JPH0731616A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

PURPOSE:To arrange a highly accurate function of correcting nonuniformity of sound velocity by providing an ultrasonic diagnostic apparatus with a second ultrasonic transmission/reception mode for detecting a time shift caused by the nonuniformity of sound velocity in vivo to improve the S/N ratio for increasing a sound pressure of a signal received and detection accuracy of the time shift. CONSTITUTION:A transmitting section 2 has two systems a transmission system 21 for detecting time shift and a transmission system 22 for displaying tomographic images. When the transmission system 21 for detecting the time shift is selected by a transmission system selecting means 23, pulses with the number thereof determined by a number of pulses control means 211 are generated by a pulse generating means 212. The number of the pulses is greater than that in the transmission for display tomographic images. As the number of pulses increases, the sound pressure of an ultrasonic wave as radiated from an electroacoustic conversion element 1 increases thereby improving the S/N ratio of the signal received with the electroacoustic conversion element 1. As a result, errors in the detection of a time shift are reduced thereby allowing improvement in correction effect.

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 displaying a tomographic image in a subject by ultrasonic waves, and more particularly to an ultrasonic diagnostic apparatus having a function of correcting non-uniformity of sound velocity in the subject. .

[0002]

2. Description of the Related Art An ultrasonic wave is transmitted to an inside of a subject, the ultrasonic wave returned by being reflected by a tissue inside the subject is received to obtain a reception signal, and a tomographic image inside the subject is obtained based on the reception signal. An ultrasonic diagnostic apparatus that is used to diagnose diseases such as internal organs by displaying the information is used. In this ultrasonic diagnostic apparatus, a so-called reception focus method is used.

FIG. 8 is an explanatory diagram of this receiving focus method. N electroacoustic conversion elements (hereinafter simply referred to as “elements”) E ₁ arranged in a predetermined direction (left and right direction in FIG. 8),
_{E 2, ..., E i,} ..., when providing electrical signals to the E _n, each of these elements _{E 1, E 2, ...,} E i, ..., are converted into ultrasonic waves E _n, the ultrasonic wave to be It is sent to the inside of the sample.

Here, this ultrasonic wave is transmitted to a large number of elements E ₁ , E
Consider a case where the light is reflected at a point a on a vertical line extending from the center 0 of ₂ , ..., E _i , ..., E _n into the subject. The reflected wave from the point a is compared with the element E ₁ on the end side far from the point a and the element E _i on the center side close to the point a from the element E ₁ far away. Also reaches the nearby element E _i first. This arrival time difference is the time when the ultrasonic wave advances by the distance difference ΔL = L1-Li, where L1 and Li are the distances from the point a to the elements E ₁ and E _i , respectively. Here, assuming that the sound velocity in the subject is uniform,
When this speed of sound is C, this time difference is represented by ΔL / C. Thus, point a and each element E ₁ , E ₂ , ..., E _i ,
..., since there is the difference in distance to each distance each other between the E _n,
Converting each distance difference into each time, each element E ₁ , E ₂ , ..., E
_i, ..., phasing processing is performed to align the time of arrival of the received signals from each other by delaying by the amount corresponding to the reception signal obtained by the E _n each time difference. This gives a
It is possible to emphasize the received signal corresponding to the ultrasonic wave reflected at the point, that is, to focus the reception at the point a. The ultrasonic waves reflected deeper in the subject reach each element later, so that each element E ₁ , E ₂ , ..., E _i ,
, E _n , the delay amounts for the respective received signals are sequentially changed and added to each other, so that not only the point a but also points a on a perpendicular line extending from the center 0 to the inside of the subject from the center 0 are continuously added. It is also possible to perform so-called dynamic focus, in which the focal point is focused. This perpendicular line is called a scanning line, and by changing each delay amount for each received signal, this scanning line is converted into an electroacoustic conversion element E ₁ , E ₂ , ..., E.
_i, ..., it can be a direction to perform a so-called sector scan to deflect the so-called linear scanning and the scanning line is moved in parallel to the (left-right direction in FIG. 8) in a fan shape lined E _n, thereby two-dimensionally in the subject A tomographic image can be obtained. Further, it is also known that a three-dimensional stereoscopic image can be obtained by arranging the electroacoustic conversion elements also in the direction perpendicular to the paper surface of FIG. 8 and scanning in this arrangement direction.

