JP4787683B2 - Ultrasonic diagnostic equipment - Google Patents

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 configured as a sine 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 due to a moving body (for example, blood flow) in the living body. Therefore, the information is taken out and subjected to frequency analysis, and a Doppler waveform reflecting the velocity information of the moving body is formed.

  Continuous wave Doppler using a continuous wave is generally superior in terms of high-speed velocity measurement compared to pulse Doppler using a pulse wave. However, in continuous wave Doppler, position measurement is difficult due to the use of continuous waves. For example, position measurement cannot be performed with a conventional general continuous wave Doppler device.

  Under such circumstances, the inventor of the present application has proposed a technique of continuous wave Doppler that can measure the position of the in vivo tissue in addition to the speed of the in vivo tissue (see Patent Document 1).

JP 2006-14916 A

  The technique described in Patent Document 1 is an epoch-making technique that is capable of measuring a position in addition to a velocity of a tissue or the like while being a technique based on continuous wave Doppler.

  The inventor of the present application has further studied the innovative technique for improving the technique described in Patent Document 1.

  The present invention has been made in such a background, and an object thereof is to provide an improved technique related to an ultrasonic diagnostic apparatus that acquires velocity information and position information using a continuous wave.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmission signal processing unit that generates a modulated transmission signal by performing frequency modulation processing on a carrier wave signal using a modulation signal. A transmission / reception unit for transmitting an ultrasonic wave corresponding to the generated modulated transmission signal to a living body, receiving a reflected wave from the living body to acquire a received signal, and a modulated transmission signal for the acquired received signal The received signal processing unit that obtains the frequency difference signal reflecting the frequency difference between the transmission and reception signals, the spectrum calculation unit that obtains the frequency spectrum of the frequency difference signal, and the frequency spectrum of the frequency difference signal A position / velocity calculation unit that obtains the position and velocity of the tissue in the living body based on the signal, and the modulation signal includes a signal part that increases the frequency and a signal part that decreases the frequency. As a result, a modulated transmission signal including an increase time zone in which the frequency increases and a decrease time zone in which the frequency decreases is generated, and the spectrum calculation unit includes a composite time zone including both the increase time zone and the decrease time zone. A complex time zone spectrum that is a frequency spectrum corresponding to the frequency spectrum, an increasing time zone spectrum that is a frequency spectrum corresponding to the increasing time zone, and a decreasing time zone spectrum that is a frequency spectrum corresponding to the decreasing time zone. The speed calculation unit is characterized in that the position and speed of the tissue in the living body are obtained based on the composite time zone spectrum, the increase time zone spectrum, and the decrease time zone spectrum.

  In a preferred aspect, the position / velocity calculation unit includes a first difference spectrum that is a difference between the composite time zone spectrum and the increase time zone spectrum, and a second difference spectrum that is a difference between the composite time zone spectrum and the decrease time zone spectrum; , And the speed of the tissue in the living body is obtained based on the first difference spectrum and the second difference spectrum.

  In a preferred aspect, the position / velocity calculation unit obtains a velocity spectrum by synthesizing the first difference spectrum and the second difference spectrum, and the first difference spectrum component and the second difference spectrum component that are complex conjugate to each other in the velocity spectrum. The speed of the tissue in the living body is obtained from the frequency difference with the difference spectrum component.

  In a preferred aspect, the position / velocity calculation unit obtains the position of the in-vivo tissue from the frequency of the intermediate point between the first difference spectrum component and the second difference spectrum component that are in a complex conjugate relationship with each other in the velocity spectrum. It is characterized by that.

  In a preferred aspect, the modulation signal is a symmetric triangular wave including a signal portion that linearly increases the frequency and a signal portion that linearly decreases the frequency.

  According to the present invention, an improved technique related to an ultrasonic diagnostic apparatus that acquires velocity information and position information using a continuous wave is provided.

