JPS6048736A - Ultrasonic diagnostic 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 ultrasonic diagnostic apparatus using an aperture synthesis method capable of obtaining ultrasonic diagnostic images with high lateral resolution.

[Technical background of the invention and its problems]

2. Description of the Related Art Ultrasonic diagnostic apparatuses that transmit and receive ultrasonic waves to obtain, for example, tomographic images of living organisms play an important role in fields such as diagnostic medicine. Therefore, when configuring this type of ultrasonic diagnostic image, it is very important to make the lateral resolution sufficiently high.

Therefore, in the past, efforts have been made to converge ultrasonic waves using a convergence method using an acoustic lens or an electron convergence method, thereby increasing the azimuth resolution. However, for example, when an electronic focusing method is used, focusing of the ultrasound waves is performed by controlling the phase of each ultrasound wave transmitted from the transducer array. As a result, the ultrasonic waves are converged to a convergence point, and the azimuth resolution there can be significantly improved, but the azimuth resolution in a region away from the convergence point is degraded.

For this reason, the image quality of the entire diagnostic image was poor. Therefore, a dynamic focus method has been proposed in which the convergence point is sequentially changed in the depth direction, but the control system is extremely complicated, and furthermore, the scanning time required to form one image is extremely long. There was a problem with it being too long.

[Purpose of the invention]

The present invention was made in consideration of these circumstances, and its purpose is to incorporate the aperture synthesis method seen in radar equipment, and to maintain azimuth resolution at all times regardless of the frequency deviation of ultrasonic waves. An object of the present invention is to provide an ultrasonic diagnostic apparatus that can obtain high quality diagnostic images.

[Summary of the invention]

The present invention detects the phase of the received signal of the ultrasonic waves transmitted and received by an ultrasonic transducer and reflected by an object, obtains a hologram signal related to the object, and uses this hologram signal and a kernel signal to perform aperture synthesis calculation. In the ultrasonic diagnostic apparatus using the aperture synthesis method, which performs Therefore, the kernel signal whose depth is given as an A parameter is modified in accordance with the frequency deviation and used for the aperture synthesis calculation.

〔Effect of the invention〕

Thus, according to the present invention, as explained below, the azimuth resolution can be sufficiently increased regardless of the depth of the object, and the azimuth can always be determined regardless of the frequency deviation caused by the attenuation of the ultrasonic waves. It becomes possible to maintain sufficiently high resolution, and it becomes possible to obtain good diagnostic images.

[Embodiments of the invention]

Next, details of the present invention will be explained through examples shown in the drawings.

FIG. 1 shows a coordinate system for explaining the aperture synthesis method, where l is an ultrasonic transducer.

This ultrasonic transducer 1 is moved and scanned in the X-axis direction, and transmits ultrasonic waves/gurus in two axial directions to an object to be examined such as a living body, and the reflected waves of the ultrasonic waves from the object 2 is to be received. Here, the ultrasonic wave generated by the ultrasonic transducer 1
If the coordinate position of the wave transmitting and receiving signal is (,,,) and the target object 2 is a point reflector and its coordinate position is (,,z), then the reflected wave received by the ultrasonic transducer 1, that is, the received signal S is represented by the following formula.

S”” f(t-tn)s(nωo (t-to)
-(1) However, in the above formula, f(t) indicates the envelope of the ultrasonic wave (Russ), and tn is given as V being the sound speed of the ultrasonic wave. Note that the depth Z of the point reflector is shown as being sufficiently deep (z>>x) compared to the position X of the ultrasonic transducer 1. Also, ω is shown as being sufficiently deep (z>>x). Also, ω is set to the center frequency of the ultrasound as 10, and ω.=2πf.

given as. Then, when the received signal S is phase-detected using reference signals whose phases differ by 90', and its high frequency components are removed through a low-pass filter,
Signals sR, s, which constitute two hologram components that are orthogonal to each other, are obtained.

Sn = Sdnωot S1 = Bcmωot With these signal components the hologram signal S for the point reflector. is SO= am + JSr −+' (t−tn) exp (jωo1n) −・
・Given as (2). The calculation of the reconstructed image A regarding the point reflector using the same mouth synthesis method is based on the hologram image S shown in the above equation (2). This is done by convolving the next kernel signal Sc8.=.xp(j"+'-"]...(3)V and taking the absolute value. This is the core of Convolution 3v (convolution operation).
In the formula, ω is ω1=2πf, where f is the fundamental frequency of the kernel signal.

is given by Therefore, the reconstructed image A is expressed as follows, where t is an integral interval.

Usually, the frequency of the ultrasonic wave is constant, and generally, the fundamental frequency f1 of the kernel signal SC is the center frequency f of the ultrasonic wave. Since it is set equal to , the reconstructed image A can be regarded as the above-mentioned reconstructed image A.

Note that the above-mentioned aperture synthesis calculation usually uses hologram data that follows the pattern of the Boroda Lum signal, that is, the so-called range coverage corrected data, but this requires a long processing time and requires a complicated hardware configuration. from,
It is assumed that the above calculation is performed using hologram data without range coverage correction and using hologram data with a constant depth of 2.

Next, let us consider a case where there is a deviation between the center frequency of the ultrasound and the fundamental frequency of the kernel signal. That is, if the fundamental frequency of the kernel signal is matched to the center frequency of the ultrasonic noculus transmitted from the ultrasonic transducer 1, a deviation will occur between the center frequency of the received signal obtained by receiving the reflected wave. There are many things. When the ultrasonic signals transmitted and received by the Tsumashi ultrasonic transducer 1 propagate through the living body to be examined,
Attenuates according to its propagation length.

Due to this attenuation, there is a property that the center frequency shifts. Figure 2 shows the attenuation of ultrasonic waves with respect to frequency at the depth of the living body.
As shown in the characteristic P, the degree of attenuation of -5°C is largely dependent on the frequency. For this reason, even if an ultrasonic wave/wavelength having a frequency distribution shown by the characteristic Q is transmitted, the frequency distribution of the reflected wave changes as shown by the characteristic R under the influence of the above-mentioned attenuation. In other words, the characteristic R is expressed as the product of the above-mentioned characteristics P and Q. As a result, its center frequency f. is f.

It will be deviated towards. Incidentally, depending on the difference in depth, the attenuation characteristic P is given with a slope corresponding to the depth, and therefore the eccentric position of the center frequency also changes.

Therefore, if the center frequency of the ultrasonic wave and the reference frequency of the kernel signal are shifted by Δf (=Δ−JGJ−) and 2π, then the following relationship holds true: ωI2 ωO−Δω (6) The reconstructed image A obtained using the kernel signal can be expressed as follows by substituting the above equation (6) into the above equation (4).

Incidentally, despite the existence of such a frequency deviation, the reconstructed image obtained using a kernel signal whose fundamental frequency is set equal to the center frequency of the ultrasound signal is the same as the above equation (7). , signal deterioration occurs by the amount (-Δω) of the second term in the last exp term on the right side. The reconstructed image will be degraded by the amount Δω due to the frequency deviation.

In view of these problems, the present invention prevents the deterioration of the reconstructed image by measuring the center frequency of the received signal using a counter and providing a kernel signal according to the deviation of the center frequency. .

That is, if we focus on the second term in the last eXp term on the right side of equation (7), we get (ω.-Δω)(X-8)2G)6-Δω (,-,)
21V y , and the first term on the right side of the above equation can be transformed as follows.

Ofo −Δf Here, 2′ is given as When the center frequency of the ultrasound is shifted by Δf as shown in this equation, the kernel signal of depth 2′ is replaced by the kernel signal of depth 2′. It can be seen that the cause of the deterioration of the reconstructed image can be removed by using the signal. Therefore, the kernel signal is given as a depth of 4 parameters, and the depth parameter is changed according to the center frequency deviation of the ultrasonic wave, and the kernel signal corresponding to the frequency deviation is used to open the aperture. By performing the compositing operation, it becomes possible to obtain a reconstructed image without deterioration.

FIG. 3 is a schematic diagram of an apparatus according to an embodiment of the present invention based on such a technical concept, and 1 is an ultrasonic transducer.

This ultrasonic transducer 1 is energized by the forceps 3,
Ultrasonic waves/wavelength pulses having a spread corresponding to the living body 4 are transmitted, and reflected waves of the ultrasonic pulses reflected within the living body 4 are received. The received signal of this reflected wave is amplified to a required level via a register 5. Phase detector 6
, 7 input a sine wave signal given from an oscillator 8, or a sine wave signal obtained by shifting the sine wave signal by 90 degrees via a phase shifter 9, which have different phases by 90 degrees. Phase detection is performed. The frequency of the sine wave signal is set equal to the resonance frequency of the ultrasonic transducer 1, and the phase-detected signal is outputted after removing high frequency components through a built-in low-pass filter. Ru. As a result, a curse hologram signal and an S-stone hologram signal, which are orthogonal to each other, are obtained from the two phase detectors 6.7, which are respectively digitized via a transducer 10.11 and then stored in a memory. 12 and 13, respectively.

On the other hand, the counter 14 receives the received signal output from the receiver 5 and measures its center frequency f. There are various methods of measuring the center frequency f using the counter 14, but for example, it is measured using a dart circuit for a certain period of time Tc (
This is done by inputting a received signal for a period of sec) and measuring the number of times N that the level of this received signal exceeds a predetermined threshold. As a result, from the relationship Tc N, the center frequency f of the received signal, that is, the ultrasonic wave
I get criticized. Using the information on the center frequency f thus measured, the 2-converter 15 converts the depth grammeter 2 from the relationship shown in equation (9) above.

For example, as shown in FIG. 4, the memory 16 stores kernel signals corresponding to depth 2 as a parameter, and corresponds to the depth 9 determined by the two converters 15. The kernel signal is read out according to the parameter. Therefore, from this memory 16, the frequency f. The measured kernel signal is shifted according to its frequency deviation, converted into 1sz-+z', and then read out.

The arithmetic processing section 17, which is mainly composed of a microprocessor, executes the aperture synthesis arithmetic processing shown in the above equation (7) from the information given from the memories 12 and 13.16, respectively. The reconstructed image A thus obtained is displayed on the display 18 as a diagnostic image.

Note that the control unit 19 controls a series of operations of each of these units.

In this way, according to the present device, the center frequency of the received signal is measured by the counter 14, and the aperture synthesis calculation is performed using the kernel signal whose depth is corrected according to the frequency deviation. It is possible to obtain a reconstructed image, that is, a diagnostic image, without deterioration due to position. Moreover, since the aperture synthesis method is used, there is no need to focus the ultrasonic waves under complicated control, and the lateral resolution can be made sufficiently high over a wide range in the depth direction. Therefore,
High-quality ultrasound diagnostic images can be obtained, and the effect is tremendous.

Note that the present invention is not limited to the above embodiments. For example, the method of measuring the center frequency using the counter 14, the process of changing the depth parameter for the kernel signal, etc. may be performed in accordance with the device specifications. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the aperture synthesis method, Fig. 2 is a diagram showing attenuation of ultrasonic waves and center frequency deviation, Fig. 3 is a schematic configuration diagram of an embodiment of the device of the present invention, and Fig. 4 is a diagram for explaining the aperture synthesis method. is the depth i? FIG. 3 is a diagram illustrating a kernel signal that is made into a RAM. 1... Ultrasonic transducer, 2... Point reflector, 3...
Gursa, 5... Receiver, 6, 7... Phase detector,
10゜11...～勺Converter, 12,13.16...
Memory, 4...Counter, 15...2 Converter, 1
7... Arithmetic processing unit.

Claims (3)

[Claims] (1) An ultrasonic transducer driven by a pulser to transmit ultrasonic waves and receive reflected waves of the ultrasonic waves from an object;
A phase detector detects the phase of the received signal of the reflected wave by the ultrasonic transducer to obtain a hologram signal related to the object, and a kernel signal necessary for aperture synthesis processing using the depth of the object as a parameter. A parameter of the depth according to the amount of deviation between a signal generator that generates a signal, a counter that measures the center frequency of the received signal, and a frequency deviation of the ultrasonic wave from the center frequency measured by this counter. and a calculation unit that executes an aperture synthesis calculation using the corrected kernel signal and the hologram signal to obtain a reconstructed image of the object. An ultrasonic diagnostic device characterized by: (2) The ultrasonic diagnostic apparatus according to claim 1, wherein the hologram signal and the Kerr multiplicity signal are each treated as dinotal data. (3) The signal generator consists of a memory that stores a kernel signal corresponding to the depth as a depth parameter, and the kernel signal is corrected from the memory by shifting the above-mentioned parameter according to the frequency deviation. The ultrasonic diagnostic apparatus according to claim 1, wherein the kernel signal to be read is changed.