However, it is known that there are fat layers, muscles, and various other tissues in the human body, and the sound velocity in the fat layers is different from that in other tissues. FIG. 9 is a diagram showing reception focus when the sound speeds are not uniform. As shown in FIG. 9, for example, when diagnosing the liver of the abdomen of a human body, the speed of sound is about 1470 m / n near the body surface.
A fat layer having a relatively slow sound speed of sec exists, a muscle layer having a sound speed of about 1540 m / sec exists below the fat layer, and a liver having a sound speed of about 1540 m / sec exists below the muscle layer. In addition, the fat layer may be deposited in muscle or liver.

As described above, if there are portions of different sound speeds in the subject, even if each delay signal is given a delay amount determined under the assumption that the sound speeds are uniform, each reception signal is received as shown in FIG. The arrival times of the signals are not uniform, and therefore, even if all of these received signals are added, the signal at the point a is not focused and the tomographic image is blurred. Here, the difference in arrival time of each received signal is referred to as "time difference". Moreover, the thickness of this fat layer varies from person to person,
It is not possible to uniformly correct each delay amount for each received signal.

As a method for solving this, a method using a cross-correlation calculation ([1] US Pat.
No. 4, [2] S. W. FLAX AND M. O'DO
NNEL, "Phase-Aberration Co
redirection Using Signals F
rom Point Reflectors andD
iffuse Scatterres: Basic P
rinciples ”IEEE TRANSACTI
ON ON ULTRASONICS, FERROE
L ECTRICS, AND FREQUENCY
CONTROL, VOL35, NO. 6, NOVE
MBER 1988, p758-p767) are known.

FIG. 10 is an explanatory diagram of a method of correcting a time shift using the cross correlation method. Here, first, assuming that the sound velocity in the subject is uniform, each delay amount is given to each reception signal, and a part of each reception signal after giving each delay amount is cut out as a correlation calculation region. The time lag is obtained as follows based on each received signal in the correlation calculation area. That is, of the cut-out received signals, the cross-correlation calculation is performed between two adjacent received signals,
The time shift Δτ between adjacent elements is obtained from the position where the obtained peak value of the cross-correlation function exists.

This time shift Δτ is calculated for all two received signals adjacent to each other, and each of the calculated time shifts Δτ is based on the arrival time of the received signal corresponding to the leftmost element in the figure, for example. Sequential integration is performed, whereby each time difference Δt of other received signals with respect to the reference received signal is increased.
Is calculated, and the respective delay amounts for the respective received signals are changed so that the respective time lags Δt are corrected, whereby the arrival times of the received signals of all the elements can be made uniform.

As a conventionally proposed method for detecting the time lag of each received signal, a method called a quadrature detection method is known in addition to the above-mentioned cross correlation method ([3] US Pat. No. 4,835,689). reference). In this quadrature detection method, the phase difference between the received signals is obtained instead of the narrowly-defined time difference between the received signals. However, the present invention does not depend on this time difference detection method, so here, “time difference” is used. Is interpreted in a broad sense to include “phase difference”.

[0011]

As described above, the wavefront disturbance of the ultrasonic wave due to the nonuniformity of the sound velocity in the subject is detected, and the time shift of the received signal between the elements is detected by using the cross correlation method or the quadrature detection method. However, one of the problems at that time is that the accuracy of time shift detection largely depends on the S / N of the received signal in the detection area.

When the transmission / reception focus is disturbed due to the non-uniformity of the sound velocity in the subject, the sound pressure of the received signal is lowered, so that S
/ N decreases, and an error occurs in the time shift detection. In particular, the received signal obtained by receiving the ultrasonic waves reflected deep inside the subject shows a significant decrease in S / N, and the time shift detection accuracy is very poor. For this reason, the time lag may be erroneously detected, and in that case, the correction effect may be small, or may be worsened due to erroneous correction.

In view of the above circumstances, the present invention improves the S / N ratio by increasing the sound pressure of the received signal, thereby improving the time deviation detection accuracy, and thus the highly accurate sound velocity non-uniformity correction function. An object of the present invention is to provide an ultrasonic diagnostic apparatus having the following.

[0014]

In the ultrasonic diagnostic apparatus of the present invention for achieving the above object, the transmitting means is arranged so that the ultrasonic waves transmitted into the subject are focused at a predetermined transmission focus point in the subject. By applying a voltage pulse of each predetermined timing generated by a plurality of electroacoustic transducers arranged in a predetermined direction, the ultrasonic waves transmitted in the subject and reflected in the subject with a plurality of electroacoustic transducers. A plurality of received signals are obtained by receiving, and a delay unit having a variable delay amount so that a plurality of received signals corresponding to ultrasonic waves reflected at substantially the same position in the subject at substantially the same time are output at substantially the same time. The present invention relates to an ultrasonic diagnostic apparatus that delays a plurality of received signals by using each other and adds them together to obtain an added signal, and displays a tomographic image of a subject based on the added signal. Further, there is provided a time shift correction means for obtaining a relative time shift between the received signals based on the received signals and controlling each delay amount of the received signal in the delay means so as to correct the obtained relative time shift. At the same time, (2) a first ultrasonic wave transmission / reception mode for obtaining a reception signal for displaying a tomographic image of the subject, and a reception for obtaining a relative time difference apart from the first ultrasonic wave transmission / reception mode A second ultrasonic wave reception mode for obtaining a signal is provided.

Here, as the second ultrasonic wave transmission / reception mode, (2_1) the number of voltage pulses applied to the electroacoustic transducer for ultrasonic wave transmission / reception once in the first ultrasonic wave transmission / reception mode A mode in which a larger number of voltage pulses are applied to the acoustic conversion element for one ultrasonic transmission / reception (2_2) than the voltage pulse applied to the electroacoustic conversion element in the first ultrasonic transmission / reception mode Mode in which a high-voltage voltage pulse is applied to the electroacoustic conversion element (2_3) The voltage pulse is applied to the electroacoustic conversion elements in a number larger than the number of electroacoustic conversion elements to which the voltage pulse in the first ultrasonic transmission / reception mode is applied. Any one of the applied modes or a combination of these modes is adopted.

[0016]

Conventionally, for example, a part of a reception signal obtained by transmitting and receiving ultrasonic waves for displaying a tomographic image (B-mode image) or the like is cut out and a cross-correlation calculation is performed to detect a time lag. A method has been proposed. However, since the received signal used for the time shift detection is for displaying a tomographic image, the number of elements used for one ultrasonic transmission / reception is limited, and transmission / reception ultrasonic waves are reduced to reduce the side lobes of the ultrasonic beam. A so-called apodizing method for weighting is adopted, which is suitable for displaying an image, but is not necessarily suitable for detecting a time shift.

The present invention has been completed in view of this point. That is, the ultrasonic diagnostic apparatus of the present invention is different from the first ultrasonic transmission / reception mode for displaying a tomographic image in the related art in that the second ultrasonic transmission / reception for detecting a time lag caused by inhomogeneity of sound velocity in the living body is used. A mode is provided, which increases the signal strength of the received signal cut out for time lag detection and improves the time lag detection accuracy. The improvement in detection accuracy leads to an improvement in the effect of correcting non-uniformity of sound velocity in the living body, and a high-resolution tomographic image with high resolution can be obtained.

