JP4503454B2 - Ultrasonic imaging device - Google Patents

Description

  The present invention relates to an ultrasonic imaging apparatus used for performing diagnosis and nondestructive examination of an organ in a living body by transmitting and receiving ultrasonic waves and displaying an ultrasonic image of a subject.

  In general, in an ultrasonic imaging apparatus such as an ultrasonic diagnostic apparatus or an industrial flaw detection apparatus, an ultrasonic probe (probe) including a plurality of ultrasonic transducers having an ultrasonic transmission / reception function is used. Using such an ultrasonic probe, the subject is scanned with an ultrasonic beam formed by combining a plurality of ultrasonic waves, and an ultrasonic echo reflected inside the subject is received. Thus, image information related to the subject is obtained based on the intensity of the ultrasonic echo. Furthermore, based on this image information, a two-dimensional or three-dimensional image relating to the subject is reproduced. As one of scanning methods using such an ultrasonic beam, so-called sector scanning is known in which a fan-shaped two-dimensional region of a subject is scanned.

  Sector scanning was originally developed as a technique for observing the heart from the intercostal space of the human body. In general, in sector scanning, a plurality of ultrasonic beams extending in the depth direction of a subject from a transmission point are sequentially transmitted in a fan shape into the subject, and the fan-shaped two-dimensional shape of the subject is transmitted by these ultrasonic beams. The area is scanned at equally spaced angles.

  When receiving an ultrasonic echo reflected from the subject, it is reflected from each of a plurality of sampling points distributed at equal intervals in the depth direction of the subject along each ultrasonic beam (sound ray). A phase matching process is performed on a plurality of reception signals based on the ultrasonic echoes to obtain an acoustic ray signal (scanning line signal) in which the focal points of the ultrasonic echoes are narrowed down. Further, the sound ray signal is detected and a process for converting the scanning method is performed, whereby an image signal for displaying an ultrasonic image on a normal display device is obtained.

Here, as shown in FIG. 12, the phase matching process for a plurality of received signals is performed on the basis of the phase control signal from the phase control circuit 112, according to N ultrasonic transducers (hereinafter, each of the N ultrasonic transducers). Is added by the adder circuit 113 after the phases of the received signals of the channel numbers ch1 to chN are shifted by the _N phase shift circuits 111 _{1 to} 111 _N , respectively.

  However, in an ultrasonic image obtained using an ultrasonic beam, a virtual image due to a sidelobe is generated in single beam transmission in which a subject is scanned with a single ultrasonic beam, and the object is covered with a plurality of ultrasonic beams. In multi-beam transmission in which the specimen is simultaneously scanned at a predetermined interval, there is a problem that a virtual image due to crosstalk occurs.

  That is, in the single beam transmission, when there is no side lobe influence, as shown in FIG. 13A, when the phase of the reception signal output from each ultrasonic transducer (element) is matched, each reception Since the time of the signals can be adjusted, an ultrasonic image in which only a real image showing the reflector is projected can be obtained. On the other hand, when there is a reflector in the direction of the side lobe of the ultrasonic beam, the phase of the received signal output from each ultrasonic transducer (element) is matched as shown in FIG. Since the reception signal of the main beam of the ultrasonic beam indicated by the white square in the figure includes the reception signal of the channel number ch3 due to the side lobe of the ultrasonic beam indicated by the black square in the figure, the reflector causes A virtual image due to the reflected side lobe is generated in the ultrasonic image.

  In addition, in the single beam transmission as shown in FIG. 14A, the intensity of the ultrasonic echo concentric with the reflector is as indicated by a broken line in FIG. Intensity peaks only occur in the vicinity of the corresponding scanning angle θ = 0 °, but in multi-beam transmission in which the subject is simultaneously scanned with three ultrasonic beams as shown in FIG. The intensity of the ultrasonic echo concentric with the body is as shown by a solid line in FIG. 14C, and an intensity peak occurs not only near the scanning angle θ = 0 ° but also near the scanning angle θ = 6 °. . This is because the spatial (direction) resolution by phase matching is not so high, and in the case of multi-beam transmission, if a reflector is located in a specific direction, crosstalk occurs due to reflection of other ultrasonic beams. It is. As a result, in multi-beam transmission, a virtual image due to crosstalk is generated in the ultrasonic image.

The following methods have been proposed as methods for improving the image quality of ultrasonic images.
Patent Document 1 below evaluates the degree of distortion due to refraction, multiple reflection, and the like based on a correlation coefficient between received signals, and when the correlation coefficient is lower than a threshold value, the excitation intensity and the reception amplification factor are made lower than a reference value. On the other hand, when the correlation coefficient is higher than the threshold value, by controlling at least one of the excitation intensity and the reception amplification factor so as to maintain the excitation intensity and the reception amplification factor at the reference value, the adverse effect on the image quality of distortion is reduced. An ultrasonic diagnostic apparatus is disclosed.
That is, in this ultrasonic diagnostic apparatus, as shown in FIG. 15, the correlation coefficient between the reception signals of the N ultrasonic transducers respectively amplified by the _N amplification circuits 121 _{1 to} 121 _N is calculated as a correlation processing circuit. determined by 123, after respectively controlled by the N amplifying circuit 121 ₁ to 121 _N gain control circuit 122 a gain (amplification factor) of based on the correlation coefficient calculated, the N amplifying circuit 121 ₁ to 121 _N The output signals are added by the adder circuit 124.

  In Patent Document 2 below, when the deflection angle of the ultrasonic beam is large, the pulse width of the drive pulse is increased in the transmission system, and filtering for the reception distance of the deflection angle adaptive dynamic bandpass filter is performed in the reception system. An ultrasonic diagnostic apparatus is disclosed in which a grating lobe generated in a direction determined by the pitch of an ultrasonic transducer and the wavelength of an ultrasonic wave is reduced by reducing the gradient of the center frequency.

Furthermore, the following Patent Document 3 adds adaptive signal processing based on a reference signal to a filter processing unit that processes signals from a large number of microphones, so that even if the inside of a plant is a highly reflective environment, Disclosed is a wave diagnostic device capable of accurately and quickly diagnosing plant abnormalities so that the position of a wave can be specified with high accuracy.
That is, in this wave diagnostic apparatus, as shown in FIG. 16, a signal obtained by adding signals from N microphones amplified by _N amplifier circuits 131 _{1 to} 131 _N by an adder circuit 133 and a reference signal, Is performed by a general adaptive array antenna in which the gains of the _N amplifier circuits 131 _{1 to} 131 _N are controlled by the gain control circuit 132 based on an error signal obtained by subtracting the signal by the subtraction circuit 134. Processing is in progress.

However, all of the methods disclosed in Patent Documents 1 to 3 are similar in waveform arrival degree (correlation) with different arrival directions, such as a virtual image due to side lobe in single beam transmission and a virtual image due to crosstalk in multi-beam transmission. There is a problem that the effect is small in order to reduce a virtual image caused by a desired ultrasonic echo (desired wave) and an undesired ultrasonic echo (interference wave). In particular, when combined with multi-beam transmission, there is a problem that undesired ultrasonic echoes (interference waves) from the same depth cannot be effectively removed.
Japanese Patent Laid-Open No. 11-235341 (paragraph 0066, FIG. 9) Japanese Patent Laid-Open No. 11-328 (paragraphs 0017, 0028, FIGS. 5, 6, and 8) Japanese Patent Laid-Open No. 11-64089 (paragraphs 0017 to 0020, FIG. 1)

  Therefore, in view of the above points, the present invention provides an ultrasonic imaging apparatus capable of effectively removing a virtual image generated in an ultrasonic image due to sidelobe in single beam transmission or crosstalk in multibeam transmission. Objective.

  In order to solve the above-described problem, an ultrasonic imaging apparatus of the present invention transmits an ultrasonic beam from a plurality of ultrasonic transducers toward a subject, and transmits an ultrasonic echo reflected from the subject to the plurality of ultrasonic waves. An ultrasonic imaging apparatus that obtains image information related to a subject by processing a plurality of received signals received by a transducer, and calculates a statistical value of a correlation value between each of the plurality of received signals and a reference signal Correlation processing means to be obtained; addition means for adding a plurality of reception signals; amplification means for amplifying the reception signals added by the addition means; and the amplification means based on a statistical value of correlation values obtained by the correlation processing means Gain control means for controlling the gain.

