JPH0471538B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an ultrasonic diagnostic apparatus that reproduces a reflected echo image by amplifying an ultrasound reflected echo in a living body using a preamplifier.

[Technical background of the invention and its problems] In ultrasonic diagnostic equipment, the depth from the body surface of the object to be observed is limited to approximately 20 cm, but it is known that the further away from the body surface, the greater the attenuation of ultrasound waves. There is. The attenuation of this ultrasound is expressed as 0.45 (dB) x (MHz) x d (cm), where the frequency of the ultrasound is (MHz) and the depth from the body surface is d (cm). Therefore, there is a difference of several tens of dB between a large reflected echo near the body surface and a small reflected echo from deep within the body.

For this reason, correction has conventionally been performed to temporally change the gain of the amplifier within one rate so that the magnitude of the reflected echo is uniform regardless of the distance from the body surface. This correction is based on the sensitivity
Time control (Sensitivity Time
Control (hereinafter referred to as STC).

However, since the reflected echo received from the ultrasound transducer is first input to the preamplifier, the preamplifier function is to prevent the preamplifier from becoming saturated even if large reflected echoes near the body surface are input.
In addition, it must be possible to amplify small reflected echoes from deep parts to a sufficient size to distinguish them from noise. Therefore, as long as the gain of the preamplifier is kept constant, it is difficult to fully exhibit the above two contradictory functions.

On the other hand, considering the sensitivity of the ultrasonic probe, if the area of the receiving transducer is the same, within the plane wave propagation sound field, that is, when the distance is short compared to the diameter of the transmitting transducer, (X<<d ² /4λ), The received voltage is almost constant, but in the case of a long distance (X>d ² /4λ),
The receiving voltage will be proportional to the area of the transmitting transducer. However, X is the depth from the body surface, d is the aperture, and λ
is the wavelength.

Therefore, when switching between ultrasonic probes with different transmitting transducer areas (for example, when using a linear electronic scanning probe and a sector scanning probe), or when switching the ultrasonic frequency, reflections from a long distance may occur. The size of the echo will change.

In this way, in order to prevent the preamplifier from becoming saturated and to be able to amplify small reflected echoes so that they can be distinguished from noise, the type of ultrasound probe must also be considered. , so far no countermeasures have been taken.

[Object of the Invention] The present invention was made in view of the above circumstances, and is capable of preventing the occurrence of saturation of the preamplifier, sufficiently amplifying even small reflected echoes, and improving the performance of ultrasonic probes. It is an object of the present invention to provide an ultrasonic diagnostic apparatus that can fully demonstrate the function of a preamplifier and reproduce accurate ultrasonic images even if the types of preamplifiers are different.

[Summary of the invention] The outline of this invention for achieving the above object is as follows:
In an ultrasonic diagnostic apparatus that amplifies in-vivo reflected echoes of ultrasound waves with a preamplifier and reproduces the increased reflected echoes, the gain of the preamplifier is lowered at the beginning of one rate, and then the gain of the preamplifier is increased as time passes. The present invention is characterized in that it has a gain control means that performs control as follows.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diaphragm of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 2 is a characteristic diagram showing changes in preamplifier gain with respect to time during one rate.

In FIG. 1, an ultrasonic probe 1 emits ultrasonic waves to a subject based on selective driving of a pulser 2 and receives reflected echoes thereof. Preamplifier 3
amplifies and outputs the reflected echo signal based on a gain characteristic determined by a control signal S _C from a control circuit 7, which will be described later. The delay circuit 4 provides a delay time for applying polarization and focus to the output of the preamplifier 3 and outputs the output. The adding circuit 5 adds the signals from the simultaneously driven transducers and outputs the result as one ultrasonic signal. The display circuit 6 converts the output from the adder circuit 5 into a video signal for display, and outputs it as an image display signal. The control circuit 7 outputs control signals for the pulser 2, delay circuit 4, adder circuit 5, and display conversion circuit 6, and also outputs the control signal S _C to the preamplifier 3 as a gain control means to control the gain of the preamplifier 3. control.

Here, with reference to FIG. 2, changes in the gain of the preamplifier 3 over time during one rate will be explained. The horizontal axis in FIG. 2 is a time axis, t _R in the diagram indicates the rate period, and t _B in the diagram indicates the blanking period. Further, the vertical axis represents the gain G of the preamplifier in a logarithmic manner. As shown in FIG. 2, the gain G of the preamplifier is reduced at the beginning of one rate period _tB , and has a characteristic of increasing with time. This characteristic is determined by the control signal _SC .

The operation of the ultrasonic diagnostic apparatus configured as above will be explained.

The reflected echo received by the ultrasound probe 1 is
As mentioned above, the echo is large near the body surface, and the deeper the echo is reflected, the smaller it is. The preamplifier 3 to which the reflected echo signal from the ultrasound probe 1 is input performs amplification based on the gain characteristics shown in FIG. Therefore, the amplification factor is low for reflected echoes near the body surface, that is, reflected echoes that are input at the beginning of one rate, and are amplified by increasing the amplification factor over time. Therefore, the preamplifier 3 does not reach a saturated state, and even small reflected echoes can be amplified to be distinguishable from noise.

In this way, by controlling the gain of the preamplifier 3 separately from the STC, it is possible to fully demonstrate its function as a preamplifier.

Next, in order to ensure diagnostic accuracy, a case will be described in which two different types of ultrasound probes are used by switching the ultrasound probes. For example, when switching between linear electronic scanning type and sector scanning type ultrasonic pleats, the aperture of the linear electronic scanning type transmitting transducer is generally smaller than that of the sector scanning type. ing. Therefore, as described above, in a sector-scanning ultrasonic probe with a large diameter, the received voltage becomes high. Therefore, if the same gain characteristics are used, there is a risk that the preamplifier will reach saturation when amplifying the reflected echo obtained by the sector-scanning ultrasonic probe.

Therefore, in such a case, as shown in FIG. 3, the gain characteristics of the preamplifier may be switched as shown in a and b. That is, when using the linear electronic scanning type, gain characteristic a is used, and when using the sector scanning type, characteristic b, which is lower than gain characteristic a, is used. In this manner, when using ultrasonic probes of different diameters, the function of the preamplifier 3 is sufficiently guaranteed by switching the gain characteristics of the preamplifier.

It goes without saying that the present invention is not limited to the embodiments described above, and includes various modifications within the scope of the gist of the invention. For example, the charge/discharge characteristics of a Miller integrating circuit or CR circuit can be used as a circuit for creating the control signal S _C that determines the gain characteristics, and the change in gain characteristics can be controlled by changing the time constant. It can also be made compatible. In addition, this invention concerns only the gain characteristics during the rate period t _R , and the blanking period t _B
Needless to say, the characteristics of this are freedom. In the embodiment, the gain G is changed from the maximum value to the minimum value during the blanking period _tB in order to prevent the generation of noise.

[Effects of the Invention] As explained above, according to the present invention, it is possible to prevent saturation in the preamplifier regardless of the size of the reflected echo, and to amplify even small reflected echoes so that they can be distinguished from noise. Accordingly, it is possible to provide an ultrasonic diagnostic apparatus that can reproduce accurate ultrasonic images.

Moreover, even if ultrasound probes are used in combination with transmitting transducers of different diameters, the preamplifier function is guaranteed and accurate ultrasound images can always be reproduced.

[Brief explanation of the drawing]

Fig. 1 shows a block diaphragm of an ultrasonic diagnostic apparatus according to the present invention, Fig. 2 is a characteristic diagram showing changes in preamplifier gain with respect to time during one rate, and Fig. 3 shows one rate when two types of probes are used. FIG. 1... Ultrasonic probe, 2... Pulsar, 3...
...Preamplifier, 4...Delay circuit, 5...Addition circuit, 6...Display switching circuit, 7...Control circuit (gain control means).

Claims (1)

[Claims] 1 In an ultrasound diagnostic device that can use multiple ultrasound probes with different transducer apertures, and that reproduces the reflected echo image by amplifying in-vivo reflection echoes caused by transmitted ultrasound from these ultrasound probes with a preamplifier, one rate At the beginning of the process, the gain of the preamplifier is lowered, and then the gain of the preamplifier is increased over time.The gain characteristics are varied according to the diameter of the transmitting transducer, which varies with the ultrasonic probe. An ultrasonic diagnostic apparatus characterized by having a gain control means for performing control.