JP2006014916A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel ultrasonic diagnostic apparatus utilizing continuous waves. <P>SOLUTION: An FM modulator 18 generates FM continuous waves based on RF (radio frequency) waves fed from an RF wave oscillator and sawtooth modulated waves fed from a sawtooth wave oscillator. Received RF signals are detected with FM continuous waves for transmission in a receiving mixer 28, and a frequency difference signal between received signals is extracted by a band-pass filter 30. Then, the position of an in-vivo tissue is calculated by a position calculation part 32 based on the frequency difference signal, and the velocity of the in-vivo tissue is calculated by a velocity calculation part 34 based on the frequency difference signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus using a continuous wave.

  As a technique using a continuous wave in an ultrasonic diagnostic apparatus, a continuous wave Doppler is known. In continuous wave Doppler, for example, a sinusoidal transmission wave of several MHz is continuously radiated into the living body, and a reflected wave from the living body is continuously received. The reflected wave includes Doppler shift information by a moving body (for example, blood flow) in the living body. Therefore, the information is extracted and subjected to frequency analysis, and a Doppler waveform reflecting the velocity information of the moving body is formed.

  On the other hand, in a radar apparatus or the like, a technique is known in which the position of a moving body is measured in addition to the speed of the moving body by applying FM modulation to a carrier wave signal that is a continuous wave (for example, Patent Document 1).

JP-A-5-40168

  As described above, although a technique for measuring the position of a moving body using a continuous wave is known in a radar apparatus or the like, it has not been realized in an ultrasonic diagnostic apparatus.

  Accordingly, an object of the present invention is to provide a new ultrasonic diagnostic apparatus using continuous waves.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred embodiment of the present invention includes a transmitter that generates a modulated transmission signal by frequency-modulating a carrier wave signal using a modulation signal, and a living body that supplies the modulated transmission signal. And a transmitter / receiver for receiving a reflected wave from a living body and outputting a reception signal, and demodulating the reception signal using the modulated transmission signal, thereby generating a frequency difference signal. And a position calculation unit that obtains the position of the in vivo tissue based on the frequency difference between the transmission and reception signals obtained from the frequency spectrum of the frequency difference signal.

  Preferably, the position calculation unit calculates the position of the tissue corresponding to the frequency difference component based on at least one frequency difference component included in the frequency spectrum. Preferably, the apparatus further includes a frequency characteristic compensation unit that controls the amplitude of the modulated transmission signal so as to compensate the frequency characteristic of the transducer. More preferably, the modulation signal is any one of a sawtooth wave, a triangular wave, and a sine wave.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmitter that frequency-modulates a carrier wave signal using a modulation signal and generates a modulated transmission signal, and supply of the modulated transmission signal A transmitter / receiver for transmitting an ultrasonic wave to a living body, receiving a reflected wave from the living body and outputting a received signal, and demodulating the received signal using the modulated transmission signal, thereby transmitting and receiving signals A receiving unit that obtains a frequency difference signal that reflects a frequency difference between them, and a speed calculation unit that obtains the speed of a tissue in a living body based on a time change of a frequency spectrum of the frequency difference signal.

  Preferably, the velocity calculation unit calculates the velocity of the tissue corresponding to the frequency difference component based on a time change of at least one frequency difference component included in the frequency spectrum. More preferably, the speed calculation unit calculates the speed from a temporal change in the phase of the frequency difference component. More preferably, the speed calculation unit includes an autocorrelation circuit for obtaining a difference between the two frequency spectra corresponding to different times.

  According to the present invention, a new ultrasonic diagnostic apparatus using a continuous wave is provided. As a result, for example, it is possible to perform tissue position measurement using a continuous wave.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof. The transmitting vibrator 10 continuously transmits a transmission wave into the living body, and the receiving vibrator 12 continuously receives a reflected wave from the living body. In this way, transmission and reception are continuously executed by different vibrators. In FIG. 1, the transmission vibrator 10 and the reception vibrator 12 are each shown as one block, but the transmission vibrator 10 and the reception vibrator 12 are each formed of a plurality of vibration elements. May be.

