JPH07236640A - Ultrasonic diagnosing device - Google Patents

Abstract

PURPOSE:To improve S/N by changing the reference frequency of a reference signal by which each received signal is multiplied for extracting a doppler deviation frequency component from a received signal according to the depth to which a sample volume is set. CONSTITUTION:An ultrasonic diagnosing device repeatedly transmits an ultrasonic pulse from a transmission system 2 connected to a probe 1 to the interior of a tested body, and repeatedly receives an echo from each discontinuous surface of an acoustic impedance in the interior of the tested body by a receiving circuit 3. The received signal is sent to a B mode processing system 4 and a doppler mode processing system 5, and in the doppler mode processing system 5, each received signal is multiplied by a reference signal from an oscillator 5B to detect a doppler signal composed of doppler deviation frequency components. In this case, according to the depth to which a sample volume is set, the oscillator 5B is controlled to change the reference frequency of a reference signal, whereby the received signal is orthogonal-phase detected by a reference signal of a frequency showing the maximum power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus for obtaining a frequency spectrum in a sample volume by analyzing a received signal in the sample volume set at an arbitrary depth in the subject.

[0002]

2. Description of the Related Art The configuration and function of a conventional ultrasonic diagnostic apparatus of this type will be described below. A plurality of piezoelectric vibrators are arranged in parallel at the tip of the probe. A transmitting system and a receiving circuit are connected to the probe. The transmission system 2 gives different delay times to the piezoelectric vibrators of the probe and repeatedly supplies the pulse drive signal. As a result, an ultrasonic pulse having a wide frequency band is transmitted into the subject. Under the B mode, the delay time given to each piezoelectric vibrator is changed little by little every time ultrasonic waves are transmitted and received. As a result, the scan surface is scanned.
Under the Doppler mode, the transmission circuit supplies a drive signal to each piezoelectric vibrator of the probe with a constant delay time for each piezoelectric vibrator. As a result, ultrasonic pulses are repeatedly transmitted in the same direction.

The echoes reflected at each interface of the acoustic impedance in the subject are received by all or part of the piezoelectric vibrator. The echo is converted into a current by each piezoelectric vibrator according to its acoustic intensity. These received signals are taken into the receiving circuit. In the reception circuit, each reception signal is individually amplified, and then a delay time opposite to that at the time of transmission is given to each piezoelectric vibrator and added. This gives reception directivity in the same direction as when transmitting. The output of the receiving circuit is the B mode processing system,
It is sent to the Doppler mode processing system. In the B-mode processing system, the output of the receiving circuit is first logarithmically amplified by the logarithmic amplifier. Then, the envelope of the output signal of the logarithmic amplifier is detected by the envelope detection circuit. This detected signal is dispersed into a digital signal via an analog-digital converter. Each digital signal is held together with position data in the image memory of the display system. The digital signals sequentially read from the image memory are sent to the TV monitor as a luminance modulation signal via the digital-analog converter, and displayed as a B-mode image (tissue image) on the TV monitor.

The Doppler mode processing system calculates a frequency spectrum (sometimes converted to a velocity distribution) of a moving object within a certain observation range (hereinafter referred to as "sample volume"). The output of the receiving circuit is sent to the two systems of phase detection circuits. The oscillator outputs a reference signal having a frequency (reference frequency) that matches the center frequency of the transmitted ultrasonic waves. This reference signal is sent directly to the phase detection circuit and is multiplied by the output signal from the reception circuit. Further, the reference signal is sent to the phase detection circuit via the quadrature phase shifter and is multiplied by the output signal from the reception circuit. As a result, the output signal from the reception circuit is subjected to quadrature detection, and the deviation between the transmission frequency f ₀ and the reception frequency f ₁ due to the Doppler effect, that is, the Doppler deviation frequency f _d and (2 · f ₀ + f _d ) A Doppler signal composed of high frequency components is detected. It should be noted that the two-phase detection circuit is provided for moving objects (in most cases, blood cells).
This is to distinguish the forward and reverse movement directions of (the blood flow approaching the probe and the blood flow moving away from the probe). The high frequency components of the Doppler signal are removed by the low pass filter. As a result, a Doppler signal having only the frequency component of the Doppler shift frequency f _d is obtained, the range gate circuit multiplies the Doppler signal by the range gate circuit, and only the Doppler signal within the range gate is output from the low-pass filter. It is clipped from the Doppler signal.

