processing without being normally present in the natural world. Is used. The transmission unit 12 includes, for example, a transmission beam former circuit 122 (see FIG. 4) that forms a transmission beam according to a transmission signal from the control unit 17, and each inorganic piezoelectric element 22 of the ultrasonic probe 2 according to the transmission beam. And a drive signal generation circuit 121 (see FIG. 4) for generating a drive signal for actually driving. Each transmission signal is given a time difference corresponding to the focal point (focus point) and / or the steering angle (azimuth). The receiving unit 13 is a circuit that receives a reception signal of an electrical signal from each organic piezoelectric element 21 of the ultrasonic probe 2 through the cable 3 under the control of the control unit 17. Output to. The receiving unit 13 includes, for example, an amplifier that amplifies the received signal with a preset amplification factor.

  As will be described later, the signal processing unit 14 filters the output of the receiving unit 13 to convert the first ultrasonic signal for transmission from the second ultrasonic signal received by the receiving unit 13 to the fundamental frequency. In this case, the fundamental frequency component and a plurality of higher-order harmonic components are extracted, added at a desired ratio, and then given to the image processing unit 15.

  The reference signal storage unit 18 includes a storage element such as a ROM or an EEPROM, and is a circuit that stores a transmission signal and a signal serving as a reference signal for correlation processing described later. A reference signal to the signal processing unit 14 may be supplied to the transmission unit 12.

  The timing generation unit 19 is a circuit that generates the operation timing of each unit of the diagnostic apparatus body 1 and outputs the operation timing to each unit that requires the operation timing.

  The image processing unit 15 is an image (ultrasonic image) of the internal state of the subject based on the fundamental frequency component and the higher-order harmonic component extracted by the signal processing unit 14 as described above under the control of the control unit 17. It is a circuit which forms. Note that the image processing unit 15 may appropriately include a function of generating a conventional B-mode tomographic image from the reception signal at the reception unit 13.

  The display unit 16 is a device that displays an ultrasonic tomographic image of the subject generated by the image processing unit 15 under the control of the control unit 17. The display unit 16 can be realized by a display device such as a CRT display, LCD, organic EL display and plasma display, a printing device such as a printer, or the like.

  The control unit 17 includes, for example, a microprocessor, a storage element, and peripheral circuits thereof. The operation input unit 11, the transmission unit 12, the reception unit 13, the signal processing unit 14, the image processing unit 15, the display unit 16, and the like. This is a circuit that performs overall control of the ultrasound diagnostic imaging apparatus S by controlling the reference signal storage unit 18 according to the function.

  FIG. 3 is a cross-sectional view of the ultrasonic transducer 20 constituting the ultrasonic probe 2 of the embodiment. As described above, the ultrasound probe (ultrasound probe) 2 transmits the first ultrasound signal into the subject, and the second probe coming from inside the subject in response to the first ultrasound signal. The apparatus for receiving the ultrasonic signal is composed of inorganic and organic piezoelectric materials, and converts between an electric signal and an ultrasonic signal by utilizing a piezoelectric phenomenon. That is, the ultrasonic transducer 20 is generally formed by laminating an organic piezoelectric element 21 on the inorganic piezoelectric element 22. Specifically, as shown in FIG. 3, a flat plate-like acoustic braking member 23 serving as a backing layer, the plurality of inorganic piezoelectric elements 22 stacked on the acoustic braking member 23, and the plurality of inorganic piezoelectric elements. The acoustic absorber 24 filled in the gap in the element 22, the common ground electrode layer 25 stacked on the plurality of inorganic piezoelectric elements 22, the intermediate layer 26 stacked on the common ground electrode layer 25, The sheet-like organic piezoelectric element 21 laminated on the intermediate layer 26 and an acoustic matching layer 27 laminated on the organic piezoelectric element 21 are configured.

  The acoustic braking member 23 is made of a material that absorbs ultrasonic waves, and absorbs ultrasonic waves radiated from the inorganic piezoelectric element 22 to the back side. The acoustic absorber 24 is made of thermosetting resin such as polyimide resin or epoxy resin, and absorbs ultrasonic waves similarly to the acoustic braking member 23 to reduce crosstalk between the plurality of inorganic piezoelectric elements 22. To do.

Each inorganic piezoelectric element 22 includes electrodes (element electrodes) 222 and 223 on both surfaces of a piezoelectric body (element piezoelectric body) 221 made of an inorganic piezoelectric material. Examples of the inorganic piezoelectric material include zirconate titanate (PZT (registered trademark)), crystal, lithium niobate (LiNbO ₃ ), potassium tantalate niobate (K (Ta, Nb) O ₃ ), and barium titanate. (BaTiO ₃ ), lithium tantalate (LiTaO ₃ ), strontium titanate (SrTiO ₃ ), and the like.

  These inorganic piezoelectric elements 22 are formed by stacking electrodes 222 and 223 on both surfaces of a sheet-like piezoelectric body 221 on which signal electrodes 224 are formed so as to penetrate the acoustic braking member 23. After being cut, each inorganic piezoelectric element 22 is cut out and the acoustic absorbing material 24 is filled between the inorganic piezoelectric elements 22, or each inorganic piezoelectric element 22 is cut out and filled with the acoustic absorbing material 24. A sheet-like member is laminated on the acoustic braking member 23. The electrode 223 is grounded through the common ground electrode layer 25, and individual drive signals are input from the drive signal generation circuit of the transmission unit 12 to the signal electrode 224 through the electrode 222 through the cable 3.

  The intermediate layer 26 is a member for laminating the organic piezoelectric element 21 on the inorganic piezoelectric element 22 and matches their acoustic impedance.

