JPS63288143A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To clearly display the attenuation characteristic of local lesion without relying on the obscurity represented by the light and shade of the brightness behind the local lesion, by displaying a zero-value contour cross-line in the state superposed on a B-mode image by utilizing such a phenomenon that the center frequency of an ultrasonic echo spectrum is shifted to a low frequency side by attenuation. CONSTITUTION:When a signal selection circuit 7 selects the output video signal of a signal processing circuit 6, the B-mode image relating to the intensity of the reflected ultrasonic wave in a living body is displayed on an image display apparatus 11 in the same way as a usual diagnostic apparatus. When the signal selection circuit 7 selects the outputs of an event counter 21, the vibrator of an array probe 1 is excited by a processing control part 10 and a transmitting drive circuit 3 to emit ultrasonic beam to the interior of the living body and receives the ultrasonic reflected signal from the interior of the living body and said signal is added and compressed by a receiving phasing circuit 4. A line group of a white or black level is displayed on the image display apparatus in addition to the usual B-mode image so as to be superposed on said image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic diagnostic apparatus, and particularly to an ultrasonic diagnostic apparatus suitable for providing images and evaluation values that reflect ultrasonic attenuation in living tissues.

[Conventional technology]

The ultrasound pulse is displayed two-dimensionally (B mode) by associating the intensity of the reflected echo from within the body of the ultrasound pulse emitted into the living body with the luminance.

The influence of attenuation characteristics on B-mode images is as follows for local lesions:
For example, if the inside of the cyst in the liver shown in section A of Figure 3 (a) is fluid, it is detected that the acoustic shadow or acoustic enhancement appears deeper than the lesion. Because the attenuation is less than the surrounding healthy tissue, areas of acoustic enhancement appear behind the bulla that are brighter than others. On the other hand, the appearance of an acoustic shadow in which the brightness behind the bleb is darker than the surrounding area, as shown in part B of FIG. 3(a), is thought to be due to the fact that the attenuation inside the bleb is greater than in the surrounding healthy area.

Conventionally, it has been common practice to distinguish the magnitude of attenuation of a lesion from the brightness and darkness behind one local lesion on a B-mode image and discuss the nature of the lesion. However, in recent years, in ultrasonic diagnosis, the correlation between the pathological condition of the tissue and the attenuation characteristics is determined by distinguishing the attenuation characteristics specific to each tissue in the living body, thereby improving the diagnostic ability of ultrasound diagnostic equipment. Many attempts are being made to improve it.

An example of a related device of this type is the device disclosed in Japanese Unexamined Patent Publication No. 59-218144.

[Problem that the invention seeks to solve]

However, discriminating brightness from light and dark requires considerable skill, and TGC (Time Gain Control)
There is a problem in that it depends on the operator depending on the setting conditions of the device such as rol) or subtle differences in brightness. Moreover, even though it produces the same acoustic shadow, it may not be the effect of attenuation. Figure 3 (b
The 0th part of ) is an example of this.1 The brightness behind it becomes darker due to scattering by a strong reflector, and it is difficult to distinguish it from a shadow due to attenuation simply by the presence or absence of a shadow.

This is the first problem.

Furthermore, among the methods for measuring the attenuation characteristics of tissues, there is estimation of the center frequency of the ultrasonic power spectrum using the zero-crossing method, which is simple in terms of hardware and is suitable for real-time measurement. Regarding this, see "Spectrum characteristics and attenuation characteristics in ultrasonic waves" by S., W., Flux et al.
1, 5.95-116 (1983). This method approximates the power spectrum of an ultrasound pulse in living tissue to a Gaussian distribution, and assuming that the attenuation of ultrasound due to propagation is proportional to frequency, the number of zero crossings λ per unit time is the center frequency of the spectrum. It takes advantage of the fact that it is roughly proportional to . That is, the power spectrum S, (f) of the incident ultrasonic wave.

Here, fo is the center frequency of the probe, σ is the pulse bandwidth, and C is the proportionality constant.

Then, the power spectrum 5(f) after propagating within the living body by a distance iWQ changes as α is the attenuation constant of the tissue. The above formula (2) can be rewritten as fc=f,-aQa''.

In other words, due to attenuation, the center frequency of the power spectrum of the ultrasonic pulse shifts by aQa2 toward the lower frequency side. On the other hand, the frequency λ of zero crossings per unit time is given by λ = 2 [f, ``+ σ'']''/'''' (3) 1Usually, since f, > σ, λ white 2f,
=2(f, -aQa2) (4).

Therefore, conventionally, in estimating the attenuation characteristics of biological tissues using the zero-crossing method, the depth dependence of the zero-crossing frequency λ of the received RF signal is determined, and the attenuation constant α is determined from the gradient thereof. That is, as shown in Fig. 5, a waveform with a certain time width (indicated by a in Fig. 5) is cut out from the received RF waveform, the number of zero crossings is taken as the frequency analysis result, and this procedure is repeated to gradually increase the time width. This is repeated while shifting (as shown by c and c in Figure 5).

But here is the second problem. In other words, if a certain time width for cutting out a waveform must be filled with ultrasonic RF pulses, a large error will occur. Figure 6 explains this situation, with waveform (a)
is an enlarged display of the waveform within the analysis time width of the received RF signal (see FIG. 6(c)), and waveform (b) shows the output waveform of the zero-crossing detector which inputs this RF multiplied signal.

In part A where no ultrasonic pulse signal exists, there is no output from the zero-crossing detector, so when counted in the analysis time width, the counted value gives a lower value than if it were all filled with RF waveforms. This indicates that even if the center frequency of the reflected RF multiplied signal does not shift to the lower frequency side, the center frequency is estimated to be apparently lower due to the loss of the reflected RF multiplied signal. Moreover, such reflected RF multiplied signal loss is often observed in echo waveforms from living bodies.

For example, when the attenuation characteristics of the liver are to be discriminated, the above-mentioned omissions are likely to occur because blood vessels, lymph vessels, and other vessels within the organ do not have echo sources inside them. conventionally,
For this reason, this problem has been avoided by emitting the ultrasound beam in a direction where there are no blood vessels. This meant that the target areas were significantly limited.

The present invention has been made in view of the above circumstances, and its first purpose is to solve the problem of brightness mentioned above as the first problem by solving the problem of brightness due to the ambiguity of the brightness behind the local lesion. The first object is to provide a means for clearly indicating the attenuation characteristics of a local lesion, and to also provide a means for discriminating whether the attenuation of an ultrasonic signal due to the lesion is due to reflection or attenuation.

A second object of the present invention is to solve the above-mentioned second problem by eliminating the effects of missing ultrasound reflected signals in discriminating the center frequency of the power spectrum of an ultrasound pulse using the zero-crossover method. The objective is to provide a means of discrimination.

[Means for solving problems]

The first object of the present invention is to detect zero-crossings in a received signal in an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image. A means for generating a pulse train, a means for counting the pulse train for a predetermined period, a means for detecting that the counted value has reached a predetermined number, and a detection time by the detection means is linearly displayed in a B-mode image. This is achieved by an ultrasonic diagnostic apparatus characterized in that it is provided with means for superimposing and displaying.

The second object of the present invention is to detect zero-crossings of received signals in an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image. means for generating a pulse train, means for counting the pulse train for a predetermined period, means for detecting a period in which the intensity of the received signal exceeds a predetermined threshold, and a zero-crossing count value in the predetermined counting period. This is achieved by an ultrasonic diagnostic apparatus characterized in that it is provided with means for determining the ratio between the period of time and the period of time.

[Effect]

In the first invention, the phenomenon in which the center frequency of the ultrasonic echo spectrum shifts to a lower frequency side due to attenuation is utilized to superimpose and display "equal zero crossing line", which will be described later, on the B-mode image. The attenuation characteristics of the local lesions described above are determined by changes in the intervals of the iso-cross lines and shifts in their appearance positions. In other words, the zero crossing of the received RF signal is detected, and every time the zero crossing occurs a certain number of times, B
The appearance position is superimposed and displayed on the mode image using white or black level. If the above procedure is performed two-dimensionally in accordance with the sweep of the ultrasound beam, an iso-zero intersection line group is obtained.