  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 block diagram showing the overall configuration thereof. The transmitting vibrator 20 continuously transmits ultrasonic transmission waves into the living body, and the receiving vibrator 22 continuously receives reflected waves from within the living body. In this way, transmission and reception are continuously executed by different vibrators. Note that the transmission vibrator 20 and the reception vibrator 22 may each be formed of a plurality of vibration elements. Then, by performing beam forming using a plurality of vibration elements, a transmission beam may be formed by the transmission vibrator 20 and a reception beam may be formed by the reception vibrator 22.

  The transmitter 18 supplies a transmission signal to the transmission transducer 20 to transmit an ultrasonic wave. An FM continuous wave (FMCW wave) signal subjected to FM modulation processing is input to the transmitter 18, and the transmitter 18 supplies a transmission signal corresponding to the FM continuous wave signal to the transmission transducer 20. An FM continuous wave is transmitted from the transmitting transducer 20.

  The FM modulator 14 modulates the RF wave supplied from the RF wave oscillator 16 based on a symmetrical triangular wave, thereby generating an FM continuous wave signal. The symmetric triangular wave is supplied from the symmetric triangular wave generator 12 to the FM modulator 14. The symmetric triangular wave includes a signal increasing portion that linearly increases the frequency and a signal decreasing portion that linearly decreases the frequency. The waveform of the symmetric triangular wave is symmetrical with the signal increasing portion and the signal decreasing portion. It is an isosceles triangle. The symmetric triangular wave generator 12 supplies a symmetric triangular wave to the FM modulator 14 under the control of the control unit 10.

  When the reflected wave from the living body is continuously received by the receiving vibrator 22, the preamplifier 24 and the main amplifier 26 amplify the received signal supplied from the receiving vibrator 22. The received RF signal (received signal) is formed and output to the mixer 28. The mixer 28 is a circuit that detects a received RF signal. The reference signal supplied to the mixer 28 is an FM continuous wave signal output from the FM modulator 14.

  Thus, the mixer 28 detects the received RF signal (received signal) using the FM continuous wave signal (transmitted signal), that is, multiplies the received RF signal and the FM continuous wave signal by the low pass filter (LPF) 30. By removing the high frequency component, a frequency difference signal between the transmission and reception signals is extracted.

  Note that the mixer 28 may generate a complex signal by performing quadrature detection on the received RF signal. In the case of quadrature detection, detection is performed using two signals as reference signals, which are an FM continuous wave signal output from the FM modulator 14 and a signal obtained by shifting the phase of the FM continuous wave signal by π / 2. Two components, an in-phase component and a quadrature component, are output.

  The frequency difference signal extracted by the LPF 30 is supplied to the spectrum calculation unit 34. The spectrum calculation unit 34 is composed of, for example, a calculator (such as a CPU or DSP) that performs an FFT calculation, and obtains a frequency spectrum related to the frequency difference signal. The spectrum calculation unit 34 obtains a frequency spectrum according to the gate period set by the gate setting unit 32. In addition, the frequency information obtained by the spectrum calculation unit 34 is appropriately processed by each unit in the subsequent stage, whereby the velocity information and the position information of the in vivo tissue are obtained.

  As described above, in this embodiment, ultrasonic waves (FMCW waves) of continuous waves that are FM-modulated with symmetric triangular waves are transmitted and received, and tissue position information and velocity information are acquired. Then, the principle of acquisition of position information and speed information according to the present embodiment will be described in detail. In the following description, the configuration (portion) shown in FIG.

  FIG. 2 is a diagram for explaining how velocity information and position information of a tissue in a living body are reflected in a frequency difference signal. FIG. 2 shows an example in which there is one target organization.

  FIG. 2A shows frequency changes of the transmission signal 60 (solid line) and the reception signal 62 (broken line) obtained from the fixed tissue. FIG. 2A shows how the instantaneous frequency of the transmission signal 60 and the reception signal 62 changes by indicating the frequency on the vertical axis with the horizontal axis as the time axis.

