JP2002325767A - Ultrasonic Doppler diagnostic apparatus and Doppler signal processing method - Google Patents

Abstract

(57) Abstract: Direction separation is performed on a Doppler signal by simplifying a hardware configuration or reducing arithmetic processing by software. An ultrasonic Doppler diagnostic apparatus includes a direction separator (61) that separates a blood flow direction and outputs Doppler sound.
The separator 61 is allocated to each of the blood flow direction and a zero inserter 61A that inserts a zero value into a digital Doppler signal to increase the number of data N times (for example, N = 2) in the time axis direction. And two complex BPFs 61B and 61C for subjecting the Doppler signal, into which the zero value has been inserted, to complex band-pass filtering, using the sampling frequency as N times the sampling frequency before inserting the zero value into the Doppler signal,
Prepare. The signals subjected to the complex bandpass filtering by the two complex BPFs 61B and 61C are output as Doppler sounds separated in the motion direction.

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 and, more particularly, to an ultrasonic Doppler having a function of outputting Doppler sound from a moving object such as a blood flow in a separated direction. The present invention relates to a diagnostic device and a Doppler signal processing method used in the diagnostic device.

[0002]

2. Description of the Related Art Conventionally, in the field of ultrasonic Doppler diagnosis, a technique of outputting a Doppler signal collected in accordance with a moving direction of a blood flow as a Doppler sound has been one effective diagnostic tool.

As a conventional technique for generating the Doppler sound,
For example, the one described in U.S. Pat. No. 5,676,148 is known. This patent publication discloses that the blood flow is forward flow or reverse flow (Re
verse) is shown.

FIG. 11 shows an outline of this direction separation method. The Doppler quadrature signal (IQ Input) is input in parallel to the forward-flow side and reverse-flow side circuits, and firstly modulated by the first-stage modulators 100A and 100B according to the bandwidth in each circuit. Can be lifted. This Doppler quadrature signal is then applied to the zero inserters 101A, 1
At 01B, zero insertion is performed, processed at LPFs 102A and 102B, and band-limited. This Doppler quadrature signal is further demodulated to a second-stage demodulator 103.
A, 103B, demodulated by the real part selector 104A, 1
The real part signal is extracted via 04B. Real number signals respectively extracted from these two circuits are Doppler sound signals on the forward and backward sides.

[0005]

However, the conventional directional separation method described above has a problem in that the configuration and the processing scale become too large whether this is performed by hardware or software. However, the entire apparatus is considerably burdened.

In practice, to implement the above-described direction separation method by hardware, four complex multipliers and four real parts L
PF is required. Also, when realizing it by software, a similar real-time process and a process of setting a coefficient in accordance with the two-stage modulator and the zero shift amount of the LPF are required.

The present invention has been made in view of such a conventional method of separating the direction of a Doppler signal, and simplifies the hardware configuration or reduces operation processing by software to reduce the direction of the Doppler signal. Can do
It is an object of the present invention to increase the speed and weight of a direction separation operation.

Further, the present invention achieves the above object and at the same time, even when a baseline shift (zero shift) is performed on the screen of the Doppler spectrum display, the Doppler sound always aligned with the Doppler spectrum display screen with respect to the direction separation of the Doppler signal. Is another purpose.

[0009]

According to one embodiment of the present invention, a complex signal obtained by processing an echo signal obtained by transmitting an ultrasonic signal to a subject is provided. An ultrasonic Doppler diagnostic apparatus comprising a separating unit that separates a moving direction of a moving object presenting the Doppler signal from a digital Doppler signal composed of a Doppler signal, wherein a zero value is inserted into the Doppler signal in the separating unit. N in the time axis direction
Zero insertion means for double length (N is a positive integer: N ≧ 2);
2) subjecting the Doppler signal with the zero value inserted thereto to complex bandpass filtering using the N times the sampling frequency before inserting the zero value into the Doppler signal as the sampling frequency, which is assigned to each of the motion directions. Complex BPFs (Bandpass Filter)
r).

According to the directional separation of the present invention, basically, zero insertion means and two complex BPFs (Complex) are used.
(BPF: CBPF), the processing is simple and the calculation load can be reduced regardless of whether this is realized by hardware or software. This promotes downsizing, cost reduction, energy saving, and high-speed processing of the ultrasonic Doppler diagnostic apparatus.

For example, there is provided Doppler sound output means for outputting a signal subjected to complex bandpass filtering by each of the two complex BPFs as Doppler sound separated from the motion direction. Thus, there is always consistency between the Doppler sound and the Doppler spectrum display with respect to the separation direction of the Doppler sound.

