JPH07178092A - Doppler ultrasonography diagnostic device - Google Patents

Abstract

PURPOSE:To process accurately the bloodstream information and other components well discriminatedly. CONSTITUTION:The real number part X and imaginary number part Y as the output of an auto-correlation device are turned into coordinates to form a complex plane, and judging regions 100, 102, 104 as two-dimensional regions surrounded by threshold curves are provided in this complex plane. In the case any point identified by the real number part X and imaginary number part Y lies within the region, judgement is passed that a clutter remaining component and noise exist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler diagnostic apparatus for displaying blood flow information in a living body based on the ultrasonic pulse Doppler method, and more particularly to removing unnecessary signals such as clutter components.

[0002]

2. Description of the Related Art In an ultrasonic Doppler diagnostic apparatus used in the medical field, a black and white tomographic image of an organ in a living body is displayed in real time, and information on blood flow flowing in the living body (average velocity) is displayed. , Variance or power) is superimposed on the tomographic image and displayed in color in real time. Therefore, as shown in the schematic configuration of FIG. 1, the ultrasonic Doppler diagnostic apparatus includes a tomographic data processing system 10 for obtaining a B-mode image and a Doppler signal processing system 12 for obtaining blood flow information. In the latter Doppler signal processing system 12, blood flow information is obtained by measuring the Doppler shift of the echo signal based on the ultrasonic pulse Doppler method.

According to the ultrasonic pulse Doppler method, ultrasonic pulses are sequentially transmitted into a living body a plurality of times in a predetermined cycle in each beam direction of the ultrasonic beam, and at that time, echo signals returned from the living body are generated. Blood flow information is obtained by calculating the phase change (Doppler shift frequency) or correlation function of the echo signals received and over the pulse period. Then, if blood flow information is extracted in each ultrasonic beam direction, two-dimensional blood flow information can be obtained and a two-dimensional Doppler image can be displayed.

The echo signals sequentially received by the pulse Doppler method include a Doppler component, which is an echo signal subjected to Doppler shift from the blood flow, and an organ (for example, a heart wall) inside the living body that is stationary or has little motion other than the blood flow. The clutter component, which is the echo signal from), and other noise are included. Therefore, it is necessary to suppress the clutter component, remove noise, and extract only the Doppler component.

FIG. 2 shows the basic configuration of the ultrasonic Doppler diagnostic apparatus.

The probe 16 and the transmission / reception circuit 18 sequentially transmit ultrasonic pulses a plurality of times in a living body at a predetermined cycle, and receive each echo signal returned from the living body.
The echo signal that has been subjected to the predetermined processing by the transmission / reception circuit 18 is input to the quadrature detection circuit 20. Then, the quadrature detection circuit 20 outputs the next complex signal Z (t) (where t is time).

Z (t) = I (t) + jQ (t) (1) That is, the I and Q signals whose phases are different by 90 ° are output. The I signal and the Q signal are converted into digital signals by the A / D converter 22, and then FIR (Fini
te Impluse Response) filter 24 and MTI (Moving
(Target Indication) is passed through a filter, etc., where the clutter component is suppressed.

Then, the I signal and the Q signal in which the clutter component is suppressed are analyzed by the conventional correlation processing unit 26 shown in FIG. At that time, in general, using the autocorrelator 28,
The autocorrelation function R (τ) of the echo signal Z (t) over the pulse period τ and the autocorrelation function R (0) of Z (t) at τ = 0 are obtained. In this case, R (τ) is a complex number as shown in the following equation, and is composed of a real number part (real number component) X (τ) and an imaginary number part (imaginary number component) Y (τ). Also, R
(0) is a real number and corresponds to the power P of the Doppler signal. R (τ) = <Z (t) · Z ^* (t + τ)> (2) = X (τ) + jY (τ) (3) Here, * represents a complex conjugate, and <> represents the above plural It represents the arithmetic mean of a finite number of data depending on the number of times transmitted. Then, the velocity / dispersion / power calculator 30 calculates the average velocity V of the blood flow from the argument θ of R (τ), and the velocity dispersion of the blood flow from the absolute value of R (τ) and R (0). While calculating T, the power P of the Doppler signal is output. Correlation processing unit 26
The average velocity V of the blood flow, the velocity dispersion T, and the power P of the Doppler signal, which are output from, are input to the discrimination processing circuit 32 next,
Here, components such as noise other than blood flow information are discriminated and selectively eliminated.

