JPH0259732B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ultrasonic diagnostic device, particularly an ultrasonic diagnostic device that transmits ultrasonic waves into a living body, receives the transmitted waves or reflected waves, and measures and displays characteristic distributions within the living body. The present invention relates to an improved ultrasonic diagnostic device that can perform

[Prior Art] The pulse echo method is often used in ultrasound diagnostic devices that transmit ultrasound waves into a living body and measure the echo signals to display tomographic images of the inside of the living body. Dynamic focusing is generally performed using an array type transducer to transmit a sharp ultrasonic beam to each point in the depth direction.
That is, by dividing the depth direction into multiple regions, transmitting and receiving ultrasound so as to focus on each region, and measuring the ultrasound reflected waves for each region, a tomographic image of the inside of the body can be obtained over a wide range. Furthermore, by increasing the number of divided regions within a certain range, a more precise tomographic image of the inside of the body can be displayed.

However, if the number of divided regions is increased, the ultrasound beam must be made even sharper, and the number of transmission and reception of ultrasound increases by the number of divided regions, so it takes time to form a tomographic image of one cross section. was occurring. For this reason, it has been proposed to apply the synthetic aperture technique, which is well known in the fields of radar and sonar applications, to ultrasound diagnostic equipment.

This synthetic aperture method involves transmitting and receiving ultrasonic waves inside a living body by repeatedly transmitting and receiving while moving the transmitting/receiving position, storing the received signal including the phase, and then converting the received waveform so that each point in the living body is focused. This is a method of synthesizing to obtain an image signal at each point, and an explanation of the waveform synthesis is shown in FIG.

In the figure, when T ₁ , T ₂ , T ₃ ...T _o is a transducer and ultrasonic pulses are transmitted sequentially from this transducer, the received waveform received by the same transducer is U ₁ (t),
The waveforms are obtained as U ₂ (t), U ₃ (t)...U _o (t). At this time, the oscillators T ₁ , T ₂ , T ₃ ,
...If you focus on a point F that is l ₁ , l ₂ , l ₃ ...l _o away from T _o and measure this point, each transducer and point F
A waveform S(t) is obtained by moving the ultrasonic waves by the time τi required for the ultrasonic wave to reciprocate between the two and adding them. That is, S(t)= _o 〓 ⁱ⁼¹ Ui(t+ti) However, it is expressed as τi=2li/c (c: speed of sound), which corresponds to adding the amplitudes on the hyperbola f in the figure, and is a large You can get the amplitude. For other points P, T ₁ , T ₂ , T ₃ ...T _o
The data on Ui(t) corresponding to the positional relationship between and point P becomes the amplitude on the hyperbola p, and when these are added, these amplitudes cancel each other out and become smaller.

Therefore, if the focus is focused on point F, each received wave of Ui(t) will be added in the same phase and the amplitude will become large, so if the position of this focus is sequentially changed, a high-resolution tomographic image can be obtained. That is understood.

However, depending on the position of the point F other than the focal point mentioned above, the received signals may be added in the same phase. This method has the drawback of producing a phenomenon that gives the impression that a sound wave beam is being emitted, a phenomenon commonly referred to as a sidelobe, which has the problem of deteriorating the image quality of tomographic images.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to remove side lobes in an ultrasonic diagnostic apparatus using a synthetic aperture method and to display a good image of characteristic distribution in a living body. The purpose of the present invention is to provide an ultrasonic diagnostic device that can perform

[Structure of the Invention] In order to achieve the above-mentioned object, the present invention provides a method for receiving transmitted waves transmitted through the living body or reflected waves reflected from the living body by ultrasonic pulses transmitted into the living body. and A/D the received signal from the receiver.
It includes an A/D converter for converting the A/D converter, and a memory for storing the A/D-converted received signals for each received signal, reads each of the received signals from the memory, adjusts the phase of each, and performs synthesis and addition. In an ultrasonic diagnostic apparatus that performs calculations to form tomographic images in a living body, between the wave receiver and the A/D converter, logarithmic amplification is performed for each received signal from the wave receiver. It is characterized in that it is provided in a logarithmic amplifier.

[Operation] According to the above configuration, since the logarithmic amplifier is provided before the A/D converter, the received signal is logarithmically amplified and then A/D converted, and further synthesized based on the synthetic aperture method. An addition operation will be performed.

Therefore, the received signal is A/D converted in a compressed state. Furthermore, since each received signal is logarithmically amplified and combined and added, it is possible to increase the difference in signal magnitude between the main lobe and the side lobe.

