JPH1099332A - Ultrasonic diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide sufficient direction separation performance and response time performance with the circuit constitution of a small scale by separating ultrasonic doppler shift signals into signals in a forward direction and the signals in a reverse direction in a complex digital filter and originating ultrasonic doppler sound corresponding to the signals in a normal direction and the signals in the reverse direction. SOLUTION: After a transmission/reception circuit 2 executes delay addition to electric signals outputted from an ultrasonic probe 1, an orthogonal detection circuit 3 orthogonally detects them, real part channel signals are outputted from a band-pass filter 4 and imaginary part channel signals are outputted from the band-pass filter 5. Then, ultrasonic doppler images are obtained by frequency-analyzing the ultrasonic doppler shift signals in a fast Fourier transformer 6 and are spectrum-displayed on a monitor 8. In the meantime, the ultrasonic doppler shift signals are successively and reversely separated into the signals in the forward direction and the signals in the reverse direction, converted into analog signals in a D/A converter 10 and outputted from speakers 12 and 14 through power amplifiers 11 and 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to biological information such as a blood flow Doppler image or a blood flow Doppler sound by transmitting an ultrasonic wave into a living body and processing a reflected wave from each tissue in the living body. To an ultrasonic diagnostic apparatus for obtaining

[0002]

2. Description of the Related Art An ultrasonic wave is transmitted into a living body, a reflected wave from each tissue in the living body is received, and the reflected wave is subjected to signal processing so that, for example, a blood flow Doppler image or a blood flow Doppler sound is generated. Ultrasonic diagnostic apparatuses that obtain biological information have the advantage of being able to diagnose soft tissues noninvasively and without a contrast agent, and are now widely used in the medical field.

FIG. 12 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to the above conventional example. This apparatus includes an ultrasonic probe 80, a transmission / reception circuit 81, a quadrature detection circuit 82, band-pass filters (BPF) 83 and 85, a fast Fourier transformer (FFT) 86, a digital scan converter (DSC) 87, It comprises a monitor 88, a direction separating circuit 89 having a phase shifter circuit, power amplifiers 90 and 92, and speakers 91 (left) and 92 (right).

The ultrasonic probe 80 includes a transmitting / receiving circuit 81
A continuous wave or a pulse wave is transmitted to the subject in accordance with the drive signal supplied from, a reflected wave is received, and an electric signal corresponding to the reflected wave is output. This electric signal is input to the transmission / reception circuit 81. The transmission / reception circuit 81 has a delay addition circuit, performs delay addition on a signal input from the ultrasonic probe 80, and outputs the signal to the quadrature detection circuit 82. The delay-added signal output from the transmission / reception circuit 81 is subjected to quadrature detection by a quadrature detection circuit 82 having two mixers of f _ref (0 °) and f _ref (90 °). The output of the mixer of f _ref (0 °) is input to the band-pass filter 83. F _ref (90
I) The output from the mixer is a band-pass filter 84.
Is output to

[0005] Bandpass filters 83 and 84 remove the low frequency clutter component and filter the output from the quadrature detection circuit 82 so as to be a signal in a required band. The bandpass filter 83 outputs a real part channel (Real-ch) signal, and the bandpass filter 84 outputs an imaginary part channel (Imag-ch) signal. Thus, a complex ultrasonic Doppler shift signal is obtained.

The obtained ultrasonic Doppler shift signal is A / D
The signal is supplied to the converter 85 and is supplied to the direction separating circuit 89 having a phase shifter circuit. A / D converter 85
The ultrasonic Doppler shift signal input to the FFT is converted into a digital signal here, and a fast Fourier transform (FFT) 86
Is output to In the high-speed Fourier transformer 86, the digital ultrasonic Doppler shift signal is subjected to frequency analysis by the high-speed Fourier transform having relatively high calculation accuracy, and thereby an ultrasonic Doppler image is obtained. This ultrasonic Doppler image is supplied to a monitor 88 via a digital scan converter (DSC) 87 and displayed in a spectrum.

On the other hand, the ultrasonic Doppler shift signal supplied to the direction separating circuit 89 having a phase shifter circuit corresponds to the above-mentioned spectrum display, and is a forward signal (Forward).
The signal is separated into a signal in the reverse direction (Reverse) and a signal in the reverse direction, and is output from the speakers 91 and 92 as audio signals through the amplifiers 90 and 92.