Also, for example, an ultrasonic probe is provided for transmitting the ultrasonic signal to the subject and receiving the echo signal from the subject. Both in the direction of moving toward and in the direction away from the ultrasound probe. Preferably, the integer multiple is twice.

As a further preferred aspect, a display means for performing Doppler spectrum display based on the echo signal,
Baseline control means capable of shifting a baseline for eliminating a folded portion on the screen of the Doppler spectrum display, and filtering of the two complex BPFs according to the shift amount when the baseline is shifted Characteristic changing means for changing characteristics. For example, it is means for changing the filter coefficient of each of the two complex BPFs according to the shift amount.

According to another aspect of the present invention, a zero value is inserted into a Doppler signal composed of a complex signal obtained by processing an echo signal obtained by transmitting an ultrasonic signal to a subject. After making the signal an integral multiple length in the time axis direction, it is assigned to each of the motion directions of the moving body presenting the Doppler signal, and
At a frequency obtained by multiplying the sampling frequency when the zero value is not inserted into the Doppler signal by the integer multiple, the Doppler signal subjected to the zero value insertion processing is double-speed sampled and subjected to complex bandpass filtering, and the complex band is filtered. There is provided a Doppler sound generation method for outputting a signal subjected to bass filtering as Doppler sound separated from the motion direction.

Further, according to another aspect of the present invention, a filter coefficient of a complex band-pass filter for subjecting a Doppler signal composed of a complex signal to a complex band-pass filtering process is given by:
A Doppler signal processing method is provided which is changed in accordance with a shift amount of a baseline performed to eliminate a folded portion on a screen of a Doppler spectrum display.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of an ultrasonic Doppler diagnostic apparatus according to the present invention.

First, the components of the ultrasonic Doppler diagnostic apparatus will be outlined. The ultrasonic Doppler diagnostic apparatus is an ultrasonic probe (hereinafter, referred to as a probe) 1 that transmits an ultrasonic signal to a subject and receives an echo signal from the subject.
1 and an apparatus main body 12 connected to the probe to obtain various images and blood flow Doppler information.

The apparatus main body 12 includes a transmission / reception unit 21 connected to the probe 11, and an envelope detector 22 and a quadrature phase detector 23 connected to a receiver of the transmission / reception unit 21. The apparatus body 12 includes a CFM mode processing block 24 and a spectrum Doppler processing block 25 connected to a quadrature phase detector 23, and a DSC (digital scan converter) connected to the envelope detector 22 and both processing blocks 24 and 25. 26. This DSC2
6 is further electrically connected to a monitor 28 via a color processor 27. The color processor 27 and the monitor 2
8 also forms a part of the apparatus main body 12.

Further, the apparatus main body 12 is provided with a Doppler sound processing block 29 obtained by extracting a signal from a part of the spectrum Doppler processing block 25, and a speaker 31 connected to the block 29 via a power amplifier 30. ing. The power amplifier 30 and the loudspeaker 31 are respectively composed of left and right amplifiers and speakers for two channels.

The apparatus main body 12 further includes a baseline shift switch 32 manually operated by a user, a baseline console code generator 33 activated in response to a signal from the switch 32, and a According to the generated code, a complex BPF (Complex
A CBPF coefficient calculator 34 for calculating a coefficient of Band Pass Filter (CBPF) is provided.

Of the above components, the spectrum Doppler processing block 25 and the Doppler sound processing block 29 are functionally constituted by software processing of a DSP (Digital Signal Processor). The CBPF coefficient calculator 34 is functionally configured by software processing of a DSP or a host computer (not shown). Further, the baseline control code generator 33 is functionally configured by software processing of a host computer (not shown).
Note that these components 25, 29, 34, and 33 may be configured by hardware circuits.

Each of the above components will now be described in more detail.
The transmitting / receiving unit 21 drives the probe 11 with a drive signal (RF signal of electric quantity) according to the B mode or the CFM mode to transmit an ultrasonic beam signal into the subject, and the probe 11 receives the ultrasound beam signal from the subject. An echo signal (an RF signal of electric quantity) is accepted, and a delay addition process at the time of reception is performed on the echo signal. The echo signal beam-focused by the delay addition is sent to the envelope detector 22 and the quadrature phase detector 23.

In this embodiment, the receiver of the transmission / reception unit 23 and the subsequent signal processing system are of a digital type. Therefore, the echo signal output from the receiver is converted into a digital signal.

The envelope detector 22 performs envelope detection on the echo signal to generate B-mode image data, and sends the image data to the DSC 26.