  According to the present invention, the signal obtained by adding the reception signals from the plurality of ultrasonic transducers is amplified based on the statistical value of the correlation value between each of the reception signals from the plurality of ultrasonic transducers and the reference signal. Although the degree of similarity (correlation) is high, it is possible to effectively reduce a virtual image caused by ultrasonic echoes (interference waves) in an undesired direction from among ultrasonic echoes coming from different directions. As a result, it is possible to effectively remove the virtual image due to the side lobe during single beam transmission and the virtual image due to crosstalk during multi-beam transmission that occur in the ultrasonic image, particularly in the case of multi-beam transmission. Undesired ultrasonic echoes (interference waves) can be effectively removed.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings, taking as an example the case of multi-beam transmission in which three ultrasonic beams are simultaneously transmitted to a subject. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a block diagram showing a configuration of an ultrasonic imaging apparatus according to an embodiment of the present invention. The ultrasonic imaging apparatus includes an ultrasonic probe (probe) 1 used in contact with a subject, and an ultrasonic imaging apparatus main body 2 connected to the ultrasonic probe 1. The ultrasonic probe 1 scans the subject by simultaneously transmitting three ultrasonic beams from the ultrasonic probe 1 toward the subject at intervals of about 6.4 °, and receives ultrasonic echoes reflected from the subject. To generate an ultrasonic image.

  The ultrasonic probe 1 includes a plurality of ultrasonic transducers 11 a constituting a one-dimensional ultrasonic transducer array 11. These ultrasonic transducers 11a are connected to the ultrasonic imaging apparatus body 2 via signal lines.

  Each of the ultrasonic transducers 11a includes, for example, a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate) or a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride). It is comprised by the vibrator | oscillator which formed the electrode at both ends of the material (piezoelectric body) which has piezoelectricity, such as. In addition, in recent years, a piezoelectric material containing PZNT (an oxide containing lead, zinc, niobium, titanium), which is expected to contribute to the improvement of sensitivity and bandwidth of an ultrasonic transducer, may be used.

  When a voltage is applied to the electrodes of such a vibrator by sending a pulsed or continuous wave electric signal, the piezoelectric body expands and contracts. By this expansion and contraction, pulsed or continuous wave ultrasonic waves are generated from the respective vibrators, and an ultrasonic beam is formed by synthesizing these ultrasonic waves. Each vibrator expands and contracts by receiving propagating ultrasonic waves and generates an electrical signal. These electrical signals are output as received signals.

The ultrasonic imaging apparatus main body 2 includes a plurality of switching circuits 20, a plurality of transmission circuits 21, a plurality of reception circuits 22, a computer 30, a recording unit 40, and a display unit 70.
The plurality of switching circuits 20 respectively connect the plurality of ultrasonic transducers 11a built in the ultrasonic probe 1 to the plurality of transmission circuits 21 when transmitting an ultrasonic beam, and receive an ultrasonic echo. The plurality of ultrasonic transducers 11 a are connected to the plurality of receiving circuits 22, respectively.

  Each of the plurality of transmission circuits 21 includes a D / A (digital / analog) converter and a class A power amplifier. The D / A converter generates a drive signal having a delay amount corresponding to the transmission direction of the ultrasonic beam based on the waveform data supplied from the computer 30. The power amplifier amplifies this drive signal and supplies it to the ultrasonic probe 1.

Each of the plurality of receiving circuits 22 includes a preamplifier, a TGC (time gain compensation) amplifier, and an A / D (analog / digital) converter. The reception signal output from each ultrasonic transducer 11a is amplified by a preamplifier, and the TGC amplifier corrects attenuation due to the distance that the ultrasonic wave has reached in the subject.
The received signal output from the TGC amplifier is converted into a digital signal by an A / D converter. The sampling frequency of the A / D converter needs to be at least about 10 times the frequency of the ultrasonic beam, and is preferably 16 times or more the frequency of the ultrasonic beam. The resolution of the A / D converter is preferably 10 bits or more.

