JP2002095662A - Ultrasound diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasound diagnostic device which saves many effective data despite of few ensembles, can increase frame rate, and can reduce color noise. SOLUTION: Only effective data are taken out and auto-correlation calculation is performed as infinite impulse response (IIR) filter processing is performed from forward on a data message of ensemble data collected by color Doppler. Then, as impulse response (IIR) filter processing is performed from backward on a data message of the ensemble data, only effective data are taken out, and auto-correlation calculation is performed. As a result, many effective data can be collected without increasing ensemble data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic diagnostic apparatus compatible with a color Doppler diagnostic method.

[0002]

2. Description of the Related Art An ultrasonic diagnostic apparatus displays real-time tomographic images, movements, blood flow information, and the like of living tissue as images using ultrasonic waves. Other diagnostic devices (eg, X
Compared to X-ray diagnostic equipment, X-ray CT equipment, MRI and nuclear medicine diagnostic equipment, etc., non-invasive examinations are possible, the equipment is small and inexpensive, and there is no exposure to X-rays, etc. Has features. Therefore, it is widely used in the circulatory system (heart), abdomen (liver, kidney, etc.), mammary gland, thyroid gland, urology, obstetrics and gynecology, and the like.

As a two-dimensional display method of a blood flow by the ultrasonic diagnostic apparatus, there is a color Doppler method. The photographing operation by the color Doppler method is as follows. First, ultrasonic waves are transmitted and received a plurality of times in the same direction in the subject.
The received ultrasonic beam removes an echo signal (clutter) from tissue by applying a high-pass filter called a wall filter to a plurality of data strings at the same depth (hereinafter, referred to as ensemble data), A Doppler image can be obtained by extracting a signal of only the blood flow and performing a predetermined process.

By the way, the above-mentioned wall filter has I
IR (Infinite Imp)
(ulse Response) filter may be used. This IIR is very excellent as a filter for an infinite data string. However, when adapting to a finite length data sequence, 0 is used before data input.
Assuming the condition that the data contains the data, a problem of a transient response occurs in that ringing occurs in the data input in the initial stage.

As a countermeasure against this, Step-Initia
There is a method called “ligation” (hereinafter, referred to as SI method). This method is a method of setting the above condition by subtracting the first data in time series from all data. However, the transient response remains even by the SI method. This is because in the second-order Butterworth type HPF in the case where the SI method is performed, ringing increases in the first four data portions and cannot be used.

That is, the biggest problem of the IIR filter is the transient response of the filter, and this problem cannot be completely solved by the SI method. These issues,
Or, the type of wall filter, the SI method II
The problems of the R filter and the like are described in detail in various documents. The only solution to the IIR filter transient response problem at this stage is to not use the first few data with transient response for estimating blood flow velocity and the like.

[0007]

By the way, in order to increase the frame rate, it is necessary to reduce the number of ensembles. For example, if the first four data with much ringing are not used as described above, two or more effective data (data with little ringing and usable as diagnostic information) are required for the autocorrelation calculation. A minimum of six ensembles is required.

However, a decrease in the number of ensembles is usually accompanied by a decrease in valid data. If the number of valid data is small, the speed estimation accuracy is reduced, the variance is extremely reduced in accuracy, and the power S / N ratio is reduced. In radiography by the color Doppler method, the presence or absence of blood flow is determined by the lower limit of power and the lower limit of speed. For this reason, when the number of ensembles is small, color noise due to misidentification increases.

That is, according to the conventional ultrasonic diagnostic apparatus, it is difficult to achieve both improvement of the frame rate and reduction of the color noise. In order to improve the frame rate, it is necessary to reduce the number of ensembles,
This is because it is necessary to secure a certain number of ensembles in order to secure valid data in a reliable number.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can secure a large number of effective data even with a small number of ensembles. It is an object of the present invention to provide an ultrasonic diagnostic apparatus that can reduce color noise.

According to a first aspect of the present invention, there is provided a data collection means for transmitting and receiving ultrasonic waves to and from a subject a plurality of times in the same direction and collecting an ultrasonic data sequence in the direction, , A first filter for extracting blood flow information from the ultrasonic data sequence input in a first order from the buffer, and a second order from the buffer. An ultrasonic diagnostic apparatus, comprising: second filter means for extracting blood flow information from the input ultrasonic data sequence.

