JP2002017725A - Ultrasound Doppler diagnostic device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve an SN ratio of an ultrasonic Doppler diagnostic apparatus for measuring a blood flow velocity and the like, and display an image of good quality. In an ultrasonic Doppler diagnostic apparatus, a first amplifier and a second amplifier are variable amplifiers, an amplitude detector for detecting an amplitude of a received signal, and an amplitude of the received signal detected by the amplitude detector. , The amplification factor of the first amplifier is adjusted to an amplification factor at which a received signal having an amplitude level free from saturation is output from the first amplifier, and the amplification factor of the first amplifier and the second amplifier are adjusted. And a gain control unit that adjusts the amplification factor of the second amplifier so that the overall amplification factor including the amplification factor of the second amplifier becomes a predetermined amplification factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler diagnostic apparatus for measuring a motion state of an internal tissue such as a blood flow velocity of a human body.

[0002]

2. Description of the Related Art Conventionally, there are a pulse method and a Doppler method as methods for measuring the state of a tissue inside a human body using an ultrasonic diagnostic apparatus. The pulse method transmits ultrasonic waves inside the living body, receives the reflected waves, and displays the image of the inside of the living body as an image. The B mode that displays the amplitude of the reflected waves and the temporal change of the moving reflection source are used. There is an M mode to be displayed. The Doppler method is used for measuring blood flow and the like, and includes a method in which a continuous wave is transmitted to a reflection source and a method in which a pulse modulated wave is transmitted to provide a distance resolution.

In a so-called ultrasonic Doppler diagnostic apparatus which measures by the Doppler method, when an ultrasonic wave hits a target such as blood cells moving in a blood vessel, a reflected wave shifts to a high frequency or a low frequency by the Doppler effect. Is applied to measure the moving speed of the target.

[0004] The Doppler method is further classified into a continuous wave Doppler method and a pulse Doppler method.

[0005] The continuous wave Doppler method is a method in which a vibrator is divided into a transmission only and a reception only to simultaneously transmit a continuous ultrasonic wave and receive a reflected wave to measure a blood flow velocity and the like.

On the other hand, the pulse Doppler method alternately repeats transmission of an ultrasonic burst wave and reception of a reflected wave using the same transducer, and the time from transmission to reception is determined by the depth of the target object. Is a method of measuring a blood flow velocity or the like specified at a certain depth.

FIG. 1 is a diagram showing an example of the configuration of an ultrasonic Doppler diagnostic apparatus.

In FIG. 1, an excitation voltage generated by a transmission / reception circuit 2 is applied to a vibrator (not shown) provided in a probe 1 to excite the vibrator, which vibrates inside a human body (not shown). To transmit. The reflected wave reflected inside the human body is received by a vibrator (not shown) to become a received signal, and the received signal is sent to the transmitting / receiving circuit 2.

The received signal received by the transmission / reception circuit 2 is filtered by a band-pass filter 18 to remove signals outside the required frequency band, and then amplified by a preamplifier 3 and multiplied by a predetermined reference signal in mixers 4 and 5. The orthogonal detection is performed, and the signal is divided into two signals.

Although the high-frequency components of the signals of each system are removed by the low-pass filter 6 or the low-pass filter 7, in addition to the Doppler signal components reflected by the target, the signals are reflected by a slow-moving non-target such as an organ or a blood vessel wall. Consisting of signal components and signal components reflected by non-moving objects such as bones,
Clutter components having a relatively high signal level are output simultaneously. However, the signal component reflected by the slow moving non-target is a component having a lower frequency than the Doppler signal component reflected by the target, and the signal component reflected by the non-moving non-target is a DC component. The low-frequency component and the DC component are removed by the high-pass filter 8 or the high-pass filter 9 to extract the Doppler signal component.

Here, in the pulse Doppler method, the sample circuit 19 or the sample circuit 20 provided between the low-pass filter and the high-pass filter is used.
Thereby, a reflected wave from a blood cell flowing at a certain depth in the human body, for example, flowing through a blood vessel is sampled.

