Ultrasonic diagnostic apparatus

The present invention relates to an ultrasonic diagnostic apparatus that obtains an image of an organ or the like in a living body by transmitting and receiving ultrasonic waves and generates an ultrasonic image used for diagnosis.

In an ultrasonic diagnostic apparatus used for medical purposes, an ultrasonic probe (probe) including a plurality of ultrasonic transducers having a function of transmitting and receiving ultrasonic waves is usually used. An image of the tissue of a subject based on the intensity of the ultrasonic echo by scanning the subject with ultrasonic beams transmitted from multiple ultrasonic transducers and receiving the ultrasonic echo reflected inside the subject. Information (B mode image) can be obtained. In addition, information on blood movement in the subject (Doppler image) can be obtained based on the frequency shift information due to the Doppler effect included in the ultrasonic echo.

In the color mode (color flow mapping mode), the two-dimensional color Doppler image obtained by the Doppler effect is combined with the normal B mode image, and the combined image is displayed. Therefore, since the transmission for acquiring the Doppler image is performed in the middle of the transmission for acquiring the B mode image, the number of transmissions per frame increases and the frame rate decreases. Further, in order to secure the sensitivity in the detection of the Doppler effect, the transmission is performed a plurality of times (4 to 10 times) in the same direction, so that the spatial resolution also deteriorates. Therefore, it is desired to reduce the image generation time in the color mode.

As a related technique, Patent Document 1 states that by shortening the image generation time and further improving the S / N of the image signal, a minute object or a moving object can be clearly displayed, and a minute part can be displayed. An ultrasonic diagnostic apparatus for the purpose of performing accurate observation is disclosed. This ultrasonic diagnostic apparatus generates a transmitted ultrasonic beam and a received ultrasonic beam by dynamic focusing using a plurality of transmitted signals having different frequencies, and electronically scans these ultrasonic beams to generate an image. It is a diagnostic device, and (a) at the center frequency of the frequency spectrum of each transmission signal, the frequency and amplitude shape are set so that the level of the frequency spectrum of other transmission signals is equal to or lower than a predetermined level, and a plurality of these. Transmission signal generation means that generates transmission signals at predetermined intervals in descending order of frequency within the transmission allowable time for each transmission / reception repetition cycle, and (b) each transmission signal generated by the transmission signal generation means is transmitted. A transmission beam forming means for forming a transmission ultrasonic beam by dynamic focusing and (c) a reception ultrasonic beam generated by transmitting each transmission signal generated by the transmission signal generation means and received are generated by dynamic focusing. Then, the output of the received ultrasonic beam is frequency-analyzed to extract the central frequency component of each transmission signal, and the frequency analysis means is arranged in a time series, and (d) each time series extracted by the frequency analysis means. It is provided with a correlation processing unit that generates an image signal on one ultrasonic line by performing mutual correlation processing on the signal of.

However, Patent Document 1 does not particularly describe the color mode. In addition, Non-Patent Document 1 discloses a general pulse Doppler device.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-321647 (pages 6-7, Fig. 2)</text></patcit></p>

<p><nplcit num="1"><text>"Handbook of Medical Ultrasound Equipment" edited by Japan Electronic Machinery Manufacturers Association, revised edition, Corona Publishing Co., Ltd., January 20, 1997, p.118-131</text></nplcit></p>

<p> Therefore, in view of the above points, the present invention can shorten the image generation time and improve the frame rate even in the color mode in which the two-dimensional color Doppler image obtained by the Doppler effect is combined with the B mode image. It is an object of the present invention to provide an ultrasonic diagnostic apparatus.</p>

<p> In order to solve the above problems, the ultrasonic diagnostic apparatus according to one aspect of the present invention transmits ultrasonic waves according to a plurality of drive signals and outputs a plurality of received signals by receiving ultrasonic echoes. Multiple drive signals are transmitted in the same direction so that an ultrasonic probe including an ultrasonic transducer and a pulse train containing a plurality of pulses each having a frequency component of an orthogonal frequency-divided multiplex wave having different center frequencies and orthogonal to each other are transmitted in the same direction. Pulse compression of a plurality of pulses having different frequency components contained in each received signal output from the transmission system signal processing means supplied to the ultrasonic probe and the ultrasonic probe receiving the pulse train from the same direction. It also includes a receiving system signal processing means that generates a B-mode image signal based on the compressed pulse.</p>

<p> According to the present invention, a plurality of pulses are pulse-compressed to generate a B-mode image signal by transmitting and receiving a pulse train including a plurality of pulses each having a frequency component of an orthogonal frequency-divided multiplex wave in the same direction, and a plurality of pulses are generated. Since the pulse of is also used for generating a Doppler image signal, it is possible to shorten the image generation time and improve the frame rate even in the color mode.</p>

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same components are designated by the same reference numerals, and the description thereof will be omitted. FIG. 1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention. This ultrasonic diagnostic apparatus has an ultrasonic probe 10 including a plurality of ultrasonic transducers 10a, a scanning control unit 11, a transmission control unit 12, and a plurality of channels corresponding to the plurality of ultrasonic transducers 10a. Section 20, B-mode image beam transducer 32, B-mode image signal generation section 33, B-mode image DSC34, Doppler image beam former 42, Doppler detection section 43, Doppler image DSC44, and image. It has a display control unit 51, a display unit 52, an operation console 61, a control unit 62, and a storage unit 63.

The plurality of ultrasonic transducers 10a of the ultrasonic probe 10 transmit ultrasonic waves toward a subject according to a plurality of applied drive signals, and receive a plurality of ultrasonic echoes propagated from the subject. Output the received signal. These ultrasonic transducers 10a are arranged one-dimensionally or two-dimensionally to form a transducer array.

Each ultrasonic transducer is, for example, a piezoelectric ceramic represented by PZT (lead zirconate titanate titanate), a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride), or the like. It is composed of a vibrator in which electrodes are formed at both ends of a material having piezoelectricity (piezoelectric body). When a pulsed or continuous wave voltage is applied to the electrodes of such an oscillator, the piezoelectric body expands and contracts. Due to this expansion and contraction, pulsed or continuous wave ultrasonic waves are generated from each oscillator, and an ultrasonic beam is formed by synthesizing the ultrasonic waves. In addition, each oscillator expands and contracts by receiving the propagating ultrasonic waves to generate an electric signal. Those electric signals are output as ultrasonic reception signals.

When the scanning control unit 11 scans a predetermined imaging area in the subject with the ultrasonic beam, the transmission direction, the reception direction, the depth of focus, and the ultrasonic beam transmitted from the ultrasonic probe 10 are super. The aperture diameter of the ultrasonic transducer array can be set. The scanning control unit 11 controls the transmission control unit 12, the B-mode image beamformer 32, and the Doppler image beamformer 42 based on these settings.

The transmission control unit 12 sets the delay time given to each of the drive signals of the plurality of ultrasonic transducers 10a based on the transmission delay pattern set by the scanning control unit 11 according to the transmission direction. Alternatively, the transmission control unit 12 may set the delay time so that the ultrasonic waves transmitted at one time from the plurality of ultrasonic transducers 10a reach the entire imaging region of the subject.

The transmission / reception unit 20 has a plurality of channels corresponding to the plurality of ultrasonic transducers 10a. Each channel of the transmission / reception unit 20 includes a drive signal generation unit 13, a transmission / reception switching unit 14, a preamplifier 21, a variable gain amplifier 22, a low-pass filter 23, an A / D converter 24, and a pulse compression unit 31. And the pulse separation unit 41.

The drive signal generation unit 13 includes a pulsar or the like that generates a drive signal to be supplied to the corresponding ultrasonic transducer 10a based on the delay time set in the transmission control unit 12. The plurality of drive signal generators 13 adjust the delay amount of the plurality of drive signals so that the ultrasonic waves transmitted from the plurality of ultrasonic transducers 10a form an ultrasonic beam, and supply the ultrasonic probes 10 to the ultrasonic probe 10. Alternatively, a plurality of drive signals may be supplied to the ultrasonic probe 10 so that the ultrasonic waves transmitted from the plurality of ultrasonic transducers 10a at one time reach the entire imaging region of the subject.