  The organic piezoelectric element 21 includes a piezoelectric body 211 made of a flat organic piezoelectric material having a predetermined thickness, an individual electrode 212 formed on one surface of the piezoelectric body 211, and the other surface of the piezoelectric body 211. And a common electrode 213 formed uniformly over substantially the entire surface of the sheet-like piezoelectric element. By configuring in this way, each organic piezoelectric element 21 can be individually operated even if it is formed as an integral sheet, and operations such as cutting out elements and filling gaps like the organic piezoelectric element 22 can be performed. It becomes unnecessary and the manufacturing process can be simplified. The individual electrode 212 outputs a reception signal to the reception beamformer of the reception unit 13.

  Depending on the number of the organic piezoelectric elements 21 and the like, a group may be constituted by some elements, and the common electrode 231 may be provided for each group. Further, in the example shown in FIG. 3, the organic piezoelectric element 21 is laminated over the entire inorganic piezoelectric element 22, but may be laminated only over a part thereof. The number of organic piezoelectric elements 21 and inorganic piezoelectric elements 22 may be the same or different, and each occupation area may be designed according to specifications required for each element. As shown in FIG. 3, when the number of organic piezoelectric elements 21 is larger than the number of inorganic piezoelectric elements 22, the size (size) of each inorganic piezoelectric element 22 can be increased. When the inorganic piezoelectric element 22 is used for transmission, the transmission power can be increased, the number of organic piezoelectric elements 21 can be increased, and reception resolution can be improved when the organic piezoelectric element 21 is used for reception. it can. For example, 4096 of 64 × 64 organic piezoelectric elements 21 are arranged in a two-dimensional matrix.

  As the organic piezoelectric material, for example, a polymer of vinylidene fluoride (VDF) can be used. Alternatively, a vinylidene fluoride copolymer can be used as the organic piezoelectric material. This vinylidene fluoride copolymer is a copolymer (copolymer) of vinylidene fluoride and other monomers. Examples of the other monomers include ethylene trifluoride, tetrafluoroethylene, perfluoroalkyl vinyl ether ( PFA), perfluoroalkoxyethylene (PAE), perfluorohexaethylene, and the like can be used. In the vinylidene fluoride copolymer, the electromechanical coupling constant (piezoelectric effect) in the thickness direction varies depending on the copolymerization ratio, and therefore an appropriate copolymerization ratio is adopted according to the specifications of the ultrasonic probe 2 and the like. For example, in the case of vinylidene fluoride / ethylene trifluoride copolymer, the copolymerization ratio of vinylidene fluoride is preferably 60 mol% to 99 mol%, and in the case of a composite element in which an organic piezoelectric element is laminated on an inorganic piezoelectric element, The copolymerization ratio of vinylidene is more preferably 85 mol% to 99 mol%. In the case of such a composite element, the other monomers are preferably perfluoroalkyl vinyl ether (PFA), perfluoroalkoxyethylene (PAE), and perfluorohexaethylene. For example, polyurea can be used for the organic piezoelectric material. In the case of this polyurea, it is preferable to produce a piezoelectric body by vapor deposition polymerization. Examples of the monomer for polyurea include a general formula and an H2N-R-NH2 structure. Here, R may include an alkylene group, a phenylene group, a divalent heterocyclic group, or a heterocyclic group which may be substituted with any substituent. The polyurea may be a copolymer of a urea derivative and another monomer. Preferred polyureas include aromatic polyureas using 4,4'-diaminodiphenylmethane (MDA) and 4,4'-diphenylmethane diisocyanate (MDI).

  The acoustic matching layer 27 is a member that matches the acoustic impedance of the inorganic piezoelectric element 22 and the acoustic impedance of the subject and matches the acoustic impedance of the organic piezoelectric element 21 and the acoustic impedance of the subject. The acoustic matching layer 27 has a shape that bulges in an arc shape, and also has a function as an acoustic lens that converges ultrasonic waves transmitted toward the subject.

  In the ultrasonic diagnostic imaging apparatus S having such a configuration, for example, when an instruction to start diagnosis is input from the operation input unit 11, the transmission unit 12 specifies based on the ROI (region of interest) under the control of the control unit 17. A delay of the beamformer 122 (see FIG. 5) is given from the steering angle (azimuth) and the depth of the focal point, and the chirp wave transmission signal formed by the PCM is generated. This transmission signal is supplied to the element to be beam-formed among the inorganic piezoelectric elements 22 of the ultrasonic probe 2 via the cable 3, and the element expands and contracts in the thickness direction and resonates. Amplitude ultrasonic vibrations can be generated. This ultrasonic vibration enters the subject as a first ultrasonic signal from the intermediate layer 26 through the organic piezoelectric element 21 and the acoustic matching layer 27. Note that the ultrasound probe 2 may be used in contact with the body surface of the subject (living body), or may be used by being inserted into the inside of the subject, for example, the body cavity of the living body.

  The ultrasonic waves transmitted to the subject are converged at the focal point of the steering angle (orientation), reflected at one or more boundary surfaces having different acoustic impedances inside the subject, and reflected ultrasonic waves ( Second ultrasonic signal). In the second ultrasonic signal, not only the frequency component of the transmitted first ultrasonic signal but also the higher frequency of an integral multiple of the first ultrasonic signal when the frequency is the fundamental frequency. Wave components are also included. For this reason, the organic piezoelectric element 21 is used for reception so that a broadband ultrasonic signal can be received. In the present embodiment, as will be described in detail below, the fundamental frequency component and the higher-order harmonic component are extracted by the signal processing unit 14 from the reception signal at the organic piezoelectric element 21, and the image processing unit 15 Used to create tomographic images. A transmission / reception switching circuit is connected to the inorganic piezoelectric element 22 so that the fundamental frequency component is received by the transmitted inorganic piezoelectric element 22 and the organic piezoelectric element 21 receives only the higher-order harmonic component. Also good.

