JP2000051215A - Ultrasonic spectrum doppler diagnosing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the circuit scale of a filter for emphasizing bloodstream components while attenuating the clutter components in an ultrasonic spectrum doppler diagnosing device. SOLUTION: This device is provided with a transmitting/receiving circuit 24 transmitting/receiving ultrasonic waves to a subject and detecting an obtaining echo signal by an orthogonal phase to obtain a doppler signal expressing a doppler shifting frequency component, an FFT window circuit 26 segmenting the doppler signal by folding a window function into the doppler signal on a time area, an FFT 27 frequency-analyzing the segmented doppler signal to obtain a frequency spectrum, a post filter 28 folding a filtering function into the frequency spectrum on a frequency area to attenuate the clutter component to emphasize a bloodstream component, a DSC 32 and a display 33 which arranges and displays the frequency spectrum passing through the filter 28 along the time base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic spectrum Doppler diagnostic apparatus, and more particularly to a filtering apparatus which attenuates low frequency components corresponding to clutter components and relatively emphasizes high frequency components corresponding to blood flow components. Regarding improvement.

[0002]

2. Description of the Related Art In conventional signal processing of a blood flow Doppler, a clutter component having a low frequency and a high power, which is a reflection component from an organ wall such as a heart, is mixed into an echo signal. In order to analyze a minute blood flow component with high sensitivity at the time of analysis, it is necessary to sufficiently remove the clutter component by a high-pass filter (HPF) before inputting to a frequency analyzer.

FIG. 6 is a block diagram showing a conventional ultrasonic spectrum Doppler diagnostic apparatus. A Doppler signal (complex quadrature detection component) is obtained by subjecting the signal received via the probe 1 to quadrature detection by the transmission / reception circuit (T & R) 2. In the pulse wave (PW) mode, a range gate (RG) 4 is applied to the Doppler signal for each rate cycle. In the continuous wave (CW) mode, the frequency band of the Doppler signal is reduced to the sampling frequency of the fast Fourier transformer (FFT) 7 instead of the range gate 4.

The clutter component is sufficiently removed by performing a filtering process on the Doppler signal on the time domain by the next high-pass filter 5. Note that the high-pass filter 5 is located upstream of the FFT 7 in the flow of signal processing, and is hereinafter referred to as a pre-filter. The pre-filter 5 is actually a time-series IIR
A type filter is employed.

The input signal of the FFT 7 is cut out to a finite length by convolving a window function such as a Hanning function in the time domain by the FFT window circuit 6 with the signal from which the clutter component has been removed by the pre-filter 5.
A frequency analysis is performed at T7. As a result, a frequency spectrum representing the strength of each frequency component is calculated. By arranging the frequency spectrum along the time axis by performing luminance modulation according to the intensity, a temporal change of the spectrum is displayed.

Here, the input word length of the FFT 7 is relatively short, about 8 bits, and if the high power clutter component is not sufficiently attenuated, it becomes saturated quickly and cannot be analyzed with high sensitivity. Therefore, the cut-off frequency of the pre-filter 5 can be switched from the operation panel 10 via the filter controller 8 in accordance with the position or the like.

Further, by operating the operation panel 10, the rate frequency fr, scroll speed and the like can be freely changed. When the rate frequency fr and the scroll speed are changed, the ratio of the resolution of the frequency (vertical direction) to the resolution of the time (horizontal direction) in the spectrum display changes. In order to keep this ratio optimal, the window controller 9 adjusts the window width of the FFT window circuit 6. For example, when the window width is reduced, the frequency resolution is reduced, and the spectrum display becomes coarse in the vertical direction.

In such a conventional apparatus, since the input word length of the frequency analyzer, that is, the FFT 7, is short, the clutter component is buried in the clutter component unless the pre-filter 5 sufficiently removes the clutter component. The sensitivity of the signal is reduced. In addition, a situation occurs in which the inside of the FFT 7 is saturated with the clutter component.

In order to avoid such a situation, it is necessary to improve the performance of the pre-filter 5, that is, a high-order IIR filter whose cutoff frequency is variable. For this reason, the circuit scale of the prefilter 5 becomes enormous.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic spectrum Doppler diagnostic apparatus which attenuates low frequency components corresponding to clutter components and relatively emphasizes high frequency components corresponding to blood flow components. To reduce the circuit scale of the filter for the purpose.

