JP3471860B2 - Ultrasound diagnostic equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transmitting an ultrasonic wave into a living body, detecting a Doppler shift frequency of a reflected wave of the ultrasonic wave from blood cells, and detecting a blood flow. The present invention relates to an ultrasonic diagnostic apparatus that displays speed. 2. Description of the Related Art A Doppler blood flow detection circuit in an ultrasonic diagnostic apparatus, when an ultrasonic wave is transmitted into a subject and an ultrasonic reflector is a mobile Blood flow information is to be detected by utilizing the Doppler phenomenon in which the frequency of the reflected wave shifts with respect to the frequency at the time of transmission.
The shift amount of the frequency, that is, the shift frequency, corresponds to the ultrasonic wave transmitting / receiving component of the blood flow velocity. The Doppler blood flow detection circuit detects the shift frequency (blood flow velocity). ,
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 a slowly moving reflector such as a side lobe. The signal 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. Note that due to the characteristics of the fast Fourier transform processing, the frequency band Δfc that can be analyzed 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 △ fsamp of the A / D converter, the filter pass frequency band △ fLPF passing through the filter circuit, and the display frequency band △ fdisp for displaying the shift frequency (blood flow velocity) are as follows. Are generally set in the relationship shown in the following equation (2). Note that the symbols "..." mean substantially the same. Δfdisp... Fsamp... FLPF / 2− (2) FIG. 7 shows these relationships and the FFT in which the aliasing phenomenon occurs.
FIG. 9 is a diagram showing an output waveform (display waveform) from
FIG. 8 is a diagram illustrating the regurgitation of the heart as an example in which the turning phenomenon is likely to occur. As shown in FIG. 8, when the regurgitant flow MR occurs in the mitral valve MV, the maximum change width of the shift frequency (blood flow velocity) increases, and a part thereof (a dotted line portion T2 'in FIG. 7). Exceeds the sampling frequency band △ fsamp and the display frequency band △ fdisp.
It appears on the opposite side across the zero position P0 of fdisp. According to the relationship of the above equation (2), a portion which is not included in the sampling frequency band △ fsamp of the filter pass frequency band △ fLPF, that is, a so-called folded portion N
1 (hatched portion) is superimposed on the noise component, and the S / N ratio of the resulting blood flow information is reduced. [0007] How to improve the S / N ratio while maintaining the relationship of equation (2). LPF frequency band Δf LPF
And set the sampling frequency band Δ accordingly.
fsamp and display the frequency band Δfdisp also caused to expand Bayoi. However, as described above, this LPF frequency band Δf
The LPF is set in consideration of a filter characteristic for removing a noise component from a slowly moving reflector such as a side lobe, and the noise component increases as the setting is made wider. Accordingly, an object of the present invention is to eliminate the occurrence of the aliasing phenomenon while maintaining the filter characteristics, and to thereby improve the S / N ratio of the resulting blood flow information. It is an object of the present invention to provide an ultrasonic diagnostic apparatus. An ultrasonic diagnostic apparatus according to the present invention transmits ultrasonic waves into a subject, receives reflected waves from a reflector, and obtains a received signal. A filter circuit for passing a component corresponding to a predetermined filter pass frequency band with respect to the received signal; A digital / digital conversion circuit, and a frequency analysis circuit for analyzing the frequency of the output of the analog / digital conversion 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. , The frequency analysis circuit
Measure the maximum value of the Doppler shift frequency output from
Means and a zero shift amount based on the measured maximum value.
Means for calculating, and a preceding
Display frequency band that defines the display range of the Doppler shift frequency
Shifts the zero position of the band to within the displayed frequency band.
Means for displaying the blood flow velocity obtained by the frequency analysis circuit . According to the present invention, an ultrasonic wave is transmitted into a subject,
A reflected wave from the reflector is received, a received signal is obtained, and only the component that matches the filter pass frequency band is passed through the received signal in the filter circuit, and the output of the filter circuit is converted by the analog / digital conversion circuit into the filter. By performing analog / digital conversion using a sample frequency band that is substantially the same as the pass frequency band, an increase in noise components can be suppressed. An embodiment will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an ultrasonic diagnostic apparatus according to one embodiment of the present invention, and FIG. 2 is a block diagram showing fmax shown in FIG.
It is a figure showing an example of a measuring device. The ultrasonic diagnostic apparatus uses an ultrasonic probe 1, a transmitting circuit 2, a receiving circuit 3, and a quadrature detecting circuit (90 ° 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 an image display device 12. For convenience of explanation, the configuration of the apparatus according to the present embodiment shows only a portion related to a continuous wave Doppler mode (CWD mode) processing system mainly related to the present invention, and obtains another ultrasonic tomographic image.