Here, the transmission control unit 12 and the plurality of drive signal generation units 13 constitute a transmission system signal processing means, and the frequencies of Orthogonal Frequency Division Multiplexing (OFDM) waves having different center frequencies and orthogonal to each other. A plurality of drive signals are supplied to the ultrasonic probe 10 so as to transmit a pulse train including a plurality of pulses having each component in the same direction. A pulse train consists of N pulses generated at predetermined pulse intervals (N is an integer greater than or equal to 2). According to the present embodiment, a B-mode image signal can be obtained by compressing a plurality of pulses having different center frequencies and having orthogonal frequency components, and a Doppler image signal can be obtained by orthogonally detecting those pulses. , The image generation time can be shortened and the frame rate can be improved.

The transmission / reception switching unit 14 switches between the output of the drive signal to the ultrasonic probe 10 and the input of the received signal from the ultrasonic probe 10. The received signal output from the ultrasonic transducer 10a that received the ultrasonic echo reflected in the subject is amplified by the preamplifier 21 and the variable gain amplifier 22, band-limited by the low-pass filter 23, and A / D. It is converted into a digital received signal by the converter 24. The A / D converter 24 supplies the digital received signal to the pulse compression unit 31 and the pulse separation unit 41.

The pulse compression unit 31 is included in the received signal output from the ultrasonic probe 10 that receives a pulse train including a plurality of pulses each having frequency components of orthogonal frequency-divided multiplex waves having different center frequencies and orthogonal to each other from the same direction. Pulse compression is performed on a plurality of pulses having different frequency components.

FIG. 2 is a diagram showing a configuration example of the pulse compression unit in FIG. In the following, a case where one pulse train contains four pulses will be described (N = 4). The i-th pulse is the pulse-modulated frequency f_iContains a sine wave of (i = 1, 2, 3, 4). The pulse compression unit 31 has a center passing frequency of f.₁~ f₄The four bandpass filters 71 to 74 and the delay time of each are τ.₁~ τ₃It is equivalently represented by the three delay elements 81 to 83 and the adder 90 that adds four frequency components. Here, the delay time τ₁~ τ₃Corresponds to the pulse interval of the pulse train.

FIG. 3 is a diagram showing the waveform of the pulse train at position A in FIG. As shown in Figure 3, one pulse train has a center frequency of f.₁~ f₄The first to fourth pulses containing each of the frequency components having the above are arranged in a time series at predetermined pulse intervals. Here, the pulse interval between the first pulse and the fourth pulse is τ.₁And the pulse interval between the second pulse and the fourth pulse is τ₂And the pulse interval between the 3rd and 4th pulses is τ₃Is.

FIG. 4 is a diagram showing waveforms of a plurality of pulses at position B in FIG. The center frequency f is provided by the bandpass filters 71 to 74 shown in FIG.₁~ f₄The first to fourth pulses containing each of the frequency components having the above are extracted, the timings of the first to fourth pulses are aligned by the delay elements 81 to 83 shown in FIG. 2, and the first to fourth pulses are aligned by the adder 90. The fourth pulse is added. Pulse compression is performed in this way, and a compressed short pulse is generated.

FIG. 5 is a diagram for explaining pulse compression on the frequency axis. As shown in FIG. 5, the adder 90 allows the center frequency f.₁~ f₄The narrow band frequency components of are added together to produce a compressed pulse with a wide band frequency component.

FIG. 6 is a diagram showing the spectrum of the compressed pulse in detail. Center frequency f₁~ f₄Since the first to fourth frequency components having the above are orthogonal to each other, for example, the center frequency (peak frequency) f of the second frequency component₂In, the other frequency components are zero.

However, when the number of frequency components to be synthesized is small, the information for constructing a short pulse having a wide band frequency component is insufficient. In such a case, the pulse compression unit 31 shown in FIG. 1 interpolates the frequency components not included in the received signal when pulse-compressing a plurality of pulses having different frequency components included in the received signal. You may try to do it.

FIG. 7 is a diagram for explaining the interpolation of frequency components. As shown in Figure 7, the center frequency f₁~ f₄The center frequency f is between the four frequency components that have₁₂, F₂₃, F₃₄By interpolating the three frequency components with, the missing information is added so that the spectrum is smoothly continuous. Such interpolation, for example, Fourier transforms the received signal and on the frequency axis, the center frequency f₁~ f₄It can be realized by adding a desired frequency component based on the four frequency components having the above, and then performing an inverse Fourier transform.

Referring again to FIG. 1, the B-mode image beamformer 32 has a plurality of delay patterns (phase matching patterns) according to the receiving direction and depth of focus of the ultrasonic echo, and is set by the scanning control unit 11. The reception focus process is performed by giving a delay to each of the plurality of pulses compressed by the pulse compression unit 31 of the plurality of channels according to the reception direction and the depth of focus, and adding the plurality of pulses. By this reception focus processing, a compressed pulse (B mode sound line signal) in which the focus of the ultrasonic echo is narrowed down is formed.

The B-mode image signal generation unit 33 generates an B-mode image signal by performing envelope detection processing on the B-mode sound line signal and further performing pre-process processing such as Log (logarithmic) compression and gain adjustment. The DSC34 for B-mode images converts the generated B-mode image signal into an image signal according to a normal television signal scanning method (raster conversion). In the above, the pulse compression units 31 to B mode image DSC34 constitute the first receiving system signal processing means.

The pulse separation unit 41 has a center passing frequency of f.₁~ f₄Contains 4 bandpass filters that have a center frequency of f₁~ f₄Separates four types of pulses, each containing a frequency component with. The four types of pulses separated by the pulse separation unit 41 of each channel are supplied to the four Doppler image beam formers 42, respectively.

Each Doppler image beamformer 42 has a plurality of delay patterns (phase matching patterns) according to the reception direction and depth of focus of the ultrasonic echo, and the reception direction and depth of focus set by the scanning control unit 11. According to this, the reception focus processing is performed by giving delays to each of the plurality of pulses output from the pulse separation unit 41 of the plurality of channels and adding the plurality of pulses. By this reception focus processing, a pulse (Dopla sound line signal) in which the focus of the ultrasonic echo is narrowed down is formed.

The Doppler detection unit 43 generates a baseband signal by multiplying the frequency component of each pulse supplied from the four Doppler image beam formers 42 by a local oscillation signal having a corresponding center frequency and performing orthogonal detection. , The frequency shift in each pulse is detected based on the phase information of the baseband signal, and a Doppler image signal is generated.

FIG. 8 is a diagram showing a configuration example of the Doppler detection unit in FIG. The Doppler detector 43 has f for each oscillation frequency.₁~ f₄Four local oscillators 111 to 114 and four orthogonal detectors 121 to 124, and their delay times are τ.₁~ τ₃Three types of delay elements 131 to 133, an adder 141 that adds four Q signals, an adder 142 that adds four I signals, and a baseband signal based on the added Q signal and I signal. It is represented equivalently by the phase calculation unit 150 that calculates the phase of the baseband signal and the differential calculation unit 160 that calculates the frequency shift by differentiating the phase of the baseband signal.

The orthogonal detector 121 is equivalently represented by two mixers 121a and 121b, a 90 ° phase shifter 121c, two low-pass filters 121d and 121e, and a phase calculation unit 121f.

Center frequency f that has passed through the bandpass filter 101₁The frequency component having the above is multiplied by the oscillation signal of the local oscillator 111 by the mixer 121a and supplied to the low-pass filter 121d. Further, the phase of the oscillation signal of the local oscillator 111 is rotated by 90 ° by the 90 ° phase shifter 121c. Center frequency f that has passed through the bandpass filter 101₁The frequency component having the above is multiplied by the oscillation signal whose phase is rotated by 90 ° by the mixer 121b and supplied to the low-pass filter 121e.

As a result, orthogonal detection is performed, and the Q signal (imaginary component) and I signal (real component) constituting the complex baseband signal are output from the low-pass filters 121d and 121e, respectively. The phase calculation unit 121f tans based on the Q signal and the I signal.^-1By performing the calculation of (Q / I), the phase shift signal representing the phase shift of the complex baseband signal is obtained.