  The computer 30 controls transmission / reception of an ultrasonic beam based on software (control program) recorded in the recording unit 40. As the recording unit 40, a recording medium such as a hard disk, a flexible disk, MO, MT, RAM, CD-ROM, or DVD-ROM can be used. The scan controller 31, the waveform data generator 32, the image signal generator 34, the image processor 35, and the reception beamforming unit 50 are realized as functional blocks by the computer 30 and software. The computer 30 has a transmission memory 33 and a reception memory 36.

  The scanning control unit 31 sequentially sets the transmission direction of the ultrasonic beam, the reception direction and the focal position of the ultrasonic echo. The waveform data generation unit 32 sequentially reads the waveform data stored in the transmission memory 33 under the control of the scanning control unit 31 and outputs the waveform data to the plurality of transmission circuits 21. These transmission circuits 21 respectively generate a plurality of drive signals based on the waveform data, and supply them to the plurality of ultrasonic transducers 11 a included in the ultrasonic probe 1.

  The reception memory 36 stores digital reception signals output from the A / D converters of the plurality of reception circuits 22 in time series for each ultrasonic transducer. The reception beam forming unit 50 performs reception focus processing by performing phase matching on a plurality of reception signals read from the reception memory 36 based on the reception direction set in the scanning control unit 31. By this reception focus processing, a sound ray signal in which the focus of the ultrasonic echo is narrowed is formed for the three transmission beams.

As shown in FIG. 2, the reception beamforming unit 50 includes N phase shift units 51 _{1 to} 51 _N that respectively shift the phases of reception signals of N ultrasonic transducers (channel numbers ch1 to chN), and scanning. A phase control unit 52 that controls the phase shift amount of the _N phase shift units 51 _{1 to} 51 _N based on the phase control signal PRef input from the control unit 31, and the N phase shift units 51 _{1 to} 51 _N An adder 53 for adding the output signals, an amplifier 54 for amplifying the output signal of the adder 53, and dispersion of lags in correlation values between the output signals of the phase shifters 51 _{1 to} 51 _N and the reference signal Ref a correlation processing unit 55 for obtaining σ _t (lag dispersion until the correlation value is maximized), a gain table memory 56 in which a gain table representing a relationship between the lag dispersion σ _t and the gain of the amplification unit 53 is stored; , With reference to the gain table stored in the obtained table memory 56, and a gain control unit 57 for controlling the gain of the amplifier 54 based on the variance sigma _t of the lug which is input from the correlation processing unit 55.

When the gain is displayed logarithmically as shown in FIG. 3A, the gain of the amplifying unit 54 is 10 ⁰ (as shown in FIG. 3B) when the lag variance σ _t is 0 to 5. When the lag variance σ _t is 5 to 35, the gain of the amplifying unit 54 is decreased linearly. When the lag variance σ _t is 5 to 35, The gain of the amplifying unit 54 is created to be 10 ⁻¹ (“0.1” when the gain is linearly displayed as shown in FIG. 3B).

  The reference signal Ref is a signal obtained using transmission beams having different spatial characteristics. Specifically, it is a reception signal obtained by transmitting one ultrasonic beam toward a point reflector. However, as shown in FIG. 4A, the received signal obtained by transmitting one ultrasonic beam toward the point reflector is not limited to the ultrasonic echo from the depth of the point reflector. Also included are ultrasonic echoes from other depths. Therefore, in order to suppress the influence of the cut-off of the cut-out section when cutting the waveform of the received signal, a window function as shown in FIG. 4B is multiplied with the received signal, and the result is shown in FIG. A reference signal Ref corresponding to an ultrasonic echo from the depth of such a point reflector is used.