  FIG. 4 is a block diagram showing a schematic configuration of the signal processing circuit 14 according to the embodiment of the present invention. It should be noted that in the signal processing circuit 14 of the present embodiment, a signal received by the organic piezoelectric element 21 is input from the receiving unit 13 to the signal processing circuit 14 and connected to each other in parallel. F1 and bandpass filters F2, F3,..., Fm. The outputs from the correlation unit F1 and the band pass filters F2, F3,..., Fm are multiplied by predetermined coefficients k1, k2,. Then, they are synthesized by the image processing unit 15 and used for image formation. The center frequency f1 of the correlation unit F1 is set to the fundamental frequency, and the center frequencies f2, f3,..., Fm of the remaining bandpass filters F2, F3,. Wave, third harmonic, fourth harmonic,...

  Next, the correlation processing in the correlation unit F1 will be described more specifically. FIG. 5 is a diagram illustrating a specific configuration example of the correlation unit F1. Here, since the amount of energy that the higher-order harmonic component occupies in the entire received signal is weak, if the correlation processing is performed after digitally converting the received analog signal (second ultrasonic signal), the quality is high. The dynamic range required for forming an ultrasonic image cannot be obtained. Therefore, it should be noted that the correlation unit F1 in the present embodiment performs the correlation processing itself by analog processing.

  Therefore, the correlation unit F1 is provided for each i organic piezoelectric elements 21, and the outputs of the corresponding organic piezoelectric elements 21 are input thereto. That is, a large number of organic piezoelectric elements 21 are connected to this correlation unit F1 in a time division manner as a group, and the i correlation units are denoted by reference numerals F1-1, F1-2, F1-3,. .., F1-i (generally referred to by the reference symbol F1). Similarly, the remaining band-pass filters F2, F3,..., Fm are provided for each i organic piezoelectric elements 21, but only one is shown in FIG. Each correlator F1 performs correlation processing between the received signal (second ultrasonic signal) from the corresponding organic piezoelectric element 21 and the reference signal set in advance by the coefficient setting unit 33, whereby the degree of coincidence between them is determined. This circuit has a similar configuration. In the present embodiment, as described above, the reference signal is the same as the transmission signal, the coefficient sequence stored in the reference signal storage unit 18 is read by the control unit 17, and the transmission beam of the transmission unit 12 is transmitted as the transmission signal. It is given to the former 122 and set in the coefficient setting unit 33 as a template data string.

  The correlation unit F1 is a circuit that calculates the correlation between the output of the reception unit 13 and the reference signal by performing an analog product-sum operation based on the CCD principle, and includes a sample hold unit 31, a charge transfer unit 32, and the coefficient A setting unit 33, a digital / analog multiplication unit 34, and an addition unit 35 are provided.

  The sample hold unit 31 is a circuit that holds the output of the reception unit 13 (the output of the organic piezoelectric element 21 connected to the sample hold unit 31) at a sampling period corresponding to the operation timing from the timing generation unit 19. . The sample hold unit 31 outputs the charge Q corresponding to the held output of the receiving unit 13 to the charge transfer unit 32 at a timing according to the operation timing.

  The charge transfer unit 32 includes a plurality of charge holding units 321-1, 321-2, 321-3,..., 321-n (hereinafter collectively referred to as reference numeral 321) that hold the charge Q. These charge holding portions 321 are connected in series. Then, at the sampling timing of the sample hold unit 31, the held charge Q is output to the subsequent charge holding unit 321, the charge Q of the previous charge holding unit is taken in, and thus the held charge Q is changed like a shift register. Transfer sequentially.

  For example, as shown in FIG. 6, such a charge transfer portion 32 is formed on the insulator layer 42 so as to be continuously disposed with the semiconductor 41, the insulator layer 42 formed on the semiconductor 41. A plurality of electrodes (gate electrodes) 43 are provided, and by applying a drive voltage having a predetermined pattern for transferring the charge Q to each of these electrodes 43, the electrodes are accumulated in a potential well below a certain electrode. The charge transfer element (charge-coupled device, CCD) TD for sequentially transferring the charge Q to the potential well below the subsequent electrode can be formed. In the example illustrated in FIG. 6, a charge transfer element TD including six electrodes 43-1 to 43-6 is illustrated. In addition, signal lines P41 to P43 for applying a voltage to the electrode 43 are connected to the electrodes 43 (43-1 to 43-6). For example, at time t1, the charge Q is held in the first potential well PW1 formed by applying a voltage to the first electrode 43-1. At time t2 (t21, t22) of the next operation timing, first, a voltage is applied to each of the first and second electrodes 43-1 and 43-2, so that the first potential well PW1 becomes the first electrode 43. -1 as well as below the second electrode 43-2, the charge Q is held in the potential well PW12 formed under these electrodes 43-1 and 43-2 (time t21). The voltage of the first electrode 43-1 is gradually changed to 0 as time elapses while the voltage of the two electrodes 43-2 is left as it is, so that the charge Q of the first potential well PW1 gradually moves to the first potential well PW2. Move (time t22). Then, at time t3 of the next operation timing, the voltage applied to the first electrode 43-1 is eliminated, so that the charge Q is applied to the potential well PW2 formed under the second electrode 43-2. Move completely. By repeating such an operation, the electric charge Q accumulated in the potential well PW1 under the first electrode 43-1 is transferred and held in the potential well PW2 under the adjacent second electrode 43-2. By performing such an operation sequentially from the downstream charge holding unit 321-n toward the upstream charge holding unit 321-1 within the sampling period, the charge in each charge holding unit 321 is changed as described above. Sequentially transferred to the subsequent stage.

