JP3691874B2 - Ultrasonic diagnostic equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an ultrasonic diagnostic apparatus that obtains a Doppler spectrum by frequency analysis of a received signal.
[0002]
[Prior art]
Ultrasound has been applied in various ways from a medical standpoint, but the mainstream is an ultrasonic diagnostic apparatus that obtains a tomographic image of a soft tissue of a living body using an ultrasonic pulse reflection method. This ultrasonic diagnostic apparatus is a non-invasive examination method and displays a tomographic image of a tissue. Compared to other diagnostic apparatuses such as an X-ray diagnostic apparatus, an X-ray CT apparatus, an MRI, and a nuclear medicine diagnostic apparatus, the ultrasonic diagnostic apparatus is real-time. It has exclusive features such as display capability, small size and low cost, high safety without exposure to X-rays, and Doppler spectrum and blood flow imaging using the Doppler effect. Here, we focus on the Doppler spectrum. As a display of the Doppler spectrum, scroll display is used as in the M mode with the Doppler frequency (speed) on the vertical axis, the time and the luminance on the horizontal axis, and the strength (power) of each Doppler frequency component.
[0003]
In the Doppler spectrum function of such an ultrasonic diagnostic apparatus, burst waves have been put into practical use for the purpose of improving sensitivity. A burst wave refers to a series of a plurality of ultrasonic pulses. The time width of the burst wave is called the burst length. In the case of a burst wave, it is necessary to devise an integration process for Doppler signals in a range gate marker, unlike a pulse wave. In the previous case shown in FIG. 7A, only the Doppler signal received during the period t1 to t2 corresponding to the depth and length of the range gate marker is taken into the integration process. T1 is the time corresponding to the depth of the range gate marker from the transmission time t0 of the burst wave (the time required for the ultrasonic wave to propagate a distance twice the depth of the range gate marker in consideration of the round trip) ), And t2 is the time when the time corresponding to the length of the range gate marker (the time required for the ultrasonic wave to propagate the distance twice the length of the range gate marker) has elapsed from t1. It is. In this previous case, the burst length τ of the burst wave is not considered, that is, the reflected wave from the same reflection source is not considered to be continuously received during the burst length τ. As understood from the sensitivity distribution, a Doppler signal from a shallow region corresponding to τ from the range gate marker is taken into the integration process.
[0004]
A case devised to solve this problem is shown in FIG. In this case, the burst length τ of the burst wave is intentionally adjusted to half of the time corresponding to the length of the range gate marker. Then, only the Doppler signal received during the period t3 to t2 in the latter half of the period t1 to t2 corresponding to the depth and length of the range gate marker is taken into the integration process. As a result, the integration period and the burst length τ match. In this case, as understood from the sensitivity distribution of the integration signal, the Doppler signal outside the range gate marker is not taken into the integration process.
[0005]
However, the case of FIG. 7B has the following problems. In order to avoid a significant decrease in distance resolution, the burst length τ of the burst wave is limited. Therefore, when the range gate marker is set to be very long, there may occur a case where the integration period becomes longer than the longest burst length τmax as shown in FIG. In this case, there is a so-called insensitive area where the Doppler signal from the range gate marker is not taken into the integration process at all.
[0006]
The Doppler spectrum function also has the following problems. In the pulse wave Doppler (PW Doppler), when the length of the range gate marker is changed, the integration period changes. This change in the integration period means that the gain changes substantially. In continuous wave Doppler (CW Doppler), the Doppler signal is applied to a high-pass filter (HPF). When the rate frequency PRF is changed, the ratio of the output band to the input band of this high-pass filter changes. However, this change in the input / output bandwidth ratio means that the gain changes substantially. Furthermore, as can be said for both PW Doppler and CW Doppler, a change in the number of data of Fast Fourier Transform (FFT) as a frequency analysis means that the gain changes substantially. Therefore, there has been a problem that the noise level also changes as the gain changes.
[0007]
In PW Doppler, a function called alternate scan has been put to practical use in order to substantially reduce the rate frequency and improve the low-speed detection capability. Usually, a scan is performed in which the ultrasonic transmission / reception operation is repeated a predetermined number of times at a rate frequency with respect to a certain raster, and the next raster is sequentially moved. On the other hand, in the alternate scan, an ultrasonic transmission / reception operation is performed once for a certain raster, and 1 is performed for several other rasters before the next ultrasonic transmission / reception operation for the same raster. The ultrasonic transmission / reception operation is performed one by one. When one raster is viewed, the interval of the ultrasonic transmission / reception operation is increased, and the rate frequency is substantially reduced. The number of ultrasonic transmission / reception operations performed in the gap between the two ultrasonic transmission / reception operations before and after the same raster is defined as the number of alternating stages. An increase in the number of alternating stages means an extension of the data acquisition time if the number of frequency analysis data is constant. The extension of the data acquisition time leads to a change in the ratio between the frequency resolution and the time resolution on the Doppler spectrum display. Since this is not desirable, many current devices are equipped with a function to keep the ratio of frequency resolution to time resolution constant by decreasing the number of frequency analysis data as the number of alternating stages increases. Yes. However, a reduction in the number of data for frequency analysis degrades (decreases) the S / N.
[0008]
[Problems to be solved by the invention]
The purpose of the present invention, the change of the integration period is pulse wave Doppler, the number of data of the change in the ratio of the output band continuous wave Doppler for the input band of the high pass filter, fast Fourier transform of the frequency analysis (FFT) It is an object to provide an ultrasonic diagnostic apparatus in which the noise level does not change even if the gain changes substantially due to changes in the above .
[0009]
[Means for Solving the Problems]
An ultrasonic diagnostic apparatus according to the present invention includes a transmission / reception unit that transmits an ultrasonic pulse into a subject and receives a reflected wave to obtain a reception signal, and a specific period according to the depth and length of the range gate marker. Means for obtaining an integrated signal by integrating the received signal output from the transmitting / receiving means, means for analyzing the frequency of the integrated signal in order to obtain a Doppler spectrum in the range gate marker, the transmitting / receiving means, And a means for multiplying the received signal by a weighting factor corresponding to 1 / ΔT RG ^1/2, where ΔT RG is an integration period by the integrating means.
According to the present invention, when the integration period changes, the gain changes substantially and the noise level changes accordingly, but the received signal is multiplied by the weighting coefficient corresponding to the integration period. By canceling the substantial gain change accompanying the change, the noise level can be kept constant.
The ultrasonic diagnostic apparatus according to the present invention includes means for transmitting an ultrasonic wave as a continuous wave into a subject and receiving a reflected wave to obtain a received signal; and filter means for attenuating a specific frequency band of the received signal; Means for multiplying the output signal of the filter means by a weighting factor corresponding to the ratio of the input band of the filter means to the output band of the filter means; and frequency analysis of the output signal of the filter means to obtain a Doppler spectrum. Means.
According to the present invention, for example, when the rate frequency changes, the ratio of the input band to the output band of the filter means changes accordingly, the gain changes substantially, and the noise level also changes. By multiplying the output signal of the filter means by a corresponding weighting factor, this substantial gain change can be canceled and the noise level can be kept constant.
An ultrasonic diagnostic apparatus according to the present invention includes a means for obtaining a received signal by transmitting an ultrasonic wave into a subject and receiving a reflected wave, and a means for frequency-analyzing the received signal with the number of data to obtain a Doppler spectrum. And means for multiplying the received signal by a weighting factor 1 / N ^1/2 , where N is the number of data.
According to the present invention, when the number of data for frequency analysis changes, the gain substantially changes and the noise level also changes. By multiplying the received signal by a weighting factor corresponding to this number of data, this substantial The gain level can be canceled and the noise level can be kept constant.