[0018]

EXAMPLES Examples of the present invention will be described below. Figure 1
FIG. 1 is a block diagram showing the configuration of an embodiment of the ultrasonic diagnostic apparatus of the present invention. The ultrasonic diagnostic apparatus shown in FIG. 1 includes a plurality of electroacoustic transducers 1 as means for radiating ultrasonic waves into the subject and receiving reflected ultrasonic waves reflected in the subject, and electroacoustic transducers. It is obtained by applying a voltage pulse to the element 1 to radiate ultrasonic waves from the electroacoustic conversion element 1 into the subject and transmitting the ultrasonic waves reflected from the inside of the subject by the electroacoustic conversion element 1. A receiving unit 3 that delays each of the received signals thus obtained, thereby phasing the respective received signals, an adding unit 4 that adds the respective received signals after the phasing processing to each other, and the added signals are converted into luminance signals. A display unit 5 for displaying on a CRT or the like, a gate unit 6 for cutting out a received signal corresponding to a certain depth in the subject as a time shift detection region from the received signal phased by the receiving unit 3, and a gate unit 6 Time from the received signal cut out by A time deviation detecting section 7 for detecting a record, and a delay amount control unit 8 for correcting the respective delay amounts in the receiving unit 3 based on the time difference obtained by the detector 7 time lag. The delay amount control unit 8 also controls the transmission unit 2, and in the present embodiment, the voltage pulse of the timing corrected based on the obtained time difference is applied to the electroacoustic conversion element 1.

In this ultrasonic diagnostic apparatus, the transmitting unit 2 further includes a transmission system 21 for detecting a time shift and a transmission system 2 for displaying a tomographic image.
The transmission system selection unit 23 has a function of selectively selecting one of the transmission systems of the two systems. The tomographic image display transmission system 22 refers to a transmission system for displaying a B-mode image of a normal ultrasonic diagnostic apparatus, and is the function itself of a conventional ultrasonic diagnostic apparatus. In addition, the transmission method 21 for detecting the time difference is the gate unit 6
This is a transmission method in which the sound pressure of the reception signal cut out in step 1 is increased to improve the accuracy of time deviation detection of the time deviation detection unit 7.

The present invention is characterized by the transmitting unit 2, and concrete embodiments of the transmitting unit 2 will be described below.
2 is a block diagram showing a first embodiment of the transmission unit 2, FIG.
FIG. 3 is a schematic diagram showing an image of the first embodiment. The transmission unit 2 shown in the first embodiment of FIG. 2 is configured such that the transmission method 21 for detecting time shift includes pulse number control means 211 and pulse generation means 212.

When the transmission method selecting means 23 selects the time shift detection transmission method 21, the pulse generating means 21
2 generates the number of pulses determined by the pulse number control means 211. The pulse number determined by the pulse number control means 211 is larger than the pulse number in the transmission for tomographic image display. FIG. 3 shows a case where the number of transmission pulses for displaying a tomographic image is one and the number of transmission pulses for time shift detection is two. When the number of pulses is two, compared to one pulse, the sound pressure of the ultrasonic waves (hereinafter referred to as “transmit pulse”) emitted from the electroacoustic transducer 1 increases, but at the same time the pulse width of the transmit pulse is widened. It is known that the distance resolution becomes poor. Therefore, in the case of transmission for displaying a tomographic image, it is generally desirable to reduce the number of pulses. However, in time shift detection transmission, it is more important to improve the S / N than the distance resolution. Therefore, in this first embodiment, the number of pulses is set to be larger than that in the case of transmission for tomographic image display, which increases the transmission pulse sound pressure, and the S / S of the reception signal received by the electroacoustic conversion element 1 is increased. N is improved. As a result, the time shift detection error is reduced, and the correction effect is expected to be improved.

FIG. 4 is a block diagram showing a second embodiment of the transmitting section 2, and FIG. 5 is a schematic diagram showing an image of the second embodiment. The transmission unit 2 shown in the second embodiment of FIG. 4 is configured such that the time shift detection transmission method 21 includes pulse voltage control means 213 and pulse generation means 212. Transmission method 21 for detecting time shift by the transmission method selection means 23
When is selected, the pulse generation means 212 generates a pulse of the voltage determined by the pulse voltage control means 213. The pulse voltage determined by the pulse voltage control means 213 is determined to be higher than the pulse voltage in the transmission for tomographic image display. However, the high voltage mentioned here must be a pulse voltage at which ultrasonic waves emitted from the electroacoustic conversion element 1 do not pose a risk to the living body.

In FIG. 5, the pulse voltage for the time shift detection transmission is shown as a higher voltage than the pulse voltage for the tomographic image display transmission. When the pulse voltage is increased, the sound pressure of the transmission pulse is increased, so that the S / N of the reception signal received by the electroacoustic conversion element 1 is improved, and as a result, the time lag detection error is reduced and the correction effect is improved. Improvement is expected. Figure 6
FIG. 7 is a block diagram showing a third embodiment of the transmission unit 2, and FIG. 7 is a schematic diagram showing an image of the third embodiment.

The transmitting section 2 shown in the third embodiment of FIG. 6 is constructed by a transmission system 21 for detecting time shift, which comprises a transmission aperture control means 214 and a pulse generation means 212. Transmission method 21 for detecting time shift by the transmission method selection means 23
When is selected, the pulse generation means 212 generates pulses for the transmission aperture determined by the transmission aperture control means 214. The transmission aperture determined by the transmission aperture control unit 214 is wider than the transmission aperture in the tomographic image display transmission.

FIG. 7 shows a case where the transmission aperture for time shift detection transmission is twice the transmission aperture for tomographic image display transmission. As shown in FIG. 7, when the transmission aperture is narrowed, the formed transmission beam width is not so narrowed at the transmission focus point, but the spread is small at points other than the transmission focus point. On the other hand, when the transmission aperture is widened,
The formed transmission beam width is narrowed down at the transmission focus point, but is extremely widened at other points than the transmission focus point. For these reasons, the transmission aperture is limited in the transmission for displaying a tomographic image, and the transmission aperture is controlled so that the transmission beam width is as constant as possible at any depth in the subject. However, the reception signal cut out by the gate unit 6 may be only in a part of the inside of the subject, for example, in the vicinity of the transmission focus point. Therefore, by widening the transmission aperture, the beam width at the transmission focus point is narrowed, and the reception signal cut out by the gate unit 6 is received. It is possible to improve the S / N of the signal. As a result, the time shift detection error is reduced, and the correction effect is expected to be improved.

In the first to third embodiments described above,
As shown in FIGS. 3, 5, and 7, the transmission apodization method of weighting the voltage of the pulse applied to the electroacoustic conversion element 1 is also adopted in the case of the transmission for time shift detection. In the case of the business transmission, the transmission apodization may not be performed. If the transmission apodization is not applied, the sound pressure of the transmission pulse will increase.

In the present invention, not only the respective aspects of the first to third embodiments described above are individually adopted, but two or three of them may be combined. Needless to say. Also, the transmission method selection means 23
Switching between the time deviation detection transmission and the tomographic image display transmission of
It may be manual or automatic.

In the case of manual operation, for example, a transmission switch for detecting a time lag is provided on the probe or the casing panel of the ultrasonic diagnostic apparatus, and when the switch is on, the transmission for time lag detection is performed, and when the switch is off, a tomographic image is displayed. It can be configured to send. In the case of automatic transmission, it is necessary to properly set the combination of the number of transmissions for time shift detection transmission and tomographic image display transmission. If a large amount of time shift detection transmission is performed, the frame rate (the number of images that can be displayed in a unit time) drops.
Therefore, as a method of preventing the frame rate from decreasing as much as possible, for example, “10 frames for transmission for tomographic image display (1
A measure such as "per 1 frame (1 screen) for time shift detection per 0 screen)" is required. Here, it is preferable that the combination of the number of transmissions can be manually set, for example, from a housing panel of the ultrasonic diagnostic apparatus.

[0029]

As described above, the ultrasonic transmission / reception device of the present invention uses (1) pulse number control, (2) pulse voltage control, and (3) transmission aperture control, in addition to tomographic image display transmission. Since the time shift detection transmission is incorporated, the sound pressure of the transmission pulse is increased, and as a result, the S / N of the received signal is improved and the time shift detection accuracy is improved. The improvement in the detection accuracy leads to an improvement in the effect of correcting the sound velocity non-uniformity in the living body, and it is possible to obtain a high-resolution and high-quality tomographic image.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an ultrasonic diagnostic apparatus of the present invention.

FIG. 2 is a block diagram showing a first embodiment of a transmission unit.

FIG. 3 is a schematic diagram showing an image of the first embodiment.

FIG. 4 is a block diagram showing a second embodiment of a transmission unit.

FIG. 5 is a schematic diagram showing an image of a second embodiment.

FIG. 6 is a block diagram showing a third embodiment of the transmission unit.

FIG. 7 is a schematic diagram showing an image of a third embodiment.

FIG. 8 is an explanatory diagram of a method of receiving focus.

FIG. 9 is a diagram showing reception focus when the sound velocity is not uniform.

FIG. 10 is an explanatory diagram of a method of correcting a time shift using a cross correlation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 electroacoustic conversion element 2 transmitter 3 receiver 4 adder 5 display 6 gate 7 time lag detector 8 delay amount controller 21 time lag detection transmission method 22 image display transmission method 211 pulse number control means 212 pulses Generation means 213 Pulse voltage control means 214 Transmission aperture control means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Saito 3-10-22 Shimochiai, Shinjuku-ku, Tokyo

Claims (4)

[Claims] 1. An ultrasonic wave transmitted into a subject is arranged in a predetermined direction with voltage pulses at predetermined timings generated by a transmitting means so that an ultrasonic wave is focused at a predetermined transmission focus point in the subject. It is applied to multiple electroacoustic transducers,
A plurality of received signals are obtained by receiving the ultrasonic waves transmitted in the subject and reflected in the subject by the plurality of electroacoustic conversion elements, and reflected at substantially the same positions in the subject at substantially the same time. A plurality of the received signals corresponding to the ultrasonic waves are output to obtain the addition signal by delaying each of the plurality of reception signals by using delay means of variable delay amount so as to be output substantially simultaneously with each other and by adding each other, In an ultrasonic diagnostic apparatus that displays a tomographic image of the subject based on the added signal, a relative time difference between the received signals is obtained based on the received signal, and the obtained relative time difference is corrected. To obtain the received signal for displaying a tomographic image of the subject while providing a time shift correction means for controlling each delay amount of the received signal in the delay means. In addition to the ultrasonic transmission / reception mode and the first ultrasonic transmission / reception mode, a second ultrasonic transmission / reception mode for obtaining the reception signal for obtaining the relative time difference is provided. Sound wave diagnostic equipment. 2. The number of the second ultrasonic transmission / reception modes is greater than the number of voltage pulses applied to the electroacoustic transducer for one ultrasonic transmission / reception in the first ultrasonic transmission / reception mode. The ultrasonic diagnostic apparatus according to claim 1, wherein the voltage pulse is applied to the electroacoustic conversion element for one ultrasonic wave transmission / reception. 3. The second ultrasonic transmission / reception mode applies to the electroacoustic conversion element a voltage pulse having a higher voltage than a voltage pulse applied to the electroacoustic conversion element in the first ultrasonic transmission / reception mode. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is in a mode to perform. 4. The second ultrasonic transmission / reception mode has voltage pulses applied to a larger number of the electroacoustic conversion elements than the number of the electroacoustic conversion elements to which the voltage pulse in the first ultrasonic transmission / reception mode is applied. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is in a mode for applying.