Noise Reduction And Aliasing Compensation In A Doppler Mode Image

• US 20090182236A1
• Filed: 01/09/2009
• Published: 07/16/2009
• Est. Priority Date: 01/10/2008
• Status: Active Grant

• Current Assignee: Samsung Medison Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Medison Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Kwon, Sung Jae, Jeong, Mok Kun
• Granted Patent: US 8,357,096 B2
• Time in Patent Office: Days
• US Class Current: 600/455
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: A61B 8/488 involving Doppler signals
• CPC Class Codes: G01S 15/584 with measures taken for suppressing velocity ambiguities, i.e. anti-aliasing
• CPC Class Codes: G01S 15/8979 Combined Doppler and pulse-echo imaging systems

Abstract

The present invention relates to an ultrasound system and a method of forming a Doppler mode image. The ultrasound system comprises a transmission/reception unit operable to transmit/receive ultrasound signals at a pulse repetition frequency (PRF) to form an n number of Doppler signals. The ultrasound system further comprises a signal processing unit. The signal processing unit computes a first mean frequency based on an n^th Doppler signal and an (n−1)^th Doppler signal and a second mean frequency based on an n^th Doppler signal and an (n−k)^th Doppler signal, wherein k is a positive integer equal to or greater than 2. The signal processing unit estimates a Doppler frequency and compensate for aliasing of the Doppler signal based on the first and second mean frequencies to produce Doppler signal with the aliasing compensated. An image processing unit operable to form a Doppler mode image based on the Doppler signals produced by the signal processing unit.

Claims

1. An ultrasound system, comprising:

a transmission/reception unit operable to transmit/receive ultrasound signals at a pulse repetition frequency (PRF) to form an n number of Doppler signals;

a signal processing unit operable to compute a first mean frequency based on an n^th Doppler signal and an (n−

1)^th Doppler signal and a second mean frequency based on an n^th Doppler signal and an (n−

k)^th Doppler signal, respectively, wherein k is a positive integer equal to or greater than 2, the signal processing unit being further operable to estimate a Doppler frequency and compensate for aliasing of the Doppler signals based on the first and second mean frequencies to thereby produce Doppler signals with the aliasing compensated; and

an image processing unit operable to form a Doppler mode image based on the Doppler signals produced by the signal processing unit.

2. The ultrasound system of claim 1, wherein the signal processing unit includes:

a quadrature demodulating unit operable to demodulate the Doppler signals into baseband signals consisting of an I signal of an in-phase component and a Q signal of a quadrature component;

a mean frequency computing unit operable to compute the first and second mean frequencies based on the baseband signals; and

a Doppler signal processing unit operable to perform the first and second signal processing based on the first and second mean frequencies.

3. The ultrasound system of claim 2, wherein the mean frequency computing unit includes:

a first mean frequency computing unit operable to compute the first mean frequency based on an n^th IQ signal and an (n−

1)^th IQ signal outputted from the quadrature demodulating unit; and

a second mean frequency computing unit operable to compute the second mean frequency based on n^th IQ signals and (n−

k)^th IQ signals outputted from the quadrature demodulating unit, wherein k is an integer equal to or greater than 2.

4. The ultrasound system of claim 3, wherein the second mean frequency computing unit computes the second mean frequency through the following equation:

5. The ultrasound system of claim 2, wherein the Doppler signal processing unit includes:

a mean frequency analyzing unit operable to analyze the first and second mean frequencies to output analysis result signals;

a first signal processing unit operable to perform a first signal processing upon the Doppler signals in response to the analysis result signals; and

a second signal processing unit operable to perform a second signal processing upon the Doppler signals in response to the analysis result signals.

6. The ultrasound system of claim 5, wherein the mean frequency analyzing unit is operable to:

output a first analysis result signal if the aliasing does not occur in the first and second mean frequencies;

output a second analyzing result, if the aliasing does not occur in the first mean frequency at a negative frequency region and the aliasing occurs in the second mean frequency;

output a third analyzing result, if the aliasing does not occur in the first mean frequency at a positive frequency region and the aliasing occurs in the second mean frequency;

output a fourth analysis result signal if the first mean frequency varies multiple times at ±

PRF/2 and the second mean frequency increases; and

output a fifth analysis result signal if the first mean frequency varies multiple times at ±

PRF/2 and the second mean frequency decreases.

7. The ultrasound system of claim 6, wherein the first signal processing unit is operable to perform the first signal processing using the following equation in response to the first analysis result signal:

8. The ultrasound system of claim 6, wherein the first signal processing unit is operable to perform the first signal processing using the following equation in response to the second analysis result signal:

9. The ultrasound system of claim 6, wherein the first signal processing unit is operable to perform the first signal processing using the following equation in response to the third analysis result signal:

10. The ultrasound system of claim 6, wherein the second signal processing unit performs the second signal processing by adding PRF to the first mean frequency aliased in a −

PRF/2 direction in response to the fourth analysis result signal, or the second signal processing unit performs the second signal processing by adding −

PRF to the first mean frequency aliased in a PRF/2 direction in response to the fifth analysis result signal.

11. A method of forming a Doppler mode image in an ultrasound system having a transmission/reception unit, a signal processing unit and an image processing unit, comprising:

a) at the transmission/reception unit, transmitting/receiving ultrasound signals at a pulse repetition frequency (PRF) to form an n number of Doppler signals;

b) at the signal processing unit, computing a first mean frequency based on an n^th Doppler signal and an (n−

1)^th Doppler signal and a second mean frequency based on an n^th Doppler signal and an (n−

k)^th Doppler signal outputted from the transmission/reception unit, respectively, wherein k is a positive integer equal to or greater than 2;

c) at the signal processing unit, estimating a Doppler frequency and compensating for aliasing of the Doppler signals based on the first and second mean frequencies to produce Doppler signals with the aliasing compensated; and

d) at the image processing unit, forming a Doppler mode image based on the Doppler signals produced by the signal processing unit.

12. The method of claim 11, wherein the step b) includes:

b1) demodulating the Doppler signals into baseband signals consisting of I signals of an in-phase component and Q signals of a quadrature component; and

b2) computing the first and second mean frequencies based on the baseband signals.

13. The method of claim 11, wherein the step b2) includes:

b21) computing the first mean frequency based on n^th IQ signals and an (n−

1)^th IQ signal outputted from at the step b1); and

b22) computing the second mean frequency based on an n^th IQ signal and an (n−

k)^th IQ signal outputted from the quadrature demodulating unit, wherein k is an integer equal to or greater than

     2).

14. The method of claim 13, wherein the step b22) is carried out using the following equation:

15. The method of claim 11, wherein the step c) includes:

c1) analyzing the first and second mean frequencies to output analysis result signals; and

c2) performing first and second signal processing in response to the analysis result signals.

16. The method of claim 15, wherein the step c1) includes:

if the aliasing does not occur in the first and second mean frequencies, outputting a first analysis result signal;

if the aliasing does not occur in the first mean frequency at a negative frequency region and the aliasing occurs in the second mean frequency, outputting a second analyzing result;

if the aliasing does not occur in the first mean frequency at a positive frequency region and the aliasing occurs in the second mean frequency, outputting a third analyzing result;

if the first mean frequency varies multiple times at ±

PRF/2 and the second mean frequency increases, outputting a fourth analysis result signal; and

if the first mean frequency varies multiple times at ±

PRF/2 and the second mean frequency decreases, outputting a fifth analysis result signal.

17. The method of claim 16, wherein the c2) includes performing the first signal processing using the following equation in response to the first analysis result signal:

18. The method of claim 16, wherein the c2) includes performing the first signal processing using the following equation in response to the second analysis result signal:

19. The method of claim 16, wherein the c2) includes performing the first signal processing using the following equation in response to the third analysis result signal:

20. The method of claim 16, wherein the c2) includes performing the second signal processing by adding PRF to the first mean frequency aliased in a −

PRF/2 direction in response to the fourth analysis result signal, or the c2) includes performing the second signal processing by adding −

PRF to the first mean frequency aliased in a PRF/2 direction in response to the fifth analysis result signal.