[0019]
Embodiment
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to the first embodiment. The ultrasonic diagnostic apparatus according to this embodiment includes an ultrasonic probe 1, a transmission / reception system (T / R) 2, a spectrum Doppler unit 3, a digital scan converter (DSC) 4, a monitor 5, and a console 6.
[0020]
The ultrasonic probe 1 is provided with a piezoelectric element array at its tip, in which a plurality of piezoelectric elements as a reversible conversion element for mechanical motion / electrical signals such as piezoelectric ceramics are arranged one-dimensionally.
[0021]
The transmission / reception system 2 has a transmission system and a reception system. The transmission system includes a pulse generator, a transmission delay circuit, and a pulser. The pulse generator repeatedly generates rate pulses at a rate frequency fr (period: 1 / fr second) of 5 KHz, for example. This rate pulse is distributed to the number of channels and sent to the transmission delay circuit. The transmission delay circuit provides each rate pulse with a delay time necessary for focusing the ultrasonic wave into a beam and determining transmission directivity. The pulser applies a transmission voltage for each channel to the piezoelectric element of the ultrasonic probe 1 at the time when the rate pulse is received from the transmission delay circuit. Thereby, an ultrasonic beam is transmitted to the subject.
[0022]
The reflected wave reflected by the discontinuity surface (reflection source) of the acoustic impedance in the subject is received by the ultrasonic probe 1 and converted into an electric signal. The electrical signals output from the ultrasonic probe 1 for each element are collected for each channel and taken into the receiving system. The reception system includes a preamplifier, a reception delay circuit, an adder, and a phase detection circuit. The electric signal is amplified by a preamplifier, given a delay time necessary for determining reception directivity by a reception delay circuit, and added by an adder. By this addition, a reception signal in which the reflection component from the direction corresponding to the reception directivity is emphasized is obtained. This received signal is phase-detected by a phase detection circuit. Thereby, a Doppler signal having a deviation frequency due to the Doppler effect is obtained. The Doppler signal is supplied to the spectrum Doppler unit 3.
[0023]
The spectrum Doppler unit 3 takes out only the Doppler signal supplied during a specific period by the range gate marker unit 8, and uses a relatively fast moving high-frequency blood flow component and a relatively slow moving low-frequency blood vessel wall or valve. Each frequency component is separated by a high-pass filter 9 and then the Doppler signal that has passed through the high-pass filter 9 is analyzed in real time by a fast Fourier transform processing circuit (FFT) 10. Doppler spectrum data representing the strength of power is generated. The specific period during which the Doppler signal is extracted by the range gate marker unit 8 is controlled by the controller 7 based on the depth and length of the range gate marker marker set on the B-mode image via the console 6.
[0024]
The Doppler spectrum data obtained by the fast Fourier transform processing circuit 10 is displayed as a Doppler spectrum on the monitor 5 via the digital scan converter 4 and a digital analog converter (not shown). As a display of the Doppler spectrum, scroll display is used as in the M mode, with the Doppler frequency (speed) on the vertical axis, the time on the horizontal axis, and the luminance as the strength (power) of each Doppler frequency component.
[0025]
The range gate marker unit 8 amplitude-modulates the Doppler signal by a multiplier (amplifier) 11 and integrates the amplitude-modulated Doppler signal by an integrator 12 for a specific period. Amplitude modulation data by the multiplier 11 is supplied from the function generation ROM 13. The specific period during which the integrator 12 performs integration is adjusted by the RG width counter 14 and the RG start position counter 15.
[0026]
The RG start position counter 15 receives supply of RG position data corresponding to the depth of the range gate marker from the controller 7. The RG start position counter 15 starts counting clock pulses (up counting) from the start of scanning, and outputs a start pulse when the count value reaches the value represented by the RG position data.
[0027]
The RG width counter 14 receives supply of RG width data corresponding to the length of the range gate marker from the controller 7. The RG width counter 14 starts counting clock pulses (up-counting) at the time when the start pulse is received from the RG start position counter 15, and continues counting until the count value reaches the value represented by the RG width data. Therefore, the count signal is output from the RG width counter 14 only for a specific period corresponding to the depth and length of the range gate marker.