The mode processing system and the like are omitted. The ultrasonic probe 1 includes a plurality of piezoelectric vibrators arranged side by side, and these vibrators repeatedly transmit and receive ultrasonic pulses to a subject. The transmission circuit 2
Although not shown, a clock generator, a transmission delay circuit, and a continuous wave drive circuit are provided, and a drive signal for driving each transducer is supplied to each transducer of the ultrasonic probe 1 on the transmission side, and an ultrasonic probe is provided. The ultrasonic pulse is transmitted from the probe 1 at a predetermined single frequency. When the ultrasonic probe 1 is driven to be transmitted by such a transmission circuit 2, an ultrasonic pulse is transmitted from the ultrasonic probe 1 into the subject, and is reflected by blood cells flowing in the subject, Received by the same transducer of the ultrasonic probe on the receiving side,
It is converted to a received signal with a Doppler shift. Of course, the ultrasonic probe on the receiving side is also commonly used as the ultrasonic probe 1 on the transmitting side. A receiving circuit 3 for receiving a reception signal obtained by transmitting and receiving the ultrasonic wave includes a preamplifier, a reception delay circuit, and an adder (not shown), and amplifies the reception signal to a predetermined level. A delay time for returning the amplified reception signal to the base of the delay time given by the transmission delay circuit is given to each transducer, and the reception signals are added and synthesized and output. The quadrature detection circuit (90-degree DD) 4 is one of Doppler demodulation circuits, and since there are many Doppler signals in the pulse Doppler method, a Doppler signal for a desired transmission spectrum is extracted based on a reference wave frequency. Is what you do. Since the Doppler demodulation circuit performs quadrature detection, the received signal is divided into two channels, multiplied by reference waves having phases different from each other by 90 degrees (quadrature detection), and unnecessary high-frequency components are removed. The band-pass filter 5 has a predetermined filter pass frequency band △ f LPF, and first forms a waveform of the output by a low-pass filter, and further forms a waveform in the Doppler signal demodulated by the low-frequency component removing filter. Eliminates low frequency components from heart wall and slow motion of valve motion. The ADC 7 converts an analog signal into a digital signal in order to connect the analog signal processing system up to the band-pass filter 6 with the fast Fourier transformer 8 and the DSC 11 which are digital signal processing systems of the downstream circuit. It is. The sampling frequency band △ fsamp of the ADC 7 is set with respect to the filter pass frequency band △ fLPF of the bandpass filter 6 according to the following equation (3). Note that the symbols "..." mean 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.
FIG. 6 is a diagram showing, in a frequency space, a relationship between a display frequency band △ fdisp and an output waveform WFFT from a fast Fourier transformer. Thus, the sampling frequency band △ fsa
Since mp is set in substantially the same relationship as the filter pass frequency band △ fLPF, noise components other than the sampling frequency band △ fsamp have already been attenuated by the band-pass filter 6, so that aliasing noise is eliminated. Will be done. As a result, the S / N ratio is higher than in the conventional case.
The ratio is improved by about 3 dB. The fast Fourier transformer 8 performs a fast Fourier transform on the output of the ADC 7 to obtain the shift frequency fn of the reflected wave. The shift frequency fn changes every moment according to the flow state of blood cells, and the sampling frequency band △ fsamp is expanded to about the same as the filter pass frequency band △ fLPF as compared with the conventional case. With this setting, the processing range of the fast Fourier transformer 8 can sufficiently capture the width of change △ fFFT of the shift frequency fn, and can obtain an output waveform WFFT without aliasing as in the related art. it can. Here, the filter pass frequency band Δf LPF
And the sampling frequency band △ fsamp are set to be substantially the same, so that the output waveform W from the fast Fourier transformer 8 is
Although no aliasing phenomenon occurs in the FFT, as shown in FIG. 3, a frequency exceeding a display frequency band Δfdisp for displaying a 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 back (dotted line) on the image display device 12 as shown in FIG. 4, but the waveform of the portion shown by the dashed line is It will not be displayed. The relationship between the bands is set based on the relationship shown in Expression (4) based on the relationship shown in Expression (3). Δfdisp... Fsamp / 2. 5, a shift amount Sf for shifting the zero position P0 to P0 'as shown in FIG.
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 measurement 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 added to an audio circuit for processing the blood flow velocity as an audible sound. A method of examining the presence or absence of a signal exceeding the initially set cutoff level of the variable high-pass filter 91 by using a comparator 92 for separating the signal from the variable high-pass filter 91 is adopted. The cut-off level of the variable high-pass filter 91 is changed by a cut-off (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 calculates the maximum value fma
x and the display frequency band △ fdisp, the variation width △ fFFT of the shift frequency fn is calculated based on the display frequency band △ fdisp
The shift amount Sf for shifting the zero position P0 to P0 'is automatically measured so as to be within disp. That is, the maximum value fma
x is compared with the highest level of the display frequency band △ fdisp, 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 sets the zero position P in accordance with the shift amount Sf.