[0011]

According to the present invention, there is provided a transmitting / receiving means for transmitting / receiving an ultrasonic wave to / from a subject, and detecting Doppler polarization by detecting an echo signal obtained by the transmitting / receiving means in a quadrature phase. Means for obtaining a Doppler signal representing a shift frequency component, means for performing frequency analysis on a Doppler signal cut out by convolving a window function on the Doppler signal in the time domain, and means for obtaining a frequency spectrum, and means for obtaining the frequency spectrum in the frequency domain. Filter means for attenuating low-frequency components corresponding to clutter components by convolving a filtering function and relatively enhancing high-frequency components corresponding to blood flow components, and a frequency spectrum passing through the filter means along a time axis. Means for displaying the images side by side.

As described above, by applying a filter on the frequency domain to the frequency spectrum after the frequency analysis, the filter is more filtered than the conventional Doppler signal on the time domain before the frequency analysis. Circuit size can be reduced. (2) The invention provides the apparatus according to (1), wherein the filtering function is a function obtained by convolving a sampling function on a frequency domain corresponding to the window function with a filtering function indicating a high-pass filter characteristic. Is set to

Since the filter in the frequency domain only convolves the filtering function with respect to the frequency spectrum, the steepness such that the low frequency component corresponding to the clutter component is completely removed and only the high frequency component corresponding to the blood flow component is left. , It is easy to give an ideal filtering function, but in this case, the frequency spectrum looks like the conventional one, and a gentle filter that is not steep in the time domain is applied to the Doppler signal before frequency analysis. Since it is very different from the case, it is difficult for a physician who is familiar with the conventional appearance to make a diagnosis, and even a risk of a misdiagnosis may occur. Actually, not only the pre-filter but also a sampling function corresponding to the window function is applied to the Doppler signal in the frequency domain. Therefore, a function obtained by convolving the sampling function with a gentle filtering function that is close to the high-pass filter characteristic of a conventional filter applied in the time domain,
By giving it to the filter means, it becomes possible to provide a conventional appearance. (3) In the apparatus according to (1), the filtering function may be determined based on a cutoff frequency for attenuating the clutter component and enhancing the blood flow component, and a window width of the window function. The apparatus further includes means for changing.

It may be necessary to change the rate frequency fr for reasons such as to increase the maximum speed detection capability, or to change the scroll speed in order to optimize the time resolution. By changing these rate frequency fr and scroll speed, in the spectrum display,
The ratio of the resolution of the frequency (vertical direction) to the resolution of the time (horizontal direction) changes. In order to keep this ratio optimal, the time width of the input data for frequency analysis is changed, and the window width of the window function is changed accordingly. In addition, since the blood flow velocity and the velocity of the organ wall vary depending on the site, the cutoff frequency must be changed each time the site is changed. By changing the filtering function in accordance with the cutoff frequency and the window width of the window function which can be optionally changed according to the situation, the clutter component is appropriately removed, and the appearance similar to the conventional one is obtained. Can be provided stably.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic spectrum Doppler diagnostic apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an ultrasonic spectrum Doppler diagnostic apparatus according to the present embodiment. A plurality of piezoelectric elements for mutually converting an electric signal and an acoustic signal are arranged at a tip portion of the ultrasonic probe 21. A transmission / reception circuit (T & R) 22 is connected to the ultrasonic probe 21.

The transmission / reception circuit 22 includes a transmission part, a reception part, and a quadrature detection part. In the transmission part, first, the clock from the clock generator is frequency-divided to about 4 kHz to 50 kHz. The transmission / reception rate (the number of transmissions / receptions per second) of the ultrasonic pulse is determined according to the frequency-divided signal, and this is generally called a rate pulse.
It is called a rate frequency or a rate frequency fr.
After appropriately delaying this rate pulse, a voltage pulse is applied to the piezoelectric element of the probe 21 from the pulser using this as a trigger. With this application, the piezoelectric element of the probe 21 mechanically vibrates, generating an ultrasonic pulse.

This ultrasonic wave propagates inside the subject, is reflected on a discontinuous surface of acoustic impedance in the middle thereof, returns to the probe 21, and mechanically vibrates the piezoelectric element.
As a result, a weak electric signal is generated from the piezoelectric element. This electric signal is taken into the receiving portion, amplified individually by the preamplifier, and then subjected to phasing addition.

The received signal generated by the phasing addition is converted into the center frequency f of the transmitted ultrasonic wave in the quadrature detection part.
Multiplied by a reference signal having the same frequency as 0, and 90
掛 け By multiplying by the phase-shifted reference signal, frequency components of the Doppler shift frequency fd and (2f0 + fd) are obtained, and from each of them, (2f0 + f) by a low-pass filter.
By removing the frequency component of d), a detection signal of two channels having different phases and having only the component of the Doppler shift frequency fd can be obtained.