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

The characteristic feature of the present invention is that it is equipped with a logarithmic amplifier that nonlinearly amplifies the received ultrasound signal, so it is possible to remove sidelobes that occur in ultrasound diagnostic equipment that uses the synthetic aperture method. This sidelobe removal will be explained based on the following.

A certain point F and point P in the living body are far enough away from the vibrator, and the lines connecting T ₁ , T ₂ , T ₃ ...T _o to points F and P can be considered parallel, so point P as shown in the figure Consider the case where the direction is at an angle θ from the direction of point F.
If the sidelobe signal from point P when focused on point F has the waveform shown on the left in FIG. 2, the received waves received by each vibrator are shifted by time τ. The time τ is expressed as τ=2d/csinθ (d: distance between transducers, c: sound speed), and in the modified formula cτ=2d sinθ, if cτ is an integral multiple of the wavelength λ (cτ=mλ )
The received waves interfere. At this time, the direction angle θm of point P
is expressed as θm=arc sin(mλ/2d) (m: integer).

That is, when the point P is in the θm direction, the reflected waves from the point P are added in the same phase (FIG. 2C), and a side lobe appears with a large amplitude, and is strongest when m=1.

Next, consider the side lobe when m=1 (in the θ1 direction).

If the directivity of each transducer is r(θ), in the conventional device, each received waveform is linearly added before being subjected to synthetic calculation based on the synthetic aperture method (for example, immediately after the receiver), so θ A side lobe in _one direction is expressed as nar(θ ₁ )...(1) where the amplitude is a and the number of oscillators is n, and this directivity r(θ) is θ=0 in the focal point F direction. Since it is normally normalized to r(0)=1, the main lobe at point F is nar(0)=na...(2).

In the conventional device, the linearly amplified received signal is subjected to a synthesis calculation based on the synthetic aperture method, and then logarithmically amplified and displayed as an image. In other words, logarithmic amplification is performed because the level difference between each received signal is so large that it becomes difficult to see when displaying an image by modulating the brightness. here,
When performing logarithmic amplification, generally, if the amplifier input signal v _i is smaller than the noise level δ, the output is treated as 0, and only if it is larger, the input signal is logarithmically amplified. If the amplifier output v ₀ is expressed by the formula, βlog(v _i /δ)...δv _i v ₀ =0...δ<|v _i | −βlog(|v _i |/δ)...δv _i (β: constant) becomes.

Therefore, by logarithmically amplifying the side lobe equation (1) and the main lobe equation (2) mentioned above, it can be expressed as an equation substituted into the equation v = δlog (v _i /δ) when δv _i in equation (3). and calculating this difference, δlog(na/δ)−δlog{nar(θ ₁ )/δ} = δlog{1/r(θ ₁ )} …(4), and this equation (4) is This represents the difference between the main lobe level and the side lobe level.

On the other hand, in the apparatus according to the present invention, each received signal is logarithmically amplified separately and then the synthesis operation is performed. In other words, the sidelobe signal before being added is ar(θ ₁ )
Since the main lobe signal is a{ir(0)=1}, if this is logarithmically amplified using equation (3), we get βlog{ar(θ ₁ )/δ} and βlog(a/δ), respectively. Become.
Then, if these signals are added, the sidelobe level is nβlog{ar(θ ₁ /δ}, and the mainlobe level is nlog(a/δ), so the difference between them is nβlog(a/δ) −nβlog {ar(θ ₁ )/δ} = βlog{1/r(θ ₁ )} ⁿ (5).

Therefore, comparing equations (4) and (5), βlog{1/r(θ ₁ )} ⁿ ≫βlog{1/r(θ ₁ )} (∴0<r(θ)<1) There is a large difference between the main lobe level and the side lobe level between the conventional device and the present invention.

That is, it is understood that according to the present invention, the difference between the main lobe level and the side lobe level can be increased, and thereby the side lobe signal can be effectively removed. That is, according to the present invention, a large difference between the main lobe level and the side lobe level can be obtained after performing the combining operation to logarithmically amplify each received signal before performing the combining operation.

FIG. 3 shows a preferred embodiment of the invention.

The ultrasonic transmitter/receiver 10 includes an array transducer 12 and a multiplexer 1 for controlling vibration of the array transducer.
4, an oscillator 16, and a controller 18.
The electrical signals obtained from the oscillator 16 based on the control of the oscillator 16 are supplied to the multiplexer 14 via the driver 20, and the electrical signals are sequentially converted into ultrasonic waves and transmitted into the living body. Further, reflected waves from inside the living body are received by each of the vibrators, and each wave received by each vibrator is logarithmically amplified by the logarithmic amplifier 22.

