JPH07178081A - Ultrasonographic diagnostic system and signal processing method therefor - Google Patents

Abstract

PURPOSE:To obtain a small-sized and light-weighted ultrasonographic probe, to remove artifacts due to multiple echo, and to obtain a good ultrasonographic diagnostic image. CONSTITUTION:This ultrasonographic diagnostic device is provided with an ultrasonic transducer 30, an ultrasonographic probe provided with a liquid transmission medium and a membrane-like substance, an ultrasonic receiving and transmitting circuit 50 for driving this ultrasonographic probe, a received signal processing means 55 for signal processing the echo information detected by the ultrasonographic probe and a displaying means 62 for displaying the signal processed echo information. In addition, the received signal processing means 55 is provided with an arithmetic function by which the tissue information of a living body is calculated by subtracting the membrane echo information coming from the membrane-like substance from the echo information of the ultrasonic pulse oscillated from the ultrasonic transducer 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus for emitting an ultrasonic pulse into a living body, processing the reflected wave signal thereof and displaying it as a living body image for medical diagnosis, and a signal processing method thereof.

[0002]

2. Description of the Related Art Ultrasound diagnostic equipment that oscillates ultrasonic pulses in a living body as a subject, processes the reflected wave signal and displays it as a living body image has become widespread, and is now an indispensable device for medical diagnosis. ing.

The ultrasonic diagnostic apparatus is roughly classified into an electronic scanning system and a mechanical scanning system according to the scanning method of the ultrasonic beam.
In this type of ultrasonic diagnostic apparatus, the electronic scanning method is predominant, but the method of mechanically scanning a large-diameter annular array transducer is excellent for diagnosing body surface organs such as the mammary gland and thyroid. The method of mechanically scanning a large-diameter annular array transducer combined with a circular transducer has a feature that an ultrasonic beam can be strongly focused in axial symmetry, and a high-resolution ultrasonic image can be obtained.

However, mechanical scanning of a large-diameter annular array oscillator requires rotation or translation of the annular array oscillator to move in the direction of the central axis, and therefore the surface (body surface) of the living body to be examined. It is necessary to interpose a liquid such as water, which has low ultrasonic attenuation and low viscous resistance, between the oscillator and the vibrator, and inevitably a closed container for containing the liquid is also required. The portion of the closed container that is in contact with the surface of the living body is the portion through which the ultrasonic beam passes, and is usually formed of a thin film material.

[0005]

When an ultrasonic pulse is oscillated from the annular array transducer while the film-like substance in the closed container is in contact with the surface of the living body, the film-like substance or the surface of the living body (body surface) is generated.
The reflection of ultrasonic waves from a part is repeatedly reflected in a liquid with little attenuation, so-called multiple reflection occurs, and multiple echoes due to this multiple reflection are displayed in the biological tissue image which is an ultrasonic image and become an artifact, which is clear. It was a hindrance in obtaining an ultrasonic image.

In order to remove the influence of artifacts on the biological tissue image obtained by ultrasonic diagnosis, the distance of the liquid portion (the length between the oscillator and the membranous substance, hereinafter referred to as the standoff) is set to be sufficiently long. Designed to. The standoff becomes larger as the diameter of the transducer becomes larger and the deeper the living body is to be observed.

In the design considering the effect of standoff,
There are no artifacts due to multiple echoes, and a sufficiently good ultrasonic diagnostic image can be obtained, but when trying to observe from the surface of the living body to a deep target site, the standoff must be lengthened according to the observed site, In addition to the large size and heavy weight of the probe, in order to obtain an ultrasonic diagnostic image with the same resolution, the diameter of the annular array transducer must be increased, which is a problem in practical use.

The present invention has been made in consideration of the above-mentioned circumstances. The ultrasonic probe can be made smaller and lighter, the artifacts due to multiple echoes can be removed, and an excellent ultrasonic diagnostic image can be obtained. An object is to provide a diagnostic device and a signal processing method thereof.

Another object of the present invention is to provide a practical ultrasonic diagnostic apparatus and a signal processing method therefor which do not require a large standoff, which enables the ultrasonic probe to be reduced in size and weight and which has improved operability. To provide.

Still another object of the present invention is to provide an ultrasonic diagnostic apparatus and a signal processing method therefor capable of obtaining a favorable ultrasonic diagnostic image by reducing the standoff to improve the lateral resolution.

Another object of the present invention is to remove the influence of multiple reflections and to display an ultrasonic diagnostic image as a good ultrasonic diagnostic image without distorting only the ultrasonic reflected waves from the in-vivo tissue and its signal processing. There is a way to provide.

Still another object of the present invention is to provide a practical ultrasonic diagnostic apparatus and a signal processing method therefor capable of observing a depth of 5 cm or more from the surface of a living body by using a small and compact ultrasonic probe. is there.

Still another object of the present invention is to mechanically scan an annular array oscillator to automatically respond to deformation of a film-like substance in contact with the surface of a living body and different body surface tissues, and to obtain an excellent ultrasonic image. An ultrasonic diagnostic apparatus that can be obtained and a signal processing method thereof are provided.

[0014]

In order to solve the above-mentioned problems, an ultrasonic diagnostic apparatus according to the present invention, as set forth in claim 1, uses an ultrasonic transducer for transmitting and receiving ultrasonic pulses and an ultrasonic wave. An ultrasonic probe provided with a propagating liquid propagation medium and a film-like substance containing the propagation medium, an ultrasonic transmission / reception circuit for driving the ultrasonic probe, and signal processing of reflected wave information detected by the ultrasonic probe. It has a reception signal processing means and a display means for displaying the signal-processed reflected wave information, and the reception signal processing means,
It is provided with a processing function of obtaining biological tissue information by subtracting the film reflected wave information from the filmy substance portion from the reflected wave information of the ultrasonic pulse oscillated from the ultrasonic transducer.