The Doppler signal cut out by the range gate circuit is integrated along the time axis by the integrating circuit. This integrated signal is sent to a high-pass filter via a sample hold circuit, and unnecessary frequency components, that is, clutter components, are removed from a portion such as an organ wall that moves slower than blood flow. The integrated signal from which the clutter component has been removed is again sent to an arithmetic circuit as a frequency analysis circuit such as a fast Fourier transform circuit via the low pass filter. The arithmetic circuit analyzes the frequency spectrum of the blood flow or the like contained in the Doppler signal cut out by the range gate by performing a real-time frequency analysis on the integrated signal from which the clutter component has been removed. The arithmetic circuit outputs this frequency spectrum as it is or after converting it into a velocity distribution to the image memory of the display system. This frequency spectrum is repeatedly calculated with a constant period. The frequency spectrum is distributed in a graph with the horizontal axis representing time and the vertical axis representing frequency, and is displayed on the TV monitor.

By the way, as described above, an ultrasonic pulse having a wide frequency band is transmitted to the inside of the subject, but the ultrasonic wave propagation attenuation differs depending on the frequency. Specifically, the higher the frequency, the greater the attenuation. The lower the value, the smaller the attenuation. Therefore, the frequency component of the echo depends on the depth of the discontinuity surface of the acoustic impedance reflected by the echo, that is, the echo from the shallow discontinuity surface has a wideband frequency component, but as the discontinuity surface becomes deeper, High frequency components are suppressed and echo frequency components are shifted to the lower side. This can cause the reference frequency of the reference signal from the oscillator to deviate from the frequency of maximum power within the frequency distribution of echoes from a discontinuity of depth. In this case, the signal component is suppressed, resulting in S
/ N will decrease.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object thereof is to improve S / N by performing quadrature phase detection with a maximum signal component. An object is to provide an ultrasonic diagnostic apparatus.

[0008]

An ultrasonic diagnostic apparatus according to the present invention repeatedly transmits an ultrasonic pulse into a subject and repeatedly receives an echo from each discontinuity surface of the acoustic impedance in the subject. The received signal is multiplied by the reference signal from the oscillator to detect a Doppler signal consisting of the Doppler shift frequency component, and the Doppler signal is range-gated and the Doppler signal in the sample volume is set to an arbitrary depth. A signal is cut out, and in the ultrasonic diagnostic apparatus that obtains the frequency spectrum in the sample volume by frequency-analyzing the cut out Doppler signal and displays the frequency spectrum, depending on the depth to which the sample volume is set. Control means is provided for controlling the oscillator to change the reference frequency of the reference signal.

[0009]

According to the present invention, the reference frequency of the reference signal from the oscillator multiplied by each received signal in order to extract the Doppler shift frequency component from the received signal depends on the set depth of the sample volume. Since it is changed, the received signal can be quadrature-phase detected with the reference signal having the frequency showing its maximum power, thereby improving the S / N.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the ultrasonic diagnostic apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to the first embodiment. A plurality of piezoelectric vibrators are arranged in parallel at the tip of the probe 1. A transmission system 2 and a reception circuit 3 are connected to the probe 1. A pulse generator 2A included in the transmission system 2 repeatedly outputs a pulse according to a rate frequency from an oscillator (not shown). The transmission circuit 2B supplies a drive signal by giving different delay times to the piezoelectric vibrators of the probe 1 at the timing when the pulse is sent from the pulse generator 2A. Under B mode,
The transmission circuit 2B gradually changes the delay time given to each piezoelectric vibrator every time the ultrasonic pulse is transmitted. Thereby, the ultrasonic beam is moved and the scan surface is scanned.
Under the Doppler mode, the transmission circuit 2B supplies a drive signal to each piezoelectric vibrator of the probe 1 without changing the delay time which differs for each piezoelectric vibrator. As a result, the ultrasonic beam is repeatedly transmitted in the same direction.

The echo reflected by each discontinuity surface of the acoustic impedance in the subject is received by all or part of the piezoelectric vibrator. The echo is converted into a current by each piezoelectric vibrator according to its acoustic intensity. These received signals are taken into the receiving circuit 3. In the receiving circuit 3, each received signal is individually amplified, and then a delay time opposite to that at the time of transmission is given to each piezoelectric vibrator and added. This gives reception directivity in the same direction as when transmitting. The output of the receiving circuit 3 is sent to the B mode processing system 4 and the Doppler mode processing system 5.

In the B-mode processing system 4, the output of the receiving circuit 3 is first logarithmically amplified by the logarithmic amplifier 4A. And
The envelope of the output signal of the logarithmic amplifier 4A is the envelope detection circuit 4
Detected at B. This detected signal is dispersed into a digital signal via an analog-digital converter (A / D-C) 4C. Each digital signal is sent to the image memory 6 of the display system 6.
It is stored in A together with the position data. Digital signals sequentially read from the image memory 6A are sent to the TV monitor 6B as a brightness modulation signal via a digital-analog converter (not shown), and as a result, displayed on the TV monitor 6B as a B-mode image (tissue image).

The Doppler mode processing system 5 calculates a frequency spectrum (which may be converted into a velocity distribution) of a moving object within a certain observation range (hereinafter referred to as "sample volume").

The sample volume setting unit 10 is, for example, a mouse, and its movement is interlocked with the sample volume marker displayed on the B mode image on the TV monitor 6B. By the confirmation input of the sample volume setting unit 10, the sample volume is set in the scan plane at an arbitrary depth.

The output of the receiving circuit 3 is sent to the phase detecting circuits 5Aa and 5Ab of two systems. The oscillator 5B outputs a reference signal. This reference signal is sent directly to the phase detection circuit 5Ab and is multiplied by the output signal from the reception circuit 3.
Further, the reference signal is sent to the phase detection circuit 5Aa via the quadrature phase shifter 5C and is multiplied by the output signal from the reception circuit 3. As a result, the output signal from the receiving circuit 3 is subjected to quadrature phase detection, and a Doppler signal composed of a Doppler shift frequency component representing a change in the receiving frequency with respect to the transmitting frequency due to the Doppler effect and a high frequency component is detected. The two-system phase detection circuits 5Aa and 5Ab are provided so that the moving direction (in most cases, blood cells) of the moving body (the blood flow approaching the probe 1 and the blood flowing away from the probe 1) can be distinguished. This is because High frequency components of the Doppler signal are removed by low pass filters (LPF) 5Da and 5Db. As a result, a Doppler signal having only the Doppler shift frequency component is obtained, and the range gate circuit 5Ea,
A range gate is applied at 5Eb. The timing of applying the range gate is controlled by the gate control unit 11 according to the depth of the sample volume set by the sample volume setting unit 10.

The Doppler signals cut out by the range gate circuits 5Ea and 5Eb are integrated along the time axis by the integrating circuits 5Fa and 5Fb. This integrated signal is sent to the high-pass filters (HPF) 5Ha and 5Hb via the sample-hold circuits (S / H) 5Ga and 5Gb, and unnecessary frequencies from a portion of the organ wall that is slower in moving than the blood flow. The component, that is, the clutter component is removed. The integrated signal from which the clutter component has been removed is again passed through the low pass filters 5Ia and 5Ib.
Is sent to the arithmetic circuit 5J as a frequency analysis circuit such as a fast Fourier transform circuit. The arithmetic circuit 5J is
By performing a real-time frequency analysis on the integrated signal from which the clutter component has been removed, the frequency spectrum of the blood flow or the like contained in the Doppler signal cut out by the range gate is analyzed. The arithmetic circuit 5J outputs this frequency spectrum as it is or after converting it to a velocity distribution to the image memory 6A of the display system 6. This frequency spectrum is repeatedly calculated with a constant period. The horizontal axis of the frequency spectrum is time,
The TV monitor 6B is distributed in a graph with the vertical axis representing frequency.
Is displayed in.