According to a second aspect of the present invention, in the apparatus according to the first aspect, the second order is reverse to the first order.

According to a third aspect of the present invention, there is provided a data collection means for transmitting and receiving ultrasonic waves to and from a subject a plurality of times in the same direction, and collecting a data sequence including a plurality of ultrasonic data in the directions. An ultrasonic diagnostic apparatus comprising: a filter unit that extracts blood flow information by performing a filtering process in a forward direction and a filtering process in a backward direction on the data sequence.

According to a fourth aspect of the present invention, in the device according to the third aspect, the filter means performs a filtering process by applying a matrix having a predetermined component to the data sequence. It is a type filter.

According to such a configuration, it is possible to secure a large number of effective data even with a small number of ensembles, and as a result, it is possible to improve a frame rate and reduce color noise.

The embodiments according to the present invention include various stages of the invention, and various inventions can be extracted by appropriate combinations of a plurality of disclosed configuration requirements.
For example, when an invention is extracted by omitting some constituent elements from all the constituent elements shown in the embodiments, when practicing the extracted invention, the omitted part is appropriately supplemented by well-known conventional techniques. It is something to be done.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment and a second embodiment of the present invention will be described with reference to the drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and repeated description will be made only when necessary.

First, a block configuration of an ultrasonic diagnostic apparatus according to the present invention will be described with reference to FIG.

FIG. 1 shows an ultrasonic diagnostic apparatus 10 according to the present invention.
FIG.

The ultrasonic diagnostic apparatus 10 includes a probe 101,
Transmission circuit 103, reception circuit 105, B-mode processing system 10
7, color Doppler processing system 109, coordinate conversion circuit 111,
An image synthesizing circuit 113 and a display monitor 115 are provided.

The probe 101 is a probe for irradiating a subject (patient) with ultrasonic waves for imaging and receiving a reflected wave from the subject, and is formed of a piezoelectric element or the like. ing.

The transmission circuit 103 has a trigger generator, a delay circuit, and a pulser circuit (not shown), and generates a pulsed ultrasonic wave and sends it to the vibration element of the probe to generate a focused ultrasonic pulse. . The ultrasonic wave generated by the transmission circuit 103 is radiated into the subject via the probe 101, and is received by the probe 101 again as an echo signal scattered by the tissue of the subject.

The receiving circuit 105 has a preamplifier, an A / D converter, a receiving delay circuit, and an adder (not shown). The echo signal output to the receiving circuit 14 for each element of the probe 11 is amplified for each channel by a preamplifier, and A / D converted by an A / D converter. And
The echo signals after the A / D conversion are phased and added by the reception delay circuit. The echo signal after this addition has a reflection component from a direction corresponding to the reception directivity emphasized.

The B-mode processing system 107 includes an echo filter 107a, a detection circuit 107b, and a LOG compression circuit 107c.
have.

The echo filter 107a is a band-pass filter (band-pass filter), and is a circuit for extracting only a necessary frequency from the frequency components of the echo signal.

The detection circuit 107b includes the echo filter 10
7a is a circuit for detecting the amplitude of the component extracted by 7a.

The LOG compression circuit 107c compresses the input echo signal with a predetermined logarithmic compression degree.

The color Doppler processing system 109 has a buffer circuit 109a, a wall filter 109b, and an autocorrelation circuit 109c.

The buffer circuit 109a is a device for temporarily storing an input data sequence of color Doppler.
The data sequence stored in the buffer circuit 109a is output to the wall filter circuit 109b in a predetermined order.

The wall filter circuit 109b is a characteristic part of the present invention, and has a configuration described later. The wall filter 109b is used to generate unnecessary strong reflection (clutter) from the myocardium or the like captured in the Doppler mode or the like.
Is a high-pass filter that removes

The autocorrelation circuit 109c is a circuit for calculating a correlation between the signals based on a plurality of echo signals having different phases and calculating an average frequency. This autocorrelation circuit 10
By 9c, the blood flow velocity and the like in the color Doppler are calculated.

