JPS60259251A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an ultrasonic diagnostic apparatus equipped with a bandpass filter that corrects a shift in ultrasonic frequency due to the depth of a reflected object.

[Technical background of the invention and its problems] The operation of an ultrasonic diagnostic apparatus including a conventional bandpass filter will be explained with reference to FIG.

The ultrasonic generation command signal from the control circuit 10 is sent to the transmission delay section 3. This transmission delay section 3 is
] - Each pulse for ultrasonic transmission having a predetermined delay time for focusing the transmitted ultrasonic waves is supplied to the pulser 2 according to a command signal from the pulse circuit 10. In accordance with this ultrasonic transmission pulse, the pulser 2 applies a high-pressure pulse to a group of vibrating elements (not shown) within the ultrasonic probe 1. Ultrasonic waves are transmitted from the vibrator to which this high-voltage pulse is applied, are focused, and enter the body of the subject. Then, it is reflected by each tissue within the subject and is received again by the ultrasound probe 1 as an ultrasound echo.

The received ultrasonic echo is converted into an electrical signal by the same group of transducers as used when transmitting in this ultrasonic probe 1,
The signal passes through a limiter (not shown) for removing high voltage pulses and is amplified by a preamplifier 4. This amplified electrical signal is input to a receiving delay section 5 which provides a delay time opposite to that for transmitting, and is combined into one signal.

This synthesized electrical signal is input to a filter 6, and the frequency shift of this electrical signal due to the depth within the subject's body at which the ultrasound echo is reflected is corrected. The electrical signal that has been corrected by the filter 6 and whose frequency band has been optimized is amplified and detected by the receiver 7, and the envelope component of the electrical signal containing ultrasound image information is extracted. Digital processing such as the following is performed, and the ultrasound image is displayed on the display unit (Brown) display 9.

Next, the operation of the filter 6 will be explained.

The frequency spectrum of the transmitted ultrasonic wave is shown in Figure 2 (a).
Shown below. In the subject's body, for example, O
,' Attenuation of ultrasonic waves occurs at 45 dB/MHz -cm, so the deeper the received ultrasonic echo, the higher the frequency (the lower the level). This is shown in the frequency spectrum as shown in Figure 2 (b )become that way.

The peak frequency of the ultrasonic echo spectrum obtained from a deep region moves to a lower frequency, narrowing the band and lowering the level. Therefore, if the electrical signals of the ultrasonic echoes are visualized as they are in the frequency band of the shallow region, the signal-to-noise ratio of the deep region cannot be obtained, and only extremely low-quality images can be obtained.

The filter 6t is intended to improve this, and the electrical signals of the ultrasonic echoes reflected from deep parts are filtered through a band-pass filter with a low center frequency and a narrow band. Correction is performed to optimize the frequency band.

In other words, by using a wide band for electrical signals of ultrasound echoes obtained from shallow parts of the subject's body, high distance resolution is maintained, while for electrical signals of ultrasound echoes obtained from deep parts of the subject's body, it is shifted. By limiting the signal band to a narrow band, the SN is improved and even weak electrical signals of ultrasonic echoes are captured.

The II structure of this bandpass filter is shown in Figure 3 (k
) and the multistage OR shown in (1) of the same figure.
A filter can be considered, but it is difficult to use a C filter because when the peak frequency is varied over a wide range, for example from 2MH2 to 15MH7, the matching impedance will be significantly different and the characteristics will be significantly disturbed, such as large ripples occurring. , OR filters are commonly used. Due to its characteristics, this OR filter does not require strict matching, but even if it is configured in multiple stages, the Q value will not be more than 0.5, and it will not be able to handle narrow-band echoes obtained from deep parts. A sufficient filter effect cannot be expected. Therefore, as shown in FIG. 4, a buffer amplifier or the like is inserted between the stages, and a multi-stage configuration is used.

Here, the CR filter f is a bypass filter, and sets the lower limit of the frequency of the electrical signal that passes through this bandpass filter. The OR filter 9 is a low-pass filter, and sets the upper limit of the frequency of the electrical signal that passes through this band-pass filter.

d between these two filters is a buffer amplifier consisting of a common emitter and a 1-mitsuta follower, which increases the impedance on the input side (and reduces the impedance on the output side) to enhance the filter effect and reduce gain loss. Correct. e is a buffer composed of a small emitter lower, and like the buffer amplifier d, the filter effect is enhanced by increasing the impedance on the input side.

The transfer function H(ω) of the circuit shown in FIG. 4 is expressed by equation 3-1.

H(ω> =Kv − [R1/(R1+1/jωc1)
]・"(1/jωC2)/ (R2+1/j(1)c2>]...3-1However, ω-
2πf, j−j=−1 1<v: Gain of amplifier.

As shown in Equation 3-1, the circuit in Figure 4 can correct the gain loss due to the overlap between the bypass filter section in the second term and the low-pass filter section in the third term using the KV in the first term, so the number of OR filter stages can be reduced. Even if it is increased, the gain will not be reduced. However, when this number of stages is increased, the circuit scale increases, which poses a practical problem.

OBJECT OF THE INVENTION] An object of the present invention is to provide an ultrasonic diagnostic apparatus in which a bandpass filter is easily configured on a small scale.

F. Summary of the Invention] To achieve the above object, the present invention is an ultrasonic device that transmits ultrasonic waves to a subject, receives ultrasonic echoes from inside the subject, and converts the ultrasonic echoes into electrical signals. a sonic probe, a filter that changes the transmission characteristics of this electrical signal over time and corrects the frequency shift of the reflected ultrasound echo due to the depth within the subject, and processes the electrical signal that has been corrected by this filter. and a display for displaying an image, wherein the filter includes a base grounded amplifier or a grounded amplifier.

[Embodiment of the Invention] FIG. 5 shows an embodiment of a band-pass filter circuit used in the ultrasonic diagnostic apparatus of the present invention. By providing a common base amplifier between the bypass filter f and the low-pass filter 9, the conventional buffer amplifier d shown in FIG. 4 can be made simple and small-scale.

The transfer function of the circuit of this embodiment is shown by equation 3-2.

H(ω)=R2/R1・[R1/(R1+ 1/jω
C1)]・(1/jωC2)/(R2+ 1/jω
C2)...3-2 (however, ω-2πf j-j-~1) As can be seen by comparing with the conventional transfer function equation 3-1, the cutoff frequency fc1=1/ This is equivalent to inserting an amplifier with a high input impedance and low output impedance with a gain of Kv = R2/R1 between a bypass filter of 2πC1R1 and a low-pass filter with a cutoff frequency of fc2 = 1/2πC2R2, and the function is the same as the conventional one. Example (equivalent to Figure 4).

In addition, since there are fewer components, a multi-stage configuration can be made more compact than conventional ones, and since it uses a common base amplifier compared to conventional examples, stable wide area operation of 10 MH2 or more is possible. becomes. Therefore, it is possible to achieve miniaturization and high performance of the ultrasonic diagnostic apparatus.

The transmission frequency band of this bandpass filter can be adjusted without taking into account impedance mismatch, for example, by using variable capacitance diodes for CI and C2 and changing the capacitance value depending on the depth, or by changing the capacitance value depending on the depth of R1, C2, This can be easily achieved by using a voltage controlled resistor and changing the resistance value depending on the depth.

The operation of the ultrasonic diagnostic apparatus when the bandpass filter of this embodiment is applied is the same as the operation of the ultrasonic diagnostic apparatus using the filter described in the conventional example, and will therefore be omitted.

Furthermore, the present invention is not limited to this one embodiment; for example, instead of using a common base amplifier using bipolar transistors, it is also possible to use a common gate amplifier using field effect transistors.

[Effects of the Invention] According to the present invention, a bandpass filter using a multi-stage CR circuit can be constructed on a small scale, and the operating range can be widened.

[Brief explanation of drawings]

Figure 1 is a block diagram of the ultrasonic diagnostic device, Figure 2 (a)
is the frequency spectrum of the ultrasonic pulse for transmission, the same figure (b
) is the frequency spectrum showing the attenuation due to the depth of reflection of the ultrasound echo inside the subject's body, Figure 3 <a> is the circuit diagram of the multi-stage C filter, and Figure 3 (b) is the circuit diagram of the multi-stage OR filter. , FIG. 4 shows a circuit diagram of a conventional band-pass filter, and FIG. 5 shows a circuit diagram of an embodiment of a band-pass filter used in the ultrasonic diagnostic apparatus of the present invention. 1...Ultrasonic probe 2...Pal 9- 6...Filter 9...Display section (CRT display) f.
... Bypass filter d ... Buffer amplifier q ... Low pass filter e ... Buffer h ... Grounded base amplifier Patent attorney Nori Chika Yu (one idiot) Figure 2 (a) (b) Figure 3 (a) (b) Figure 4 Figure 5

Claims (1)

[Claims] An ultrasound probe that transmits ultrasound waves to a subject, receives ultrasound echoes from inside the subject, and converts these ultrasound echoes into electrical signals, and a characteristic that transmits these electrical signals over time. An ultrasonic diagnostic apparatus comprising: a filter that corrects the frequency shift of an ultrasound echo due to the depth inside a subject; and a display that processes the electrical signal corrected by the filter and displays it as an image. , an ultrasonic diagnostic apparatus characterized in that the filter includes a common base amplifier or a common gate amplifier.