# US 5,706,817 A · Filtering method for ultrasonic color doppler imaging system

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- Number: US 5,706,817 A
- Document ID: US5706817A
- Status: Granted
- Kind: A
- Application number: 08/646,526
- Filed: 1996-05-07
- Granted: 1998-01-13
- Earliest claimed: 1995-05-08
- Assignees: Medison Co., Ltd.
- Inventors: Tai-kyong Song; Jae-gyoung Kim; Cheol-an Kim
- Web page: https://patentgrep.com/patent/US5706817A

## CPC

- G01S 7/52071: {Multicolour displays; using colour coding; Optimising colour or information content in displays, e.g. parametric imaging}
- G01S 7/52026: {Extracting wanted echo signals (Doppler systems G01S15/50; Doppler short range imaging systems G01S15/8979)}
- H03H 17/04: Recursive filters
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

An ultrasonic color Doppler imaging system, and particularly a filtering method for removing a clutter signal from an ultrasonic image is provided. A modified infinite impulse response (IIR) filter to which a moving target indicator (MTI) principle is applied, can sufficiently suppress an undesired transient phenomenon shown in a conventional general IIR filter, and realize a steep characteristic curve which is the same as that of the conventional IIR filter, using a small order. Thus, a frame rate of the image system can be improved and a real-time processing is possible. However, first three signals output from such a filter do not represent a characteristic of a filter accurately. Thus, first three kinds of data which cause an inaccuracy to a filter characteristic are removed from a filter processing, to render an accuracy in realization of a modified IIR filter.

## Claims

### Claim 1

A method for filtering an ultrasonic Doppler signal in an ultrasonic Doppler system for real-time image processing of an ultrasonic Doppler signal, including a digital high-pass filter of an infinite impulse response type which eradicates a low-frequency component contained in an ultrasonic Doppler signal irrespective of a cut-off frequency, said ultrasonic Doppler signal filtering method comprising the steps of:
filtering time samples of the Doppler signal to obtain corresponding samples of an output signal;
periodically removing a predetermined number of initial samples of said output signal samples; and
periodically using samples of said output signal that follow said initial samples, to provide a real-time image processing of the ultrasonic Doppler signal.

### Claim 2 (depends on 1)

The ultrasonic Doppler signal filtering method according to claim 1, wherein said predetermined number of initial samples of said output signal comprise three initial output signal samples.

### Claim 3 (depends on 2)

The ultrasonic Doppler signal filtering method according to claim 2, wherein said removing step is performed during every range gate in the Doppler system.

### Claim 4 (depends on 1)

The ultrasonic Doppler signal filtering method according to claim 1, wherein said ultrasonic signal is one reflected from a living body.

### Claim 5 (depends on 4)

The ultrasonic Doppler signal filtering method according to claim 4, wherein said ultrasonic signal reflected from the living body is for diagnosing a dynamic state of a blood flow of the living body.

### Claim 6 (depends on 1)

The ultrasonic Doppler signal filtering method according to claim 1, further including the step of computing the following intermediate outputs W.sub.1 (Z) and W.sub.2 (Z) with respect to a signal K which initially returns from a range gate: ##EQU8## where a and b are coefficients.

### Claim 7 (depends on 6)

The method according to claim 6, wherein output samples Y(n) with respect to input samples X(n) are determined in accordance with the following equation:
Y(n)=X(n)-W.sub.1 (n)+W.sub.2 (n),
where,
W.sub.1 (n)=X(n-1)-a{W.sub.1 (n-1)-X(n-1)}-bW.sub.2 (n);
W.sub.2 (n)=W.sub.1 (n)-X(n-1).

### Claim 8 (depends on 7)

The method of claim 7, wherein the output samples Y(0), Y(1) and Y(2) are periodically removed from the filter output.