  The digital / analog multiplication unit 34 includes a plurality of digital / analog multipliers (DA multipliers) 341-1 to 341- provided corresponding to the charge holding units 321 (321-1 to 321-n) of the charge transfer unit 32. n (when generically referred to, this is indicated by reference numeral 341 below). The DA multiplier 341 multiplies the charge Q of the corresponding charge holding unit 321 by the coefficient g (l) (0 ≦ g (l) <1) preset by the coefficient setting unit 33, and adds the multiplication results. This is a circuit for outputting to the unit 35. More specifically, g (l) × Q = g1 (l) × 2-1Q + g2 (l) × 2-2Q + g3 (l) × 2-3Q +... + Gn (l) × 2-nQ Therefore, in the DA multiplier 341, the charge (analog signal) Q held in the charge holding unit 321 is divided into two equal parts, and one is further divided into two equal parts. −2Q, 2-3Q,..., 2-nQ are generated, and each of these charges is a binary expression g1 (l), g2 (l), g3 of a coefficient g (l) that is a multiplier. (L),..., Gn (l) are discarded, and the electric charges picked up from them are integrated into one, whereby the multiplication of g (l) × Q is performed by analog processing.

  Such a DA multiplier 341 can also be configured using a charge transfer element (charge coupled device), and can be configured including, for example, a charge dividing unit CD and a charge integrating unit SD. For example, as shown in FIG. 7, the charge dividing unit CD that divides one charge Q into two charges is divided into a semiconductor 51, an insulator layer 52 formed on the semiconductor 51, an insulator And a plurality of electrodes (gate electrodes) 53 (53-1 to 53-6) continuously formed on the layer 52, each of which includes one set of three electrodes 53 and one divided portion CDk. FIG. 7 shows a first divided portion CD1 including the electrodes 53-1 to 53-3 and a second divided portion CD2 including the electrodes 53-4 to 53-6. In addition, signal lines P51 to P53 for applying a voltage to the electrode 53 are connected to the electrodes 53 (53-1 to 53-6).

  In such a charge dividing section CD, a potential well PW is formed in the semiconductor 31 under the electrode 53 by applying a voltage to the electrode 53 from the outside. The depth of the potential well PW is controlled by the potential applied to the corresponding electrode 53 from the outside. In such a charge dividing unit CD, a predetermined pattern is driven so as to divide the charge Q into the electrodes 53-1 to 53-3; 53-4 to 53-6 in the first and second dividing units CD1 and CD2. By applying a voltage, the charge Q held in the first division unit CD1 is equally divided into two charges Q1, Q2 (Q1 = Q2 = Q / 2), and each of the charges Q1, Q2 is first And held in the second division parts CD1 and CD2.

  For example, at time t11, the first state of the first divided portion CD1 formed by applying a voltage to the third electrode 53-3 of the first divided portion CD1 as an initial state (before being divided into two equal parts and before being divided). It is assumed that the charge Q is held in the potential well PW3. Then, at time t12 of the next operation timing, a voltage is applied to each of the second and third electrodes 53-2 and 53-3 of the first division unit CD1 and the first electrode 53-4 of the second division unit CD2. Thus, the first potential well PW3 of the first division part CD1 is not only under the third electrode 53-3 but also under the second electrode 53-2 of the first division part CD1 and the first electrode 53 of the second division part CD2. −4 also spreads, and the charge Q is held in the potential well PW234 formed under each of the electrodes 53-2 to 53-4.

  At time t13 of the next operation timing, the voltage applied to the third electrode 53-3 of the first division unit CD1 is eliminated, and the second electrode 53-2 and the second division unit of the first division unit CD1 are eliminated. When a voltage is applied to the first electrode 53-4 of CD2, a charge Q is formed below the second electrode 53-2 of the first divided part CD1, and the first electrode of the second divided part CD2 Divided and held in potential wells PW4 formed below 53-4. The charge Q accumulated in one potential well PW3 in this way is divided into two equal parts to potential wells PW2 and PW4 adjacent to the potential well PW3 by applying a drive voltage of a predetermined pattern to the electrode 53. Retained.

  Subsequently, in FIG. 7, at the time t14 of the next operation timing, the first division unit CD1 applies a voltage to the first and second electrodes 53-1, 53-2, thereby the first division unit CD1. The second potential well PW2 extends not only under the second electrode 53-2 but also under the first electrode 53-1, and the charge Q1 (= Q / 2) is transferred to the first and second electrodes 53-1, 53-. 2 is held in the potential well PW12 formed below. In the second divided portion CD2, a voltage is applied to the first and second electrodes 53-4 and 53-5, so that the first potential well PW4 of the second divided portion CD2 is below the first electrode 53-4. In addition, the charge Q2 (= Q / 2) spreads below the second electrode 53-5 and is held in the potential well PW45 formed below the first and second electrodes 53-4 and 53-5.