[0028]
The integrator 12 executes integration only during the period when the count signal is output from the RG width counter 14. Thereby, only the amplitude-modulated Doppler signal within a specific period is extracted as an integration signal.
[0029]
Thus, the period (integration period) of the Doppler signal extracted by the range gate unit 8 depends on the RG position data and the RG width data from the controller 7. In other words, it will be understood that the controller 7 can freely change the start time of the integration period and its time width by adjusting the RG position data and the RG width data.
[0030]
The function generation ROM 13 outputs the coefficient to the multiplier 11 only for a specific period during which the count signal is output from the RG width counter 14. The Doppler signal is amplitude-modulated by the multiplier 11 according to the coefficient from the function generation ROM 13.
[0031]
The function generation ROM 13 stores a plurality of types of weighting factors in advance. The function generation ROM 13 is supplied with a count value signal from the RG width counter 14 and a function selection signal from the controller 7 as an address signal. The coefficient of the address part corresponding to the address signal is read from the function generation ROM 13. The controller 7 selectively supplies one function selection signal corresponding to the sensitivity characteristic selected via the console 6 from the plurality of types of function selection signals to the function generation ROM 13. The function here means the time change of the coefficient read from the function generation ROM 13. Under the first function selection signal, a constant coefficient (= 1.0) is read from the function generation ROM 13, that is, it behaves as if there is no amplitude modulation processing. Under the second function selection signal, a coefficient that changes with time so as to satisfy, for example, a Hamming window function is read from the function generation ROM 13.
[0032]
Next, the operation of the present embodiment will be described. Here, the terms used below are defined. The time corresponding to the depth of the range gate marker is defined as the time required for the ultrasonic wave to propagate a distance twice the depth of the range gate marker in consideration of the round trip of ultrasonic transmission / reception. The time corresponding to the length of the range gate marker is defined as the time required for the ultrasonic wave to propagate a distance twice the length of the range gate marker.
[0033]
The controller 7 has a first mode and a second mode. The first mode is applied when the half of the time corresponding to the length of the range gate marker and the burst length τ of the burst wave match, and the second mode is the time corresponding to the length of the range gate marker. This is applied when the burst length τ (longest burst length τmax) of the burst wave is shorter than half. As described with reference to FIG. 7B, the burst length τ of the burst wave is positively adjusted to half the time corresponding to the length of the range gate marker. Depending on the range gate marker to be set, the burst length τ (maximum length of the burst wave) is longer than half of the time corresponding to the length of the range gate marker because the burst length τ is limited for the purpose of suppressing a significant drop. Occurs when the burst length τmax) is short.
[0034]
In the first mode, as described with reference to FIG. 7B, the burst length τ of the burst wave is intentionally adjusted to half the time corresponding to the length of the range gate marker. Only the Doppler signal supplied during the period of time t3 to t2 is taken into the integration process by the range gate unit 8. The time t3 is the time when the burst length τ has elapsed from the time t1, and the time t1 is the time when the time ΔTd corresponding to the depth of the range gate marker has elapsed from the transmission time t0 of the burst wave. The time t2 is the time when the time ΔTRG corresponding to the length of the range gate marker has elapsed from the time t1, that is, the time corresponding to the deepest part of the range gate marker. The integration period is set to half the time ΔTRG (ΔTRG / 2) corresponding to the length of the range gate marker. In the first mode, as understood by looking at the sensitivity distribution of the integration signal, the Doppler signal outside the range gate marker is preferably not taken into the integration process at all.
[0035]
FIGS. 2A and 2B are time charts showing the integration start time and the time width of the integration period in the second mode. FIG. 2A corresponds to the first function selection signal. FIG. 5B corresponds to the second function selection signal.