  The transmitter 14 supplies a transmission signal to the transmission transducer 10 to transmit an ultrasonic wave. The transmitter 14 receives an FM-modulated FM continuous wave (FMCW wave), and a transmission wave corresponding to the FM continuous wave is transmitted from the transmitting transducer 10.

  The FM modulator 18 is an FM continuous wave based on the RF wave supplied from the RF wave oscillator 22 and the sawtooth modulation wave supplied from the sawtooth wave oscillator 20 (reference numeral 40 in FIG. 3 described in detail later). (Transmission waveform in FIG. 4A described in detail later) is generated. Then, the amplitude control unit 16 controls the amplitude of the FM continuous wave generated by the FM modulator 18 so as to compensate the frequency characteristics of the transmitting transducer 10 and the receiving transducer 12.

  FIG. 2 is a diagram for explaining amplitude control in the amplitude control unit (reference numeral 16 in FIG. 1). In the following description, the parts shown in FIG.

  FIG. 2A shows the amplitude-frequency characteristics of a probe including the transmitting transducer 10 and the receiving transducer 12, and the amplitude of the probe varies depending on the frequency indicated on the horizontal axis. Therefore, the amplitude control unit 16 compensates the frequency characteristics of the probe by controlling the amplitude of the FM continuous wave according to the frequency with the characteristics shown in FIG. In other words, the amplitude of the FM continuous wave is controlled in accordance with the frequency so that the characteristic is opposite to the amplitude characteristic of the probe, and the amplitude of the ultrasonic wave transmitted from the probe is kept uniform within the frequency band. To compensate.

  Returning to FIG. 1, the preamplifier 24 and the main amplifier 26 perform amplification processing on the received signal supplied from the receiving transducer 12, forms a received RF signal, and outputs the received RF signal to the receiving mixer 28. The reception mixer 28 is a circuit that detects a received RF signal. The reference signal supplied to the reception mixer 28 is an FM continuous wave generated by the FM modulator 18. Here, the FM continuous wave whose amplitude is controlled by the amplification controller 16 may be supplied to the reception mixer 28 as a reference signal. In this way, the reception mixer 28 detects the reception RF signal by the FM continuous wave for transmission, and the band-pass filter (BPF) 30 extracts the frequency difference signal between the transmission and reception signals. The frequency difference signal will be described in detail later using FIG. 3 and FIG.

  Note that the reception mixer 28 may perform quadrature detection on the received RF signal to generate a complex signal. In the case of quadrature detection, detection is performed using two continuous waves as reference signals, which are an FM continuous wave output from the amplitude control unit 16 and a continuous wave in which the phase of the FM continuous wave is shifted by π / 2. And two components of orthogonal components may be output.

  The frequency difference signal extracted by the BPF 30 is supplied to the position calculation unit 32 and further to the speed calculation unit 34 via the position calculation unit 32.

  The position calculation unit 32 calculates the position of the in vivo tissue based on the frequency difference signal, and the speed calculation unit 34 calculates the speed of the in vivo tissue based on the time change of each frequency spectrum corresponding to each frequency difference signal. To do. The position calculation unit 32 and the speed calculation unit 34 are configured by, for example, a calculator (such as a CPU or DSP) that performs an FFT calculation. The tissue position information and speed information obtained by the position calculation unit 32 and the speed calculation unit 34 are output to the display unit 36. For example, an in-vivo tomographic image based on the position information, a Doppler image based on the speed information, A color Doppler image or the like is displayed on the display unit 36.

  As described above, in this embodiment, ultrasonic waves (FMCW waves) of continuous waves that are FM-modulated with sawtooth waves are transmitted and received to acquire tissue position information and velocity information. Then, the principle is explained in full detail next. In the following description, the parts shown in FIG.

  FIG. 3 is a diagram for explaining the principle of acquiring position information from the frequency difference signal. FIG. 3 shows an example in which a received signal is acquired from one target tissue. 3A shows how the transmission frequency 40 and the reception frequency 42 change over time, and FIG. 3B shows the time change of the frequency difference between the transmission and reception signals (frequency difference signal 44). Is shown. The transmission frequency 40 corresponds to the frequency change of the ultrasonic wave transmitted from the transmission transducer 10, and the reception frequency 42 corresponds to the frequency change of the reflected wave from the tissue received by the reception transducer 12. . The frequency difference signal 44 is a signal extracted by the BPF 30.

