JPH0775639A - Ultrasonic diagnostic device - Google Patents

Abstract

PURPOSE:To provide the ultrasonic diagnostic device which eliminates a turning back phenomenon, while maintaining a filter characteristic, and can improve an S/N ratio of blood flow information being a result object caused thereby. CONSTITUTION:This device is provided with a means for transmitting an ultrasonic wave into an examine, receiving a reflected wave from a reflecting body, and obtained a received signal, and a filter circuit 6 for allowing a component conforming to a specific filter passing frequency band to pass through with regard to the received signal. Moreover, this device is provided with an analog/ digital converting circuit 7 having almost the same sample frequency band as the filter passing frequency band, and for allowing the output of the filter circuit 6 to be subjected to analog/digital conversion, a frequency analyzing circuit for deriving blood flow velocity by detecting a Doppler deviation frequency of a reflected wave by a blood flow of a transmitted ultrasonic wave by allowing the output of the analog/digital converting circuit 7 to be subjected to frequency analysis, and a display system 12 for displaying its blood flow velocity.

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 transmitting an ultrasonic wave into a living body, detecting the Doppler shift frequency of the reflected wave of the ultrasonic wave from a blood cell, and displaying the blood flow velocity.

[0002]

2. Description of the Related Art A Doppler blood flow detecting circuit in an ultrasonic diagnostic apparatus detects a reflected wave from a moving body when the ultrasonic reflecting body is a moving body when the ultrasonic wave is transmitted into the subject. The Doppler phenomenon in which the frequency shifts with respect to the frequency at the time of transmission is used to detect blood flow information.
The frequency shift amount, that is, the shift frequency corresponds to the ultrasonic transmission / reception direction component of the blood flow velocity, and the Doppler blood flow detection circuit detects the shift frequency (blood flow velocity). ,
After the echo signal obtained by receiving the reflected wave is passed through a filter circuit such as an LPF (low pass filter) that removes unnecessary signal components (noise components) from slow-moving reflectors such as side lobes, It is converted into a digital signal by an A / D converter, and a fast Fourier transform (frequency analysis) process which is a digital signal processing system is performed. Due to the characteristics of the fast Fourier transform processing, the frequency band that can be analyzed Δfc is A / D
It depends on the sampling frequency fsamp in the converter, and the relationship is as shown in the following equation (1).

−fsamp / 2 <Δfc <+ fsamp / 2 − (1) Of the signals input to the frequency analysis circuit (FFT), frequency components outside the frequency band Δfc cause a so-called aliasing phenomenon.

Here, the sampling frequency band Δfsamp of the A / D converter, the filter pass frequency band ΔfLPF passing through the filter circuit, and the display frequency band Δfdisp for displaying the shift frequency (blood flow velocity) , Are generally set according to the relationship shown in the following equation (2). The symbol “...” Means substantially the same.

Δfdisp ... Δfsamp ... ΔfLPF / 2- (2) FIG. 7 shows these relationships and the FFT in which the aliasing phenomenon occurs.
It is a diagram showing an output waveform (display waveform) from
FIG. 8 is a diagram showing the reciprocal regurgitation of the heart as an example of the case where the return phenomenon is likely to occur. As shown in FIG. 8, when regurgitation MR occurs in the compensation valve MV, the maximum change width of the shift frequency (blood flow velocity) increases, and a part thereof (dotted line portion T2 ′ in FIG. 7). Exceeds the sampling frequency band Δfsamp and the display frequency band Δfdisp, and the section T2 ′ is displayed in the display frequency band Δ due to the folding phenomenon.
It goes across the zero position P0 of fdisp and appears on the opposite side.

Further, according to the relationship of the above equation (2), a portion of the filter pass frequency band ΔfLPF which is not included in the sampling frequency band Δfsamp, a so-called folded portion N.
1 (hatched portion) is superimposed on the noise component, and the S / N ratio of the blood flow information obtained as a result decreases.

In order to improve the S / N ratio while maintaining the relationship of the equation (2), the LPF frequency band ΔfLPF
And set the sampling frequency band accordingly.
The fsamp and the display frequency band Δfdisp may be expanded. However, as described above, this LPF frequency band Δ
The fLPF is set in consideration of the filter characteristic for removing the noise component from the slow-moving reflector such as the side lobe, and the wider it is set, the more the noise component increases.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to improve the S / N ratio of blood flow information resulting from the elimination of the aliasing phenomenon while maintaining the filter characteristics. A diagnostic device is provided.