The reference signal Ref may be a signal having a waveform estimated from a known transmission sound pressure waveform and an average frequency characteristic of the subject. Specifically, a signal obtained as follows is referred to as a reference signal Ref.
In advance, underwater, an impulse-driven sound pressure waveform X _TDX (t) at the focal position is measured. The sound pressure waveform X _TDX (t) corresponds to the impulse response of the electronic circuit. This sound pressure waveform X _TDX (t), a spatial filter H _SPEC (f) determined by the positional relationship between the spatial position of the subject and the focal position, and an average frequency-dependent attenuation exp (α · L · f) of the subject The signal X _r (t) obtained by the following equation is used as a reference signal Ref.
X _r (t) = IFFT [exp (α · L · f) × H _SPEC (f) × FFT {X _TDX (t)}]
Here, the unit of the attenuation coefficient α is dB / (cm · MHz),
The unit of the distance L is cm,
The unit of the frequency f is MHz.

  In the case of performing multi-beam transmission in which the subject is simultaneously transmitted at intervals of about 6.4 ° with three ultrasonic beams as in the ultrasonic imaging apparatus according to the present embodiment, three ultrasonic waves are used. Although three reception beam forming units 50 are provided corresponding to the respective beams, a single beam that scans the subject with one ultrasonic beam using the plurality of ultrasonic transducers 11a of the ultrasonic probe 1 is used. In the case of transmission, only one receive beamforming unit 50 is provided.

  The image signal generation unit 34 generates an image signal representing the luminance in a plurality of pixels to be displayed on the display device, based on the sound ray signal (array output) output from the reception beam forming unit 50. For example, the image signal generation unit 36 detects the envelope of the waveform represented by the sound ray signal, and generates the image signal by converting the scanning method.

  The image processing unit 35 performs image processing such as gradation processing and contour enhancement processing on the image signal output from the image signal generation unit 34 as necessary. The display unit 70 includes, for example, a display device such as a CRT or LCD, and displays an ultrasonic image based on the image signal output from the image processing unit 35.

  Next, the operation of the ultrasonic imaging apparatus according to this embodiment will be described. For simplicity of explanation, 16 ultrasonic transducers 11a (channel numbers ch1 to ch16) are used and three ultrasonic beams B1 to B3 (see FIG. 9) are spaced at an interval of about 6.4 °. The case of transmitting simultaneously will be described. Further, a case will be described in which the reference signal Ref corresponding to the ultrasonic echo from the depth of the point reflector as shown in FIG. 4C is used as the reference signal Ref used in the correlation processing unit 55 in FIG. .

  When transmitting the three ultrasonic beams B1 to B3 simultaneously, the waveform data generation unit 32 of the computer 30 sequentially reads the waveform data stored in the transmission memory 33 under the control of the scanning control unit 31. And output to the transmission circuit 21 connected to each of the 16 ultrasonic transducers 11a.

  In each transmission circuit 21, a drive signal for simultaneously transmitting the three ultrasonic beams B1 to B3 from the 16 ultrasonic transducers 11a at intervals of about 6.4 ° is generated. The generated drive signal is output from the transmission circuit 21 via the switching circuit 20 to the corresponding ultrasonic transducer 11a. Thereby, three ultrasonic beams B1 to B3 are simultaneously transmitted from the 16 ultrasonic transducers 11a of the ultrasonic probe 1 toward the subject.

  The 16 received signals obtained by the 16 ultrasonic transducers 11a by receiving the respective ultrasonic echoes generated by the reflection of the three ultrasonic beams B1 to B3 from the subject are the ultrasonic probes. 1 to the corresponding receiving circuit 22 through the switching circuit 20. The 16 received signals are amplified by a preamplifier in each receiving circuit 22, corrected for attenuation due to the ultrasonic reach by a TGC amplifier, and then converted to a digital signal by an A / D converter. The 16 received signals converted into digital signals are stored in the reception memory 36 in time series for each ultrasonic transducer.

Here, when a reflector is placed on the center line of the ultrasonic transducer array 11 as shown in FIG. 5A, the ultrasonic echo generated by the reflection of the three ultrasonic beams B1 to B3 from the reflector. Are received by the 16 ultrasonic transducers 11a, as shown in FIGS. 5B and 5C, depending on the difference in distance between the ultrasonic transducers 11a and the reflectors. Therefore, in the three phase shifters 51 _{1 to} 51 ₁₆ shown in FIG. 2 of the three reception beam forming units 50 (in this example, since the number of ultrasonic transducers 11a is 16, N = 16). The reception focus process is performed by performing phase matching corresponding to the directions of the ultrasonic beams B1 to B3 on the 16 reception signals read from the reception memory 36. Thereby, the sound ray signal in which the focus of the ultrasonic echo is narrowed is formed for the three transmission beams (ultrasonic beams B1 to B3).

