JPH02177948A - Ultrasonic diagnostic device - Google Patents

Abstract

PURPOSE:To prevent a false image from being generated by plurally scanning a distant object and to obtain the ultrasonic picture of satisfactory resolution over a wide range from a short distance to a long distance by providing a level shift circuit, with which the threshold level of an echo signal is highly changed on time proportionally with the observed distance. CONSTITUTION:The output of a detection circuit 26 is supplied to one input end of an adder 27a in a level shift circuit 27 and -Vcc is supplied through the drain-source route of an FET 27b and resistor 27c to the other input end. Then, the output of the adder 27a is supplied to a diode 27b. A necessary reference signal is supplied to the gate of the FET 27b and a resistance value between the drain and source of the FET 27b is controlled. Then, a level shift signal is obtained so that the potential of a point A can be changed with the passage of time. Next, the level shift signal is mixed with an echo signal from the detection circuit 26 in the adder 27a and after that, namely, the echo signal is cut by the threshold level which is highly changed with the passage of time. Finally, a signal of a fixed voltage or below is cut from the output by the diode 27d. Thus, the echo signal suppressed with the noise component of the long distance or a weak signal is obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an ultrasonic diagnostic apparatus.

[Conventional technology]

As a conventional ultrasonic diagnostic device, for example, Japanese Patent Application Laid-Open No. 57-18
As disclosed in Japanese Patent No. 2186, by performing STC correction to correct long-distance attenuation of echo signals and dynamic range correction to emphasize contrast, images at long distances can be made clearer. There are some that are displayed.

[Problem to be solved by the invention]

However, as shown in FIG. 5, the width of the ultrasonic beam 2 emitted from the ultrasonic transducer l increases as it goes farther from the focal point f, and the sound pressure on the central axis increases as shown in FIG. As shown, it reaches a maximum at the focal position f, and decreases before and after that. Note that the sound pressure locus shown by the solid line in FIG. 5 indicates a sound pressure of 16 dB from the central axis sound pressure. Therefore, when objects 3t' at different positions are scanned as shown in FIGS. 7A-C, their ultrasonic images are respectively shown in FIGS. 8A-8.
It becomes as shown in C. That is, when the object 3 is near the focal position as shown in FIG. 7A, a clear ultrasound image 4 is obtained as shown in FIG.
As shown in Figures B and C, if the position is far from the focal point, it will be scanned multiple times by different beams, so Figure 8B
, C, a pseudo image 5 is displayed as a flow of ultrasound images, resulting in a decrease in resolution at a distance.

Such a decrease in resolution at a distance is caused especially when the opening area of the ultrasonic transducer 9 is small, such as the miniature probe 8 inserted through the forceps channel 7 of the endoscope 6 as shown in FIG. This is noticeable when the beam cannot be focused at a distance.

However, such a decrease in resolution at a long distance cannot be resolved with the ultrasonic diagnostic device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-182186, and this conventional device is designed to emphasize echo signals at a far distance. Therefore, there is a problem in that the false image is displayed more clearly on the monitor, leading to misdiagnosis.

This invention was made by focusing on these conventional problems, and effectively prevents the occurrence of false images caused by multiple scanning of distant objects, and provides ultra-high resolution images with good resolution from short to long distances. It is an object of the present invention to provide an ultrasonic diagnostic apparatus appropriately configured to obtain a sonic image.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an ultrasonic diagnostic apparatus that projects ultrasound onto a subject and obtains an ultrasound image of the subject based on the echo signal S. A level shift circuit is provided in which the threshold level of the echo signal changes highly over time in proportion to the observation distance.

[For production]

Here, the level shift circuit cuts the echo signal at a threshold level that changes highly over time in proportion to the observation distance, thereby artificially reducing the echo signal scanned by the ultrasonic beam so that the beam width does not widen even at a distance. It has the effect of obtaining.

