JPS6329630A - Ultrasonic sonic velocity measuring apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention relates to an ultrasonic diagnostic device that uses ultrasound to obtain information inside a living body, and particularly relates to an ultrasound diagnostic device that uses ultrasound to obtain information inside a living body. The present invention relates to an ultrasonic diagnostic device having a function of accurately measuring the speed of sound.

(Conventional 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 improving due to recent advances in high-speed scanning equipment. It has become popular. Since this ultrasonic diagnostic method is a pulse reflection method, it is superior in operability compared to a transmission method, and the diagnostic sites to which it can be applied are not so limited are also cited as reasons for its widespread use.

Recently, there has been an increasing demand for quantification of a single image in such ultrasonic diagnostic methods. Quantification of images is considered to be particularly effective in differential diagnosis of benign and malignant organ diseases.

However, in the conventional pulse reflection method, the reflected wave intensity is determined not only by the difference in acoustic impedance (product of density and sound speed) between tissues in the body.

Shape of the reflecting surface 2. Angle of incidence of the ultrasonic beam on the reflecting surface,
Quantification of images has been extremely difficult because it depends on the amount of ultrasound absorbed in the living body, and it is difficult to separate and detect this information.

On the other hand, the conventional method of measuring only the speed of sound is transmission-type ultrasonic C
Although it is still in the research stage, its performance is gradually improving (Reference: Greenle
af, J, F, et, at, Acoustic
al Holography.

vol, 61975). However, the transmission method has a major drawback in that it cannot be applied to areas where there are bones or gas in the ultrasound propagation path, so it can only be used in very limited areas such as mammary gland examinations.

On the other hand, a method has been devised in recent years to measure the speed of sound inside an organ using the pulse reflection method. Figure 6 shows the intrahepatic sound velocity measurement method reported by Akamatsu et al.

In this method, two ultrasonic transducers 51 and 52 with strong directivity are used for transmitting and receiving, respectively, and the ultrasonic waves transmitted from the transmitting ultrasonic transducer 51 are transmitted to each transducer 51 and 52. central axis PP', QQI
The time it takes to reflect near the intersection O of This method calculates the average speed of sound in the liver from the calculated expected propagation distance.

Since the sound velocity obtained by this method is the average sound velocity within the propagation path, it is considered effective for diagnosing diffuse diseases such as liver cirrhosis in which the metal body in the liver has uniform acoustic characteristics. Not applicable to diseases. In addition, the sound speed in the epidermis or fat layer, which has a different sound speed than the inside of the liver, is also mixed in, and in this case, refraction also occurs, so there is a drawback that the measurement error in the sound speed is large.

For example, in FIG. 6, if the speed of sound in the living tissue is uniformly Co, then the speed of sound can be determined accurately. However, t is the measured value of the propagation time. However, if there is another tissue (for example, a fat layer) 53 with a different sound velocity on the body surface side of the measurement area 54, the intersection R of the boundary surface and the transmitting and receiving beam,
8, refraction of the ultrasound beam occurs and the actual propagation distance (RO
'S) is different from the set propagation distance (RO8), so the speed of sound in the region to be measured 54 cannot be determined accurately from equation (1).

(Problem to be solved by the invention) In this way, in conventional devices, when there is another tissue on the body surface side that has a different sound velocity, the ultrasound beam is refracted at the boundary surface and the propagation There is a problem in that the speed of sound in the area to be measured cannot be accurately determined because an error occurs in the distance.

An object of the present invention is to provide an ultrasonic diagnostic apparatus that can accurately measure the ultrasonic sound velocity in a desired region within a living body without being greatly influenced by body surface tissue layers.

[Structure of the invention]

(Means for Solving the Problems) The present invention comprises a transmission transducer group and a reception transducer group as a part of arranged transducers, and first and second reception transducers placed at a predetermined interval. The receiving beam direction of the transducer group is almost perpendicular to the transducer plane, and the transmitting beam radiated from the first and second transmitting transducer groups placed at both ends of the receiving transducer group is The first . a second transmit beam; This makes it possible to measure the speed of sound in the area surrounded by the second receiving beam.

(Operation) FIG. 1 shows the arrangement of an ultrasonic transducer and the principle of measurement for the purpose of measuring the speed of sound in the body according to the present invention.

As shown in the figure, an array type ultrasonic transducer is placed on the body surface, and one part of the array type ultrasonic transducer is used as the transmitting transducer section 1).
12. Allocated as reception transducer sections 13 and 14. That is, the reception transducer section 13.14
Transmitting transducer sections 1) and 12 are installed at both ends of each device. Radiation angle θ of the transmitted beam. is electronically controlled as described below. Transmission transducer 1)
and 12 is θ. , −θ. It has a strong transmission directivity in the direction of Of the ultrasonic waves scattered at point A in the living body 54, only the ultrasonic waves scattered at point A are received by the receiving transducer 13, and only the ultrasonic waves scattered at point B are received by the receiving transducer 14 and converted into electrical signals. . Similarly, the transmitting beam from the transmitting transducer is scattered at 6 points and D point and received by the receiving transducer 14, 13, respectively. The time required for the sound waves transmitted from the transmitting transducer 1) to be scattered by the scatterers at A and B and received by the receiving transducer 13.14 is shown in each of the times 1 and 1.1) □. . Similarly, the propagation time 128.12□ for the ultrasonic waves transmitted from the transmitting transducer 12 to be scattered by D and C and received by the receiving transducers 13 and 14 is as follows. However, “QA # t!A l tFCI t
HC is n each.

The propagation times in EA, FC, and HC are shown, and Co is the sound speed in the region of interest ACBD. Here, the incident angle of the transmission beam is set to θoBF=d0, and the sound velocity within the region of interest is determined when there is no body surface tissue.

The time difference Δt defined by the following formula is becomes.

That is, the sound speed Co in the region of interest can be calculated from the following equation by determining the propagation time difference Δt.

Next, a case where the sound velocity C1 of the body surface tissue is different from 00 will be considered. For example, in the case of a fat layer where CX<Co, the transmitted ultrasonic beam is refracted at the boundary surface 55 as shown by the broken line in FIG.

Assuming that the boundary surface 55 is parallel to the transducer surface, the radiation angle of the ultrasonic beam transmitted from the transducer is θ. If the refraction angle at the boundary is θ, then the area AI C
The sound speed C0 at T BI DI can be determined by the following equation.

However, Δt1 is a propagation time difference that can be obtained from propagation time measurement similarly to (3). In (5), 0g is an unknown quantity, so this equation cannot be used directly, but since the relationship from Snell's law always holds, (6) is used to calculate θ in (5).

By eliminating ', 00 can be calculated from the following equation.

On the other hand, α shown in (6) can be easily set in the case of electronic beam deflection using an array transducer. The principle will be explained below with reference to FIG.

Taking the transmitting transducer 1) in FIG. 2 as an example, when transmitting an ultrasound beam in the direction θ using N transducers with an interval a, the delay time td (i.e. 1 )-1 transducer 1)-n transducer (n
-1) When driving with td) set at 4, the radiation angle θ is expressed by the following formula.

However, the figure shows the speed of sound in the medium in contact with the transducer. That is, in this case, θ cannot be determined independently, but is always determined as a ratio to the sound speed of the medium. (6
) and (8), α is a known quantity determined by the specifications of the measurement system.

Therefore, by using force, it is possible to accurately estimate the speed of sound at the measurement site even when body surface tissue intervenes.

Further, in FIG. 2, the case where the body surface layer is parallel to the transducer surface has been described, but even if it is not parallel, the influence of refraction can be significantly reduced as long as the shape is not extremely complicated.

FIG. 4 shows an embodiment of the invention.

The array type ultrasonic transducer 2o is placed in contact with the living body 54. Among these transducer elements, the first transmitting transducer section 1) or the second transmitting transducer section 12 (composed of four elements in the figure) is used to emit ultrasound into the living body. is carried out. That is, the above portion of the array type transducer 10 is selected by a switching circuit 19 controlled by the scanning controller 2o, and a transmission drive pulse is sent thereto. Immediately after the transmission drive pulse is applied to the transmission transducer unit and the ultrasonic pulse is emitted into the living body, the mode is switched to the reception mode, and the transmission mode is switched to the first reception transducer unit 13 or the second reception transducer unit 13. The scattered waves from the region where the transmitting and receiving beams intersect are selected by the switching circuit 14 and received.

The configuration of the transmitting/receiving circuit section is similar to that of an electronic scanning ultrasonic device, and the synchronous pulse generator 21 generates a synchronous pulse generator.
The repeated pulse signal of 00 μsec is delayed for a predetermined time by the transmission delay circuit 22 and then supplied to the pulser circuit 23, where a transmission drive pulse is generated. On the other hand, during reception, the in-vivo scattering signal converted into an electrical signal by the first or second reception transducer is sent to the switching circuit 1.
9, the signals are amplified by the first stage amplifier 24, delayed by the receiving delay circuit 25, and then combined by the adder 26. In this case, the transmission delay circuit 22 is given a delay time for deflecting the transmission beam by 00 and the delay time for converging the beam at the same time, and the reception delay circuit 25 is given a convergence delay time. The summed signals are passed through a logarithmic amplifier 31 to obtain a conventional ultrasound image (B-mode tomography).
, and is sent to an A/D converter 33 via a wave detector 32, where it is converted into a digital signal and stored in an image memory within a DSC (digital scan converter) 34.

On the other hand, in order to measure the speed of sound, the output of the adder 26 is ST
After being subjected to C correction, etc., envelope detection and A/D conversion are performed, and the data is temporarily stored in the buffer memory 29. The arithmetic unit 30 measures the propagation time and estimates the internal sound velocity value from the signal stored in the buffer memory 29. The method for calculating the propagation time will be described below. FIG. 5 shows a received waveform after envelope detection obtained when, for example, the first transmitting transducer section 1) and the first receiving transducer section 13 are used. When measuring propagation time, methods such as measuring the front etch of the waveform or the peak position can be considered, but when scatterers are densely present, such as in a living body, interference occurs and the waveform after detection is extremely complex as shown in the figure. Therefore, it is difficult to perform accurate measurement from the peak position.

Furthermore, in the case of the reflection method, it is impossible to define the front edge. Therefore, a centroid measurement method is desirable. However, there are reflectors (
For example, when there are intrahepatic blood vessels, signals from the reflectors are often mixed in as shown in Figure 5, so it is necessary to limit the time domain (range) for calculating the center of gravity. For example, first, the peak position tm of the received signal (Fig. 5 0)
The center of gravity is calculated within a predetermined width Δ around this position.

The propagation time t1) can be found from . However, P1□(1)
is the received waveform after detection.In the present invention, it is possible to measure the ultrasound velocity in the body using a single array-type ultrasound transducer, so it has excellent scanning performance. ) can also be displayed in real time, making it easy to accurately set the region of interest where the speed of sound is to be measured.

Furthermore, the position and beam angle of the transmitting/receiving ultrasonic transducer can be easily changed by electronic means, and the region of interest can therefore be changed at high speed, making it possible to perform two-dimensional internal sound velocity mapping.

[Effects of the Invention] As described above, according to the present invention, the ultrasonic sound velocity in a desired region within a living body can be accurately measured without being influenced much by body surface tissue layers.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of local sound velocity measurement using a linear array transducer, Figure 2 is a diagram showing changes in the wave measurement unit when sound waves are refracted at the body surface layer, and Figure 3 is an electronic A diagram showing the principle of the beam deflection method, FIG. 4 is a block diagram of an embodiment of the present invention, FIG. 5 is a diagram showing the centroid measurement method for calculating propagation time, and FIG. 6 is a diagram showing the conventional average sound velocity in the body. It is a figure showing a measurement method. 10...Array type transducer, 1). 12...
- Transmission transducer section, 13.14... Reception transducer section, 53... Integral surface tissue layer, 54...
- Observed organ, 55... Tissue boundary surface, 51... Single transducer for transmission, 52... Single transducer for reception, 52... Single transducer for reception, 19... Switching circuit, 20...
Scanning controller % 21...Rate pulse generator, 22...Delay circuit for transmission, 23...Pulser, 24...Preamplifier, 25...Delay circuit for reception, 26...Adder, 27...detection circuit, 28...
A/D converter, 29...buffer memory, 30...
Arithmetic unit, 31... Logarithmic amplifier, 32... Detection circuit,
33... A/D converter, 34... Image memory, 35
...CR, T0 agent Patent attorney Nori Chika Yudo Kikuo Takehana Figure 1 Figure 2 Figure 3 Figure 5

Claims (2)

[Claims] (1) a drive circuit for selectively driving the arrayed transducers to transmit ultrasound into a medium; a transmission delay circuit for deflecting a transmission ultrasound beam transmitted by the drive circuit; a receiving circuit for selectively using a transducer to receive ultrasound from within a medium;
In an ultrasonic device equipped with means for measuring the propagation time from the reception time of the received signal and means for calculating the speed of sound in a medium from the propagation time, the transmitting and receiving transducer groups are arranged in the array of transducers. The reception beam directions of the first and second reception transducer groups, which are arranged at a predetermined distance apart, are substantially perpendicular to the transducer plane, and the reception transducer groups are placed at both ends of the reception transducer group. The transmitting beams emitted from the first and second transmitting transducer groups are electronically deflected within the medium so as to intersect the receiving beams, so that the transmitting beams emitted from the first and second transmitting transducer groups are
, an ultrasonic sound speed measurement device that enables sound speed measurement in an area surrounded by a second reception beam. (2) The sound velocity value of the area surrounded by the transmitting and receiving beams is the first
, the propagation time until the ultrasonic waves transmitted from the second transmitting transducer group are scattered in the medium and received by the first and second receiving transducer groups, and the first and second receiving transducers. 2. The ultrasonic sound velocity measuring device according to claim 1, wherein the ultrasonic sound velocity is calculated from the interval and the delay time given in the transmission beam deflection.