JPS60185539A - Aperture synthetic image 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 [Technical Field of the Invention] The present invention relates to an imaging device that synthesizes multiple images using an aperture synthesis method using sound waves.

[Technical background of the invention and its problems]

The aperture synthesis method is a technique that uses a transducer with a small aperture to synthesize an equivalently large aperture through signal processing, and is applied to ultrasound imaging devices such as ultrasound diagnostic equipment. The principle of this aperture synthesis method will be explained using FIG.

The transmitting and receiving transducers T and R move along the X axis while transmitting and receiving ultrasonic waves, and the X coordinate of the transmitting transducer T is expressed as XT% of the receiving transducer,
-Set the ROX coordinates to X t + X d. The transmitting transducer T.

It is assumed that the emitted ultrasonic waves do not spread in the direction perpendicular to the X axis and the two axes. It is also assumed that the sensitivity distribution of the receiving transducer R does not spread in the direction perpendicular to the X-axis and the y-axis.

The ultrasonic wave emitted from the transmitting transducer T is reflected by the point reflector P, and the reflected wave is received by the receiving transducer R.

By phase-detecting this received signal, orthogonal components are extracted, and the (2) component H0 and the blood component H8 are obtained. Let us consider a complex number H as shown in the following equation in which these two components are the real part and the imaginary part, respectively, and call this a hologram.

1 ((xt, xd, zo, t) = Hc-jug(1
), C0 is a proportionality constant, B is the composite sensitivity distribution determined by the sound pressure distribution of the ultrasound emitted from the transmitting transducer T and the sensitivity distribution of the receiving transducer, and PT is the transmitting transducer T. Ultrasound emitted from °
The envelope of the wave pulse, LT, is the distance between the transmitting transducer T and the point reflector P, and LRo is the receiving transducer R.
and the distance between point reflector P, respectively. Also ha, At
Each of φ is expressed by the following formula.

Xt=)ET XO 4π2 φ =□ λ Here, λ indicates the wavelength of the ultrasonic wave. Note that the exponential function part is obtained by introducing Fresnel approximation to LTO and LILO.

Is the composite image of the point reflector P a combination of the hologram of the point reflector P and exp (JA x2)? It is obtained by calculating the region sum and then taking its absolute value, and the result is expressed by the following formula.

In addition, in equation (3), B is a rectangle, and its width is NΔX
It has been infiltrated as such. Further, ΔX represents the movement pitch of the transmitting transducer T, and C7 is represented by the following equation.

c, =-c. −exp[−jφ]・expCjA■−
xo)2・@xp[-jA■1o)xd]...(4)
The problem here is the position of the virtual image of the grating lobe. The first from the main lobe, which is the original statue.
Letting the distance to the grating globe be Xg, this can be expressed as follows according to equation (3).

“−4...(5) g Alx 2.

This equation shows that the position of the grating lobe becomes closer to the main lobe as the moving pitch ΔX of the transmitting transducer T becomes larger.

If this Xg is smaller than NΔX, which is the width of BT and BR, the grating lobe will appear as a virtual image. Therefore, in order to prevent the generation of a virtual image, it is necessary to make the moving pitch ΔX of the transmitting transformers 7' and 7' sufficiently small. The moving pitch of the transducer T is determined by the arrangement pitch of the transducers. Therefore, in order to prevent a virtual image from occurring, this arrangement pitch must be made sufficiently small. However, it is not necessarily easy to reduce the arrangement pitch of the transducers in terms of manufacturing an ultrasonic transducer.

[Purpose of the invention]

An object of the present invention is to provide an aperture synthesis imaging device that can easily realize a scanning section by increasing the tolerance regarding the movement pitch of the transmission position of the sound wave emitted to the area to be imaged compared to the conventional one. It is to provide.

[Summary of the invention]

In scanning using sound waves such as ultrasonic waves, the present invention performs the first scan with the distance between the transmitting position and the receiving position as X, and sets this distance to Xd as the moving pitch ΔX of the transmitting position.
A second scan is performed with X, +ΔX added to The image information is obtained by combining the data obtained by the second scan with the kernel data and adding the calculation results of the sum of the sums.

〔Effect of the invention〕

According to the present invention, during the first scanning and during the second scanning, the first
Even though the phases of the grating globes differ by 1800 degrees, the first grating globe at the position in the conventional case is ultimately canceled out, so even if the movement pitch of the transmission position is twice that in the conventional case, a composite image without a virtual image can be obtained. can be obtained.

Therefore, it becomes easier to realize a scanning section using ultrasonic waves or the like.

[Embodiments of the invention]

An embodiment in which the present invention is applied to an electronic scanning ultrasound diagnostic apparatus will be described below. FIG. 2 is a block diagram thereof.