  That is, in the reception beam forming unit 50 at the uppermost stage in FIG. 1, reception focus processing is performed by performing phase matching in the direction of the ultrasonic beam B1 on the 16 reception signals. In this example, as shown in FIG. 6A, the ultrasonic beam B1 is about 3.2 ° left and right about an angle of about −6.4 ° from the center line of the ultrasonic transducer array 11. Therefore, even if phase matching is performed on 16 received signals corresponding to ultrasonic echoes from a reflector placed on the center line of the ultrasonic transducer array 11, the phase matching is performed. As shown in FIG. 6B, the received signals do not coincide with each other in time.

  In the reception beam forming unit 50 in the second stage of FIG. 1, reception focus processing is performed by performing phase matching in the direction of the ultrasonic beam B2 on the 16 reception signals. In this example, as shown in FIG. 7A, the ultrasonic beam B2 is transmitted so as to scan a range of about 3.2 ° to the left and right with the center line of the ultrasonic transducer array 11 as the center. Therefore, when phase matching is performed on the 16 received signals corresponding to the ultrasonic echoes from the reflector placed on the center line of the ultrasonic transducer array 11, as shown in FIG. Each received signal matches in time.

  In the lowermost receive beamforming unit 50 in FIG. 1, receive focus processing is performed by performing phase matching in the direction of the ultrasonic beam B3 on the 16 received signals. In this example, as shown in FIG. 6A, the ultrasonic beam B3 is about 3.2 ° left and right about an angle of about 6.4 ° from the center line of the ultrasonic transducer array 11. Since it is transmitted so as to scan the range, even if phase matching is applied to the 16 received signals corresponding to the ultrasonic echoes from the reflector placed on the center line of the ultrasonic transducer array 11, Similar to the ultrasonic beam B1, the received signals do not coincide with each other in time.

The phase shift amount in each of the phase shift units 51 _{1 to} 51 ₁₆ in FIG. 2 is controlled by the phase control unit 52 based on the phase control signal PRef input from the scan control unit 31 in FIG.

  The 16 received signals phase-matched as described above are input to the correlation processing unit 55 in each reception beam forming unit 50, added by the adding unit 53, and then input to the amplifying unit 54. Is done.

  In the correlation processing unit 55, each of the 16 received signals subjected to phase matching is subjected to a window function as shown in FIG. 8A and then a reference signal as shown in FIG. 8B. Correlation with Ref is taken. FIG. 8 shows an example of the ultrasonic beam B1.

Thereafter, the correlation processing unit 55 obtains a lag variance σ _t of correlation values between each of the 16 received signals and the reference signal Ref. The obtained correlation value lag variance σ _t is output from the correlation processing unit 55 to the gain control unit 57.

FIG. 9B shows each of the 16 received signals when the reflector is placed on the center line (direction of θ = 0 °) of the ultrasonic transducer array 11 as shown in FIG. An example is shown in which the lag variance σ _t of the correlation value with the reference signal Ref is obtained. FIG. 10B shows the reflector in the direction of about 6.4 ° from the center line of the ultrasonic transducer array 11 (θ = direction of about 6.4 °) as shown in FIG. An example is shown in which the lag variance σ _t of the correlation value between each of the 16 received signals and the reference signal Ref is obtained. Further, FIG. 11B shows that the two reflectors are approximately 6.4 on the center line of the ultrasonic transducer array 11 (direction of θ = 0 °) and the center line as shown in FIG. An example is shown in which the lag variance σ _t of the correlation value between each of the 16 received signals and the reference signal Ref when placed in the direction of ° (the direction of θ = 6.4 °) is obtained.

2, after the gain table shown in FIG. 3 is read from the gain table memory 56, the lag of the correlation value input from the correlation processing unit 55 is referred to with reference to the read gain table. Based on σ _t , the gain of the amplifying unit 54 is obtained.