  At time t15 of the next operation timing, in the first division unit CD1, the voltage applied to the second electrode 53-2 of the first division unit CD1 is eliminated, and the first electrode 33 of the first division unit CD1 is eliminated. −1 is applied with a voltage, the charge Q1 divided into two equal parts is held in the first potential well PW1 of the first divided portion CD1 formed under the first electrode 53-1 of the first divided portion CD1. The In the second division unit CD2, the voltage applied to the first electrode 53-4 of the second division unit CD2 is eliminated, and the voltage is applied to the second electrode 53-5 of the second division unit CD2. Thus, the charge Q2 divided into two equal parts is held in the second potential well PW5 of the second divided portion CD2 formed under the second electrode 53-5 of the second divided portion CD2.

  In this way, the charge dividing unit D is held in the third potential well PW3 of the first dividing unit CD1 by applying a driving voltage having a predetermined pattern that divides the charge Q into two equal parts. The electric charge Q is divided into two equal parts and led to the second potential well PW2 (first potential well PW1) of the first divided portion CD1 and the second potential well PW5 (third potential well PW6) of the second divided portion CD2. By holding, the charge Q can be divided into two equal parts.

  The charge integration unit SD that integrates a plurality of charges into one charge is also formed on the semiconductor 61, the insulator layer 62 formed on the semiconductor 61, and the insulator layer 62, for example, as shown in FIG. A plurality of continuously formed electrodes (gate electrodes) 63 (63-1 to 63-6), and a single integrated portion SDk including a set of three electrodes 63, FIG. 8 illustrates a first integration unit SD1 including the electrodes 63-1 to 63-3 and a second integration unit SD2 including the electrodes 63-4 to 63-6. Further, signal lines P61 to P63 for applying a voltage to the electrode 63 are connected to the electrodes 63 (63-1 to 63-6).

  In such a charge integration portion SD, a potential well PW is formed in the semiconductor 61 under the electrode 63 by applying a voltage to the electrode 63 from the outside. The depth of the potential well PW is controlled by the potential applied to the corresponding electrode 63 from the outside. In such a charge integration unit SD, a driving voltage having a predetermined pattern that integrates charges into the electrodes 63-1 to 63-3; 63-4 to 63-6 in the first and second integration units SD1 and SD2 is applied. By applying, the first charge Q1 held in the first integration part SD1 and the second charge Q2 held in the second integration part SD2 are combined into one charge Q (Q = Q1 + Q2). The charge Q is integrated and held in the first integration unit SD1 (second integration unit SD2).

  For example, at time t21, as an initial state (before addition processing), the first potential well PW1 of the first integrated unit SD1 formed by applying a voltage to the first electrode 63-1 of the first integrated unit SD1 The first charge Q1 is held, and the second charge Q2 is held in the second potential well PW5 of the second integration part SD2 formed by applying a voltage to the second electrode 63-5 of the second integration part SD2. ing. At time t22 of the next operation timing, in the first integration unit SD1, a voltage is applied to the first and second electrodes 63-1 and 63-2 of the first integration unit SD1, so that the first integration unit SD1 The first potential well PW1 extends not only under the first electrode 63-1, but also under the second electrode 63-2, and a first charge Q1 is formed under the first and second electrodes 63-1, 63-2. Held in the potential well PW12. In the second integration unit SD2, a voltage is applied to the first and second electrodes 63-4 and 63-5 of the second integration unit SD2, so that the second potential well PW5 of the second integration unit SD2 Not only under the two electrodes 63-5 but also under the first electrode 63-4, the second charge Q2 is held in the potential well PW45 formed under the first and second electrodes 63-4 and 63-5. The

  At time t23 of the next operation timing, in the first integration unit SD1, the voltage applied to the first electrode 63-1 of the first integration unit SD1 is eliminated, and the voltage is applied to the second electrode 63-2. As a result, the first charge Q1 held in the potential well PW12 formed under the first and second electrodes 63-1 and 63-2 is integrated with the first integration formed under the second electrode 63-2. It is moved and held in the second potential well PW2 of the part SD1. In the second integration unit SD2, the voltage applied to the second electrode 63-5 of the second integration unit SD2 is eliminated, and the voltage is applied to the first electrode 63-4. The second charge Q2 held in the potential well PW45 formed under the two electrodes 63-4 and 63-5 moves to the first potential well PW4 of the second integrated portion formed under the first electrode 63-4. Held. By such an operation, the first charge Q1 of the first integration unit SD1 approaches the second integration unit SD2, and the second charge Q2 of the second integration unit SD2 approaches the first integration unit SD1, and the first integration unit SD1 The second electrode 63-2 and the first electrode 63-4 of the second integration part SD2 are arranged with one electrode (the third electrode 63-3 of the first integration part) 63 therebetween.

  Then, at the time t24 of the next operation timing, the third electrode 63-3 of the first integration unit SD1 that separates the first charge Q1 of the first integration unit SD1 from the second charge Q2 of the second integration unit SD2. The same voltage as the voltage applied to the second electrode 63-2 of the first integration unit SD1 and the first electrode 63-4 of the second integration unit SD2 is applied to the first integration unit SD1. The second potential well PW2 extends not only under the second electrode 63-2 but also under the third electrode 63-3, and the first potential well PW4 of the second integration part SD2 is not only under the first electrode 63-4. As a result of extending below the third electrode 63-3 of the first integration unit SD1, the second electrode 36-2 and the third electrode 63-3 of the first integration unit SD1 and the first electrode 63- of the second integration unit SD1. Potential well PW over 4 34 is formed, a first charge Q1 of the first integrated portion SD1 and the second charge Q2 of the second integration section SD2 is integrated.