On the other hand, the quadrature phase detector 23 has a digital mixer and a low-pass filter for two channels corresponding to the real part component and the imaginary part component, respectively, and performs quadrature phase detection on the echo signal. Thereby, the quadrature phase detector 23 outputs a digital amount of the echo signal subjected to the quadrature phase detection. By this detection, a baseband Doppler signal (real component and imaginary component: IQ signal) is extracted from the echo signal. This Doppler signal is output from the CFM processing block 24.
And transmitted to the spectrum Doppler processing unit 25.

The CFM processing block 24 includes a CT buffer 41 and a wall filter 4 in order from the signal input side.
2, an autocorrelator 43 and a CFM calculator 44 are provided. The output of the CFM calculator 44 is sent to the DSC 26.

Thus, the Doppler signal is transmitted to the CT buffer 4
1, the processing of the wall filter 42, the autocorrelator 4
3 and the CFM (Color F
It is converted into two-dimensional blood flow information through low mapping processing in order.

Specifically, the CT buffer 41 applies a “Corner Turning Bu” to the Doppler signal.
The buffer filter 42 buffers the ultrasonic scan raster called “ffer” and packetizes the data for the next processing. The wall filter 42 is a high-pass filter that removes clutter components caused by low-frequency walls of the Doppler signal. .
The clutter component is removed from the Doppler signal by the wall filter 42.

The autocorrelator 43 performs autocorrelation processing on the Doppler signal. In other words, by the autocorrelation process called a pulse pair, a complex autocorrelation coefficient and its differential value serving as a source of the blood flow information calculation in the next stage are calculated from the echo signal. The CFM calculator 44 calculates the estimated values of the velocity V, the power P, and the variance T of the Doppler signal based on the autocorrelation value at the previous stage, and performs an angio process. The angio treatment mainly performs temporal smoothing of the power to improve the detection sensitivity of the blood flow.

The information on the velocity V, the power P, and the variance T is calculated for each sample point on the scan cross section to form two-dimensional blood flow information. This blood flow information is sent to the DSC 26.

In the DSC, B-mode image data and two-dimensional blood flow information are coordinate-transformed from an ultrasonic scan to a standard TV scan, and two-dimensional blood flow information is synthesized into a B-mode image (gray-scale tomographic image). Is performed. The image data obtained by synthesizing the blood flow information is sent to the color processor 27 and subjected to a coloring process with reference to an RGB look-up table (LUT). This gives the final CFM
(Color flow mapping) image data is generated, and this CFM image is displayed on the monitor 28.

On the other hand, spectrum Doppler processing block 2
5 includes a wall filter 51, a CINE buffer 52, an FFT 53, and a post operation unit 54 in order from the input side as shown in FIG.

As a result, the above-mentioned digital Doppler signal (IQ signal) is also sent to the wall filter 51 to remove clutter components such as a heart wall. This Doppler signal is temporarily stored in a CINE buffer 52 for cine reproduction, and then subjected to fast Fourier transform by the FFT 53. Specifically, the fast Fourier transform of the FFT 53 multiplies the Doppler signal on the time axis by a window function and converts the Doppler signal into data on the frequency axis (spectrum data). The spectrum data is sent to the post-calculator 54, where the spectrum is converted into a power dimension, and spectrum averaging processing, median filter processing, compression processing corresponding to the display range, and the like are performed.

The spectrum data thus post-processed is sent to the DSC 26. This DSC 26 is
(Scan conversion of B-mode image) processing and “Trace Di
While performing the “sp (Doppler trace display)” process, one frame of image data is generated together with the above-described mapping image of blood flow information. This image data is sent to the monitor 28 via the color processor 27 described above. Thus, the spectrum data is displayed as a two-dimensional periodogram.

Further, as shown in FIG. 1, the spectrum Doppler processing block 25 is provided with a Doppler sound processing block 29.

The Doppler sound processing block 29 is a CINE buffer 52 of the spectrum Doppler processing block 25.
Is provided with a direction separator 61 for inputting the output data. On the output side of the separator 61, a pitch converter 62 and a post-operation unit 63 are sequentially provided.

The direction separator 61 includes a wall filter 51.
Direction of the Doppler signal passing through the probe 11 (the blood flow flowing toward the probe 11 or the
From the blood stream flowing away from). Specifically, the direction separator 61 separates the Doppler signal (IQ signal) into a positive-side frequency component (Forward component) and a negative-side frequency component (Reverse component). Both separated frequency components are supplied to the next-stage pitch converter 6.
According to 2, the frequency is converted to a frequency of a voice pitch that is easy to hear as necessary.

The audio signal is further subjected to muting processing, oversampling filter processing, and D / A conversion by the post-processing unit 63 at the next stage.
The oversampling filter is a process of converting a sample rate of a scan system of an audio sound into a high-speed sampling frequency for D / A conversion, and smoothing the audio signal (removing high-frequency noise).

The analog audio signal thus post-processed is power-amplified by the power amplifier 30 and supplied to the left and right speakers 31 by a Forward component / Revers.
Assigned as e component. Thereby, the forward flow Doppler sound and the backward flow Doppler sound are emitted from the left and right speakers 31, so that the blood flow flowing toward the probe 11 and the blood flow moving away from the probe 11 can be distinguished from the sound. .

The Doppler sound processing block 29 partially utilizes the configuration of the spectrum Doppler processing block 25,
The processing is performed after the INE buffer 52. Therefore, the Doppler signal stored in the cine memory can be displayed, and the Doppler sound can be reproduced.

On the other hand, the baseline shift switch 32
Is a switch on the operation panel for adjusting the zero line of the spectrum Doppler display, and is manually operated by an operator in the present embodiment.

When the operator operates the baseline shift switch 32 to perform a baseline shift (this operation is also called a zero shift), this switch signal is output to the next-stage baseline control code generator 33. In the code generator 33, software for generating a baseline control code is activated in response to the switch input. By this activation, the code signal for controlling the baseline is generated by the DSC 26
Is output to In the CFM mode, the coloring table of the V (average flow velocity) code of the RGB LUT is updated according to the switch input, and in the spectrum Doppler mode, the display position in the Y direction is changed.

In the case of the CFM mode or the spectrum Doppler mode, the ultrasonic pulse is a PRF (pulse repetition frequency).
Is transmitted and received on the basis of For this reason, the Doppler signal F
The frequency analysis by FT is restricted by the sampling time interval. Basically, half of the sampling frequency is the Nyquist frequency, and the frequency components exceeding this are displayed by folding back to the baseband. This phenomenon is called aliasing.

Since the Doppler signal is a complex number signal, the observation range of the frequency of the Doppler signal is basically in the range of "-1/2 to +1/2" of the sampling frequency. Even in the case where aliasing occurs, the aliasing is apparently eliminated by operating the baseline shift switch 32 and re-reading the position of frequency = 0 (center).
It is possible to display a spectrum Doppler image having good connection with the aliasing component exceeding the frequency of / 2.

The code signal for controlling the above-mentioned baseline is supplied from a generator 33 to a CBPF coefficient calculator 34.
Is also output to The arithmetic unit 34 performs a complex BPF (CBP) forming the direction separator 61 in accordance with the code signal.
The coefficient of F) is calculated based on an algorithm described later,
Output to the separator 61. Thereby, the coefficient of the complex BPF is changed.

As a result, aliasing has occurred until then, and the Doppler sound that was heard from the left and right speakers 31 on the forward and reverse sides (upside down) has been eliminated in order to eliminate the folded display. When the above-mentioned baseline shift process is performed, a Doppler sound that is not turned over by the left and right speakers 31 is output according to the above-mentioned coefficient change, which matches the display without folding. In the case of this Doppler sound, it is necessary to output a frequency component equal to or higher than the Nyquist frequency. Therefore, the output frequency after the processing is higher than the sample frequency at the time of input.

The outlines of the Doppler sound processing block 29 and the CBPF coefficient calculator 34 in this ultrasonic Doppler diagnostic apparatus are as described above. However, since these two components have a configuration related to the subject of the present invention, The configuration and operation will be described in detail below.

(Configuration and Operation of Audio Direction Separation) FIG. 2 shows the configuration of the direction separator 61 described above. The direction separator 61 includes a zero inserter 61A composed of two channels of a real component component and an imaginary component component for inputting a Doppler signal (IQ signal) that is a complex number signal, and an inserter 6A.
Two complex bandpass filters (C
omplex BPF (CBPF) 61B, 61C. One CBPF 61B is assigned to the forward flow side, and the other CBPF 61C is assigned to the reverse flow side. It can be seen that this configuration is significantly simplified as compared with the configuration of FIG. 11 showing an example of a conventional directional separator.

The zero inserter 61A inputs a Doppler signal and inserts zero (0) between the signal values. This is because the zero insertion causes the length of the Doppler signal in the time series direction to be an integer N times (N = 2, 3,...)
This is performed for each of the real part channel and the imaginary part channel. For example, when doubling (N = 2), zero is inserted between each signal value for the real part signal and the imaginary part signal of the Doppler signal. This example is shown in FIGS. 3 (a) and 3 (c). By inserting every other signal value = zero, FIG.
(C), the waveform of the original Doppler signal (for example, the imaginary part channel) is arranged in the time series direction in the order of zero, signal value, zero, signal value,. Thereby, the waveform of the Doppler signal is doubled in the time axis direction.

The zero insertion unit 61A executes the above-described zero insertion operation by software based on the calculation algorithm of the following equation (1). Note that the same expression is shown using pseudo code.

[0052]

(Equation 3)

Now, assuming that the above-mentioned zero insertion is performed at N = 2, the power spectrum of the original Doppler signal (for example, the imaginary part channel) before the zero insertion shown in FIG. It is represented as shown in FIG. On the other hand, the power spectrum of the Doppler signal of FIG. 3C obtained by zero insertion is expressed as shown in FIG.
That is, the original spectrum component becomes lower (compressed image), and another spectrum component appears on the negative side instead.

The zero-inserted Doppler signal is a CBPF
61B and 61C, respectively, and subjected to band-pass filtering processing. In the band pass filtering, the coefficients of the CBPFs 61B and 61C are controlled according to the shift amount of the baseline. This shift amount information is passed from the baseline control code generator 33 to the CBPF coefficient calculator 34.

The coefficient controlled CBPFs 61B and 61B
C filters the Doppler signal, thereby providing an audio signal for Doppler sound that is substantially directionally separated beyond Nyquist.

A series of processes including the calculation of the filter coefficient will be described in detail.

4 (a) and 4 (b), when the Doppler spectrum display is performed, a folded portion (a portion (A) in FIG. 4 (a)) occurs, and the operator shifts the baseline shift switch 32. An example is shown in which the base line BL of the Doppler spectrum image has been shifted by operation. By shifting the baseline BL by −0.25 (that is, the baseline shift amount BLS = −0.2
5), as shown in FIG. 5B, the folded portion (A) moves beyond the Nyquist frequency, and a well connected Doppler spectrum is obtained on the display.

In parallel with the display of the Doppler spectrum, the baseline control code generator 33
The CBPF 61 according to the shift amount of the baseline described above.
B, Set the bandwidth and center frequency of 61C. This setting is a multiple N of zero insertion and CBPF 61B, 61C
Is performed in accordance with the multiple N of the sampling frequency.

Now, the CBP on the forward stream side
The bandwidth and center frequency of F61B are set to FB and FBC, respectively.
When the bandwidth and center frequency of the CBPF 61C on the reverse flow (Reverse) side are RB and RBC, respectively,
Baseline shift BL when N = 2, ie, double zero insertion and sampling frequency of “2 · fs”
The values according to the amount of S are as shown in Table 1.

[0060]

[Table 1]

In the actual design, the bandwidth is set to be small in consideration of the cutoff characteristics of the filter.

The calculation algorithm of the bandwidths and center frequencies of the CBPFs 61B and 61C is represented by the following equation (2) using pseudo codes.

[0063]

(Equation 4)

The coefficients of the CBPFs 61B and 61C are calculated by the CBPF coefficient calculator 34 by software so as to correspond to the shift amounts of the bandwidths and the center frequencies of the CBPFs 61B and 61C on the upstream and downstream sides calculated as described above.

First, FIG. 5A shows a complex BPF having a bandwidth FB, and FIG. 5B shows a complex BPF shown in FIG.
Is shifted by FBC. The transfer function of the model in FIG. 3A is H (Z), and Z is Z = e.
xp (j * w) and (w: angular frequency), the transfer function of the model in FIG.
(Z ′) = H ′ (Z). The input to the model of FIG. 9A is X (Z) and the output is Y (Z). Each of the transfer functions H (Z) and H '(Z) is calculated by equation (3).

[0066]

(Equation 5) Here, the coefficient sequences ai and bi are, for example,

[B, A] = BUTTER (N, fc) is obtained as a function of a Butterworth filter of cutoff frequency = fc and order = N. The BUTTER function is a library function of the commercially available mathematical software “Matlab” (Matlab), and is a function for calculating coefficients of an Nth-order low-pass filter. Using this BUTTER function, the coefficient sequences B and A of the filter are obtained.

As described above, as an example, the complex band-pass filter has a function [B, B] having a coefficient sequence [ai, bi].
A] = Butterworth filter represented by BUTTER (N, fc). As the complex bandpass filter, a filter such as Bessel, Chebyshev, or elliptic, which can freely select a cutoff characteristic, may be used.

