JPH06237928A - Ultrasonic diagnostic equipment - Google Patents

Abstract

(57) [Abstract] [Objective] In the analog / digital conversion part of the ultrasonic diagnostic equipment, the cost is low and the performance is excellent by improving the S / N ratio without increasing the number of bits of the A / D converter. Realize an ultrasonic diagnostic device. A / D converters 4-1 to 4-4 for converting a reception signal into a digital signal in synchronization with a transmission signal, a pseudo noise source 6 for generating a pseudo noise signal in synchronization with the transmission signal, and the reception Adder 3-1 to add the pseudo noise signal to the signal
3-4 means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus having an A / D converter.

[0002]

2. Description of the Related Art In recent years, ultrasonic diagnostic equipment has been used in memory and CP.
As digital circuit components such as U have become widespread and the price has been reduced, there is a tendency that much of the signal processing inside the diagnostic device is performed by digital circuits.

However, since the part relating to the transmission and reception of ultrasonic waves is performed by an analog circuit, it is customary to convert the analog signal into a digital signal by an A / D converter in any block in the device. For example, as a conventional example, there is a configuration as shown in FIG.

In FIG. 15, reference numeral 1 denotes a probe composed of N oscillators, but here N = 4 for simplification.
There is. 2-1 to 2-4 are pulser receivers, 7 is a control unit, 14 is a detector, 15 is a digital scan converter (hereinafter abbreviated as DSC), 16 is a display unit, 47 is A /
The D converter 48 is an analog beam combiner.

A description of the operation in this example is omitted because it is already widely known, but the echo signals are delayed and added, detected, and then A / D converted, and the circuits thereafter are constituted by digital circuits. .

Another example of using the A / D converter is a Doppler blood flow meter as shown in FIG. In FIG. 16, 1 is a probe composed of N transducers,
Here, N = 4 is set for simplification. 2-1-2-
4 is a pulsar receiver, 7 is a control unit, 8 and 9 are multipliers, 1
0 is a quadrature signal generator, 11 and 12 are low-pass filters,
13 is a signal processing unit, 15 is a DSC, 16 is a display unit, 48
Is an analog beam combiner, and 49 and 50 are A / D converters.

Since the operation in this example is also widely known, the description thereof will be omitted. After removing the clutter components by the low-pass filters 8 and 9, A / D conversion is performed and frequency analysis is performed.

Further, as an example of performing A / D conversion,
A color flow blood flow imaging device as shown in FIG. 17 may be used. In FIG. 17, 1 is a probe composed of N transducers, but here, for simplification, N is used.
= 4. 2-1 to 2-4 are pulser receivers, 7
Is a control unit, 8 and 9 are multipliers, 10 is a quadrature signal generator,
13 is a signal processing unit, 15 is a DSC, 16 is a display unit, 48
Is an analog beam synthesizer, 49 and 50 are A / D converters,
Reference numerals 51 and 52 are MTI filters.

Although the operation of this example is also well known, its explanation will be omitted. However, after the phase detection, A / D conversion is performed and the clutter component is removed by a digital circuit.

As a fourth conventional example for performing A / D conversion, a configuration as disclosed in Japanese Patent Laid-Open No. 61-8039 is known. FIG. 18 shows its configuration. In FIG. 18, reference numeral 1 is a probe, and in this case, 4CH is provided to simplify the explanation.
And the system. 2-1 to 2-4 are pulser receivers, 4-1 to 4-4 are A / D converters, 5 is a digital beam combining unit, 7 is a control unit, 8 and 9 are multipliers, 10 is a quadrature signal generator. , 11 and 12 are filters, 13 is a signal processing unit, 14 is a detector, 15 is a DSC, and 16 is a display unit.

Next, the operation of FIG. 18 will be described. The pulse trigger signal from the control unit 7 is the pulser receiver 2-1.
Is input to 2-4. The pulser trigger signal is phase controlled to provide electronic focusing or steering. The four pulser receivers 2-1 to 2-4 transmit drive pulses for driving the oscillators T1 to T4 by pulse trigger signals. The ultrasonic waves reflected in the subject are received by the same transducers T1 to T4, and the pulser receivers 2-1 to 2-1.
It is amplified in 2-4 and sent to the A / D converters 4-1 to 4-4. The reception signals converted into digital signals by the A / D converters 4-1 to 4-4 are delayed and added by the digital beam combining section 5.

In the pulse Doppler or color flow blood flow imaging apparatus, the quadrature signal generator 10 is composed of the multipliers 8 and 9.
Is multiplied by the reference signal produced by
After the unnecessary component is removed by 2, the signal processing unit removes the clutter component and calculates the speed, and the result is displayed on the display unit 16 via the DSC 15.

In the B mode, the wave is detected by the wave detector 14 and displayed on the display unit 16 via the DSC 15.

[0014]

However, in the ultrasonic diagnostic apparatus having the conventional A / D converter, there is a problem that the dynamic range is limited due to the use of the A / D converter.

For example, in the B mode, it is difficult to adjust the input gain. A gain setting that is too high leads to saturation at the input of the A / D converter and a correct output cannot be obtained. Further, when the gain setting is low, the number of effective bits is small, so that the dynamic range of the image is reduced, or the resolution in the vertical and horizontal directions is reduced due to an error during beamforming.

