JPH0546222B2 - - 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 synthetic 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 oscillators in this oscillator array 1 are pulse generators (pulsars)
The pulse signal of a predetermined frequency generated in step 2 is sent to amplifier 3.
It is composed of a piezoelectric element that vibrates and generates ultrasonic waves when applied via the transducer switch 4, and generates 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 X, and the same transducers receive reflected ultrasonic waves from the object.
One line of data is transferred from the transducer switcher 4 to the amplifier 5.
and analog/digital (A/D) converter 6
After temporarily storing it in the line memory 7 via the oscillator, it is stored in the frame memory 8 corresponding to each vibrator. The image of the object It is observed by displaying one screen on the display 11 via the converter 10.

(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 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 with By configuring this structure, a sufficiently large reception aperture is secured and the energy of the received ultrasonic waves is increased to obtain a sufficient S/N ratio, while the amount of calculation required for aperture synthesis is reduced and the calculation speed is increased. This makes it possible to improve performance and simplify calculation processing.

(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 in this device 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 an imaging procedure described below. 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. Hereinafter, it will be explained that an image of the object X can be obtained by transmitting and receiving ultrasonic waves using such a group of elements.

First, as shown in FIG. 3, 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)d
t(2) Here, ω ₁ and ω ₂ are the minimum and maximum angular frequencies included in the transmitted ultrasound, respectively, and ω ₁ =ω ₂ may be satisfied. 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), so h(r _R , r _T , t)=1/W∫〓 ² 〓 ₁ H( r _R , r _T , ω) ex
p(jωt)dω=1/WA _r ∫ r _T ∫ r∫〓 ² 〓 ₁ ρ(r)exp{jω(t−t _c )}dωdrdr _T (8) Here, W=ω ₂ −ω ₁ Bandwidth.

Based on this ultrasonic propagation time information h (r _R , r _T , t), the three-dimensional reflectance of the object A distribution, that is, a three-dimensional pixel at the position r _I 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, Ф＝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=a, Ф≒ω/C{2(z _I −z) + (x _I ² −x ² )/a+(y _I ² −
y ² )／α x _I −x／ax _T −y _I −y／ay _T −x _I −x／ax _R
−y _I −y/ay _R }(12).

Therefore, by substituting equation (12) into equation (10) and performing integration with respect to ω, the following equation is obtained.

I (r _I ) = ∫ rρ(r)exp{jΦ ₁ }・1/A ∫ r _T exp{jΦ ₂ }dr _T・1/A ∫ r _R exp{jΦ ₃ }dr _R・sinc {W/C (z _I −z)}dr (13) Here, Φ ₁ =W _n /C{2(z _I −z)+(x _I ² −x ² )/a+(y _I ²
−y ² )/a} Φ ₂ =W _n /C{−(x _I −x)/ax _T −(y _I −y)/ay _T
} Φ ₃ =W _n /C{-(x _I -x)/ax _R -(y _I -y)/ay _R
} W _n = ω ₁ + ω ₂ /2 sinc {W/C (z _I − z)} = sin {W/C・(z _I − z)
}/W/C・(z _I −z) Calculating the integral term by r _T in the above equation (13) yields the following.

1/A _T ∫ ∫ r _T exp{jΦ ₂ }dr _T =lsinc{W _n l/2Ca(x _I −x)}・[
sinc{W _n X _T /2Ca(x _I −x)} * _Ш (W _n l _T /2Ca(x _{I −}
/2Ca(y _I −y)}(14) Here, W _n /2Ca(x _I −x)=μ (15) W _n /2Ca(y _I −y)=υ (16) 14) The formula is 1/A _T ∫ ∫ r _T exp{jΦ ₂ }dr _T = lsinc {lu)・[sinc(X _T u)＊Ш
(l _T u)]・sinc(Y _T υ) (17). However, Ш(l _T u)= _+∞ 〓 ^n=-∞ δ(n−l _T u)=l _T+∞ 〓 ^n=-∞ δ(n/l _T −u)
(18) (δ is a 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. 4a.

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

1/A _R ∫ ∫ r _R exp{jΦ ₃ }dr _R =lsinc{W _n l/2Ca(x _I −x)}・[
_{sinc { W n _ _}
x))] ・sinc{W _n Y _R /2Ca(y _I −y)}=lsinc(lu)・
[sinc(X _R u) *Ш(l _R u)]・sinc(Y _R υ) (19) Therefore, when the variable u is taken on the horizontal axis in equation (19), the beam pattern of the receiving element group is , as shown in FIG. 4b.

By substituting equations (17) and (19) above into equation (13),
The reconstructed image is I(r _I )= ∫ ∫ rρ(r)exp{jΦ ₁ }・{lsic(lu)} ²・[sinc(X _T u
)*Ш(l _T u)]・[sinc(X _R u)*Ш(l _R u)]・sinc(Y _T υ)・sinc(Y _R υ)・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. 4c is obtained.

As can be seen from FIG. 4a and b, 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 (X _T , X _R ), and transducer switching. In this case, by discretely selecting the receiving element groups 32, a grating globe is generated in the receiving beam pattern. 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 globe peak value of the receiving beam pattern. That is, 1/
The design of the shape of the transducer array and the selection of the element groups should be done so that X _T =1/l _R. As a result, a beam pattern with the grating globe removed as shown in FIG. 4c is obtained.

Although the embodiment shown in FIG. 1 has been described above, the present invention is not limited thereto. For example, the fifth
As shown in the figure, the analog circuits of the delay circuit 26 and adder 27 in the embodiment of FIG. 1 are replaced with an A/D converter 33 and a digital calculation circuit 34, and the calculation circuit 34 performs delay synthesis processing. It's okay. According to this configuration, 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 transducers in a transducer array constitute a transmitting element group, and other discretely located transducers By configuring a receiving element group with a large area, it is possible to irradiate the object with focused ultrasonic waves and receive reflected waves with high energy, and a sufficient S/N ratio can be obtained for the reconstructed image. Since the data is captured by a small number of discrete receiving elements, the amount of calculation required is small, and it is possible to improve the calculation speed and simplify the calculation process.

[Brief explanation of the drawing]

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. FIG. 5 is a diagram showing another embodiment of the present invention, and FIG. 6 is a diagram showing 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, 21... Vibrator array, 22... Pulse generator, 23... Amplifier, 24... Vibrator switch, 2
5...Amplifier, 26...Delay circuit, 27...Adder, 28...A/D converter, 29...Digital scan converter, 30...Display device, 31...
Transmitting element group, 32...Receiving element group, 33...A/
D converter, 34... Arithmetic circuit.

Claims (1)

[Claims] 1. A transducer array formed by arranging a plurality of ultrasonic receiving transducers; a switching means for sequentially switching the transducers in the transducer array to transmit and receive ultrasonic waves;
and an image reproduction processing means for obtaining a reflected image of the object by aperture synthesis processing from the ultrasound waves received by the transducers in the transducer array. An ultrasonic imaging device characterized in that a transducer constitutes a transmitting element group, and other discretely located transducers constitute a receiving element group having a larger aperture area than the transmitting element group.