For example, as shown in FIGS. 9A to 9C, when the reflector is placed on the center line of the ultrasonic transducer array 11 (direction of θ = 0 °), the center of the ultrasonic transducer array 11 is set. The correlation value lag dispersion σ _t at θ = −6.4 ° corresponding to the ultrasonic beam B1 transmitted in the direction of about −6.4 ° from the line is indicated by a point P1 in FIG. 9B. Therefore, with reference to the gain table shown in FIG. 3B, the gain of the amplifying unit 54 in FIG. 2 is set to 0.1 (10 ⁻¹ ). As a result, the echo intensity indicated by the output signal of the amplifying unit 54 in FIG. 2 is reduced from about −28 dB at θ = −6.4 ° indicated by the point Q1 in FIG. 9C to about 48 dB indicated by the point Q1 ′. Is done.

Further, the dispersion σ _t of the correlation value lag at θ = 0 ° corresponding to the ultrasonic beam B2 transmitted on the center line of the ultrasonic transducer array 11 is approximately as shown by a point P2 in FIG. 9B. Therefore, referring to the gain table shown in FIG. 3B, the gain of the amplifying unit 54 in FIG. 2 is 1 (10 ⁰ ). As a result, the echo intensity indicated by the output signal of the amplifying unit 54 in FIG. 2 remains 0 dB at θ = 0 ° indicated by the point Q2 in FIG. 9C.

Furthermore, the variance σ _t of the correlation value lag at θ = 6.4 ° corresponding to the ultrasonic beam B3 transmitted in the direction of about 6.4 ° from the center line of the ultrasonic transducer array 11 is shown in FIG. ) Is about 40 as indicated by a point P3, and the gain of the amplifying unit 54 in FIG. 2 is set to 0.1 (10 ⁻¹ ) with reference to the gain table shown in FIG. As a result, the echo intensity indicated by the output signal of the amplifying unit 54 in FIG. 2 is reduced from about −25 dB at θ = 6.4 ° indicated by the point Q3 in FIG. 9C to about 45 dB indicated by the point Q3 ′. The
As a result, as shown in FIG. 9C, virtual images due to multi-beam transmission that occur around θ = −6.4 ° and around θ = 6.4 ° can be removed.

  Similarly, when the reflector is placed in a direction of about 6.4 ° (θ = 6.4 ° direction) from the ultrasonic transducer array 11, as shown in FIGS. However, as shown in FIG. 10C, virtual images caused by multi-beam transmission that occur near θ = −6.4 ° and θ = 0 ° can be removed.

  Further, as shown in FIGS. 11A to 11C, the reflector is placed on the center line of the ultrasonic transducer array 11 (direction of θ = 0 °) and in the direction of about 6.4 ° from the center line (θ = Even in the case of setting in the direction of 6.4 °, a virtual image caused by multi-beam transmission that occurs in the vicinity of θ = −6.4 ° can be removed.

The sound ray signals output from the three reception beam forming units 50 are input to the image signal generation unit 34.
In the image signal generation unit 34, an image signal is generated based on the sound ray signals input from the three reception beam forming units 50. The generated image signal is subjected to image processing such as gradation processing and contour enhancement processing in the image processing unit 39. Thereby, the ultrasonic image from which the virtual image by multi-beam transmission is removed is displayed on the display unit 70.

In the above description, the gain of the amplifying unit 54 in FIG. 2 is obtained based on the variance σ _t of the lag of the correlation value between each of the 16 received signals and the reference signal Ref. Statistic of correlation values between the reference signal Ref and the reference signal Ref (for example, the average value of the correlation values, the variance of the correlation values, the average value of the lags until the correlation value is maximized, and the The gain of the amplifying unit 54 can be obtained based on dispersion and the like.

Further, although the case of multi-beam transmission has been described as an example, even in the case of single beam transmission, the reception beam forming unit 50 uses the lag variance σ _t of the correlation value between each of the 16 reception signals and the reference signal Ref, etc. 2 is obtained, the virtual image due to the side lobe generated in the ultrasonic image can be removed.

