JPS6336777B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention emits ultrasonic pulses to a subject such as a human body, receives the reflected waves, and finally displays them in a format such as a B-mode echogram image as necessary. The present invention relates to a method for receiving reflected waves in an ultrasonic diagnostic apparatus.

The attenuation of ultrasonic waves in the subject, ie, a biological tissue such as a human body, is relatively large and cannot be ignored. When performing ultrasonic testing using the pulse-echo method, reflected waves from a close distance and with less attenuation during the round trip are received first.
Messages from further away that are subject to more attenuation are successively received. Therefore, when receiving such reflected waves, there is a reception method in which the gain of the receiver is initially reduced starting from the sending time of the transmitted wave pulse, and as time passes, the gain is increased and reception is performed. (This is generally called TGC) is generally adopted.

However, such a conventional TGC reception system has a drawback in that it cannot compensate for the dispersion of the medium. That is, distant or low-level reflected waves, so-called weak reflected waves, can only be received to a certain extent by simply increasing the degree of amplification. Considering the reflection characteristics of the reflection source and the dispersion of the medium (the higher the frequency, the greater the loss), it is appropriate to observe weak reflection sources at lower frequencies when viewed from the probe. be.

As a countermeasure, there is a method (for example, U.S. Pat. No. 4,016,750) in which the center frequency fo of the receiving filter is unilaterally lowered as the distance (or time) from the reflection source increases. be.
However, although this method is effective in a target area composed of reflection sources where the received level monotonically decreases with distance, in reality it has various attenuation characteristics, dispersion characteristics, or reflection abilities. In a target area where objects are mixed, the distance and the reflected wave level do not always have a constant, monotonous correspondence, so it cannot be said that this is always an effective reception method.

In view of these points, an object of the present invention is to selectively receive the frequency region with the highest amount of information among the reflected waves from the reflection source according to the properties of the reflection source, and to obtain more precise information about the subject. The present invention aims to provide a reflected wave receiving method for an ultrasonic diagnostic apparatus that can obtain tomographic images.

Another object of the present invention is to provide an ultrasonic diagnostic apparatus that can capture both a reflection source that emits a low-level reflected wave and a reflection source that emits a high-level reflected wave and display it as a diagnostically useful B-mode echogram. The aim is to provide a method for receiving reflected waves.

The present invention will be described in detail using the drawings. FIG. 1 is a diagram showing the main part of a signal processing means for explaining a reflected wave receiving method of an ultrasonic diagnostic apparatus according to the present invention.

In Figure 1, A ₁ to _{A 4} are logarithmic amplifiers, LM ₁
~LM ₃ is a limiter, BPF ₁ ~ _{BPF 4} are band pass filters with different center frequency and passband bandpass characteristics, DET ₁ ~ _{DET 4} are detectors, DL ₁ ~ _{DL 3} are delay lines, As is a summing amplifier. The reflected wave signal received by the probe (not shown) is input to the first stage logarithmic amplifier _A1 .
Here, logarithmic amplification is performed at an appropriate amplification factor. The output is led to the first band pass filter BPF ₁ and is passed through the limiter LM ₁ to the logarithmic amplifier in the next stage.
Guided by A ₂ . The output of this logarithmic amplifier A ₂ is guided to the second band pass filter BPF ₂ and passed through the limiter LM ₂ to the next stage logarithmic amplifier.
Guided by A ₃ . Also, the output of this logarithmic amplifier A ₃ is guided to the third band pass filter BPF 3, as were the outputs of amplifiers A ₁ and A ₂ , and is passed through the limiter LM ₃ to the final stage logarithmic amplifier _. Guided by A ₄ . Last stage logarithmic amplifier A ₄
The output of is given to a fourth band pass filter BPF ₄ . These logarithmic amplifiers A ₂ to _{A 4} are coupled to limiters LM ₁ to LM ₃ , respectively, to form the main part of the receiving system as a sequentially saturated logarithmic amplifier circuit. The first-stage logarithmic amplifier _A1 section is in charge of the wave), and the last-stage logarithmic amplifier _A4 section is in charge of the weakest level region. Center frequencies f ₁ , f ₂ , f ₃ , f ₄ of band pass filters BPF ₁ to BPF ₄
are selected as f ₁ > f ₂ > f ₃ > f ₄ , and the respective bandwidths are also appropriately selected. band pass
The AC signals that have passed through the filters BPF ₁ to BPF ₄ are applied to detectors DET ₁ to _{DET 4} and detected, respectively. The outputs of the detectors are summed by a summing amplifier As and output as a video signal.
The output of the detectors DET ₁ to _{DET 3} up to the stage is a delay line that obtains a time delay to correct the delay of the output signal obtained at each stage with the final stage as a reference.
It is led to the summing amplifier As via DL ₁ to DL ₃ . For delay lines DL ₁ to _{DL 3} , the delay time is longer as the previous stage is used, and each delay time is determined including the time delay derived from the bandwidth of each band pass filter. The timings of the four signals are made to be aligned during addition.