A plurality of different reference frequency data are stored in the storage device 8 which is, for example, a ROM, and different depths are associated with the respective reference frequency data. Reference frequency data corresponding to the depth of the sample volume recognized by the gate control unit 11 is selectively read from the storage device 8 to the control circuit 7. The control circuit 7 controls the oscillator 5B according to the reference frequency data selectively read from the storage device 8. As a result, the oscillator 5B outputs a reference signal having a reference frequency that matches the reference frequency data. Specifically, the oscillator 5B divides an original signal of 60 KHz contained in the device, for example, to generate a reference signal of a desired reference frequency. The storage device 8 holds a plurality of different frequency division frequency data, and each frequency division frequency data corresponds to a different depth. Gate control unit 11
The divided frequency data corresponding to the depth of the sample volume recognized in step S1 is selectively read out from the storage device 8 to the control circuit 7, and the control circuit 7 sets the oscillator 5B at this divided frequency.
The original signal is frequency-divided by this, thereby generating a reference signal having a desired reference frequency.

Each of the plurality of types of reference frequency data stored in the storage device 8 is determined as a frequency indicating the maximum power in the frequency distribution of echoes from the corresponding depth. The plurality of types of reference frequency data having different corresponding depths are determined by actual measurement or calculation.
In the case of actual measurement, an echo is received from a discontinuous surface at a certain depth, the frequency distribution of this echo is measured, and the frequency showing the maximum power in this measured frequency distribution is selected as the reference frequency. This operation is repeated while changing the depth of the discontinuous surface to obtain reference frequency data of various depths. Also, in the case of calculation, ultrasonic propagation attenuation curves having different depths are used. The ultrasonic propagation attenuation curve is
It is well known, and represents the change of the ultrasonic wave propagation attenuation rate according to the height of the frequency at the same depth along the frequency axis, and is determined for each depth. The frequency distribution of echoes at each depth is estimated by multiplying the frequency distribution of echoes of depth 0, which is equal to the distribution of transmitted ultrasonic waves, by ultrasonic propagation attenuation curves of different depths. The frequency showing the maximum power for each of the different frequency distributions is selected as the reference frequency.

Next, the operation of this embodiment will be described. Figure 2 is T
It is a figure which shows the display screen of V monitor 6B. When the sample volume setting unit 10 is operated by the operator, the sample volume marker displayed together with the B-mode image on the TV monitor 6B moves in association with this movement. By the confirmation input of the sample volume setting unit 10, the sample volume is set in the scan plane at an arbitrary depth.

FIG. 3 shows the correspondence between the depth held in the storage device 8 and the reference frequency. FIG. 4A shows the frequency distribution of the transmitted ultrasonic wave, FIG. 4B shows the frequency distribution of the echo from the depth 0, and FIG. 4C shows the echo from the depth d1. The frequency distribution of is shown in FIG.
In (d), the frequency distribution of the echo from the depth d2 (d1 <d2) is shown. f0 represents the center frequency of the transmitted ultrasonic wave. In FIGS. 4C and 4D, the alternate long and short dash line indicates the ultrasonic wave propagation attenuation curve at the depth d1 and the ultrasonic wave propagation attenuation curve at the depth d2, respectively.

The gate control unit 11 recognizes the depth of the sample volume set by the sample volume setting unit 10. In accordance with this depth, the gate controller 11 controls the timing of the range gate applied by the range gate circuits 5Ea and 5Eb to the Doppler signal. This allows
Only the Doppler signal in the sample volume set by the sample volume setting unit 10 is low-pass filter 5Da,
It is cut out from the full depth Doppler signal from 5Db.

The depth data of the sample volume recognized by the gate control unit 11 is taken into the control circuit 7. Reference frequency data corresponding to the depth of the sample volume is selectively read from the storage device 8 to the control circuit 7. The control circuit 7 controls the oscillator 5B according to the reference frequency data selectively read from the storage device 8. As a result, the oscillator 5B outputs a reference signal having a reference frequency that matches the reference frequency data.

