JPS6279045A - Ultrasonic diagnostic apparatus using synthetic method - 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] [Industrial Application Field] The present invention relates to an ultrasonic diagnostic apparatus using a synthetic aperture method, and in particular, to transmitting ultrasonic waves into a subject and receiving the reflected waves to detect tomographic images within the subject. The present invention relates to an ultrasonic diagnostic device using a synthetic aperture method that can measure and display images.

[Prior art 1] The pulse echo method is often used in ultrasonic diagnostic equipment that transmits ultrasound waves into the subject, measures the echo signals, and displays KH2 images inside the subject. In general, dynamic focus technology is used to transmit a sharp ultrasonic beam to each point in the depth direction using an array type transducer. With this dynamic focus, the depth direction is divided into multiple regions, ultrasound is transmitted and received so that each region is focused on, and the ultrasound reflected waves from each region are measured. It is possible to obtain tomographic images, and by increasing the number of divided regions within a certain range, more precise lli inside the subject can be obtained.
Layer images can be displayed as images.

However, although the ultrasonic beam becomes sharper by increasing the number of divided areas, there is a drawback that it takes time to form one tomographic image because the number of times the ultrasonic waves are transmitted and received increases by the increased number of divided areas. For this reason, it has been proposed to apply the technique of the synthesis method, which is well known in the application fields of radar and sonar, to ultrasonic diagnostic equipment.

This composite amount [] method involves repeating transmission and reception while moving the transmitting/receiving position to transmit and receive ultrasonic waves within the subject, and after storing the received signal including the phase, each point within the subject is focused. This is a method of synthesizing the received waveforms to obtain an image signal of each point by 1υ, and this will be explained in detail based on FIG.

In the figure, T , T , T3. ... Assume that T is a vibrator and that there is a point fouling body P in front of it.

Then, when ultrasonic pulses are transmitted sequentially from these transducers, the received waveform received by the same transducer is u (t),
A waveform expressed as LJ (t), u3 (t) - u, (t) is obtained by 111, and this received waveform is recorded as a function of t during 115. As shown on the left side of FIG. 5, the received waveform recorded in this manner is composed of reflected waves from the point [ ], and in the synthetic aperture technique, a tomographic image is formed from this waveform data.

That is, in order to focus on point F shown in the figure, the received waveform U1 (t)(1-1...
・For waveform 5(n), waveform 5(
t). In other words, the oscillator Ti
, and the distance from point F to Q, the waveform s (t) is expressed as (2) where τ -2Q, /C (C: speed of sound)... (2).

Here, the operation of moving u and (t) to add and cover them corresponds to tightening the amplitude on the hyperbola indicated by a or p in the figure. In other words, when focusing on point F, it becomes the sum of the amplitudes on the hyperbola a, and the waves from point P are added at different phases, resulting in the tightening result s (t) becomes a small value. On the other hand, when the focal point F is made to coincide with the point P, that is, when the focus is placed on the point P, the amplitudes on the hyperbola p are added, and as is clear from the figure, each received waveform is added with the same phase. Therefore, the addition result, that is, a much larger value than 5(t)j.

According to the synthetic aperture technology as described above, it is possible to focus on any point from the data obtained by transmitting and receiving ultrasonic pulses for each of the imagers T1 to T1, and the focus By sequentially changing the positions, one tomographic image sequence is formed. In this case, since the focus corresponds to a pixel, a high-resolution image can be obtained. With this synthetic aperture technology, information on many focal points can be obtained at once by one transmission and reception of the camera element.
- It is possible to obtain information inside the subject extremely effectively without the disadvantage that the number of transmission and reception of ultrasonic pulses increases as the number of focal points increases as in the Kass technique.

In the above explanation, the same transducer is used to transmit and receive ultrasound, but in the synthetic frontage technology, there is no need to receive ultrasound using the same transducer, and it is not necessary to transmit the ultrasound. Ultrasonic waves can also be easily received with the camera element. For example, in response to the transmission of a transducer, an imager T.
In the case of 1 + received by this transducer, the signal can be easily synthesized by moving by (Q・+Q・ )/C when consolidating the waveform received by this transducer. .

