JPS5869537A - Ultrasonic photographing apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a transmitting and receiving device of an ultrasonic imaging apparatus that displays a tomographic image of an irradiation site using reflected pulses obtained by intermittently emitting ultrasonic pulses to a subject.

First, the transmitting device will be explained.

Conventionally, in such ultrasonic imaging devices, the electric pulse signal that intermittently drives the transducer to transmit ultrasonic pulses is either (a) a sharp pulse close to an impulse as shown in FIG. ) Figure 2A, a.

It was a burst signal consisting of one to several waves with a frequency waveform matching the resonant frequency of the vibrator as shown in FIG. In the case of the pulse (b), as shown in Figure 1B, the frequency vs. amplitude spectrum distribution is almost uniform over a wide band (hereinafter simply "
spectral distribution. ), and the spectral distribution of the ultrasonic pulse emitted thereby is determined by the resonant frequency characteristic of the transducer shown in FIG. 1C, and is approximately the same as the frequency characteristic as shown in FIG. (B)
In the case of a burst, as shown in FIG. 2B, the spectral distribution is determined by the wave number of the burst with the resonant frequency fo of the vibrator as the center. In FIG. 2B, the solid line shows the spectral distribution when driving with one burst wave (solid line) of a in FIG. 2A, and the dotted line shows the spectral distribution when driving with three burst waves (dotted line). As shown in the second diagram, the spectral distribution of the ultrasonic pulse emitted by a burst with such a spectral distribution becomes narrower than the frequency characteristic determined by the resonant frequency characteristic of the transducer as the wave number of the burst increases. . Ultimately, in both cases (a) and (b), the spectral distribution of the ultrasonic pulse emitted from the transducer has a center frequency that coincides with the resonance frequency fo of the transducer, and is determined by the resonance frequency characteristics of the transducer. It is almost the same as or narrower than the characteristic. Moreover, since the ultrasonic pulse passes through the transducer twice, once for transmission and once for reception, the spectral distribution of the received signal becomes even narrower. Therefore, as a result, in the conventional ultrasonic imaging apparatus, an image is constructed of signals having a spectral distribution in a narrow range centered on the resonant frequency of the transducer used.

In an ultrasound imaging device, the resolution in the distance (depth) direction is determined by the length and duration of the ultrasound pulse, and the shorter the pulse length, the better the resolution. Also, the length of the ultrasound pulse is influenced by the spectral distribution of the ultrasound pulse, with pulses with broader spectral distributions having shorter lengths, as shown in FIG. FIG. 3A shows the spectral distribution when the pulse length is long, and FIG. 3B shows the spectral distribution when the pulse length is short. In other words, widening the spectral distribution of ultrasonic pulses improves distance resolution.

However, even if you try to widen the spectral distribution of the ultrasonic pulse, with the conventional method, the spectral distribution will become narrow due to the resonant frequency characteristics of the transducer (Fig. 1C), so it is difficult to shorten the length of the ultrasonic pulse. was difficult and had its limits.

On the other hand, it is already known that a tomographic image obtained by an ultrasonic imaging device changes depending on the frequency of the emitted ultrasonic waves. That is, increasing the frequency improves the resolution in the azimuth (spread) direction, and conversely decreasing it decreases the resolution. Regarding sensitivity, the higher the frequency, the higher the amount of attenuation, so if the frequency is raised, the sensitivity at long distances will decrease, making it difficult to observe well. On the other hand, if you lower the frequency, you can observe over long distances. This means that a device with a specific vibrator frequency, for example, a device whose purpose is to increase the frequency and improve resolution at short distances, has advantages in one aspect but disadvantages in the other. Therefore, conventionally, when there are several different purposes such as when the observation site only needs to be observed at a short distance or when it is desired to observe over a long distance, several types of oscillators are prepared corresponding to those purposes and these are used. There was a problem that it had to be replaced before use.

In view of the above-mentioned circumstances, the transmitting device used in the present invention distorts the electric pulse signal that drives the vibrator in advance and operates (corrects) it so that its spectral distribution changes, thereby counteracting the resonant frequency characteristics of the vibrator. It emits ultrasonic pulses with a desired spectral distribution. The correction operation for changing the spectral distribution of the driving pulse of the transducer differs depending on the purpose of the tomographic image to be obtained. Hereinafter, the principle and examples of the transmitting device used in the present invention will be explained with reference to the drawings.

Among the above conventional problems, the spectral distribution of the ultrasonic pulse becomes narrow band due to the resonant frequency characteristics of the transducer, and the distance resolution decreases due to the longer pulse length. By forcibly driving at a plurality of frequencies shifted from the resonant frequency, it is possible to widen the spectrum distribution of the emitted ultrasonic pulse and shorten the pulse length.

FIG. 4 is a spectrum distribution diagram for explaining this. FIG. 4A shows a situation when the resonant frequency of the vibrator is set to fo and the vibrator is driven with one burst wave of frequency fo. The left side of the figure shows the spectral distribution of this drive pulse and corresponds to the solid curve in FIG. 2B. ), the right side of the figure shows the spectral distribution of the ultrasonic pulse (corresponds to the solid curve in the second figure). The drive pulse waveform and ultrasonic pulse waveform are shown at the upper right of each spectrum distribution diagram. The ultrasonic pulse in this case becomes a long pulse as shown in FIG. 3A. FIG. 4B shows fl-upper fo
, f2=2fl, and the situation is shown when the vibrator is driven by simultaneously applying one burst wave having two frequencies of 1.5 fl + '2. In the diagram on the left side of the same figure, the dotted curves each represent the spectral distribution of one burst wave having the frequency ft + f2, and the solid curve represents the composite spectral distribution. However, the composite spectral distribution is drawn by halving the actual composite value. The drive pulse waveform in this case becomes a distorted waveform as shown in the upper right corner of the figure. When the drive pulse waveform is distorted in this way, the transducer is forcibly driven against the resonance frequency characteristics of the transducer as shown in Figure 1C, and the spectral distribution of the emitted ultrasonic pulse is as shown in Figure 4. As shown in the diagram on the right side of B, the band becomes relatively wide. The pulse length is also shortened as shown in the upper right corner of the figure, and therefore the length of the reflected pulse is also shortened, and the distance resolution of the tomographic image is improved. Here, the frequency is fl t
'202 types have been shown, but various combinations are also possible.

Further, among the above conventional problems, differences in tomographic images due to differences in frequency can be dealt with as follows. That is, by forcibly driving the vibrator by applying a signal with a frequency different from its resonant frequency fo, the center frequency of the ultrasonic pulse emitted against the resonant frequency characteristics of the vibrator is moved to some extent, and This generates more frequency components than the resonant frequency than conventional methods.

In this way, the spectral distribution of the ultrasound pulse can be changed to some extent without having to change the transducer each time to change the frequency of the ultrasound pulse, and it is possible to obtain tomographic images with different characteristics for various purposes. I can do this.

For example, if a burst of frequency fo=f1 is added to a burst of frequency fo, the center frequency and spectral distribution of the emitted ultrasonic pulse will shift to a lower direction, and the sensitivity at a long distance can be improved. , and the frequency f
When a burst of frequency 1,5fO=f2 is added to the burst of O, the center frequency and spectral distribution of the emitted ultrasonic pulse move higher, and the resolution can be improved.

In this way, only one type of vibrator can be used to serve different purposes, but the above is just one example and other combinations are of course possible.

FIG. 5 is a block diagram showing a first example of a transmitting device used in the present invention, and FIG. 6 is a waveform diagram for explaining its operation. A, B, ..., J in Fig. 6 are the 5th
The signals appearing at the positions of ■, ■, ..., ■ shown in the figure are shown. A circuit for receiving the reflected pulse of the transmitted pulse by the transmitting device used in the present invention will be explained later. In the figure, (1) is a synchronization signal generating circuit which generates a synchronization signal as shown in FIG. 6A and supplies it to the transmitting circuit and the receiving circuit. (2)
A fundamental frequency oscillation circuit generates a fundamental frequency burst as shown in FIG. 6B in synchronization with a synchronizing signal. (3) is a frequency variable circuit for changing the fundamental frequency, and (4) is a burst wave number variable circuit for changing the burst wave number.

(51) y (52) +..., (5n) are frequency divider circuits with different frequency division ratios, and in Figure 6 C, D, and E, the frequency divider circuit (51) is 1/ 2. (52) is '/3 t
(5n) has a frequency division ratio of 1/60, that is, the waveform is shown when n=3. (61) + (62) t...
...t (6n) is a waveform shaping circuit that converts the frequency-divided burst into a sine wave burst, as shown in FIGS. 6F and G.

H indicates the output waveform. (7) is a selection circuit that selects a desired one from among these burst waves. The figure shows the case where signals G and H in FIG. 6 are selected.

(8) is an adder circuit whose output is as shown in FIG. 6J. (9) is a vibrator that transmits ultrasonic pulses and receives reflected pulses.

Although not shown in the above example, the amplitude level of each burst signal can be made variable, and the waveform shaping does not necessarily have to be a sine wave burst.

In this way, by selecting the number of frequency division ratios of the frequency dividing circuit, such as two, it is possible to generate pulse waveforms having various spectral distributions depending on the purpose.

FIG. 7 is a block diagram showing a second example of a transmitting device used in the present invention. In the figure, parts corresponding to those in FIG. 5 are given the same reference numerals. In this example, separate burst wave oscillation circuits (lh) + (112) are synchronized with the synchronization signal.
, . . . t (lln), each burst wave is generated separately. It is also possible to generate bursts of different frequencies and wave numbers in the Nokust wave oscillation circuits (111) to (lln).

FIG. 8 is a block diagram showing a third example of a transmitting device used in the present invention, and FIG. 9 is a waveform diagram for explaining its operation. In this example, instead of simultaneously generating and adding a plurality of types of Nost waves in parallel, they are generated and added with a time shift.

In the figure, illustration of the selection circuit is omitted. Figure 9 A-H
8 shows signal waveforms corresponding to the positions in FIG. 8a-h.

FIG. 9H shows the case where n=3 and the bursts E, F, and G in FIG. 9 are added, as in the case of FIG. 5. Note that the waveform shown in FIG. 9H in which the frequency changes continuously can also be generated using a sweep oscillation circuit.

FIG. 10 is a block diagram showing a fourth example of a transmitting device used in the present invention. In the figure, (131).

(132) s...-...+ (13n) is a read-only memory (ROM) in which waveforms with various required spectral distributions are stored in advance. α: waveform selection (ROM selection) signal generation circuit, 05): ROM
This is a read clock generation circuit. That is, in this example, waveform reading of the selected ROM in synchronization with the synchronization signal,
The signal is passed through an OR circuit αe and then subjected to D/A conversion by a digital-to-analog converter σD to drive a vibrator (9).

When using the transmitting device as described above, by driving the transducer with a corrected electric pulse that changes the spectral distribution of the electric pulse applied to the transducer, the length of the ultrasonic pulse is shortened and the resolution in the distance direction is increased. In addition, it is possible to obtain good tomographic images suitable for various purposes by changing the spectral distribution of ultrasound pulses without replacing the transducer.

Next, the receiving device will be explained.

In general, the attenuation characteristics of living bodies for ultrasound waves change the frequency to f
(MHz), the propagation distance is D (Cm), and the attenuation is A (dB).
), then A = fpD...(1) is given, and P (constant) is around 1.

In order to correct this amount of attenuation, a method is used in which the sensitivity of the receiving amplifier is changed over time in accordance with the propagation distance.

If the sensitivity of the receiving amplifier is G (dB) and the magnitude of the amplified signal is a constant value, then A 10=K...m-(2
) to G: to -f D ------(3)
Therefore, the temporal rate of change of the sensitivity of the receiving amplifier is a function of the frequency f. However, in the past, it has been common practice to select this rate of change in accordance with the vicinity of the resonant frequency of the probe, or to set a constant value from the operation panel of the device. In any case, in the conventional method, the temporal change rate of sensitivity G is
It becomes a constant value that is set.

In an actual ultrasonic imaging device, a pulse waveform is used for ultrasonic waves. Ultrasonic pulses always have a certain range of frequency bands, not just specific frequencies. Therefore, if the rate of change in sensitivity versus time of the receiving amplifier is set to match a specific frequency fO within this frequency band, the correction will be excessive for frequency components lower than fo, and for frequency components higher than fo'. It is too small for that. This means that the received reflected echo is not completely corrected for the attenuation characteristics of the living body, resulting in waveform distortion and deterioration of the tomographic image.

Therefore, the amount of attenuation to be corrected in the receiving amplifier is different for each frequency component, and the rate of change in sensitivity with respect to time must also be given a different value for each frequency component.

FIG. 11A is a spectral distribution diagram showing the change in frequency versus amplitude depending on the distance of the ultrasonic pulse, and FIG. 11B is
It is a diagram showing changes in sensitivity versus time that should be given for each frequency in order to correct it. In FIG. 11A, curve a is the spectral distribution of the transmitted waveform, and curve a is the distance (depth) Dz
Curve C shows the spectral distribution at distance D2, and curve d shows the spectral distribution at distance D3 (where /I A1 D3>02 >DI). Further, fo is the center frequency of the spectral distribution a, and fl is the center frequency of the spectral distribution d.

f2 indicates a higher frequency than fo. In FIG. 11B, tl and '2t'3 are respectively distances D1. D2.
The propagation time corresponding to D3, Sfo, Sfl, Sr1
are frequencies fo, f1., respectively. The change in sensitivity versus time for f2 is shown.

However, since Sfo, Sfl, and Sr1 have limits in the dynamic range and range in an actual device, curves such as those shown by broken lines may be used. Also, G,
is the sensitivity at time 0, Gl t e21 G3 is the sensitivity at time t1. t2. The sensitivity at t3 is shown.

In this way, the receiving device used in the present invention continuously changes the sensitivity of the receiving amplifier not only with respect to propagation time but also with respect to frequency components in order to obtain different correction characteristics for each frequency component, thereby achieving more accurate correction. to reduce waveform distortion,
This prevents deterioration of tomographic images.

FIG. 12 is a curve diagram showing changes in frequency characteristics of sensitivity versus time by the receiving device used in the present invention.

In the figure, the same symbols as in Figure 11 have the same meanings.
) The expressions so, stl, Si2, st3 are
Each time t=0. t=t1, t==t2,
The frequency characteristic of sensitivity versus time at t=t3 is shown. Moreover, the broken line in the figure indicates the practical range due to the above-mentioned limitations.

By giving such a change in frequency characteristics to the sensitivity versus time, the received reflected electrical signal (echo) has more accurate sensitivity correction for each of its constituent frequency components, resulting in less distortion. It is possible to display tomographic images in waveforms.

FIG. 13 is a block diagram schematically showing a receiving device used in the present invention. In the figure, the part surrounded by the broken line is the receiving device. For convenience of explanation, the transmitting circuit (19) is assumed to be the same as the conventional one. Oscillator (9), synchronous signal generation circuit (1
), XY sweep signal generation circuit Q4), logarithmic amplifier 0j)
, the detection circuit (2) and the display device (c) are the same as the conventional ones, so their explanation will be omitted.The time vs. sensitivity frequency characteristic correction circuit (1) changes the time vs. The synchronizing signal generating circuit (1) generates a synchronizing signal for intermittently generating ultrasonic pulses and sends it to the transmitting circuit O06), and also adjusts the sensitivity of the receiving amplifier in synchronization with this. In order to change the time and frequency, a synchronization signal is sent to the time-sensitivity frequency characteristic correction circuit (2).

FIG. 14 is a block diagram showing a first example of the time-sensitivity frequency characteristic correction circuit 00) in FIG. 13. In this example, the time-sensitivity frequency characteristic correction circuit is a tuned amplifier circuit (251
) s (25z), . . . t (25n) connected in a staggered manner. Stagger stage number n
is selected depending on the desired band characteristics. Each tuned amplifier circuit can use a known circuit as shown in FIG.
By changing the voltage of 9), the amplification degree can be adjusted to
It can be made variable by controlling the gate voltage of each, but other methods may also be used.

Tuning frequency control signal generation circuit (261) t (262
)t...

(26n) and amplification control signal generation circuit <271) t
(272).

...s (27n) is each tuned amplifier circuit (251), (252) t... in synchronization with the synchronization signal.
・* A sweep signal is generated to vary the tuning frequency and amplification degree of (25n) (see Fig. 17), but the characteristics of each stage are determined according to the desired frequency characteristics.

FIG. 16 is a frequency characteristic curve diagram of sensitivity versus time showing an example of operation when the circuit of FIG. 14 is used as a three-stage stagger. In this way, by moving the tuning frequency of each tuned amplifier circuit to a lower side with time and simultaneously changing the amplification degree of each stage, it is possible to obtain a desired time-sensitivity frequency characteristic. FIG. 17 is a waveform diagram for explaining the circuit operation of FIG. 14. In the figure, a, b-d, e-g
, h indicate signal waveforms appearing at positions ■, ■~■, ■~■, and ■ shown in FIG.

FIG. 18 is a block diagram showing a second example of the time-sensitivity frequency characteristic correction circuit used in the present invention.

In the example shown in Fig. 14, the tuning frequency of the tuned amplifier circuit was changed over time, but in this example, all the required bands are divided into multiple narrow bands, and each frequency is fixed, and the amplification level is The desired characteristics can be obtained by changing only the following. Narrow band amplification variable tuning amplifier (311) + (31z) in the figure.

(31n) may be configured by a combination of a narrow band filter and a variable amplifier circuit, or may use a narrow band tuning amplifier whose amplification degree can be changed. In addition, instead of parallel connection,
You can also use a staggered method connected in series.

When the receiving device described above is used, the received reflected echoes are corrected more accurately than conventional ones for the attenuation characteristics of the living body, and waveform distortion is reduced and tomographic image deterioration is prevented. Since the frequency characteristics of the amplifier can be set arbitrarily, in addition to correcting the amount of attenuation mentioned above, it is also possible to correct the characteristics of the transducer, emphasize low frequency components to improve long-range sensitivity, and improve resolution. This has the advantage of allowing operations such as emphasizing high frequency components.

The present invention is a combination of the above-described transmitting device and receiving device, and is characterized in that the frequency characteristic of the sensitivity versus time of the receiving circuit is changed in accordance with the manipulation of the spectral distribution performed during transmission. Although the effects described above can be obtained by using the above-mentioned transmitting device or receiving device alone, by combining the transmitting device and the receiving device, it is possible to obtain a signal with a more desired spectral distribution than by using the transmitting device and the receiving device alone. As a result, it is possible to obtain a tomographic image that is more accurately attenuated or enhanced in accordance with desired characteristics.

Furthermore, by combining the two, it is possible to have the transmitting circuit perform part of the desired correction characteristic and the receiving circuit to perform part of the desired correction characteristic.

In this way, it is possible to more accurately correct the amount of attenuation, and it is also possible to further enhance the degree of emphasis on the spectral distribution of the waveforms that make up the tomographic image depending on the tomographic image being sought, further increasing the degree of improvement of the tomographic image. be able to.

In addition, when the above-mentioned transmitter is forcibly driven by adding a frequency lower than the resonant frequency of the transducer in order to improve the sensitivity at a long distance, the center frequency and spectral distribution of the emitted ultrasonic pulse are low. While the sensitivity at long distances improves by moving toward the opposite direction, the resolution at short distances deteriorates. In this case, using the above-mentioned receiving device has a great effect. That is, during the period when reflected echoes from a short distance are being received, the sensitivity correction amount for high frequency components is made larger than the normal change in time versus sensitivity frequency characteristic. In this way, it is possible to correct the spectral distribution by emphasizing high-frequency components in the opposite way to the transmitting side, and prevent deterioration of resolution.

As described above, the present invention has the advantage of being able to obtain tomographic images that meet a wide range of purposes, such as improving long-distance sensitivity without replacing transducers or deteriorating resolution. be.

FIG. 19 is a block diagram showing an embodiment of the present invention.

In the figure, parts corresponding to those in FIG. 13 are given the same reference numerals. However, the transmitting circuit α■ has a spectral distribution correction circuit, and the transmitting waveform is selected by the output from the transmitting waveform selection circuit marked a, and the time vs. sensitivity frequency characteristic of the receiving amplifier is also set accordingly. This is different from FIG. 13 in this point. It goes without saying that the present invention is not limited to this example.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the spectral distribution of conventional ultrasonic pulses, Figure 3 is an explanatory diagram of the relationship between the length of the ultrasonic pulse and its spectral distribution, and Figure 4 is an explanation of the principle of the transmitter used in the present invention. Fig. 5 shows the first part of the transmitting device used in the present invention.
6 is a waveform diagram for explaining its operation. Section 7 is a block diagram showing a second example of the transmitting device used in the present invention. FIG. 8 is a block diagram showing the second example of the transmitting device used in the present invention. FIG. 9 is a waveform diagram for explaining its operation. FIG. 10 is a block diagram showing a fourth example of the transmitter used in the present invention. FIG. 11A is an ultrasonic A spectral distribution diagram showing changes in frequency vs. amplitude depending on the distance of the pulse, Figure 11B is a diagram showing changes in sensitivity vs. time to be given for each frequency for correction, and Figure 12 is a diagram showing changes in sensitivity vs. time by the receiving device used in the present invention. Curve diagram showing changes in frequency characteristics of sensitivity, 1st
3 is a block diagram showing an outline of the receiving device used in the present invention, FIG. 14 is a block diagram showing a first example of the time-sensitivity frequency characteristic correction circuit shown in FIG. 13, and FIG. A circuit diagram showing a specific example of an amplifier circuit, FIG. 16 is a time vs. sensitivity frequency characteristic curve diagram showing an example of the operation of the circuit in FIG. 14, FIG. 17 is a waveform diagram for explaining the operation of the circuit in FIG. 14, and FIG. 18 19 is a block diagram showing a second example of a time-sensitivity frequency characteristic correction circuit of a receiving apparatus used in the present invention, and FIG. 19 is a block diagram showing an embodiment of the present invention. (19)...Spectral distribution correction transmission circuit, (
2C1l...Time vs. sensitivity frequency characteristic correction circuit in the receiving device. <22Ω20 -1-1E <= Legal District ♀ Partial Procedural Amendment December 4, 1982 1, Case Description 1982 Patent Application No. 167662 2, Title of Invention Ultrasonic Imaging Device 3 , Person making the amendment 4, Agent 1-8-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo (
New housing building) 6. Number of inventions increased by amendment 7° Amendment (7) Sentence f Elephant Detailed explanation of the invention in the specification column 8, Contents of the amendment (1) Page 7 of the specification, lines 8-9 “Two Frequency...1
``waves'' is corrected to ``one burst wave with frequency f1 and two burst waves with frequency f2''. (2) Lines 11 to 12 of page 7 [of frequency fl...1 wave] are defined as "1 burst wave with frequency fl and frequency f
2 bursts with 2 waves.” (3) On page 13, line 8, "If it is set to a constant value" is corrected to "If it is set to a constant value and the initial value of the signal is AO". (4) Same page 13, line 9 JA+G=Kj as r (Ao-A)
Correct as +G=KJ. (5) Same page 13, line 10 [(3=to-fpD J to rG=
Correct it to -AO+fpDJ. that's all

Claims (1)

[Claims] In an ultrasonic imaging device that displays a tomographic image of the radiation site using reflected pulses obtained by intermittently emitting ultrasonic pulses to a subject, frequency versus amplitude of an electric pulse applied to a transducer that emits the ultrasonic pulses. A spectral distribution correction circuit is provided which corrects the spectral distribution so that an ultrasonic pulse having a desired predetermined frequency versus amplitude spectral distribution is emitted against the resonant frequency characteristics of the transducer, and The transducer is forcibly driven by an electric pulse to emit an ultrasonic pulse having the desired frequency versus amplitude spectral distribution, and a reflected electric signal obtained from the reflected pulse is transmitted from the ultrasonic pulse emission position to the emission site. The reflected electrical signal is amplified by a time-to-sensitivity change rate set in advance corresponding to the ultrasonic propagation time related to the distance to Ultrasonic imaging characterized in that a time-sensitivity frequency characteristic correction circuit that generates a reflected electric signal corrected by changing the rate of change in frequency characteristic is provided, and the tomographic image is displayed based on the corrected reflected electric signal. Device.