  The transmission frequency 40 is generated by the sawtooth oscillator 20. The transmission frequency 40 is an FM modulated wave that changes in frequency from −Δω to Δω during the time Tm, and changes in a sawtooth frequency. The transmission wave modulated by the sawtooth wave propagates through the living body and is reflected by the tissue. For this reason, the wave is received with a delay according to the round-trip propagation distance. This is shown by the reception frequency 42. That is, the reception frequency 42 is acquired by being shifted from the transmission frequency 40 by the delay time τ.

また、送信周波数４０は、時間Ｔｍの間に−ΔωからΔωまで周波数が変化するため、単位時間当たりの周波数変化は、次式のようになる。

このため、図３（Ｂ）に示す期間１，３，５における送受信信号間の周波数差Δδと、期間２，４，６における送受信信号間の周波数差Δδは、それぞれ次式のようになる。

時間τ＝２Ｌ／ｃであるため、期間１，３，５における送受信信号間の周波数差Δδを考えると、

となる。したがって、期間１，３，５における送受信信号間の周波数差Δδを知ることで、既知の値であるΔω，Ｔｍ，ｃから、数４を利用して、探触子から対象組織までの距離Ｌを求めることができる。 Time τ corresponds to the round-trip propagation time of the ultrasonic wave. Therefore, when the distance from the probe to the target tissue is L and the sound speed is c, the time τ is expressed by the following equation.

Further, since the frequency of the transmission frequency 40 changes from −Δω to Δω during the time Tm, the frequency change per unit time is expressed by the following equation.

Therefore, the frequency difference Δδ between the transmission / reception signals in the periods 1, 3, and 5 and the frequency difference Δδ between the transmission / reception signals in the periods 2, 4, and 6 shown in FIG.

Since time τ = 2L / c, considering the frequency difference Δδ between transmitted and received signals in periods 1, 3, and 5,

It becomes. Therefore, by knowing the frequency difference Δδ between the transmission and reception signals in the periods 1, 3, and 5, the distance L from the probe to the target tissue can be obtained from the known values Δω, Tm, c using Equation 4. Can be requested.

  FIG. 4 is a diagram for explaining the principle of acquiring position information from a frequency difference signal, and FIG. 4 shows an example in which received signals are acquired from a plurality of target tissues.

  FIG. 4A shows a transmission waveform (FM continuous wave: FMCW wave) supplied to the transmission vibrator 10. FIG. 4B shows how the transmission frequency 40 and the plurality of reception frequencies 42a to 42d change with time. The plurality of reception frequencies 42a to 42d respectively correspond to reception signals from target tissues existing at different depths. Each of the plurality of reception frequencies 42a to 42d is received with a delay with respect to the transmission frequency 40 in accordance with the depth of the corresponding tissue.

  FIG. 4C shows how the frequency difference signals 44a to 44d, which are differences from the transmission frequency 40, change with time for each of the plurality of reception frequencies 42a to 42d. The frequency difference signals 44a to 44d are signals that are collectively extracted by the BPF 30. That is, the BPF 30 outputs a signal in which the frequency difference signals 44a to 44d are superimposed.

  The position calculation unit 32 extracts a frequency difference signal for each depth from the superimposed signal. For this reason, the position calculation unit 32 sets a window in the signal processing time zone 48 shown in FIG. 4C, analyzes the frequency of the output signal from the BPF 30 using the FFT, for example, in the set window, The frequency power spectrum shown in FIG. 4D is acquired.

  The frequency power spectrum shown in FIG. 4D corresponds to the frequency spectrum of the signal in which the frequency difference signals 44a to 44d are superimposed. Therefore, the waveform includes the spectrum components 50a to 50d at the frequency positions of the frequency difference signals 44a to 44d.

  Therefore, the position calculation unit 32 extracts a signal of a necessary frequency band, and then converts it into each spectrum component 50a to 50d of the frequency spectrum by FFT or the like, and performs signal processing of the frequency difference signals 44a to 44d from the frequency component. A frequency difference Δδ in the time zone 48 is obtained. Thus, for each depth, the distance L corresponding to the depth (position) of each tissue is obtained from the frequency difference Δδ and the known values Δω, Tm, c using Equation 4.