In the Doppler mode, a blood flow echo is mixed with an echo having a large amplitude from a blood vessel wall, so that a wide dynamic range is required, but due to the narrow dynamic range of the A / D converter. Blood flow information is lost.

To solve these problems, a highly accurate A / D converter having a wide dynamic range is required, but it is extremely expensive.

The invention of claim 1 is to solve such a conventional problem. Even though the received signal is converted into digital data by the low resolution A / D converter, B
It is an object of the present invention to provide an excellent ultrasonic diagnostic apparatus capable of realizing high-sensitivity phase detection in the Doppler mode by eliminating image deterioration due to saturation in the A / D converter input and a decrease in the effective number of bits in the mode. It is what

The invention of claim 2 is to solve such a conventional problem, and in spite of converting a received signal into digital data by a low resolution A / D converter,
In the B mode, image deterioration due to saturation at the input of the A / D converter and a decrease in the number of effective bits is eliminated, and
An object of the present invention is to provide an excellent ultrasonic diagnostic apparatus capable of removing noise with a simple circuit while realizing highly sensitive phase detection in the Doppler mode.

The invention of claim 3 is to solve such a conventional problem, and in spite of converting a received signal into digital data by a low resolution A / D converter,
It is an object of the present invention to provide an excellent ultrasonic diagnostic apparatus which eliminates image deterioration due to saturation at the input of an A / D converter and a decrease in the number of effective bits in the B mode, and has a miniaturized circuit scale. .

The invention according to claim 4 is to solve such a conventional problem by using an A / D converter having a low resolution.
An object of the present invention is to provide an excellent ultrasonic diagnostic apparatus that realizes highly sensitive phase detection in the Doppler mode even though the received signal is converted to digital data, and that has a reduced circuit scale. Is.

The invention of claim 5 is to solve such a conventional problem, and by using a low resolution A / D converter,
In spite of converting the received signal to digital data, in the B mode, deterioration of the image due to saturation at the input of the A / D converter and a decrease in the number of effective bits is eliminated, and in the Doppler mode, high-sensitivity phase detection is performed. It is an object of the present invention to provide an excellent ultrasonic diagnostic apparatus that is realized and has a reduced circuit scale.

The invention of claim 6 is to solve such a conventional problem. When the ratio of the center frequency of the echo to the sampling frequency of the A / D converter is large in the B mode, the echo is generated in the Doppler mode. An object of the present invention is to provide an ultrasonic diagnostic apparatus that realizes particularly excellent expansion of the dynamic range when the signal bandwidth is wide and has excellent image quality.

The invention according to claim 7 is a concrete implementation of the differentiating circuit according to claim 5, and is for enabling noise reduction during A / D conversion.

The invention of claim 8 also concretely realizes the differentiating circuit according to claim 5, and is for enabling noise reduction during A / D conversion.

The invention of claim 9 also enables noise reduction at the time of A / D conversion, and facilitates realization of a specific circuit.

The invention of claim 10 also facilitates the concrete realization of the circuit and realizes the noise reduction during A / D conversion.

[0028]

In order to achieve the above object, the invention of claim 1 is an A / D converter for converting a reception signal into a digital signal in synchronization with a transmission signal, and a pseudo noise signal in synchronization with the transmission signal. The above-mentioned object is achieved by having means for generating the noise and means for adding the pseudo noise to the input signal of the A / D converter.

In order to achieve the above object, the invention of claim 2 comprises an A / D converter for converting a received signal into a digital signal in synchronization with a transmission signal, and means for generating a pseudo noise signal in synchronization with the transmission signal. The object is achieved by having means for adding the pseudo noise to the input signal of the A / D converter and an integrator for integrating the digital data converted by the A / D converter.

In order to achieve the above object, the third aspect of the present invention comprises an A / D converter for converting a received signal into a digital signal in synchronization with a transmission signal, and means for generating a pseudo noise signal in synchronization with the transmission signal. A means for adding the pseudo noise to the input signal of the A / D converter and an integrator for integrating the digital data obtained by the A / D converter, and the integration section of the integrator is set to the center frequency of the echo. The above object is achieved by changing the values in conjunction with each other.

In order to achieve the above object, the invention of claim 4 comprises an A / D converter for converting a received signal into a digital signal in synchronization with a transmission signal, and means for generating a pseudo noise signal in synchronization with the transmission signal. A means for adding the pseudo noise to the input signal of the A / D converter and an integrator for integrating the digital data obtained by the A / D converter, and the integration section of the integrator is set to the echo bandwidth. The above object is achieved by changing the values in conjunction with each other.

In order to achieve the above object, the invention of claim 5 includes an A / D converter for converting a received signal into a digital signal in synchronization with a transmission signal, and means for generating a pseudo noise signal in synchronization with the transmission signal. A means for adding the pseudo noise to the input signal of the A / D converter, and an integrator for integrating the digital data obtained by the A / D converter, and the integration with one of the peak frequencies of the spectrum of the pseudo noise The above-mentioned object is achieved by matching the zero frequency response portions of the container.

In order to achieve the above object, the sixth aspect of the present invention comprises an A / D converter for converting a received signal into a digital signal in synchronization with a transmission signal, and means for generating a pseudo noise signal in synchronization with the transmission signal. A differentiating means for obtaining an instantaneous slope of the received signal, a means for multiplying the differential signal of the received signal obtained by the differentiating means by the pseudo noise signal, and the A / D
The above object is achieved by having means for adding a signal obtained by multiplying the pseudo noise and the differential signal to the input signal of the converter and an integrator for integrating the digital data obtained by the A / D converter. is there.

In order to achieve the above object, the invention of claim 7 achieves the above object by using an analog differentiator as means for differentiating the received signal of claim 5.

In order to achieve the above-mentioned object, the invention of claim 8 uses a digital difference device for taking a difference of digital data obtained from an A / D converter as means for differentiating the received signal of claim 5, The above object is achieved.

The invention of claim 9 is optimal by calculating from the quantized slope data obtained by the method of claim 7 or the slope data obtained by the method of claim 8. The object is achieved by generating the smallest dither signal amplitude.

The invention of claim 10 is a quantized version of the slope data obtained by the method of claim 7, or claim 8
The above object is achieved by performing an operation from the data of the slope obtained by the above method and selecting the optimum one from the data of several dither signals having different amplitudes prepared in advance and adding it to the input signal.

[0038]

Therefore, according to the first aspect of the invention, the pseudo noise signal synchronized with the transmission signal and the reception signal are added to the A / D converter, and the Doppler signal processing is performed on the digital output. , A / D converter can be improved in resolution.

According to the second aspect of the present invention, the pseudo noise signal synchronized with the transmission signal and the reception signal are added to the A / D converter, and noise is removed from the digital output by the integrator. Therefore, the resolution of the A / D converter can be further enhanced.

Further, according to the third aspect of the present invention, since the basic period of the pseudo signal synchronized with the transmission signal changes in association with the transmission frequency band, the period of the pseudo noise signal is long especially when the transmission frequency is low. Therefore, the resolution of the A / D converter can be further improved.

According to the fourth aspect of the present invention, since the basic period of the pseudo signal synchronized with the transmission signal changes in association with the bandwidth of the transmission signal, the pseudo noise signal is generated especially when the bandwidth of the transmission signal is narrow. This has the effect that the cycle can be made longer and the resolution of the A / D converter can be further increased.

According to the fifth aspect of the invention, the spectrum of the pseudo noise signal synchronized with the transmission signal coincides with the frequency at which the response of the integrator is zero, and the digital output causes noise by the integrator. Since it is removed, there is an effect that the resolution of the A / D converter can be further enhanced.

Further, according to the invention of claim 6, since the amplitude of the pseudo noise signal synchronized with the transmission signal changes in association with the inclination of the reception signal, the reception signal is a high frequency signal or a large amplitude signal. This has the effect of keeping the quantization noise low during A / D conversion.

Further, according to the invention of claim 7, there is an effect that the inclination of the received signal can be accurately obtained by a simple method by obtaining the inclination of the received signal by the analog differentiator.

Further, according to the invention of claim 8, since the inclination of the received signal is obtained from the difference of the A / D converted digital data, there is an effect that the variation of the circuit can be eliminated and the adjustment portion can be made unnecessary.

Further, according to the invention of claim 9, since the amplitude of the dither signal can be kept small at all times, the required specifications of the device used in the circuit can be lowered and the problem such as crosstalk can be caused. Also has the effect of being able to solve.

Further, according to the invention of claim 10, since the amplitude of the dither signal can be limited, there is an effect that the circuit can be simplified.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to the present invention in which delay addition is performed by a digital circuit using an array type probe. In FIG. 1, reference numeral 1 denotes an array type ultrasonic probe, which is composed of N transducers T1 to TN. In this example, N =
4 is set. 2-1 to 2-4 are pulser receivers, 3-
1 to 3-4 are adders, 4-1 to 4-4 are A / D converters,
5 is a digital beam combining unit, 6 is a pseudo noise source, 7 is a control unit, 8 and 9 are multipliers, 10 is a quadrature signal generation unit, 11,
Reference numerals 12 and 17 are filters, 13 is a signal processing unit, 14 is a detection unit, 15 is a scan converter (hereinafter referred to as DSC), 16
Is a display unit.

Next, the operation of the above embodiment will be described.
In FIG. 1, first, a trigger signal from the control unit 7 is input to the pulsers 2-1 to 2-4. The trigger signal is phase controlled to perform electron focusing and sector scanning. The four pulser receivers 2-1 to 2-4 generate drive pulses by the trigger signal and drive the oscillators T1 to T4. By this driving, the transducers T1 to T4 transmit ultrasonic waves in the set direction.

The ultrasonic waves reflected in the subject are received by the same transducers T1 to T4, and the pulser receivers 2-1 to 2-4.
And is sent to the adders 3-1 to 3-4. The received signals are added to the signal from the pseudo noise source 6 in the adders 3-1 to 3-4. The outputs of the adders 3-1 to 3-4 are
It is converted into a digital signal in the A / D converters 4-1 to 4-4. The received signals converted into digital signals by the A / D converters 4-1 to 4-4 are delayed and added in the digital beam combining section 5. In the digital beam synthesizing unit 5, each reception signal is added with a delay time so that the reception sensitivity becomes maximum in the direction in which the ultrasonic wave is transmitted.

The outputs of the digital beam combiner 5 thus obtained are multiplied by the COS and SIN outputs of the quadrature signal generator 10 in the multipliers 8 and 9. The outputs of the multipliers 8 and 9 are filters 11 and 1 having low-pass characteristics.
At 2, the high frequency components are attenuated. The multipliers 8 and 9, the quadrature signal generator 10, and the filters 11 and 12 form a phase detection circuit.

Based on the outputs of the filters 11 and 12, the signal processing unit 13 obtains a pulse Doppler output by an FFT operation or a color flow output by a correlation operation, and inputs it to the DSC 15. At the same time, the output of the digital beam combiner 5 is also input to the filter 17. The function of the filter 17 will be described in detail later.

The output of the filter 17 is detected by the detector 14 and input to the DSC 15 as B mode image data. The output data of the signal processing unit 13 and the detection unit 14, which are scan-converted into TV signals in the DSC 15, are displayed in the display unit 16.
Is displayed in.

Next, the operation of the pseudo noise source 6 will be described in detail. The role of the pseudo noise source 6 is, for example, the hp journal 1
"B. Allen Montijo," Digit, published in pp70-76 in the June 1988 issue.
al Filtering in a High-Sp
ed Digitizing Oscillosco
There are known examples of dithering techniques such as "pe". However, in the pulse Doppler mode and the color flow mode of the ultrasonic diagnostic apparatus of the present invention, the pseudo noise source 6 generates pseudo noise in synchronization with the trigger signal output from the control unit 7, that is, the generation timing of the sound wave. At the same time, the pseudo noise source 6 is A / D
It is also synchronized with the sample clocks of the converters 4-1 to 4-4. Therefore, when the ultrasonic beams are transmitted in the same set direction, the value of the pseudo noise at the timing of the m-th sample clock with reference to the trigger signal of the control unit 7 becomes N (m), and the number of transmissions becomes It is constant regardless.

As an example, the pseudo noise value N (m) is shown in FIG.
As shown in FIG. 5, a sawtooth waveform having an amplitude of 0.75 with 4 sample clocks as one cycle is used. In this case, N
(M) can be expressed as follows.

N (m + 0) = 0.00 N (m + 1) = 0.25 N (m + 2) = 0.50 N (m + 3) = 0.75 Subtracting the DC component from these data gives the following values. Become.

N (m + 0) =-0.375 N (m + 1) =-0.125 N (m + 2) = 0.125 N (m + 3) = 0.375 1 LSB of the A / D converter is equal to 1 in amplitude. , A / D
It is assumed that a DC signal with an amplitude of 1.51 is input to the converter. If there is no dither signal at this time, assuming that the threshold level of the A / D converters is 1.5, the outputs of the four A / D converters are all 2, and an error of 0.49 occurs. .

On the other hand, when a dither signal is added, 4
Two outputs are 1.135, 1.385, 1.635, 1.
885, the average of these is 1.51, and the error is 0.01.

In this example, the maximum value of the normal quantization error is ± 0.5, whereas the average value of the quantization error when the process of adding the pseudo noise signal and taking the average is performed is ± 0.5.
It decreases to 0.125 and 1/4. When A / D conversion is performed by this method, the sampling speed is equivalently reduced, but the quantization error is reduced. The pseudo noise source 6 generates noise for such a purpose. The pseudo noise signal has a period and a waveform such that its frequency spectrum does not overlap with the band of the received signal.

The pseudo noise and the received signal are added by adders 3-1 to 3-3-
4 is added and converted into digital data by the A / D converters 4-1 to 4-4, and then delayed and added in the digital beam combining section 5. In the B mode, the delay-added received signal is passed through the filter 17. Filter 1
7 has a low-pass characteristic, and the component of the pseudo noise signal included in the reception signal delayed and added by the filter 17 has a frequency band different from that of the original reception signal (echo) and is higher than the frequency band of the reception signal. Since it exists there, it is removed by this filter. The received signal that has passed through the filter 17 is subjected to envelope detection by the detection unit 14, and the DSC 15
Is displayed on the display unit 16 via.

In the Doppler blood flow meter or the Doppler image device, the delay-added received signals are input to the multipliers 8 and 9. In the multipliers 8 and 9, the signals are mixed with two reference signals that are orthogonal to each other, and are input to the filters 11 and 12. The filters 11 and 12 are intended to remove harmonic components in the phase detection output, but can also be used to remove pseudo noise signals.

As a result of the phase detection, the band of the received signal is shifted to DC and low frequency band. Although the spectrum of the pseudo noise signal also shifts in frequency, its band does not overlap with that of the received signal, so that only the received signal can be extracted by the filters 11 and 12 having the low-pass characteristic. The signal processing unit 13 calculates blood flow information from the received signal in which only low frequency components are extracted by the filters 11 and 12, and displays it on the display unit 16 through the DSC 15.

In the B mode, and in the pulse Doppler blood flow meter and the color flow imaging apparatus, the S / N ratio can be improved by the above method.

FIG. 3 is a block diagram showing an ultrasonic diagnostic apparatus according to the second embodiment, which performs delay addition with a digital circuit. In this embodiment, the pulse Doppler blood flow meter and the color flow imaging device are particularly emphasized.

In FIG. 3, reference numeral 1 denotes an array type ultrasonic probe, which is composed of N transducers T1 to TN. In this example, N = 4 is set to simplify the description. 2-1 to 2-4 are pulsar receivers, 3-1 to 3
-4 is an adder, 4-1 to 4-4 are A / D converters, 5 is a digital beam combining unit, 6 is a pseudo noise source, 7 is a control unit,
Reference numerals 8 and 9 are multipliers, 10 is a quadrature signal generator, 11, 12 and 17 are filters, 13 is a signal processing unit, 14 is a detector, 15 is a DSC, 16 is a display unit, and 18 is an integrator.

Next, the operation of the above embodiment will be described.
This embodiment differs from the first embodiment in that an integrator 18 is inserted between the digital beam combiner 5 and the multipliers 8 and 9. The integrator 18 is intended to remove the pseudo noise signal in the delay-added received signal.

The characteristics of the integrator as a low-pass filter and the spectrum of pseudo noise will be described.

The frequency component of the pseudo noise signal whose period is 4 as described above and whose data is the repetition of -0.375, -0.125, 0.125, 0.375 is basically FIG. 4 shows a spectrum that is composed of a component and harmonics that are integral multiples of the component and is quantized by adding the input signal of a relatively low single frequency. That is, the noise components are concentrated near the Nyquist frequency and half the frequency thereof. As a filter for removing such noise, for example, there is a filter for averaging four data.

FIG. 5 shows the frequency characteristic of this filter.
It can be seen that in this filter, the quantization noise can be reduced because the attenuation is large in the vicinity of the Nyquist frequency and its half frequency.

As described above, by superimposing the frequency of which the frequency response of the integrator is zero on the spectrum of the pseudo noise signal, it is possible to effectively improve the S / N ratio.

In the first embodiment, the filter 11,
In FIG. 12, both the removal of the harmonic component in the phase detection output and the removal of the pseudo noise signal were performed. However, as in the second embodiment, by separating the pseudo noise signal removal filter, the filter 11, The characteristics required for No. 12 are relaxed, and it is easy to realize. Further, the removal of the pseudo noise signal by the integrator is simpler than the construction of a general filter and can be realized at low cost.

FIG. 6 shows a block diagram of an ultrasonic diagnostic apparatus for performing delay addition in a digital circuit according to the third embodiment of the present invention. In this embodiment, the emphasis is on the B-mode configuration.

In the Doppler blood flow meter and the Doppler image device, the focus position can be fixed at one point, but in the B mode, the focus position needs to be dynamically changed. In FIG. 6, reference numeral 1 denotes an array-type ultrasonic probe, which is composed of N transducers T1 to TN. In this example, N = 4 is set to simplify the description. 2-1 to 2-4 are pulser receivers, 3-1 to 3-4 are adders, and 4-1 to 4-4 are A.
/ D converter, 5 is a digital beam combining unit, 6 is a pseudo noise source, 7 is a control unit, 8 and 9 are multipliers, 10 is a quadrature signal generating unit, 11 and 12 are filters, 13 is a signal processing unit, and 15
Is a DSC, 16 is a display unit, and 20-1 to 20-4 are integrators.

Next, the operation of the above embodiment will be described.
The above-described embodiment is different from the first embodiment in that integrators 20-1 to 20-4 are provided between the A / D converters 4-1 to 4-4 and the digital beam combiner 5. As described above, in the B mode, the focus position needs to be dynamically changed. Therefore, after delay-adding the received signals, the data A / D-converted at equal intervals and the data interval are not constant, and There is a problem that the frequency component of the pseudo noise added to the signal changes.

Therefore, in each channel, the integrators 20-1 to 20-4 are used after the A / D converters 4-1 to 4-4 to remove the pseudo noise component before the delay addition. .

In this case, the integrators 20-1 to 20-4 lower the data rate of the received signals of the respective channels, which causes a problem that the delay addition accuracy in the digital beam combiner 5 decreases. For this reason, the integrator filter used in this portion needs to be configured as shown in FIG. 7, for example. In FIG. 7, 21 to 23 are latches, and 24 is an adder. The input signal is sequentially shifted from the latch 21 to the latches 22 and 23, and the four data of the input and the outputs of the latches 21 to 23 are added by the adder 24. With this method, the output data rate of the adder 24 can be made equal to the input data rate.

According to the principle, the longer the basic period of the pseudo noise signal is, the higher the S / N ratio is in this system for improving the S / N by adding the pseudo noise signals and performing A / D conversion. It is obvious that the longer the fundamental period of the pseudo noise signal is, the lower the spectrum appears at the frequency. If the frequency of the pseudo-noise signal and the frequency of the received signal overlap, this method will not hold, but in the ultrasonic diagnostic apparatus, usually, there is not one transmission frequency.
When a low transmission frequency is used, the basic period of the pseudo noise signal can be lengthened to further improve the S / N ratio.
Specifically, the number of steps of the pseudo noise signal in FIG. 2 may be increased.

FIG. 8 is a block diagram of an ultrasonic diagnostic apparatus using the array type probe in the third embodiment and performing delay addition in a digital circuit. In FIG. 8, reference numeral 1 is an array type ultrasonic probe, and N transducers T1 to T1 are arranged.
It is composed of TN. In this example, N = 4 is set to simplify the description. 2-1 to 2-4 are pulser receivers, 3-1 to 3-4 and 27-1 to 27-4 are adders, 4-1 to 4-4 are A / D converters, and 5 is a digital beam combiner. , 6 is a pseudo noise source, 7 is a control unit, 8, 9 and 25-1 to 25-4 are multipliers, 10 is an orthogonal signal generation unit, 11, 12 and 17 are filters, 13 is a signal processing unit, and 14 is Detector, 15 DSC, 16 display, 26
-1 to 4 are blocks for detecting the inclination of the input signal.

Next, the operation of the above embodiment will be described.
This embodiment is different from the first embodiment in that there are multipliers 25-1 to 25-4, inclination detectors 26-1 to 26-4 and adders 27-1 to 27-4. S / described in the first embodiment
The method of improving the N ratio has a problem that the degree of improvement of the S / N ratio decreases when the frequency of the received signal is high or the amplitude thereof is large. This is because the frequency characteristic of noise in the signal obtained by A / D converting the sum of the dither signal and the input signal approaches white noise.

By the way, when the input signal is A / D converted to obtain some data, the amount of quantization noise in each data varies. If the frequency of the input signal is not so low compared to the sampling frequency, or if the A / D
If the quantization unit of the converter is large to some extent, the same input signal is converted into an A / D signal by two methods, that is, a method of adding a dither signal by the above method and a method of only taking an average of data. Upon conversion, when comparing the respective corresponding data, depending on the data, the addition of the dither signal results in less quantization noise, but for other data, the simple addition averaging results in less quantization noise. This is considered to be related to the amount of change in a minute section near the sampling point of the input signal, that is, the slope at that point.

For example, -0.375, -0.125,
A dither signal having an amplitude of 0.75 composed of 0.125 and 0.375 has an effect of reducing the quantization noise to 1/4 when the input has a DC component, that is, a slope of 0. When a signal having a slope of −0.25 in one sampling time is input, the quantization noise reducing effect is lost.

When the amplitude of the dither signal is set to 0.5, the effect of reducing the quantization noise when the input is DC is reduced, but the effect of reducing the quantization noise for an input having a slope of -0.25 is dithered. This is improved compared to the case where the signal amplitude is 0.75. That is, the amount of quantization noise in an input signal having a certain slope is reduced by inputting a dither signal having a certain amplitude. Therefore, it is considered possible to obtain data with less quantization noise at any sampling point by always detecting the slope of the input signal by some means and changing the amplitude of the dither signal based on it. .

FIG. 9 shows the relationship between the slope of the input signal, the amplitude of the dither signal and the S / N ratio. In this figure, the horizontal axis represents the slope of the input signal and the vertical axis represents the amplitude of the dither signal, and the S / N ratio when these are used as parameters is plotted in the form of contour lines. The part where the S / N ratio is good and the part where the S / N ratio is not good are arranged on a straight line. Therefore, if the slope of the input signal is x and the slope of the dither signal is y, y = ax + b
A / D conversion with a good S / N ratio can be performed by appropriately determining a and b in the equation.

In the block diagram of FIG. 8, the pseudo noise generated by the pseudo noise source 6 and the inclination detecting units 26-1 to 26-4 are used.
Slope of the input signal detected at (corresponds to ax of ax + b)
In addition, b of (ax + b) is added by the adders 27-1 to 27-4.
Multiplier 25-1 based on the data added
Controls the amplitude of the dither signal input to ~ 4,
The signal processing as described above is realized by adding the result to the input signal.

As a concrete example of the inclination detecting units 26-1 to 26-4, there is one using an analog differentiating circuit as shown in FIG. In FIG. 10, 28 and 29 are resistors, 30 is a capacitor, and 31 is an operational amplifier.

On the other hand, a digital method is also conceivable. FIG. 11 is an example thereof, and in FIG. 11, 4 is A
/ D converter, 33 and 34 are latches, 35 is a subtractor, 36
Is a D / A converter.

The operation in FIG. 11 will be described. The data digitized by the A / D converter 4 is input to the latch 33. The latch 33 holds the output of the A / D converter 4 again at the timing of the next A / D conversion 4, and the data held so far is held by the latch 34. Subtractor 35
The data held in the latches 33 and 34 is input to the input terminal, and the data obtained by subtracting the data in the latch 33 from the data in the latch 34 is output. The output of the subtractor 35 is D
It is input to the / A converter 36 and analog data is output. This data is used as the differential output. Subtractor 3
The larger the time interval between the two data input to 5, the larger the number of bits can be obtained, but the error increases when the change in the slope of the input signal is large. Therefore, consider the nature of the input signal. Will be decided.

FIG. 12 is a block diagram of a main part of a quantization noise reducing method using a dither signal in an ultrasonic diagnostic apparatus according to the fourth embodiment of the present invention. 12 in FIG.
Is an A / D converter, 7 is a control unit, 37 and 38 are latches, 3
Reference numeral 9 is a subtractor, 40 is a memory, 41 is a counter, and 42 is a D / A converter. Next, the operation of this embodiment will be described. The input data converted into a digital signal by the A / D converter 4 is taken into the latches 37 and 38, and the subtractor 3
The process up to the point where the difference is calculated in 9 is the same as in the embodiment shown in FIG. In the present embodiment, the output of the subtractor 39 is input to the memory 40, and the memory 4 is referred to by referring to the address of the counter 41 that counts one cycle of the dither signal.
The data written in 0 is output, converted into an analog signal by the D / A converter 42, and added to the input signal by an adder (not shown).

In the embodiment of FIG. 8, the slope of the input signal and the amplitude of the dither signal have a relationship represented by a linear function, but with this method, the amplitude of the dither signal is proportional when the slope becomes large. As a result, problems such as jumping into other circuits as noise and narrowing the dynamic range in A / D conversion occur.

By the way, as can be seen from FIG. 9, there is not only one optimum dither signal amplitude for reducing the quantization noise of an input signal having a certain slope. For example, quantization noise can be minimized by adding a dither signal having an amplitude of 0.75 to an input signal having a slope of 0, but the amplitude of the dither signal is 3.7.
The same effect can be obtained when the number is set to 5. Conversely, if there is a dither signal with an amplitude of −1.5 to 1.5, it is possible to A / D-convert the input signal of all the slopes with the least quantization noise. In this embodiment, paying attention to this fact, a method of covering the input signals of all the inclinations within the limited amplitude range of the dither signal is adopted.

For example, if there is a time difference of 4 samplings between the latch 37 and the latch 38 for data acquisition,
Only the lower two bits of the output of the subtractor 39 need to be sent to the memory 37. By adopting this method, the memory capacity can be reduced.

FIG. 13 is a block diagram of a main part of a quantization noise reducing method using a dither signal in an ultrasonic diagnostic apparatus according to the fifth embodiment of the present invention. 13 in FIG.
Is an A / D converter, 37 and 38 are latches, and 39 is a subtractor 4
3 is a selection control circuit, 44 and 45 are dither signal sources, and 46 is a selection circuit.

The operation of this embodiment will be described. In this embodiment, the dither amplitude is limited to some and selected. Figure 9
In the graph, the change in the quantization noise amount when the slope of the input signal is changed while the amplitude of the dither signal is kept constant is obtained as shown in FIG. In FIG. 14, (a) shows the case where the dither amplitude is 0, and (b) shows the case where the dither amplitude is 1.5. When (a) and (b) are compared, it can be seen that the values of the slopes of the input signals in the portions with relatively large noise are different. Therefore, for example, when the slope Δχ of the input signal per sampling is (n + 0.25) <Δχ ≦ (n + 0.75) (n is an integer), the dither signal amplitude is set to 0, and n <Δχ ≦ (n + 0.25) ) (N is an integer) or (n + 0.75) <Δχ ≦ (n + 1) (n is an integer), the dither signal amplitude is set to 1.5, and the quantization noise amount with the input slope as a parameter is The characteristics are as shown in (c) of 14.

As described above, if dither signals having different amplitudes are prepared and a dither signal having an amplitude that reduces the quantization noise is selected from the slope of the input signal, the S / N ratio for the entire input signal is improved. To do. In this example, the dither signal has two amplitudes, but the same method can be applied when the dither signal has three or more amplitudes. The degree of improvement in the S / N ratio that can be expected when using this method is lower than when a dither signal having an optimum amplitude is always added, but it has an advantage that the circuit configuration is simple.

The operation of the block diagram of FIG. 13 will be described. In FIG. 13, the operation up to the point where the subtracter 39 outputs the difference data is the same as in the fourth embodiment. When this difference data is input to the selection control circuit 43, the dither signal of the amplitude A of the dither signal source 44 and the dither signal source 4 are input in this circuit.
A dither signal having an amplitude B of 5 and having less quantization noise is selected by the method described above, and the selection information is sent to the selection circuit 46. The selection circuit 46 selects and outputs the amplitude of the dither signal based on the output of the selection control circuit 43. By using the method according to the present embodiment in combination with the method according to the fourth embodiment, it is possible to obtain the same effect while further reducing the circuit scale.

In the first, second and third embodiments of the present invention, the ultrasonic diagnostic apparatus in which the delay addition is performed by the digital circuit is described, but in the case where the A / D conversion is performed after the delay addition. It is obvious that the present invention can be applied to the Doppler blood flow meter or the color flow blood flow imaging device described in the conventional example.

[0098]

As is apparent from the above-described embodiment, the present invention adds a received signal to a pseudo noise signal synchronized with a transmission signal, performs A / D conversion, and then limits the band of the A / D converter. It has the effect of improving the resolution. Further, the use of the integrator as the means for removing the pseudo signal has the effect of simplifying the configuration and realizing it at low cost.
Further, by changing the basic period of the pseudo noise signal in conjunction with the band or bandwidth of the transmission signal, it is possible to realize a higher S / N ratio when the bandwidth is narrow or when the bandwidth is low. Has the effect that it is possible.