As shown in FIG. 6, in the conventional discrimination method, attention is paid to the fact that the noise power is small, and the blood flow information is obtained by comparing the magnitude of the power P of the Doppler signal, that is, R (0) with a predetermined threshold value. Whether or not it is determined. As shown in FIG. 6, the discrimination processing circuit is composed of a comparator 34 and a gate 36. For each of V, T, and P, a gate is required for the discrimination process, but in FIG. 6, only one gate 36 is shown as a representative, and its input is V,
Shown as T and P. The operation of the discrimination processing circuit 32 will be described. P is compared with a predetermined threshold S by a comparator 34, and if P <S, that is, if the output of the correlation processing unit 26 is determined to be a component other than blood flow information. The output of the comparator 34 shuts off the gate 36. Gate 3 otherwise
The V, T, and P signals input to 6, that is, blood flow information, passes through the gate as it is.

The blood flow information from which noises and the like have been eliminated is input to an image display circuit 38 including a DSC (Digital Scan Converter), where it is color coated and then superimposed on the B-mode tomographic image as a color image. It is displayed on the display 40.

[0011]

In FIG. 2, the FIR
The filter 24 is a high-pass filter, and clutter components of low frequency are mainly suppressed by this filter.
However, there is also a clutter component having a large amplitude that cannot be suppressed by the FIR filter 24, and these are output from the FIR filter 24 as unnecessary noise. Hereinafter, this is referred to as a clutter residual component.

Also, since the Doppler component having a low blood flow velocity, that is, a low Doppler shift frequency is suppressed, the power of the signal becomes small.

That is, in the conventional discrimination processing circuit 32,
Depending on the magnitude of the power P of the signal input to the circuit,
Since it is determined whether the blood flow information itself is present, noise is eliminated, but at the same time, blood flow information based on the Doppler component with low power is also lost. In addition, clutter residual components may not be sufficiently removed and may be displayed.

The present invention has been made in view of the above problems, and an object thereof is to perform discrimination processing of blood flow information and components other than blood flow information with high accuracy, and a discrimination processing with a simple circuit configuration. An object is to provide an ultrasonic Doppler diagnostic apparatus having a circuit.

[0015]

In order to achieve the above object, the present invention performs an autocorrelation operation on a received signal after detection and outputs the autocorrelation result as a real number component and an imaginary number component. A circuit, a discrimination circuit for inputting the real number component and the imaginary number component, and discriminating an unnecessary signal from a combination of the values of the both, and a circuit for performing the unnecessary signal removal processing according to the discrimination result. And

[0016]

According to the above construction, the unnecessary signal component consisting of noise and clutter residual component is discriminated based on the combination of the real number component and the imaginary number component which are the autocorrelation results. here,
It is difficult to determine the noise and the clutter residual component when the discrimination is performed only by the power, but in the present invention, when the distribution of the noise and the clutter residual component is represented on the complex plane, they are in a constant area. In contrast to the conventional method, the present invention effectively eliminates the unnecessary signal by considering both the real number component and the imaginary number component independently.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an overall schematic configuration of an ultrasonic Doppler diagnostic apparatus according to the present invention. Further, FIG. 2 shows a basic configuration of the ultrasonic Doppler diagnostic apparatus according to the present invention. In FIG. 1, as described above, the probe 1
The ultrasonic pulse is transmitted to the inside of the living body and the echo signal returned from the inside of the living body is received by the 6 and the transmitting / receiving circuit 18. The echo signal which has been subjected to the predetermined processing by the transmission / reception circuit 18 is input to the tomographic data processing system 10 and the Doppler signal processing system 12.

