JPH05237103A - Ultrasonic diagnostic device - Google Patents

Abstract

PURPOSE:To realize the ultrasonic diagnostic device for obtaining the best image by varying a frequency of an output signal in accordance with depth in a D mode. CONSTITUTION:In the ultrasonic diagnostic device having a B mode system having a dynamic filter 3, and a Doppler system for executing a synchronous detection for using a local oscillation signal from a local oscillator as a reference signal, this device is provided with a chirp oscillator 14 for generating a chirp signal as a local oscillator for supplying a reference signal for detecting a Doppler signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus,
In particular, the present invention relates to an ultrasonic diagnostic apparatus with improved Doppler mode.

[0002]

2. Description of the Related Art When ultrasonic waves are radiated into a subject, the ultrasonic waves are transmitted through a living tissue as a medium, but there is a difference in acoustic impedance from tissues such as organs and surrounding tissues such as lesions. A part of the transmitted ultrasonic wave is reflected back from. An apparatus for processing the returned ultrasonic waves and displaying an image is an ultrasonic diagnostic apparatus.

Although there are many modes for displaying images on the ultrasonic diagnostic apparatus, B mode and Doppler mode (hereinafter referred to as D mode) are usually used. In the B mode, a subject is scanned with an ultrasonic beam, an echo signal from the subject is reconstructed and displayed based on the position of the ultrasonic probe and the ultrasonic beam direction, and a two-dimensional tomographic image is obtained. It is a method. Also, the echo reflected from a moving object such as blood flow in the subject is frequency-shifted due to the movement of the ultrasonic ray in the direction of the sound ray. The D mode is a method of measuring the speed of the direction and the moving direction.

Generally, when an ultrasonic wave signal is transmitted to the inside of a subject and its echo is received, the sound transmission of the human body is extremely dispersive, and in the case of wide band transmission, echo is generated in the shallow and deep areas. The spectrum is different, and the higher frequencies are strongly attenuated in the deeper parts, so the overall frequency shifts to the lower frequencies. Therefore, B
In the mode, a dynamic filter is used so that the frequency characteristic of the received signal and the frequency characteristic of the receiver match in order to eliminate the influence of the shift due to the difference in depth.
Further, since a single frequency is used as the reference frequency for detection in the D mode, a fixed frequency filter is used as the filter.

FIG. 3 shows a circuit example of a conventional ultrasonic diagnostic apparatus receiving circuit. In the figure, reference numeral 1 is a probe for transmitting and receiving ultrasonic waves, and 2 is a beamformer for phasing and adding the received signals forming the sound ray into a serial signal. Reference numeral 3 is a dynamic filter input to a B-mode circuit for B-mode display, which shifts the center frequency of the filtering region according to the echo depth to prevent the sensitivity from being lowered. This output is detected by the detector 4, converted into a television mode signal by the DSC 5, and displayed on the CRT 6.

On the other hand, in the D mode, it is filtered by the fixed frequency band filter 7 and input to the mixers 8A and 8B. The local oscillator 9 oscillates a local oscillation signal having a fixed frequency of frequency f ₀ and is input to the mixer 8A and the 90 ° phase shifter 10. The 90 ° phase shifter 10 phase-shifts the local oscillation signal by 90 ° and inputs it to the mixer 8B. The mixer 8A outputs a signal having a frequency f ₀ , for example, Asin ω ₀ as a reference signal, and outputs the I signal, and the mixer 8B outputs Acos ω ₀ t as a reference signal and outputs a Q signal. From the I signal and the Q signal, the Doppler calculation unit 11
Then, the Doppler shift frequency is calculated, the velocity v of the reflector is obtained, converted into a television mode signal by the DSC 5, and displayed on the CRT 6. Similarly, in the CF calculation unit 12, I
The velocity v of the reflector and the dispersion value σ of the velocity are obtained from the signal and the Q signal, and similarly, color display is performed on the CRT 6 via the DSC 5. The system controller 13 gives a rate pulse to the beamformer 2 and controls the operation of other parts.

[0007]

By the way, in order to increase the sensitivity of Doppler in the deep portion, the local oscillation signal having a low center frequency is used as the reference frequency for detection. On the other hand, in the near area, a sharper narrow band Doppler signal can be obtained by detecting using a high frequency reference frequency. However, in the D mode, a single frequency is used as the reference frequency for detection as described above.

The present invention has been made in view of the above points, and an object thereof is to realize an ultrasonic diagnostic apparatus in D mode, in which the frequency of an output signal is changed according to the depth to obtain the best image. Especially.

[0009]

SUMMARY OF THE INVENTION The present invention which solves the above-mentioned problems includes a B-mode system having a dynamic filter,
In an ultrasonic diagnostic apparatus having a Doppler system that performs synchronous detection using a local oscillation signal from a local oscillator as a reference signal,
In synchronization with the rate pulse from the system controller, when the depth of the reflector is small, the frequency is low, and when the depth is large, a local oscillation signal that is a chirp signal with a high frequency is generated to generate the first mixer and the second mixer. It is characterized in that it is provided with a chirp oscillator for performing synchronous detection.

[0010]

The chirp oscillator generates the chirp signal synchronized with the rate pulse output from the system controller, supplies the reference signal to the first mixer and the second mixer to perform synchronous detection, and In the D mode of the diagnostic apparatus, a Doppler signal having a frequency according to depth is obtained.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals. In the figure, 14 is a chirp oscillator that receives a rate pulse from the system controller 13 and that synchronizes with the rate pulse and changes the oscillation frequency according to the depth.
The oscillation waveform of the chirp oscillator 14 is as shown in FIG.

In FIG. 2, reference numeral 21 is a rate pulse input from the system controller 13 to the beamformer 2 and the chirp oscillator 14. 22 is a rate pulse 21
This is an oscillation frequency waveform in which the frequency sweeps from 3.5MHz to 2.5MHz in synchronism with. Since the echo is reflected from a deeper place as it goes away from the rate pulse 21, the oscillation frequency is lowered.

Next, the operation of the embodiment configured as described above will be described. Since the B-mode system is the same as the conventional circuit shown in FIG. 3, the description thereof will be omitted. The received signals that have been phased and added by the beam former 2 are input to the mixers 8A and 8B. The chirp oscillator 14 oscillates a chirp signal that sweeps linearly from 3.5 MHz to 2.5 MHz as shown in FIG. The chirp signal is input to the mixer 8A as a reference signal to detect the received signal and output the I signal. Also, the chirp signal is 90 °
The signals are input to the phase shifter 10 and phase-shifted by 90 °, and then input to the mixer 8B as a reference signal, and the received signal is detected and a Q signal is output. This output signal is calculated by the Doppler calculation unit 11 as described in the conventional example of FIG.
Is required. Further, in the CF calculation unit 12, the velocity v and the variance value σ of the velocity are obtained and displayed on the CRT 6 via the DSC 5. As for the display of the output of the CF calculation unit 12, the color display is changed according to the output v, and the length on the screen is changed according to the magnitude of σ.

As described above, the chirp oscillator 14
Oscillates the local oscillation frequency in synchronization with the rate pulse, and oscillates a high frequency at a shallow place near the transmission pulse and a low frequency at a deep place far from the transmission pulse,
Since the sensitivity is increased for a long-distance target and the sensitivity is high for a short-distance target because the distance is short, the resolution for low flow velocity is improved and a beautiful spectrum can be created.

The B-mode dynamic filter 3
In synchronism with (tracking of the bandpass filter), that is, when the center frequency of the B-mode dynamic filter 3 and the local oscillation frequency for D-mode detection are matched and shifted with depth, the B-mode and the D-mode are shifted. It becomes easier to deal with.

[0017]

As described in detail above, according to the present invention, it becomes possible to obtain the best image by changing the frequency of the output signal according to the depth in the D mode. The effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an oscillation frequency waveform of the chirp oscillator in the D mode of the present invention.

FIG. 3 is a block diagram of a conventional ultrasonic diagnostic apparatus having B mode and D mode.

[Explanation of symbols]

 1 probe 5 DSC 6 CRT 8A, 8B mixer 10 90 ° phase shifter 11 Doppler arithmetic unit 12 CF arithmetic unit 13 system controller 14 chirp oscillator

Claims (1)

[Claims] 1. B with a dynamic filter (3)
In an ultrasonic diagnostic apparatus having a mode system and a Doppler system for performing synchronous detection using a local oscillation signal from a local oscillator as a reference signal, the depth of a reflector is small in synchronization with a rate pulse from a system controller (13). When the frequency is low and when the depth is large, a local oscillation signal that is a high frequency chirp signal is generated to cause the first mixer (8A) and the second mixer (8B) to perform synchronous detection (14). )
An ultrasonic diagnostic apparatus comprising: