JP2010162082A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved apparatus configuration in an ultrasonic diagnostic apparatus for utilizing continuous waves and extracting in-vivo information from a selected position. <P>SOLUTION: Modulated continuous waves outputted from a modulation processing part 20 are delayed in delay circuits 26I and 26Q and supplied to the respective mixers of a reception mixer 30 as reference signals. In the delay circuits 26I and 26Q, by matching the phase of reception signals from a target depth with the phase of reference waves, demodulation signals from the target depth are selectively extracted. then, ultrasonic beams are scanned, the ultrasonic beams are formed in a plurality of directions, and the reception signals are acquired along the ultrasonic beams in the same period as the cycle of modulation in the modulation processing part 20 in each direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  A continuous wave Doppler is known as a technique using a continuous wave of an ultrasonic diagnostic apparatus. In continuous wave Doppler, for example, a transmission wave that is a sine wave of several MHz is continuously emitted 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, by extracting the Doppler shift information and performing frequency analysis, a Doppler waveform reflecting the velocity information of the moving body can be formed.

  Continuous wave Doppler using a continuous wave is generally superior in speed measurement at a higher speed than pulse Doppler using a pulse wave. Under such circumstances, the present inventor has conducted research on continuous wave Doppler. As one of the results, Patent Document 1 proposes a technique related to continuous wave Doppler (FMCW Doppler) subjected to frequency modulation processing.

  On the other hand, with continuous wave Doppler, position measurement is difficult due to the use of continuous waves. For example, a conventional general continuous wave Doppler device (a device that does not use FMCW Doppler) cannot perform position measurement. On the other hand, the inventor of the present application proposes an extremely innovative technique that can selectively extract Doppler information from a desired position in a living tissue by FMCW Doppler in Patent Document 2.

JP 2005-253949 A JP 2008-289851 A

  The technology of FMCW Doppler described in Patent Literature 1 and Patent Literature 2 is an epoch-making technology with the possibility of ultrasonic diagnosis that has never existed before. The inventor of the present application has further studied further about this revolutionary technology improvement. In particular, research has been repeated focusing on techniques for extracting in-vivo information from a desired position (selected position) using continuous waves.

  The present invention has been made in such a background, and an object thereof is to provide an improved apparatus configuration in an ultrasonic diagnostic apparatus that extracts in-vivo information from a selected position using a continuous wave. It is in.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmission signal output unit that outputs a transmission signal of a continuous wave modulated based on a periodic signal, and the transmission signal There is a correlation between a transmitting / receiving unit that obtains a reception signal by transmitting a corresponding ultrasonic transmission wave to a living body and receiving a reception wave accompanying the transmission wave from the living body, and a selected position in the living body. A demodulation processing unit that obtains a demodulation signal corresponding to the selected position by performing demodulation processing on the received signal using the adjusted reference signal, and an in-vivo information extraction unit that extracts in-vivo information from the demodulation signal And forming an ultrasonic beam in a plurality of directions by scanning the ultrasonic beam, and for each direction, the ultrasonic beam is converted into an ultrasonic beam in a period corresponding to a natural number multiple of the period of the periodic signal. Along with getting the received signal along That.

  In the above aspect, a continuous wave transmission signal modulated based on a periodic signal is used, and a reception signal along the ultrasonic beam in a period corresponding to a natural number multiple of the period of the periodic signal. Is acquired. Therefore, for example, the received signal can be acquired while maintaining the periodicity of the periodic signal, and for example, the periodicity of the periodic signal is maintained with respect to the demodulated signal obtained from the received signal. It is possible to perform FFT processing and the like.

  In a preferred aspect, the ultrasonic diagnostic apparatus scans an ultrasonic beam over a plurality of frames, and shifts the directions of the ultrasonic beams between two adjacent frames in time, and An ultrasonic beam is formed in a direction.

  In a desirable mode, the ultrasonic diagnostic apparatus forms a plurality of reception signals corresponding to a plurality of times by forming an ultrasonic beam a plurality of times for each direction, and based on the plurality of reception signals. In vivo information is extracted from a combined demodulated signal obtained by the combining process.

  In a preferred aspect, the ultrasonic diagnostic apparatus intensively scans an ultrasonic beam within a region of interest in a living body.

  In a desirable mode, the ultrasonic diagnostic apparatus has a depth of the ultrasonic beam in the region of interest set in the entire region as compared with a case where the ultrasonic beam is scanned in the entire region capable of scanning. The resolution in the depth direction is improved by reducing the width of the selected position with respect to the direction.

  In a preferred aspect, the transmission signal output unit outputs a continuous wave transmission signal whose frequency is periodically changed.

  In a preferred aspect, the transmission signal output unit outputs a continuous wave transmission signal whose phase is periodically changed by phase shift keying based on a periodic signal sequence.

  In a preferred aspect, the transmission signal output unit outputs a continuous wave transmission signal whose frequency is periodically changed by frequency shift keying based on a periodic signal sequence.

  The present invention provides an improved apparatus configuration in an ultrasonic diagnostic apparatus that extracts in-vivo information from a selected position using a continuous wave.