The detected signal is supplied to a range gate (RG) 24.
Apply gate to cut out the Doppler signal of the sample volume set to an arbitrary depth. In addition, continuous wave (CW)
In the mode, the frequency band of the Doppler signal is reduced to the sampling frequency of the fast Fourier transformer (FFT) 27 instead of the range gate 24.

The Doppler signal cut out by the range gate 24 is subjected to frequency analysis by a fast Fourier transformer (FFT) 27 via a prefilter 25 and an FFT window circuit 26. This pre-filter 25 has a function only to narrow the dynamic range for the unit for processing the audio sound, and attenuates a low-frequency component corresponding to a clutter component like a conventional pre-filter, It has no function of relatively emphasizing high frequency components corresponding to blood flow components. Therefore, removing the pre-filter 25 does not affect the frequency analysis.

The FFT window circuit 26 cuts out the input data to the FFT 27 to a finite length by convolving the Doppler signal with a window function such as a Hanning function in the time domain. The FFT 7 performs a frequency analysis on the Doppler signal. As a result, a frequency spectrum representing the strength of each frequency component is calculated.

Here, the input word length of the FFT 27 is set to be sufficiently long, for example, about 32 bits, so that the Doppler signal whose power is relatively unstable due to the removal of the clutter component is not stably saturated. Have been.

The operation panel 31 can freely change the rate frequency fr, scroll speed, and the like. When these rate frequency fr and scroll speed are changed, time (horizontal)
The ratio of the resolution of the frequency (vertical direction) to the resolution of the image changes. The window controller 30 adjusts the window width of the window function of the FFT window circuit 26 so as to keep this ratio optimal.

In the signal processing flow, the post filter 28 located immediately downstream of the FFT 27 convolves the filtering function on the frequency spectrum obtained by the FFT 7 in the frequency domain, that is, weights each frequency component. do. Since this filtering function is set to high-pass type filter characteristics,
In the post filter 28, a low frequency component corresponding to the clutter component is attenuated, and a high frequency component corresponding to the blood flow component is relatively emphasized.

The filtering function of the post-filter 28 includes a cut-off frequency set by the filter controller 29 from the operation panel 31 according to the position, and a frequency (vertical direction) with respect to the resolution of time (horizontal direction).
The optimum resolution is switched and set based on the window width of the window function of the FFT window circuit 26 adjusted by the window controller 30 in order to maintain the optimal resolution ratio.

The frequency spectrum that has passed through the post filter 28 is subjected to luminance modulation according to its intensity in the digital scan converter 32, arranged along the time axis, and displayed on the display 33 as a time-dependent change in the spectrum. Is displayed.

As described above, the pre-filter 25 is not provided with the filter function of attenuating the low-frequency component corresponding to the clutter component and relatively emphasizing the high-frequency component corresponding to the blood flow component as in the related art. By providing the post-filter 28 downstream of the FFT 27, the size of a filter circuit that attenuates low-frequency components corresponding to clutter components and relatively emphasizes high-frequency components corresponding to blood flow components is reduced. be able to. The reason for this is that when a Doppler signal is filtered in the time domain before frequency analysis as in the prior art, a high-order IIR filter of about the 7th order with a variable cutoff frequency is required. By performing on the frequency domain, it is possible to reduce the weight of each frequency component by a simple circuit that assigns a weight according to the filtering function.

Next, a filtering function (filter characteristic) given to the post filter 28 will be described. The filter processing in the frequency domain only convolves the filtering function with the frequency spectrum, so that the low-frequency component corresponding to the clutter component is completely removed, and the cut-off frequency that leaves only the high-frequency component corresponding to the blood flow component It is easy to give the ideal filter characteristics that change steeply in this case, but in this case, the appearance of the display of the frequency spectrum is steep in the time domain with respect to the Doppler signal before the frequency analysis as in the past. This is significantly different from the case of applying a non-filter, so that it is difficult for a doctor who is familiar with the conventional appearance to make a diagnosis and even a risk of a misdiagnosis may occur.

Therefore, by giving to the post-filter 28 a filtering function showing a filter characteristic similar to that of the conventional pre-filter, that is, a non-steep filter characteristic whose attenuation rate gradually changes near the cut-off frequency, a view similar to the conventional one can be obtained. Is realized.

Further, a filtering function obtained by convolving a sampling function described below with a filtering function corresponding to a filter characteristic similar to that of the conventional pre-filter is given to the post-filter 28, so that the spectrum Is even more conventional.