The configuration and operation of the orthogonal detectors 122 to 124 are the same as those of the orthogonal detector 121. The phase shift signals output from the orthogonal detectors 121 to 123 are input to the delay elements 131 to 133, respectively, and four types of phase shift signals θ₁~ θ₄Timing is aligned. Therefore, four types of phase shift signal θ₁~ θ₄The detection accuracy can be improved by adding and averaging. Furthermore, by differentiating the phase shift signal that has been added and averaged, a frequency shift signal that represents the frequency shift in a plurality of pulses is obtained, and the speed of the moving object in the subject is determined based on the frequency shift signal. The Doppler image signal to be represented is obtained.

On the other hand, the Q signal and I signal output from the orthogonal detectors 121 to 123 are input to the delay elements 131 to 133, respectively, and the timings of the four types of Q signal and I signal are aligned. The adder 141 adds four types of Q signals, and the adder 142 adds four types of I signals, so that the detection accuracy when calculating the frequency shift can be improved. The phase calculation unit 150 tans based on the Q signal and the I signal after addition.^-1By performing the calculation of (Q / I), the average phase shift signal φ that represents the phase shift in the four types of pulses on average is obtained. Further, the differential calculation unit 160 obtains a frequency shift signal representing a frequency shift in a plurality of pulses by differentiating the average phase shift signal φ, and further, based on the frequency shift signal, in the subject. The Doppler image signal representing the speed of the moving body is obtained.

FIG. 9 is a diagram for explaining in detail the operation of the Doppler detection unit shown in FIG. As shown in FIG. 9, a plurality of pulse trains are received in each frame. The pulses contained in those pulse trains are represented by P (i, j, k). Here, i represents the frame number, j represents the pulse train number in each frame, and k represents the pulse number in each pulse train. Further, in each pulse train, the first pulse P (i, j, 1) to the fourth pulse P (i, j, 4) have a center frequency f.₁~ f₄Each contains a frequency component having.

FIG. 10 is a diagram showing a Q signal and an I signal obtained by orthogonally detecting the pulse train shown in FIG. 9. By orthogonally detecting the pulse P (i, j, k), the Q signal Q (i, j, k) and the I signal I (i, j, k) can be obtained.

11A to 11C are diagrams showing the phase shift obtained based on the Q signal and the I signal shown in FIG. Based on the Q signal Q (i, j, k) and the I signal I (i, j, k) shown in FIG. 10, tan^-1By performing the calculation of (Q (i, j, k) / I (i, j, k)), the phase shift signal θ (i, j, k) representing the phase shift in each pulse can be obtained.

FIG. 11A shows the case where a high-speed moving speed (flow velocity) is detected, and the phase shift signals θ (i, j, 1), θ (i, j, 2), θ (i, j, 3). , Θ (i, j, 4), ..., The velocity of the moving object in the subject is detected. FIG. 11B shows a case where a general moving speed (flow velocity) is detected, and the average phase shift signal φ (i, j) obtained by averaging the phase shift signal θ (i, j, k) in each pulse train. ), The velocity of the moving object in the subject is detected. FIG. 11C shows a case where a low-speed moving speed (flow velocity) is detected, and is applied based on the average phase shift signals φ (1, j), φ (2, j), ... Between frames. The velocity of the moving object in the sample is detected.

Referring to FIG. 1 again, the Doppler image DSC44 converts the Doppler image signal generated by the Doppler detection unit 43 into an image signal according to a normal television signal scanning method (raster conversion). In the above, the pulse separation unit 41 to the DSC44 for Doppler image constitute the second reception system signal processing means.

The image display control unit 51 generates an image signal for display by synthesizing the image signal supplied from the DSC34 for B mode image and the image signal supplied from the DSC44 for Doppler image in the color mode.

The console 61 includes a keyboard, an adjustment knob, a mouse, and the like, and is used when an operator inputs commands and information to the ultrasonic diagnostic apparatus. The control unit 62 controls each unit of the ultrasonic diagnostic apparatus based on commands and information input using the console 61. In the present embodiment, the scanning control unit 11, the transmission control unit 12, the pulse compression unit 31 to the image display control unit 51, and the control unit 62 cause the central processing unit (CPU) and the CPU to perform various processes. It is composed of software for the purpose, but these may be composed of a digital circuit or an analog circuit. The above software is stored in the storage unit 63. As the recording medium in the storage unit 63, a flexible disk, MO, MT, RAM, CD-ROM, DVD-ROM, or the like can be used in addition to the built-in hard disk.