In order to solve the above-mentioned problems, the ultrasonic diagnostic apparatus according to the present invention is subjected to signal processing by the reception signal processing means as described in claim 2 in addition to the contents described in claim 1. The film reflected wave information is the multiple reflected wave information reflected once or more by the ultrasonic transducer and twice or more by the film-like substance portion, and as described in claim 3,
The ultrasonic probe is provided with a swivel drive mechanism that supports an annular array type ultrasonic transducer so that the ultrasonic transducer can swing back and forth, and the swivel drive mechanism constitutes an ultrasonic probe of a mechanical scanning type. like,
The received signal processing means includes a memory for storing the film reflected wave information, and the film reflected wave information that can be set in advance is stored in the memory. Further, as described in claim 5, the received signal processing means is A quadrature detection circuit for quadrature detecting the film reflected wave information is provided, and the quadrature detection circuit performs signal processing on the amplitude information and the phase information of the film reflected wave information, and further, as described in claim 6, the received signal processing means. Has a digital signal processing circuit for calculating the film reflected wave information from the transfer function of the ultrasonic transducer and the film substance using the first reflected wave information detected by the ultrasonic probe, As described in 7, the received signal processing means is a digital signal processing circuit in which the film reflected wave information is calculated using the first reflected wave information from the film substance portion in the scanning direction immediately before the ultrasonic probe. Equipped Those were.

Further, in order to solve the above-mentioned problems,
In the ultrasonic diagnostic apparatus according to the present invention, as described in claim 8 in addition to the contents of claim 6 or 7, the digital signal processing circuit outputs the calculated film reflected wave information from the film substance portion. Is adjusted and output at a time interval that is an integer multiple of the time of receiving the reflected wave of the first ultrasonic pulse of, and the outputted film reflected wave information is subtracted from the reflected wave information of the ultrasonic pulse by a calculator. Is set to.

Further, in order to solve the above-mentioned problems, in the ultrasonic diagnostic apparatus according to the present invention, in addition to the contents described in claim 1, as described in claim 9, the received signal processing means comprises: An adjusting circuit is provided which makes at least one of the amplitude and time phase of the film reflected wave information variable, and
As described in, the ultrasonic transducer is provided with an annular array type ultrasonic transducer, while the liquid propagation medium is mainly composed of water with little attenuation of ultrasonic waves, and a mechanical scanning ultrasonic probe is used. Is.

Further, in order to solve the above-mentioned problems, the signal processing method of the ultrasonic diagnostic apparatus according to the present invention has the following features.
As described in 1, receiving the reflected wave information from the living body of the ultrasonic pulse oscillated from the ultrasonic transducer,
This is a method of subtracting the multiple reflected wave information from the ultrasonic transducer surface and the biological body surface portion from this biological reflected wave information, and displaying the biological tissue reflected wave information from which the multiple reflected wave information has been removed, on the display means.

[0019]

In the ultrasonic diagnostic apparatus and the signal processing method thereof according to the present invention, the information of the reflected wave from the living body of the ultrasonic pulse oscillated from the ultrasonic transducer of the ultrasonic probe is signal-processed to be processed from the membranous substance portion. Since the biological tissue information excluding the film reflected wave information (multiple reflected wave information) of No. 1 is displayed on the display means, the multiple reflected waves from the membranous substance portion do not enter the visual field of the display means, and thus the standoff is performed. It is possible to eliminate the artifacts due to multiple reflected waves without needing to do so, to reduce the size and weight of the ultrasonic probe, and to significantly improve the operability of the ultrasonic probe and increase the reliability.

The ultrasonic transducer of the ultrasonic probe uses an annular array type vibrator to perform electron focusing of a variable aperture or ultrasonic pulse, and when the outer diameter of the ultrasonic transducer is the same, the ultrasonic transducer is placed on the surface of the living body. The closer the position can be located, that is, the smaller the standoff, the more the lateral resolution can be improved, so that a good ultrasonic diagnostic image can be obtained.

In this ultrasonic diagnostic apparatus, the time and the waveform at which multiple reflections occur on the ultrasonic probe differ depending on the scanning line direction of the ultrasonic transducer, so that the ultrasonic pulse from the film-shaped substance portion in each scanning line direction is different. It is necessary to use the first reflected wave information. Since the film reflected wave information that is multiple reflection occurs later than the first reflected wave,
The first reflected wave information is digitized and stored in the memory, and the appropriate time phase (phase) and amplitude control are performed to consider the phase and amplitude of the film reflected wave information by multiple reflection from the reflected wave information of the ultrasonic probe. Then, only the reflected wave information from the in-vivo tissue is displayed without distortion.

Even if the portion of the film-like substance in contact with the surface of the living body is deformed, the waveforms and positions of the second and subsequent reflected waves (multiple reflected waves) are estimated from the first reflected wave information which is the source of the multiple reflections. Since the artifact due to the multiple reflection is removed from the reflected wave information of the ultrasonic probe in which the reflected wave of the biological tissue and the multiple reflected wave are superposed, it is possible to automatically cope with the deformation of the membrane portion and the deformation of the living body surface.

Since an ultrasonic probe which can be used even at 5 MHz or less can be used in this ultrasonic diagnostic apparatus, it is possible to observe in-vivo tissue at a depth of 5 cm or more from the surface of the living body, and usually in most diagnostic areas. Use, eg 3.5M
A practical ultrasonic probe can be realized in the Hz to 5 MHz band, and particularly when an annular array type ultrasonic transducer is used by a mechanical scanning method, an ultrasonic diagnostic apparatus having a remarkably excellent image quality can be obtained.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 exemplifies an ultrasonic diagnostic apparatus according to the present invention. In this ultrasonic diagnostic apparatus, a mechanical scanning type ultrasonic probe 10 is connected via a cable 11 to a main body casing 12 of the ultrasonic diagnostic apparatus. It is detachably connected to the side.

