JP2597360B2 - Ultrasound diagnostic equipment - Google Patents

Description

The present invention relates to an ultrasonic diagnostic apparatus that irradiates an ultrasonic pulse to a subject, receives a reflected wave thereof, and captures a tomographic image of the subject, In particular, the present invention relates to an improvement in a method of transmitting and receiving ultrasonic pulses.

[Conventional technology]

In general, as this type of ultrasonic diagnostic apparatus, for example, an ultrasonic diagnostic apparatus for B-mode disclosed in “Ultrasonic Technology Handbook (Nikkan Kogyo) P810-813” or “Ultrasonic Medicine (Medical Publishing) P81-84” Ultrasound diagnostic devices are the mainstream. The B-mode ultrasonic diagnostic apparatus uses an ultrasonic transducer with a small aperture to obtain a substantially constant degree of convergence (quantile resolution) in the depth direction (the direction normal to the transducer plane). Is transmitted and received.

[Problems to be solved by the invention]

The B-mode ultrasonic diagnostic apparatus described above is configured to widen the focus range by weakening the degree of convergence, and thus has a disadvantage that the quantile resolution is poor.

Therefore, an object of the present invention is to provide an ultrasonic diagnostic apparatus whose resolution is dramatically improved as compared with a conventional ultrasonic diagnostic apparatus.

[Means for solving the problem]

The present invention solves the above problems and achieves the object,
The ultrasonic diagnostic apparatus of the present invention is configured as follows.

(1) An ultrasonic diagnostic apparatus according to the present invention includes a transmitter arranged to irradiate an ultrasonic pulse obliquely to a tomographic plane of a subject to be detected, and a transmitter on the tomographic plane by the transmitter. An ultrasonic lens arranged so as to focus a reflected wave from the tomographic plane of an ultrasonic pulse applied in time series to one detection line to form a tomographic image, and a reflected wave from the detection line The reflected wave is output as an electric signal in synchronism with the timing at which the reflected wave from the detection line is imaged in time series by the ultrasonic lens, which is arranged at a position where the ultrasonic lens forms an image. An ultrasonic imaging element composed of a plurality of elements, and movement control of a transmission position in the transmitter so as to scan the detection line in a direction substantially orthogonal to the detection line in order to obtain the tomographic image. Control means Has become a thing was.

(2) The ultrasonic diagnostic apparatus according to the present invention is the apparatus according to the above (1), wherein the transmitter includes a plurality of transmitters arranged in a direction substantially orthogonal to a detection line in the tomographic plane. A linear array vibrator, and a multiplexer for selecting a vibrator to be excited among the plurality of linear array vibrators, wherein the multiplexer is a part of the plurality of linear array vibrators for one detection line. Select the oscillator group of
Further, each transducer of the transducer group is sequentially selected such that the ultrasonic pulse generated by excitation of the transducer group reaches an arbitrary point on the detection line at substantially the same time. .

(3) The ultrasonic diagnostic apparatus according to the present invention is the apparatus according to the above (1), wherein the electric signal converted by the ultrasonic imaging device is sensitive by the distance of the ultrasonic pulse and its reflected wave. Further, there is provided a correction means for correcting so that there is no difference between them.

[Action]

By taking such means, the following effects are exhibited. Since the ultrasonic pulse is applied obliquely to the tomographic plane, the ultrasonic pulse is applied to the tomographic plane in time series. As a result, tomographic images formed on the wave receiving surface of the ultrasonic imaging element are also formed in time series. Therefore, if a tomographic image to be formed in a time series is extracted as an electric signal from the image sensor in synchronization with the imaging timing, one tomographic image in the subject is detected.

〔Example〕

FIG. 1 is a diagram showing the overall configuration of the first embodiment of the present invention. In the figure, A is a probe, B is a device main body, and C is a subject.

On the opposing end face of the probe A facing the subject C, the bellows-type container 1 that stably contacts the surface of the subject C so as to surround the opposing end face is mounted. A sound absorbing material for preventing irregular reflection of ultrasonic waves is mounted on the inner wall of the container 1. An acoustic medium 2 is sealed inside the container 1. As the acoustic medium 2, for example, water is used. Since the sound speed of water varies depending on the temperature, it is not shown,
A temperature control mechanism for keeping the water at a constant temperature and a defoaming mechanism for removing bubbles are attached to the container 1.

The transmitter 3 is attached to the opposite end face of the probe A. It is composed of linear array transducers arranged in a direction substantially orthogonal to the detection line in the tomographic plane 4, and is arranged so as to irradiate the ultrasonic pulse obliquely to the tomographic plane 4 of the subject C to be detected. ing.