The coordinate conversion circuit 111 has a B-mode processing system 1
07 or a circuit which receives an output signal from the color Doppler processing system 109 and converts the scanning line signal sequence of the ultrasonic scan into a scanning line signal sequence of a general video format represented by a television or the like.

The image synthesizing circuit 113 synthesizes character information of various setting parameters, scales, a guidance image described later, etc. into one frame, and generates a video signal as a video signal.
15 is output.

The display monitor 115 is a monitor composed of a CRT or the like, and displays a tomographic image representing the shape of the subject tissue based on the input video signal.

Next, the bidirectional filter processing executed by the ultrasonic diagnostic apparatus according to the present invention will be described. In the following description, a case will be described where the ensemble size N in the same direction of the transmission pulse transmitted from the transmission circuit is N = 6.

FIGS. 2A, 2B and 2C are views for explaining the concept of the bidirectional filter processing executed by the ultrasonic diagnostic apparatus 10. FIG. The arrows schematically show the vector amount of the received data.

FIG. 2A shows the order of applying a conventional IIR type wall filter to, for example, six ensemble data strings. The filtering process is executed from the first received data 1a to the data 6a in order (hereinafter, the filtering process executed according to the received order is referred to as “forward filtering process”). Further, as SI, subtraction from all data is performed from the first data 1a. Then, HPF is applied to the subtracted value. Secondary Butterworth H
In the case of PF, the transient response exists in the first four data. Therefore, the first four data are not used as diagnostic information, and only the last two data are output to the subsequent autocorrelation circuit. In FIG. 2A, x indicating that data 1a to 4a is not used as diagnostic information is attached, and o indicating data 5a and 6a is used as diagnostic information.

The ultrasonic diagnostic apparatus 10 according to the present invention
Performs the forward filter processing shown in FIG. 2A and performs the following backward filter processing.

FIG. 2B is a diagram for explaining the backward filter processing executed by the ultrasonic diagnostic apparatus 10. As in FIG. 2A, the arrows schematically show the vector amount of the received data.

As shown in FIG. 2B, in the backward filter processing, the filter processing is executed from the last input data 6a. Therefore, when the wall filter is applied in reverse order from the last data 6a, the data 2a and the data 1a
Are valid data and output to the subsequent autocorrelation circuit.

FIG. 2C is a diagram showing a processing procedure for data obtained by the above-described bidirectional filter processing.

As shown in FIG. 2C, an autocorrelation operation is performed on the data 5a and 6a obtained by the forward filter processing, and the data 1a and 2a obtained by the reverse filter processing are used. An autocorrelation operation is performed. These autocorrelation calculations are performed by the autocorrelation circuit 109c shown in FIG. 1, but the order is not limited.

By calculating the average from the data 5a and 6a obtained by the forward filter processing and the data 1a and 2a obtained by the backward filter processing,
Power is required.

Accordingly, the ultrasonic diagnostic apparatus 10 according to the present invention
Can double the number of autocorrelation data and the number of data for power calculation, and can greatly improve the speed / variance estimation accuracy. As a result, the S / N ratio can be improved.

Next, the configuration of the wall filter circuit 109b for realizing the above-described bidirectional filter processing will be described in detail.

FIG. 3 is a diagram showing a configuration of the wall filter circuit 109b, and shows a configuration of a second-order IIR filter using a delay element.

In FIG. 3, for example, to construct a second-order Butterworth-type high-pass filter with fc = 0.156, a
_{0 = 0.4904, a 1 = -0.9808} , a 2 = 0.
_{4904, b 1 = -0.7017, b} 2 = 0.2600
What is necessary is just to set the coefficient.

In the bidirectional filter processing executed by the ultrasonic diagnostic apparatus 10, a forward filter processing for inputting a received data string in a forward direction and a reverse filter processing for inputting a received data string in a backward direction are executed. You. Therefore, two sets of the wall filter circuit 109b shown in FIG. 3 are provided, and the forward and backward filter processes are executed in parallel. Further, a configuration may be adopted in which only one wall filter circuit 109b is provided, and processing is performed at high speed in the order of the forward direction and the reverse direction. The input sequence of the data sequence to the wall filter circuit 109b is determined by the buffer circuit 10
It is adjusted at 9a.

According to such a configuration, the wall filter processing is executed from the forward direction and the reverse direction, so that the number of data usable for diagnosis can be increased without increasing the number of data to be received. Therefore, speed estimation accuracy and sensitivity can be improved, and the number of ensembles can be reduced. As a result, the frame rate can be improved with the conventional number of received data.

(Second Embodiment) In a second embodiment, an example will be described in which the bidirectional filter processing described in the first embodiment is executed by a matrix-type wall filter. According to the second embodiment, the configuration of the device can be further simplified.

The matrix type wall filter obtains a filtered data string Y by applying a matrix W to an input data string D. Therefore, the filter processing by the filter can be expressed by the equation Y = WD. This filter is a time-varying type (time
(variant) FIR filter.

Equation 1 shown below is the same as in the first embodiment.
It is an example of a matrix filter when the number of ensembles N = 6.

[0053]

(Equation 1)

The IIR filter for finite length data is
This can also be realized by this matrix filter. That is, if the input of t ≦ 0 is 0, the IIR filter at t = n is equivalent to the FIR filter having the first n values of the impulse response of the IIR filter as coefficients. Note that the coefficient of t> n is 0. Furthermore, to perform SI, if the number of ensembles is 6,
What is necessary is just to multiply W by the matrix S of Expression 2 described below.

[0055]

(Equation 2)

That is, it is expressed by the equation Y = (SW) D. Here, the product (SW) of the matrix S and the matrix W on the right side of Equation 2 is represented by a 6 × 6 matrix. Therefore, by executing the integration in advance, Expression 2 can be expressed in the same form as Expression 1.

Second-order Butterworth type high-pass filter (fc)
= 0.156), the matrix when the number of ensembles obtained by performing SI is 6 is, for example, as follows.

[0058]

(Equation 3)

Here, to prevent transient response, the fifth and sixth results when the IIR filter is applied in the forward direction, and the fifth and sixth results when the IIR filter is applied in the reverse direction.
In order to output only the sixth result and the sixth result, the following matrix filter may be used.

[0060]

(Equation 4)

Y1 is the sixth result of the IIR filter output applied in reverse, and y2 is the fifth result. The output of y3 and y4 is 0. In y5, I applied from the forward direction
The fifth result of the IR filter output and the sixth result are entered in y6.

Thereafter, an autocorrelation operation is performed. The autocorrelation operation executed in the present embodiment is performed as follows:
When expressed as n + jIn, it is expressed by the following equation.

[0063] ^{_{c n = y n-1 y}} n * = R n-1 R n + I n-1 I n + j (R n I n-1 -R n -1 I n) ( Equation 5) Here, the asterisk Represents the complex conjugate. When the autocorrelation operation shown in Expression 5 is performed on y in Expression 4, y3, y
4 are both 0, the data string after the operation is (c
1,0,0,0, c5). That is, if one or more rows having all the coefficients are inserted between the backward filter and the forward filter, it is possible to prevent the calculation between the two in the autocorrelation calculation.

Next, the average value is calculated. Since the three data are known to be 0 in advance, averaging is performed by dividing the total sum by two. If the result is defined as C, a result of (p1, p2, 0, 0, p5, p6) is obtained by the calculation of pn = ynyn *. The power average can be obtained by averaging each component of the result.

Next, a spatial filter is applied to the ensemble average C and P data. Specifically, a spatial filter is applied to each of C and P between the data of the adjacent ultrasonic beam and the distance direction adjacent to the current ultrasonic beam.

Finally, the speed estimation unit for performing the speed / variance estimation is obtained by Expression 6, and the variance estimation value is obtained by Expression 7.

V = atan (imag (C ′) / real (C ′)) (Equation 6) σ = 1− | C ′ | / P (Equation 7) In the power display, P is used after being subjected to LOG compression. Is done.

According to the configuration described above, the following effects can be obtained.

First, with respect to P, a data amount twice as large as that of the related art can be obtained. Therefore, the S / N ratio is also 2 ^1/2
2 times, and can be improved by 3 dB.