The center frequency of the complex BPF represented by the model of FIG.
In order to have the band characteristic shown by the model in FIG.

(Equation 7) May be calculated. Here, when the angular frequency w is represented by a frequency f normalized by a sampling frequency, w = 2πf.

The operation algorithm for the above-described order N filter coefficient and its center frequency shift is represented by the following equation (4) using pseudo code.

[0070]

(Equation 8)

The CB of the coefficient sequence [Bfd, Afd], [Brd, Ard] on the forward / reverse side obtained by equation (4)
By the PFs 61B and 61C, the output X after zero insertion by the zero inserter 61A is sampled at a sampling frequency of N times (for example, 2 times) and subjected to complex filtering. The operation algorithm of this filter is shown in the following equation (5) using pseudo code.

[0072]

(Equation 9)

The output X after zero insertion is a complex number.
The BPFs 61B and 61C are among the complex-filtered signals, the signals Real (Y1) and Re on the real channel side.
al (Y2) is output as a forward-flow side and reverse-flow side audio signal at the same sampling frequency N times (for example, twice) as the input.

The operation and effect of the above processing will be described in comparison with the direction separation of Doppler sound when zero insertion is not performed.

FIG. 6 shows a contradiction occurring between the direction separation of the Doppler sound and the Doppler spectrum display when the above-mentioned zero insertion is not performed. 4A and 4B, the sampling frequency of the FFT 53 is also N times (for example, N times) without zero insertion.
= 2), the correspondence between the Doppler spectrum display and the audio sound separation is as shown in FIG.
This is schematically illustrated as in (c) ((b) in the figure shows a case where the baseline shift is not performed).

In the power spectrum shown in FIG.
If the positive frequency band is assigned to the forward flow side (Forward) and the negative frequency band is assigned to the reverse flow side (Reverse), the Doppler sound in the folded portion (A) is output as an audio component within the Nyquist frequency on the reverse flow side. You. In the Doppler spectrum display at this time, as shown in FIG. 4 (b), the folded portion is continuously displayed on the forward flow side beyond the Nyquist frequency. In other words, there is a discrepancy between the Doppler sound and the Doppler spectrum display in the direction of movement of the blood flow forming the folded portion (A) with respect to the probe 11, which confuses the operator. This contradiction, under such circumstances,
It does not change even if the allocation method of the forward flow side and the reverse flow side of the Doppler sound is reversed.

However, according to the direction separation of the Doppler sound according to the present embodiment, as described above, a method combining zero insertion and CBPF is employed. At this time, the correspondence between the direction separation of the Doppler sound and the Doppler spectrum display is represented as shown in FIG. The example of FIG. 7 shows a case of zero insertion of N = 2 in the zero inserter 61A and sampling at twice the sampling frequency of 2 · fs in the CBPFs 61B and 61C as shown in FIG. 3 described above.

In this case, the power spectrum shown in FIG. 7A has two spectra in the positive and negative bands as shown in FIG. 3D described above, and its frequency component is before zero insertion. Lower than. It is assumed that the separation directions of the Doppler sounds on the forward flow side and the reverse flow side are allocated in the same manner as described above. In this case, in the Doppler spectrum display of FIG. 4B in which the base line BL is shifted, the folded portion (A)
Since the frequency component of exceeds the Nyquist frequency on the forward stream side, as shown in FIG. 7C, it is output as a Doppler sound in the forward stream direction.

For this reason, even when the zero line shift shown in FIG. 4 is performed, in the Doppler spectrum display of FIG. 4B, the portion (A) displayed beyond Nyquist and the speaker on the downstream side of that portion are displayed. The consistency with the audible Doppler sound is ensured.

Here, FIGS. 8 to 10 show the results of simulations performed by the inventor based on the present invention.

First, as a precondition, a clutter component (frequency:-) imitating a Doppler signal obtained from an actual living body is used.
0.08 * fs, power: 0 dB), blood flow component (frequency: + 0.24 * fs, power: -10 dB), and white noise (power: about -60 dB) were set.
Under this condition, as the parameters of the signal processing of the direction separator 61 shown in FIG.
Filter order = 8 was set.

FIG. 8 shows the input signal waveforms (real part channel, imaginary part channel), the power spectrum thereof, and the signal spectrum after zero insertion. In the input signal, two peaks can be confirmed at -0.08 and +0.24. The spectrum after zero insertion has -0.08 and +
In addition to 0.24, their alias component +0.9
A total of four peaks can be confirmed at 2 and -0.76. Here, since the signal after zero insertion is signal-processed at twice the sampling frequency, the spectrum after zero insertion shown in FIG. 8 is displayed with a frequency range of -1 to +1.