[0036]
In the second mode, as shown in FIGS. 2A and 2B, only the Doppler signal supplied during the integration period from time t1 'to time t2' is taken into the integration process by the range gate unit 8. The time t1 'is the time when half the burst length τ (τ / 2) has elapsed from the time t1, and the time t1 has passed the time ΔTd corresponding to the depth of the range gate marker from the burst wave transmission time t0. It's time. Time t2 'is the time when time ΔTRG corresponding to the length of the range gate marker has elapsed from time t1'. The integration period is set to a time ΔTRG corresponding to the length of the range gate marker. In the second mode, there is no dead area in the range gate marker, as can be seen by looking at the sensitivity distribution of the integrated signal.
[0037]
As described above, in the second mode, integration is started at time t1 ′ delayed by τ / 2 from time t1 corresponding to the depth of the range gate marker, and time ΔTRG corresponding to the length of the range gate marker, By continuing the integration, Doppler signals from a range corresponding to τ / 2 are taken into the integration process on the shallower side and the deeper side than the range gate marker, respectively, but compared with the case of FIG. The amount (area) of Doppler signals taken outside the range gate marker is absolutely reduced. Further, as understood from comparison with FIG. 7C, even in the case of facing a case where the integration period becomes longer than the burst length τ, the dead area in the range gate marker can be completely eliminated.
[0038]
Further, as understood from the sensitivity distribution of the integrated signal in FIG. 2B, a coefficient that changes over time so as to satisfy, for example, a Hamming window function is read from the function generation ROM 13 and multiplied by the Doppler signal. The sensitivity distribution becomes higher near the center, and the sensitivity distribution in the range corresponding to τ / 2 is suppressed on each of the shallower side and the deeper side than the range gate marker.
(Second Embodiment)
FIG. 3 is a block diagram of an ultrasonic diagnostic apparatus according to the second embodiment. The ultrasonic diagnostic apparatus according to the present embodiment includes an ultrasonic probe 21, a transmission / reception system (T / R) 22, a spectrum Doppler unit 23, a digital scan converter (DSC) 24, a monitor 25, and a console 26.
[0039]
The ultrasonic probe 21 is the same as the ultrasonic probe 1 of the first embodiment. The transmission / reception system 22 is improved so that the transmission / reception system 2 of the first embodiment can selectively generate an ultrasonic wave as a pulse wave (PW) or a continuous wave (CW), and an analog Doppler signal is generated. An ADC is added to the last stage so as to digitize and output the data. The wide-pass filter 30 is the same as the wide-pass filter 9 of the first embodiment. The fast Fourier transform processing circuit 31 is the same as the fast Fourier transform processing circuit 10 of the first embodiment. The digital scan converter 24 is the same as the digital scan converter 4 of the first embodiment. The monitor 25 is the same as the monitor 5 of the first embodiment.
[0040]
During PW, the Doppler signal from the transmission / reception system 22 is supplied to the RG integration circuit 28. During CW, the Doppler signal from the transmission / reception system 22 is supplied to the CW band filter 29. As shown in FIG. 4A, the RG integration circuit 28 integrates the Doppler data of the number of data N by the adder 331 and the delay circuit 332 inserted in the feedback path to the adder 331. Of course, the delay time of the delay circuit 332 is set to the ADC sampling period ΔTS. The number N of data depends on the integration period ΔTRG corresponding to the length of the range gate marker and is determined by the controller 27 based on ΔTRG / ΔTS. A multiplier 32 for multiplying the Doppler data by a coefficient corresponding to the integration period ΔTRG is provided before the adder 331. The coefficient is given by the controller 27 at 1 / N ^1/2 based on the number of data N.
[0041]
By adding Doppler data by the number N of data, the signal level is increased N times, while the noise level is increased N ^1/2 times. Therefore, the noise level varies depending on the length of the range gate marker, that is, the integration period, that is, the variation in the number of added data. In the present embodiment, by multiplying the Doppler data by a coefficient 1 / N ^1/2 , the noise level is reduced regardless of the variation in the length of the range gate marker, that is, the variation in the integration period, that is, the variation in the number of added data. Can be kept constant.
