JPS62121355A - Ultrasonic image pickup device - Google Patents

Abstract

PURPOSE:To add and average the beam patterns of a reflected image and to eliminate the influence of noise by changing the frequency of the signal for driving oscillators for ultrasonic wave transmission in an oscillator array and obtaining the reflected ultrasonic image corresponding thereto. CONSTITUTION:A pulse generator 22, an oscillator selector 24 and an adder, etc. are provided. The generator 22 varies the circuit constant thereof automatically and generates the pulse signals of various frequencies. For example, the circuit 22 is constituted of a resonance circuit 22a consisting of R, L, C, a trigger circuit 22b, a circuit constant selector 22c, a high voltage supply circuit 22d, and a thyristor 22e. Several signals of different frequencies are generated by LC to determine the central frequency and RC to determine a time constant. More specifically, C is charged by the circuit 22 and the thyristor 22e is turned on by the circuit 22b to discharge the C so that the frequency corresponding to the circuit 22a is generated. Such frequency is selected 22c to generate the signals of different frequencies. The signals from the selector 24 are processed by an adder, etc., by which the reflected image corresponding thereto is obtd. and is averaged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic imaging device that irradiates an object with ultrasonic waves and obtains a reflected image thereof.

(Prior Art) Conventionally, as this type of a-sound imaging device, there is an aperture synthesis type ultrasonic diagnostic device as shown in FIG.

This uses a transducer array l consisting of a large number of transducers (for example, 64) as a means for transmitting ultrasonic waves to an object X such as a human body and receiving reflected ultrasonic waves from the object X. We are prepared. The oscillators in this oscillator array l are
A pulse signal of a predetermined frequency generated by a pulse generator (pulser) 2 is applied via an amplifier 3 and a transducer switcher 4 to vibrate and generate ultrasonic waves, while generating voltage when receiving ultrasonic waves. It is composed of piezoelectric elements. Further, the transducer switching device 4 sequentially switches the transducers in the transducer array l to transmission or reception.

When this device is in operation, ultrasonic waves are emitted from the transducers in the transducer array 1 toward the object The data is temporarily stored in line memory 7 from switch 4 via amplifier 5 and analog/digital (A/D) converter 6, and then stored in frame memory 8 corresponding to each vibrator. The image of the object X is obtained by sequentially switching and scanning the transducers in the transducer array 1, storing the data of all lines in the frame memory 8, and then performing image reproduction processing in the arithmetic unit 9.
It is observed by displaying one screen on the display 11 via the digital scan converter 10.

(Problems to be Solved by the Invention) However, in such conventional ultrasonic imaging devices, ultrasonic waves are emitted toward the target object from the transducer with a small opening area in the transducer array. Therefore, the irradiation energy decreases, especially in the living body, and the energy of the received ultrasonic waves also decreases. Therefore, the received signal is easily affected by noise, and side lobes are generated particularly in the vicinity of the transmission frequency, so there is a problem that the S/N ratio of the reproduced image is low.

(Means for Solving the Problems) The present invention has been made in view of such conventional problems, and includes a transducer array comprising a plurality of ultrasonic transmitting/receiving transducers arranged, and A switching means for transmitting and receiving ultrasonic waves by sequentially switching the transducers in the transducer array, and an image +If for obtaining a reflected image of the object by aperture synthesis processing from the ultrasonic waves received by the transducers in the transducer array. Raw processing - In an ultrasonic imaging device equipped with an L stage, by changing the frequency of the signal that drives the ultrasonic transmitting transducer in the transducer array, and obtaining and averaging the corresponding ultrasonic reflection images. , the effects of noise such as side lobes are removed, and a high S/N ratio can be obtained in the reproduced image.

(Embodiments) Hereinafter, embodiments of the present invention shown in the accompanying drawings will be described.

FIG. 1(a) is a diagram showing the configuration of an ultrasonic diagnostic apparatus according to the present invention, and 21 is a transducer array or a probe, and the transducers in this transducer array are generated by a pulse generator 22. When a variable frequency pulse signal is applied via an amplifier 23 and a transducer switch 24, the piezoelectric element vibrates to generate Mi sound waves, and generates a voltage when receiving eight hill waves.

Further, the transducer switching device 24 has a function of sequentially switching the transducers in the transducer array 21 into transmitting elements or receiving elements according to an imaging procedure described later. The receiving section of the transducer switch 24 outputs a display via a plurality of amplifiers 25 and delay circuits 26, an adder 27 that adds the outputs thereof, an A/D converter 28, and a digital scan converter 29. Connected to r630.

Next, the imaging procedure of this device will be explained.

According to the present invention, when capturing an image, several ultrasound signals having different frequencies are irradiated onto the target object, and an image corresponding to the ultrasound signals is obtained. Therefore, the pulse generator 22 is configured to automatically vary its circuit constant (for example, time constant) to generate pulse signals of various frequencies. For example, as shown in FIG. 1(b), this includes a resonance circuit 22a made up of R, L, and C, a trigger circuit 22b, and a circuit constant switch 2.
2c, a high voltage supply circuit 22d, and a thyristor 22e, and generates several signals with different frequencies using LC that determines the center frequency and RC that determines the time constant. That is, C is charged by the high voltage supply circuit 22d, and C is released by turning on the thyristor 22e by the trigger circuit 22b, thereby generating a frequency corresponding to the resonance circuit 22a. By switching this using the circuit constant switch 22c, signals with different frequencies can be generated.

Transducer array? Each of the transducers (2) is sequentially switched to a transmitting element by the transducer/J switch 24, and is driven by the pulse wave signal output from the pulse generator 22 to generate an ultrasonic wave according to the frequency.

Further, each transducer receives reflected ultrasound from the object X by being switched to a receiving element by the switch 24, and sends the received signal to a subsequent arithmetic processing unit via the switch 24.

Such switching to a transmitting element or a receiving element by the transducer switch 24 may be performed by switching and scanning for each transducer as in the conventional example shown in FIG. Since the synthesis process is performed from data for each child, the amount of calculation is large, resulting in problems such as a decrease in calculation speed and a complicated calculation processing unit. Therefore, in the embodiment shown in FIG. 1, as shown in the second factor, the transmitting element group 31 is composed of a relatively small number (for example, 5) of adjacent oscillators in the oscillator array 21, and from these oscillators, the target While emitting focused ultrasound toward an object, another discretely located transducer constitutes a receiving element group 32 having a larger aperture area than the transmitting element group 31 to receive reflected ultrasound from the object, The circuit is configured such that the received signals are processed from the transducer switch 24 through a plurality of amplifiers 25 and a delay circuit 26 and an adder 27.

Hereinafter, it will be explained that an image of the object X can be obtained by transmitting and receiving ultrasonic waves according to the embodiment shown in FIG. 1(a).

First, as shown in FIG. 3, consider a coordinate system in which the origin is the center of the transmitting element group 31 formed in the transducer array 21, and the transmitting and receiving surface of the array is the (x, y) plane. The width of the transducer is I, and the transducer spacing of the transmitting element group 31 is I.
T, the transducer spacing of the receiving element group 32 is liF, the aperture lengths of the transmitting element group 31 are XT and YT, and the aperture lengths of the receiving element group 32 are XF and Yk. In this example, 1
r=l.

XT <XF! , YT=Y* and 6° Now, if the position of one transducer in the transmitting element group is 1'T = (XT, Vr, 0), the time domain and frequency domain of the transmitted ultrasound are as follows, respectively. It is determined as follows.

5v (rr, t) S7 (1'7, ω) Here, ω1. ω2 are the minimum and maximum angular frequencies included in the transmitted ultrasound, respectively, and ω1 = ω2 may be T.
o is the time width.

Next, the reflection coefficient of an object located at a distance r = (x, y, z) from the origin is assumed to be frequency-independent for the sake of simplicity, and is assumed to be P (r), and 1 of the receiving element group is
If the position of the transducer is t'l = (X1e, 'ltz * 0), the received reflected ultrasound is expressed as follows.

SR(rI!, rv, t) = fP (1')ST(r7.t-tc)dr
(3) S(< (rp, r7, (,))
= f P (r)ST (r7, ω)e
xp(-jωtc)dr (C is the speed of the ultrasonic wave) indicates the delay time.

Equations (3) and (4) above are for the case where ultrasonic waves are received by one transmitting element, so considering the entire transmitting element group, s*(rr, t'T, t) drdr7 (5) SR (t'12, t'7, (11) eexp(
−jωt() dr dr7 (6) However.

A, = XT・YT (Aperture surface a of transmitting element group) is written (
By dividing equation (6) by equation (2), the hologram H (rr, r7, ω) of the object Propagation time information h (r2.

r7. t) is obtained. That is, Because it is, A Cr1P, r71 L) dωdrdr7 (8) Here, W=ω2−ω1 is the bandwidth.

This ultrasonic propagation time information h (t”*, rT* t)
By performing the following aperture synthesis processing on each vibrator of the receiving element group 32 based on , a three-dimensional reflectance distribution, that is, a three-dimensional reconstructed image of the object X can be obtained. That is, where rr = (XI, YI, ZI)A2 =X
* -YP (Aperture area of receiving element group) This equation (8) can be realized by performing d delay processing by the delay circuit 26 and synthesis processing by the adder 27 of the device shown in FIG.
Obtain an ultrasound reflection image of the line.

As shown in FIG. 2, by sequentially scanning the positions of both the transmitting element group 31 made up of adjacent transducers and the receiving element group 32 made up of discretely located transducers, You can get sound wave images.

Hereinafter, the reconstructed image will be analyzed based on equation (9).

First, by substituting equation (8) into equation (9), we get P (
r) exp(j Φ) dωdrdr7 dr2 However, Φ=ω(tl tc) = (Irx rt I+Ir* −rx Il
r-rt l I? ”[-rll) (11) Here, if Z-work #Z=α, then Vr 'S' Vr) (12) α is obtained by Fresnel approximation.

Therefore, by substituting equation (12) into equation (10) and calculating the equity for ω, the following equation is obtained.

1 (t”x) = f P (r) exp(jΦ
1) φ−f exp (jΦ2 1 drvT r
T φ−1exp (jΦ3)dr* ARr F! *5inc (-(zI-z)) dr (13 days, 5lnc (-(Z I Z) ) above (13
) Calculating the integral term by rT in the equation results in the following.

Here, if we set, equation (14) is = 1sinc Cflu u) yu[5ine (XT u> *m (,2TM) ]
m 5 Inc (Y7 v) (17). However, (δ is the delta function), and the tree is a convolution (
convolution).

Therefore, when the variable U is taken on the horizontal axis in equation (17), the beam pattern of the transmitting element group is as shown in FIG. 4(a).

Similarly, when calculating the integral term by ry in equation (13), we get
It will look like this:

= 5ine (text U) * [5inc (XRu) zero m (JL*u)] skewer 5i
ne (Y2 v ) (19
) Therefore, when the variable U is plotted on the horizontal axis in equation (19), the beam pattern of the receiving element group is as shown in FIG. 4(b).

By substituting the above (+7) and equation (19) into equation (13), the reconstructed image is 1 (rx) = f P (r) expNΦ1)
・(See5inc (文 u))2 ・[5inc (XT u)*m (Jar u)
]-[5inc (XRu) *m C1tz u)]
esinc(Y2O) ・5inc(Y2 υ) Therefore, if the variable U is plotted on the horizontal axis, Figure 4 (C)
A beam pattern as shown in is obtained.

As can be seen from FIGS. 4(a) and 4(b), the beam patterns of the transmitting element group 31 and the receiving element group 32 are determined by the shape of the transducer array 21, that is, the transducer width (cross), the transducer spacing (falling , exchange k), aperture width (X, , grating lobes are generated. Therefore, it is necessary to select the transmitting element group 31 so as to minimize this influence, and to do so, it is necessary to select the transmitting element group 31 so that the zero crossing of the transmitting beam pattern is superimposed on the grating lobe peak value of the receiving beam pattern. /
All you need to do is design the shape of the transducer array and select the element group so that XT = 1 / l *. By doing this, a beam pattern with grating lobes removed as shown in Figure 4(e) can be obtained. .

Although the embodiment shown in FIG. 1 has been described above, the present invention is not limited thereto. For example, the analog circuits of the delay circuit 26 and adder 27 in the embodiment of FIG.
It is also possible to replace it with a D converter and a digital arithmetic circuit, and perform delay synthesis processing with this digital arithmetic circuit.
This makes it possible to improve the precision of arithmetic processing. Further, the present invention is not limited to diagnostic devices, but can be widely applied to imaging devices such as underwater sonar.

(Effects of the Invention) As described above, according to the present invention, there is provided a transducer array formed by arranging a plurality of ultrasonic transmitting/receiving transducers, and a transducer array that sequentially switches the transducers in the transducer array to transmit ultrasonic waves. In an ultrasonic imaging apparatus equipped with a switching means for transmitting and receiving, and a synthesis processing means for obtaining a reflected image of an object through synthesis processing from ultrasonic waves received by the transducers in the transducer array, By changing the frequency of the signal that drives the sound wave transmitting transducer and obtaining ultrasound reflection images accordingly, we can eliminate the effects of noise such as side lobes by averaging the beam patterns of the reflection images. Remove and reproduce enough S.
/N ratio can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram of transducer scanning, Fig. 3 is a diagram showing the transducer array and the coordinate system of the object, and Fig. 4 is an ultrasonic wave. A diagram showing a beam pattern, FIG. 5, is a diagram showing a conventional example. 1----1 transducer array, 2-111 pulse generator, 3-111 amplifier, 4-111 transducer switching device, 5-111 amplifier, 6----A/D Converter, 7---line memory, 8-111 frame memory, 9-111 arithmetic unit, 10---to digital scan controller, 11--
- one display, 21-- one transducer array, 22-- pulse generator, 23-- one amplifier, 24-- one transducer switch, 25-- one amplifier, 26-- --Delay circuit, 27---Adder, 28---A/D converter. 29 ---- Digital scan converter. 30---One display, 31---One transmitting element group, 32---Receiver: , one H-f group. Previous applicant: Designated agent of the Director of the Institute of Industrial Science and Technology Sub-agent of Kohei Sato, Director of the Institute of Industrial Science and Technology Patent attorney Susumu Special applicant: Tokyo S1ki Co., Ltd. Agent
Br Physician Y
Figure 2 of just sucking balls

Claims (1)

[Claims] A transducer array comprising a plurality of ultrasonic transducer transducers arranged, a switching means for sequentially switching the transducers in the transducer array to transmit and receive ultrasonic waves, and a transducer in the transducer array. In an ultrasonic imaging device comprising an image reproduction processing means for obtaining a reflected image of a target object from received ultrasonic waves by aperture synthesis processing, the frequency of a signal for driving an ultrasonic transmission transducer in the transducer array is changed. 1. An ultrasonic imaging device characterized in that a reflected image is obtained and averaged accordingly.