The tomographic data processing system 10 is a circuit for obtaining a B-mode tomographic image. The output is the image display circuit 38.
And is displayed on the display 40. On the other hand, the Doppler signal processing system 12 has the circuit configuration shown in FIG. 2 and is a circuit for obtaining the average velocity V of the blood flow, the velocity dispersion T of the blood flow, or the power P of the Doppler signal as described above. . The output is input to the image display circuit 38. Then, this is color-coated by the image display circuit 38 and superimposed on the black and white B-mode tomographic image and displayed on the display 40 in color.

In the Doppler signal processing system 12, the discrimination processing circuit 42 according to the present invention shown in FIG. 3 can discriminate the blood flow information and the components other than the blood flow information with higher accuracy than before. This determination processing will be described below.

Experiments have shown that noise and clutter residuals are found in the complex plane of the autocorrelator output R (τ) (ie X
The distribution is as shown in FIG. 4A on the plane where (τ) · jY (τ) is plotted on the horizontal and vertical axes.

As shown in FIG. 4 (A) 102, since the frequency of clutter is low, the clutter residual component is distributed in the vicinity of the X (τ) axis on the right side (positive side) of the complex plane of R (τ). (The argument of R (τ) of this component is small).

On the other hand, regarding the noise, when independent white noise is added to the I signal and the Q signal, the statistical value of the noise in R (τ) is analyzed, and the expected value of the noise component is the imaginary number of R (τ). In the part Y (τ), it becomes 0, whereas in the real part X (τ), a term of noise squared remains. If this is taken as the bias b in X (τ), for example, F shown in FIG. 7 as a filter for suppressing clutter components.
When using an IR filter, b is given by the following equation.

[0024]

[Equation 1] As can be seen from the equation (4), b is proportional to the noise variance (power) σ ² in the I signal or the Q signal and the autocorrelation of the coefficient a _i of the FIR filter whose impulse response length is N. To do. Since the FIR filter is a high pass filter, b usually has a negative value.

Therefore, it can be seen that the noise is distributed biased to the left side (negative side) of the origin of the complex plane of R (τ) as shown in FIG. 4 (A) 100. The size and shape of the distribution area are the number of times of averaging in the above equation (2), the power of noise, a and N of the FIR filter, the gain of the device,
Etc.

As described above, since the distribution areas of noise and clutter residual components can be identified on the complex plane of R (τ), the apparatus of the present embodiment has an appropriate threshold value according to these distribution areas. By setting (discrimination boundary line of unnecessary signal), the blood flow information and the components other than the blood flow information are accurately discriminated. That is, a discrimination area as a two-dimensional area surrounded by a threshold curve is provided in a complex plane formed by coordinating the real part X and the imaginary part Y which are outputs of the autocorrelator, and the real part X and the imaginary part Y are provided. If the point specified by is within the area, the presence of clutter residual components and noise is determined.

FIG. 3 shows the configuration of the discrimination processing circuit 42 in this embodiment. The operation will be described below. First, from the correlation processing unit 26, the complex output of the autocorrelator 28, that is, the real part X and the imaginary part Y of R (τ), and the average velocity V of the blood flow calculated by the velocity / dispersion / power calculator 30. A signal having velocity dispersion T and power P of the Doppler signal is output, and these signals are input to the discrimination processing circuit 42.
The determination processing circuit 42 includes a threshold table 4 including a storage medium.
4, a comparator 46 and a gate 48.

At the address terminal of the threshold table 44, Y
The sign bit (shown as sgn in FIG. 3) and X are supplied. In the threshold value table 44, the value of each threshold value corresponding to the sign of Y and the value of X is stored in advance. In the present embodiment, as shown in FIGS. 4 (A) 100 and 102, different thresholds are set for each of the noise and clutter residual distribution regions, or as shown in FIG. 4 (B) 104. One threshold is set for these areas. These thresholds are set by parameters such as the number of times of averaging in equation (2), the power of noise and clutter residual components, the impulse response length N of the FIR filter and its coefficient a _i , and the gain of the device. , Can be changed by these parameters. In that case, one is provided with a circuit that automatically optimizes the threshold according to a plurality of parameters.