In addition, by matching the spectral frequency of the pseudo noise signal and the zero frequency of the frequency response of the integrator, the pseudo noise signal can be removed efficiently. Furthermore, by linking the amplitude with the slope of the received signal, it is possible to improve the resolution even for high-frequency signals and large-amplitude signal inputs, and as means for detecting the slope of the input signal, an analog differentiator or digital This has the effect of enabling realization by using the differentiator.

Further, by suppressing the amplitude of the dither signal to a small amplitude, problems such as crosstalk can be solved and the performance of the components used in the circuit can be reduced. In addition, there is an effect that the circuit scale is reduced by a method of selecting the amplitude of the dither signal from some limited in advance.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of a waveform of pseudo noise used in the embodiment of the present invention.

FIG. 3 is a block diagram of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention (applicable to pulse Doppler and color flow).

FIG. 4 is an explanatory diagram of signal processing of the present invention.

FIG. 5: Frequency characteristic of integrator filter

FIG. 6 is a block diagram of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention (applicable to B mode).

FIG. 7 is a block diagram of an integrator filter with an improved output rate.

FIG. 8 is a block diagram of an ultrasonic diagnostic apparatus according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram showing the relationship between the slope of the input signal and the S / N ratio in the third embodiment of the present invention.

FIG. 10 is an example of a circuit of an analog differentiator in the third embodiment of the present invention.

FIG. 11 is an example of a block diagram of a digital differentiator used in the third embodiment of the present invention.

FIG. 12 is a block diagram of a pseudo noise generator according to a fourth embodiment of the present invention.

FIG. 13 is a block diagram of a pseudo noise generator according to a fifth embodiment of the present invention.

FIG. 14 is an explanatory diagram of the S / N ratio in the fifth embodiment of the present invention.

FIG. 15 is a block diagram of a conventional ultrasonic diagnostic apparatus of analog delay addition method.

FIG. 16 is a block diagram of a conventional Doppler blood flow meter.

FIG. 17 is a block diagram of a conventional color flow blood flow imaging device.

FIG. 18 is a block diagram of a conventional ultrasonic diagnostic apparatus of digital delay addition method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Probe 2-1-4 Pulser receiver 3-1-4 Adder 4-1-4 A / D converter 5 Digital beam combining part 6 Pseudo noise source 7 Control part 8, 9 Multiplier 10 Quadrature signal generator 11, 12 Filter 13 Signal Processing Unit 14 Detector 15 DSC 16 Display Unit 17 Filter 18 Integrator 20-1 to 4 Integrator 21 to 23 Latch 24 Adder 25-1 to 4 Multiplier 26-1 to 4 Slope Detection Unit 27-1 to 4 Adder 28, 29 Resistor 30 Capacitor 31 Operational amplifier 33, 34 Latch 35 Subtractor 36 D / A converter 37, 38 Latch 39 Subtractor 40 Memory 41 Counter 42 D / A converter 43 Selection control circuit 44, 45 Dither signal source 46 Selection circuit 47 A / D converter 48 Analog beam combiner 49, 50 A / D converter 51, 52 MTI fill Ta

Claims (10)

[Claims] 1. An A / D converter for converting a reception signal into a digital signal in synchronization with a transmission signal, a means for generating a pseudo noise signal in synchronization with the transmission signal, and adding the pseudo noise signal to the reception signal. An ultrasonic diagnostic apparatus comprising means. 2. The ultrasonic diagnostic apparatus according to claim 1, further comprising an integrator as means for removing the pseudo noise signal. 3. The ultrasonic diagnostic apparatus according to claim 1, wherein the fundamental period of the pseudo noise signal is changed in association with the center frequency of the transmission signal. 4. The ultrasonic diagnostic apparatus according to claim 1, wherein the fundamental period of the pseudo noise signal is changed in association with the bandwidth of the transmission signal. 5. The ultrasonic diagnostic apparatus according to claim 2, wherein one of the peak frequencies of the spectrum of the pseudo noise signal is matched with the frequency at which the integrator response characteristic is zero. 6. The ultrasonic diagnostic apparatus according to claim 1, wherein the amplitude of the pseudo noise signal changes according to the inclination of the input signal. 7. The ultrasonic diagnostic apparatus according to claim 6, wherein an analog differentiator is used as means for detecting the inclination of the input signal. 8. The method according to claim 6, wherein the inclination of the input signal is obtained from the difference between digital data obtained by A / D conversion.
The ultrasonic diagnostic apparatus described. 9. The ultrasonic diagnostic apparatus according to claim 6, wherein the optimum and smallest amplitude of the dither signal is calculated from the obtained inclination of the input signal. 10. From the obtained slope of the input signal, optimum is selected from among data of dither signal having different amplitudes prepared in advance so that the magnitude of the quantization noise when the input signal is A / D converted becomes smaller. 7. The ultrasonic diagnostic apparatus according to claim 6, wherein the ultrasonic diagnostic apparatus is selected.