  Then, at time t25 of the next operation timing, the voltage applied to the second electrode 63-2 of the first integration unit SD1 is canceled and applied to the first electrode 63-4 of the second integration unit SD2. When the voltage is canceled and a voltage is applied to the third electrode 63-3 of the first integration unit SD1, the first charge Q1 of the integrated first integration unit CD1 and the second integration unit SD2 are second. The charge Q2 is held in the third potential well PW3 of the first integration unit SD1 formed below the third electrode 63-3 of the first integration unit SD1, and the addition result Q (= Q1 + Q2) is obtained.

  In this way, the charge integration unit SD applies the drive voltage of a predetermined pattern to each electrode, thereby causing the first charge Q1 held in the potential well PW of the first integration unit SD1 and the potential well of the second integration unit SD2. The second charge Q2 held in PW is led to and integrated with one potential well PW, whereby the first charge Q1 of the first integration unit SD1 and the second charge Q2 of the second integration unit SD2 are combined. It can be added as it is. That is, the charge integration unit SD can add the first charge Q1 of the first integration unit SD1 and the second charge Q2 of the second integration unit SD2 in an analog manner.

  The DA multiplier 341 includes, for example, a plurality of the bit division units CD connected in series of several bits according to the binary expression of the coefficient g (l), and the charge integration unit SD, and the charge holding unit 321. The charge amount Q corresponding to the output value is divided into two equal parts by the charge dividing unit CD as described above, and one of them is divided into two equal parts by the subsequent charge dividing unit CD in the two divided charge dividing parts CD. , By repeating this, a plurality of charges of 2-1Q, 2-2Q, 2-3Q,..., 2-nQ are generated, and each of these charges is represented by a binary expression g1 ( l), g2 (l), g3 (l),..., gn (l), and by integrating the picked-up charges in the charge integration unit SD, the multiplication of G (l) × Q is analog. Is something that can be done with. Therefore, in the rounding according to the binary representation g1 (l), g2 (l), g3 (l),..., Gn (l) of the coefficient g (l), if the bit is 0, it is discarded. If is 1, leave it. For example, when multiplying by Q × 0.36827 (decimal number), it becomes Q × 0.01011110 (binary number), and Q × (0 + 0/2 + 1/4 + 0/8 + 1/16 + 1/32 + 1/64 + 1/128 + 0 / 256). The multiplication results in the DA multipliers 341-1 to 341-n are added to each other by the adding unit 35 configured in the same manner as the charge integrating unit SD, and each correlating unit F1-1, F0-2, F0-. 3,..., F0-i outputs Y1, Y2,. In the DA multiplier 341, the charge amount Q of the charge holding unit 321 is transferred via the sensing floating gate, and the charge amount Q equal to the output value (charge amount Q) of the charge holding unit 321 is held.

  As described above, the correlation unit F1 uses the charge Q that is an analog signal and, as described above, is a device that includes an analog product-sum operation device based on the CCD principle that can perform delay (transfer), multiplication, and addition. By using this, correlation processing calculation can be performed with high resolution, high speed and low power consumption.

  In the correlation unit F1 having such a configuration, since the charge Q to be handled is a positive value, for example, between the reception unit 13 and the sample hold unit 31 in order to handle both positive and negative outputs of the reception unit 13. An absolute value conversion circuit that outputs the absolute value of the input signal and outputs a positive / negative sign (sign bit string) in the input signal may be interposed in between. In this case, the sign (sign bit string) is These units are configured to propagate through the sample and hold unit 31, the charge transfer unit 32, the digital / analog multiplication unit 34, and the addition unit 35 in accordance with the processing of the absolute valued signal.

  Such a DA multiplier 341 includes, for example, Japanese Patent Application Laid-Open No. 6-237173 (Japanese Patent No. 2599679), Japanese Patent Application Laid-Open No. 6-350453 (Japanese Patent No. 2955734), and Japanese Patent Application Laid-Open No. 7-335866 (Patent No. 2). No. 2,665,726) and JP-A-8-050546 can also be referred to.

  The coefficient setting unit 33 is a circuit that sets the coefficient g (l) for each DA multiplier 341 of the digital / analog multiplication unit 34 based on the reference signal stored in the reference signal storage unit 18.

  The correlation unit F1 having such a configuration operates as follows. The correlation process in the correlation unit F1 is a process for determining how similar two waveforms are. For example, when there are two number sequences xn and zn, the correlation value Y expressed by the following equation 1 is large. The two sequences are similar.

Y = Σxkzz (1)
However, Σ calculates the sum from k = 1 to k = n.

  Here, the transmission signal (reference signal) is s (t), and the transmission signal s (t) including noise is the reception signal x (t). ) Is Y, a steep peak is detected at the moment when the reference signal s (t) and the received signal x (t) overlap as shown by the wavy line in FIG. The larger this peak is, the more closely received the signal is similar to the reference signal s (t). In FIG. 9, the transmission signal s (t) is indicated by a thick solid line, and the reception signal x (t) is indicated by a thin solid line. Further, in FIG. 9, although the correlation peak seems to be shifted, after the correlation calculation between the reference signal s (t) and the received signal x (t), the correlation result is output in accordance with the signal start timing. As a result, a relative time delay occurs in the digital calculation, and this waveform is obtained.

  In practice, as shown in FIG. 5, a continuous reception signal x (t) received by the receiving unit 13 is sampled and held at time τ, and discrete quantities f (t), f (t−τ), f ( t−2τ), f (t−3τ), f (t−4τ),. In the example shown in FIG. 5, f (t) = xa (1), f (t−τ) = xa (2), f (t−2τ) = xa (3), f (t−3τ) = xa ( 4), f (t−4τ) = xa (5),. Therefore, the correlation value Y is obtained by multiplying the coefficients g (1) to g (l) corresponding to each of them and taking the sum as shown in Equation 2.