0 is changed to P0 ', and a CWD mode image is output according to the monitor scanning method of the image display device 12. The image display device 12 displays the CWD mode image after converting it into an analog signal. As described above, the filter pass frequency band △ f LPF of the band pass filter 6, the sampling frequency band △ f samp of the ADC 7, and the display frequency band △ f disp for displaying the blood flow velocity of the image display device 12 are expressed by the following equation: 4), the output after frequency analysis by the fast Fourier transformer 8 does not have a folding phenomenon as in the conventional case.
That is, by automatically setting the zero shift amount Sf so that the change width △ fFFT of the shift frequency fn falls within the display frequency band △ fdisp, the change of the shift frequency fn, that is, the change of the blood flow velocity can be entirely displayed. . The present invention is not limited to the above-described embodiment, but can be variously modified and implemented. For example, as described above, the measuring device for measuring the maximum value fmax of the shift frequency fn may be another device that is generally 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. However, the change width ΔfFFT of the shift frequency fn is sufficiently wide and the display frequency band If the value does not fall within the range of fdisp, there is a case where not all of the blood flow velocities can be displayed only by the response using the zero shift. The hatched 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
n may also be measured, and the width of the display frequency band △ fdisp may be automatically adjusted to △ fdisp 'according to the maximum value fmax and the minimum value fmin. A minimum value measurement circuit having a filter characteristic opposite to that of the fmax measurement circuit is connected in parallel to the fmax measurement circuit and the FFT 8, and the minimum value fmin and the maximum value fmax are input, and the width and display frequency band specified for them are input. Δfdisp and display frequency band Δfdisp
May be additionally provided with a circuit that changes the value to △ fdisp ′ according to the width. Expression (4) Δfdisp... Fsamp / 2.
If the relationship of LPF / 2 is set in advance as in equation (5), it is not necessary to adjust the display frequency band. Δfdisp ... Δfsamp ... ΔfLPF- (5) As described above, according to the present invention, an ultrasonic wave is transmitted into a subject and a reflected wave from a reflector is received. The filter circuit then passes only the components that match the filter pass frequency band in the filter circuit, and the output of the filter circuit is sampled by an analog / digital conversion circuit into a signal substantially the same as the filter pass frequency band. By performing analog / digital conversion using a frequency band, it is possible to provide an ultrasonic diagnostic apparatus capable of suppressing an increase in noise components. Further, the output of the analog / digital conversion circuit is frequency-analyzed 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 a maximum value of the Doppler shift frequency, calculating a zero shift amount based on the maximum value, and shifting a zero position of a display frequency band defining a display range of the Doppler shift frequency according to the zero shift amount. By displaying the blood flow velocity obtained by the frequency analysis circuit within the range of the display frequency band, an ultrasonic wave capable of displaying the entire range of the detected Doppler shift frequency (blood flow velocity) can be displayed. A diagnostic device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to one embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of an fmax measuring circuit shown in FIG. FIG. 3 shows the relationship between the filter pass frequency band △ fLPF of the bandpass filter shown in FIG. 1, the sampling frequency band △ fsamp of the ADC, and the display frequency band △ fdisp of the image display device, and the output waveform from the fast Fourier transformer. The figure which shows an example. FIG. 4 is a view showing a display waveform when the output waveform shown in FIG. 3 is directly displayed on an image display device. FIG. 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. 1; FIG. 6 is a view showing a state of change of a display frequency band Δfdisp as a modification of the embodiment. FIG. 7 shows an example of a relationship between a filter pass frequency band △ fLPF of a band pass filter of a conventional device, a sampling frequency band △ fsamp of an ADC, and a display frequency band △ fdisp of an image display device, and an output waveform from a fast Fourier transformer. FIG. FIG. 8 is a diagram showing a portion where a reverse flow is likely to occur in which a turning phenomenon is likely to occur. [Description of Signs] 1 ... Ultrasonic probe, 2 ... Transmission circuit, 3 ... Reception circuit, 4 ...
Quadrature detection circuit, 6: bandpass filter, 7: analog-to-digital converter, 8: fast Fourier converter, 9: fma
x measurement circuit, 10: zero shift setting circuit, 11: digital scan converter, 12: image display device.

Claims (1)

(57) [Claim 1] Means for transmitting an ultrasonic wave into a subject, receiving a reflected wave from a reflector, and obtaining a received signal, and a predetermined filter for the received signal A filter circuit that passes a component that matches a pass frequency band, an analog / digital conversion circuit that has a sample frequency band that is substantially the same as the filter pass frequency band, and that performs analog / digital conversion on the output of the filter circuit; / a frequency analysis circuit for determining the blood flow velocity by detecting the Doppler shift frequency of the reflected wave by the ultrasonic blood flow that the transmitting by frequency analysis of the output of the digital conversion circuit, output from the frequency analysis circuit Doppler shift frequency
Means for measuring the maximum value of the number, and calculating the zero shift amount based on the measured maximum value
Means and the Doppler shift frequency according to the calculated zero shift amount.
The zero position of the display frequency band that defines the display range
Frequency analysis within the range of the displayed frequency band.
Means for displaying the blood flow velocity obtained by the circuit .