The Doppler signal extracted by removing the high-frequency component, the low-frequency component and the DC component from the received signal is amplified by the variable amplifier 10 or the variable amplifier 11, and is amplified by the A / D converter 12 or the A / D converter 13 After that, it is converted into a digital signal carrying time function information such as blood flow velocity by frequency analysis in the FFT analysis unit 14.

On the other hand, the received signal received by the transmitting / receiving circuit 2 is converted into a digital signal by the tomographic image processing circuit 15. F
The digital signal output from the FT analysis unit 14 or the tomographic image processing circuit 15 is subjected to coordinate conversion and interpolation by the display control circuit 16 to be converted into an analog image signal, and then displayed on the image display device 17. .

Here, the Doppler-shifted frequency of the Doppler signal is proportional to the moving speed of the target.
The Doppler shifted frequency can be converted to speed. Also, the reflected wave shifts to a higher frequency or a lower frequency than the frequency of the transmitted ultrasonic wave depending on the moving direction of the target. Determine the moving direction.

[0015]

An analog multiplying circuit is usually used for the mixer of the above configuration. However, since the analog multiplying circuit has relatively large noise, the gain of the preamplifier is increased and the signal level input to the mixer is increased. Must be increased to improve the SN ratio.

However, the received signal contains a clutter component having a relatively high signal level reflected by the non-target, and when the gain of the preamplifier is increased, the clutter component is also amplified at the same time. As a result, the output signal is saturated. It is easy to cause harmonics.

If the harmonic component is sampled, a false waveform may be displayed at the display position of the velocity component where there should be no blood flow waveform. Also, if saturation occurs when the Doppler signal component and the clutter component are superimposed, a false waveform called a mirror image of a shape obtained by folding the original blood flow waveform on an axis of zero speed may be caused on the screen. . Further, the weak blood flow signal overlapping the clutter component may be collapsed due to the saturation, and the blood flow waveform may not be easily generated.

Therefore, in order to prevent such a problem from occurring, the gain is fixed low so that saturation does not occur in the preamplifier even when a reflected wave having a high amplitude is received from a non-target object. The gain of the waveform is ensured mainly by adjusting the amplification factor of a variable amplifier provided after the high-pass filter.

In view of the above circumstances, the present invention improves the SN ratio of a weak signal caused by the Doppler shift of the frequency generated when an ultrasonic wave is reflected by a target moving in a living body, and provides good quality. It is an object of the present invention to provide an ultrasonic Doppler diagnostic device capable of displaying an image.

[0020]

An ultrasonic Doppler diagnostic apparatus according to the present invention, which achieves the above object, transmits an ultrasonic wave into a living body and receives and receives the ultrasonic wave reflected back in the living body. An ultrasonic transmitting / receiving unit for obtaining a signal, a first amplifier for amplifying a received signal obtained by the ultrasonic transmitting / receiving unit, and an ultrasonic wave in the living body from the received signal amplified by the first amplifier. A Doppler extractor for extracting a Doppler signal which is a signal component caused by a Doppler shift of a frequency generated upon reflection; a second amplifier for amplifying the Doppler signal extracted by the Doppler extractor; An ultrasound output Doppler diagnostic apparatus comprising: an image output unit that outputs an image based on a Doppler signal output from an amplifier; wherein the first amplifier and the second amplifier are variable amplifiers, and the amplitude of the reception signal is Detect An amplitude detector that detects the amplitude of the received signal detected by the amplitude detector, and outputs an amplification factor of the first amplifier to a received signal having an amplitude level that is free from saturation from the first amplifier. The amplification of the second amplifier is adjusted so that the total amplification obtained by combining the amplification of the first amplifier and the amplification of the second amplifier is a predetermined amplification. And a gain control unit for adjusting the rate.

As described above, the first and second amplifiers for amplifying the received signal are variable amplifiers, and the amplification factor of the first amplifier reaches, for example, a saturation level based on the amplitude detected by the amplitude detector. If not, the gain is increased, and if it exceeds the saturation level, the gain is adjusted to a level that avoids saturation, such as lowering the gain. The excess or deficiency amplification factor is covered by the second amplifier, so the first amplifier is fixed. The gain of the received signal can be obtained more than in the case where Therefore, SN
The ratio can be improved and a good quality image can be displayed.