FIG. 9 shows a base line shift (BL
S) is the downstream side after directional separation when Forward is (Forward)
d) and a reverse side (Reverse) waveform and power spectrum are shown. In this case, +0.2 on the downstream side
It can be seen that four components pass and the -0.08 component attenuates about 30 dB, while the -0.08 component passes on the backflow side.

FIG. 10 shows the waveforms and power spectrums on the forward flow side and the reverse flow side after the direction separation when the baseline shift (BLS) is +0.4. In this case, the base line moves to +0.4, and the band from +0.4 to +0.5 is on the forward flow side, so that no signal exists in this band and no Doppler sound is generated. Conversely, since the band on the reverse flow side expands from +0.4 to -0.5, the -0.76 component, which is the alias component of the +0.24 component as well as the -0.08 component, is generated as Doppler sound. You can see that.

Since the direction separating circuit of the present invention can be basically composed of two complex BPFs (Complex BPF: CBPF), the processing is simple regardless of whether it is realized by hardware or software. so,
The load can be reduced.

Table 2 compares the algorithm based on the configuration shown in FIG. 11, which is the conventional method described above, with the algorithm based on the configuration shown in FIG. 2 according to the present invention in terms of the amount of signal processing. This signal processing is performed from the point of view of real-time processing by using parameters (for example, PRF (Pulse R
(e.g., epi frequency (Frequency), baseline shift amount, Doppler switching in forward / reverse direction, etc.), and a non-real-time calculation process for outputting a Doppler sound. Both processes are the same in terms of load, but the former is mainly software processing and the latter is mainly hardware processing.

In the case of the direction separation method according to the present invention, since filtering of complex numbers is used, the weight of the load varies depending on the architecture, but as can be seen from Table 2, non-real-time processing and real-time processing In both processes, the load is reduced by about half compared to the conventional method.

[0088]

[Table 2]

As a result, the ultrasonic Doppler diagnostic apparatus according to the present invention can significantly downsize, reduce costs, save energy, and speed up processing as compared with the conventional ultrasonic Doppler diagnostic apparatus.

The configuration of the ultrasonic Doppler diagnostic apparatus according to the present invention is not limited to the configuration of the above-described embodiment, and those skilled in the art can understand the scope of the present invention described in the appended claims. The present invention can be appropriately modified within the above, and those forms are also included in the present invention. For example, the equations (1) to
The operation according to (5) can be executed as software processing of a signal processing chip such as a DSP, and can be executed by ASCI or FPG.
The processing can also be executed by a hardware device such as A.

[0091]

As described above, according to the ultrasonic Doppler diagnostic apparatus of the present invention, the direction of the Doppler signal can be separated by simplifying the hardware configuration or reducing the arithmetic processing by software. Therefore, the speed and weight of the direction separation operation can be reduced. At the same time, even when the baseline shift (zero shift) is performed on the screen of the Doppler spectrum display, the Doppler sound consistent with the Doppler spectrum display screen can always be generated with respect to the direction separation of the Doppler signal.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a circuit configuration centering on a direction separator.

FIG. 3 is a view for explaining insertion of a zero into a Doppler signal and a power spectrum.

FIG. 4 is a screen diagram illustrating a return in Doppler spectrum display.

FIG. 5 shows a power spectrum of a BPF having a bandwidth of FB and a BP obtained by shifting its center frequency by “FBC”.
The figure which shows the power spectrum of F.

FIG. 6 is a diagram illustrating direction separation processing when zero insertion is not performed.

FIG. 7 is a view for explaining direction separation processing when zero insertion is performed (N = 2).

FIG. 8 is a graph showing simulation results.

FIG. 9 is a graph showing a simulation result.

FIG. 10 is a graph showing simulation results.

FIG. 11 is a schematic block diagram showing an example of conventional audio direction separation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Probe 12 Main body 21 Transmitter / receiver 23 Quadrature phase detector 24 CFM processing block 25 Spectrum Doppler processing block 26 DSC 27 Color processor 28 Monitor 29 Doppler sound processing block 30 Power amplifier (left and right) (for Doppler sound output means of the present invention) 31 Speaker (left and right) (corresponding to Doppler sound output means of the present invention) 32 Baseline shift switch (corresponding to baseline control means of the present invention) 33 Baseline control code generator (corresponding to the baseline control means of the present invention) 34 CBPF coefficient calculator (corresponding to the characteristic changing means of the present invention) 61 Direction separator 61A Zero inserter (corresponding to the zero inserting means of the present invention) 61B, 61C Complex BPF