For example, when the sample volume is set to the depth d1 by the sample volume setting unit 10, as shown in FIG. 4C, the echo from the depth d1 has a high frequency component attenuated more than a low frequency component. Received strongly,
In the frequency distribution of the echo, the frequency showing the maximum power drops from f0 to f1. Data indicating the reference frequency f1 corresponding to the depth d1 is read from the storage device 8 to the control circuit 7. The oscillator 5 is controlled by the control circuit 7.
The reference frequency of the reference signal from B is set to this f1. The reference signal of the reference frequency f1 is multiplied by the reception signal from the reception circuit 3 in the quadrature phase detection circuits 5Aa and 5Ab, and the Doppler signal having the Doppler shift frequency component is detected. Therefore, the Doppler shift frequency can be detected by the quadrature phase detection with the reference signal having the reference frequency with which the maximum power can be obtained at the depth d1, and as a result, the S / N is improved.

Similarly, for example, the sample volume setting section 10 causes the sample volume to be deeper than the depth d1 by d2.
When set to the depth d2, as shown in FIG.
The echo from is strongly attenuated as compared with the case where the high frequency component is d1, so that in the frequency distribution of the echo,
The frequency showing the maximum power drops from f0 to f2 which is lower than f1. Data indicating the reference frequency f2 corresponding to the depth d2 is read from the storage device 8 to the control circuit 7.
By the control of the control circuit 7, the reference frequency of the reference signal from the oscillator 5B is set to this f2. This reference frequency f2
Is multiplied by the received signal from the receiving circuit 3 by the quadrature detection circuits 5Aa and 5Ab, and the Doppler signal having the Doppler shift frequency component is detected. Therefore, the Doppler shift frequency can be detected by the quadrature phase detection with the reference signal having the reference frequency with which the maximum power is obtained at the depth d2, and as a result, the S / N is improved.

Next, the second embodiment will be described. FIG. 5 is a block diagram of the ultrasonic diagnostic apparatus according to the second embodiment.
Note that, in FIG. 5, the same parts as those in FIG.

In the present embodiment, the echo frequency distribution is actually obtained using the received signal in the sample volume, the frequency showing the maximum power of this frequency distribution is specified, and the reference frequency that matches this specified frequency is set. The reference signal which it has is output from the oscillator 5B and is multiplied by the received signal.

For the output of the receiving circuit 3, the echo frequency distribution is actually obtained using the received signal in the sample volume,
It is sent to the reference frequency detection circuit 9 for specifying the frequency showing the maximum power of this frequency distribution. In the reference frequency detection circuit 9, the output of the reception circuit 3 is range-gated by the range gate circuit 9A. The timing for applying the range gate is controlled by the gate controller 11 at the same timing as the range gate circuits 5Ea and 5Eb of the Doppler mode processing system 5. As a result, the sample volume setting unit 10 is detected from the received signal of the full depth from the receiving circuit 3.
Only the received signal corresponding to the depth of the sample volume set by is cut out. The received signal cut out by the range gate circuit 9A is an analog-digital converter (A / D-
C) It is sent via 9B to an arithmetic circuit 9C as a frequency analysis circuit such as a fast Fourier transform circuit. The arithmetic circuit 9C analyzes the frequency distribution in the sample volume by performing a real-time frequency analysis of the reception signal cut out by the range gate circuit 9A. This frequency distribution is analyzed each time an ultrasonic pulse is repeatedly transmitted and received.

The averaging circuit 9D averages a predetermined number of frequency distributions having different measurement times sent to the arithmetic circuit 9C and calculates a new frequency distribution. The frequency distribution analyzed by the arithmetic circuit 9C fluctuates according to the fact that noise and speckles, which are dominated by random noise, change over time because the examination target is blood flow. This fluctuation can be suppressed by averaging a predetermined number of frequency distributions with different measurement times. For example, in Doppler mode, transmission and reception of ultrasonic waves are repeated 128 times in the same direction. The arithmetic circuit 9C calculates a frequency distribution for each ultrasonic transmission / reception, and the averaging circuit 9D averages these 128 frequency distributions in order to suppress the influence of noise and speckles. Calculate the distribution. This new frequency distribution approximates, for example, FIGS. 4 (c) and 4 (d). The frequency (eg, f1 or f2) corresponding to the maximum power of the new frequency distribution averaged by the averaging circuit 9D is the maximum value detecting circuit 9E.
Detected in.