  As described above, in this embodiment, an FM continuous wave formed by a modulation process using a symmetric triangular wave is transmitted. Therefore, as shown in FIG. 2A, the transmission signal 60 includes an increase time zone in which the frequency increases linearly and a decrease time zone in which the frequency decreases linearly, and the waveform of the transmission signal 60 is It is an isosceles triangle. And the same waveform is periodically repeated for every time Tm, and the transmission signal 60 as a continuous wave is formed.

  A transmission signal 60 in FIG. 2A corresponds to a transmission wave transmitted from the transmitting transducer 20 into the living body, and after being transmitted from the transmitting transducer 20, the living body travels in the depth direction. Propagate towards. On the other hand, the received signal 62 in FIG. 2A corresponds to the received signal acquired by the receiving transducer 22, and a signal reflected from one fixed tissue existing at a certain depth (position) is obtained. Show. Therefore, a delay time according to the position of the target tissue exists between the transmission signal 60 and the reception signal 62. The delay time appears as a frequency difference between the transmission signal 60 and the reception signal 62.

  FIG. 2B shows a frequency difference between the transmission signal 60 and the reception signal 62 shown in FIG. The time axis shown on the horizontal axis of FIG. 2B is aligned with the time axis of FIG. 2A, and the vertical axis of FIG. 2B shows the frequency difference.

  As shown in FIG. 2B, there is a frequency difference fb associated with the position (depth) between the transmission signal 60 and the reception signal 62 in FIG. That is, a time lag (delay of the reception signal 62) occurs between the transmission signal 60 and the reception signal 62 due to a delay according to the position of the target tissue, so that the transmission signal 60 and the reception signal 62 at the same time A frequency difference fb appears between them. The frequency difference fb appears in the same amount in each of the increase time zone and the decrease time zone of the transmission signal 60.

  The position (depth) L of the target tissue can be calculated from this frequency difference fb. The calculation principle is described in detail in Patent Document 1 (Japanese Patent Laid-Open No. 2006-14916). The principle is applied to this embodiment as follows.

  In the present embodiment, if the frequency increases from 0 to Δf during the time Tm / 2 when the frequency of the transmission signal 60 increases, the frequency change per unit time becomes 2Δf / Tm. The propagation time τ from when the ultrasonic wave transmitted from the transmitting transducer 20 propagates by the distance L to the target tissue, reflected from the position and returned to the receiving transducer 22 is τ = 2L. / C. c is the speed of sound in the tissue.

  Therefore, the frequency difference fb between the transmission signal 60 and the reception signal 62 is obtained as fb = (2Δf / Tm) × (2L / c) by multiplying the frequency change per unit time by the propagation time. Can do. Therefore, by measuring the frequency difference fb, the position (depth) L of the target tissue can be calculated using Δf, Tm, c which are known values.

  Thus, when the target tissue is a fixed tissue, the position L can be calculated relatively easily from the frequency difference fb. However, in the case of a mobile tissue, it is necessary to consider the influence of Doppler shift accompanying the movement.

  FIG. 2C shows frequency changes of the transmission signal 60 (solid line) and the reception signal 62 (broken line) obtained from the moving tissue. That is, like FIG. 2A, FIG. 2C shows how the instantaneous frequency of the transmission signal 60 and the reception signal 62 changes by showing the frequency on the vertical axis with the horizontal axis as the time axis. Yes.

  Also in the case of a mobile tissue, a time lag (delay of the reception signal 62) occurs between the transmission signal 60 and the reception signal 62 according to the position thereof, so that the transmission signal 60 and the reception signal 62 at the same time are generated. A frequency difference fb appears between In the case of a moving tissue, a Doppler shift fd accompanying the movement of the tissue further appears. That is, in FIG. 2C, the reception signal 62 is shifted in the vertical axis direction with respect to the transmission signal 60 due to the influence of the Doppler shift fd.

  FIG. 2D shows the frequency difference between the transmission signal 60 and the reception signal 62 in FIG. The time axis shown on the horizontal axis of FIG. 2D is aligned with the time axis of FIG. 2C, and the vertical axis of FIG. 2D shows the frequency difference.

  Between the transmission signal 60 and the reception signal 62 in FIG. 2C, as shown in FIG. 2D, in addition to the frequency difference fb associated with the position (depth), the Doppler shift fd associated with the movement of the target tissue. Appears. The influence of the Doppler shift fd is different between the increase time zone and the decrease time zone of the transmission signal 60. That is, the frequency difference considering the Doppler shift fd is (fb−fd) in the increase time zone of the transmission signal 60 and (fb + fd) in the decrease time zone.

  FIG. 2 shows an example in which there is one target tissue. In this case, the Doppler shift fd is calculated by adding the frequency difference in the increase time zone and the frequency difference in the decrease time zone shown in FIG. The frequency difference fb accompanying the position can be canceled by obtaining the difference between the frequency difference in the increase time zone and the frequency difference in the decrease time zone. However, the reflected wave obtained from the living body includes a plurality of reflected waves obtained from a plurality of tissue portions.

  FIG. 3 is a diagram for explaining how a plurality of reflected waves obtained from a plurality of tissue portions are reflected in a frequency difference signal.

  FIG. 3A shows the waveforms of the transmission signal 60 and the waveforms of a plurality of reception signals 62 corresponding to a plurality of reflected waves. That is, like FIG. 2A and the like, FIG. 3A shows how the instantaneous frequency of the transmission signal 60 and the reception signal 62 changes by indicating the frequency on the vertical axis with the horizontal axis as the time axis. ing. In FIG. 3A, the plurality of received signals 62 correspond to signals obtained from different positions (depths). Therefore, a delay amount corresponding to the position of the tissue portion exists between the transmission signal 60 and each reception signal 62. The amount of delay differs for each received signal 62.

  FIG. 3B shows a frequency difference between the transmission signal 60 and each reception signal 62 in FIG. The time axis shown on the horizontal axis of FIG. 3B is aligned with the time axis of FIG. 3A, and the vertical axis of FIG. 3B shows the frequency difference.

  As shown in FIG. 3B, there is a frequency difference according to the position of the tissue portion between the transmission signal 60 and the reception signals 62 in FIG. The frequency difference is different for each received signal 62. For this reason, a plurality of frequency differences appear in the waveform shown in FIG. 3B, and it can be seen that the waveform is more complex than when only one frequency difference shown in FIG. 2B appears.

  In FIG. 3, the influence of the Doppler shift is ignored. However, when the Doppler shift is involved, the Doppler shift is reflected in each waveform shown in FIG. 3B, resulting in a more complicated waveform. In the present embodiment, speed information and position information of a plurality of tissue portions are extracted from such a complicated waveform. The principle will be described below.

  FIG. 4 is a diagram for explaining the frequency spectrum obtained by the spectrum calculation unit. The spectrum calculation unit 34 performs an FFT calculation or the like on the frequency difference signal to obtain a frequency spectrum of the frequency difference signal. As described with reference to FIG. 3B, the frequency difference signal includes a frequency difference component corresponding to the position of the tissue portion.

  FIG. 4A shows the frequency spectrum of the frequency difference signal. Since the frequency difference signal includes a frequency difference component corresponding to the position of the tissue portion, a spectrum of a plurality of frequency difference components appears in the frequency spectrum shown in FIG. 4A along the frequency axis direction. Yes. The frequency difference becomes larger as the tissue portion exists at a deeper position (far position). That is, the spectrum that exists in the right direction (the direction in which the frequency increases) of the horizontal axis in FIG. 4A corresponds to the spectrum obtained from the tissue portion at a deeper position.

  In FIG. 4, the spectrum obtained from the fixed tissue is shown on six broken lines parallel to the vertical axis. The six broken lines correspond to different positions and frequencies. Accordingly, the spectrum of the fixed tissue corresponding to each broken line shown in FIG. 4A corresponds to that obtained from six fixed tissues existing at different positions. The higher the frequency is, the more the tissue is obtained from the tissue existing in the deep position.