A large-aperture ultrasonic lens 5 is attached to a central portion of the opposing end surface of the probe A substantially parallel to the tomographic plane 4. The ultrasonic lens 5 focuses the reflected wave from the tomographic plane 4 and forms a tomographic image on the receiving surface of the ultrasonic imaging element 6 installed inside the probe A. The ultrasonic lens 5 has an acoustic impedance of the acoustic medium 2.
And a material whose sound speed is different from that of the acoustic medium 2. As the substance, when the acoustic medium 2 is water, a plastic material such as an acrylic resin is preferable. If it is a plastic material, an aspherical lens can be easily formed by molding. Both sides of the ultrasonic lens 5 are coated with acoustic matching layers 5a and 5b. The ultrasonic lens 5 may be a single lens or a combination lens, and further includes a zoom mechanism for removing, enlarging, and reducing aberration, and a focus adjustment mechanism. You may.

The ultrasonic imaging element 6 has a function of converting the sound pressure distribution of the ultrasonic wave received on the ultrasonic wave receiving surface into a time-series electric signal (video signal).

Inside the probe A, a multiplexer 7 for selecting a linear array transducer of the transmitter 3, multiplexers 8 and 9 for extracting electric signals from the ultrasonic imaging device 6,
A preamplifier 10 for amplifying the extracted electric signal, a time gain control signal generating circuit 11 for increasing the degree of amplification of the preamplifier 10, that is, a gain over time, and the like are housed.

The apparatus body B has a pulse generator 12, a delay line 13
A pulse supply source 15 comprising a logarithmic amplifier 16, a detection circuit 17,
A signal processing circuit 25 including an adding circuit 18, a black clipping circuit 19, an integrating circuit 20, a comparing circuit 21, a switching circuit 22, a multiplier 23, a frame memory 24, etc., and a TV monitor 26 for displaying a video signal. Is housed.

FIG. 2 is a perspective view showing a configuration of the transmitter 3 and a positional relationship between the transmitter 3 and the tomographic plane 4. As shown in the figure, the transmitter 1 has an arrow Y on the tomographic plane shown in FIG.
An acoustic lens 31 for diffusion, an acoustic matching layer 32, and an electroacoustic transducer 33 are laminated and fixed on a damper member 34 so that the ultrasonic beam is uniformly irradiated in the direction. Thus, a group of transducers 3a of the transmitter 3 is selected by the multiplexer 7 shown in FIG. 1, and the output pulse from the pulse generator 12 is supplied to the selected group of transducers 3a by the delay line 13a. When an excitation pulse delayed by a predetermined time is applied to excite the group of transducers, an ultrasonic pulse is superimposed on one line 4a on the tomographic plane 4 with a time difference. The delay amount of the delay line 13 is set so that the transmitted ultrasonic wave is focused on the tomographic plane 4 in the direction of arrow X. When the ultrasonic pulse is irradiated on the line 4a in the order of M, N, L, the reflected echo is reflected on the ultrasonic imaging device 6 by the ultrasonic lens 5 as shown in FIG. , n, and l in order of time.

FIG. 3 is a perspective view showing the configuration of the ultrasonic imaging device 6 shown in FIG. As shown in FIG. 3, the ultrasonic imaging device 6 has a structure in which a signal electrode 62, an electroacoustic transducer 63, a ground electrode 64, and an acoustic matching layer 65 are laminated and fixed on an element mounting base 61 also serving as acoustic damping. Has become. The signal electrode 64 and the ground electrode 64 are each divided into a plurality of parts in different directions as described later. The electroacoustic transducer 63 is PVDF, PVF
_{As shown in 2,} the material having less acoustic coupling in the lateral direction is advantageous because only the electrode needs to be divided. When an electroacoustic conversion material such as PZT is used, it is necessary to perform mechanical cutting.

FIG. 4 is a diagram showing a means for extracting an electric signal from the ultrasonic imaging element 6. As shown in FIG. 4, the signal electrode 62 of the ultrasonic imaging element 6 is divided into a plurality of parts in a direction parallel to the arrow X direction in FIG. Also, the ground electrode 64 on the back side
It is also divided into a plurality in the direction orthogonal to the above, that is, in the direction parallel to the direction of arrow Y in FIG. The multiplexers 9 and 8 are connected to the electrodes 62 and 64, respectively. The common electrode 8a of the multiplexer 8 is connected to the ground. The common electrode 9a of the other multiplexer 9 is connected to the preamplifier 10 shown in FIG. By switching the multiplexers 8 and 9 in this manner, each element of the ultrasonic imaging device 6 can be sequentially selected, and m, n, l are placed on the ultrasonic imaging device 6.
Can be extracted in real time as time-series electrical signals.