1 is a diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention. It is a figure for demonstrating the transmission signal of the continuous wave formed by PSK. It is a figure which shows the frequency spectrum of a transmission signal, a reception signal, and a demodulation signal. It is a figure for demonstrating the position selectivity in PSK. It is a figure for demonstrating the relationship between the voltage of a multiplier output, and the phase of a reference signal. It is a figure for demonstrating the transmission signal of the continuous wave formed by FSK. It is a figure which shows the relationship between the phase of the reference wave in FSK, and a multiplier output. It is a figure for demonstrating the acquisition period of the received signal in this embodiment. It is a figure for demonstrating the scanning of the ultrasonic beam in this embodiment. It is a figure for demonstrating the scanning of the ultrasonic beam using a region of interest.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a functional 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 performed by different vibrators, and transmission / reception is performed by a so-called continuous wave Doppler method.

  The continuous wave used in the present embodiment is modulated based on a periodic signal. The modulated continuous wave is formed by the modulation processing unit 20. The modulation processing unit 20 performs modulation processing on the RF wave supplied from the RF wave oscillator 22 based on the periodic signal supplied from the modulation signal generating unit 24 to generate a continuous wave.

  As the modulation processing in the modulation processing unit 20, analog modulation processing such as frequency modulation (FM) and phase modulation (PM) and digital modulation processing such as phase shift keying (PSK) and frequency shift keying (FSK) are suitable. is there. The waveform of the continuous wave formed in the modulation processing unit 20 will be described in detail later. The modulation processing unit 20 outputs the modulated continuous wave to the transmission beamformer (transmission BF) 14.

  The transmission beamformer (transmission BF) 14 outputs transmission signals to a plurality of vibration elements included in the transmission transducer 10. The transmission beam former 14 receives a digitally modulated continuous wave. The transmission beamformer 14 performs a delay process corresponding to each vibration element on the continuous wave to form a transmission signal corresponding to each vibration element. Note that power amplification processing may be performed on the transmission signal corresponding to each vibration element formed in the transmission beam former 14 as necessary. Thus, a transmission beam is formed by the modulated continuous wave.

  The reception beam former (reception BF) 16 forms a reception beam by phasing and adding a plurality of reception signals obtained from a plurality of vibration elements included in the reception transducer 12. The reception beamformer 16 performs delay processing corresponding to the vibration signal obtained from each vibration element, and adds a plurality of reception signals obtained from the plurality of vibration elements, thereby processing the reception beam. Form. Note that a plurality of received signals may be supplied to the reception beam former 16 after processing such as low noise amplification is performed on the received signals obtained from the respective vibration elements. In this way, a reception RF signal along the reception beam is obtained.

  The reception mixer 30 is a circuit that performs quadrature detection on the received RF signal to generate a complex baseband signal, and is composed of two mixers 32 and 34. Each mixer is a circuit that mixes the received RF signal with a predetermined reference signal.

  The reference signal supplied to each mixer of the reception mixer 30 is generated based on a digitally modulated continuous wave (transmission signal). That is, the continuous wave output from the digital modulation processing unit 20 is delayed in the delay circuit 26I and the delay circuit 26Q, and the continuous wave delayed in the delay circuit 26I is supplied to the mixer 32, and is delayed in the delay circuit 26Q. The continuous wave is supplied to the mixer 34.

  The delay circuit 26I and the delay circuit 26Q perform delay processing on the continuous wave by a delay amount corresponding to the depth of the target selection position, and output a delayed reference signal. Each of the delay circuit 26I and the delay circuit 26Q can be formed by, for example, an n-stage shift register. In this case, a tap having a delay amount corresponding to the depth of the selected position is selected from the n-stage taps of the shift register, and a reference signal (delayed continuous wave) corresponding to the depth of the selected position is selected from the selected tap. Is output.

  Note that the delay circuit 26I and the delay circuit 26Q perform delay processing by shifting the phase of the continuous wave by π / 2. As a result, an in-phase signal component (I signal component) is output from the mixer 32, and a quadrature signal component (Q signal component) is output from the mixer 34. The high-frequency components of the in-phase signal component and the quadrature signal component are cut by LPFs (low-pass filters) 36 and 38 provided at the subsequent stage of the receiving mixer 30 and the demodulated signal only in the necessary band after detection is extracted. Is done.

  As will be described in detail later, the received mixer output signal (demodulated signal), which is the result of the mixing process of the received RF signal and the reference signal executed by each mixer, contains many received signal components from the target selected position. It is. In the LPFs 36 and 38, the DC signal component included in the received signal component from the selected position is extracted.

  FFT circuits (fast Fourier transform circuits) 40 and 42 perform an FFT operation on each demodulated signal (in-phase signal component and quadrature signal component). As a result, the demodulated signal is converted into a frequency spectrum in the FFT circuits 40 and 42. The frequency spectrum output from the FFT circuits 40 and 42 is output as frequency spectrum data with a frequency resolution δf depending on circuit setting conditions and the like.

