JPH0515535A - Ultrasonic doppler video apparatus - Google Patents

Abstract

PURPOSE:To obtain a blood stream image of high quality by removing clutters efficiently from a limited number of data in an ultrasonic Doppler video apparatus. CONSTITUTION:A blood stream signal containing a clutter component detected with a phase detector 3 is converted into a digital signal with an A/D converter 4. The digital signal is applied to a clutter component approximating device 5a to approximate a clutter signal and the results are subtracted from the original signal with a subtracter 5b to remove the clutter component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler imaging device used for medical purposes.

[0002]

2. Description of the Related Art An ultrasonic Doppler imaging device is capable of displaying blood flow information by utilizing the fact that the echo of an ultrasonic pulse transmitted to the inside of a body causes a Doppler shift to a moving object. As a kind of conventional device, the one shown in FIG. 3 is known. The apparatus shown in FIG. 4 includes a probe 101, a transceiver 102, a phase detector 103, an A /
A D converter 104, an MTI filter 105 using an IIR filter, a blood flow information calculation means 106, and a display 107 are provided. When displaying blood flow information with this device, an ultrasonic pulse is transmitted from the transmitter / receiver 102 into the subject through the probe 101, and the transmitted ultrasonic pulse depends on the tissue inside the subject, blood flow, or the like. When reflected, an echo signal resulting from this reflection is transmitted to the probe 101.
To be detected by. Then, after the echo signal detected by the probe 101 is converted into an electric signal, it is sent to the phase detector 103 via the transceiver 102 so that the phase detector 103 detects the Doppler shift signal from the echo signal. Is becoming Doppler shift signal is A /
The digital signal is converted by the D converter 104 and input to the MTI filter 105. The MTI filter 105 is a kind of low-pass filter, and is capable of attenuating the clutter component having a low frequency component in the echo signal obtained from the tissue or blood vessel wall of the subject and extracting only the blood flow component. The blood flow component extracted by the MTI filter 105 has its velocity, variance, power, etc. calculated by the blood flow information calculation means 106, and the calculation result is displayed on the screen of the display 107.

[0003]

Generally, in an ultrasonic Doppler imaging apparatus, since the blood flow information is displayed two-dimensionally, it is necessary to move the acoustic scanning line. In order to have real-time display, the number of data per sample volume at one place is small, and it is common that the number of data is from several points to ten or more points.

However, although an IIR filter is generally used as the MTI filter, there is a problem in that since the number of data points is small, a transient response appears in the output and accurate blood flow information cannot be obtained.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide an excellent ultrasonic Doppler imaging apparatus capable of obtaining accurate blood flow information.

[0006]

In order to achieve the above object, the present invention provides a transmitting means for transmitting an ultrasonic wave to a subject, a receiving means for receiving an echo signal reflected in the subject, and a receiving signal. A detection means for detecting the Doppler shift signal, and a filter for approximating the clutter component in the Doppler shift signal with a sine wave, and subtracting the approximated signal from the Doppler shift signal. It is configured to remove the clutter component inside.

[0007]

Therefore, according to the present invention, by removing the clutter component from the Doppler shift signal, the blood flow component can be effectively extracted from the signal in which the clutter signal and the blood flow component are mixed. ..

[0008]

1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 1 is a probe, 2 is a transmission / reception circuit, and 3 is a circuit.
Is a phase detector and 4 is an A / D converter. Reference numeral 5 is an MTI filter, which is composed of a clutter component approximator 5a and a subtractor 5b. 6 is a blood flow information calculation means, and 7 is a display.

Next, the operation of the above embodiment will be described.
The electrical pulse generated from the transmitter / receiver circuit 2 is transmitted to the probe 1
Is converted into an ultrasonic pulse and transmitted to a subject (not shown), an echo signal is returned from the subject to the probe 1, converted into an electric signal, and a Doppler shift signal is detected by the phase detector 3, and the A / D is detected. It is converted into a digital signal by the converter 4. Next, the signal digitized by the A / D converter 4 is input to the clutter component approximator 5a and the subtractor 5b of the MTI filter 5.

Next, the operation of the clutter component approximator 5a will be described. The inputs of the clutter component approximator 5a are I1, I
, ..., In and Q1, Q2, ..., Qn. At this time, first using (Equation 1), the input data (I1 + jQ
1), (I2 + jQ2), ..., (In + jQn) phases φ1, φ2, ..., φn.

[0011]

[Equation 1]

Next, the input data (I1
+ JQ1), (I2 + jQ2), ..., (In + jQn)
, An of the vector magnitudes A1, A2, ...

[0013]

[Equation 2]

The values thus obtained are substituted into (equation 3) and (equation 4) of the least squares method, and the phases φ1, φ2, ..., φ
The constants a0 and a1 of the linear function (Equation 5) that approximates n are obtained.

[0015]

[Equation 3]

[0016]

[Equation 4]

[0017]

[Equation 5]

I1, I2, ..., Using the average value Aave of the amplitudes obtained by a0, a1 and (Equation 6)
In and Q1, Q2, ..., Qn can be approximated by (Equation 7) and (Equation 8).

[0019]

[Equation 6]

[0020]

[Equation 7]

[0021]

[Equation 8]

By the way, the input data of the clutter component approximator 5a is a mixture of blood flow and clutter components. Generally, the difference in gain between clutter and blood flow is about 40 dB, and clutter is very large. Further, the Doppler shift signals of clutter and blood flow can be regarded as sine waves in a short time such that n times of I and Q data are obtained. From these facts, the approximate values obtained in (Equation 7) and (Equation 8) represent only a single frequency, that is, it can be considered that this is an approximation of the clutter component in the input component. ..

Therefore, the clutter signal in the input signal can be attenuated and the blood flow signal can be extracted by subtracting the approximate values of I and Q obtained in (Equation 7) and (Equation 8) from the input signal. From this blood flow signal, the blood flow information calculation means 6 calculates the velocity, dispersion, power, etc., and the result of this calculation is displayed on the display 7.

FIG. 2 shows the MTI filter 5 in this embodiment.
3A is an operation explanatory diagram of FIG. 3A, in which FIG. In FIG. 2, 10 is the Doppler shift signal,
11 is the approximate value of the clutter component obtained by the above operation,
Reference numeral 12 is a value obtained by subtracting the clutter approximation value 11 from the Doppler shift signal 10 and indicates the output of the MTI filter 5.

In FIG. 2, the amplitude ratio between the clutter component and the blood flow signal is about 15 dB, and the frequency ratio is about 5 times. At this frequency ratio, the clutter component can be effectively removed even at an amplitude ratio of about 60 dB. Has been confirmed.

Therefore, according to the present embodiment, the clutter can be removed by subtracting the signal approximating the clutter signal from the signal containing the clutter component, and a high-quality blood flow image can be obtained.

Further, in consideration of the principle, the clutter can be removed even if the frequency of the clutter becomes high, so that it is not necessary to switch the cutoff frequency of the filter as in the case of using the conventional filter.

[0028]

As is apparent from the above embodiment, the present invention subtracts the approximate value of the clutter component by the sine wave from the Doppler shift signal, so that no transient frequency component is generated and high-quality blood is generated. You can get a flow image.

Further, since it is not necessary to change the parameter of the filter depending on the height of the frequency of the clutter component, there is no complexity in use.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an ultrasonic Doppler imaging apparatus according to an embodiment of the present invention.

FIG. 2A is a characteristic diagram showing the amplitude of an I signal in this embodiment. FIG. 2B is a characteristic diagram showing the amplitude of a Q signal in this embodiment.

FIG. 3 is a schematic block diagram of a conventional ultrasonic Doppler imaging device.

[Explanation of symbols]

 1 Probe 2 Transceiver 3 Phase Detector 4 Clutter Component Approximator 5 MTI Filter 5a Clutter Component Approximator 5b Subtractor 7 Blood Flow Information Calculator 8 Display

Claims (1)

Claim: What is claimed is: 1. A transmitter for transmitting an ultrasonic wave to a subject, a receiver for receiving an echo signal reflected in the subject, and a detector for detecting a Doppler shift signal from the received signal. An ultrasonic Doppler imaging apparatus comprising: and a filter that approximates a clutter component in the Doppler shift signal with a sine wave and subtracts the approximated signal from the Doppler shift signal.