  FIG. 5 is a diagram for explaining the principle of acquiring speed information from the frequency difference signal, and shows the time change of the frequency spectrum of the frequency difference signal.

  FIG. 5 is a two-dimensional representation of the frequency spectrum described with reference to FIG. 4D using a frequency axis and a time axis. The frequency axis in FIG. 5 is the vertical axis in FIG. Corresponding to Therefore, also in FIG. 5, the spectrum at a predetermined frequency corresponds to a reflected wave from a depth corresponding to that frequency. In FIG. 5, the frequency spectrum is represented by a complex amplitude including an amplitude component and a phase component. The length of each spectrum bar represented in a bar shape in FIG. 5 corresponds to the amplitude, and the slope of the bar. Corresponds to the phase.

  If the target tissue is fixed, the frequency spectrum obtained from the target tissue is constant regardless of time. That is, in FIG. 5, in the spectrum of the frequency corresponding to the fixed tissue, the length and inclination of the bar are constant regardless of time. On the other hand, when the target tissue is moving, the frequency spectrum obtained from the target tissue changes with time. That is, in FIG. 5, in the spectrum of the frequency corresponding to the moving tissue, the length and inclination of the bar change with time. Therefore, by analyzing the time variation of the amplitude component and the phase component of the frequency spectrum, the velocity corresponding to the frequency component, that is, the tissue velocity corresponding to the frequency component can be obtained.

  FIG. 6 is a diagram for explaining the principle of acquiring speed information from a frequency difference signal, and is a complex representation of each frequency component (Δδ1 to Δδ4) of a frequency spectrum at a predetermined time. Each frequency component (Δδ1 to Δδ4) in FIG. 6 corresponds to a plurality of different frequency components arranged in the frequency axis direction in FIG.

  The speed calculator 34 analyzes the signal obtained by converting the output signal from the BPF 30 into the frequency amplitude spectrum by the position calculator 32, that is, the frequency difference signal shown in FIG. 4C using, for example, FFT. Then, as shown in FIG. 6, each frequency component (Δδ1 to Δδ4) is complex-represented by two components, an I channel signal component and a Q channel signal component. FIG. 6 shows the complex amplitude of each frequency component of the frequency spectrum at a predetermined time. The speed calculation unit 34 obtains each frequency component in a complex expression at each time, and changes the time variation for each frequency component. To analyze.

  Since each frequency component (Δδ1 to Δδ4) corresponds to the received signal of the tissue at each depth, the tissue at each depth (position) is analyzed by analyzing the time change of each frequency component (Δδ1 to Δδ4). Can be determined.

  FIG. 7 shows a modification of the ultrasonic diagnostic apparatus shown in FIG. 1, and FIG. 7 is a block diagram showing the overall configuration.

  7, parts having the same reference numerals as those shown in FIG. 1 have the same configuration and operation as those in FIG. As described in FIG. 1, also in FIG. 7, the frequency difference signal between the transmission and reception signals is output from the BPF 30.

  The FFT 60 performs frequency analysis on the frequency difference signal (a signal corresponding to FIG. 4C) output from the BPF 30, and generates a complex signal of the frequency spectrum (a signal corresponding to FIG. 5) at each time.

  The multiplier 72 multiplies the complex signal of the current time frequency spectrum input from the FFT 60 by the complex signal of the frequency spectrum of a predetermined time before input via the delay line 70, and the low-pass filter 74 The difference between the complex signals at the two times is extracted. The speed calculation circuit 76 analyzes the time fluctuation for each frequency component of the frequency spectrum from the difference between the complex signals at two times extracted by the low-pass filter 74.

  Since each frequency component corresponds to the received signal of the tissue at each depth, the velocity of the tissue at each depth (position) can be obtained by analyzing the time change of each frequency component. The speed is displayed on the speed / speed dispersion display section 78.

  As shown in FIG. 7, a dispersion calculation circuit 80 is provided to calculate the speed dispersion from the complex signal of the frequency spectrum for each time output from the FFT 60 and display it on the speed and speed dispersion display section 78. You may let them.