The direction separating circuit 89 receives an ultrasonic Doppler shift signal composed of a real part channel (Real-ch) signal and an imaginary part channel (Imag-ch) signal as shown in FIG. The circuit 100 shifts the phase of the imaginary part channel signal by, for example, 90 °. Further, the direction separating circuit 89 adds and subtracts the real part channel signal and the imaginary part channel signal whose phase is shifted by 90 °, thereby converting the ultrasonic Doppler shift signal into a signal in the forward direction and a signal in the reverse direction. Signal (Reverse).

The forward and backward signals obtained by the direction separation by the direction separation circuit 89 are represented as follows. First, the ultrasonic Doppler shift signal (complex)
Is the frequency which is the sum of the components of - [omega] _r in the component and the amplitude b of the frequency omega _f in the amplitude a, the real part channel (Real-ch) component of the ultrasonic Doppler shift signals, and the imaginary part channel ( The Imag-ch) component is assumed as in the following equation (1).

[0010] Real (t) = a · cos (ω f · t) + b · cos (-ω r · t) Imag (t) = a · sin (ω f · t) + b · sin (-ω r T) (1) Then, the forward signal (Forward) and the reverse signal (Reverse) are represented by the following equations (2) and (3).

[0011] Forward (t) = a · cos (ω f · t) + b · cos (ω r · t) + a · cos (ω f · t) - b · cos (ω r · t) = 2a · _{cos (ω f · t) ...} (2) Reverse (t) = a · cos (ω f · t) + b · cos (ω r · t) - a · cos (ω f · t) + b · cos ( ω _r · t) = 2b · cos (ω _r · t) (3) The conventional ultrasonic diagnostic apparatus based on the principle of directional separation as described above has the following problems.

Phase shifter circuit 1 of the direction separating circuit
00 has a problem that the circuit configuration becomes large-scale because it is composed of an analog circuit in which a plurality of all-pass filters are cascaded. Further, as shown in FIG. 14, there is a problem that the degree of separation is reduced depending on the band, and sufficient directional separation performance cannot be obtained. Further, since the analog circuit requires complicated adjustment, there is a disadvantage in cost.

Meanwhile, there is an ultrasonic diagnostic apparatus described in Japanese Patent Application Laid-Open No. 2-198242 filed by the same applicant as the present invention. This apparatus reproduces Doppler sound when reproducing an FFT (fast Fourier transform) image of a blood flow Doppler. This device has the following disadvantages. That is,
Since the sample rate of the FFT is in units of a pulse rate repetition frequency (PRF), there is a drawback in that it is difficult to match the tone to live when Doppler sound is synthesized. Further, since the sound is generated after the Fourier transform processing and the power calculation processing are completed, there is a disadvantage that the response is poor from the viewpoint of processing time.

[0014]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ultrasonic diagnostic apparatus which has sufficient directional separation performance and response time performance in generating ultrasonic Doppler sound and has a small circuit configuration. It is in.

[0015]

Means for Solving the Problems To solve the above problems and achieve the object, the ultrasonic diagnostic apparatus of the present invention uses the following means. (1) An ultrasonic diagnostic apparatus according to the present invention includes an acquisition unit that transmits an ultrasonic wave to a subject and receives a reflected wave thereof to collect an ultrasonic Doppler shift signal, and is obtained by the collection unit. Separating means comprising a complex digital filter for separating the ultrasonic Doppler shift signal into a forward signal and a backward signal, and responding to the forward signal and the backward signal output from the separating means. Sounding means for emitting ultrasonic Doppler sound. (2) An ultrasonic diagnostic apparatus according to the present invention is the apparatus according to the above (1), wherein the complex digital filter of the separating means comprises a non-recursive filter. (3) An ultrasonic diagnostic apparatus according to the present invention is the ultrasonic diagnostic apparatus according to the above (1), wherein the complex digital filter of the separating means is constituted by a recursive filter. (4) The ultrasonic diagnostic apparatus according to the present invention is the apparatus according to the above (1), wherein the waveform of the ultrasonic Doppler shift signal collected by the collecting means is discontinuous due to folding on a spectrum display. Zero shift means for preventing the shift from occurring, wherein the separating means is interlocked with the zero shift of the zero shift means.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention. The ultrasonic diagnostic apparatus according to the present embodiment includes an ultrasonic probe 1, a transmission / reception circuit 2, a quadrature detection circuit 3, a band-pass filter (B
PF) 4 and 5, Fourier Transformer (FFT) 6, Digital Scan Converter (DSC) 7, Monitor 8,
Direction separation circuit 9, D / A converter 10, power amplifier 11
, 13, speakers 12 (left) and 14 (right), and a zero shift circuit 15.