[0009]

An ultrasonic diagnostic apparatus according to the present invention is a means for transmitting an ultrasonic wave into a subject and receiving a reflected wave from a reflector to obtain a reception signal; A filter circuit that passes a component of a signal that matches a predetermined filter pass frequency band, and an analog / digital converter that has a sample frequency band that is substantially the same as the filter pass frequency band and that performs an analog / digital conversion on the output of the filter circuit Circuit, and a frequency analysis circuit for determining the blood flow velocity by detecting the Doppler shift frequency of the reflected wave due to the blood flow of the transmitted ultrasonic wave by frequency-analyzing the output of the analog / digital conversion circuit, and its frequency analysis circuit. And a display system for displaying the flow velocity.

[0010]

According to the present invention, ultrasonic waves are transmitted into the subject,
The reflected wave from the reflector is received, the received signal is obtained, only the component of the received signal that matches the filter pass frequency band is passed through, and the output of the filter circuit is passed through the analog / digital conversion circuit to the filter. By performing analog / digital conversion using a sample frequency band that is substantially the same as the pass frequency band, it is possible to suppress an increase in noise components.

[0011]

Embodiments will be described below with reference to the drawings. 1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention, and FIG. 2 is a fmax shown in FIG.
It is a figure showing an example of a measuring device.

The ultrasonic diagnostic apparatus has a system controller (not shown) as a control center of the entire system, and the ultrasonic probe 1, the transmitting circuit 2, the receiving circuit 3 and the quadrature detecting circuit (90 degree D
D) 4, band pass filter (BPF) 6, analog /
Digital converter (ADC) 7, fast Fourier transformer (FFT) 8, fmax measuring circuit 9, zero shift amount setting circuit 10, digital scan converter (DSC)
11 and the image display device 12. Note that, for convenience of explanation, the configuration of the apparatus of this embodiment is shown only for the part related to the continuous wave Doppler mode (CWD mode) processing system to which the present invention is mainly applied, and other ultrasonic tomographic images are obtained.
The mode processing system etc. are omitted.

The ultrasonic probe 1 comprises a plurality of piezoelectric vibrators arranged side by side, and these vibrators repeatedly transmit and receive ultrasonic pulses to and from a subject. The transmission circuit 2 is
Although not shown, it is equipped with a clock generator, a transmission delay circuit, and a continuous wave drive circuit, and supplies a drive signal for driving each transducer to each transducer of the ultrasonic probe 1 on the transmission side. An ultrasonic pulse is transmitted from the tentacle 1 at a predetermined single frequency. When the ultrasonic probe 1 is driven to be transmitted by such a wave transmission circuit 2, an ultrasonic pulse is transmitted from the ultrasonic probe 1 into the subject and reflected by blood cells flowing in the subject, Received by the same transducer of the ultrasonic probe on the receiving side,
Converted to a received signal with Doppler shift. Of course, the ultrasonic probe on the receiving side is also commonly used as the ultrasonic probe 1 on the transmitting side.

Although not shown, the wave receiving circuit 3 for receiving the received signal obtained by transmitting and receiving the ultrasonic wave includes a preamplifier, a reception delay circuit, and an adder, and amplifies the received signal to a predetermined level. A delay time for returning the amplified received signal to the basis of the delay time given by the transmission delay circuit is given to each transducer, and the received signals are added and synthesized and output.

The quadrature detection circuit (90 degree DD) 4 is one of the Doppler demodulation circuits. Since many Doppler signals exist in the pulse Doppler method, the Doppler signal for the desired transmission spectrum is extracted by the reference wave frequency. To do. Since this Doppler demodulation circuit performs quadrature detection, it divides the received signal into two channels, multiplies them by reference waves having 90 ° different phases (quadrature detection), and removes unnecessary high-frequency components.

The band-pass filter 5 has a predetermined filter pass frequency band ΔfLPF. First, the output is waveform-formed by a low-pass filter, and then the Doppler signal demodulated by the low-frequency component removing filter is used. It removes low-frequency components from the heart wall and slow-moving bodies of valve movement.

The ADC 7 converts an analog signal into a digital signal in order to connect the analog signal processing system up to the bandpass filter 6 and the fast Fourier transformer 8 and the DSC 11 which are digital signal processing systems of the downstream circuit. Is. The sampling frequency band Δfsamp of the ADC 7 is set to the filter pass frequency band ΔfLPF of the bandpass filter 6 according to the following equation (3). The symbol “...” Means substantially the same.

Δfsamp ... ΔfLPF- (3) FIG. 3 shows the filter pass frequency band ΔfLPF, the sampling frequency band Δfsamp, and the image display device 12 described later.
2 is a diagram showing in a frequency space the relationship between the display frequency band Δfdisp and the output waveform WFFT from the fast Fourier transformer.

In this way, the sampling frequency band Δfsa
Since mp is set in substantially the same relationship as the filter pass frequency band ΔfLPF, the noise components other than the sampling frequency band Δfsamp have already been attenuated by the bandpass filter 6, so the aliasing noise is eliminated. Will be done. As a result, compared to the conventional case, S / N
The ratio improves by about 3 dB.

The fast Fourier transformer 8 obtains the shift frequency fn of the reflected wave by subjecting the output of the ADC 7 to fast Fourier transform. This shift frequency fn changes every moment according to the flow state of blood cells, and the sampling frequency band Δfsamp is expanded to approximately the same level as the filter pass frequency band ΔfLPF as compared with the conventional case. Since the setting range is set as follows, the processing range of the fast Fourier transformer 8 can sufficiently capture the variation width ΔfFFT of the shift frequency fn, and an output waveform WFFT having no aliasing as in the conventional case can be obtained. it can.

Here, the filter pass frequency band ΔfLPF
And the sampling frequency band Δfsamp are set to be substantially the same, the output waveform W from the fast Fourier transformer 8
Although the FFT does not cause the aliasing phenomenon, as shown in FIG. 3, a frequency exceeding the display frequency band Δfdisp for displaying the blood flow velocity in the image display device 12 which is generally set to be narrower than those frequency bands. A component (hatched portion) is generated, and the portion is not folded and displayed (dotted line) on the image display device 12 as shown in FIG. 4, but the waveform of the portion shown by the one-dot chain line is It will not be displayed. The relationship between the bands is set by the relationship shown in Expression (4) based on the relationship of Expression (3).

[Delta] fdisp ... [Delta] fsamp / 2 ... [Delta] fLPF / 2- (4) Then, in the fmax measuring circuit 9 and the zero shift amount setting circuit 10, the variation width [Delta] fFFT of the shift frequency fn is displayed in this display frequency band [Delta] fdisp. As shown in FIG. 5, the shift amount Sf for shifting the zero position P0 to P0 '
Is automatically measured.

The fmax measuring circuit 9 measures the maximum value fmax of the shift frequencies fn output from the fast Fourier transformer 8. Although various measuring methods are conceivable, here, as shown in FIG. 2, a variable high-pass filter 91 and an output of the variable high-pass filter 91 are used as noise in an audio circuit that processes blood flow velocity as audible sound. And a comparator 92 which separates the signal from the variable high-pass filter 91 is used to check the presence or absence of a signal that exceeds the initially set cutoff level of the variable high-pass filter 91. The cutoff level of the variable high-pass filter 91 changes depending on the cutoff (CF) signal from the comparator 92. This makes it possible to measure the maximum value fmax of the continuously supplied shift frequencies fn.

The zero shift amount setting circuit 10 has a maximum value fma.
Based on x and the display frequency band Δfdisp, the change width ΔfFFT of the shift frequency fn is set to the display frequency band Δf.
The shift amount Sf for shifting the zero position P0 to P0 'is automatically measured so as to fit in disp. That is, the maximum value fma
x is compared with the highest level of the display frequency band Δfdisp, and the shift amount Sf is set so that they are substantially the same.

The shift amount Sf is supplied to the DSC 11, and the DSC 11 receives the zero position P according to the shift amount Sf.
0 is changed to P0 ', and a CWD mode image is output according to the monitor scanning system of the image display device 12. The image display device 12 converts the CWD mode image into an analog signal and then displays it.

As described above, the filter pass frequency band ΔfLPF of the bandpass filter 6, the sampling frequency band Δfsamp of the ADC 7, and the display frequency band Δfdisp for displaying the blood flow velocity of the image display device 12 are expressed by the formula ( By setting in accordance with the relationship of 4), the output after frequency analysis by the fast Fourier transformer 8 does not cause the folding phenomenon as in the conventional case, and further, the output,
That is, by automatically setting the zero shift amount Sf so that the change width ΔfFFT of the shift frequency fn is contained in the display frequency band Δfdisp, it is possible to display all the changes of the shift frequency fn, that is, the blood flow velocity changes. .

The present invention is not limited to the above-described embodiments, but can be modified in various forms. For example, as described above, as the measuring device for the maximum value fmax of the shift frequency fn, other commonly used device may be used.