The logarithmically amplified received wave signal is then supplied to the orthogonal detector 24 and subjected to hologram conversion. That is, the electrical signal output from the oscillator 16 is supplied to the multipliers 28 and 30 via the transfer device 26,
A cosine wave and a sine wave having the center frequency of the transmitted ultrasound are multiplied by the amplified received signal, and by inputting this to the low-pass filters 32 and 34 and removing the carrier wave, information on the amplitude and phase of the received signal can be obtained. A signal (hologram) is obtained.

In this embodiment, the logarithmic amplifier is placed before the quadrature detector 24, but it can also be placed after the quadrature detector 24, as shown in FIG. 4c. Of course, the logarithmic amplifier has memory 40
It does not necessarily need to be placed in front of , and can be placed at any location before the synthetic addition operation based on the synthetic aperture method is performed. However, as will be described later, in order to reduce the capacity of the memory 40, the logarithmic amplifier must be placed before the memory 40, or more precisely before the A/D converter provided in front of it.

The hologram obtained in this way is
A/D converted by converters 36 and 38 and stored in memory 40
is supplied to and temporarily stored. Generally, in an A/D converter or a digital memory, the larger the fluctuation range of the input signal, the larger the number of bits in the A/D converter and the larger the memory capacity. However, in the apparatus according to the present invention, the amplitude variation range of the hologram described above is compressed by using the logarithmic amplifier 22, and signal recording or processing becomes easy.

Next, the hologram recorded in the memory 40 is multiplied again by the above-mentioned cosine wave and sine wave by the multipliers 42 and 44, and reproduced by the adder 46 into a received wave signal before orthogonal detection. The output of the adder 46 is input to the arithmetic unit 48, and by moving the received signals of each transducer by an appropriate time interval and performing an addition operation, information at each focal point within the living body can be obtained, and the tomographic image inside the living body is an image. An image is formed on a TV monitor 52 via a memory 50.

Furthermore, by repeatedly updating the contents of the area of the memory 40 corresponding to each vibrator, the latest hologram is always stored, and the TV monitor 5
2, it becomes possible to appropriately display a tomographic image based on updated new information.

In this example, the transmitted and received signals are transmitted using the same transducer, but the ultrasonic wave may be received by a transducer different from the transducer that transmitted it, or a pair of transducers may be mechanically scanned. Ultrasonic waves can also be transmitted and received, and the same effect can be obtained even when the received ultrasonic waves are not only reflected waves from inside the living body but also transmitted waves.

[Effects of the Invention] As explained above, according to the present invention, since the ultrasonic transmitted waves or reflected waves in the living body received by each transducer are nonlinearly amplified and recorded, synthetic aperture technology can be used to The side lobes that occur when combining images at each focal point within a living body are removed, making it possible to obtain highly accurate tomographic images of the living body through transmitted and received waves.
It becomes possible to provide information useful for diagnosing diseases.

Furthermore, since a logarithmic amplifier is provided between the receiver and the A/D converter, highly accurate reception information can be obtained even if the number of bits of the A/D converter is reduced.
In addition, memory capacity can be reduced,
Because of this, it is possible to quickly perform synthetic arithmetic processing on received signals.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the synthetic aperture method, Fig. 2 is an explanatory diagram of the side lobe, Fig. 3 is an explanatory diagram showing a preferred embodiment of the ultrasonic diagnostic apparatus according to the present invention, and Fig. 4 is an explanatory diagram of the logarithmic amplifier. It is an explanatory diagram of arrangement. 10...Transmitter/receiver, 12...Array transducer, 18
...Controller, 22...Logarithmic amplifier, 40...Memory, 48...Arithmetic unit, 52...TV monitor.

Claims (1)

[Scope of Claims] 1. A receiver for receiving a transmitted wave transmitted through the living body or a reflected wave reflected from the living body by an ultrasonic pulse transmitted into the living body, and reception from the receiver. an A/D converter that A/D converts a signal; and a memory that stores the A/D converted received signal for each received signal, reads each of the received signals from the memory, and calculates the phase of each of the received signals. In an ultrasonic diagnostic apparatus that adjusts and performs synthesis and addition operations to form a tomographic image of an in-vivo body, between the wave receiver and the A/D converter, the reception signal from the wave receiver is connected to the receiver. An ultrasonic diagnostic device characterized by being provided with a logarithmic amplifier that logarithmically amplifies each signal.