Claims (13)

[Claims] 1. A separation for separating a moving direction of a moving object presenting a Doppler signal from a digital Doppler signal composed of a complex signal obtained by processing an echo signal obtained by transmitting an ultrasonic signal to a subject. In the ultrasonic Doppler diagnostic apparatus provided with means, a zero value is inserted into the separation means so that the number of data is N times longer in the time axis direction (N is a positive integer: N ≧ 2). Inserting means for assigning the Doppler signal having the zero value inserted therein to a complex band bus, wherein the sampling frequency is N times the sampling frequency before the zero value is inserted into the Doppler signal, and the Doppler signal is assigned to each of the motion directions. Two complex BPFs (Bandpass Filter) to be filtered
r), an ultrasonic Doppler diagnostic apparatus, comprising: 2. The Doppler sound output device according to claim 1, wherein the signal subjected to complex bandpass filtering by each of the two complex BPFs is output as the Doppler sound separated from the motion direction. Ultrasonic Doppler diagnostic device equipped with: 3. The ultrasonic Doppler diagnostic apparatus according to claim 1, further comprising: an ultrasonic probe for transmitting the ultrasonic signal to the subject and receiving the echo signal from the subject. The ultrasonic Doppler diagnostic apparatus, wherein the moving direction is both a direction in which the moving body moves toward the ultrasonic probe and a direction in which the moving body moves away from the ultrasonic probe. 4. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein the integral multiple is two times. 5. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein a display means for displaying a Doppler spectrum based on the echo signal, and a folded portion on a screen of the Doppler spectrum display. Baseline control means for shifting the baseline to eliminate the noise, and characteristic changing means for changing the filtering characteristics of the two complex BPFs according to the shift amount when the baseline is shifted. Ultrasonic Doppler diagnostic device. 6. The ultrasonic Doppler diagnostic apparatus according to claim 5, wherein the characteristic changing unit is a unit that changes a filter coefficient of each of the two complex BPFs according to the shift amount. apparatus. 7. The ultrasonic Doppler diagnostic apparatus according to claim 6, wherein each of said two complex BPFs is formed as a digital filter, and said characteristic changing means is functionally formed by software processing. Ultrasonic Doppler diagnostic device. 8. A Doppler signal composed of a complex signal obtained by processing an echo signal obtained by transmitting an ultrasonic signal to a subject, and inserting a zero value into the Doppler signal to make the signal an integer multiple length in the time axis direction. After that, the processing of the insertion of the zero value at a frequency obtained by multiplying the sampling frequency when the zero value is not inserted into the Doppler signal by the integer is assigned to each of the motion directions of the moving body presenting the Doppler signal A Doppler sound generating method for sampling the received Doppler signal at a double speed and applying the complex bandpass filtering, and outputting the signal subjected to the complex bandpass filtering as the Doppler sound separated from the motion direction. 9. A shift amount of a base line for eliminating a folded portion on a screen of a Doppler spectrum display by using a filter coefficient of a complex band pass filter for subjecting a Doppler signal composed of a complex signal to a complex band pass filtering process. Doppler signal processing method changed according to. 10. The Doppler signal processing method according to claim 9, wherein the filter coefficient is changed by changing a filter coefficient of a complex band-pass filter having a predetermined bandwidth and a center frequency = 0 by: = Z * exp (-j * FBC) (where the transfer function of the complex BPF having the predetermined bandwidth before shifting = H (Z), the transfer function of the BPF of the predetermined bandwidth obtained by shifting the center frequency by FBC = H (Z ') =
H '(Z), Z = exp (j * w), FBC: complex BP
The shift amount of the center frequency of F, w: angular frequency. ) Is a method for processing Doppler signals. 11. The Doppler signal processing method according to claim 10, wherein a filter coefficient of the complex band-pass filter having the predetermined bandwidth and the center frequency = 0 is (Here, N: filter order, ai, bi: coefficient) A method of processing a Doppler signal obtained as a coefficient sequence [ai, bi] by calculation. 12. The Doppler signal processing method according to claim 9, wherein the Doppler signal to be filtered by the complex bandpass filter has a zero value inserted into a Doppler signal obtained from an echo signal. The complex band-pass filter is a signal obtained by multiplying the sampling frequency when the zero value is not inserted into the Doppler signal by the integer, A Doppler signal processing method in which bandpass filtering is performed on a Doppler signal in which a value is inserted by double-speed sampling. 13. A program for causing a computer to execute the procedure for processing a Doppler signal according to claim 11. Description: