JPH0554785B2 - - Google Patents

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 ultrasonic imaging apparatus, there is an aperture synthesis type ultrasonic diagnostic apparatus as shown in FIG.
This uses a transducer array 1 consisting of a large number (for example, 64) of transducers arranged 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 transducers in this transducer array 1 vibrate and generate ultrasonic waves when a pulse signal of a predetermined frequency generated by a pulse generator (pulsar) 2 is applied via an amplifier 3 and a transducer switcher 4. On the other hand, it is composed of a piezoelectric element that generates a voltage when it receives ultrasonic waves. Further, the transducer switching device 4 sequentially switches the transducers in the transducer array 1 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 After being temporarily stored in a line memory 7 through an amplifier 5 and an analog/digital (A/D) converter 6,
It is stored in the 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 and converting the data to the digital scan converter 10.
The images can be observed by displaying one screen on the display 11 via.

(Problems to be Solved by the Invention) However, in such conventional ultrasonic imaging devices, ultrasonic waves are spread and irradiated toward the target object from the transducer with a small opening area in the transducer array. Therefore, especially in the living body, the irradiation energy decreases and the energy of the received ultrasound also decreases, making it impossible to obtain a sufficient S/N ratio in the reconstructed image.
Since the aperture synthesis calculation is performed from data stored in the frame memory corresponding to each transducer, the amount of calculation is large.
There was a problem in that it was difficult to improve the calculation speed or simplify the calculation process.

(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 reproduction processing means for obtaining a reflected image of the object by aperture synthesis processing from the ultrasonic waves received by the transducers in the transducer array. In an ultrasonic imaging device equipped with a transducer array, a small number of adjacent transducers in the transducer array constitute a transmitting element group, and other discretely located transducers constitute a receiving element group. By increasing the number of receiving element groups and expanding the receiving aperture area as the distance to the object increases, it is possible to supplement the energy of the received ultrasonic waves at any distance and obtain a sufficient S/N ratio. This allows a uniform image of the object to be obtained.

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

FIG. 1 is a diagram showing the configuration of an ultrasonic diagnostic apparatus according to the present invention. Reference numeral 21 represents a transducer array or a probe, and the transducers in this transducer array have a predetermined frequency generated by a pulse generator 22. It is composed of a piezoelectric element that vibrates and generates ultrasonic waves when a pulse signal is applied thereto via the amplifier 23 and the transducer switch 24, and generates a voltage when receiving the ultrasonic waves.

The transducer switching device 24 has a function of sequentially switching the transducers in the transducer array 21 to a transmitting element group or a receiving element group according to the imaging procedure described later, and in particular, to change the receiving aperture area according to the imaging distance. , is provided with a distance setting device 24a that automatically or manually inputs distance data from the transducer array 21 to the object X to the switching device 24.

The receiving section of the transducer switcher 24 transmits the 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. is connected to the device 30.

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

According to the present invention, as shown in FIGS. 1 and 2, a transmitting element group 31 is configured by a small number (in this case, five) of adjacent vibrators among the vibrators constituting the vibrator array 21, From those oscillators to the object
At the same time, other discretely located transducers constitute a receiving element group 32 having a larger aperture area than the transmitting element group 31, and receive the ultrasonic wave reflected by the object X. do. As shown in FIG. 3, the receiving aperture by the receiving element group 32 is
The imaging distance sent from the distance setter 24a, that is, the distance from the object X to the transducer array 21, increases as the distance increases, and the signals from these receiving elements form one line of video. In this way,
As the distance increases, the level of the received ultrasonic waves decreases, but by increasing the number of receiving elements, the decrease in level can be compensated for, and images with uniform power and resolution can be obtained at any distance.

Hereinafter, it will be explained that an image of the object X can be obtained by transmitting and receiving ultrasonic waves by the above-described transmitting and receiving element group.

First, as shown in FIG. 4, consider a coordinate system in which the center of the transmitting element group 31 of the transducer array 21 is the origin and the transmitting and receiving surface of the transducer is the (x, y) plane. In the figure, the width of the transducer is l, the transducer spacing of the transmitting element group is l _T , the transducer spacing of the receiving element group is l _R , the aperture length of the transmitting element group is X _T and Y _T , the transducer spacing of the receiving element group is Letting the aperture lengths be X _R and Y _R , in this example, l _T =l, X _T <X _R , and Y _T = Y _R.

Now, if the position of one transducer in the transmitting element group is r _T = (x _T , y _T , 0), the time domain and frequency domain expressions of the complex signal of the transmitted ultrasound are as follows, respectively. determined.

S _T (r _T , t)=∫〓 ² 〓 ₁ S _T (r _T , ω)exp(jωt)dω(1
) S _T (r _T , ω) = 1/T _C ∫ ^T ₀ S _T (r _T , t) exp (−jωt) dt(2) Here, ω ₁ and ω ₂ are the transmitted ultrasound waves, respectively. At the minimum and maximum angular frequencies involved, ω ₁ =ω ₂ may be true. T _C 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 ρ(r), and the position of one oscillator in the receiving element group is If r _R = (x _R , y _R , 0), the received reflected ultrasound is expressed as follows.

S _R (r _R , r _T , t) = ∫ rρ(r)S _T (r _T , t−t _C ) dr (3) S _R (r _R , r _T , ω) = ∫ rρ(r)S _T (r _T , ω) exp (−jωt _C ) dr (4) However, t _C = |r−r _T |+|r _R −r|/C (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 _R (r _R , t) = 1/A _T ∫ r _T ∫ rρ(r)S _T (r _T , t−t _C ) drdr _T (5) S _R (r _R , ω) = 1/A _T ∫ r _T ∫ rρ(r)S _T (r _T , ω)・exp(−jωt _C ) drdr _T (6) However, A _T =X _T・Y _T (Aperture area of transmitting element group) If the above equation (6) is divided by equation (2), the hologram H of the object (r _R , r _T , ω) is obtained, and by performing inverse Fourier transform on this, the ultrasonic propagation time information h (r _R , r _T , t) between the object X and the transducer array 21 is obtained. It will be done. That is, H(r _R , r _T , ω)=S _R (r _R , ω)/S _T (r _T ,
ω)=1/A _T ∫ r _T ∫ rρ(r)exp(−jωt _C ) drdr _T (7) Therefore, h(r _R , r _T , t)=1/W∫〓 ² 〓 ₁ H (r _R
, r _T , ω)exp(jωt)dω = 1/WA _T ∫ r _T ∫ r∫〓 ² 〓 ₁ ρ(r)exp{jω(t−t _C )}dωdrdr _T (8) Here, W= ω ₂ −ω ₁ is the bandwidth.

Based on this ultrasonic propagation time information h (r _R , r _T , t), the three-dimensional reflectance of the object A three-dimensional image at the distribution, ie, the position r of the reproduction point, is obtained. That is, I (r _I ) = 1/A _R ∫ r _R h (r _R , r _T , t _I ) dr _R (9) where, r _I = (x _I , y _I , z _I ) t _I = | r _I −r _T |+|r _R −r _I |/C A _R =X _R・Y _R (Aperture area of receiving element group) This equation (9) is expressed by the delay circuit 2 of the device shown in FIG.
This can be realized by performing delay processing by 6 and compositing processing by adder 27 to obtain a 1-line ultrasonic reflection image.

As shown in FIG. 2, by sequentially scanning the positions of both the transmitting element group 31 consisting of adjacent transducers and the receiving element group 32 consisting of discretely located transducers, one frame of ultrasonic waves is generated. You can get the picture.

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

First, by substituting equation (8) into equation (9), I(r _I )=1/A _R A _T W ∫ r _R ∫ r _T ∫ r∫〓 ² 〓 ₁ ρ(r)exp｛jΦ｝dωdrdr _T dr _R (10) However, Φ=ω(t _I −t _C )=ω/C(｜r _I −r _T ｜+｜r _R −r _I ｜
−|r−r _T |−|r _R −r|) (11) Here, if we set z _I ≒z=α, then Φ≒ω/C{2(z _I −z) + (x _I2 ^{− x2} )
/α+(y _I ² −y ² )/α−(x _I −x)/αx _T −(y _I −y
) / αy _T − (x _I − x) / αx _R − (y _I − y) / αy _R
}(12).

Therefore, by substituting equation (10) into equation (12), I(r _I )=1/A _R A _T W ∫ r _R ∫ ∫ r _T ∫ _r ∫〓 ² 〓 ₁ ρ(r)exp[jω /C{2(Z _I −Z)+(x
_I ² −x ² /a)+(y _I ² −y ² /a) −(x _I −x/ax _T +(y _I −y/ay _T )−(x _I −
x / ax _R ) + (y _I - y / ay _R )}] dωdrdr _T dr _R However, W = ω ₂ - ω ₁ Newly, B = 1/C {2 (z _I - z) + (x _I ² −x ² /a+y _I ² −y ² )
/a) −(x _I −x/ax _T + (y _I − y) ay _T ) −(x _I − x/ax _R + (y _I − y) ay _R )}, then I(r _I )=1/A _R A _T ∫ r _R r _Tr ρ(r)・1/W∫〓 ² 〓 ₁ exp(jωB)dωdrdr _T dr _R.

Here, 1/W∫〓 ² 〓 ₁ exp(jωB)dω = 1/jBW[exp(jωB)]〓 ² 〓 ₁ = 1/jBW{exp(jBω ₂ )−exp(jBω ₁ )} = 1/ jBW{cos(Bω ₂ )−jsin(Bω ₂ ) −cos(Bω ₁ )−jsin(Bω ₁ )} = 1/jBW{−2sinB/2(ω ₂ +ω ₁ ) sinB/2(ω ₂ −ω ₁ ) +2jcosB/2(ω ₂ +ω ₁ ) sinB/2(ω ₂ −ω ₁ )} = 1/jBW[2sinB/2(ω ₂ −ω ₁ ) × {−sinB/2(ω ₂ +ω ₁ )+jcosB/ 2(ω ₂ +ω
₁ )}] = sinB/2(ω ₂ −ω ₁ )/B/2W{cosB/2(ω
₂ +ω ₁ ) +jsinB/2(ω ₂ +ω ₁ )} = sinB/2W/B/2Wexp{jB/2(ω ₂ +ω ₁ )
} = sinc(B/2W)exp(jBWm) However, since W=ω ₂ −ω ₁ Wm=ω ₂ +ω ₁ /2, I(r _I )=1/A _R A _T ∫ r _R ∫ r _R ∫ r _T ∫ _r ρ(r)sinc [W/C(z _I −z)+W/2C(x _I ² −x ²
/a+y _I ² −y ² /a) −W/2C(x _I −x/ax _T +y _I −y/ay _T )−W/
2C(x _I −x/ax _R +y _I −y/ay _R )] ×exp[jWm/C{2(z _I −z)+x _I ² −x ² /a+
y _I ² −y ² /a}−jWm/C(x _I −x/ax _T +y _I −y/ay
_T ) −jWm/C(x _I −x/ax _R +y _I −y/ay _R )] dr
dr _T dr _RThen , change the integration order and sinc[W/C(z _I −z)+W/2C(x _I ² −x ² /a+y _I ² −
y ² /a) −W/2C(x _I −x/ax _T +y _I −y/ay _T ) −W/2C(x _I −x/ax _R +y _I −y/ay _R )] ≒sinc[W /C(z _I −z)], I(r _I )≒∫ _r ρ(r)×exp[jWm/C{2(z _I −z)+
(x _I ² −x ² /a+y _I ² −y ² /a)] ×1/A _T ∫ ×1/A _T ∫ r _T exp[−jWm/C(x _I −x/ax _T +y _I −y /ay _T )]d
r _T ×1/A _R ∫ ×1/A _R ∫ r _R exp[−jWm/C(x _I −x/ax _R +y _I −y/ay _R )]d
r _R × sinc [W/C (z _I - z)] dr , and formula (13) is obtained.

I (r _I ) = ∫ rρ(r)exp{jΦ ₁ } ・1/A _R ∫ r _T exp{jΦ ₂ }dr _T・1/A _R ∫ r _R exp{jΦ ₃ }dr _R・sinc {W /C(z _I −z)}dr (13) Here, Φ ₁ = Wm/C{2(z _I −z) + (x _I ² − x ² )/α + (y _I ² − ^{y 2} ) /α} Φ ₂ = Wm/C{−x _I −x/αx _T −y _I −y)/αy _T } Φ ₃ = Wm/C{−x _I −x/αx _R −y _I −y)/ αy _R } Wm=ω ₁ +ω ₂ /2 sinc{W/C(z _I −z)} = sin{W/C・(z _I −z)}/W/C・(z _I −z) Above ( Calculating the integral term by r _T in equation 13) gives the following:

1/A ∫ r _T exp{jΦ ₂ }dr _T = lsinc{Wml/2Cα(x _I −x)} ・[sinc{WmX _T /2Cα(x _I −x)} *m(Wml _T /2Cα(x _I −x))] ・sinc{WmY _T /2Cα(y _I −y)} (14) Here, Wm/2Cα(x _I −x)=u (15) Wm/2Cα(y _I −y)= v (16), equation (14) becomes 1/A ∫ ∫ r _T exp{jΦ ₂ }dr _T = lsinc (lu)・[sinc (X _T u) * m
(l _T u)]・sinc(Y _T v) (17). However, m(l _T u)= _+∞ 〓 ^n=-∞ δ(n−l _T u)=l _T+∞ 〓 ^n=-∞ δ(n/l _T − u) (18) (δ is the delta function ), and * indicates convolution.

Therefore, when the variable u is plotted on the horizontal axis in equation (17), the beam pattern of the transmitting element group becomes as shown in FIG. 5a.

Similarly, when calculating the integral term due to r _R in equation (13), we get
It will look like this:

1/A ∫ r _R exp{jΦ ₃ }dr _R = lsinc{Wml/2Cα(x _I −x)} ・[sinc{WmX _R /2Cα(x _I −x)} *m(Wml _R /2Cα(x _I −x))] ・sinc{WmY _R /2Cα(y _I −y)} = lsinc(lu) ・[sinc(X _R u)*m(l _R u)] ・sinc(Y _R 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. 5b.

By substituting equations (17) and (19) above into equation (13),
The reconstructed image is I(r _I )= ∫ rρ(r)exp{jΦ ₁ } ・{lsinc(lu)} ²・[sinc(X _T u)*m(l _T u)] ・[sinc(X _R u )*m(l _R u)] ・sinc(Y _T v) ・sinc(Y _R v) ・sinc {W/C(z _I − z)} dr (20). Therefore, if the variable u is plotted on the horizontal axis, a beam pattern as shown in FIG. 5c is obtained.

As can be seen from FIGS. 5a and 5b, transmitting element group 3
1 and the receiving element group 32 are determined by the shape of the transducer array 21, that is, the transducer width l, the transducer spacing l _T , l _R , the aperture width X _T , X _R , and the transducer switching device 2
In this case, by discretely selecting the receiving element groups 32, a grating rope is generated in the receiving beam pattern. Therefore, it is necessary to select the transmitting element group 31 so as to minimize this influence.
To do this, superimpose the zero crossing of the transmit beam pattern on the grating globe peak value of the receive beam pattern, that is, 1/X _T =
It is sufficient to design the shape of the vibrator array and select the element group so that _R is 1/l. As a result, a beam pattern with the grating rope removed as shown in FIG. 5c is obtained.

Although the embodiment shown in FIG. 1 has been described above, the present invention is not limited thereto. For example, the delay circuit 26 and adder 27 in the embodiment of FIG.
The analog circuit may be replaced with an A/D converter and a digital arithmetic circuit, and the delay synthesis process may be performed by this arithmetic circuit. Thereby, the accuracy of delay processing can be improved. 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, a small number of adjacent oscillators in a oscillator array constitute a transmitting element group, and other discretely located oscillators constitute a receiving element group. However, as the distance from the transducer array to the target object increases, the number of receiving element groups is increased and the receiving aperture area is expanded, so that the energy of the received ultrasonic waves can be supplemented and sufficient S/N can be achieved at any distance.
Not only can the ratio be determined, but also a uniform image of the object can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of transducer scanning, FIG. 4 is a diagram showing the coordinate system of the transducer array and the object, and FIG.
The figure shows an ultrasonic beam pattern, and FIG. 6 shows a conventional example. 1... Vibrator array, 2... Pulse generator, 3
...Amplifier, 4...Resonator switcher, 5...Amplifier, 6...A/D converter, 7...Line memory,
8... Frame memory, 9... Arithmetic unit, 10...
Digital scan converter, 11...Display device, 21...Resonator array, 22...Pulse generator, 23...Amplifier, 24...Resonator switch, 2
4a...Distance setting device, 25...Amplifier, 26...
Delay circuit, 27...Adder, 28...A/D converter, 29...Digital scan converter, 3
0... Display unit, 31... Transmitting element group, 32... Receiving element group.

Claims (1)

[Scope of Claims] 1. A transducer array formed by arranging a plurality of ultrasonic transducer transducers, a switching means for sequentially switching the transducers in the transducer array to transmit and receive ultrasonic waves, and and an image reproduction processing means for obtaining a reflected image of an object by aperture synthesis processing from the ultrasound waves received by the transducers in the transducer array, wherein a small number of adjacent transducers in the transducer array In addition to forming a transmitting element group, a receiving element group is formed by other discretely located transducers, and as the distance from the transducer array to the object increases, the number of receiving transducers increases to increase the receiving aperture area. An ultrasonic imaging device characterized in that it is configured to magnify.