In the ultrasonic probe 10 of the mechanical scanning system, a biaxial motor 15 is housed in a probe body 13, and a cylindrical moving body 17 is slidable in an axial direction on one output shaft 16a of the motor 15. It is spline-connected to the rotating body. A circumferential guide groove 18a is formed in the tubular moving body 17, and a manually operable positioning operation lever 19 is engaged with the guide groove 18a. The manual operation of the operating lever 19 allows the tubular moving body to move. 17 is slid in the axial direction of the output shaft 16a.

The cylindrical moving body 17 is composed of a rotary shaft 20.
Is integrally or integrally provided, and a vibrator holder 22 is connected to a free end side of the rotary shaft 20 via a link mechanism 21. The link mechanism 21 is the rotary shaft 20.
A connecting rod 23 that is vertically connected to the free end side of
A support arm 25 connected to the connecting rod 23 via a spherical bearing 24 is provided. The support arm 25 is branched in the middle into, for example, two branches, and protrudes from the vibrator holder 22 at the tips of the branch arms 25a and 25b. Supporting bosses 26a, 2
6b is supported, and the turning drive mechanism 28 is configured. The oscillator holder 22 is driven by the turning drive mechanism 28, so that the oscillator holder 22 is supported by the support shafts 29a and 29b (see FIG. 3).
(Corresponding to point O) of the above).

The transducer holder 22 supports an annular array type ultrasonic transducer 30 as an ultrasonic transducer having a concave disk shape. As shown in FIG. 2, the ultrasonic transducer 30 has an annular array structure in which a circular ultrasonic transducer 31 is combined with a concentric disk to have a contrast resolution and a thin lumen structure, which is advantageous for high frequency and large aperture ( For example, by setting it to 36 mmφ), a high spatial resolution can be obtained. Annular array type ultrasonic transducer 30
Is formed into a concave disk shape, so that the oscillated ultrasonic pulse has a focusing effect.

As shown in FIG. 3, a probe container 33 having a closed structure is provided below the ultrasonic probe 10, and the annular array ultrasonic transducer 30 is accommodated in the probe container 33. The liquid propagation medium 35 is enclosed. As the propagation medium 35, a liquid such as water or oil having a small attenuation of ultrasonic waves and a small viscous resistance is used. A liquid containing water as a main component and having little ultrasonic attenuation is preferably used.

At the lower end of the probe container 33, a flexible resin thin film 36 such as rubber is stretched as one of flexible film substances, and the ultrasonic probe 10 is interposed through the resin thin film 36.
Is brought into close contact with the surface 38 of the living body 37 which is the subject.

However, the ultrasonic pulse oscillated from the ultrasonic oscillator 30 is the liquid propagation medium 35 and the resin thin film 3.
6. It propagates through the living body surface 38 into the living body 37 and is reflected by the tissues in the living body. On the contrary, the ultrasonic wave reflected by the tissue in the living body is received by the ultrasonic transducer 30 through the living body surface 38, the resin thin film 36 and the liquid propagation medium 35.
The signal is sent to a signal processing circuit 40, which is an electric circuit shown in FIG.

On the other hand, the ultrasonic transducer 30 in the ultrasonic probe 10 is reciprocally rotationally driven by the driving of the turning drive mechanism 28, and moves reciprocally around the point O (reciprocating swing). The left end and right end positions of the ultrasonic transducer 30 due to the reciprocating stroke movement are shown by chain lines 30a and 30b, respectively.

The ultrasonic transducer 30 is formed in a concave disk-shaped annular array type structure, ultrasonic pulses are oscillated in the direction of the central axis of the ultrasonic transducer 30, and the reflected waves of ultrasonic waves are also directed in the same direction. It When the ultrasonic transducer 30 faces the centerline O-O1 direction, ultrasonic waves are transmitted and received in the centerline O-O1 direction. When the ultrasonic transducer 30 is swung in the direction of the center line O-O2 indicated by the chain line, when it is oriented in the direction of the center line O-O2 and in the direction of the center line O-O3, the center line O
Ultrasonic waves are transmitted and received in the -O3 direction and in the intermediate direction between them. The signal intensity of the reflected wave of the ultrasonic wave is intensity-modulated and displayed on the cathode ray tube as the display position at the corresponding position to obtain the ultrasonic cross-sectional image.

FIG. 5 shows how the ultrasonic pulse oscillated from the ultrasonic transducer 30 is transmitted and received on the time axis.

Consider a case where the ultrasonic transducer 30 faces the center shown by the solid line in FIG. The rectangular wave pulse UP shown in FIG. 4A is the ultrasonic pulse transmission circuit 41 shown in FIG.
Is a pulse output from the rate pulse generator 43, and is a pulse which is divided from the reference clock and is repeated at, for example, 5 KHz. This 5 KHz is called a rate frequency. The pulser 44 is driven at the trailing edge of the rate pulse, and the ultrasonic wave pulse indicated by the symbol E in FIG.

The oscillated ultrasonic pulse E propagates in the liquid propagation medium 35, is reflected by the resin thin film 36 and the living body surface 38, and is the first reflected wave R1 which is a film reflected wave.
Is received by the ultrasonic transducer 30. Ultrasonic transducer 3
The distance between 0 and the resin thin film 36 is X, and the liquid propagation medium 3
When the sound velocity of 5 is C, the time t1 until the ultrasonic pulse E oscillated from the ultrasonic transducer 30 receives the first reflected wave R1 from the resin thin film 36 and the living body surface 38 is

[Equation 1] t1 = 2 · X / C (1)

The first reflected wave R1 impinges on the ultrasonic transducer 30, the sound pressure is converted into a voltage, is taken out through a lead wire (not shown), and is reflected by the ultrasonic transducer 30. The reflected wave propagates through the liquid propagation medium 35 and reaches the resin thin film 36 and the living body surface 38 again, where it is reflected again and reaches the ultrasonic transducer 30 to generate the second reflected wave signal R2. The ultrasonic pulse is repeatedly reflected thereafter, and the third, fourth, ... Reflected wave signals R3, R4 are sequentially generated. The film reflected waves after the second reflected wave signal R2 are referred to as multiple reflected waves.