  The Doppler information analysis unit 44 extracts Doppler information from the demodulated signal converted into a frequency spectrum. At this time, since the delay relationship between the reference signal and the reception signal is adjusted by the delay circuits 26I and 26Q in advance according to the depth of the selected position in the living body, the Doppler information from the selected position is selectively displayed. Extracted into The relationship between the adjustment of the delay relationship and the extraction of Doppler information from the selected position will be described in detail later. The Doppler information analysis unit 44 extracts Doppler information for each depth (each position) in the living body, and calculates the velocity of the tissue in the living body for each depth on the ultrasonic beam (sound ray), for example. Output in real time. Note that the speed of each position of the in-vivo tissue may be calculated two-dimensionally or three-dimensionally by scanning an ultrasonic beam.

  The display processing unit 46 forms, for example, a Doppler waveform or a graph including depth and velocity information based on the velocity for each depth (position) of the living tissue, and the display unit 48 displays the formed Doppler waveform or graph. To display in real time. Each unit in the ultrasonic diagnostic apparatus shown in FIG. 1 is controlled by the system control unit 50. That is, the system control unit 50 performs transmission control, reception control, display control, and the like.

  Next, position selectivity in the present embodiment will be described. In this embodiment, an ultrasonic wave corresponding to the modulated continuous wave is transmitted and received to obtain a reception signal, and the delay relationship between the reference signal and the reception signal is determined according to the depth of the selected position in the living body. The Doppler information is selectively extracted as in-vivo information from the selected position by adjusting and performing a demodulation process by strengthening the correlation between the received signal from the selected position and the reference signal. As a modulation method in the modulation processing unit 20, analog modulation processing such as frequency modulation (FM) and phase modulation (PM) and digital modulation processing such as phase shift keying (PSK) and frequency shift keying (FSK) are preferable. . Therefore, position selectivity will be described for each modulation method.

<Position selectivity by frequency modulation (FM) and phase modulation (PM)>
When performing analog modulation processing in the modulation processing unit 20 of FIG. 1, for example, when performing frequency modulation (FM modulation) or phase modulation (PM modulation), the modulation processing unit 20 includes an RF wave supplied from the RF wave oscillator 22, A continuous wave is generated based on a modulation wave such as a sine wave or a sawtooth wave supplied from the modulation signal generator 24.

RF wave of a frequency _{f 0} with respect to (a carrier wave), FMCW transmission wave subjected to FM modulation by a sine wave of a frequency _{f m} can be expressed by the following equation. In the following expression, Delta] f is 0-P value of the frequency fluctuation range is (zero peak value maximum frequency shift), is β is the ratio of the maximum frequency deviation Delta] f and the modulation frequency f _m is a modulation index of FM.

In addition, the FMCW received wave with Doppler shift can be expressed by the following equation, where α is a round-trip attenuation in the living body. In the following equation, the Doppler shift with respect to f _m is neglected because it is smaller than the shift amount f _d of f ₀ .

The received waveform represented by the equation (2) is a signal waveform (received RF signal) received via the receiving transducer 12. In the FMCW Doppler, in the demodulation process for the received RF signal, the received wave is multiplied by the FMCW transmission wave as a reference signal. As described with reference to FIG. 1, the continuous wave (FM continuous wave) output from the modulation processing unit 20 is delayed in the delay circuits 26I and 26Q and supplied to the mixers 32 and 34 as reference signals. The delay circuit 26I and the delay circuit 26Q perform delay processing by shifting the phase of the continuous wave by π / 2. Therefore, the reference signal v _rI (t) supplied to the mixer 32 and the reference signal v _rQ (t) supplied to the mixer 34 can be expressed by the following equations.

In Equation 3, φ _mr represents the phase of the reference signal that can be arbitrarily set by the delay processing in the delay circuits 26I and 26Q, and φ _0r represents the carrier wave determined in accordance with the phase of the arbitrarily set reference signal. The amount of phase change is shown.

In the receiving mixer 30, quadrature detection is performed as demodulation processing. That is, the mixer 32 executes a process corresponding to the multiplication of the received RF signal v _R (t) and the reference signal v _rI (t), and the mixer 34 receives the received RF signal v _R (t) and the reference signal v. A process corresponding to the multiplication of _rQ (t) is executed.

The multiplication v _DI (t) of the reception RF signal v _R (t) and the reference signal v _rI (t) in the mixer 32 is expressed by the following equation. Note that the component of the frequency 2f ₀ is deleted during the calculation of the following equation. This is a frequency component removed by the LPF 36.

  Here, the following formula for the Bessel function is used.

  Using the formula of Formula 5, Formula 4 is further calculated as the following formula.

On the other hand, the multiplication v _DQ (t) of the reception RF signal v _R (t) and the reference signal v _rQ (t) in the mixer 34 is expressed as follows. Note that the component of the frequency 2f ₀ is deleted during the calculation of the following equation. This is a frequency component removed by the LPF 38.

Here, a complex baseband signal is defined based on v _DI (t) in Expression 6 and v _DQ (t) in Expression 7. _{First, v} DI (t) and _v DC contained in the DQ (t) (DC) component, the even-order harmonics of the modulation frequency _{f m} expressed by the following equation.