The ultrasonic probe 1 transmits a continuous wave or a pulse wave to the subject according to the drive signal supplied from the transmission / reception circuit 2, receives the reflected wave, and responds to the reflected wave. Outputs electrical signals. The transmission / reception circuit 2 has a delay addition circuit, performs delay addition on the electric signal output from the ultrasonic probe 1, and outputs the electric signal to the quadrature detection circuit 3. The signal after delay addition output from the transmission / reception circuit 2 is subjected to quadrature detection by a quadrature detection circuit 3 having two mixers of f _ref (0 °) and f _ref (90 °). The output of the mixer of f _ref (0 ゜) is input to the band-pass filter 4. The output of the mixer at f _ref (90 °) is output to the band-pass filter 5.

The band-pass filters 4 and 5 remove the low-frequency clutter component and filter the output from the quadrature detection circuit 3 so as to be a signal in a required band. From the bandpass filter 4, the real channel (Real
-ch) signal, and the imaginary part channel (Imag-ch) signal is output from the band-pass filter 5. Thus, a complex ultrasonic Doppler shift signal is obtained. In the present embodiment, the ultrasonic Doppler shift signal is configured to be obtained as a digital signal.

The obtained ultrasonic Doppler shift signal is supplied to a fast Fourier transformer (FFT) 5 and further supplied to a direction separating circuit 9. In the fast Fourier transformer 5,
The frequency of the digital ultrasonic Doppler shift signal is analyzed by the fast Fourier transform having relatively high calculation accuracy, and an ultrasonic Doppler image is obtained. This ultrasonic Doppler image
The data is supplied to a monitor 8 via a digital scan converter (DSC) 7 and displayed in a spectrum.

On the other hand, the ultrasonic Doppler shift signal supplied to the direction separating circuit 9 is separated into a forward signal (Forward) and a reverse signal (Reverse) corresponding to the above-mentioned spectrum display. After being converted into an analog signal by the A / A converter 10, the speakers 12 (left) and 14 are converted into audio signals via power amplifiers 11 and 13.
(Right).

The direction separating circuit 9 is composed of a complex digital filter for separating the direction of audio. As shown in FIG. 2, a real part channel (Real-ch) signal and an imaginary part obtained by complex quadrature detection are provided. Channel (Imag-ch)
An ultrasonic Doppler shift signal comprising a signal and a zero shift amount from the zero shift circuit 15 are input, audio direction separation is performed, and a forward signal (Forward) and a reverse signal (Reverse) are output. Things. Here, the complex digital filter is a complex IIR (non-recursive) filter including a second-order IIR component and an FIR component. The order of the filter is not limited to the second order, and may be, for example, the fourth order or the sixth order. By the way, by increasing the order of the filter, the shoulder characteristics become steep, so that a higher directional separation ability can be realized.

FIG. 3 to FIG. 5 are diagrams showing transfer functions constituting this complex IIR filter. Note that ω _S is the sampling angular frequency in the complex digital filter.
FIG. 3 is a diagram illustrating frequency characteristics of the transfer function H (Z) of the complex IIR filter. H (Z) assumes a low pass filter (LPF) with a bandwidth of about ω _{S / 2} .
FIG. 4 shows the transfer function Hf (Z) of the complex IIR filter.
FIG. 5 is a diagram showing the transfer function Hr (Z). Hf (Z) is a transfer function for shifting the frequency of Z by + ω _{S / 4} , and
(Z) is a transfer function for shifting Z by -ω _{S / 4} . Here, the conversion from FIG. 3 to FIG. 4 changes Z = exp (j ^* ω) to Z = exp (j ^* (ω−π / 2)), and the conversion from FIG. = Exp (j ^* ω)
Is set to Z = exp (j ^* (ω + π / 2). These conversions are variable according to the amount of zero shift from the zero shift circuit 15. This makes it possible to realize zero shift of audio linked to the display spectrum. By the way, when the order of the filter is increased as described above, the shoulder characteristic around ± ω _{S / 2} becomes steep, and a high directional separation ability can be realized.

FIG. 6 is a block diagram showing a specific example of the complex IIR filter and showing an algorithm configuration thereof. Here, as a complex IIR filter including a second-order IIR component and an FIR component, a biquad type (BIQUA
AD) A filter is employed. In FIG. 6, 50
Is an adder, 51 and 52 are data registers, 53 is a coefficient multiplier, and 54 is a multiplier for inverting the sign after multiplying the coefficients. The transfer functions H (Z), Hf (Z) and Hr (Z) are represented by the following equations (4) to (6).

[0024]

(Equation 1) Also, a complex Hf (Z) loop and a complex Hr
The loop of (Z) is shown in the following equations (7) and (8).

[0025]

(Equation 2)

According to this embodiment, the direction separation performance as shown by the characteristic curve A in FIG. 7 can be obtained. This shows a sufficient separation performance in a required band as compared with the characteristic curve B of the conventional example shown in FIG.

FIG. 8 shows the zero shift on the spectrum display. In the display example on the left side of FIG. 8, a part of the spectrum is folded from the upper part of the screen to the lower part of the screen, thereby forming a discontinuous waveform. In this case, as shown in the display example on the right side of FIG. 8, the position of “0” is lowered to the lower part of the screen according to the zero shift amount calculated by the zero shift circuit 15, thereby preventing the discontinuity of the waveform due to the folding. Thus, the observer can observe a continuous waveform. Then, according to the present embodiment, audio direction separation according to the zero shift amount calculated by the zero shift circuit 15, that is, zero (zero) shift of the audio is performed.

As described above, according to the first embodiment, since the direction separating circuit 9 is constituted by using a complex digital filter composed of a complex IIR filter, sufficient separation performance and response time can be obtained regardless of the band. In addition to obtaining performance, the circuit configuration can be made relatively small. Also, complicated adjustments such as analog circuits are not required. Further, since the audio zero shift corresponding to the spectrum display of the blood flow Doppler image is realized, more accurate blood flow Doppler sound can be obtained.

(Second Embodiment) The second embodiment is a modification of the first embodiment. That is, the direction separating circuit 9 of the first embodiment is configured using a complex digital filter composed of a complex IIR filter, whereas the direction separating circuit 9 of the second embodiment is formed of a general FIR (recursive type) filter. And a complex digital filter. Note that components other than the direction separating circuit 9 are the same as in the first embodiment.

FIG. 9 is an explanatory diagram showing the principle of direction separation by a complex FIR filter of the ultrasonic diagnostic apparatus according to the second embodiment of the present invention. In FIG. 9, ω _S is the sampling angular frequency of the complex digital filter.

Hf (Z) is in the first frequency range (0 to ω
_{S / 2} ), that is, the filter characteristics of the forward signal. A complex inverse FFT is performed on this Hf (Z),
As a result, the complex time-domain signals CFowreal (t), CFowimag
(t) is obtained. Note that the inverse Fourier transform of a function having a pass band of the frequency domain 0 to + ω _{S / 2} may be performed, for example, according to the following equation (9).

[0032]

(Equation 3)

After the above conversion, the complex time domain signal CFowreal
(t) and CFowimag (t) are multiplied by the window function W (t), respectively.
As shown in the following equation (10), complex coefficient sequences CFreal (τ) and CFimag (τ) in the discrete time domain for the forward signal are obtained.
As the window function W (t), one that drops the side rope of the spectrum, such as Hamming or Blackman, is used.

[0034]

(Equation 4)

Subsequently, as shown in FIG. 10, a filter in the second frequency domain (−ω _{S / 2} ０0), that is, a reverse signal is assumed, and inverse FFT is performed in the same manner as in the case of the forward signal. And a window function to obtain a complex coefficient sequence in the discrete time domain for the backward signal. In FIG. 10, the complex time domain signal and the discrete time domain complex coefficient sequence shown in FIG. 9 are omitted.

First, Hr (Z) is in the second frequency domain (−
ω _{S / 2} ０0), that is, the filter characteristics of the backward signal. A complex inverse FFT is performed on this Hr (Z), thereby obtaining complex time-domain signals CRevreal (t), CR
Get evimag (t). The inverse Fourier transform of a function having a pass band of the frequency domain −ω _{S / 2} ０0 may be performed, for example, according to the following equation (11).

[0037]

(Equation 5)

After the above conversion, the complex time domain signal CRevreal
(t) and CRevimag (t) are multiplied by the window function W (t),
As shown in the following expression (12), complex coefficient sequences CRreal (τ) and CRimag (τ) in the discrete time domain for the backward signal are obtained.
As the window function W (t), one that drops the side rope of the spectrum, such as Hamming or Blackman, is used.