The intervals of the respective film reflected waves are the time intervals of t1 expressed by the equation (1), and the amplitude of each reflected wave is R
1, R2, R3, ...
The waveforms of R2, R3, ... Are slightly different.

Further, the time t1 when the reflected wave of the ultrasonic beam is generated has different time intervals because the distance X differs depending on the oscillation direction of the ultrasonic beam. For example, in the O-O2 direction which is the left end direction with respect to the center line O-O1 direction in FIG.
The distance X between the ultrasonic transducer 30 and the resin thin film 36 increases, and the arrival time t1 of the reflected wave also increases.

As a method of displaying the ultrasonic cross-sectional image, a scanning line is set in the direction of the ultrasonic beam in which the ultrasonic pulse UP is oscillated, and the distance X and the arrival time t1 of the reflected wave are made to correspond on the scanning line. In general, the direction in which brightness modulation display is performed by the reflected wave amplitude is performed.

Therefore, the first reflected wave signal R1 is displayed at the position of the distance X from the ultrasonic transducer 30. As the ultrasonic cross-sectional image, a portion A surrounded by a hatch in FIG. 3 is displayed, the upper limit is the line of the film portion corresponding to the resin thin film 36 and the living body surface 38, and the lower limit is the reflected wave after ultrasonic pulse oscillation. Determined by the maximum display time to be displayed. If the maximum display time is fixed, the arc O2-O1-O3 shown in FIG. Both sides of the portion A surrounded by the hatch are determined by the maximum value of the scanning angle of the ultrasonic beam, for example, ± 20.

The first reflected wave signal R1 from the resin thin film 36 and the living body surface 38 is displayed at the position of the living body surface,
The second reflected wave signal R2 is displayed at a position 45 apart from the surface of the living body by a distance X. Resin thin film 36 and living body surface 3
If 8 is a plane, the signal R2 due to the second reflected wave is
Is displayed at a position 45 at a distance X from the living body surface 38, and the reflected wave signals R2, R3, ... After the second become a disturbance as multiple reflection artifacts.

In the actual ultrasonic diagnosis, when the oscillated ultrasonic wave pulse enters the living body 37 from the living body surface 38, there is a living body tissue 46, and there is reflection from this living body tissue 46. As shown in C), the mixed reflected wave signal M in which the reflected wave from the in-vivo tissue 46 and the multiple reflected waves R2, R3, ... Which are the film reflected waves from the resin thin film 36 and the living body surface 38 are superimposed. Becomes Multiple reflected wave signals R2, R
.. are relatively easy to recognize because they are generated in a line shape at equal intervals overlapping the cross-sectional image created by the reflected wave from the in-vivo tissue 46. However, the ultrasonic cross-sectional image overlaps with important findings. It is not suitable for a practical device because it makes it difficult to read.

In FIG. 3, only the second reflected wave signal R2 is shown as reference numeral 45 as the multiple reflection, but the ultrasonic probe 10 is made as small and lightweight as possible, and the ultrasonic transducer 30 is made as close to the living body surface 38 as possible. When the azimuth resolution of the ultrasonic cross-sectional image is increased by approaching to the position, the distance X becomes smaller, so that not only the second reflected wave R2 but also the third reflected wave R3.
After that, the ultrasonic cross-sectional image may be displayed in an overlapping manner.

This ultrasonic diagnostic apparatus employs a mechanical scanning type (mechanical sector) ultrasonic probe 10.
The mixed reflected wave signal (reflected wave information of the ultrasonic probe 10) M shown in FIG. 5 (C) in which the multiple reflection of the ultrasonic pulse UP and the reflection from the living body 37 are mixed to the multiple reflected wave shown in FIG. 4 (B). Only the waveform signal (membrane reflected wave information) R2, R3 ... Is subtracted to remove the effect of multiple reflection on the ultrasonic cross-sectional image, and the ultrasonic wave cross section is obtained by the reflected wave signal (in-vivo tissue information) R shown in FIG. It is designed to generate an image.

Next, the signal processing for removing the waveform of the reflected wave due to the multiple reflection from the mixed reflected wave waveform of the reflected wave from the living tissue and the multiple reflected wave will be described.

The electric circuit shown in FIG. 4 is a signal processing circuit 40 accommodated in the main body casing 12 side of the ultrasonic diagnostic apparatus.
Then, the signal processing circuit 40 for removing the influence of the multiple reflected waves
Is shown.

The signal processing circuit 40 includes an ultrasonic transducer 30.
An ultrasonic pulse transmission circuit 41 that transmits an ultrasonic pulse for driving is provided. The ultrasonic pulse transmission circuit 41 for transmitting an ultrasonic pulse is a microcomputer or a CPU (hereinafter, CP
U. ) A pulse generator 43 for generating a rate frequency of, for example, 5 KHz divided from 48 reference clocks
And a pulser 44 is triggered by the rate pulse generator 43. Rate pulse generator 43
When a pulse voltage is applied to the pulsar 44 triggered by, the ultrasonic pulse indicated by the symbol E in FIG. 5B is applied to the ultrasonic transducer 30, and the ultrasonic transducer 30 indicates the ultrasonic wave indicated by the symbol E. The pulse is made to oscillate.