Y = Σf (t−kτ) g (k) (2)
However, Σ calculates the sum from k = 1 to k = n.

  In this way, by multiplying the charge amount Qk stored in each stage of the charge holding unit 321 of the charge transfer unit 32 by the coefficient g (l) corresponding to the reference signal (template) and taking the sum, noise is included. Whether a signal is present or not can be calculated with a high S / N ratio.

  On the other hand, the outputs Y2, Y3,..., Ym from the bandpass filters F2, F3,..., Fm connected in parallel to the correlation unit F1 are the coefficient units K1, K2,. , Dm is delayed by a time corresponding to the transfer delay time in the charge transfer unit 32 and the transfer and calculation processing time in the DA multiplier 341 in the delay units D1, D2,. The output from the corresponding correlation unit F1 via the coefficient unit K1 is added and input to the image processing unit 15 as an output Y ′. The coefficient units K1, K2,..., Km and the adder H1 constitute an adding unit.

  The image processing unit 15 includes a phase variation detection unit 151, a delay correction unit 152, and a phasing addition unit 153. The phase variation detection unit 151 is a circuit that detects a phase variation from each output Y ′ of the signal processing unit 14. It is known that the average sound speed between the focal point and the piezoelectric elements 21 and 22 of the ultrasonic probe 2 is different for each of the piezoelectric elements 21 and 22, so that the phase is shifted. The phase variation detector 151 detects this phase shift.

  The delay correction unit 152 performs the sound velocity correction as described above on each output Y ′, and gives a delay (phase) by giving a time difference corresponding to the focal point (focus point) and / or the steering angle (azimuth). ). The phasing addition unit 153 is a circuit that performs phasing addition of the output Y ′ subjected to the sound velocity correction and the delay correction by the delay correction unit 152. Then, the image processing unit 15 generates an ultrasonic image based on the added value Y (t).

  At this time, among the outputs of the i organic piezoelectric elements 21, the signal level of the third harmonic component (center frequency f3) obtained from the bandpass filter F3 is detected by the level detection unit 37. The control unit 17 normalizes the amplitude of the third harmonic in the remaining sound ray by setting the maximum value of the third harmonic amplitude of the element corresponding to the central sound ray of the transmission ultrasonic wave to 1.0. The normalized values are set to the coefficients k1, k2, k3,..., Km of the coefficient units K1, K2, K3,. FIG. 10 shows the situation.

  In FIG. 10, the central sound ray is indicated by reference symbol A, the sound rays on both sides are indicated by reference symbols B and C, and only the fundamental frequency and the third harmonic are shown, and suffixed numbers 1 and 3 are assigned, respectively. Therefore, in FIG. 10, when the level of the third harmonic of the central sound ray A is A3, 1 / A3 is set to the coefficient k3 of the coefficient unit K3, and the output becomes 1.0, and the fundamental frequency Is multiplied by 1.0 as the coefficient k1. On the other hand, when the level of the third harmonic of the left and right sound rays B and C is set to B3 and C3, 1 / A3 is also set to the coefficient k3, and the output becomes B3 / A3 and C3 / A3. The amplitudes B3 / A3, C3 / A3 are set to the coefficient k1, and the fundamental frequency outputs are B1, B3 / A3, C1, C3 / A3.

  FIG. 11 shows a result of an experiment by the inventor of the present application, and is a simulation image when the method of the present invention is applied to a reflective object in water. FIG. 11A shows an image based on the blur of the output Y1 of the correlation unit F1, and FIG. 11B shows an image based on the blur of the third harmonic Y3 obtained from the bandpass filter F3. The state in which ultrasonic waves are incident from the left side of the figure is shown, and therefore, the vertical (y) direction in the figure represents the azimuth resolution, and the horizontal (x) direction represents the distance (depth) resolution. As shown in FIG. 11A, at the fundamental frequency, the frequency is low, so that the beam expands and the azimuth resolution is inferior. However, the matched filter processing by the correlator F1 does not generate an extra signal, a high S / N is obtained, and the timing of returning can be accurately detected. In this way, high performance is obtained for penetration (distance resolution in the depth direction).

  On the other hand, as shown in FIG. 11 (b), in the third harmonic, the frequency is high, so that the beam is narrow and high azimuth resolution is obtained, but extraction is performed by the pre-ringing and post-ringing. A signal other than the signal is generated, the S / N is lowered, and the distance resolution is extremely inferior.

  Therefore, by obtaining outputs Y1 ′, Y2 ′,..., Ym ′ obtained by adding these signals as described above, the distance resolution, the azimuth resolution, and the S / N are all obtained as shown in FIG. Can be improved.

  As described above, in the ultrasonic diagnostic imaging apparatus S of the present embodiment, the first ultrasonic signal transmitted from the transmission unit 12 is used as a pulse, and thereby the second ultrasonic signal received by the reception unit 13. Among them, the signal processing unit 14 extracts the same fundamental frequency component as the transmitted first ultrasonic signal by the correlation unit F1, while the higher-order harmonic component generated by the nonlinear distortion of the subject is in the passband. Bandpass filters F2, F2,. Extract with Fm. Then, the correlation unit F1 and the band pass filters F2, F2,. The outputs from Fm are given predetermined weights in the coefficient multipliers K1, K2,..., Km, added by the adding unit H1, and supplied to the image processing unit 15.