  Further, the position calculation circuit 62 obtains the depth (distance L) of each tissue from the frequency difference Δδ and the known values Δω, Tm, c for each depth, using Equation 4. Then, information based on the obtained position (for example, a tomographic image or the like) is displayed on the position display unit 64.

  As mentioned above, although preferred embodiment of this invention was described, this embodiment (including the modification) has the following advantages.

  Generally, when a pulse wave is used (in the case of a pulse method), the peak power of an ultrasonic pulse must be increased in order to improve the SNR. In order to increase the peak power of the ultrasonic pulse, the circuit configuration becomes complicated, for example, it is necessary to increase the breakdown voltage of the circuit of the transmission unit and to take measures to prevent leakage to the reception side. Of course, when the peak power of the ultrasonic pulse is increased, it is necessary to consider the influence of the peak sound pressure on the living body. Further, when the distance resolution is ensured by the pulse method, it is necessary to keep the receiving system in a wide band in order to reduce the rise time and fall time of the pulse.

  In this embodiment, since a continuous wave is used, the frequency band of the frequency spectrum signal obtained by frequency-converting the demodulated baseband signal by FFT or the like can be narrowed, and the signal-to-noise ratio compared to the pulse method. An improvement in (SNR) can be expected. Moreover, the distance resolution can be made equal to or higher than that of the pulse method. Further, in the present embodiment, compared with the pulse system, it is not necessary to increase the breakdown voltage, so that the circuit configuration can be simplified, and further, it is advantageous for downsizing of the apparatus and low power consumption.

  As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention. For example, a triangular wave or a sine wave may be used as the modulation wave signal instead of the sawtooth wave.

1 is a block diagram showing an overall configuration of an ultrasonic diagnostic apparatus according to the present invention. It is a figure for demonstrating the amplitude control in an amplitude control part. It is a figure for demonstrating the principle which acquires positional information from a frequency difference signal. It is a figure for demonstrating the principle which acquires positional information from a frequency difference signal. It is a figure for demonstrating the principle which acquires speed information from a frequency difference signal. It is a figure for demonstrating the principle which acquires speed information from a frequency difference signal. It is a block diagram which shows the modification of the ultrasonic diagnosing device shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Transmission vibrator | oscillator, 12 Reception vibrator | oscillator, 16 Amplitude control part, 18 FM modulator, 20 Sawtooth wave oscillator, 32 Position calculating part, 34 Speed calculating part.

Claims (8)

A transmission unit that frequency-modulates a carrier wave signal using a modulation signal and generates a modulated transmission signal;
A transmitter / receiver for transmitting ultrasonic waves to a living body by supplying the modulated transmission signal, receiving a reflected wave from the living body and outputting a reception signal;
A receiver that demodulates the received signal using the modulated transmission signal, thereby obtaining a frequency difference signal;
A position calculation unit for obtaining a position of a tissue in a living body based on a frequency difference between transmission and reception signals obtained from a frequency spectrum of the frequency difference signal;
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 1,
The position calculation unit calculates the position of the tissue corresponding to the frequency difference component based on at least one frequency difference component included in the frequency spectrum,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
A frequency characteristic compensator for controlling the amplitude of the modulated transmission signal so as to compensate the frequency characteristic of the transducer;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The modulation signal is any one of a sawtooth wave, a triangular wave, and a sine wave.
An ultrasonic diagnostic apparatus. A transmission unit that frequency-modulates a carrier wave signal using a modulation signal and generates a modulated transmission signal;
A transmitter / receiver for transmitting ultrasonic waves to a living body by supplying the modulated transmission signal, receiving a reflected wave from the living body and outputting a reception signal;
A receiver that demodulates the received signal using the modulated transmission signal, thereby obtaining a frequency difference signal reflecting a frequency difference between the transmitted and received signals;
A speed calculation unit for determining the speed of the tissue in the living body based on the time change of the frequency spectrum of the frequency difference signal;
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 5,
The velocity calculation unit calculates the velocity of the tissue corresponding to the frequency difference component based on the time change of at least one frequency difference component included in the frequency spectrum.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 6,
The speed calculation unit calculates the speed from a temporal change in the phase of the frequency difference component.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 7,
The speed calculation unit includes an autocorrelation circuit for obtaining a difference between two frequency spectra corresponding to different times,
An ultrasonic diagnostic apparatus.

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