Further, in the above description, it is assumed that the emitted ultrasonic waves are non-directional, but this synthetic aperture technique is also applied when the ultrasonic waves have sharp directivity.

For example, in FIG. 5, (2j+1) pieces of T 4 − J
4-G If we simultaneously excite the transducers of J and transmit m sound waves with sharp directivity, then the ultrasonic waves propagate along the straight line connecting transducer T4 and point F, and this It can be assumed that the signal does not propagate in any other direction.

Therefore, when (2j+1) oscillators are excited simultaneously, oscillators T, T2 . ... After simultaneously storing the received signals of each transducer of To, the synthetic aperture technique is applied as follows. In other words, the received signal of each vibrator is
(t), u2 (t) .

5(4) −in u, (t −t τ 4
+ τ 1 ) ... (3) τ di/
C...(4) [Problems to be solved by the invention] Problems with the prior art However, in the ultrasonic diagnostic apparatus using the synthetic aperture method described above, it is necessary to record the output signal of each transducer individually. Therefore, if the voltage level of these output signals is very small, there is a drawback that the signal to tIi sound ratio (SN ratio) becomes poor. This deterioration of the SN ratio causes a decrease in the diagnostic distance in the ultrasonic diagnostic apparatus.

In other words, as the ultrasonic pulse propagates inside the subject, the amplitude of the ultrahigh waves decreases as the propagation distance becomes longer, so if the S/N ratio deteriorates, the echo signal returned from deep inside the subject will be buried in noise. As a result, it becomes impossible to obtain a good tomographic image.

There is no problem when the diagnosing distance is short, but when the diagnosing distance is long, that is, in the deep part of the subject, a clear image cannot be obtained.

Purpose of the Invention The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to obtain a highly clear tomographic image with a good signal-to-noise ratio even when the ultrasonic transmission/reception distance is good, that is, even deep inside the subject. An object of the present invention is to provide an ultrasonic diagnostic apparatus using a synthetic aperture method that can be used.

[Means and effects for solving the problems] In order to achieve the above object, the present invention provides a transceiver that transmits an ultrasonic pulse into a subject and receives the reflected echo, and a transceiver that can be obtained with this transceiver. A memory that stores a received signal directly or after converting it into a signal with information equivalent to this received signal, and adjusts the phase of each signal at a predetermined focal position within the subject from a plurality of received signals stored in this memory. In an ultrasonic diagnostic apparatus using a synthetic aperture method, the addition circuit adds a received signal or a signal having information equivalent to the received signal multiple times before storing it in the memory. It is characterized by having the following.

According to the above configuration, a received signal obtained from inside the subject is converted into a digital signal by an A/D converter, or a signal having information equivalent to the received signal, for example, is converted at 90 degrees by a quadrature detector. The received signals, which are made into two signals with different phases, are then converted into digital signals and supplied to an adder circuit. Then, the received signals are added multiple times in an adding circuit, and the added signal is stored in the memory. Therefore, the signal output from the adder circuit becomes a received signal with a high SN ratio, and this received signal is recorded in the memory output! Then, a signal synthesis operation is performed.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows the basic configuration of the present invention, and FIG. 2 shows an embodiment of an ultrasonic diagnostic apparatus using the synthetic aperture method.

In FIG. 1, a transceiver 10 includes an oscillator 12, a driver 14. Consisting of a vibrator 16 and an amplifier 18, an oscillator 12
The oscillation signal outputted from the oscillation signal is converted into a pulse signal with a constant repetition period by the driver 14 and is supplied to the vibrator 16. The ultrasonic pulses generated by the transducer 16 are then transmitted into the subject.

This transducer 16 simultaneously receives reflected echoes reflected from within the subject, and this echo signal is supplied to an amplifier 18, where it is amplified as desired and then converted into a digital signal by an A/D converter 20. supplied to In the synthetic aperture method, a received signal is once recorded in the memory 22 in its waveform as it is, and a signal at a specific point is phase-adjusted and synthesized from the plurality of received signals recorded in the memory 22.