  Therefore, when a band limiting filter is used for the fundamental frequency component f1, pre-ringing or post-ringing occurs in addition to the extracted signal, and the S / N is reduced. By performing the correlation processing, such an extra signal is not generated, the S / N can be improved, and the return timing can be accurately detected. Furthermore, by making the transmission ultrasonic signal into a pulse, the detection capability of the signal can be increased by the pulse compression effect, and the distance resolution can be improved more than the distance resolution determined by the wavelength of the physical frequency. Together with the improvement of S / N and the improvement of timing accuracy, the penetration (distance resolution in the depth direction) can be improved, the contrast with noise becomes clear, and the contrast can also be improved. FIG. 12 schematically shows the improvement of the penetration, and FIG. 13 schematically shows the improvement of the contrast. That is, in FIG. 12, as shown in (a), when the signal of the minimum detection level V1 can only be detected up to the depth D1, when the S / N is improved by the correlation processing, as shown in (b). Furthermore, the detection level for the same reflector having the depth D1 rises to V2, and the search depth can be increased to the depth D2 at the minimum detection level V1. In FIG. 13, as shown in (a), when noise of level V4 is generated with respect to the signal of level V3, the signal strength is increased by the pulse compression method. As shown, the level of the signal rises to V5, and the contrast with the noise floor of the level V4 can be clarified.

  In addition, in the correlation process, an appropriate correlation calculator (matched filter) can be realized for the fundamental frequency component f1 that can use the transmission signal itself as a reference signal, but at any level. For the higher order harmonics f2, f3,... That are difficult to predict, it is difficult to realize such an appropriate correlation calculator (matched filter), that is, stored in the reference signal storage unit 18. Since it is difficult to create a template data string, it is possible to limit the unrelated band by using the conventional bandpass filters F2 to Fm, and to use only for improving the azimuth resolution, so that the structure of the filter can be made silent. The azimuth resolution can be improved without complication. Thus, distance resolution, azimuth resolution, and S / N can be improved.

  In addition, high-resolution higher-order harmonic components that are severely attenuated are suitable for viewing shallow parts (short-distance parts), but the fundamental frequency components that reach far away are inferior in resolution (far-distance parts). Suitable for viewing. Therefore, as the weight setting unit, the coefficients k1, k2,..., Km of the coefficient units K1, K2,. By setting according to at least one of the depths, it is possible to form a higher-accuracy ultrasonic image more suitable for diagnosis from a shallow part to a deep part and by weighting. Here, the diagnostic part and the diagnostic depth of the subject can be represented by an elapsed time with the focal point of the first and second ultrasonic signals and the transmission time of the first ultrasonic signal as the time origin, for example, The coefficients k1, k2,..., Km are set according to the focal point and elapsed time.

  Furthermore, the transmission unit 12 does not have a simple Gaussian envelope waveform in the pulse as the first ultrasonic signal, and a signal frequency that is as redundant and unnatural as possible from the viewpoint of increasing noise resistance. By using a chirp wave that increases or decreases over time, a range side rope (temporal side rope) can be suppressed.

  Further, by configuring the correlation unit F1 with an analog product-sum operation device based on the CCD principle, it is possible to perform correlation processing more appropriately even with a weak signal level.

  Furthermore, the ultrasonic transducer 20 is configured by laminating an organic piezoelectric element 21 capable of receiving ultrasonic waves in a relatively wide band on an inorganic piezoelectric element 22 capable of transmitting large power for transmission. High-order harmonic components can be received with high sensitivity.

DESCRIPTION OF SYMBOLS S Ultrasonic image diagnostic apparatus 1 Diagnosis apparatus main body 2 Ultrasonic probe 11 Operation input part 12 Transmission part 121 Drive signal generation circuit 122 Transmission beam former 13 Reception part 14 Signal processing part 15 Image processing part 151 Phase variation detection part 152 Delay Correction unit 153 Phased addition unit 16 Storage unit 17 Control unit 18 Reference signal storage unit 20 Ultrasonic transducer 21 Organic piezoelectric element 22 Inorganic piezoelectric element 31 Sample hold unit 32 Charge transfer unit 33 Coefficient setting unit 34 Digital analog multiplication unit 35 Addition F1 Correlator F2, F3,..., Fm Bandpass filters K1, K2,.

Claims (4)

A transmission unit that transmits a first ultrasonic signal into the subject, a reception unit that receives a second ultrasonic signal in which the first ultrasonic signal is reflected in the subject, and A signal processing unit that extracts a desired signal component by performing predetermined signal processing on the received signal, an image processing unit that creates a tomographic image in the subject from the extraction result of the signal processing unit, and the created In an ultrasonic diagnostic imaging apparatus configured to include a display unit that displays a tomographic image,
The transmitter transmits the first ultrasonic signal in pulses,
The signal processing unit
When the frequency of the first ultrasonic signal is a fundamental frequency, the second ultrasonic wave is output from the output of the receiving unit by performing correlation processing between the output of the receiving unit and a preset reference signal. A correlation unit for detecting a component of the fundamental frequency included in the signal;
A filter that extracts one or more preset higher harmonic components from the output of the receiver;
An ultrasound diagnostic imaging apparatus, comprising: a correlation unit; and an adding unit that applies a predetermined weight to each output from the one or a plurality of filters.   The ultrasonic image diagnostic apparatus according to claim 1, further comprising a weight setting unit that sets a weight in the adding unit according to at least one of a diagnosis part and a diagnosis depth in the subject.   The ultrasonic diagnostic imaging apparatus according to claim 1, wherein the transmission unit uses a chirp wave as the pulse.   The ultrasonic transducer in the transmission unit and the reception unit is formed by laminating an organic piezoelectric element for reception on an inorganic piezoelectric element for transmission. Ultrasonic diagnostic imaging equipment.