The interval between these equal-zero intersection lines reflects the attenuation characteristics of the previous region, and the analysis results will be briefly described below.

Formula (3) quoted from the above-mentioned report on S, W, flux, etc.
, usually fc)σ, so from depth Q to Q+
Assuming that zero crossing occurs N times during ΔQ, to find the above ΔQ, the propagation velocity can be set to C and then solved. The inventors obtained these results. From this, it can be seen that the interval between the iso-zero intersection lines is inversely proportional to the center frequency of the power spectrum in that region.

A detailed explanation of the present invention using the example of the liver shown above will be as follows. FIG. 4(a) corresponds to FIG. 3(a). In the fluid cyst in part A, the attenuation inside the cyst is smaller than in other healthy parts, so the center frequency at the back of the cyst is higher than in the adjacent healthy part. Therefore, a certain number of zero crossings occur over a shorter distance than in other healthy areas.

As a result, in the section A, a group of equizero intersection lines convex upward is superimposed and displayed. In addition, in part B of FIG. 3(a), the attenuation inside the cyst is larger than in other healthy areas, so the center frequency of the power spectrum behind the cyst becomes lower. For this reason, the appearance of a certain number of zero crossovers is cursed over longer distances compared to other healthy parts. As a result, in the B section, a group of equal zero crossing lines convex downward is superimposed and displayed.

In this way, the attenuation characteristics within the cyst, which is a local lesion, are primarily 1
Second, the magnitude of the attenuation is expressed as the amount of shift above and below the iso-zero intersection line group.Secondly, the magnitude of the attenuation is expressed as the amount of shift relative to other healthy parts, that is, the line group It can be clearly evaluated by the size of the interval.

Finally, using FIG. 4(b) corresponding to FIG. 3(b), it is shown that according to the present invention, it is possible to determine whether a shadow due to attenuation of a single reflected signal is due to reflection or high attenuation. show.

Part 0 in Figure 3(b) is 1, for example, like gallstones.

Ultrasonic waves are attenuated by a strong reflection source, which creates an acoustic shadow behind them. By the way, the center frequency does not shift due to attenuation due to attenuation and attenuation due to single reflection, and the frequency dependence of the single reflection phenomenon can be almost ignored.
This is because they are weak. Therefore, even behind the reflection source, the center frequency of the power spectrum remains the same as in other healthy areas, and therefore, as shown in FIG. 4(b), the shift in the iso-zero cross number line is slight.

The above describes an example of application of the present invention to local lesions, but the present invention is also useful in a wider range of organs.For example, as schematically shown in Fig. 4(c), Depending on the two-dimensional distribution, the iso-zero cross number lines appear in a polygonal shape and with varying intervals, and it is also possible to estimate the distribution of attenuation characteristics within the organ from the shape.

Note that in the second aspect of the invention, amplitude information of ultrasonic pulses, which has not been used in the past, is used to detect the number of zero crossings. In FIG. 6, the omission of the ultrasonic signal affects the discrimination of the center frequency because it is normalized to a constant time width. Therefore, in the present invention, the time width is equivalently shortened depending on the presence or absence of the signal. , the center frequency is determined by the ratio of the zero-crossing count value to this effective time width.

That is, in FIG. 7, the detected output (indicated by a broken line) is obtained for the received RF signal (a), the magnitude is compared with a predetermined threshold, and the counted value of the zero-crossing output and this The ratio of the comparison output to the high level time is determined as the true zero-crossing output frequency λ.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus showing an embodiment of the first invention. In FIG. 2 is a transmitting/receiving switch that selects the transmitting/receiving aperture and changes the signal flow associated with transmitting/receiving; 3 is a transmitting drive circuit that excites and drives each transducer of the transmitting aperture; 4 is each transducer selected as the receiving aperture. 5 is a receiving phasing circuit that performs addition that matches the phase of the received signals and logarithmic compression of the added signal; 5 is a detection circuit;

6 is FTC (Fast Time Con5tant)
This shows a signal processing circuit such as 7 is a signal selection circuit composed of an analog multiplexer, and 8 is an AD converter.

Reference numeral 9 indicates an image memory for storing B-mode images and the contour lines described below, 11 indicates an image display device, IO indicates a processing control unit that controls each of the above circuits, 20 indicates an analog comparator, and 21 indicates an event counter. The feature of the embodiment is that the signal selection circuit 7. Analog comparator 20. The point is that an event counter 21 is provided.

In the ultrasonic diagnostic apparatus of this embodiment configured as described above, when the signal selection circuit 7 selects the output video signal of the signal processing circuit 6, it selects the reflected ultrasound in the living body, as in a normal diagnostic apparatus. The B-mode image related to the intensity of is displayed on the image display device [
11 is displayed.

The operation when the signal selection circuit 7 selects the output of the event counter 21 will be described below based on the signal diagram of FIG. 2. When excited by the processing control unit IO and the transmission drive circuit 3, the transducer of the array probe 1 emits an ultrasound beam into the living body, and the ultrasound reflected signal from within the body is received by the transducer. , are added and compressed by the receiving phasing circuit 4 (FIG. 2(b): received RF signal).

The received RF signal is appropriately band-limited and then converted into a pulse train by the analog comparator 20. If the reference value of the comparator is the ground potential.

This comparator operates as a zero-crossing detector.

The pulse train is counted by the event counter 21, and a carry signal train (FIG. 2(d): counter carry signal) is output every time the counted value exceeds the maximum counted value of the counter. The carry signal is expanded to a certain width by a pulse width expansion means (not shown) so that it can be easily seen during display, and is applied to the selection control terminal of the signal selection circuit 7 (second
Figure (e): m selection signal).

The signal selection circuit 7 selects the white or black level when the 1 selection signal is High level, and selects the output of the signal processing circuit 6 when the 1 selection signal is Low level, and supplies the selected signal to the AD converter 8. Such a procedure is performed at a constant repetition period, and the ultrasound beam is swept, thereby obtaining a two-dimensional ultrasound image (FIG. 2(a): transmission control signal).

According to the second embodiment, in addition to the normal B-mode image, the image display device 11 displays a group of lines at a white or black level superimposed on the image display device 11.
Is displayed. The appearance positions of these line groups! 11 corresponds to the time when the carry signal of the counter 21 is generated, and the interval thereof is inversely proportional to the zero-crossing frequency of the received RF signal, in other words, the apparent frequency. It is something that can be realized.

Note that the counter 21 is preferably a so-called event counter, that is, the enable terminal of the counter is controlled so that counting can be performed at a predetermined time interval from a specific depth. In this embodiment, an enable signal whose appearance position Δτ is variable is used with the rising edge of the transmission control signal as the reference point (Fig. 2(c): enable
e signal). As a result, it is possible to measure the deviation of the iso-zero intersection line using an arbitrary depth of the B-mode image as a base line and only within an arbitrary region of interest.

In the above embodiment, a comparator and an event counter are used as a means for detecting the center frequency and generating equal zero crossing lines with intervals inversely proportional to the center frequency, but other digital circuit means 1, such as an AD converter and a digital comparator, are used. etc. may also be used. Furthermore, in the above embodiment, the signal selection circuit is switched according to the pulse train that appears on the zero intersection number line, but the output of the signal processing circuit and this pulse train may simply be added. Furthermore, when a color CRT is used as an image display device.

The B-mode image may be displayed as a black-and-white high-gradation image, and the equal zero-crossing lines may be displayed in color, and both may be displayed in a superimposed manner.

Next, FIG. 8 shows an embodiment of the second invention. FIG. 8 is a block diagram of an ultrasonic diagnostic apparatus showing an embodiment of the second invention.
11. 20 and 21 indicate the same elements as those of the embodiment shown in FIG. 1 above.

Further, 22 is a DA converter, 23 and 26 are sample and hold circuits, 24 is a comparator that inputs the video detection signal, 25 is an integrator, 27 is a divider, and 28 is the divider 27.
The output of λ (zero crossing frequency) - a two-dimensional representation of depth
Y display is shown. Note that (2) is a time control unit that performs the above display control.

In the ultrasonic diagnostic apparatus of this embodiment configured as described above, the received RF signal output of the receiving phasing circuit 4 (FIG. 9(b)
) is first applied to the RF comparator 20 (operating as a '8 crossing detector) to generate a zero crossing output pulse train. This pulse train is counted by the event counter 21, and the counted output is converted by the DA converter 22 into a gradually increasing polygonal line (see FIG. 9(f)).

In this example, the period of repeated ultrasonic transmission is divided into three equal parts, and each time width is used as the measurement period of the zero-crossing frequency (
9(a) and (e)), event counter 2
1 is reset at each starting time.

By configuring as described above, the output of the DA converter 22 is at the end point of this time width (t, t2 and tr in FIG. 9).
), it is proportional to the previous zero-crossing frequency. At this time, the sample hold circuit 23
This value is held until the next end point.

On the other hand, the output of the detector 5 (see FIG. 9(c)) is applied to the video comparator 24 and compared with a predetermined threshold,
A comparison output (see FIG. 9(d)) is generated.

When this signal is at High level, the received RF signal is present, and when this signal is at Low level, it indicates that the received RF signal is missing. This comparison output is converted by the integrator 25 into a gradually increasing polygonal waveform (see FIG. 9(g)).

This integral output is also reset at the rise and fall of the counting width signal (see Figure 9 (e)), and at the end point of this time width, the time during which the received RF signal existed within the counting period, respectively. The output is proportional to the sum of . At this end time, the value of this output is held by the sample hold circuit 26 until the next end time. Therefore, the output of the divider 27 (see FIG. 9(h)), which receives the outputs of the sample and hold circuits 23 and 26 as input, gives the ratio between the number of zero crossings and the effective counting time width. As stated, an output proportional to the true zero-crossing frequency is obtained regardless of the loss of the received RF signal.

If this output is input to the Y input of the X-Y display 28 and the sawtooth wave corresponding to the repeated transmission of ultrasonic waves from the time control unit 12 is input to the X input, the vertical axis will appear on the X-Y display 28. A curve is obtained in which the horizontal axis represents the depth within the body and the zero-crossing frequency.

Here, the actual measured values for the received RF signal shown in FIG. 6 are as follows.

In other words, the center frequency of the RF multiplied signal is 3.5 MI (z), but the zero-crossing output is 1 for the analysis time width of 3.6 μs.
7 times, therefore, according to the conventional method, λ= −= 4
, 72 MHz 3.6, which is significantly different from the true value of 7.0 MHz. On the other hand, according to the device of this embodiment, the detection comparison output is High.
The h level time is 2.39μS, and the zero crossing frequency is.

λ = - = 7, 11 MHz 2.39 , which agrees well with the true value.

According to experiments conducted by the present inventors, the conventional method sometimes shows only half the true value due to the effects of omissions, whereas
According to this example, it has been confirmed that the value falls within ±5% of the true value.

In the above embodiment, for convenience of explanation, the count width signal is set to 173, which is the transmission repetition time width, but of course,
Other widths may be used. In this case, a frequency analysis waveform as shown in the lower part of FIG. 5 is obtained on the X-Y display 28, and the attenuation constant (α) of the living tissue is determined from the slope .

In the above embodiment, the comparator outputs of the video domain and the RF domain were used and relied on analog calculations. However, the present invention is not limited to this. In fact, the RF reception output of the reception phasing circuit is High-speed AD conversion is performed and stored in a 1-line memory, which is then transferred to the memory in the personal computer, and the above-mentioned detection and comparison operation for the detection output, zero-crossing counting for the RF multiplied signal, and the zero-crossing counting value and effective counting time width are performed. Good results have been obtained even when the calculation of the ratio of , etc. is processed using software.

Furthermore, in this embodiment, an example was shown in which the B-mode image and the frequency analysis waveform were displayed on separate displays;
They may be superimposed and displayed on one display.

Note that in calculating the center frequency, the accuracy depends on the threshold of the video band comparator that determines the effective counting time.Normally, this threshold is approximately equal to the received RF
It is preferable to use the noise level of the signal, but if this threshold value is set large and an error occurs in the effective counting time width, it is also possible to correct it using the calculated center frequency itself.1For example, as shown in Figure 9. In , the value of the center station wave number at time t2 may deviate greatly from that at 70 and t3 depending on the setting of the threshold value.

In such a case, the average value of t□ and t is used as the value of t2. Such an operation is also considered appropriate because the distribution of the attenuation characteristics of tissues in a living body is continuous and drastic changes are unlikely.

〔Effect of the invention〕

As described above, according to the first invention, in an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image, the zero-crossing of the received signal is means for detecting and generating a pulse train, means for counting the pulse train for a predetermined period, means for detecting that the counted value has reached a predetermined number, and a detection time by the detection means in B mode. Since we have provided a means to superimpose and display the image in a linear manner, we have provided a means to clearly show the attenuation characteristics of a local lesion without depending on the ambiguity of the brightness behind the local lesion, and we have also provided a means for clearly indicating the attenuation characteristics of the local lesion, as well as a means to clearly show the attenuation characteristics of the local lesion, without depending on the ambiguity of the brightness behind the local lesion. This has the remarkable effect that it is possible to realize a means for discriminating whether attenuation is due to reflection or attenuation.

Further, according to the second invention, in an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image, a zero-crossing of a received signal is detected. means for generating a pulse train; means for counting the pulse train for a predetermined period; means for detecting a period in which the intensity of the received signal exceeds a predetermined threshold; By providing a means for determining the ratio to the period, it is possible to realize a discriminating means that is hardly affected by the omission of an ultrasonic reflected signal when discriminating the center frequency of the power spectrum of an ultrasonic pulse using the zero-crossover method. It is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus showing an embodiment of the first invention, FIG. 2 is a time chart of signals in the embodiment shown in FIG. 1, and FIG. 3 is an acoustic wave in a B-mode image. Figure 4 is a diagram showing the display form in the example, Figure 5 is a diagram showing the principle of attenuation determination by the zero-crossing method, and Figure 6 is the conventional zero-crossing method. 7 is a diagram showing the principle of the second invention,
FIG. 8 is a block diagram of an ultrasonic diagnostic apparatus showing an embodiment of the second invention, and FIG. 9 is a time chart of signals in the embodiment shown in FIG. 1: Array probe, 2: Transmission/reception switch, 3: Transmission drive circuit, 4: Reception phasing circuit, 5: Detection circuit, 6: Signal processing circuit, 7: Signal selection circuit, 8: AD converter, 9 : Image memory, IO: Processing control section, 11: Image display device, 12: Time control section, 20/24: Analog comparator, 21:
Event counter, 22: DA converter, 23, 26: Sample hold circuit, 25: Integrator, 27: Divider, 2
8: X-Y display. ^ ^ ^
^ ^, 5 Q
Q zu ■－ノ
−ノ ＋＋ −ノ
-No. 3 (a) (b) No. 4
figure . (a) (b) Figure 5 Depth Figure 6 (c) 1μS Analysis time width (3,6μS) Figure 7 Zero crosser output waveform Figure 9 Received RF signal counting signal (e)

Claims (1)

[Claims] 1. In an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image, a pulse train is generated by detecting zero crossings of the received signal. a means for generating the pulse train, a means for counting the pulse train for a predetermined period, a means for detecting that the counted value has reached a predetermined number, and a detection time by the detecting means is linearly superimposed on a B-mode image. - An ultrasonic diagnostic device characterized by being provided with a display means. 2. In an ultrasonic diagnostic apparatus that transmits ultrasonic pulses into a living body and receives and processes the reflected waves to obtain an echo intensity distribution image, means for detecting zero crossings of a received signal and generating a pulse train; means for counting the pulse train for a predetermined period; means for detecting a period during which the intensity of the received signal exceeds a predetermined threshold; and means for calculating the ratio of the zero-crossing count value in the predetermined counting period to the period. An ultrasonic diagnostic device characterized by being provided with.