In addition, in order to obtain reflected waves of various frequencies distributed over a wide range from various reflection sources, the drive waveform of the probe should be a step waveform (which can be substituted by the rising edge of a triangular wave), and should be as impulse-like as possible. It is desirable to transmit ultrasonic waves. It is also desirable that the reflected wave receiving circuit has a wide band, and it is appropriate that at least the first stage logarithmic amplifier _A1 has a wide band. Note that a preamplifier may be provided in the logarithmic amplifier _A1 , but in that case, the preamplifier also needs to have a sufficiently wide band.

The operation when receiving reflected waves in such a configuration will be described next. The probe is driven with a step-like drive signal as shown in FIG. 2A, and ultrasonic waves as shown in FIG. 2B are emitted to the subject. Such impulse-like ultrasonic waves are partially reflected at the interface of the medium inside the subject, and the reflected waves are received by the probe. An example of a received reflected wave is shown in FIG. 2C. This received wave is a high-level reflected wave A from a strong reflection source or a reflection source close to the probe.
(occupies a relatively wide frequency spectrum)
and a low-level reflected wave B (having mainly a low frequency spectrum) from a weak reflecting source or a reflecting source located far from the probe.
It consists of two reflected waves. This signal is successively amplified by a successive saturation type logarithmic amplifier circuit. At this time, the reflected wave A
Since it is mainly made up of higher frequency components, it passes through the preceding band pass filter, which has a band that includes this frequency. On the other hand, all the unit logarithmic amplifiers in the subsequent stage were hit by the limiter and limited when the reflected wave A was amplified.
Since a so-called saturation signal is input, each stage actually outputs a predetermined saturation value, regardless of the actual frequency characteristics of those stages. In addition, since the reflected wave B is composed of a lower frequency, it passes safely through the subsequent band pass filter that has a band that includes this frequency, and the band pass filter that receives the output from the earlier stage does not pass. Either they are cut off because their passbands are different, or even if there is a frequency signal within the passband, the signal level is low and it does not contribute to the detection output. Therefore, the signals obtained by passing through the band pass filter are as shown in FIG. A low frequency signal like this is obtained. These signals a and b are each detected by a corresponding detector, and the signals of the amplification stage having a delay line are time-delayed by the delay line, and then summed by a summing amplifier As, resulting in a logarithmically compressed video signal. It is synthesized as a signal and output.

In this way, lower-level reflected waves are received in a limited bandwidth at lower frequencies, and conversely, strong reflected waves from sources giving high-level reflections are received in a limited bandwidth at lower frequencies. can be received in a band containing higher frequencies that can better represent the fine structure of the reflected source.

Although the configuration diagram of the embodiment shows a case where the amplifier circuit system is configured with four stages, the number of stages is not limited to this and can be increased or decreased as appropriate. Furthermore, even if the delay times are not precisely matched and added as in the embodiment, simply adding the outputs of the respective detectors may be sufficiently practical depending on the purpose. FIG. 3 shows another configuration example for implementing the present invention, and the first point is that the bandwidth is narrowed toward the later stages.
This is different from the method shown in the figure. i.e. logarithmic amplifier
_A1 to _A4 each have a band pass band with different characteristics.
Filters BPF ₃₁ to _{BPF 34} are installed in front, and the output of each logarithmic amplifier is directly connected to a detector (DET ₁ to _{DET 4} ).
The configuration is such that the wave is detected by

The frequency bandwidths F ₁ , F ₂ , F ₃ , F ₄ of the band pass filters BPF ₃₁ to BPF ₃₄ are wider in the first stage and narrower in the later stages, depending on the selection characteristics of the filters in each stage. is selected to be included in the total up to the previous stage. As a result, the characteristics of filter BPF ₃₁ are applied to the output of the first stage amplifier circuit, and the characteristics obtained by multiplying the characteristics of each filter up to the previous stage by the characteristics of the filter are imposed on the outputs of the second and subsequent stages. , Therefore, a characteristic multiplied by the characteristics of all the filters BPF ₃₁ to _{BPF 34} acts on the output of the final stage circuit.

6. The reflected wave receiving method of the present invention can be effectively and consistently realized by the sequential cascading method as described above.

Note that the filters BPF ₃₁ to BPF ₃₄ shown in FIG. 3 do not necessarily need to be band pass filters, and may be partially or entirely configured as a low pass (or high pass) filter. Also in this case, the delay lines DL1 _{to DL3} are not indispensable and may be omitted depending on the purpose.

FIG. 4 shows still another configuration example for implementing the reflected wave receiving method of the present invention, in which the level of the reflected wave is determined and the impulse response of the receiving system is changed accordingly to receive the reflected wave. It is configured so that it can be done. In Figure 4, EXC is the probe
TD drive circuit, A ₄₁ and A ₄₂ are logarithmic amplifiers, VF is a variable characteristic circuit, DET ₄₁ is a detector, CMP is a comparator,
LPF is a smoothing means, and usually a low-pass filter is used. The drive circuit EXC drives the probe TD to emit ultrasonic waves, and the reflected waves are sent to the probe.
The electrical signal is received via the TD and appropriately amplified by the first-stage logarithmic amplifier _A41 . Next, after passing through the variable characteristic circuit, the logarithmic amplifier A ₄₂ and the detector
A video signal containing a DC component is obtained by amplification and detection through DET ₄₁ . Comparator CMP this video signal
The result is compared with a reference value, that is, a semi-fixed reference voltage V _ref , and the result is passed through a low pass filter LPF to remove high frequency components, perform appropriate rounding, and then fed to the variable characteristic circuit VF to perform feedback control. is being carried out. The variable characteristic circuit VF is constructed so that the frequency band of signal processing changes according to the control voltage applied from the low pass filter LPF, and one implementation thereof is shown in FIG. This consists of a delay line DL ₅₁ with a tap and a variable coefficient coupler K ₅₁ connected to this tap, respectively.
K _5o and a summing amplifier As ₅₁ that adds the outputs of these variable coefficient couplers K ₅₁ to K _5o , and is what is called a transversal signal processing circuit. The delay line with taps DL ₅₁ has multiple taps, one end of which is connected to the load resistor R ₅₁ , and is inserted and connected between each of these taps and the common line to adjust the static voltage according to the externally applied control voltage. Variable capacitance with variable capacitance CV ₅₁ ~ CV _5o
It is composed of By changing the capacitance of these variable capacitors, the signal propagation speed of this delay line is changed, thereby changing the unit sampling rate on the time axis at which signal processing is performed, and thus the frequency given by the entire structure. It is now possible to change the characteristic or scale factor of the impulse response.

The variable capacitances CV ₅₁ to CV _5o are, for example, variable capacitance diodes CVna, CVnb connected in anti-series, and a relatively high resistance value whose one end is connected to their common connection point, as shown in Fig. 6. By applying a control voltage from the other end of the resistor ₆₁ , the capacitance can be increased without requiring a bypass of the signal current flowing through _the variable capacitance diode. It can be changed. Such an anti-series configuration is more advantageous in preventing interference between the signal to be processed and the control voltage, especially when high-speed control is desired.

In any case, when performing such transversal signal processing, it is necessary to use a variable delay line.
It is not necessary to use all the taps in DL ₅₁ , and you can safely ignore the parts where the coefficients can be approximated to zero. Furthermore, the signal processing for the sample value sequence on the time axis is not limited to such a specific transversal structure, and may be performed using a general digital filter or the like. In that case, the scale factor of the impulse response or frequency characteristic can be freely adjusted by changing the sampling frequency.

In either configuration, the comparator CMP may be a so-called comparator with a nominally infinite gain, but it may also be an ordinary differential amplifier with a finite moderate gain.

Furthermore, an integrator can also be applied to the low pass filter LPF. However, the response time of this feedback system must be sufficiently slower than one vibration of the waveform of the reflected wave, but the response time of the entire transmission and reception system of the ultrasonic pulse echo system must be on the time axis, that is, on the acoustic ray (Z axis). It is undesirable to be much slower than the resolution unit because it causes unexpected changes in image quality. It is best to select a delay time that is approximately the same as the resolution unit.

That is, even with the configuration shown in FIG.
The technical idea of the present invention can be realized in the same way as the circuit shown in FIG. That is, for high-level reflected waves from a reflection source that gives a strong level of reflection or from a reflection source close to the probe, only high-frequency signal components are extracted and processed. In an ultrasonic diagnostic apparatus, the higher the frequency of the signal, the higher the resolution can be, and the fine structure of the medium can be clearly seen. On the other hand, low-level reflected waves from a reflection source that gives a low-level reflection or a reflection source that is far from the probe are received while emphasizing the low range that matches the occupied spectrum and improving the S/N ratio. It is processed as follows.

As explained above, the reflected wave receiving method of the present invention extracts and processes the received signal by changing the frequency characteristics of the circuit depending on the level of the received reflected wave. Waves are received in a high frequency band, and low-level reflected waves are received in a low frequency band.

According to the method of the present invention, compared to a conventional method using only TGC, that is, a receiving means that simply controls only the amplification factor of the receiving system according to the distance of the reflection source (corresponding to the return time of the reflected wave). , a homogeneous and more precise B-mode image can be obtained regardless of the distance.

Although the present invention does not preclude the configuration in combination with the TGC method, a practically precise B-mode image can be obtained only by the receiving method of the present invention.

Furthermore, according to the present invention, areas with a strong reflected wave level (mainly those representing the fine structure), where the conventional TGC method collapses even when logarithmic compression is applied, making it impossible to understand the fine structure of the target object. The part expressed by the reflected waves of high frequency components) is processed so that it is received in the high frequency band, so the overall reception ranges from bright areas to dark areas.
A B-mode image with a large amount of information regarding the fine structure of the target object can be obtained.

Furthermore, the simple method based on the above-mentioned U.S. Pat. No. 4,016,750 applies unilaterally modified frequency characteristics to a target object that is located beyond a large body cavity that is transparent and has low attenuation. Therefore, the appearance of the target object ahead will be different depending on where such a body cavity exists and where it does not. It will be understood that a countermeasure against this problem is to carry out signal processing based on the dispersion actually experienced by the ultrasonic waves. In this case, dispersion can be better understood by using as an index the amount of attenuation suffered, that is, the strength of the reflected wave coming from the target object, as adopted in the present invention. Therefore, the present invention can obtain more substantial tomographic images without being affected by the presence or absence of body cavities, as described above.

[Brief explanation of the drawing]

FIG. 1 is a main part configuration diagram for explaining the reflected wave receiving method of the ultrasonic diagnostic apparatus according to the present invention, FIG. 2 is an operation waveform diagram for explaining the reflected wave receiving method, and FIGS. 3 and 4 The figure shows another configuration example for carrying out the present invention, FIG. 5 is a configuration diagram showing an embodiment of the variable characteristic circuit VF shown in FIG. 4, and FIG. 6 shows a specific example of a variable capacitor. FIG. A ₁ ~ _{A 4} , A ₄₁ , A ₄₂ ... Logarithmic amplifier, LM ₁ ~ _{LM 3}
… Limiter, BPF ₁ ~ BPF ₄ , BPF ₃₁ ~ _{BPF 34} … Band pass filter, DET ₁ ~ DET ₄ , DET ₄₁
…Detector, DL ₁ to DL ₃ …Delay line, As,
As ₅₁ ...summing amplifier, VF...variable characteristic circuit, CMP...
Comparator, LPF...Low pass filter, DL ₅₁ ...
Delay line with tap, L...inductance,
CVna, CVnb...variable capacitance diode, K ₅₁ ~ K _5o
...Variable coefficient combiner.

Claims (1)

[Scope of Claims] 1. In an ultrasonic diagnostic apparatus configured to emit ultrasonic waves to a subject, receive and process the reflected waves by a signal processing means, and perform B-mode display based on the processed signals. , wherein the signal processing means receives the reflected wave signal in a high frequency band when the level of the reflected wave signal is high, and receives it in the low frequency band when the level of the reflected wave signal is low. Reflected wave reception method for ultrasonic diagnostic equipment. 2. The signal processing means includes a logarithmic amplifier that logarithmically amplifies the reflected wave signal, and a variable characteristic circuit whose frequency band when processing the reflected wave signal via the logarithmic amplifier changes in accordance with an external control voltage. , a detector that detects the reflected wave signal via this variable characteristic circuit to obtain a video signal; a comparator that compares the output of this detector with a reference value; and a comparator that smoothes the output of this comparator and obtains a video signal. Claim 1, further comprising: smoothing means for obtaining a control voltage to be fed back to the circuit; and a frequency band for signal processing is changed according to the level of a received reflected wave signal. Reflected wave reception method of the ultrasonic diagnostic device described. 3. The signal processing means includes: a successive saturation type logarithmic amplifier circuit formed by cascading a plurality of logarithmic amplifiers each having a limiter for limiting the amplitude of the input signal; It consists of multiple band pass filters with different characteristics, multiple detectors that individually detect the outputs of these band pass filters, and the outputs of these detectors are finally summed and amplified. a summing amplifier for obtaining a logarithmically compressed video signal; A reflected wave receiving system for an ultrasonic diagnostic apparatus according to claim 1, characterized in that: 4. The signal processing means is a successive saturation type formed by cascading a plurality of logarithmic amplifiers, each of which is preceded by a band pass filter with a different frequency band and a limiter for limiting the amplitude of the input signal. A logarithmic amplifier circuit, a plurality of detectors that respectively detect the outputs of the logarithmic amplifiers, and a summing amplifier that ultimately adds and amplifies all the outputs of these detectors to obtain a logarithmically compressed video signal. The ultrasonic wave according to claim 1, characterized in that the signal processing is performed so that the frequency band becomes higher as the band pass filter is connected to the logarithmic amplifier in the preceding stage. Reflected wave reception method for diagnostic equipment. 5. The ultrasonic diagnostic apparatus according to claim 2, wherein the variable characteristic circuit is configured such that the sampling rate of the input reflected wave signal changes depending on an external control voltage. Wave reception method. 6 The variable characteristic circuit uses an LC ladder type delay line having a large number of intermediate taps, a variable capacitance diode is connected between each of these taps and a common line, and the external control voltage is applied to the variable capacitance diode. a plurality of variable coefficient combiners each connected to each or a selected portion of the plurality of intermediate taps; and a variable coefficient combiner configured to add the outputs of the variable coefficient combiners. 3. A reflected wave receiving method for an ultrasonic diagnostic apparatus according to claim 2, characterized in that the method comprises a summing amplifier.