[0042]
As shown in FIG. 4B, the CW band filter 29 includes an FIR type low-pass filter (FIR LPF) 34, IIR to limit the frequency band of Doppler data from the input band fin to the output band fout. A series of low pass filters (IIR LPF) 35 are connected in series. A multiplier 36 for multiplying the filtered Doppler data by a coefficient is provided on the output side of the IIR type low-pass filter 35. This coefficient is given by the controller 27 at (fin / fout) ^1/2 based on the ratio of the input band fin and the output band fout.
[0043]
Limiting the input band fin to the output band fout is equivalent to applying a gain of 1 / (fin / fout) ^1/2 <1, which is a ratio between the input band fin and the output band fout. This means that the noise level fluctuates accordingly. In this embodiment, by multiplying the output data of the FIR type low pass filter 34 and the IIR type low pass filter 35 by a coefficient (fin / fout) ^1/2 , the input band fin and the output band fout and The noise level can be kept constant regardless of the fluctuation of the ratio.
[0044]
As shown in FIG. 4C, the fast Fourier transform processing circuit 31 performs fast Fourier transform processing on the Doppler data with the number of data N in the fast Fourier transform processing unit 38 according to the length of the range gate marker, that is, the integration period. To serve. A multiplier 37 for multiplying the Doppler data by a coefficient is provided in the preceding stage of the fast Fourier transform processing unit 38. The coefficient is given by the controller 27 at 1 / N ^1/2 based on the number of data N.
[0045]
By applying the Doppler data to the fast Fourier transform process with the number of data N, a gain of N1 ^{/ 2} is applied to the noise level substantially. Therefore, the noise level varies depending on the variation in the number of data. In the present embodiment, by multiplying the Doppler data by the coefficient 1 / N ^1/2 , the noise level can be kept constant regardless of the variation in the number of data.
(Third embodiment)
FIG. 5 is a block diagram of an ultrasonic diagnostic apparatus according to the third embodiment. The ultrasonic probe 41 is the same as the ultrasonic probe 1 of the first embodiment. The fast Fourier transform processing circuit 50 is the same as the fast Fourier transform processing circuit 10 of the first embodiment. The digital scan converter 44 is the same as the digital scan converter 4 of the first embodiment. The monitor 45 is the same as the monitor 5 of the first embodiment.
[0046]
The ultrasonic diagnostic apparatus according to the present embodiment includes an ultrasonic probe 41, a transmission / reception system 42, a spectrum Doppler unit 43, a digital scan converter (DSC) 44, a monitor 45, a system controller 46, a Doppler controller 47, and a console 48. Is done. The transmission / reception system 42 is configured to be able to drive the ultrasonic probe 41 and execute alternate scanning. The alternate scan is a normal scan in which an ultrasonic transmission / reception operation is repeated a predetermined number of times at a rate frequency for a certain raster, and then moves to the next raster sequentially. The ultrasonic transmission / reception operation is performed once, and the ultrasonic transmission / reception operation is performed once for several other rasters before the next ultrasonic transmission / reception operation for the same raster. Looking at the raster, the interval between ultrasonic transmission / reception operations is increased, the rate frequency is substantially lowered, and the low-speed detection capability is improved. The number of ultrasonic transmission / reception operations of other rasters performed between two ultrasonic transmission / reception operations before and after the same raster is defined as the number of alternating stages. Further, the transmission / reception system 42 is configured to be able to change the number of alternating stages according to the control of the system controller 46. Further, the transmission / reception system 42 is configured to be able to change the transmission voltage in accordance with the control of the Doppler controller 47.
[0047]
The spectrum Doppler unit 43 includes a multiplier 49 for Doppler gain correction and a fast Fourier transform processing circuit 50. If the output of the transmission / reception system 42 is not digital but analog, the multiplier 49 is replaced with an amplifier.
