JPH01153145A - Annular array ultrasonic probe - Google Patents

Abstract

PURPOSE:To suppress the deterioration of image quality generated by the refraction of beam at the boundary of the coupling solution in an ultrasonic probe and a living body to the min. degree, by bringing the contact surface of an acoustic window with a medium to be measured to nearly level. CONSTITUTION:When the radius of curvature of the wave front shift of the equivalent radius of curvature of a convex annular array transducer is set to r2, the radius of curvature of an acoustic window is set to r1, the sonic velocity of the coupling solution sealed in the acoustic window is set to c1 and the sonic velocity in a medium to be measured is set to c2, ultrasonic waves are converged to the position separated by r2 from the transducer at the time of c1=c2. The shift DELTAr of the converging point generated at the time of c1=c2 is approximately represented by formula (wherein DELTAc=c2-c1). In this formula, the relation between DELTAr and r1 can be rewritten as DELTAr=K(1+r2/r1) (wherein K is a constant). From this formula, it is understood that DELTAr becomes min. at the time of r1=infinity , that is, the shape of the window is planar with respect to a living body. When an annular array ultrasonic probe provided with the acoustic window having the above-mentioned shape is used, the shift of the ultrasonic beam converging point generated by that of the sonic velocity of the coupling solution in the probe is different from that of the living body can be suppressed to the min. degree.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an ultrasonic diagnostic device that obtains tomographic images of a living body using ultrasonic waves. The present invention relates to an ultrasonic diagnostic device with high resolution.

(Prior technology) Diagnostic methods using ultrasound have the advantage of being able to diagnose soft tissue without placing any burden on the patient, and are non-invasive, and are rapidly becoming popular due to recent advances in high-speed scanning equipment. I've done it. Since this ultrasonic diagnostic method is a pulse reflection method, it is easier to operate than the transmission method, and the diagnostic areas to which it can be applied are not so limited, which is another reason why it has become so popular.

There are two high-speed scanning methods: an electronic scanning method and a mechanical scanning method.

The latter has a larger ultrasound probe part than the former,
For this reason, although the operability is somewhat inferior, the device can be realized with a relatively simple mechanism, and as will be described later, if an annular array type transducer is adopted, it is possible to obtain biological tomographic images superior to that of electronic scanning devices. Become.

Conventional mechanical scanning ultrasound diagnostic equipment uses a method in which one ultrasound transducer is mechanically rotated or oscillated at high speed. It consists of a mechanical part that mechanically moves the transducer, a coupling solution that prevents the movement of the transducer from directly touching the living body and transmits only the ultrasonic waves into the body, and an acoustic window that directly contacts the living body. Initially, flat transducers were used, but today, planar disk-shaped transducers are used to converge ultrasound beams in vivo and obtain tomographic images with excellent resolution. Transducers are commonly used. In this method, a transmitting circuit for driving the transducer to radiate ultrasound into the living body and a receiving circuit for amplifying and detecting the ultrasound reflected waves from the living body received by the transducer are each Since only one channel is required, the electronic circuit configuration is extremely simple, but the disadvantage is that the ultrasound beam is limited to only one location within the body. Therefore, a clear ultrasound image can be obtained in the area where the ultrasound waves are converged, but a good image is still not obtained in other areas.

In order to solve these problems, mechanical scanning diagnostic devices employing annular array type transducers have recently begun to be put into practical use. As shown in FIG. 2, the annular array type ultrasonic transducer is composed of one disc-shaped transducer placed at the center and several ring-shaped transducers. In the following, four ring-shaped transducers will be explained as an example. These single disk-shaped transducer and ring-shaped transducer are arranged on a flat plate or concave surface so that their centers coincide, and a transmitting/receiving circuit is connected to each transducer. The transmitting circuit and the receiving circuit each have an independent delay circuit, and by controlling the delay time, it is possible to vary the transmitting and receiving convergence points of the ultrasonic beam. For example, in the case of an annular array transducer placed on a concave surface, if each transducer is used simultaneously without delay time control, the ultrasonic beam will be focused at a distance equal to the radius of curvature of the surface. Furthermore, by giving a delay time difference to the drive signal or reception signal of each transducer, the focal length can be moved back and forth. That is, it becomes possible to control the convergence point of the ultrasonic beam by electronic means. Furthermore, by combining a plurality of ring transducers and a transmission/reception delay circuit, dynamic focusing becomes possible, and an ultrasonic tomographic image with excellent resolution can be obtained regardless of the distance from the transducer. Dynamic focus is a method of transmitting and receiving ultrasonic waves while changing the convergence point and synthesizing an image from only the signals near the focal point. In this case, since the image is always composed of signals obtained by scanning with the narrowest ultrasonic beam, high resolution can be achieved over a wide range.