In FIG. 2, the ultrasonic probe 1 is constituted by a transducer play made up of a large number of transducers arranged in a line. Each transducer emits ultrasonic waves with a certain spread into the living body. Reflected waves from various parts within the body are received by a predetermined vibrator and converted into electrical signals (referred to as received signals). The resonant frequency of the vibrator is usually between 2 and 10 M
It is assumed to be Hz. The noggler 2 drives each element in the globe 1, and in synchronization with the pulse from the scan controller 10, transmits the transducer IcJI movement 29, 3 designated by the scan controller 10. Each vibrator is sequentially switched and driven at a constant cycle.

Note that the number of transducers used for transmitting or receiving ultrasonic waves - times is appropriately set in the range of one to several as necessary. The received signal obtained by the probe 1 is amplified by the receiver 3 to a required level. The degree of amplification is set to a necessary value depending on the level of the input received signal.

The phase detector 42.5 multiplies the received signal from the receiver 3 by two sine waves having a 90° phase difference supplied from the scan controller 10, and sends the result to the loaf 4.
Phase detection is performed by passing the signal through a filter. The frequencies of these sine waves match the resonant frequency of the vibrator. The outputs of the phase detectors 4 and 5 have orthogonal components, t, b cosine (cos) components X(t), and sine (S I
N) component Y(t) is obtained, and each of the next stage A
/D converter 6, 7 (C-AI)C, S-ADC)
is input.

The C-ADC 6 and the S-ADC 7 sample and digitize (2) components X(t) and *components Y(t), respectively. In this case, the sampling pitch is determined in consideration of the duration of reflected waves from point reflectors within the body. For example, if the duration is 2 μm 1ee, the appropriate sampling pitch is about 400 nsec, which is one-fifth of that duration. This sampling pitch is determined by the sampling clock sent from the scan controller 10, and sampling and digitization are performed in synchronization with this clock. In this way, (2) component X(t
)+dz components y(t) are all 8-bit digital values, for example. The digitized component and component are stored in the C-manual buffer memory 8 and the s-manpower buffer memory 9, respectively. Data is written to these buffer memories 8 and 9 from the scan controller 10 to the C-ADC 6 and C-ADC 6.
- It is performed in synchronization with the sampling clock that is also supplied to the ADC 7. Then, the digitized orthogonal components (components in CIM e) are sequentially written into the manual buffer memories 8 and 9 in synchronization with the sampling clock. The manual buffer memories 8 and 9 have a capacity necessary to store received signals corresponding to a series of reflected waves obtained by one emission of ultrasonic pulses. After all writing is completed, the stored data is sequentially output by the computer 11 and transferred to the image memory 12.

The image memory 12 can store data for four images. This is the filter component X(t) read from C-manual buffer memory 8 and S-manual buffer memory 9 and -
It is used to store each component y(t).

The configurations of the areas for storing X(t) and Y(t) in the image memory 12 are schematically shown in FIG. That is, the possible values of the X and y addresses are θ to 511, and are associated with the scanning direction and the depth direction, respectively. Each address can store 8 bits of data.

The output memory 13 is for storing image data of a composite image of in-vivo tissues obtained as a result of calculations in the computer 11, and its configuration is the same as that of the image memory 12, as shown in FIG. It has become. The output buffer memory 13 is connected to the timing controller 14
It is constantly read out in synchronization with the clock from The reading is performed in accordance with the scanning on the television monitor 16. The timing controller 14 performs r-event readout control for displaying the image data stored in the output buffer memory 13 on the television monitor 16 and generates a television synchronization signal.

The image data from the output backup memory 13 is D/
The signal is converted into an analog image signal by the A converter 15 and mixed with a synchronization signal from the timing controller 14 . The composite video signal, which is the mixed output, is then input to the television monitor 16, and a composite image is displayed.

The computer 1 has the following three functions.

(1) Control of scan controller 10 ゛(
2) Transfer of digitized orthogonal component data (3) Image synthesis processing The μs component 8+8-stored in the manual buffer memory 9. The computer 11 sequentially reads out these data from the large-capacity memories 8 and 9 and stores them in the image memory 1.
The information is sequentially stored at an address determined by the position and depth of the driven vibrator in 2.

Of the instructions given by the computer 11 to the scan controller 10, the instructions relating to ultrasonic scanning are particularly important and are related to the features of the present invention. This will be explained below.

Ultrasonic scanning is the first step. The second scan is performed in two parts. The difference between the first scan and the second scan is the setting of the reception position.

That is, in the first scan, the computer 11
A command is given to the scan controller 10 so that the receiving position is set at a position one transducer away from the transmitting position. Ku 17, vibrator ^-5 + I J -, 凋-mu J
-L → Toss Fu Ko (-/# Itya Tatami Fu 81
The transmission position is instructed to be scanned by moving the transmission position by Δχ with an interval of 1tttvmin as jX. As an example, the interval between the receiving position and the transmitting position is jX here, but it does not necessarily have to be jX, but is 2ΔX.

It may be set to 3ΔX, and furthermore, the interval may be set to 01 and the same transducer may be used for transmission and reception. On the other hand, in the second scan, a command is given so that the interval between the transmitting and receiving positions is equal to the interval in the first scan plus jX, or F)21x.