The ultrasonic pulse E oscillated from the ultrasonic transducer 30 is the resin thin film 36 and the living body surface 38 shown in FIG.
While being multiple-reflected by the
It is also reflected from. The mixed reflected wave signal M in which reflections and multiple reflections from the living tissue 46 are mixed is converted from a sound pressure signal into a voltage signal (electrical signal) by the ultrasonic transducer 30 and extracted, and input to the ultrasonic pulse receiving circuit 49. It The ultrasonic pulse receiving circuit 49 and the ultrasonic pulse oscillating circuit 41 constitute an ultrasonic pulse transmitting / receiving circuit 50.

The mixed reflected wave signal M input to the ultrasonic pulse receiving circuit 49 is guided to the amplifier 52 via the limiter 51 and is amplified therein. The limiter 51 is a limiter that prevents the high-voltage transmission high-frequency pulse from the ultrasonic pulse transmission circuit 41 from being input to the ultrasonic pulse reception circuit 49.

In the conventional ultrasonic diagnostic apparatus, the output from the amplifier 52 of the ultrasonic pulse receiving circuit 49 is amplitude-detected by the detection circuit and A / D converted, and then cross-sectional image information is created by the digital scan converter. It is adapted to be displayed on the display means.

In the signal processing circuit 40 shown in FIG. 4,
The mixed reflection signal M output from the ultrasonic pulse receiving circuit 49 is input to the A / D converter 56 of the reception signal processing means 55 as it is as a high frequency signal of 2 to 10 MHz and is A / D converted.

The reception signal processing means 55 inverts the output from the A / D converter 56, the memory 57 in which the multiple reflected wave signal is stored for each scanning line, and the memory 57, and the amplitude and phase of the memory output. Finely adjust the memory output to ON / O.
An adjusting circuit 58 for FF, an arithmetic unit 59 such as an adder for adding the memory output to the output from the A / D converter 56,
It has a detection circuit 60 for detecting the amplitude of the output of the arithmetic unit, and a digital scan converter 61 for creating ultrasonic cross-sectional image information from the output from the detection circuit 60. The tissue image) information is displayed as an ultrasonic cross-sectional image on the display device 62 such as a television monitor.

The adjusting circuit 58 of the reception signal processing means 55 has a function of inverting the output of the memory 57, a function of finely adjusting the amplitude and phase (time phase) of the multiple reflected wave signal, and a memory output of O.
It has the function of turning off and on.
Controlled by. The CPU 48 is controlled so that the memory output signal read from the memory 57 corresponds to the scanning line scanned by the ultrasonic transducer 30.

The ON / OFF function of the adjusting circuit 58 is turned off.
Then, when the display device 62 is observed, as shown in FIG. 3, the images of the first reflected wave signal R1 which is the first film reflected wave at the positions of the resin thin film 36 and the living body surface 38 are the second, third, ... The images of the line-shaped multiple reflected wave signals R2, R3 ... Corresponding to the second, third ... Reflected wave signals R2, R3.
It is observed as shown in FIG.

Next, when the ON / OFF function is turned ON by utilizing the inverting circuit incorporated in the adjusting circuit 58, the multiple reflected wave signal which is the memory output with the phase inverted is adjusted.
8 and the inverted memory output signal is added to the output signal (mixed reflected wave signal M) from the A / D converter 56, and the line-shaped multiple reflected wave image on the display device 62 is reduced. When the amplitude and phase of the adjusting circuit 58 are finely adjusted, the disappearance state of the multiple reflected wave image is confirmed, and then the memory 5
The multiple reflection wave information and the fine adjustment function stored in 7 are temporarily fixed, and then the ultrasonic probe 30 is applied to the living body as the subject for diagnosis. Reference numeral 64 is ground.

The storage of the multiple reflected wave information in the memory 57 is performed by using a phantom (not shown). The surface layer of the phantom has the same acoustic impedance (1.5 to 1.6 × 10 ⁶ kg / m ² sec) as that of the body skin, and the inside has the same acoustic impedance as that of the body skin layer. Made of uniform material without reflection. The ultrasonic probe 10 is applied to this phantom and the reflected wave R1
, R2, R3, ..., The reflected wave signal is converted into a digital signal by the A / D converter 56, and the output from the A / D converter 56 is stored in the memory 57 for each scanning line. The multiple reflection wave information is stored in the memory 57 for each scanning line.

However, since the conditions of the phantom and the living body are slightly different, the ON / OFF function of the adjusting circuit 58 is turned off even when the inside of the living body 37 is actually observed, and the reflection from the tissue 46 in the living body is reflected. Check the wave image (multiple reflected wave image superimposed on the biological tissue image), and use the fine adjustment function of the amplitude and phase of the adjustment circuit 58 so that the effect of the multiple reflected wave image is minimized. It may be set to obtain an image. In that case, it is not necessary to measure and store the multiple reflection wave waveform for each scanning line stored in the memory 57 each time, and since the ultrasonic probe 10 has a fixed value, the waveforms are synthesized. CPU 58
May be supplied to the memory 57.

Although the adjusting circuit 58 shown in FIG. 4 has been described as having the inverting circuit for inverting the memory output, the adjusting circuit 58 does not necessarily have to include the memory output inverting circuit. When the inverting circuit is not provided, the arithmetic unit 59 of the reception signal processing means 55 acts as a subtractor, and the memory output is subtracted from the output of the A / D converter 56.

Further, in the signal processing circuit 40 shown in FIG.
A / D converter 56 directly outputs a high frequency signal of 2 to 10 MHz
A / D conversion allows high-speed A with high clock frequency
Although a / D converter is required, a quadrature detection circuit is provided in front of the A / D converter 56 to perform quadrature detection, thereby reducing the A
It becomes possible to use a / D converter.

FIG. 6 shows a signal processing circuit 70 having a low speed A / D converter. Signal processing line 40 of FIG.
The same components as those in FIG.

In the signal processing circuit 70 shown in FIG. 6, the output from the amplifier 52 of the ultrasonic pulse receiving circuit 49 is input to the two mixers 72a and 72b of the reception signal processing means 71. The signals input to the mixers 72a and 72b are the CPU
It is possible to take out quadrature detection by multiplying with reference waves having different phases by 90 ° from 48 reference clocks, and take out as signal information having amplitude and phase. Each high frequency component subjected to the quadrature detection is cut by the low pass filters 73a and 73b, the low frequency component is allowed to pass, and the A / D converters 74a and 74b perform A / D conversion.
D-convert. A quadrature detection circuit 75 is composed of the mixers 72a and 72b and the low pass filters 73a and 73b.
In this case, the A / D converter 56 shown in FIG.
A slower speed is sufficient, and power consumption and cost can be reduced.

Next, another method for removing the influence of multiple reflected waves in the ultrasonic diagnostic apparatus will be described.

This method estimates the reflected wave information after the second reflected wave information from the first reflected wave information and the transfer function, and removes the influence of multiple reflected waves.

In the application of this method, the ultrasonic probe 10 is provided with a resin thin film 36 having high flexibility, and when the resin thin film 36 is brought into contact with the living body surface (body surface) 38, it is deformed according to the shape of the body surface, When the body surface comes to a position slightly different from the position assumed by the phantom, and the first reflected wave waveform is effective for the situation of the body surface (skin or subcutaneous) of an individual.

Since the ultrasonic probe 10 is usually used for diagnosis by changing contact with the living body surface (body surface) 38 one after another, the film deformation occurs when the resin thin film 36 is soft and the body surface portion is also formed. Change. Therefore, the distance X from the ultrasonic transducer 30 to the resin thin film 36 differs for each scanning line, and the distance X slightly changes every moment, and the reflected wave waveform also changes accordingly. Therefore, the state of multiple reflection detected by the ultrasonic probe 10 slightly changes every scanning line, and the influence of multiple reflected waves must be subtracted in consideration of this change.

Now, the ultrasonic transmission pulse waveform oscillated from the ultrasonic probe 10 shown in FIG.
(T), the received waveform of the first reflected wave R1 is f1 (t), and the received waveforms of the multiple reflected waves R2, R3 ...
(T), f3 (t) ..., and these Fourier transforms are F0 (.omega.), F1 (.omega.), F2 (.omega.), F3 (.omega.) ... Fourier transformed F0 (ω), F1 (ω), F
2 (ω), F3 (ω) ... Are expressed as a function in the frequency domain, and f0 (t), f1 (t), f2 (t), f3
It is equivalent to (t) ....

Further, the transfer function of the reflected wave with respect to the incident wave of the ultrasonic pulse at the resin thin film 36 and the living body surface 38 is G
(Ω), the transfer function of the reflected wave with respect to the incident wave of the ultrasonic wave on the vibrator surface of the ultrasonic vibrator 30 is H (ω), and the ultrasonic pulse is converted from the sound pressure signal to the voltage signal by the ultrasonic vibrator 30. Let I (ω) be the transfer function

[Equation 2]

[Equation 3] Here, assuming that the resin thin film 36 and the living body surface 38 are perfect reflectors, the transfer function G (ω) = 1, and the Fourier transformed reception waveforms F1 (ω), F2 at this time are obtained.
If (ω) is F1 ⁰ (ω) and F2 ⁰ (ω),

[Equation 4]

[Equation 5] Becomes

If the received waveforms of the multiple reflected waves R2, R3 ... Are f2 (t), f3 (t).

[Equation 6]

[Equation 7] From the equations (2), (2) 'and the equations (3), (3)', the transfer functions G (ω) and H (ω) are

[Equation 8]

[Equation 9] It is represented by.

In this case, the first reflected wave waveform f1 (t) can be directly observed, and the second and subsequent reflected wave waveforms f2.
(T), f3 (t) ... Are transfer functions G (ω), H shown in the first reflected wave waveform f1 (t) and equations (6) and (7).
It can be estimated from (ω).

In practice, the transfer functions G (ω), H (ω)
Can be obtained from the reflected wave waveform of the oscillated ultrasonic wave by setting the ultrasonic probe 10 in the air (in the air) or on a resin plane such as acrylic. Since the convolution is the inverse transform of the Fourier transform, the actual operation may be the convolution operation.

From the actually measured first reflected wave waveform f1 (t) and transfer functions G (ω) and H (ω), second and subsequent reflected wave waveforms f2 (t), f3 (t) ... Thus, the waveforms f2 (t), f3 (t) ... Of multiple reflections can be sequentially calculated.

The time at which multiple reflection occurs on the ultrasonic probe 10 can be obtained as an integral multiple of the time t1 at which the first reflected wave R1 arrives. This time t1 is slight but changes momentarily.

In this way, the received waveform in which the reflected wave from the in-vivo tissue 46 and the multiple reflection are mixed (mixed reflected wave information)
Waveform of multiple reflected waves (film reflected wave information) f2 calculated from
The effect of multiple reflection can be removed by subtracting (t), f3 (t) ...

In this case, the memory 57, the adjusting circuit 58 and the CPU 48 shown in FIG.
Waveforms f2 (t) and f3 of reflected waves from (t) to the second and subsequent ones
It is necessary to have a function of calculating (t) ... With equations (4) and (5).

FIG. 7 shows the first reflected wave R1 and the transfer function G.
The signal processing circuit 80 of the ultrasonic diagnostic apparatus suitable for calculating and removing the influence of multiple reflection from (ω) and H (ω) is partially shown. The other configuration of the signal processing circuit 80 is the same as that of the signal processing circuit 40 shown in FIG.

This signal processing line 80 is provided with a reception signal processing means 81, a first memory 83 and a second memory 84 whose operation is controlled by a digital signal processing circuit 82, and is the n-th ultrasonic probe 10. The A / D converter 56 converts the ultrasonic reception signal (mixed multiple wave signal) obtained in the scanning direction into
It is / D converted and stored in the first memory 83. This first
Simultaneously with the storage in the memory 83, the A / D converted signal is calculated by the high speed digital signal processing device (hereinafter referred to as DCS) 82. The calculation in the DSP 82 is the first reflected wave waveform f1.
After (t) is input, it is performed at high speed during the time t1 until the arrival of the second reflected wave.

The calculation of this DSP 82 is performed by the ultrasonic transducer 3
Based on the waveform f1 (t) of the first (first) reflected wave in which the ultrasonic pulse oscillated from 0 is reflected from the resin thin film 36 and the living body surface 38, the above-mentioned expressions (4) and (5) are used.
Waveform f2 of the second and subsequent reflected waves calculated by the formula
(T), f3 (t) ... Are calculated. The calculated second and subsequent reflected wave waveforms f2 (t), f3 (t) ... Are transmitted to the second memory 84 at a time interval that is an integral multiple of the arrival time of the first reflected wave waveform f1 (t). It is stored in the memory 84. Second
In the memory 84, the waveforms f2 (t) and f3 (t) of multiple reflection obtained by calculation from the first reflected wave waveform f1 (t)
... is remembered.

The multiple reflected wave information stored in the second memory 84 is sent to the adjusting circuit 58, and the amplitude and phase of the multiple reflected wave information (the effect of phase inversion or multiple reflection is minimized in this adjusting circuit 58 ( Fine adjustment of (time phase) is performed and A / D
The calculator 59 adds the mixed reflected wave information (living tissue information + multiple reflected wave information) directly output from the converter 56. If the adjusting circuit 58 does not have a phase inversion function,
The arithmetic unit 59 functions as a subtracter for subtracting the multiple reflected wave information of the adjusting circuit 58 from the mixed reflected wave information.

In this case, the calculation in the DSP 82 is such that after the first reflected wave waveform f 1 (t) is input, the second reflected wave waveform f
2 (t) is reached during time t1 and D
Although high-speed calculation is required for SP82, the waveforms of multiple reflected waves in adjacent scanning directions are considered to be approximately equal, and D
The calculation result of SP82 is temporarily stored in the second memory 84, and the arrival time t1 for the next (n + 1) th reflected wave waveform signal in the scanning direction is n instead of calculating the (n + 1) th multiple reflected wave waveform. The th calculation waveform may be used. By this arithmetic signal processing, the arithmetic time in the DSP 82 can be reduced by about one digit.

The arithmetic signal processing of the signal processing circuit 80 shown in FIG. 7 can be applied to the signal processing circuit shown in FIG.

In the embodiment of the present invention, the mechanical scanning type ultrasonic diagnostic apparatus has been described. However, when an ultrasonic wave propagation medium such as water is used between the ultrasonic transducer and the living body surface of the subject. Also, multiple reflection can be removed by a similar method.

[0083]

As described above, in the ultrasonic diagnostic apparatus and the signal processing method thereof according to the present invention, the information of the reflected wave from the living body of the ultrasonic pulse oscillated from the ultrasonic transducer of the ultrasonic probe is obtained. Since the biological tissue information obtained by removing the film reflected wave information (multiple reflected wave information) from the membranous substance portion by signal processing is displayed on the display means, a good ultrasonic diagnostic image can be obtained, and this image can be obtained. Since the multiple reflected waves from the film-like substance part do not enter the field of view, there is no need for a standoff, and even if the standoff is small, the artifacts due to the multiple reflected waves can be removed, and the ultrasonic probe can be made smaller and lighter. As a result, it is possible to provide a practical ultrasonic diagnostic apparatus in which the operability of the ultrasonic probe is significantly improved and the reliability is improved.

The ultrasonic transducer of the ultrasonic probe may have a small stand-off when the outer diameter of the ultrasonic transducer is the same when electron focusing of a variable aperture or ultrasonic pulse is performed using an annular array type oscillator. Therefore, the ultrasonic transducer can be positioned close to the surface of the living body, the lateral resolution can be improved, and a good ultrasonic diagnostic image can be obtained.

In this ultrasonic diagnostic apparatus, the time and waveform at which multiple reflections occur in the ultrasonic probe differ depending on the scanning line direction of the ultrasonic transducer, so that the ultrasonic pulse from the film-shaped substance portion in each scanning line direction is different. It is necessary to use the first reflected wave information. Since the film reflected wave information that is multiple reflection occurs later than the first reflected wave,
The first reflected wave information is digitized and stored in the memory, and the appropriate time phase (phase) and amplitude control are performed to consider the phase and amplitude of the film reflected wave information by multiple reflection from the reflected wave information of the ultrasonic probe. Then, only the reflected wave information from the in-vivo tissue is accurately displayed without distortion.

Even if the portion of the membranous substance in contact with the surface of the living body is deformed, the waveforms and positions of the second and subsequent reflected waves (multiple reflected waves) are estimated from the first reflected wave information which is the source of multiple reflections. Since the artifact due to the multiple reflection is removed from the reflected wave information of the ultrasonic probe in which the reflected wave of the biological tissue and the multiple reflected wave are superposed, it is possible to automatically cope with the deformation of the membrane portion and the deformation of the living body surface.

Since a small and compact ultrasonic probe that can be used even at 5 MHz or less can be used in this ultrasonic diagnostic apparatus, it is possible to observe an in-vivo tissue at a depth of 5 cm or more from the surface of the living body, and most of them are usually used. Used in the diagnostic area of, for example, a practical ultrasonic probe in the band of 3.5 MHz to 5 MHz can be realized, and in particular, when a mechanical scanning type annular array ultrasonic transducer is used, ultrasonic diagnosis with significantly superior image quality is achieved. The device is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

FIG. 2 is a diagram showing a mechanical scanning type ultrasonic probe provided in the ultrasonic diagnostic apparatus according to the present invention and a state in which the probe is brought into contact with the surface of a living body.

FIG. 3 is a view showing an annular array type ultrasonic transducer adopted in an ultrasonic probe.

FIG. 4 is a diagram showing an example of a signal processing circuit of the ultrasonic diagnostic apparatus according to the present invention.

5A is an example of a rate pulse as a reference pulse emitted from a pulsar, FIG. 5B is an example of multiple reflection pulses of an ultrasonic pulse, and FIG. 5C is a reflection wave and multiple reflection of in-vivo tissue. The figure which respectively shows the example of the reflected wave waveform only from a biological tissue obtained by subtracting a multiple reflected pulse waveform from a mixed reflected waveform.

FIG. 6 is a diagram showing a first modification of the signal processing circuit of the ultrasonic diagnostic apparatus according to the invention.

FIG. 7 is a diagram showing a second modification of the signal processing circuit of the ultrasonic diagnostic apparatus.

[Explanation of symbols]

 10 Ultrasonic Probe 11 Cable 12 Main Body Casing 13 Probe Main Body 15 Motor 30 Ultrasonic Transducer (Ultrasonic Transducer) 33 Probe Container 35 Liquid Propagation Medium 36 Resin Thin Film (Membrane Material) 37 Living Body (Subject) 38 Living Body Surface 40, 70, 80 Signal processing circuit 41 Ultrasonic pulse transmitting circuit 43 Rate pulse generator 44 Pulser 48 CPU (personal computer) 49 Ultrasonic pulse receiving circuit 50 Ultrasonic pulse transmitting / receiving circuit 51 Limiter 52 Amplifying circuit 55 Received signal processing means 56 A / D Converter 57 Memory 58 Adjustment circuit 59 Operation unit (adder) 60 Detection circuit 61 Digital scan converter 62 Display means 72a, 72b Mixers 73a, 73b Low-pass filter 74a, 74b A / D converter 75 Quadrature detection circuit 81 Received signal processing hand 82 digital signal processing circuit 83 first memory 84 a second memory

Claims (11)

[Claims] 1. An ultrasonic transducer including an ultrasonic transducer for transmitting and receiving ultrasonic pulses, a liquid propagation medium for propagating ultrasonic waves, and a film-like substance containing the propagation medium, and an ultrasonic wave for driving the ultrasonic probe. A transmission / reception circuit, a reception signal processing means for signal-processing the reflected wave information detected by the ultrasonic probe, and a display means for displaying the signal-processed reflected wave information, the reception signal processing means,
An ultrasonic diagnostic apparatus having a processing function of obtaining biological tissue information by subtracting film reflected wave information from a filmy substance portion from reflected wave information of an ultrasonic pulse oscillated from an ultrasonic transducer. 2. The film reflected wave information signal-processed by the reception signal processing means is multiple reflected wave information reflected once or more by the ultrasonic transducer and twice or more by the filmy substance portion. Ultrasonic diagnostic equipment. 3. An ultrasonic probe is provided with a swivel drive mechanism for supporting an annular array type ultrasonic transducer so that the ultrasonic transducer can swing back and forth, and the swivel drive mechanism constitutes a mechanical scanning type ultrasonic probe. Ultrasonic diagnostic equipment. 4. The ultrasonic diagnostic apparatus according to claim 1, wherein the reception signal processing means includes a memory for storing the film reflected wave information, and the film reflected wave information which can be set in advance is stored in the memory. 5. The received signal processing means comprises a quadrature detection circuit for quadrature detection of film reflection wave information, and the quadrature detection circuit performs signal processing on amplitude information and phase information of the film reflection wave information.
The ultrasonic diagnostic apparatus described. 6. The digital signal processing, wherein the reception signal processing means calculates the film reflected wave information from the transfer function of the ultrasonic transducer and the film substance using the first reflected wave information detected by the ultrasonic probe. The ultrasonic diagnostic apparatus according to claim 1, further comprising a circuit. 7. The reception signal processing means comprises a digital signal processing circuit for calculating the film reflected wave information using the first reflected wave information from the film material portion in the scanning direction immediately before the ultrasonic probe. The ultrasonic diagnostic apparatus according to claim 1. 8. The digital signal processing circuit adjusts the calculated film reflected wave information to a time interval that is an integral multiple of the time for receiving the reflected wave of the first ultrasonic pulse from the film substance portion. The ultrasonic diagnostic apparatus according to claim 6 or 7, wherein the output information of the film reflected wave is set to be subtracted from the reflected wave information of the ultrasonic pulse by a calculator. 9. The ultrasonic diagnostic apparatus according to claim 1, wherein the reception signal processing means includes an adjusting circuit that makes at least one of the amplitude and time phase of the film reflected wave information variable. 10. The ultrasonic transducer is provided with an annular array type ultrasonic transducer, while the liquid propagation medium is mainly composed of water with little attenuation of ultrasonic waves, and a mechanical scanning type ultrasonic probe is used. 1. The ultrasonic diagnostic apparatus according to 1. 11. Received reflected wave information from a living body of an ultrasonic pulse oscillated from an ultrasonic transducer, subtracting multiple reflected wave information from the ultrasonic transducer surface and body surface portion from this living body reflected wave information, A signal processing method for an ultrasonic diagnostic apparatus, characterized in that the biological tissue reflected wave information from which the multiple reflected wave information has been removed is displayed on the display means.