Next, a second embodiment of the present invention will be described. FIG. 12 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention. In the second embodiment, the transmission / reception unit 20a and the Doppler detection unit 43a are used instead of the transmission / reception unit 20 and the Doppler detection unit 43 in the first embodiment shown in FIG. Other points are the same as those in the first embodiment.

In the transmission / reception unit 20a, the pulse separation unit 41a has a center passing frequency of f.₁~ f₄In addition to the four bandpass filters that are, each delay time is τ₁~ τ₃It contains three delay elements. These can also serve as the bandpass filters 71 to 74 and the delay elements 81 to 83 of the pulse compression unit shown in FIG. Therefore, in the second embodiment, the pulse compression unit 31a is composed of only the adder. Further, the delay elements 131 to 133 shown in FIG. 8 are not required in the Doppler detection unit 43a.

In the second embodiment of the present invention, the pulse separation unit 41a, the pulse compression unit 31a, the beam former 32 for B-mode image, the B-mode image signal generation unit 33, and the DSC34 for B-mode image are the first receiving systems. It constitutes a signal processing means. The pulse separation unit 41a, the Doppler image beamformer 42, the Doppler detection unit 43a, and the Doppler image DSC44 constitute a second receiving system signal processing means.

The present invention can be used in an ultrasonic diagnostic apparatus that captures an image of an organ or the like in a living body by transmitting and receiving ultrasonic waves and generates an ultrasonic image used for diagnosis.

<figref num="1">It is a block diagram which shows the structure of the ultrasonic diagnostic apparatus which concerns on 1st Embodiment of this invention.</figref><figref num="2">It is a figure which shows the structural example of the pulse compression part in FIG.</figref><figref num="3">It is a figure which shows the waveform of the pulse train at the position A of FIG.</figref><figref num="4">It is a figure which shows the waveform of a plurality of pulses at the position B of FIG.</figref><figref num="5">It is a figure for demonstrating pulse compression on a frequency axis.</figref><figref num="6">It is a figure which shows the spectrum of the compressed pulse in detail.</figref><figref num="7">It is a figure for demonstrating the interpolation of a frequency component.</figref><figref num="8">It is a figure which shows the structural example of the Doppler detection part in FIG.</figref><figref num="9">It is a figure for demonstrating the operation of the Doppler detection part shown in FIG. 8 in detail.</figref><figref num="10">It is a figure which shows the Q signal and I signal obtained by orthogonal detection of the pulse train shown in FIG.</figref><figref num="11A">It is a figure which shows the phase shift obtained based on the Q signal and I signal shown in FIG.</figref><figref num="11B">It is a figure which shows the phase shift obtained based on the Q signal and I signal shown in FIG.</figref><figref num="11C">It is a figure which shows the phase shift obtained based on the Q signal and I signal shown in FIG.</figref><figref num="12">It is a block diagram which shows the structure of the ultrasonic diagnostic apparatus which concerns on 2nd Embodiment of this invention.</figref>

10 Ultrasonic probe 10a ultrasonic transducer 11 Scan control unit 12 Transmission control unit 13 Drive signal generator 14 Transmission / reception switching unit 20, 20a Transmitter / receiver 21 Preamplifier 22 Variable gain amplifier 23 Low pass filter 24 A / D converter 31, 31a Pulse compression unit 32 Beamformer for B-mode images 33 B mode image signal generator 34 DSC for B-mode images 41, 41a Pulse separator 42 Beamformer for Doppler images 43, 43a Doppler detector 44 DSC for Doppler images 51 Image display control unit 52 Display 61 console 62 Control unit 63 Storage 71 ~ 74 Bandpass filter 81 ~ 83 Delay element 111 ~ 114 Local oscillator 121 ~ 124 Orthogonal detector 131 ~ 133 Delay element 141, 142 adder 150 Phase calculation unit 160 Derivative calculation unit