Further, in the above embodiment, the zero shift amount Sf is set by measuring only the maximum value fmax of the shift frequency fn, but the change width ΔfFFT of the shift frequency fn is sufficiently wide and the display frequency band Δf. If it does not fit in fdisp, there may be a case where all the blood flow velocity cannot be displayed only by the correspondence by the zero shift. The shaded portion in FIG. 6 is a waveform portion that is not displayed in this case. In this case,
Not only the maximum value fmax of the shift frequency fn but also the minimum value fmi
Also, n may be measured, and the width of the display frequency band Δfdisp may be automatically adjusted to Δfdisp ′ according to the maximum value fmax and the minimum value fmin. A minimum value measuring circuit having a filter characteristic opposite to that of the fmax measuring circuit is connected in parallel to the fmax measuring circuit and the FFT8, and the minimum value fmin and the maximum value fmax are input to determine the width and the display frequency band specified by them. Display frequency band compared with △ fdisp △ fdisp
It suffices to additionally provide a circuit that changes Δfdisp ′ to Δfdisp ′ according to the width. Note that expression (4) Δfdisp ... Δfsamp / 2 ... Δf
If the relationship of LPF / 2 is set in advance as in Expression (5), it is possible to eliminate the need to adjust the display frequency band. △ fdisp… △ fsamp… △ fLPF- (5)

[0029]

As described above, according to the present invention, an ultrasonic wave is transmitted into the subject, a reflected wave from a reflector is received, a received signal is obtained, and the received signal is filtered by a filter circuit. Only the component that matches the filter pass frequency band is passed, and the output of the filter circuit is analog / digital converted by the analog / digital conversion circuit using a sample frequency band that is substantially the same as the filter pass frequency band. It is possible to provide an ultrasonic diagnostic apparatus capable of suppressing an increase in the noise.

In addition, the output of the analog / digital conversion circuit is subjected to frequency analysis by a frequency analysis circuit to detect the Doppler shift frequency of the reflected wave due to the blood flow of the transmitted ultrasonic wave to obtain the blood flow velocity. , Measuring the maximum value of the Doppler shift frequency, calculating a zero shift amount based on the maximum value, and shifting the zero position of the display frequency band that defines the display range of the Doppler shift frequency according to the zero shift amount. The ultrasonic wave capable of displaying the entire range of the detected Doppler shift frequency (blood flow rate) by displaying the blood flow rate obtained by the frequency analysis circuit within the range of the display frequency band. A diagnostic device can be provided.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of an fmax measuring circuit shown in FIG.

3 is a diagram showing the relationship between the filter pass frequency band ΔfLPF of the bandpass filter shown in FIG. 1, the sampling frequency band Δfsamp of the ADC and the display frequency band Δfdisp of the image display device, and the output waveform from the fast Fourier transformer. The figure which shows an example.

FIG. 4 is a diagram showing a display waveform when the output waveform shown in FIG. 3 is displayed as it is on an image display device.

5 is a diagram showing the output waveform shown in FIG. 3 when the zero position is shifted according to the zero shift amount by the zero shift amount setting circuit shown in FIG.

FIG. 6 is a diagram showing how the display frequency band Δfdisp is changed as a modification of the present embodiment.

FIG. 7 shows an example of the relationship between the filter pass frequency band ΔfLPF of the bandpass filter of the conventional device, the sampling frequency band Δfsamp of the ADC and the display frequency band Δfdisp of the image display device, and an example of the output waveform from the fast Fourier transformer. FIG.

FIG. 8 is a diagram showing a portion where backflow is likely to occur due to a folding phenomenon.

[Explanation of symbols]

1 ... Ultrasonic probe, 2 ... Transmitting circuit, 3 ... Receiving circuit, 4 ...
Quadrature detection circuit, 6 ... Band pass filter, 7 ... Analog-digital converter, 8 ... Fast Fourier transformer, 9 ... fma
x measuring circuit, 10 ... Zero shift setting circuit, 11 ... Digital scan converter, 12 ... Image display device.

Claims (2)

[Claims] 1. A means for transmitting an ultrasonic wave into a subject and receiving a reflected wave from a reflector to obtain a reception signal, and a component which matches a predetermined filter pass frequency band for the reception signal. A filter circuit, an analog / digital conversion circuit having a sample frequency band substantially the same as the filter pass frequency band, for analog / digital converting the output of the filter circuit, and a frequency analysis of the output of the analog / digital conversion circuit. And a display system that displays the blood flow velocity by detecting the Doppler shift frequency of the reflected wave due to the blood flow of the transmitted ultrasonic wave to obtain the blood flow velocity. And ultrasonic diagnostic equipment. 2. A means for measuring a maximum value of the Doppler shift frequency output from the frequency analysis circuit, a means for calculating a zero shift amount based on the maximum value, and the display according to the zero shift amount. The system further comprises means for transferring a zero position of a display frequency band defining a display range of the Doppler shift frequency in the system and displaying the blood flow velocity obtained by the frequency analysis circuit within the range of the display frequency band. The ultrasonic diagnostic apparatus according to claim 1, wherein: