JP2589894B2 - Ultrasonic Doppler imaging device - Google Patents

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 apparatus used for medical purposes.

[0002]

2. Description of the Related Art An ultrasonic Doppler imaging apparatus is capable of displaying blood flow information by utilizing the fact that the echo of an ultrasonic pulse transmitted into the body causes a Doppler shift with respect to a moving object. FIG. 3 shows a known type of conventional device. The device shown in FIG. 4 includes a probe 101, a transceiver 102, a phase detector 103, an A /
It comprises a D converter 104, an MTI filter 105 using an IIR filter, a blood flow information calculation means 106, and a display 107. When blood flow information is displayed by this device, an ultrasonic pulse is transmitted from the transceiver 102 into the subject via the probe 101, and the transmitted ultrasonic pulse is transmitted by a tissue or blood flow in the body of the subject. When reflected, an echo signal due to the reflection is generated by the probe 101.
Is to be detected. Then, after the echo signal detected by the probe 101 is converted into an electric signal, the signal 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. Has become. The Doppler shift signal is A /
The signal is converted into a digital signal by the D converter 104 and input to the MTI filter 105. The MTI filter 105 is a kind of low-pass filter, and attenuates a clutter component having a low frequency component in an echo signal obtained from a tissue or a blood vessel wall of a subject, and can extract only a blood flow component. The blood flow component extracted by the MTI filter 105 is calculated by the blood flow information calculation means 106 for speed, variance, power, and the like, and the calculation result is displayed on the screen of the display 107.

[0003]

Generally, in an ultrasonic Doppler imaging apparatus, it is necessary to move an acoustic scanning line in order to display blood flow information two-dimensionally. In order to provide real-time display, the number of data per one sample volume is reduced, and it is general that the number of data increases from several to more than ten.

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

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

[0006]

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 Detecting means for detecting the Doppler shift signal, and a filter for approximating a 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 therein.

[0007]

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

[0008]

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention. In FIG.
Is a phase detector, and 4 is an A / D converter. An MTI filter 5 includes a clutter component approximator 5a and a subtractor 5b. 6 is a blood flow information calculating means, and 7 is a display.

Next, the operation of the above embodiment will be described.
The electric pulse generated by the transmitting / receiving circuit 2
Is converted to an ultrasonic pulse, transmitted to a subject (not shown), the echo signal returns to the probe 1 from the subject, is converted to an electric signal, and the Doppler shift signal is detected by the phase detector 3, and the A / D The signal is converted by the converter 4 into a digital signal. 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, the input data (I1 + jQ) is calculated using (Equation 1).
.., Φn of (I2 + jQ2),..., (In + jQn).

[0011]

[Formula 1] φn = tan ⁻¹ (Qn / In)

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

[0013]

(Equation 2)

By substituting the values obtained in this way into (Equation 3) and (Equation 4) of the least squares method, the phases φ1, φ2,.
The constants a0 and a1 of (equation 5) of the linear function approximating n are obtained.

[0015]

(Equation 3)

[0016]

(Equation 4)

[0017]

## EQU5 ## φn = a1 * n + a0

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

[0019]

(Equation 6)

[0020]

In = Aave cos (φn)

[0021]

Qn = Aave sin (φn)

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

Therefore, the blood flow signal can be extracted by attenuating the clutter signal in the input signal by subtracting the approximate values of I and Q obtained in (Expression 7) and (Expression 8) from the input signal. The speed, variance, power and the like are calculated from the blood flow signal by the blood flow information calculating means 6, and the calculation result is displayed on the display 7.

FIG. 2 shows an MTI filter 5 according to this embodiment.
5A is a diagram illustrating an I signal, and FIG. 5B is a diagram illustrating a Q signal. In FIG. 2, 10 is a Doppler shift signal,
11 is an approximate value of the clutter component obtained by the above operation,
Reference numeral 12 denotes a value obtained by subtracting the approximate clutter value 11 from the Doppler shift signal 10, and indicates an 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, clutter can be removed by subtracting a signal approximating a clutter signal from a signal containing a clutter component, and a high-quality blood flow image can be obtained.

Furthermore, considering the principle, clutter can be removed even if the frequency of the clutter increases, so that there is no need to switch the cutoff frequency of the filter as in the case of using a conventional filter.

[0028]

As is apparent from the above embodiment, the present invention subtracts the approximate value of the clutter component from the sine wave from the Doppler shift signal, thereby eliminating the occurrence of transient frequency components and providing high quality blood. You can get a flow image.

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

[Brief description of the 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 the present embodiment; FIG. 2B is a characteristic diagram showing the amplitude of a Q signal in the present embodiment;

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

[Explanation of symbols]

 DESCRIPTION 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 calculation means 8 Display

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-274238 (JP, A) JP-A-2-264644 (JP, A) JP-A-3-244443 (JP, A) JP-A 57- 169687 (JP, A) JP-A-63-296735 (JP, A)

Claims (1)

(57) [Claims] A transmitting means for transmitting an ultrasonic wave to a subject; a receiving means for receiving an echo signal reflected in the subject; a detecting means for detecting a Doppler shift signal from the received signal; An ultrasonic Doppler imaging apparatus comprising: a filter that approximates a clutter component in a signal with a sine wave and subtracts the approximated signal from the Doppler shift signal.