Further, the Doppler extractor comprises a mixer for multiplying the received signal amplified by the first amplifier by a predetermined reference signal, and the amplitude detector comprises: It is preferable to detect the amplitude of the received signal immediately before the signal is input to the receiver.

As described above, by detecting the amplitude immediately before the mixer, the received signal input to the mixer can be easily maintained at a constant level.

Further, it is preferable that the amplitude detector has a peak hold circuit having a configuration in which a held peak value gradually leaks, and the peak value of the received signal is detected by the peak hold circuit. .

As described above, if the peak value is detected and the gain is adjusted, the received signal can have the highest gain without reaching the saturation level, and the held peak value is gradually increased. Therefore, the gain can be adjusted gently following the level reduction of the received signal.

The ultrasonic transmitting / receiving section transmits an ultrasonic burst wave into a living body, and the amplitude detector detects the ultrasonic burst wave transmitted into the living body. It is preferable to detect the amplitude of the received signal at the timing when the reflected wave reflected at the desired observation point is received.

As described above, in the pulse Doppler method, a signal having the best SN ratio can be obtained for a desired observation point.

Further, between the first amplifier and the Doppler extractor, amplitude suppression for suppressing a portion exceeding a predetermined amplitude level in the reception signal output from the first amplifier to the predetermined amplitude is performed. It is also a preferable embodiment to include a limiter that performs the operation, and a filter that reduces a harmonic component generated due to suppression of the amplitude to a predetermined amplitude by the limiter.

As described above, by providing the limiter for suppressing the amplitude and the filter for reducing the harmonic component, the received signal having an excessively high signal level when searching for the observation point in the living body can have a predetermined amplitude. To prevent screen disturbance.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described.

FIG. 2 is a block diagram of an ultrasonic Doppler diagnostic apparatus according to the first embodiment of the present invention.

As shown in FIG. 2, the ultrasonic Doppler diagnostic apparatus includes a probe 1, and the probe 1 includes a vibrator (not shown). The transmission / reception circuit 2 generates an excitation voltage and sends the excitation voltage to a vibrator (not shown) of the probe 1. The vibrator excited by the excitation voltage transmits an ultrasonic wave to a target in the human body, receives a reflected wave reflected by the target, and obtains a reception signal. After the obtained reception signal is sent to the transmission / reception circuit 2, signals outside the necessary frequency band are removed by the band-pass filter 18 and the first amplifier 2
Amplified by 1. This first amplifier is a variable amplifier capable of changing the amplification factor, and the amplification factor is adjusted by a gain control unit described later so as to avoid saturation of the amplifier.

The received signal amplified by the amplifier is subjected to quadrature detection multiplied by the reference signal by the mixers 4 and 5, and is divided into two signals.
After that, the high-frequency component composed of the sum of the frequency of the received signal and the frequency of the reference signal is removed from the signal of each system in the low-pass filter 6 or the low-pass filter 7,
In addition to the Doppler signal component reflected from the target, the signal level is relatively high, including the signal component reflected from a slow moving non-target such as an organ or blood vessel wall or the signal component reflected from a non-moving non-target such as a bone. , So-called clutter components are output simultaneously. Of these, the component reflected by the slow-moving non-target object is a lower-frequency component than the Doppler signal component reflected by the target having a frequency that is the difference between the frequency of the received signal and the frequency of the reference signal. Since the component reflected by the non-target object is a DC component, the low-frequency component and the DC component are removed by the high-pass filter 8 or the high-pass filter 9, and only the Doppler signal component is extracted.

Here, in the pulse Doppler method, it is necessary to sample only a reflected wave reflected at a desired observation point in a received signal transmitted by transmitting an ultrasonic burst wave into a living body. Therefore, the sample circuit 19 or the sample circuit 20 is provided between the low-pass filter and the high-pass filter, and the sample circuit samples a signal based on a reflected wave reflected at a desired observation point.