  FIG. 4 (a) also shows a spectrum obtained from the moving tissue. As described with reference to FIGS. 2 and 3, the frequency difference signal obtained from the moving tissue includes a component corresponding to the position of the moving tissue and a Doppler shift component accompanying the movement of the moving tissue. As shown in FIG. 2D, the Doppler shift component has different influences on the frequency difference between the increase time zone in which the frequency increases and the decrease time zone in which the frequency decreases. That is, the Doppler shift component (fd) may be added or subtracted.

  Therefore, in FIG. 4A, the spectrum obtained from the moving tissue is only the Doppler shift component (corresponding to fd in FIG. 2) before and after the frequency (corresponding to fb in FIG. 2) corresponding to the position of the moving tissue. It appears at a shifted frequency position.

  In FIG. 4A, a fixed tissue exists at the position of each moving tissue. That is, FIG. 4A shows a case where there are six moving tissues corresponding to each of the six fixed tissues, which corresponds to a state where the fixed tissue and the moving tissue corresponding to each other exist at substantially the same position. To do. The frequency spectrum of FIG. 4A is obtained from, for example, six blood vessels existing at different depths. In that case, the fixed tissue corresponds to the blood vessel wall and the like, and the moving tissue corresponds to the blood flow flowing in the blood vessel. Note that the measurement target of the ultrasonic diagnostic apparatus of the present embodiment is not limited to blood vessels.

  In FIG. 4A, the spectra obtained from the same moving tissue appearing symmetrically before and after the spectrum of each fixed tissue are in a complex conjugate relationship with each other. That is, one spectrum of the complex conjugate appears on the positive direction side of the vertical axis, and the other spectrum of the complex conjugate appears on the negative direction side of the vertical axis.

  The spectrum obtained from the same mobile tissue includes two spectra that are complex conjugate to each other because the influence of the Doppler shift component on the frequency difference is different between the increase time period and the decrease time period. ing.

  FIG. 4B shows a frequency spectrum (increase time zone spectrum) corresponding to an increase time zone in which the frequency of the transmission signal increases linearly. As is clear from comparison with FIG. 4A, in the frequency spectrum shown in FIG. 4B, the spectrum of the mobile tissue appears only on the upper side (the higher frequency side) of the fixed tissue. On the other hand, FIG. 4C shows a frequency spectrum (decrease time band spectrum) corresponding to a decrease time period in which the frequency of the transmission signal decreases linearly. In the frequency spectrum shown in FIG. 4C, the spectrum of the moving tissue appears only on the lower side of the fixed tissue (the smaller frequency side).

  Thus, by obtaining the spectrum separately in the increase time zone and the decrease time zone, it is possible to extract only one of the two spectra having a complex conjugate relationship obtained from the same mobile tissue.

  The spectrum shown in FIGS. 4A to 4C is obtained by the spectrum calculation unit 34. The spectrum calculation unit 34 obtains a spectrum corresponding to the gate period set by the gate setting unit 32. The gate setting unit 32 synchronizes the gate period corresponding to the increased time period in which the frequency of the transmission signal increases and the gate period corresponding to the decreased time period in which the frequency of the transmission signal decreases with the symmetrical triangular wave generated on the transmission side. To set.

  Then, the spectrum calculation unit 34 obtains an increase time band spectrum (FIG. 4B) from the frequency difference signal in the gate period corresponding to the increase time period, and calculates from the frequency difference signal in the gate period corresponding to the decrease time period. Decrease time zone spectrum (FIG. 4C) is obtained. Further, the spectrum calculation unit 34 calculates a composite time zone spectrum (FIG. 4A) corresponding to a composite time zone including both an increase time zone and a reduction time zone from a frequency difference signal for which no gate period is set. Ask. The various spectra obtained in this way are output to the subsequent sections of the spectrum calculation section 34.

  FIG. 5 is a diagram for explaining the calculation for the frequency spectrum obtained by the spectrum calculation unit.

  FIG. 5 (d) shows the difference between the composite time zone spectrum of FIG. 4 (a) and the increased time zone spectrum of FIG. 4 (b). As a result of subtracting the increased time zone spectrum from the composite time zone spectrum, in FIG. 5D, only the spectrum of the mobile tissue that appears below the fixed tissue (the side with the lower frequency) is extracted. Note that the process of subtracting the increased time zone spectrum from the composite time zone spectrum is executed by the subtractor 36.