  INDUSTRIAL APPLICABILITY The present invention can be used in an ultrasound imaging apparatus that is used to perform diagnosis and non-destructive inspection of an organ in a living body by transmitting and receiving ultrasound and displaying an ultrasound image of a subject. .

1 is a block diagram illustrating a configuration of an ultrasonic imaging apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the receiving beam forming part 50 shown in FIG. It is a figure for demonstrating the content of the gain table stored in the gain table memory 56 shown in FIG. It is a figure for demonstrating the reference signal Ref used in the correlation process part 55 shown in FIG. It is a figure which shows the waveform before phase matching of the received signal from each ultrasonic transducer in the case of placing a reflector on the center line of the ultrasonic transducer array. It is a figure which shows the waveform after the phase matching to the direction of the ultrasonic beam B1 of the received signal from each ultrasonic transducer in the case of putting a reflector on the center line of the ultrasonic transducer array. It is a figure which shows the waveform after the phase matching to the direction of the ultrasonic beam B2 of the received signal from each ultrasonic transducer in the case of placing a reflector on the center line of the ultrasonic transducer array. It is a figure for demonstrating the correlation process in the correlation process part 55 shown in FIG. It is a figure for demonstrating how to obtain the gain of the amplification part 54 shown in FIG. It is a figure for demonstrating how to obtain the gain of the amplification part 54 shown in FIG. It is a figure for demonstrating how to obtain the gain of the amplification part 54 shown in FIG. It is a figure for demonstrating the phase matching process with respect to the conventional several received signal. It is a figure for demonstrating generation | occurrence | production of the virtual image by the side lobe at the time of single beam transmission. It is a figure for demonstrating generation | occurrence | production of the virtual image by the crosstalk at the time of multibeam transmission. FIG. 10 is a diagram for explaining a technique for improving the image quality of an ultrasonic image in the ultrasonic diagnostic apparatus disclosed in Patent Literature 1. It is a figure for demonstrating the adaptive signal process based on the reference signal currently performed with the general adaptive array antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Ultrasonic imaging device main body 11 Transducer array 11a Ultrasonic transducer 20 Switching circuit 21 Transmission circuit 22 Reception circuit 30 Computer 31 Scan control part 32 Waveform data generation part 33 Transmission memory 34 Image signal generation part 35 Image Processing unit 36 Reception memory 40 Recording unit 50 Reception beam forming unit 51 _{1 to} 51 _N phase shift unit 52 Phase control unit 53 Addition unit 54 Amplification unit 55 Correlation processing unit 56 Gain table memory 57 Gain control unit 70 Display unit

Claims (4)

By transmitting an ultrasonic beam from a plurality of ultrasonic transducers toward the subject and processing a plurality of received signals obtained by receiving ultrasonic echoes reflected from the subject by the plurality of ultrasonic transducers An ultrasonic imaging apparatus for obtaining image information relating to the subject,
Correlation processing means for obtaining a statistical value of a correlation value between each of the plurality of received signals and a reference signal;
Adding means for adding the plurality of received signals;
Amplifying means for amplifying the received signal added by the adding means;
Gain control means for controlling the gain of the amplifying means based on the statistical value of the correlation value obtained by the correlation processing means;
An ultrasonic imaging apparatus comprising: Further comprising phase matching processing means for performing phase matching processing on the plurality of received signals in accordance with arrival direction information of the ultrasonic echoes,
The correlation processing means obtains a statistical value of a correlation value between each of a plurality of received signals phase-shifted by the phase matching processing means and a reference signal;
The ultrasonic imaging apparatus according to claim 1.   The statistical value of the correlation value is an average of correlation values between each of the plurality of received signals and the reference signal, variance of correlation values between each of the plurality of received signals and the reference signal, The average value of the lag until the correlation value between each and the reference signal becomes maximum, or the dispersion of the lag until the correlation value between each of the plurality of received signals and the reference signal becomes maximum. Item 3. The ultrasonic imaging apparatus according to Item 1 or 2.   The reference signal is a signal having a waveform estimated from a known transmission sound pressure waveform and an average frequency characteristic of a subject, or a signal obtained using transmission beams having different spatial characteristics. The ultrasonic imaging apparatus of any one of -3.

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