A characteristic feature of the present invention is that the received signal is stored in the memory 22.
The signal is added several times before being recorded in the data, and an adder circuit 24 for performing this signal addition is provided between the A/D converter 2S20 and the memory 22. This addition circuit 24
reads the previously written data from the specific memory location in the memory 22 to be written and adds this to the digital signal provided by the A/D converter 20. This added receiving 11 signal is one of the radiated Jj3 sound pulses.
Since this is a pulse-by-pulse signal, the SN ratio of the received signal 8 will be improved by amplifying it multiple times. Next, the extent to which this SN ratio actually improves will be explained using numbers.

Generally, the received signal S is an Iha signal component S. m sound component n is I
J(10), which is shown by the following equation.

SmS o +n
... Ku 5) This (
In equation 5), the signal component S. has a definite value, but the ode component (child) has a definite value and needs to be treated as a random variable, and normally the expected value of the IB component n is 0.

Furthermore, if the standard deviation of n is used as a parameter representing the magnitude of fluctuation in the noise component n, and this is k by σ, the S/N ratio of the signal S expressed by equation (5) is S. /σ.

On the other hand, if the signal expressed by equation (5) is applied m times, this signal Sl becomes a signal expressed by the following equation.

- (6) In this equation (6), the noise component "1" indicates that the subscript l is the first independent sample of n.
) is 1.11, which is the same as n in the normal case, and is O, but its standard deviation is J-plane a.

Therefore, the SN ratio of the signal added m times is as follows.

...(7) Here, when comparing 5NIt(So/σ) when no addition is performed and the SN ratio when addition is performed (formula <7) above),
It can be seen that when pruning was performed m times, the S/N ratio was improved by 4 m times. Note that even when the received signals are converted by a quadrature detector or the like and then added, the relationships of equations (5) to (7) are held, and the S/N ratio is similarly improved.

By adding the received signals multiple times in the above manner, the S/N ratio of the received signal is J=-? deep inside the subject,
In other words, it is possible to obtain clear and sharp tomographic images in areas where the diagnostic distance is long.

Next, a description will be given of how much the diagnostic distance ratio 1 increases in the ultrasonic diagnostic apparatus. Assuming that in the embodiment device, the diagnostic distance without caulking is 10 CIll, this state can be interpreted as follows. In other words, the amplitude of the signal is 21, which is about the same as the amplitude of the sound component II:t, but it is returned from a deeper part than this. -The signal is further attenuated by the substances that exist in the middle, so
The amplitude becomes smaller than the noise component, and as a result, it becomes impossible to extract it as the Iha signal.

On the other hand, if, for example, the addition is performed m times as in the present invention, the S/N ratio becomes 4 times better as mentioned above, for example!
If it is added once, the SN ratio will improve by 2 (8).
-, even if the signal component and the noise component have the same amplitude, by adding them four times, the signal component will have twice the amplitude of the three following components. Considering this in terms of ultrasonic attenuation, the attenuation of ultrasonic waves within the subject is, for example, approximately 3 dB/cm in the case of 3.5H1lz ultrasonic waves. Since the peak of 0 dB is about -6 dB, the distance within the subject at which the amplitude of the ultrasonic wave is 172 is about 2 cm.

Therefore, the SN ratio of the received signal is doubled! This is equivalent to increasing the B-sound wave transmission/reception distance by 2 cm.

As a result, considering the round-trip propagation distance, the diagnostic distance is approximately 1 c.
It is understood that m becomes longer. In this case, the number of crimping operations was considered to be four, but the diagnostic distance can be further increased by increasing this number of crimping operations.

Next, a specific second example of the ultrasonic diagnostic apparatus to which the present invention is applied will be explained.
The embodiment shown in the figure will be explained.

In the embodiment, a plurality of vibrators 16 are arranged, and a specific vibrator 16 from among these vibrators 16 is selected by a multiplexer 26.