The reference signal frequency selection circuit 9F selects the maximum value detection circuit 9E from the divided frequency band obtained by dividing the original signal.
The frequency division frequency closest to the frequency corresponding to the maximum power detected in is selected. The control circuit 7 controls the oscillator 5B based on this frequency division frequency data. As a result, the reference signal having the same reference frequency as the frequency corresponding to the maximum power detected by the maximum value detection circuit 9E is generated from the oscillator 5B,
It is supplied to the quadrature detection circuits 5Aa and 5Ab.

Therefore, the Doppler shift frequency can be detected by quadrature detection by multiplying the Doppler signal by the reference signal having the reference frequency that provides the maximum power at the depth, and as a result, the S / N is improved. In this embodiment, the reference frequency is adjusted based on the frequency distribution of the actually received signal, so that the S / N can be improved as compared with the first embodiment. Moreover, the time required for analyzing the frequency distribution, averaging, and identifying the frequency showing the maximum power can be executed in several tens of msec required for 128 times of ultrasonic wave transmission / reception, and the real-time property is not impaired. It is needless to say that the present invention is not limited to the above-described embodiments and can be variously modified and implemented without departing from the gist thereof.

[0031]

As described above, according to the present invention, in order to extract the Doppler shift frequency component from the received signal, the reference frequency of the reference signal from the oscillator multiplied by each received signal is Since the received signal is changed according to the set depth, it is possible to detect the quadrature phase of the received signal at the frequency exhibiting the maximum power thereof, thereby providing the ultrasonic diagnostic apparatus with improved S / N.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a sample volume set in a B-mode image.

FIG. 3 is a diagram showing a change according to a depth of a frequency showing a maximum power included in an echo.

FIG. 4 is a diagram showing frequency components of transmitted ultrasonic waves and echoes from discontinuous surfaces having different depths.

FIG. 5 is a block diagram of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Probe, 2 ... Transmission system, 3 ... Reception circuit, 4 ... B mode processing system, 5 ... Doppler mode processing system, 6 ... Display system, 7 ...
Control circuit, 8 ... Storage device, 10 ... Sample volume setting unit, 11 ... Gate control unit.

Claims (3)

[Claims] 1. An ultrasonic pulse is repeatedly transmitted into a subject, echoes are repeatedly received from each discontinuous plane of acoustic impedance in the subject, and each received signal is multiplied by a reference signal from an oscillator. A Doppler signal composed of Doppler shift frequency components is detected, a range gate is applied to the Doppler signal to cut out the Doppler signal in the sample volume set to an arbitrary depth, and the cut Doppler signal is subjected to frequency analysis. In the ultrasonic diagnostic apparatus for obtaining the frequency spectrum in the sample volume by performing the, the control means for controlling the oscillator to change the reference frequency of the reference signal according to the set depth of the sample volume An ultrasonic diagnostic apparatus characterized by: 2. A storage means for holding frequency data indicating a maximum power of a frequency distribution of each echo from each discontinuous surface having a different depth, wherein the control means has a depth to which the sample volume is set. The ultrasonic diagnostic apparatus according to claim 1, wherein the oscillator is controlled according to the frequency data selectively read from the storage unit to change the reference frequency of the reference signal. 3. A frequency distribution of the received signal in the sample volume is frequency-analyzed to obtain a frequency distribution in the sample volume, and a detection means for detecting a frequency showing the maximum power of the frequency distribution is further provided, and the control means is provided. The ultrasonic diagnostic apparatus according to claim 1, further comprising: controlling the oscillator according to a frequency indicating the maximum power detected by the detecting means to change the reference frequency of the reference signal.