FIG. 2A shows a window function W1 in the time domain.
(T) is shown. fr is the rate frequency (unit H)
z), the number of data of the FFT 27 is N, the time width Ww of the FFT 27 is N / fr, and the window width of the window function W1 (t) is N · Ww /
fr. Window function W1 in Doppler signal in time domain
When (t) is applied, in the frequency domain, the sampling function PW (f) as shown in FIG. 2B is convolved with the Doppler signal in the frequency domain. Therefore, conventionally,
The spectrum of the Doppler signal is changed not only by the pre-filter but also by the FFT window circuit 26 at the time of clipping by the window function.

Therefore, as shown in FIG. 3, the sampling function PW (f) corresponding to the window function W1 (t) is convolved with the filtering function P1 (f) corresponding to the same filter characteristics as the conventional prefilter. By giving the filtering function P2 (f) obtained by the embedding to the post-filter 28, the appearance of the spectrum becomes further closer to the conventional one.

The filtering function P1 (f) of the conventional prefilter can be changed by the cutoff frequency. The sampling function PW (f) is a window function W1 (t)
The window function W1 (t) is defined by the window width, and the window width of the window function W1 (t) is determined depending on the time width N / fr of the FFT 27. Then, the cut-off frequency is changed according to the part, and the time width N / fr of the FFT 27 is changed when the rate frequency fr is changed.
It is changed so that the ratio of the resolution of the frequency (vertical direction) to the resolution of the time (horizontal direction) is kept optimal. Accordingly, the filtering function P2 (f) applied to the post filter 28 following the cutoff frequency and the window width of the window function.
Is changed by the filter controller 29 so that
Even if the cutoff frequency and the window width change,
The appearance of the spectrum can be made closer to the conventional one (see FIGS. 4 and 5). It is needless to say that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

[0034]

According to the present invention, in an ultrasonic spectrum Doppler diagnostic apparatus, a filter for attenuating low frequency components corresponding to clutter components and relatively emphasizing high frequency components corresponding to blood flow components is provided. The circuit scale can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ultrasonic spectrum Doppler diagnostic apparatus according to a preferred embodiment of the present invention.

2A is a diagram showing an example of a window function given to the FFT window circuit diagram of FIG. 1, and FIG. 2B is a diagram showing a sampling function in the frequency domain of the window function.

FIG. 3 is a view showing a principle of deriving a filter characteristic given to the post filter of FIG. 1;

FIG. 4 is a diagram illustrating filter characteristics of a post filter set when a window width is 64 and a cutoff is ４.

FIG. 5 is a view showing filter characteristics of a post filter set when a window width is 256 and a cutoff is 1/64.

FIG. 6 is a block diagram of a conventional ultrasonic spectrum Doppler diagnostic apparatus.

[Explanation of symbols]

 Reference Signs List 21 ultrasonic probe, 22 transmission / reception circuit (T & R), 24 range gate, 25 prefilter, 26 FFT window circuit, 27 fast Fourier transformer (FFT), 28 post filter, 29 filter controller 30 ... window controller, 31 ... operation panel, 32 ... digital scan converter (DSC), 33 ... display.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takanobu Uchibori 2-16-4 Akabane, Kita-ku, Tokyo F-term (reference) in Toshiba Medical System Engineering Co., Ltd. 4C301 AA02 DD01 DD03 DD04 EE05 EE15 GB02 HH04 HH54 JB06 JB07 JB32 JB34 JB35 JB38 JB42 JB50 KK09 KK36 LL04

Claims (3)

[Claims] A transmitting / receiving means for transmitting / receiving an ultrasonic wave to / from a subject; and a means for obtaining a Doppler signal representing a Doppler shift frequency component by detecting an echo signal obtained by the transmitting / receiving means in a quadrature phase. A means for obtaining a frequency spectrum by subjecting the Doppler signal cut out by convolving a window function to the Doppler signal on a time domain to obtain a frequency spectrum, and convolving a filtering function on the frequency domain with the frequency spectrum to cope with a clutter component. Filter means for attenuating the low-frequency component to be applied and relatively emphasizing the high-frequency component corresponding to the blood flow component, and means for displaying the frequency spectrum passing through the filter means along the time axis. Ultrasound spectrum Doppler diagnostic equipment. 2. The filtering function according to claim 1, wherein the filtering function is a function obtained by convolving a sampling function on a frequency domain corresponding to the window function with a filtering function indicating a high-pass filter characteristic that changes gradually near a cutoff frequency. 2. The ultrasonic spectrum Doppler diagnostic apparatus according to claim 1, wherein: 3. The apparatus according to claim 2, further comprising: a unit configured to change the filtering function based on a cutoff frequency for attenuating the clutter component and enhancing the blood flow component, and a window width of the window function. The ultrasonic spectrum Doppler diagnostic apparatus according to claim 1, wherein