That is, as shown in FIG. 1A, the isobaric attenuation rate characteristics from the central axis sound pressure of the ultrasonic beam emitted from the ultrasonic transducer 11 are different when the same object is on the central axis and when the same object is on the central axis. The echo signal is stronger when it is on the central axis and becomes weaker as it moves away from the center, so the width becomes wider as it goes farther away. In FIG. 1A, the solid line indicates the beam profile at a central axis sound pressure of "fy・r -18 dB, the - dotted diagonal line indicates the beam profile at -12 dB, and the double dotted line indicates the beam profile at -16 dB. Here, , the beam profile in which the beam width at each position x, y, and z from the ultrasonic transducer 11 is approximately a is 18 dB at distance X and 11 dB at distance #y.
6dB.

At distance 2, it is -6 dB. Therefore, if the beam width is arbitrarily set and the low-level signals in the echo signal are suppressed as the distance from the ultrasonic transducer 11 increases, the beam can be narrowed down as shown in FIG. 1B. This makes it possible to perform dynamic focusing from short distances to long distances, making it possible to obtain ultrasonic images with good resolution.

〔Example〕

FIG. 2 shows an embodiment of the present invention.

As shown in FIG. 9, this embodiment is applicable to a miniature probe used through a forceps channel of an endoscope, etc., and a transmission trigger is sent from the control circuit 2o to the transmission circuit 21. For example, frequency 5MHz
, a transmission pulse with a transmission voltage of 100 V is sent to the ultrasonic transducer 22.
This causes the ultrasonic transducer 22 to project an ultrasonic wave with a frequency of 5 Ml (z) onto the subject (not shown). The reflected ultrasonic wave is received by the ultrasonic transducer 22 and converted into an electrical signal, and the echo signal is amplified by, for example, 60 dB in the amplifier circuit 23 and converted into a log signal.
The signal is supplied to an amplifier 24, where it is logarithmically compressed and the signal is emphasized.

Here, the ultrasonic waves transmitted and received by the ultrasonic transducer 22 are transmitted and received over time (
Therefore, the obtained echo signal on the center axis attenuates as the distance from the transducer surface increases, as shown in FIG. For this reason, if this echo signal is divided into, for example, 64 gradations depending on the signal level and displayed as an image, the image at a deep position will become very faint. Therefore, in this embodiment, the STC circuit 25 corrects the attenuation bone by increasing the gain according to the distance so that the sound pressure on the center axis (solid line) in FIG. 6 becomes constant as shown by the broken line.

In this way, the echo signal subjected to STC correction is supplied to the detection circuit 26, and a signal with a voltage of, for example, 0.6 V or higher is detected to obtain an echo signal as shown in FIG. 3A. The signal is supplied to the level shift circuit 27.

The level shift circuit 27 includes an adder 27a, a PET
27b.

The adder 27a is configured with a resistor 27c and a diode 27d, and the output of the detection circuit 26 is supplied to one input terminal of the adder 27a, and the PI! The output of this adder 27a is provided to diode 27d by providing -Vcc via the drain-source path of T 27b and resistor 27c.

Further, a required reference signal is supplied to the gate of FIT 27b, thereby causing Fl! ? By controlling the resistance value between the drain and source of 27b, a level shift signal is obtained in which the potential at point A changes with time as shown in FIG.
After mixing this level shift signal and the echo signal from the detection circuit 26 in the adder 27a, that is, after cutting the echo signal at a threshold level that increases with time, a signal below a certain voltage is output from the adder 27d. Make sure to cut it with. In this way, an echo signal with suppressed long-distance noise components and weak signals as shown in FIG. 3B is obtained.

Note that the reference signal supplied to the gate of the PHT 27b is a signal on the central axis depending on the distance from the transducer surface so that the width of the ultrasonic beam is approximately equal, as explained in Fig. 1A and B. It is determined by how many dB below the signal is to be cut.

The output of the level shift circuit 27 is supplied to a dynamic range variable circuit 28. Dynamic range variable circuit 28
are operational amplifier 28a1 load resistor 28b, FET2
8c and a feedback load resistor 28d, the output of the level shift circuit 27 is supplied to the non-inverting input terminal of the operational amplifier 28a, and the inverting input terminal is grounded via the load resistor 28b, as well as the feedback load resistor 28d and the FET 28c.
The output terminal of the operational amplifier 28a is connected to the output terminal of the operational amplifier 28a through the source-drain path of the amplifier 28a. Further, a required reference signal similar to the reference signal in the level shift circuit 27 is supplied to the gate of the PET 28c, and this controls the feedback resistance of the operational amplifier 28a, so that the amplification of the distant signal is increased. Make it. In this way, the output of the level shift circuit 27 is amplified by the dynamic range variable circuit 28 by increasing the degree of amplification of the distant signal to compensate for the signal cut in the level shift circuit 27. Obtain an echo signal as shown in C.

The output of the dynamic range variable circuit 28 is converted into a digital signal of, for example, 64 gradations by an A/D converter 29, and then
Digital scan converters (D, S,
C) 30, and the data stored in S and C 30 is converted into a video signal by a D/^ converter 31 to display an ultrasound image on a monitor (not shown).

In this way, according to this embodiment, the far-distance signal is suppressed and amplified from the detected echo signal, so that the beam width of the ultrasonic wave projected from the ultrasonic transducer 22 can be changed from the short-distance signal to the detected echo signal. It is possible to equivalently maintain a predetermined width over a long distance, making dynamic focusing possible. Therefore, it is possible to effectively prevent the generation of false images due to multiple scans of distant objects, and it is possible to obtain ultrasonic images with good resolution from short distances to long distances.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, the present invention can be effectively applied not only to miniature probes but also to other ultrasonic diagnostic apparatuses, since it can similarly prevent the occurrence of false images due to overlapping of ultrasonic beams on the far side. In addition, dynamic range variable circuit 2
8 is a multiplier or VC^ (Voltage Condenser) that receives the output of the level shift circuit 27 and the reference signal as inputs.
It is also possible to configure the circuit with a troll amplifier (troll amplifier), thereby simplifying the circuit configuration. Furthermore, the level shift circuit 27 is not limited to the stage subsequent to the detection circuit 26, but also extends from the ultrasonic transducer 22 to the A/D converter 29.
It can be provided in any part of the receiving circuit system described above, and the STC circuit 25 and dynamic range variable circuit 28 can also be omitted.

〔Effect of the invention〕

As described above, according to the present invention, since the level shift circuit cuts the echo signal at a threshold level that changes highly over time in proportion to the observation distance, it is possible to eliminate false images caused by multiple scanning of distant objects. This can be effectively prevented, and ultrasonic images with good resolution can be obtained from short distances to long distances.

[Brief explanation of the drawing]

1A and 1B are diagrams for explaining the invention in detail; FIG. 2 is a block diagram showing an embodiment of the invention; FIGS. 3A to 3C are diagrams showing echo signal waveforms of each part; FIG. 4 is a diagram showing an example of a level shift signal in the level shift circuit shown in FIG. 2, and FIGS. 5 to 9 are diagrams for explaining conventional techniques. 11... Ultrasonic transducer 20... Control circuit 21
... Transmission circuit 22 ... Ultrasonic transducer 23
... Amplification circuit 24 ... Log amplifier 25
...STC circuit 26...Detection circuit 27.
...Level shift circuit 28...Dynamic range variable circuit 29...A/
D converter 30...D, S, C31...D/
A converter Fig. 3 Fig. 7 Fig. 8

Claims (1)

[Claims] 1. In an ultrasonic diagnostic apparatus that projects ultrasound onto a subject and obtains an ultrasound image of the subject based on the echo signal, the threshold level of the echo signal changes over time in proportion to the observation distance. An ultrasonic diagnostic device characterized by being provided with a level shift circuit that changes highly.