  FIG. 5 (e) shows the difference between the complex time zone spectrum of FIG. 4 (a) and the reduced time zone spectrum of FIG. 4 (c). As a result of subtracting the reduced time zone spectrum from the composite time zone spectrum, in FIG. 5E, only the spectrum of the mobile tissue that appears above the fixed tissue (the side with the higher frequency) is extracted. Note that the process of subtracting the reduced time zone spectrum from the composite time zone spectrum is executed by the subtractor 38.

  FIG. 5 (f) shows a spectrum obtained by adding the spectrum of FIG. 5 (d) and the spectrum of FIG. 5 (e), and the spectrum of FIG. In comparison with FIG. 4A, in FIG. 5F, the spectrum corresponding to the fixed tissue is removed, and only the spectrum corresponding to the six mobile tissues is left. As described above, the spectra obtained from the same mobile tissue are in a complex conjugate relationship with each other. The distance on the frequency axis (frequency difference) between the spectra having a complex conjugate relationship with each other corresponds to a Doppler shift (twice fd in FIG. 2) proportional to the moving speed of each moving tissue.

  FIG. 6 is a diagram for explaining processing for obtaining the velocity and position of the moving tissue from the spectrum of the moving tissue. FIG. 6G is a waveform showing the spectrum peak frequency (position on the frequency axis at which the spectrum peaks) and the spectrum polarity of each mobile tissue shown in FIG. The waveform shown in FIG. 6G is obtained by the peak detector 42.

  The peak detection unit 42 detects the peak of each spectrum in FIG. Further, the peak detector 42 determines the polarity of each spectrum, that is, whether the spectrum appears on the positive direction side or the negative direction side of the vertical axis in FIG. Each peak waveform of 6 (g) is obtained. Thereby, each peak waveform becomes a waveform indicating the peak position and polarity of the corresponding spectrum. Note that the amplitude of each peak waveform is normalized. For example, it can be expressed as a digital signal by setting the amplitude of the peak in the positive direction to “+1” and the amplitude of the peak in the negative direction to “−1”.

  In the present embodiment, a set of peak waveforms obtained from the same moving tissue is derived by adding adjacent peak waveforms to a plurality of peak waveforms obtained as shown in FIG. When adjacent peak waveforms are added, each peak waveform is normalized to “+1” or “−1”, so that two types of addition results can be obtained depending on how the adjacent peak waveforms are combined. For example, as shown in FIG. 6G, the combination result in which the addition results of adjacent peak waveforms are all “0” and the addition result of adjacent peak waveforms are “0, +2, −2, 0, There is a combination that becomes “+2”.

  Since the spectrum obtained from the same mobile tissue is in a complex conjugate relationship, the two peak waveforms corresponding to the same mobile tissue have different polarities, and the addition result of these two peak waveforms is “0”. . Therefore, the adjacent peak determination unit 44 selects a combination method in which the addition results of adjacent peak waveforms are all “0”.

  For example, the adjacent peak determination unit 44 obtains the absolute value of the addition result of the pair of adjacent peak waveforms for each pair, and when the absolute values of all the pairs are summed, the combination whose sum is “0”. Select the direction. Alternatively, the one whose total value is smaller than other combinations is selected. For example, in the example shown in FIG. 6G, the sum of absolute values is “0” in the case of a combination method in which the addition results of adjacent peak waveforms are all “0”, and addition of adjacent peak waveforms is performed. In the case of a combination method that results in “0, +2, −2, 0, +2”, the total absolute value is “6”.

  FIG. 6 (h) shows the result of deriving a set of peak waveforms obtained from the same mobile tissue. In FIG. 6 (h), the wavy line shown on the frequency axis indicates how to combine adjacent peak waveforms, and the peak waveforms that are not separated by the wavy line are peak waveforms obtained from the same moving tissue. Become a pair. When a set of peak waveforms obtained from the same moving tissue is determined, an intermediate position on the frequency axis of two peak waveforms constituting the set is obtained.