As described above, the high frequency component, the low frequency component, and the DC component are removed from the received signal, and the Doppler signal component is extracted. The extracted Doppler signal is further amplified by the second amplifier 22 or the second amplifier 23. The second amplifier is a variable amplifier, and its gain is adjusted by a gain control unit to be described later so that the overall gain combined with the gain of the first amplifier becomes a predetermined gain set by the operator. You.

The amplified Doppler signal is then subjected to A / D
The signal is converted into a digital signal by the converter 12 or the A / D converter 13 and further subjected to frequency analysis such as fast Fourier transform in the frequency analysis unit 14 to be converted into a digital signal carrying time function information such as blood flow velocity. You.

On the other hand, the tomographic image display circuit 15 is
Is converted into a digital signal to be displayed as a tomographic image.

The digital signal converted by the frequency analysis unit 14 or the digital signal converted by the tomographic image processing circuit 15 is converted into an analog signal by performing coordinate conversion and interpolation calculation in a display control circuit 16 and then converted into an analog signal. It is displayed on the device 17 as an ultrasonic diagnostic image.

The present embodiment further includes an amplitude detector 24 and a gain controller 25.

The amplitude detector 24 is a circuit for detecting the amplitude of the received signal, and the circuit configuration will be described later.

The gain controller 25 adjusts the amplification factor of the first amplifier 21 based on the amplitude detected by the amplitude detector 24 within a range not reaching the saturation region, and adjusts the amplification factor of the second amplifier 21 with the amplification factor of the second amplifier. The amplification factor of the second amplifier is adjusted so that the overall amplification factor becomes the amplification factor set by the operator.

FIG. 4 is a diagram showing a configuration example of the circuit of the amplitude detector. In FIG. 4, B1 and B2 are buffer amplifiers having high input impedance and low output impedance, D is a diode, R1 and R2 are resistors, C is a capacitor, and A / D is a converter for converting an analog signal to a digital signal. A reception signal for detecting the amplitude is input to the amplifier B1. When the amplitude of the input signal increases, a current flows through the diode D and the resistor R1, and the capacitor C holds the peak value of the input signal. When the input signal is smaller than the previous peak value, the diode D is turned off,
Charge gradually leaks from the capacitor C via the resistor R2, and the held peak value gradually decreases. In this case, the peak value is held in the capacitor C by keeping the resistance value of the resistor R1 small and the resistance value of the resistor R2 large. The peak value is digitized by an A / D converter and read by a gain control unit 25 shown in FIG. 2 to adjust the amplification factor of the amplifier.

Returning to FIG. 2, the description will be continued.

If the amplitude detector 24 is provided at a position where the amplitude of the received signal immediately before being input to the mixers 4 and 5 can be detected, the level of the signal input to the mixer can be easily maintained at a constant value. Can be. However, the present invention is not limited to this position. For example, it may be provided at a position where the output of the first amplifier 21 is directly detected.
May be provided in the preceding stage.

The gain control section 25 uses, for example, a microprocessor to make the peak value of the first amplifier 2 higher.
If the saturation voltage is smaller than 1, the amplification factor of the first amplifier 21 is increased and increased, and the amplification of the second amplifier 22 or the second amplifier 23 is controlled so that the overall amplification factor set by the operator does not change. By performing an operation of reducing the rate and reducing the rate, the amplification rates of the two amplifiers can be adjusted.

That is, if the amplitude of the received signal is 1
/ 2 (minus 6 db), the gain of the first amplifier 21 is increased by 6 db, and the gains of the second amplifier 22 and the second amplifier 23 are decreased by 6 db. Conversely, when the amplitude of the received signal is larger than the saturation voltage, the gain of the first amplifier 21 is reduced, and the second amplifier 22 and the second amplifier 23
, The maximum gain can be secured without the first amplifier 21 being saturated, and the entire gain set by the operator can be satisfied by the gain of the second amplifier.

It is preferable that the change of the amplification factor by the gain control section is usually performed several times per second to once per several seconds.

As described above, the two amplifiers are variable amplifiers, and the gain of the first amplifier for amplifying the received signal is adjusted so as to avoid saturation from clutter components and the like included in the received signal. Further, since the amplification factor of the second amplifier is adjusted to allocate the entire amplification factor,
An ultrasonic Doppler diagnostic apparatus having an improved ratio and capable of displaying high-quality images can be provided.

Next, a second embodiment of the present invention will be described.

FIG. 3 is a block diagram of an ultrasonic Doppler diagnostic apparatus according to a second embodiment of the present invention.

The present embodiment is a case where the ultrasonic Doppler diagnostic apparatus is used by the pulse Doppler method, and a description will be given focusing on differences from the first embodiment.

In the amplitude detector of the first embodiment, the amplitude is always detected. In this system, a timing signal is generated at a timing at which a reflected wave reflected at a desired observation point in a living body is received. Since the reception signal is sampled by the timing signal, the amplitude is also detected at that timing.

Therefore, the first difference from the first embodiment is that a timing control section for generating a timing signal is provided, and the received signal is sampled by the generated timing signal, and the amplitude is also detected. It is.

When an ultrasonic burst wave is transmitted from a transducer (not shown) provided in the probe 1 to a desired observation point, the timing controller 36 receives a reflected wave reflected only at the observation point by the transducer. Generate a timing signal according to the timing.

The sample unit 37 or the sample unit 38 outputs only a signal based on a reflected wave reflected at a desired observation point from a signal orthogonally detected by the mixer 4 or the mixer 5 based on the timing signal generated by the timing control unit 36. Sample.

The amplitude detector 34 is a circuit for detecting the amplitude of the received signal based on the timing signal in order to detect the amplitude of the received signal at the timing of sampling in the sampling section.
The circuit configuration will be described later.

If the amplitude detector 24 is provided at a position where the amplitude of the received signal immediately before being input to the mixers 4 and 5 can be detected, the level of the signal input to the mixer can be easily maintained at a constant value. can do. However, the position is not limited to this position.
May be provided at a position where the output of the first amplifier 31 is directly detected, or may be provided before the first amplifier 31.

The gain controller 35 adjusts the amplification factor of the first amplifier 31 within a range not reaching the saturation region based on the amplitude detected by the amplitude detector 34, and adjusts the gain of the second amplifier 32 or the second amplifier 32. The gain of the second amplifier 32 or the second amplifier 33 is adjusted such that the overall gain combined with the gain of the amplifier 33 is the gain set by the operator.

FIG. 5 is a diagram showing an example of a circuit configuration of the amplitude detector.

In FIG. 5, B1 and B2 are buffer amplifiers having a high input impedance and a low output impedance.
1 and S2 are analog switches, D is a diode, R1 and R2 are resistors, C is a capacitor, and A / D is a converter for converting an analog signal into a digital signal.

The received signal for detecting the amplitude is input to the amplifier B1. S2 just before the sampling timing
Is closed, the capacitor C is discharged to make the charge zero, and S2 is opened. When S1 is closed in accordance with the sampling timing, the peak value detected at the sampling timing is held in the capacitor C. This sampled peak value is digitized by an A / D converter,
Is read by the gain control unit 35, and the gain of the amplifier is adjusted. S1 is opened at the end of the sampling timing, and the electric charge held in the capacitor C is closed and S2 is discharged.

Returning to FIG. 3, the description will be continued.

In the present embodiment, the limiter 19 for suppressing the amplitude of the reception signal variably amplified by the first amplifier 31 and the low-pass filter 1 for removing harmonic components
8, which is the second difference from the first embodiment.

Since the received signal after the operator has found the desired observation point and fixed the probe 1 becomes a relatively stable signal, there is no problem even if the amplification factor is automatically assigned. , While looking for the desired observation point,
Suddenly, the received signal may increase and the amplifier may saturate. Therefore, the limiter 19 is connected to the first amplifier 31
In the latter stage, the amplitude is suppressed to suppress an excessive amplitude exceeding a predetermined amplitude level, and the band-pass filter 18 conventionally used is used as a low-pass filter to reduce harmonics generated by amplitude suppression or the like.

Here, when the signal is saturated, a mirror image may be generated, but the mirror image cannot be prevented even if the harmonics are removed by the limiter 19 and the filter 18. However, simulations have shown that mirror images are less likely to occur when asymmetrical saturation occurs than when saturation occurs with the polarity of the signal waveform being symmetrical between the positive and negative sides. did. Therefore, limiter 1
No. 9 can suppress the occurrence of a mirror image to a low level by performing amplitude suppression at different amplitudes on the positive and negative sides of the signal waveform.

[0066]

As described above, according to the present invention, the signal-to-noise ratio of a weak signal caused by the Doppler shift of the frequency generated when an ultrasonic wave is reflected in a living body is improved, and good quality is achieved. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of an ultrasonic Doppler diagnostic apparatus.

FIG. 2 is a block diagram of the ultrasonic Doppler diagnostic apparatus according to the first embodiment of the present invention.

FIG. 3 is a block diagram of an ultrasonic Doppler diagnostic apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration example of a circuit of an amplitude detector.

FIG. 5 is a diagram illustrating a configuration example of a circuit of an amplitude detector.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 probe 2 transmission / reception circuit 3 preamplifier 4,5 mixer 6,7 low-pass filter 8,9 high-pass filter 10,11 variable amplifier 12,13 A / D converter 14 frequency analysis unit 15 tomogram analysis unit 16 display control circuit 17 image display Device 18 Band-pass filter 19, 20 Sample circuit 21, 31 First amplifier 22, 23, 32, 33 Second amplifier 24, 34 Amplitude detector 25, 35 Gain control unit 27 Image output unit 36 Timing control unit 37, 38 Sample part

Claims (6)

[Claims] An ultrasonic transmitting / receiving unit for transmitting an ultrasonic wave into a living body, receiving an ultrasonic wave reflected back in the living body, and receiving a received signal, and receiving the ultrasonic wave transmitted / received by the ultrasonic transmitting / receiving unit A first amplifier for amplifying a signal, and a Doppler signal which is a signal component caused by a Doppler shift of a frequency generated when the ultrasonic wave is reflected in the living body from the received signal amplified by the first amplifier. And a second amplifier for amplifying the Doppler signal extracted by the Doppler signal, and an image output unit for outputting an image based on the Doppler signal output from the second amplifier. An ultrasonic Doppler diagnostic apparatus, wherein the first amplifier and the second amplifier are variable amplifiers, an amplitude detector for detecting an amplitude of the received signal, and the received signal detected by the amplitude detector. Based on the amplitude of And adjusting the amplification factor of the first amplifier to an amplification factor at which a received signal having an amplitude level free from saturation is output from the first amplifier, and adjusting the amplification factor of the first amplifier to the amplification factor of the second amplifier. A gain control unit that adjusts the amplification factor of the second amplifier so that the overall amplification factor including the amplification factor of the second amplifier becomes a predetermined amplification factor. . 2. The apparatus according to claim 2, wherein said Doppler extractor comprises a mixer for multiplying the received signal amplified by said first amplifier by a predetermined reference signal, wherein said amplitude detector comprises: 2. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein the amplitude of the received signal immediately before being input to the device is detected. 3. The amplitude detector according to claim 1, further comprising a peak hold circuit configured to gradually leak a held peak value, wherein the peak hold circuit detects a peak value of the received signal. The ultrasonic Doppler diagnostic apparatus according to claim 1, wherein 4. The ultrasonic transmitter / receiver for transmitting an ultrasonic burst wave into a living body, wherein the amplitude detector comprises:
The detection of the amplitude of a received signal at a timing at which a reflected wave of an ultrasonic burst wave transmitted into the living body reflected at a desired observation point in the living body is received. 2. The ultrasonic Doppler diagnostic apparatus according to 1. 5. An amplitude suppressor for suppressing a portion exceeding a predetermined amplitude level of a received signal output from the first amplifier between the first amplifier and the Doppler extracting section to the predetermined amplitude. And a filter for reducing a harmonic component generated due to being suppressed to a predetermined amplitude by the limiter.
An ultrasonic Doppler diagnostic apparatus as described in the above. 6. The ultrasonic Doppler diagnosis according to claim 5, wherein said limiter performs amplitude suppression to an amplitude below an amplitude level different from each other depending on the polarity of a received signal input to said limiter. apparatus.