JPH0515534A - Ultrasonic doppler rheometer - Google Patents

Abstract

PURPOSE:To provide an ultrasonic Doppler rheometer which allows the obtaining of the best sensitivity at all possible depths to be examined. CONSTITUTION:A frequency control section 32 and a variable frequency oscillating section 33 are combined to change a phase detection reference signal 41 according to a timing signal from a timing generating section 31. A phase detection is performed with a phase shifter 5, a multiplier 6 and a low pass filter using the phase detection reference signal 41 as reference signal thereby enabling the obtaining of the best sensitivity at all depths to be examined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler blood flow meter for measuring blood flow in the body and displaying an image by utilizing the Doppler phenomenon of ultrasonic waves in the medical field.

[0002]

2. Description of the Related Art An ultrasonic two-dimensional Doppler blood flow meter is known which utilizes the Doppler phenomenon of ultrasonic waves to correlate blood flow distribution in a living body with colors and superimposes it on a black and white two-dimensional tomographic image. ing. The configuration of the device is shown in FIG.

In FIG. 6, a transmitter 1 receives a timing pulse at a constant time interval from an oscillator 2 and irradiates an ultrasonic pulse from a probe 3 into a living body. The echo of the applied ultrasonic pulse is converted into an electric signal by the probe 3 and amplified by the receiving unit 4. On the other hand, the oscillator 2 outputs the reference signal 21 having a constant frequency, and the phase shifter 5 produces the reference signal 22 obtained by shifting the phase of the reference signal 21 by 90 degrees. The above two reference signals 2
1 and 22 and the echo signal 23 from the receiving unit 4 multiply the multiplier 6
After being mixed by, the signal is filtered by the low-pass filter 7 and the phase component of the frequency of the reference signal is extracted. The processing by the multiplier 6 and the low-pass filter 7 is called phase detection or quadrature detection.

The phase-detected signal is A / D converted by an A / D converter 8 and a clutter component is removed by an MTI filter 9, and then three kinds of blood flow information signals, that is, velocity signals, are output from a complex operation unit 10. 24, distributed signal 25, and power signal 26. The blood flow information signal is input to a digital scan converter (hereinafter abbreviated as DSC) 12 together with the B signal from the envelope detection unit 11, is converted into an appropriate TV signal, is output to a monitor 13, and is two-dimensional. A blood flow image is displayed.

[0005]

However, in the above-mentioned conventional ultrasonic Doppler blood flow meter, as a well-known property of the ultrasonic echo signal, the center frequency of the echo signal from the deep portion is the center of the echo signal from the shallow portion. Despite the characteristic of being lower than the frequency, there is a problem in that the frequency of the reference signal 22 is constant for all the depths of interest, and thus it is not possible to obtain the best sensitivity over all the depths of interest. It was

The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent ultrasonic Doppler blood flow meter which has a high sensitivity over all depths to be examined.

[0007]

In order to achieve the above object, the present invention provides a transmitting means for transmitting an ultrasonic wave in a living body and a receiving means for receiving an echo of a transmitted ultrasonic wave from a reflector in the living body. A timing generating means for generating the timing of transmitting an ultrasonic wave, a variable frequency generating means for generating a reference signal whose frequency changes in synchronization with the transmission of the ultrasonic wave, and a phase detection of an echo signal with reference to the reference signal. And a speed calculating means for calculating the motion speed of the reflector based on the phase information from the phase detecting means.

Further, in addition to the above structure, a speed correction means for correcting the speed according to the change of the reference frequency is provided.

[0009]

Therefore, according to the present invention, the phase detection reference signal is changed according to the depth to be detected, so that the phase detection according to the frequency of the echo signal is performed.

Further, according to the present invention, the blood flow velocity is corrected according to the change in the phase detection reference signal, and the blood flow velocity is displayed accurately.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a first embodiment of the present invention, in which the same parts as in the conventional example are designated by the same reference numerals. In FIG. 1, reference numeral 21 is a timing generation unit that generates a timing for emitting an ultrasonic pulse, and is connected to the transmission unit 1 and the frequency control unit 32. The probe 3 is connected to the transmitter 1 and the receiver 4, and the receiver 4 is connected to the multiplier 6 and the envelope detector 11. Reference numeral 33 is a variable frequency oscillator capable of changing the oscillation frequency, and is connected to the phase shifter 5 and the multiplier 6. Reference numeral 7 is a low-pass filter that removes harmonic components. This output is A / D converted by the A / D converter 8, calculated by the complex calculation unit 10, input to the monitor 13 via the DSC 12, and displayed as an image. To be done.

Next, the operation of the first embodiment will be described. Upon receiving the transmission timing pulse generated by the timing generation unit 31, the frequency control unit 32 generates the frequency control signal 42 for generating the phase detection reference signal 41 matched with the frequency characteristic of the received signal in the variable frequency oscillation unit 33. . The phase detection reference signal 41 is input to the multiplier 6 directly and via the 90-degree phase shifter 5, and is mixed with the reception signal 23 output by the reception unit 4. After that, the low-pass filter 7 removes the harmonic component, so that the phase signal 43 of the signal component having the same frequency as the phase detection reference signal 41 is extracted from the reception signal 23. The phase signal 43 is A / D converted, and then converted into three types of blood flow information signals, that is, a velocity signal 44, a dispersion signal 45, and a power signal 46 by the MTI filter 9 and the complex calculation unit 10. The blood flow information signal, together with the B mode signal, is D
It is converted into an appropriate image signal by the SC 12 and displayed on the monitor 13.

Here, in describing the frequency generated by the variable frequency oscillating unit 33, the frequency characteristic due to the difference in the reflection depth of the ultrasonic echo signal in the living body will be described first. FIG. 2 is a diagram showing the positions of the probe 3 and the subject 34. A is a shallow place, B is an intermediate depth place, and C is a deep place. FIG. 3 is a diagram showing the frequency characteristics of the ultrasonic echo signal at the respective test depths at the locations A, B, and C in FIG. As shown in FIG. 3, it is a well known fact that an ultrasonic signal in a living body has a higher attenuation of a high frequency component as an echo signal from a deeper place.

Therefore, the variable frequency oscillator 33 sets the oscillation frequency to A when receiving the echo signal from the place A, and sets the oscillation frequency to A when receiving the echo signal from the place B, When the echo signal from the location C is being received, the oscillation frequency is set to C. FIG. 4 shows the relationship between the frequency of the phase detection reference signal 41 generated by the variable frequency oscillator 33 and time. In FIG. 4, times a, b, and c correspond to times at which echo signals from the locations A, B, and C are received, respectively.

As described above, according to the first embodiment,
The variable frequency oscillating unit 33 controlled by the frequency control unit 32 generates the phase detection reference signal according to the frequency shift of the echo signal, so that the best sensitivity can be obtained at all the depths to be detected.

FIG. 5 is a block diagram showing the configuration of the second embodiment, which is the same as the configuration of the first embodiment shown in FIG. The operation of the second embodiment will be described. The velocity signal 44 calculated by the complex calculation unit 10 is expressed by the following equation (1) between the velocity signal 44 and the blood flow velocity v in the subject.
Have the relationship shown in.

V = c Δθ / 2ω ₀ T (1) where, v: blood flow velocity of the subject Δθ: velocity signal 44ω ₀ : frequency of phase detection reference signal 41 T: ultrasonic pulse repetition signal c: coefficient The speed correction unit 35 corrects the speed according to the change of the frequency ω ₀ of the phase detection reference signal 41 from the frequency control signal 47 output from the frequency control unit 32 according to the equation (1), and the corrected speed signal 48 to DSC12
Output to.

As described above, according to the second embodiment,
Since the velocity correction unit 35 corrects the velocity in accordance with the change in the frequency ω ₀ of the phase detection reference signal 41, it has an effect of being able to display an accurate blood flow velocity at all test depths.

In the first and second embodiments, the phase detection is performed by the analog method. However, the receiving unit 4 performs A / D conversion of the received signal and the phase detection is performed by the digital method. Is also good.

[0020]

As is apparent from the above embodiment, the present invention is such that the frequency of the phase detection reference signal is changed, and the phase detection reference according to the difference in the frequency characteristic of the echo signal due to the reflection depth is performed. Since the phase detection is performed by the signal, there is an effect that the best sensitivity can be obtained at all depths to be detected.

Further, since the velocity correction unit is provided to correct the relative change in the detected velocity due to the frequency change of the reference signal, there is an effect that the accurate blood flow velocity can be displayed at all the depths to be examined.

[Brief description of drawings]

FIG. 1 is a block diagram showing an ultrasonic Doppler blood flow meter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between a probe and a body part to be examined.

FIG. 3 is a characteristic diagram showing frequency characteristics of an echo for each test site.

FIG. 4 is a characteristic diagram illustrating a time change of a phase detection reference signal frequency according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing an ultrasonic Doppler blood flow meter according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional ultrasonic Doppler blood flow meter.

[Explanation of symbols]

1 transmitter 3 probe 4 receiver 5 phase shifter 6
Multiplier 7 Low-pass filter 8 A / D converter 9 MT
I filter 10 complex operation unit 12 digital scan converter 13 monitor 31 timing generation unit 32
Frequency control unit 33 Variable frequency oscillation unit 35 Speed correction unit

Claims (2)

[Claims] 1. A transmitting means for transmitting ultrasonic waves into a living body,
Receiving means for receiving the echo of the transmitted ultrasonic wave from a reflector in the living body, timing generating means for generating the timing of transmitting the ultrasonic wave, and generating a reference signal whose frequency changes in synchronization with the transmission of the ultrasonic wave. Variable frequency generating means, phase detecting means for phase detecting an echo signal with reference to the reference signal, and speed calculating means for calculating the motion speed of the reflector based on the phase information from the phase detecting means. An ultrasonic Doppler blood flow meter equipped with. 2. The ultrasonic Doppler blood flow meter according to claim 1, further comprising a velocity correction means for performing velocity correction according to a change in the reference frequency.