[0048]
A console 48 is connected to the system controller 46. The number of alternating stages can be changed via the console 48.
As shown in FIG. 6, the Doppler controller 47 includes a data number adjustment controller 51 and a Doppler sensitivity correction controller 52. The controller 51 for adjusting the number of data performs fast Fourier transform so that the ratio of the frequency resolution to the time resolution is constant on the display of the Doppler spectrum even if the rate frequency fPRF is substantially changed by changing the number of alternate stages. This is for adjusting the number of frequency analysis data of the processing circuit 50. This adjustment method is well known and will be described briefly. The number of alternating stages is K, the rate frequency is fPRF, the scroll speed is S, the pixel ratio representing the ratio of the time width to the frequency width corresponding to one pixel is Pn, and the coefficient is α. First, the parameter AA is obtained according to the equation (1).
[0049]
AA = α. ((FPRF.S) / (Pn.K)) (1)
Here, the number of data is N ′. N ′ = Ww · N is given. N is the reference data number (usually the minimum data number), and Ww is the ratio of the data number to the reference data number (N ′ / N). If the number of selectable data is 16, 32, 64, 128, 256, for example, N = 16, and in this case, Ww = 1, 2, 4, 8, or 16.
[0050]
Then, Ww is obtained according to equation (2).
Ww = AA / N ² (2)
If the obtained Ww does not match any of 1, 2, 4, 8, and 16, the one closest to the obtained Ww is selected. The number of data N ′ (= Ww · N) is determined from the obtained or selected Ww.
[0051]
In principle, when the number of alternating stages is n times, the number of data for frequency analysis is changed to 1 / n ^1/2 times. The fast Fourier transform processing circuit 50 receives information on the determined data number Ww · N from the data number adjustment controller 51, and uses the Doppler signal for frequency analysis with the data number Ww · N. The information on the data number Ww · N determined by the data number adjustment controller 51 is also supplied to the Doppler sensitivity correction controller 52. The Doppler sensitivity correction controller 52 is also supplied with information on the number of alternating stages K from the system controller 46.
[0052]
The Doppler sensitivity correction controller 52 is for suppressing S / N fluctuations due to fluctuations in the number of data of frequency analysis. For example, when the number of alternating stages is changed so as to reduce the low speed detection capability to half value, the number of data of frequency analysis is reduced to ^{1/2 1/2} times. This reduction in the number of data reduces the S / N by about 0.8 dB. In order to suppress this decrease in S / N, the Doppler gain of the multiplier 49 for Doppler gain correction is lowered by about 0.8 dB compared to the number of alternating stages before the change, and the noise level is lowered by about 0.8 dB. Thereby, the effect that a noise level can be kept constant irrespective of the number of data is acquired. However, as a matter of course, the signal level decreases by about 0.8 dB as the noise level decreases. In order to compensate for this decrease in signal level, the transmission voltage is increased 1.09 times before the change in the number of alternating stages. By such Doppler gain adjustment and transmission voltage adjustment, even if the number of alternating stages increases and the number of data decreases, the effect that S / N does not deteriorate can be obtained.
The present invention is not limited to the above-described embodiment, and can be implemented with various modifications.
[0053]
【The invention's effect】
An ultrasonic diagnostic apparatus according to the present invention includes a transmission / reception unit that transmits an ultrasonic pulse into a subject and receives a reflected wave to obtain a reception signal, and a specific period according to the depth and length of the range gate marker. Means for obtaining an integrated signal by integrating the received signal output from the transmitting / receiving means, means for analyzing the frequency of the integrated signal in order to obtain a Doppler spectrum in the range gate marker, the transmitting / receiving means, And a means for multiplying the received signal by a weighting factor corresponding to 1 / ΔT RG ^1/2, where ΔT RG is an integration period by the integrating means.