Second, in the calculation of variance, if the data is 1
Since the number of sets increases from two to two, the accuracy of dispersion can be improved. In the related art, the variance is a temporal variation parameter, and thus cannot be accurately obtained by a single pulse pair.

Third, spatial fluctuation can be observed by smoothing the average value of the autocorrelation function two-dimensionally in the distance direction and between adjacent ultrasonic beams. For example, in the case of a blood flow such as an eddy, the time variation and the spatial variation of the flow velocity occur at the same time.
Spatial filters are effective.

Although the present invention has been described based on the embodiments, various changes and modifications can be made by those skilled in the art within the scope of the concept of the present invention. It is understood that examples also fall within the scope of the present invention. For example, as shown below, various modifications can be made without changing the gist.

In the second embodiment, a case has been described in which filter processing is performed with an ensemble number N = 6 using a matrix type filter. However, the present invention is effective even when the ensemble number N is 6 or more. Hereinafter, a case where the number of ensembles N = 10 will be described as an example.

When the ensemble number N = 10, the matrix operation is as shown in the following Expression 8.

[0075]

(Equation 5)

As shown in Expression 8, the matrix size is
It is 13 × 10. Of the ten data, the first four data are not used for the transient response, but the latter six data are used.
6 for each of the forward filter output and the reverse filter output
Using data, zero data is inserted between them. As a result, 13 data are output. As described above, autocorrelation calculation, averaging, spatial filtering, and velocity / variance estimation are performed on the 13 data.

According to the configuration in which the number of ensembles N = 10, the power is changed from the average of 6 data to the average of 12 data, so that an S / N improvement of 3 dB can be expected. In the variance, variation of 5 to 10 data is observed, so that the accuracy can be improved.

When the number of ensembles increases, the following points should be noted.

That is, as the number of ensembles increases, the correlation between the forward direction and the reverse direction increases. For example, Equation 8
In the above, since the correlation between y1 and y13 is high, effects such as noise reduction are low even if averaging is performed. Therefore, for example, Equation 8
In which the matrix size is 10 × 1 which is the same as that of the ensemble
It is also possible to set the size to 0.

[0080]

As described above, according to the present invention, it is possible to secure a large number of effective data even with a small number of ensembles, and as a result, it is possible to improve the frame rate and reduce the color noise. Can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an ultrasonic diagnostic apparatus 10 according to the present invention.

FIGS. 2A, 2B, and 2C are diagrams for explaining the concept of bidirectional filter processing performed by the ultrasonic diagnostic apparatus 10. FIGS.

FIG. 3 is a diagram illustrating a hardware configuration of a wall filter circuit 109b, and illustrates a second-order IIR using a delay element;
FIG. 2 shows a configuration diagram of a filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Ultrasonic diagnostic apparatus 101 ... Probe 103 ... Transmission circuit 105 ... Receiving circuit 107 ... B-mode processing system 107a ... Echo filter 107b ... Detection circuit 107c ... LOG compression circuit 109 ... Color Doppler processing system 109a ... Buffer circuit 109b ... Wall filter 109c: autocorrelation circuit 111: coordinate conversion circuit 113: image synthesis circuit 115: display monitor

Claims (4)

[Claims] 1. A data collecting means for transmitting and receiving ultrasonic waves to and from a subject a plurality of times in the same direction and collecting an ultrasonic data sequence in the direction, and a buffer for temporarily storing the ultrasonic data sequence. Means, first filter means for extracting blood flow information from the ultrasonic data string inputted in the first order from the buffer means, and said ultrasonic data string inputted in the second order from the buffer means And a second filter means for extracting blood flow information from the apparatus. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein said second order is a reverse order of said first order. 3. A data collection means for transmitting and receiving ultrasonic waves a plurality of times to and from a subject in the same direction, and collecting a data sequence composed of a plurality of ultrasonic data in the direction, An ultrasonic diagnostic apparatus, comprising: filter means for extracting blood flow information by performing filter processing in a forward direction and filter processing in a reverse direction. 4. An ultrasonic wave according to claim 3, wherein said filter means is a matrix type filter for executing said filter processing by applying a matrix having a predetermined component to said data sequence. Diagnostic device.