_{Then, v} DI (t) and _v DQ (t) in the included components of the modulation frequency _{f m,} expressed by the following equation odd harmonics component of the modulation frequency _{f m.}

More of the equation (8) and equation (9), in the baseband signal after the quadrature detection, Doppler signal containing Doppler shift f _d is composed of a DC component as the modulation frequency f _m and harmonic components of the modulation frequency f _m It can be seen that it appears as a double sideband wave for each of the components. In communications engineering, this type of signal format is called Double-Sideband Suppressed-Carrier (DSB-SC).

Here, when aligned the phase of the received signal and the reference signal to each other, that is, delay circuits 26I, consider the case where to match the adjusted and phi _m and phi _mr by the delay processing in the 26Q and (φ _{mr =} φ _m). When φ _mr and φ _m are matched, k in Equation 4 is 0. When this result is applied to the Bessel function of Equation 5, only the value of the 0th-order Bessel function is 1 and the values of the other Bessel functions are 0, as shown in the following equation.

  When the result shown in Equation 10 is applied to Equation 8 and Equation 9, the following equation is obtained.

Equation 11 shows that if the phase φ _mr of the reference wave (reference signal) is set to the phase difference φ _m between transmission and reception, only the Doppler signal corresponding to the DC component (DC signal component) can be extracted by compression conversion. Yes. The value and the polarity of the resulting complex Doppler frequency f _d represents the speed and the polarity of the fluid, such as blood flow. It can also be seen that the amplitude of the Doppler signal does not depend on the phase of the carrier wave and the reference wave.

In this embodiment, as described below, Doppler information at a specific position can be obtained with a relatively good SNR, as in the case of PW Doppler (pulse Doppler). In Equation 6 to Equation 9, kβ that is a factor of J ₀ (kβ) that controls the amplitude of the Doppler signal will be considered. From the definition of k in Equation 4, kβ can be expressed as the following equation.

Equation 12 means that kβ changes in a sine wave shape depending on the depth d. Due to the nature of the first-order Bessel function, when kβ is 0, J ₀ (kβ) becomes the maximum value. From Equation 12, etc., if the phase φ _m of the received signal from the target depth matches the phase φ _{mr of the} reference wave, kβ can be set to 0, and at a depth at which kβ becomes 0, J ₀ (kβ) is maximized and the amplitude of the Doppler signal is maximized. That is, in the delay circuits 26I and 26Q, the amplitude of the Doppler signal from the target depth is maximized by matching the phase φ _m of the received signal from the target depth with the phase φ _{mr of the} reference wave. Thus, the Doppler signal can be selectively extracted.

  As described above, the selection position where the Doppler signal is selectively extracted is determined based on the delay processing in the delay circuits 26I and 26Q. The system control unit 50 in FIG. 1 controls the delay time in the delay circuits 26I and 26Q according to the depth of the target selection position.

  Instead of the frequency modulation process, a phase modulation process (PM process) that is generally well known as the same angle modulation method as the frequency modulation process may be used. That is, the same waveform as the FM continuous wave output from the modulation processing unit 20 or an equivalent waveform may be formed by performing phase modulation processing on the carrier wave signal.

<Position selectivity by phase shift keying (PSK)>
FIG. 2 is a diagram for explaining a continuous wave transmission signal formed by phase shift keying (PSK). FIG. 2A shows a waveform of an RF signal (RF wave) output from the RF wave oscillator (reference numeral 22 in FIG. 1). The RF signal is a continuous wave having a constant frequency (for example, about 5 MHz). FIG. 2B shows an example of a periodic signal sequence output from the modulation signal generator (reference numeral 24 in FIG. 1). The modulation signal generator generates a binary code (pseudo-random signal) whose value is randomly changed as shown in FIG. 2B, for example.

  FIG. 2C shows a modulated continuous wave (transmission signal) formed in a modulation processing unit (reference numeral 20 in FIG. 1) functioning as a PSK modulator. The modulation processing unit performs phase shift keying (PSK) modulation processing on the RF signal in FIG. 2A based on the binary code in FIG. The modulation processing unit maintains the phase of the RF signal in the bit period where the binary code is “1”, and inverts (shifts 180 degrees) the phase of the RF signal in the bit period where the binary code is “−1”. The transmission signal in FIG. 2C is formed. In this way, for example, a continuous wave ultrasonic wave corresponding to the transmission signal in FIG. 2C is output from the transmission vibrator (reference numeral 10 in FIG. 1) and is generated via the reception vibrator (reference numeral 12 in FIG. 1). A received signal is obtained from the body.

FIG. 3 is a diagram illustrating frequency spectra of a transmission signal, a reception signal, and a demodulation signal. FIG. 3A shows a transmission signal formed in a modulation processing unit functioning as a PSK modulator, that is, a frequency spectrum of a PSK-modulated continuous wave. The frequency f ₀ is the frequency of the RF signal. Frequency spacing sidebands are spread around the frequency f ₀ of the RF signal is a repetition frequency f _p of the pseudo random signal (binary code in FIG. 2 (B)). In addition, there is a so-called null point where the power of the sideband spreading around the frequency f ₀ is 0 (zero). The frequency interval from the frequency f ₀ to the null point is the reciprocal of the 1-bit time interval T of the pseudo-random signal (binary code in FIG. 2B).

  FIG. 3B shows the frequency spectrum of the received signal. The received signal has the same waveform as the transmitted signal when attenuation in the living body is ignored. Therefore, the frequency spectrum of the reception signal shown in FIG. 3B is almost the same as the frequency spectrum of the transmission signal shown in FIG. However, the phase differs between the transmission signal and the reception signal according to the propagation time of the ultrasonic wave in the living body.

  In the present embodiment, the transmission signal formed in the modulation processing unit (reference numeral 20 in FIG. 1) is subjected to delay processing to form a reference signal, and the reception mixer (reference numeral 30 in FIG. 1) uses the reference signal. Then, mixer processing (multiplication of the reference signal and the received signal) is performed on the received signal. As will be described in detail later, in this mixer processing, the correlation between the received signal from the depth corresponding to the phase of the delayed reference signal (the depth of the target position) and the reference signal is strengthened and maximized, The correlation between the received signal from other depths and the reference signal becomes extremely small.

  FIG. 3C shows the frequency spectrum of the demodulated signal obtained by the mixer processing. The demodulated signal in FIG. 3C corresponds to the multiplication result of the reference signal and the received signal when the correlation is maximum. That is, the multiplication result between the received signal from the target position and the reference signal whose phase is matched to the depth of the target position is the demodulated signal in FIG.

The demodulated signal shown in FIG. 3C includes a DC signal component and a harmonic component that is twice the frequency f ₀ of the RF signal. The Doppler signal appears in a form attached to these components. In the LPF (reference numerals 36 and 38 in FIG. 1), the harmonic component is cut and only the DC signal component is extracted. Therefore, in the FFT circuit (reference numerals 40 and 42 in FIG. 1), FIG. Only the frequency spectrum of the DC signal component is formed among the DC signal component and the harmonic component twice the frequency f ₀ shown in FIG. Then, in the Doppler information analysis unit (reference numeral 44 in FIG. 1), a Doppler signal is extracted from the frequency spectrum of the DC signal component shown in FIG. 3C and is present at the target selected position based on the Doppler shift amount and the like. The blood flow velocity is calculated. Since quadrature detection is performed in the receiving mixer (reference numeral 30 in FIG. 1), the polarity of the flow velocity can also be determined. The clutter signal may be extracted from the frequency spectrum of the DC signal component, and the position of the blood vessel wall existing at the selected position may be calculated.

  FIG. 4 is a diagram for explaining position selectivity in PSK. The sharpness of the correlation between the received signal and the reference signal depends on the periodic signal sequence formed in the modulation signal generator (reference numeral 24 in FIG. 1). In order to sharpen the correlation, a code sequence that is put to practical use in pulse compression, such as a PN (Pseudo Noise) sequence, an M sequence, or a Goley sequence, is used as a code sequence of a pseudo random signal that is a periodic signal sequence. Use it. As a simple example, position selectivity when a PN code of n = 3 is used will be described with reference to FIG.

The length of the PN code when n = 3 is 7 (= 2 ³ −1) bits. Since this sequence repeats indefinitely, this pseudo-random pattern has a line spectrum that is the reciprocal of the repetition period. When a 2-phase PSK modulation of 0-π is applied to a carrier wave having a frequency f ₀ using this signal, the time waveform is as shown in FIG.

The reception signal is a signal in which the transmission signal is delayed by a delay time corresponding to the target depth and is attenuated by the tissue. If the attenuation is ignored, for example, the waveform of the received signal in FIG. 4 is obtained. FIG. 4 shows the result (multiplier output) of multiplying the received signal by changing the phase of the reference signal obtained by delaying the transmission signal from φ ₁ to φ ₆ .

From FIG. 4, the direct current component of the multiplier output (mixer output) is maximized in the case of φ ₃ in which the phases of the reference signal and the received signal match. In addition, the AC component is only a carrier wave and its harmonic component, which is a characteristic when the phases of the reference signal and the received signal match. The frequency spectrum of this signal is as shown in FIG. Further, from FIG. 4, when the phase is other than phi _3, since the positive and negative voltage is generated at random as the multiplier outputs, these average voltage is very small.

  FIG. 5 is a diagram for explaining the relationship between the voltage of the multiplier output and the phase of the reference signal. FIG. 5 shows the correspondence between the phase of the reference signal and the multiplier output. In FIG. 5, the peak of the total value appears at every repetition period of the PN pattern, and the voltage (total value) is extremely small in the phase other than the peak. The length of the PN pattern in this example is 7 bits, and “20”, which is a total of about 3 cycles, that is, 20 bits, is the maximum value. On the other hand, in the phases other than the peak, the sum is −2 or −4, which is extremely smaller than “20”.

  In this way, the position selectivity that selectively detects the reflected wave power and Doppler information from the target depth by adjusting the phase of the reference signal so as to correspond to the received signal from the target selection position. Is realized.

<Position selectivity by frequency shift keying (FSK)>
FIG. 6 is a diagram for explaining a continuous wave transmission signal formed by frequency shift keying (FSK). FIG. 6I shows an example of a periodic signal sequence output from the modulation signal generator (reference numeral 24 in FIG. 1). The modulation signal generator generates a binary code (pseudo-random signal) whose value is randomly changed as shown in FIG. 6 (I), for example. As a code sequence of a pseudo-random signal that is a periodic signal sequence, a code sequence that is put to practical use in pulse compression such as a PN (Pseudo Noise) sequence, an M sequence, or a Goley sequence may be used.

FIG. 6 (II) shows a modulated continuous wave (transmission signal) formed in a modulation processing unit (reference numeral 20 in FIG. 1) functioning as an FSK modulator. The modulation processing unit performs digital modulation processing on the RF wave (carrier wave) by frequency shift keying based on the binary code in FIG. 6I to form a continuous wave transmission signal. For example, the modulation processing unit sets the frequency f ₁ in the bit period where the binary code is “1” and the frequency f ₂ in the bit period where the binary code is “0”, thereby transmitting the ultrasonic wave of FIG. Form a signal.

  In this way, for example, continuous wave ultrasonic waves corresponding to the ultrasonic transmission signal of FIG. 6 (II) are output from the transmission vibrator (reference numeral 10 in FIG. 1) and passed through the reception vibrator (reference numeral 12 in FIG. 1). Thus, a received signal can be obtained from the living body. Also in the case of frequency shift keying (FSK), the transmission signal formed by the modulation processing unit (reference numeral 20 in FIG. 1) is subjected to delay processing to form a reference signal, and a reception mixer (reference numeral 30 in FIG. 1). ), The mixer process (multiplication of the reference signal and the received signal) is performed on the received signal using the reference signal. In this mixer processing, the correlation between the received signal from the depth corresponding to the phase of the delayed reference signal (the depth of the selected position) and the reference signal is strengthened and maximized, and from other depths. The correlation between the received signal and the reference signal becomes extremely small.

  FIG. 7 is a diagram illustrating the relationship between the phase of a reference wave (reference signal) in FSK and the multiplier output. The graph shown in FIG. 7 corresponds to an example using a pseudo-random pattern that changes in a cycle of 7 bits, and the vertical axis of the graph shown in FIG. 7 indicates the total of the multiplier outputs obtained in the 7-bit period. Value. Further, the horizontal axis of the graph shown in FIG. 7 indicates the phase of the reference wave (reference signal) with respect to the received signal, that is, the phase difference between the received signal and the reference signal. The horizontal axis in FIG. 7 indicates the relative magnitude of the phase when T, which is a 1-bit time, is used as a reference unit.

  When the phase difference between the reference signal and the received signal is 0 (zero), the pseudo-random patterns of the received signal and the reference signal match each other. Therefore, the total value of the multiplier outputs obtained within the 7-bit period is “ +7 ". Therefore, in FIG. 7, the multiplier output value when the phase of the reference wave is 0 is “+7”. On the other hand, when a phase difference occurs between the reference signal and the received signal, the pseudo random patterns of the received signal and the reference signal are shifted from each other. Therefore, the total value of the multiplier outputs obtained within the 7-bit period is “ +1, 0, -1 "and so on. When the phase of the reference wave is shifted by 7 as a relative value, the 7-bit pseudo-random signal is shifted by one cycle, so that the multiplier output value is an extremely large value “ +7 ".

  Thus, in the case of FSK as well, as in the case of PSK (see FIG. 5), there is position selectivity according to the phase of the reference signal.

  The position selectivity for each modulation method is as described above. Furthermore, in the present embodiment, an ultrasonic beam is formed in a plurality of directions by scanning the ultrasonic beam, and the natural number of the period of the periodic signal output from the modulation signal generator 24 for each direction. A reception signal is acquired along the ultrasonic beam in a period corresponding to the double.

FIG. 8 is a diagram for explaining a reception signal acquisition period in the present embodiment. FIG. 8A shows a time-varying waveform of the received signal in the case of the FM modulation method. Sinusoid of frequency f _m from a modulation signal generator 24 is outputted, using the transmission signal of a continuous wave which has been FM-modulated on the basis of the sine wave, the period T _m, as shown in FIG. 8 _(A) (= 1 A reception signal with a periodicity of / f _m ) is obtained.

FIG. 8B shows the instantaneous frequency change of the received signal shown in FIG. As shown in FIG. 8 (B), the instantaneous frequency of the received signal is periodically changed in the period T _m. In this embodiment, to match one acquisition period of the received signal for the ultrasonic beam (beam scanning time) cycle T _m of a transmission signal and a reception signal. That is, the received signal indicated by the solid line within the beam scan time shown in FIG. 8B is associated with one ultrasonic beam (received beam).

The reception signal obtained via each ultrasonic beam (reception beam) is demodulated in the reception mixer 30 and supplied to the FFT circuits 40 and 42 via the LPFs 36 and 38. The FFT circuits 40 and 42 perform an FFT operation on the demodulated signals (in-phase signal component and quadrature signal component demodulated signals). In the FFT operation, frequency conversion is generally performed by regarding a signal to be processed as a periodic signal that is continuously repeated. That is, in the present embodiment, as shown in FIG. 8 (B), is regarded as periodic signal which repeats with a period T _m as the received signal by the solid line obtained by the period T _m is shown by a broken line FFT operation Is done.

In the present embodiment, since the matched acquisition period of the received signal (beam scan time) in the period T _m of a transmission signal and a reception signal, it is possible to perform an FFT operation while maintaining the periodicity of the transmitted and received signals it can. FIG. 8C and FIG. 8D show a comparative example with the present embodiment.

FIG. 8 (C) shows an example in which slightly larger than the period T _m beam scanning time. In the example of FIG. 8 (C), the repeating the solid line of the received signal obtained at the beam scan time periodically becomes a waveform as shown by a broken line, the periodicity of the received signal with a period T _m is not maintained. For example, in the example of FIG. 8C, the instantaneous frequency changes discontinuously at the portion where the waveforms are periodically joined, and a frequency spectrum that should not be included in the received signal appears. there is a possibility.

Figure 8 (D) shows an example in which reduced slightly wider than the period T _m beam scanning time. Also in the example of FIG. 8 (D), the repeating the solid line of the received signal obtained at the beam scan time periodically becomes a waveform as shown by a broken line, also the period of the received signal with a period T _m is not maintained . Unlike the comparative examples of FIG. 8C and FIG. 8D, in the example of FIG. 8B, it is possible to perform the FFT operation while maintaining the periodicity of the received signal.

Even if the beam scan time for one ultrasonic beam is set to a natural number multiple (2 times, 3 times,...) Of the period T _m of the received signal, reception is performed as in FIG. It is possible to perform an FFT operation while maintaining the periodicity of the signal.

Further, FIG. 8 illustrates the case of the FM modulation system, but in the case of the PSK modulation system, the repetition period T _P (see FIG. 4) of the pseudo random pattern corresponds to the period T _m of the FM modulation system. book may be a natural number times or period T _P match the beam scanning time period T _P for the ultrasonic beam. Also in the case of the FSK modulation method, the beam scan time for one ultrasonic beam may be made to coincide with the repetition cycle of the pseudo random pattern or be a natural number multiple of the cycle.

  FIG. 9 is a diagram for explaining scanning of the ultrasonic beam in the present embodiment. The sector shown in FIG. 9 shows the scanning plane on which the ultrasonic beam is scanned, and the solid line and the dashed arrow shown in the sector scanning plane show the ultrasonic beam.

In the present embodiment, the ultrasonic beam is electronically scanned to successively form the ultrasonic beam in a plurality of directions to form a fan-shaped scanning surface. In order to maintain the real-time property, it is necessary to complete an image forming process such as a demodulation process and an FFT process related to a reception signal of one ultrasonic beam within a period of acquiring a reception signal of one ultrasonic beam. is there. For example, the acquisition period of the received signal relating to one of the ultrasonic beam (beam scan time) and T _f, to complete the signal processing for one reception signal of the ultrasonic beam within a period T _f.

For example, if the number of ultrasonic beams per frame is 2N, that is, if the total number of ultrasonic beams in the scanning plane shown in FIG. 9 is 2N, an image of one frame is constructed. The time required for is 2NT _f .

As a technique for improving the speed of image construction, a technique of reducing the number of ultrasonic beams per frame can be considered. For example, the angle between the ultrasonic beams is increased, and only the solid ultrasonic beam shown in FIG. 9 is used. Thus, the number of ultrasonic beams becomes N present, it can speed up the image construction by half the NT _f the time required to construct an image of one frame.

Furthermore, the ultrasonic beams may be formed in a plurality of directions for each frame while the directions of the ultrasonic beams are shifted from each other between two temporally adjacent frames. For example, in FIG. 9, N ultrasonic beams indicated by solid lines are formed in a certain frame, and N ultrasonic beams indicated by broken lines are formed in the next frame. Thus, the image construction time per frame while maintaining the NT _f, it is possible to improve the resolution of the angular direction of the ultrasonic beam.

  Also, for each direction, an ultrasonic beam is formed a plurality of times, a plurality of reception signals corresponding to the plurality of times are acquired, and Doppler information is extracted based on the plurality of reception signals to construct an image. May be. For example, two ultrasonic beams are formed twice at the same angle, and a reception signal is acquired for each ultrasonic beam. Then, the received signal obtained for each ultrasonic beam is demodulated to obtain a demodulated signal, and two demodulated signals obtained from the two ultrasonic beams are added. Necessary signals are simply added, and randomly generated noise has a statistically low addition effect, so that the signal-to-noise ratio (SNR) can be improved as a result.

  FIG. 10 is a diagram for explaining scanning of an ultrasonic beam using a region of interest. The sector shown in FIG. 10 shows the entire scanning area where the ultrasonic beam can be scanned electronically. A region of interest (ROI) having a shape obtained by deforming a trapezoid along a sector is set in the entire scanning region. The region of interest is set at, for example, a notable part in the living body. Therefore, the ultrasonic beam may be intensively scanned within the region of interest.

  For example, it is possible to increase the resolution of the image in the region of interest to be noticed by scanning the ultrasonic beam with high density in the region of interest. For example, in comparison with a scanning mode in which 2N ultrasonic beams are formed in a sector-shaped entire scanning region, if 2N ultrasonic beams are formed only in the region of interest (ROI), the image construction time per frame The image resolution in the beam scanning direction can be improved in the region of interest while maintaining the above.

  Further, the resolution in the depth direction may be improved by reducing the width of the selected position in the depth direction of the ultrasonic beam in the region of interest. For example, it is assumed that the width (selection width) of the selected position is Δd and the number of selection widths for one ultrasonic beam is M in all scans in which an ultrasonic beam is formed in the entire scan area. On the other hand, by limiting the selection position in the region of interest and setting the selection width to Δd / 2 and the number of selection widths to M, for example, the resolution in the depth direction can be improved. In comparison with full scanning, if the number of ultrasonic beams that are limitedly scanned in the region of interest and the number of selected widths are made the same, the image in the beam scanning direction in the region of interest is maintained while maintaining the image construction time. It becomes possible to improve the resolution and the image resolution in the depth direction.

  In the example of FIG. 10, the multiplication value of the selection width Δd and the number M of the selection widths in the case of full scanning is the length in the depth direction of the image obtained by full scanning, and ultrasonic waves are generated in the region of interest. A product of the selection width Δd / 2 and the number M of the selection widths when forming the beam in a concentrated manner is the length in the depth direction of the region of interest. Incidentally, in the example of FIG. 10, the selection width in the region of interest is Δd / 2, but the selection width may be set to Δd / 3, for example, according to the desired resolution.

  In the case of the FM modulation method, the selection width is determined according to the magnitude of the modulation index β (see Equation 1), and in the case of the PSK modulation method and the FSK modulation method, the length of 1 bit of the pseudo random pattern. It is determined according to (period). That is, a desired selection width can be realized by adjusting the magnitude of the modulation index β and the length of one bit of the pseudo-random pattern.

  Further, the image construction speed may be improved by intensively scanning the ultrasonic beam within the region of interest. For example, when the ultrasonic beam is intensively scanned in the region of interest, the ultrasonic beam is formed at the same angular interval as in the case of full scanning. As a result, the number of ultrasonic beams can be reduced as compared with the case of full scanning, and as a result, the image construction time per frame is shortened and the image construction can be speeded up.

  When the ultrasonic beam is intensively scanned within the region of interest, the processing time of the received signal per ultrasonic beam is shortened by reducing the number of selection widths with a selection width of Δd. May be. Of course, the number of ultrasonic beams may be reduced to speed up image construction while maintaining the selection width at Δd / 2 and the number of selection widths at M.

  The preferred embodiments of the present invention have been described above, but the above-described preferred embodiments of the present invention are merely examples in all respects, and do not limit the scope of the present invention. The present invention includes various modifications without departing from the essence thereof. For example, modulated continuous wave data may be stored in a memory or the like, and the continuous wave may be generated based on data read from the memory.

  20 modulation processing unit, 22 RF wave oscillator, 24 modulation signal generation unit, 26I, 26Q delay circuit, 40, 42 FFT circuit, 44 Doppler information analysis unit.

Claims (8)

A transmission signal output unit that outputs a transmission signal of a continuous wave modulated based on a periodic signal;
A transmission / reception unit for obtaining a reception signal by transmitting an ultrasonic transmission wave corresponding to the transmission signal to a living body and receiving a reception wave accompanying the transmission wave from the living body;
A demodulation processing unit that obtains a demodulated signal corresponding to the selected position by performing a demodulation process on the received signal using a reference signal whose correlation with the selected position in the living body is adjusted;
An in-vivo information extracting unit for extracting in-vivo information from the demodulated signal;
Have
The ultrasonic beam is formed in a plurality of directions by scanning the ultrasonic beam, and the received signal is acquired along the ultrasonic beam in each period in a period corresponding to a natural number multiple of the period of the periodic signal. To
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The ultrasonic beam is scanned over a plurality of frames, and the ultrasonic beams are formed in a plurality of directions for each frame while shifting the directions of the ultrasonic beams between two adjacent frames in time.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1 or 2,
For each direction, an ultrasonic beam is formed a plurality of times to obtain a plurality of received signals corresponding to the plurality of times, and the living body is obtained from a synthesized demodulated signal obtained by a synthesis process based on the received signals. Extract information,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3,
Intensively scanning the ultrasound beam within the area of interest in the body,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4,
By reducing the width of the selected position in the depth direction of the ultrasonic beam in the region of interest set in the entire area, compared to the case where the ultrasonic beam is scanned in the entire area where scanning is possible. Improve resolution in the depth direction,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5,
The transmission signal output unit outputs a continuous wave transmission signal whose frequency is periodically changed.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5,
The transmission signal output unit outputs a continuous wave transmission signal whose phase is periodically changed by phase shift keying based on a periodic signal sequence.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 5,
The transmission signal output unit outputs a continuous wave transmission signal whose frequency is periodically changed by frequency shift keying based on a periodic signal sequence.
An ultrasonic diagnostic apparatus.

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