In this way, the threshold value H is output from the threshold value table 44 according to the sign of Y and the value of X, and is input to the comparator 46. Y is connected to one terminal of the comparator 46, and the output of the comparator 46 is connected to the gate 48. In the gate 48, the average velocity V of the blood flow, the velocity dispersion T or the power P of the Doppler signal is input. For each of V, T, and P, a gate 48 is required for the discrimination process, but in FIG. 3, only one gate is shown as a representative, and its input is shown as V, T, and P.

When Y <H, that is, when the output of the autocorrelator 28 is determined to be a noise or clutter residual component, the comparator 46 cuts off the gate or sets the output of the gate to 0. This eliminates components other than blood flow information. In other cases, the V, T, and P signals input to the gate 48 are determined as blood flow information, pass through the gate as they are, are input to the image display circuit 38, and are displayed on the display 40.

Next, a modified example of this embodiment will be described below.

If the threshold value is vertically symmetrical with respect to the X axis as shown in FIG. 4, the sgn (symbol of Y) signal input to the threshold value table 44 of FIG. 3 is omitted, and Y is absolute instead. After passing through the value circuit, the absolute value of Y | Y | can be input to the comparator 46.

Further, the comparator 46 of FIG. 3 may be omitted, and the discrimination processing circuit 42 may use a two-dimensional threshold table 50 of X and Y as shown in FIG. In this, the output (1 or 0) of the threshold table 50 opens and closes the gate 48 depending on whether the coordinates by X and Y input to the threshold table 50 are outside or inside the threshold.

Further, as described above, the bias b shown in the equation (4) is generated in X. Therefore, in FIG. 3 or FIG. 5, a value obtained by subtracting b from the X value by a subtracter (not shown) can be input to the threshold value tables 44 and 50.
This corresponds to shifting the origin of the complex plane shown in FIG. 4 to the left by | b | for the output of the autocorrelator 28.

In any of the configurations, it is possible to effectively suppress clutter components and the like that could not be eliminated conventionally, by determining whether or not the signal is an unnecessary signal by the combination of X and Y.

[0036]

As described above, according to the present invention,
Noise and clutter residual components can be effectively removed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic Doppler diagnostic apparatus.

FIG. 2 is a block diagram showing a basic configuration of an ultrasonic Doppler diagnostic apparatus.

FIG. 3 is a block diagram showing a configuration of a discrimination processing circuit according to the present invention.

FIG. 4 is a principle explanatory view showing the principle of the present invention.

FIG. 5 is a diagram showing a modification of the discrimination processing circuit according to the present invention.

FIG. 6 is a block diagram of a conventional discrimination processing circuit.

FIG. 7 is a diagram showing a configuration of an FIR filter.

[Explanation of symbols]

 26 Correlation Processing Unit 28 Auto-Correlator 30 Velocity / Dispersion / Power Calculator 42 Discrimination Processing Circuit 44, 50 Threshold Table 46 Comparator 48 Gate

Claims (2)

[Claims] 1. An autocorrelation circuit for performing an autocorrelation operation on a received signal after detection and outputting the autocorrelation result as a real number component and an imaginary number component, and the real number component and the imaginary number component are input, and both of them are input. An ultrasonic Doppler diagnostic apparatus comprising: a discriminating circuit for discriminating an unnecessary signal from a combination of values; and a circuit for removing the unnecessary signal according to the discrimination result. 2. The apparatus according to claim 1, wherein the discrimination circuit includes a threshold table configured by a threshold value set for each value of the real number component, and the imaginary number component is compared with the threshold value for determination. An ultrasonic Doppler diagnostic apparatus characterized by being performed.