Then, by applying electrical signals obtained by the oscillator 12 and driver 14 to the selected transducer 16, ultrasound is transmitted into the subject, and the received signals received by these transducers 16 are sent to the amplifier 18. supply

The output of this amplifier 18 is supplied to a quadrature detector 28, and is converted into a signal with a phase difference of 90 degrees by a sine wave signal and a cosine wave signal supplied to the other input of this quadrature detector 28. Note that 90 degree phase shifts 30 are provided to shift the cosine wave signal by 1q. As shown in FIG. The signal is also applied to the multiplier 32 with a sine wave signal, which is then combined with the received signal provided from the other input before being input to the low pass filters 34 and 36.

These low-pass filters 34 and 36 shift the frequency band of the signal to the lower frequency side and remove unnecessary signals such as carrier waves of the received signal, which has the advantage of facilitating subsequent processing. Note that since the signal after quadrature detection does not lose the amplitude and phase information of the input signal, the information within the subject contained in the received signal is not lost. The signal after such orthogonal detection is recorded in the memory 22, and is called a hologram.

In order to further form a tomographic image from such a hologram, as shown in FIG. 4, the output of the memory 22 is again multiplied and added by a cosine wave signal and a sine wave signal. Therefore, the output signal of the adder 42 in the figure is equal to the input signal of the quadrature detector 28, and a synthesis operation is performed on this signal.

In this way, the received signal obtained by the transceiver 10 is not directly input to the memory 22, but is converted into a signal having information equivalent to the received signal, that is, a signal that has been orthogonally detected, and then recorded in the memory 22. do.

In the present invention, the received signal is recorded multiple times before being recorded in this memory 22, and in the embodiment, two A/D converters 544, 46 and two adder circuits 48, 50 are provided.

Therefore, the two signals outputted from the quadrature detector 28 and having different phases by 90 degrees are respectively supplied to the A/D converters 44.46 and converted into digital signals.
The adder circuits 48 and 50 add the signals input a predetermined number of times and store them in the memory 22. This addition control is performed by the control circuit 54, which controls the signals to be added a predetermined number of times, and at the same time controls the number of times the same vibrator is excited by the multiplexer 26 in the transceiver 10 described above. ing.

The output signal of the quadrature detector 28 that has been added a predetermined number of times in this way is stored as a signal with an improved S/N ratio. is stored as a hologram containing internal information of the subject.

Then, the output of the memory 22 is supplied to a synthesis calculation circuit 56, and by appropriately reading out the hologram at a specific point corresponding to the focal point from the memory 22 and performing necessary synthesis calculations, a tomographic image can be formed. In this case, the value of each pixel of the tomographic image determined by the synthesis calculator 56 is held in the image memory 58 and displayed on the television monitor 60 as one tomographic image.

[Effects of the Invention] As explained above, according to the present invention, the received signals are added multiple times before the received signals for the synthesis calculation are recorded in the memory, so that the received signals with an extremely high SN ratio can be By performing a synthesis calculation based on this received signal, the diagnostic distance can be made longer than in the past. As a result, in the ultrasonic diagnosis 1i apparatus using the synthetic aperture method, a tomographic image of the deep part of the subject can be displayed, and the diagnostic area by ultrasonic images is significantly expanded.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the basic configuration of the present invention (not shown), Fig. 2 is a block diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus using the synthetic aperture method according to the present invention, and Figs. 3 and 4 are reception diagrams. FIG. 5 is a block diagram illustrating orthogonal detection of signals, and is a diagram illustrating the synthetic aperture method. 10... Transmitter/receiver 16... Vibrator 22... Memory 24, = 18.50... Addition circuit 28...
Quadrature detector 56...Synthesis arithmetic unit.

Claims (1)

[Claims] (1) A transceiver that transmits ultrasonic pulses into the subject and receives the echo signals, and the received signal obtained by this transceiver is stored directly or after being converted into a signal with information equivalent to the received signal. In an ultrasonic diagnostic apparatus using a synthetic aperture method, which includes a memory and a synthesis calculator that adjusts the phase and synthesizes signals at predetermined focal positions within a subject from a plurality of received signals stored in the memory. . An ultrasonic diagnostic apparatus using a synthetic aperture method, comprising an adding circuit that adds a received signal or a signal having information equivalent to the received signal multiple times before storing it in the memory.