[0039]

(Equation 6)

In this way, a complex coefficient sequence in the discrete time domain is obtained for each of the band of the forward signal and the band of the backward signal. FIG. 11 is a block diagram showing an algorithm configuration of a complex FIR filter according to a specific example of the direction separation principle. This complex FIR filter constitutes a convolution filter that realizes a complex convolution (convolution integral) on the time axis for an example of a complex coefficient in the discrete time domain obtained as described above. Note that the number of taps of this filter is n.

The following equations (13) and (14) are equations for the above algorithm. According to the following equation (13), a forward signal Forward (t) is obtained. According to the following equation (14), a signal Reverse (t) in the reverse direction is obtained.

[0042]

(Equation 7)

By the way, the convolution operation of four terms consisting of each of the complex coefficient sequences of the forward signal and each of the complex coefficient sequences of the backward signal requires a huge amount of calculation. Therefore, in the present embodiment, the convolution operation is performed only on the real part channel component of the forward signal and the real part channel component of the backward signal.

As described above, according to the second embodiment, since the direction separating circuit 9 is constituted by a complex digital filter composed of an FIR filter, as in the first embodiment, sufficient irrespective of the band is used. Separation performance and response time performance can be obtained, and the circuit configuration can be made relatively small. Also, complicated adjustments such as analog circuits are not required. Further, since the audio zero shift corresponding to the spectrum display of the blood flow Doppler image is realized, more accurate blood flow Doppler sound can be obtained.

Note that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications. For example, the first,
In the second embodiment, the case where the direction separating circuit is configured using the IIR filter and the FIR filter has been described. However, the present invention is not limited to this, and can be realized by other digital filters.

[0046]

As described above, according to the present invention, it is possible to provide an ultrasonic diagnostic apparatus having a small circuit configuration with sufficient directional separation performance and response time performance in generating ultrasonic Doppler sound. .

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a principle of audio direction separation of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 3 is a diagram showing a frequency characteristic of a transfer function H (Z) of a complex IIR filter of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 4 is a view showing frequency characteristics of a transfer function Hf (Z) of the complex IIR filter of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 5 is a diagram showing a transfer function Hr (Z) of a complex IIR filter of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 6 is a block diagram showing an algorithm configuration of a complex IIR filter of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 7 is a view showing a direction separation characteristic of a direction separation circuit of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 8 is an explanatory diagram showing a zero shift of the ultrasonic diagnostic apparatus according to the first embodiment.

FIG. 9 is an explanatory diagram showing the principle of direction separation by a complex FIR filter of the ultrasonic diagnostic apparatus according to the second embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a principle of direction separation by a complex FIR filter of the ultrasonic diagnostic apparatus according to the second embodiment.

FIG. 11 is a block diagram showing an algorithm configuration of a complex FIR filter of the ultrasonic diagnostic apparatus according to the second embodiment.

FIG. 12 is a block diagram showing a schematic configuration of an ultrasonic diagnostic apparatus according to a conventional example.

FIG. 13 is a block diagram showing a configuration of a direction separating circuit of an ultrasonic diagnostic apparatus according to a conventional example.

FIG. 14 is a diagram showing a direction separation characteristic of a direction separation circuit of an ultrasonic diagnostic apparatus according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultrasonic probe 2 ... Transmission / reception circuit 3 ... Quadrature detection circuit 4, 5 ... Bandpass filter 6 ... Fast Fourier transformer (FFT) 7 ... Digital scan converter (DSC) 8 ... Monitor 9 ... Direction separation Circuit 10 D / A converter 11, 13 Power amplifier 12, 14 Speaker 15 Zero shift circuit

Claims (4)

[Claims] 1. A collection unit for transmitting an ultrasonic wave to a subject and receiving a reflected wave thereof to collect an ultrasonic Doppler shift signal, and an ultrasonic Doppler shift signal obtained by the collection unit. Separating means comprising a complex digital filter for separating the signal into a forward signal and a backward signal; and emitting ultrasonic Doppler sound according to the forward signal and the backward signal output from the separating means. An ultrasonic diagnostic apparatus comprising: a sound generating unit. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein said complex digital filter of said separating means is constituted by a non-recursive filter. 3. The ultrasonic diagnostic apparatus according to claim 1, wherein said complex digital filter of said separating means comprises a recursive filter. 4. The apparatus according to claim 1, further comprising: a zero shift unit configured to prevent a waveform of the ultrasonic Doppler shift signal collected by the collection unit from becoming a discontinuous waveform due to folding on a spectrum display. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is interlocked with the zero shift of the zero shift means.