(Problems to be Solved by the Invention) As described above, by employing an annular array type transducer, dynamic focus can be realized with a relatively simple circuit configuration, and high-resolution images can be obtained. However, in order to obtain a clear image using dynamic focusing, it is important that the ultrasound beam is focused on a preset location. It is often difficult to actually converge the beam at the set convergence point in mechanical scanning, and the maximum The cause is that when the sound speed in the living body and the sound speed in the coupling solution differ, refraction of sound waves occurs at the interface.

In general, even if the speeds of sound are different between the two, if the respective sound speed values are known in advance, it is possible to correct the shift in the focal point due to refraction that occurs at the interface by controlling the delay time of the transmitter/receiver circuit. However, even though the sound speed of the coupling solution can be known in advance, the sound speed in the living body cannot be accurately measured using current measurement techniques. was unreasonable, and therefore the effect of dynamic focus was not sufficiently obtained.

The present invention aims to solve the problem of image quality deterioration caused by beam refraction at the boundary between the coupling solution in the ultrasound probe and the living body when applying the dynamic focus method of the conventional antenna array type ultrasound diagnostic device as described above. The aim is to minimize the

(Example) Before describing specific examples, the validity of the present invention will be discussed. FIG. 3 is an explanatory diagram thereof, in which the radius of curvature of the wavefront shift with a uniform radius of curvature of the concave annular array transducer is rz, and the radius of curvature of the acoustic window is rl. In addition, the sound velocity of the coupling solution sealed in the acoustic window is 01
, if the speed of sound in the observed medium (in this case, a living body) is C2, then when % c1+=CM, the ultrasonic waves are focused at a position r2 away from the transducer. On the other hand, the deviation Δr of the convergence point that occurs when C1≠02 is approximately expressed by the following equation.

Δr= −ΔC* rz” (rl + rz)
/C1/rl °°°■ However, ΔC=e,
-cl The shape of the acoustic window of the conventional mechanical sector type ultrasound probe is convex with respect to the living body, and generally r, >
It was rl. For example, the focal length (r,
) Radius of curvature (rl) of the acoustic window for 50-150 m
is like 20 nm. In this case, we will discuss the difference between the set focus point and the actual focus point due to the difference in sound speed between the coupling solution and the living body. Figure 4 shows the sound speed of the coupling solution at 1,500 m/see and the window material's sound speed at 2,000 m/see.
c, and the biological sound velocity is 1400m/sec-1600m/
This figure shows the relationship between the set focal point (FP) and the actual focal point (Xo) when the focal point is changed within the range of see. As shown in this figure, for example, the set focal point FP=100 m
In the case of m/sec, this means that the actual focal point of the ultrasonic beam may deviate by -30 mm to +40 mm. Therefore, conventional methods have been used to correct the focal point using electronic control methods, etc. Although it is necessary,
Unless the speed of sound inside the body is clear, it is impossible to correct it.

By the way, in ■, the relationship between Δr and r work is Δr = K
It can be rewritten as (1+rz/rt). However, K is a constant, where Δr
It can be seen that is minimized when r1=ψ, that is, when the window shape is flat with respect to the living body. Under the same conditions as in Figure 4, the coupling solution, window material, and biological sound speed are r,
Figure 5 shows the magnitude of the shift in the focal point when = ω. When a flat acoustic window is used as shown in this figure, the shift is extremely small compared to the conventional method, and it is difficult to correct it. It turns out that this is not necessarily necessary.

FIGS. 1(a) and 1(b) show a cross-sectional view and external appearance of an embodiment of an ultrasound probe according to the present invention. The probe does not necessarily have to be axially symmetrical, and the surface that comes into contact with the living body may be rectangular. However, the edges must be rounded to a degree that does not cause pain to the subject if it hits the living body.

Furthermore, if it is difficult to come into contact with a living body, it is possible to have a slightly curved surface in only one direction.

FIG. 6 shows the configuration of an ultrasonic diagnostic apparatus using the annular array transducer of the present invention. 1 and four ring-shaped transducers 4-2 to 4-5 arranged around it. These transducers each include transmitters (balsa) 5-1 to 5-5 for driving the transducers to radiate ultrasonic waves into the living body, and in-vivo waves received by the transducers. Preamplifiers 6-1 to 6-5 are connected to amplify ultrasonic reflected signals from. During transmission, the ultrasonic radiation timing signal generated from the oscillator 10 is sent to the transmission delay circuits 7-1 to 7-5, and a delay time necessary for focusing the ultrasonic beam for transmission is given to the balsas 5-1 to 5. -5 trigger pulse. That is, the delay times of the transducer drive pulses of the balsers 5-1 to 5-5 are determined by the delay circuits 7-1 to 7-5. Transducers 4-1 to 4-5 are balsa 5-1 to 5
-5 to radiate ultrasonic waves into the living body 1 through the coupling solution 3 and the acoustic window 2. On the other hand, the ultrasonic signals reflected from the inside of the living body 1 are transmitted to the transducers 4-1 to 4-4.
-5, the signals are converted into electrical signals, amplified by preamplifiers 5-1 to 5-5, and then sent to reception delay circuits 8-1 to 8-5. The receiving delay circuits 8-1 to 8-5 are for setting the ultrasonic convergence point during reception, and the five received signals given a predetermined delay time are added by an adder 9 and one There will be two signals. This signal is sent to the logarithmic amplifier 11 as in conventional ultrasound diagnostic equipment. A through the detection circuit 12
The /D converter 13 converts the signal into a digital signal, and the sample/hold circuit 14 samples the signal from the focusing area and stores it in the image memory 15. Image memo January 5
Once the image data for one image is accumulated, it is displayed on the CRT monitor in TV format.

By the way, in the case of an annular array using a concave transducer, it goes without saying that the actual wavefront is determined by combining the curvature of the surface and the delay time.

〔Effect of the invention〕

As described above, by using the ultrasound probe for annular array with the acoustic window shape according to the present invention, the deviation of the ultrasound beam focus point caused by the difference in sound speed between the coupling solution in the probe and the living body can be minimized. This makes it possible to obtain high resolution ultrasonic tomographic images.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the probe of the present invention, Fig. 2 is a diagram showing the configuration of an annular array transducer, Fig. 3 is a diagram illustrating the shift of the focal point due to refraction at the acoustic window, and Fig. 4 5 is a diagram showing the magnitude of the focal point shift in the conventional acoustic window shape, FIG. 5 is a diagram showing the magnitude of the focal point shift in the acoustic window shape of the present invention, and FIG. 6 is a diagram showing the magnitude of the focal point shift in the acoustic window shape of the present invention. It is a figure showing the diagnostic device used. 1... Biological body 2... Acoustic window 3... Coupling solution 4... Annular array transducer 5... Balsa 6... Preamplifier 7... Delay circuit for transmission 8... Reception delay circuit 9...adder
1o... Oscillator 11... Logarithmic amplifier
12...Detection circuit 13...A/D converter 14...Sample/hold circuit 15...Image memory 16...CRT monitor Mixed agent Kensuke Chika and Mitsuyuki Matsuyama Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] An annular structure comprising an ultrasonic transducer in which a plurality of ring-shaped transducers are arranged substantially concentrically, a mechanism for mechanically moving the transducer, a coupling solution surrounding the transducer, and an acoustic window. An annular array ultrasonic probe, characterized in that a portion of the acoustic window that contacts the medium to be measured is substantially flat.