In the following explanation, for convenience, the data obtained in the first scan (
als component and self-component) will be referred to as first data, and the data obtained in the second scan will be referred to as second data.

In each of the first and second scans, the scan controller''') 10 immediately scans the
Controls the 41 Lusa 2 and receiver 3 so that transmission and reception are performed using the designated transducer.

The image composition process starts after these first and second scans are completed. This will be explained in detail below.

The basis of image synthesis processing is calculation of a condelusion sum of first data, second data, and data of a predetermined function (hereinafter referred to as a kernel). The predetermined function is
2)), which is the wavelength of the ultrasonic wave,
It is determined by the distance between the transmitting and receiving transducers, the depth of the position where images are to be synthesized, and the distance from the transducer. The final composite tIli image is obtained by adding the condelus sum of the first data and kernel data to the condelus sum of the second data and kernel data, and taking the absolute unity. When such image synthesis processing is performed, the distance from the main rope to the first grating glow f at the edge of the point reflector is 2 compared to the conventional one.
In other words, even if the arrangement pitch of the transducers is twice that of the conventional one, no virtual image will occur. This point will be explained below.

In the coordinate system shown in FIG. 1, the hologram of the point reflector becomes 5(1). The result U(X) of the confluence of this hologram and the kernel data is expressed by equation (3).

Here, ΔX is the arrangement pitch of the vibrator, and X6=Δ
Assuming that
, = 2ΔX, this results in the total sum of the 27'-th data and the kernel data. Assuming that these are respectively J(X) Hu2←), the final composite image U (X) will be as follows.

Uo(X) = l u, (x) −112(X) 1
If we calculate the value of the exponential part of 10exp[-JA(X-x0)Δs], if Δs is small, as is usually the case, it will be less than -1.

On the other hand, when the position of the grating lobe of the first term is small, it almost coincides with the position of the grating lobe of the second term. Therefore, by adding u+(x) and 2(,), their first grating globes cancel each other out.

Therefore, when ultrasound scanning and synthesis processing is performed as in the present invention, the first grating globe corresponding to the conventional case disappears, and the second grating globe corresponding to the conventional case replaces the new first grating globe. Therefore, even if the arrangement pitch of the vibrators is twice that of the conventional one, no virtual image will occur. - Specifically, the above-described image composition processing is performed under the control of the computer 11 as follows. FIG. 4 is a flowchart showing the algorithm of this image composition processing.

That is, the computer 11 first stores data from the image memory 12 in the portion closest to the 17'-th transducer, including the first r-side A11 (1=1 to 511).
The first row of data All is read out. The kernel data Bll corresponding to this data All, stored in advance in the memory of the computer 1, is read out, and the condelusion sum of these data All and Bll is calculated. Next, the computer 11 uses the image memory 1
From kernel f-IB21. ! : Calculate the convolution sum of x. Then, add it to the previous calculation result and take the absolute value. This completes the image synthesis process for the first row of rabbits. This result is stored in the output buffer memory 13. Computer 12 then connects the first and second
Similar processing is performed on the second line of 7'-1, and the result is stored in the output/data memory 13. Such processing is repeatedly executed up to the 511th line, from 1 to 511, and the image synthesis processing for -images is completed.

It should be noted that the present invention may be modified in various ways without departing from the scope thereof.For example, in the above embodiment, an example in which the present invention is applied to an electronic scanning type device is described, but the present invention is applicable to a single vibration type device. It can also be applied to devices that use a mechanical rental system.

Although ultrasonic waves are used for scanning, it goes without saying that audio frequency sound waves may be used if the purpose is not to image inside a living body.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the principle of the aperture synthesis method, FIG. 2 is a block diagram showing the configuration of an embodiment of the invention, and FIG. 3 is a diagram showing the configuration of the image memory and output buffer memory in the same embodiment. FIG. 4, which is for illustration purposes only, is a flowchart showing an algorithm for image composition processing in the same embodiment. 1... Ultrasonic floats, 4, 5... Phase detector, 6
．． 7... A/D converter, 8.9... Input buffer memory, 10... Scan controller, 1... Computer, 12... Image memory, 13... Output buffer memory, 15...A/D converter, 16...TV monitor.

Claims (1)

[Scope of Claims] Means for transmitting sound waves to a region to be imaged, and means for receiving reflected waves from the region of the sound waves transmitted to this means and obtaining received signals corresponding to the reflected waves. scanning means for sequentially changing transmission and reception positions in these means; means for extracting orthogonal components of the received signal; and image synthesis means for synthesizing images by an aperture synthesis method based on the orthogonal components. The scanning means measures the distance between the transmitting position and the receiving position in the first scan and the second scan by changing the distance between the transmitting position and the receiving position. The image synthesizing means is configured to change the sum of the orthogonal components and the kernel obtained by the first scan, and the orthogonal component and the kernel obtained by the second scan. 1. An aperture synthetic image device characterized in that it is configured to obtain image information by adding complete, -s, and sums.