  FIG. 6 (i) shows the result of obtaining the intermediate position for each pair of peak waveforms, and the intermediate position of each group is indicated by a diamond on the frequency axis. The frequency indicated by the rhombus corresponds to the frequency (frequency difference fb in FIG. 2) associated with the position (depth) of each moving tissue. Therefore, the position of each moving tissue can be obtained from the frequency of the diamond-shaped portion shown in FIG. 6 (i), that is, the intermediate position between the two peak waveforms. In addition, when calculating | requiring the position of a moving tissue from the frequency accompanying the position of a moving tissue, the principle described in patent document 1 is utilized as demonstrated previously.

  The distance on the frequency axis (frequency difference) between the two peak waveforms corresponds to a Doppler shift (twice fd in FIG. 2) proportional to the moving speed of the moving tissue corresponding to the set of peak waveforms. Therefore, from the distance on the frequency axis between the two peak waveforms, the moving speed of the moving tissue corresponding to those peak waveforms can be obtained. As a technique for obtaining the speed from the Doppler shift component, a conventionally known technique is used. In the present embodiment, the position and speed of the moving tissue are obtained by the position / velocity information calculation unit 46.

  The adjacent peak synthesizing unit 48 synthesizes spectrum components corresponding to adjacent peak waveforms. That is, the spectra shown in FIG. 5F obtained from the same moving tissue and having a complex conjugate relationship with each other are synthesized, and a synthesized spectrum proportional to the reflected power obtained from the moving tissue is obtained. The obtained composite spectrum is shifted to a frequency corresponding to the position of the moving tissue. The adjacent peak combining unit 48 obtains a combined spectrum for each moving tissue and outputs it to the image forming unit 50.

  FIG. 7 is a diagram for explaining a velocity position image formed by the image forming unit 50. Each spectrum display shown in FIG. 7 corresponds to a composite spectrum obtained from each mobile tissue. That is, a composite spectrum is obtained from each of the six mobile tissues shown in FIG. 4A, and each obtained composite spectrum is displayed by shifting to the corresponding position (position on the frequency axis) of the mobile tissue. It is. The combined spectrum is proportional to the reflected power obtained from the mobile tissue. Therefore, each spectrum display shown in FIG. 7 shows the magnitude of the reflected power of the mobile tissue existing at that position (position on the frequency axis). Will show.

  Moreover, on each spectrum display of FIG. 7, the display mode of the arrow which shows the magnitude | size and direction of the speed | velocity | rate of each moving tissue is provided. That is, the speed of each moving tissue is represented by the length of the arrow, and the direction of the speed is represented by the direction of the arrow. The speed position image shown in FIG. 7 is displayed on a monitor, for example, and the user can visually confirm the position and speed of the moving tissue from the speed position image displayed on the monitor.

  The position and velocity of the moving tissue are determined by scanning the ultrasonic beam in a two-dimensional plane and obtaining each spectrum display (synthetic spectrum) shown in FIG. 7 from each of the plurality of ultrasonic beams obtained by the scanning. It is also possible to express on a two-dimensional fault. For example, since the combined spectrum of each moving tissue is proportional to the reflected power obtained from the moving tissue, an image corresponding to the B-mode image is formed by setting the luminance on the tomographic image according to the combined spectrum. It becomes possible.

  Further, the subtractor 52 obtains the difference between the spectrum shown in FIG. 4A obtained by the spectrum calculator 34 and the spectrum shown in FIG. 5F obtained by the adder 40, so that only the spectrum corresponding to each fixed tissue is obtained. Can be extracted. Then, the position information calculation unit 54 obtains the position (depth) of each fixed tissue from the spectrum corresponding to each fixed tissue, and reflects the position information of the fixed tissue in the velocity position image formed by the image forming unit 50. May be. Also, the polarity of the velocity with respect to the tomographic plane may be displayed in color. For example, the blood flow from the front to the back of the tomographic plane may be displayed in blue, and the blood flow from the back to the front may be displayed in red.

  As mentioned above, although preferred embodiment of this invention was described, this embodiment has the following advantages, for example.

  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 spectrum band of the demodulated baseband signal can be narrowed, and an improvement in signal-to-noise ratio (SNR) can be expected compared to the pulse method. Moreover, the distance resolution can be kept equal to 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.

  In the present embodiment, in addition to measuring the velocity of the target tissue, the position of the target tissue can be measured in spite of using the continuous wave. Furthermore, the upper limit of the measurement speed is not limited by the modulation frequency. Further, in the velocity measurement of a plurality of moving tissues scattered on the ultrasonic beam, it becomes possible to measure at a low velocity that could not be measured by the conventional pulse method or the conventional continuous wave Doppler.

  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.

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 a mode that the speed information and position information of a biological tissue are reflected in a frequency difference signal. It is a figure for demonstrating a mode that the some reflected wave obtained from a some tissue part is reflected in a frequency difference signal. It is a figure for demonstrating the frequency spectrum calculated | required by the spectrum calculating part. It is a figure for demonstrating the calculation with respect to the frequency spectrum calculated | required by the spectrum calculating part. It is a figure for demonstrating the process which calculates | requires the speed and position of a mobile tissue from the spectrum of a mobile tissue. It is a figure for demonstrating the speed position image formed by the image formation part.

Explanation of symbols

  12 symmetrical triangle wave generator, 14 FM modulator, 34 spectrum calculation unit, 46 position velocity information calculation unit, 50 image forming unit.

Claims (5)

A transmission signal processing unit that generates a modulated transmission signal by performing frequency modulation processing on the carrier wave signal using the modulation signal;
A transmission / reception unit for transmitting an ultrasonic wave corresponding to the generated modulated transmission signal to a living body, receiving a reflected wave from the living body and acquiring a reception signal;
A reception signal processing unit that obtains a frequency difference signal reflecting a frequency difference between transmission and reception signals by performing demodulation processing on the acquired reception signal using a modulated transmission signal;
A spectrum calculation unit for obtaining a frequency spectrum of the frequency difference signal;
A position / velocity calculation unit for obtaining the position and velocity of the tissue in the living body based on the frequency spectrum of the frequency difference signal;
Have
The modulated signal includes a signal portion that increases the frequency and a signal portion that decreases the frequency, thereby generating a modulated transmission signal including an increase time zone in which the frequency increases and a decrease time zone in which the frequency decreases. ,
The spectrum calculation unit includes a composite time zone spectrum that is a frequency spectrum corresponding to a composite time zone including an increase time zone and a reduction time zone, an increase time zone spectrum that is a frequency spectrum corresponding to the increase time zone, and a decrease. Find the reduced time zone spectrum, which is the frequency spectrum corresponding to the time zone,
The position velocity calculation unit obtains the position and velocity of the in vivo tissue based on the composite time zone spectrum, the increase time zone spectrum, and the decrease time zone spectrum,
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The position velocity calculation unit obtains a first difference spectrum that is a difference between a composite time zone spectrum and an increase time zone spectrum, and a second difference spectrum that is a difference between the composite time zone spectrum and the decrease time zone spectrum; Obtaining the velocity of the tissue in the living body based on the first difference spectrum and the second difference spectrum;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The position velocity calculation unit obtains a velocity spectrum by synthesizing the first difference spectrum and the second difference spectrum, and includes a first difference spectrum component and a second difference spectrum component that are in a complex conjugate relationship with each other in the velocity spectrum. Find the speed of tissue in vivo from the frequency difference between
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The position / velocity calculation unit obtains the position of the tissue in the living body from the frequency of the intermediate point between the first difference spectrum component and the second difference spectrum component that are in a complex conjugate relationship with each other in the velocity spectrum.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4,
The modulation signal is a symmetrical triangular wave including a signal portion that linearly increases the frequency and a signal portion that linearly decreases the frequency.
An ultrasonic diagnostic apparatus.

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