According to the present invention, when the integration period changes, the gain changes substantially and the noise level changes accordingly, but the received signal is multiplied by the weighting coefficient corresponding to the integration period. By canceling the substantial gain change accompanying the change, the noise level can be kept constant.
The ultrasonic diagnostic apparatus according to the present invention includes means for transmitting an ultrasonic wave as a continuous wave into a subject and receiving a reflected wave to obtain a received signal; and filter means for attenuating a specific frequency band of the received signal; Means for multiplying the output signal of the filter means by a weighting factor corresponding to the ratio of the input band of the filter means to the output band of the filter means; and frequency analysis of the output signal of the filter means to obtain a Doppler spectrum. Means.
According to the present invention, for example, when the rate frequency changes, the ratio of the input band to the output band of the filter means changes accordingly, the gain changes substantially, and the noise level also changes. By multiplying the output signal of the filter means by a corresponding weighting factor, this substantial gain change can be canceled and the noise level can be kept constant.
An ultrasonic diagnostic apparatus according to the present invention includes a means for obtaining a received signal by transmitting an ultrasonic wave into a subject and receiving a reflected wave, and a means for frequency-analyzing the received signal with the number of data to obtain a Doppler spectrum. And means for multiplying the received signal by a weighting factor 1 / N ^1/2 , where N is the number of data.
According to the present invention, when the number of data for frequency analysis changes, the gain substantially changes and the noise level also changes. By multiplying the received signal by a weighting factor corresponding to this number of data, this substantial The gain level can be canceled and the noise level can be kept constant.
[Brief description of the drawings]
FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment.
FIG. 2 is a time chart showing an integration period according to the first embodiment.
FIG. 3 is a block diagram of an ultrasonic diagnostic apparatus according to a second embodiment.
4 is a block diagram of the RG integration circuit, CW band filter, and FFT in FIG. 3;
FIG. 5 is a block diagram of an ultrasonic diagnostic apparatus according to a third embodiment.
6 is a block diagram of the Doppler controller of FIG. 5. FIG.
FIG. 7 is an explanatory diagram of a conventional problem corresponding to the first embodiment.
[Explanation of symbols]
1 ... ultrasonic probe,
2 ... transmission and reception system,
3 ... Spectrum Doppler unit,
4 ... Digital scan converter,
5 ... Monitor,
6 ... Console,
7 ... Controller,
8 ... Range gate unit,
9 ... High-pass filter,
10: Fast Fourier transform processing circuit,
11 ... multiplier,
12 ... integrator,
13 ... Function generation ROM,
14 ... RG width counter,
15: RG start position counter.

Claims (3)

Transmitting / receiving means for transmitting an ultrasonic pulse into the subject and receiving a reflected wave to obtain a received signal;
Means for obtaining an integrated signal by integrating the received signal output from the transmitting / receiving means in a specific period according to the depth and length of the range gate marker;
Means for frequency analysis of the integrated signal to obtain a Doppler spectrum in the range gate marker;
Provided between the transmitting / receiving means and the integrating means, and means for multiplying the received signal by a weighting coefficient corresponding to 1 / ΔT RG ^1/2, where ΔT RG is the integration period of the integrating means. A characteristic ultrasonic diagnostic apparatus. Means for transmitting an ultrasonic wave as a continuous wave into a subject and receiving a reflected wave to obtain a received signal;
Filter means for attenuating a specific frequency band of the received signal;
Means for multiplying the output signal of the filter means by a weighting factor according to the ratio of the input band of the filter means to the output band of the filter means;
An ultrasonic diagnostic apparatus comprising: means for frequency analysis of an output signal of the filter means in order to obtain a Doppler spectrum. Means for obtaining a received signal by transmitting an ultrasonic wave into a subject and receiving a reflected wave;
Means for frequency analysis of the received signal by the number of data to obtain a Doppler spectrum;
An ultrasonic diagnostic apparatus comprising: means for multiplying the received signal by a weighting factor 1 / N ^1/2 , where N is the number of data.

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