Thus, by irradiating the ultrasonic pulse obliquely into the subject C, only one line of reflected echo on the tomographic plane 4 of the subject C can be extracted as a time-series signal.
The linear array transducer of the transmitter 3 is switched to move (scan) the transmission position, and at the same time, the detection line of the ultrasonic imaging element 6 is switched by the multiplexer 8 and the arrival of the ultrasonic pulse by the multiplexer 9 (connection). If the element is switched to a high speed (about 200 nsec) in accordance with the (image) time, only a tomographic image of the subject C to be imaged can be taken out in real time as an electric signal.

The resolution of the ultrasonic imaging element 6 is determined substantially on the tomographic plane 4 by the aperture angle of the ultrasonic lens 5 and the frequency of the ultrasonic pulse. Expressed by the equation, it becomes 2.44F / Dλ. Here, F is the focal length of the lens, D is the diameter of the lens, and λ is the wavelength of the ultrasonic wave. The resolution in the direction perpendicular to the tomographic plane 4 is obtained by multiplying the pulse width of the ultrasonic wave by 1 / sin θ. θ is the angle between the transmitted ultrasonic wave and the imaging section.

To be more precise, the resolution in the direction of the arrow X on the imaging section is obtained by multiplying the convergence distribution in the azimuthal direction of the ultrasonic lens 5 by the directivity of the transmission beam, and the resolution in the direction of the arrow Y is The convergence distribution in the azimuthal direction is obtained by multiplying the envelope waveform of the ultrasonic pulse by 1 / cos θ. Also fault plane 4
The resolution in the direction perpendicular to the vertical axis is obtained by multiplying the envelope waveform of the ultrasonic pulse by 1 / sin θ and the convergence distribution of the ultrasonic lens 5 in the axial direction. Thus, the resolution in the present embodiment was improved to about seven times that of the conventional device.

Next, processing of the received signal will be described. The electric signal extracted from the common electrode 9a of the multiplexer 9 is amplified by the preamplifier 10. This preamplifier 10 is an amplifier having a good noise figure, and converts the received signal into an S / N signal in a later circuit.
Amplified sufficiently to prevent ratio degradation. In addition, since the distance of the ultrasonic pulse is different between the M portion and the L portion on the tomographic plane 4 in FIG. 2, if the gain of the preamplifier 10 is constant, a difference occurs in sensitivity due to attenuation in the subject C. Would.
However, the preamplifier 10 is operated by the signal from the time gain control signal generation circuit 11 so that the gain increases as time passes. Therefore, the above sensitivity difference does not occur.

The output of the preamplifier 10 is the logarithmic amplifier 16 in the main unit B.
To enter. Here, logarithmic amplification is performed in accordance with the dynamic range (about 60 dB) of the ultrasonic echo signal. Next, it is detected by the detection circuit 17 and converted into a video signal.
This video signal is input to the adding circuit 18. Here, after adding the voltage V1 for gain adjustment, the black clip circuit
At 19, the voltage below 0V is clipped.

The voltage V1 is obtained as follows. The output signal of the black clip circuit 19 is input to the integration circuit 20, where the average value of the video signal for one frame is obtained. This one
Average value of video signal for frame and automatic gain setting voltage V2
Are compared by the comparison circuit 21, and the difference is amplified. The amplified automatic gain adjustment (AGC) voltage V3 and the manual gain adjustment voltage V4 are switched by the switching circuit 22 and output as the gain adjustment voltage V1.

The video signal whose gain has been adjusted as described above is input to the multiplier 23, where it is multiplied by the dynamic range control voltage V5 in order to adjust the display range, that is, to adjust the dynamic range. Then, the video signal is
The data is input to the frame memory 24, where the time conversion and the addition of the synchronizing signal corresponding to the TV scanning are performed and supplied to the TV monitor. Thus, the tomographic image is displayed on the TV monitor 26.

By the way, as a method of reading out the electric signal from the ultrasonic imaging element 6, a double-line reading method (two-line reading method in this example) as shown in FIGS. 5 and 6 can be used.

According to the method shown in FIG. 5, there is an advantage that the complete image time can be reduced. If a pulse compression function using a chirp wave as shown in Japanese Patent Application No. 61-245777 is incorporated into this imaging method, the duration of the transmitted chirp wave is relatively long, so the double-line readout described above is performed. Depending on the method, it is necessary to take a long switching time. When performing double-line reading as shown in FIG. 5, it is necessary to relax the degree of convergence of the linear array transducer of the transmitter 3 in the direction of arrow X in FIG. 2 so as to extend over two lines. Incidentally, if the ultrasonic wave beam for transmission is irradiated obliquely, it may be uniformly irradiated on the tomographic plane 4, but it is necessary to suppress the ghost echo due to irregular reflection and multiple reflection. As described above, the resolution in the direction of the arrow X in FIG. 2 is obtained by multiplying the convergence distribution of the ultrasonic lens 5 by the directivity of the transmission beam.
In this embodiment, the transmission beam is focused on the detection line for the purpose of improving the resolution.

According to the system shown in FIG. 6, there is an advantage that the switching speed of the multiplexers 91 and 92 can be reduced.

Next, a second embodiment of the present invention will be described. Since ultrasonic waves are coherent waves, speckle patterns are likely to occur. Although the above-mentioned speckle pattern is considerably reduced by transmitting a pulse, it cannot be completely removed.

FIG. 7 is a view showing a second embodiment for removing the above-mentioned drawbacks and further improving the resolution. 73 is the first
This is an ultrasonic transmitter similar to the ultrasonic transmitter 3 of the embodiment.
74 is an imaging lens, and 75 is an ultrasonic imaging element.

Each time imaging of one screen is completed, imaging is performed while moving the imaging lens 74 and the imaging element 75 in the direction of the arrow. At this time, the imaging surface of the imaging element 75 is set to a position where an image is formed each time. The plurality of images obtained in this manner are amplified by the amplifier 76 and added and averaged by the accumulator 78 via the enhancement circuit 77. The enhancement circuit 77 is for correcting "blurring" caused by the cumulative addition.

According to this embodiment, the speckle pattern is removed, the resolution is improved, and the S / N ratio is improved. The scanning by moving the imaging lens 74 and the imaging element 75 may be a two-dimensional scanning in order to increase the number of times of imaging. Instead of moving and scanning the imaging lens 74 and the imaging device 75, a plurality of sets of the imaging lens 74 and the imaging device 75 are prepared in advance as shown in FIG. 8, and these are switched and used. Is also good.

It should be noted that the present invention is not limited to the above embodiments, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

〔The invention's effect〕

According to the present invention, an ultrasonic pulse arriving with a time difference from a tomographic plane is formed at a predetermined timing on an ultrasonic imaging element by an ultrasonic lens, and the formed tomographic image is synchronized with the imaging timing. Since the signals are converted into electric signals and sequentially taken out, a tomographic image whose resolution is dramatically improved as compared with the conventional device can be accurately obtained by a device having a simple circuit configuration.

Since the resolution in the direction of the arrow X on the imaging section is related to the directivity of the transmission beam, the resolution can be further increased according to the embodiment having the means for selecting a linear array transducer.

Also, since the reaching distance of the ultrasonic pulse and its reflected wave is different in each part of the tomographic plane, there is a concern that a difference may occur in sensitivity due to attenuation in the subject. If this is followed, the problem can be avoided.

[Brief description of the drawings]

FIGS. 1 to 4 show a first embodiment of the present invention.
2 is a perspective view showing a relationship between a transmitter and a tomographic plane, FIG. 3 is a perspective view showing a configuration of an ultrasonic imaging element, and FIG. 4 is an ultrasonic imaging apparatus. It is a figure which shows the means which takes out an electric signal from an element. FIGS. 5 and 6 are diagrams showing modified examples of the means for extracting an electric signal from the ultrasonic imaging element in the first embodiment. FIG. 7 is a diagram showing a configuration of a main part in a second embodiment of the present invention, and FIG.
It is a figure showing the modification of an example. A: probe, B: apparatus body, C: subject, 3:
Transmitter, 4 ... tomographic plane, 5 ... ultrasonic lens, 6 ... ultrasonic imaging element.

Claims (3)

(57) [Claims] 1. A transmitter arranged so as to irradiate an ultrasonic pulse obliquely to a tomographic plane of a subject to be detected, and a transmitter for transmitting one ultrasonic signal to one detection line on the tomographic plane. An ultrasonic lens arranged so as to form a tomographic image by converging a reflected wave from the tomographic surface of an ultrasonic pulse applied in a series, and a reflected wave from the detection line being imaged by the ultrasonic lens And an ultrasonic wave composed of a plurality of elements that output the reflected wave as an electric signal in synchronization with the timing at which the reflected wave from the detection line is imaged in time series by the ultrasonic wave. An image sensor, and control means for moving and controlling the transmission position of the transmitter so as to scan the detection line in a direction substantially orthogonal to the detection line to obtain the tomographic image. Characterized by The ultrasonic diagnostic apparatus. 2. A transmitter comprising: a plurality of linear array vibrators arranged in a direction substantially perpendicular to a detection line in the tomographic plane; and a vibrator to be excited among the plurality of linear array vibrators. And a multiplexer that selects a part of the plurality of linear array transducers for one detection line, and is generated by excitation of the transducer group. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein each of the transducers of the transducer group is sequentially selected such that the ultrasound pulse reaches an arbitrary point on the detection line at substantially the same time. 3. The apparatus according to claim 1, further comprising a correction unit configured to correct the electric signal converted by the ultrasonic imaging element so that a difference does not occur in the sensitivity depending on the reach of the ultrasonic pulse and its reflected wave. Item 7. An ultrasonic diagnostic apparatus according to Item 1.