Ultrasonic harmonic image segmentation

• US 20010039381A1
• Filed: 02/12/2001
• Published: 11/08/2001
• Est. Priority Date: 02/16/2000
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Burns, Peter N., Simpson, David Hope
• Granted Patent: US 6,508,767 B2
• Time in Patent Office: Days
• US Class Current: 600/443
• 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 8/481 involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream analysis of echo signal exploiting properties of a contrast enhancer in devices for short-range imaging with acoustic waves G01S7/52039
• CPC Class Codes: A61B 8/488 involving Doppler signals
• CPC Class Codes: G01S 15/8963 using pulse inversion
• CPC Class Codes: G01S 15/8981 Discriminating between fixed and moving objects or between objects moving at different speeds, e.g. wall clutter filter
• CPC Class Codes: G01S 7/52038 involving non-linear properties of the propagation medium or of the reflective target
• CPC Class Codes: G01S 7/52039 exploiting the non-linear response of a contrast enhancer, e.g. a contrast agent diagnostic techniques involving the use of contrast agents A61B8/481
• CPC Class Codes: G01S 7/52046 Techniques for image enhancement involving transmitter or receiver image enhancement by image data processing G06T5/00

Abstract

An ultrasonic diagnostic imaging apparatus and method are provided for segmenting signals from nonlinear targets such as microbubble contrast agents. Received echo signals are separated into their constituent linear and nonlinear components by a Doppler filter using pulse inversion separation. A threshold level is derived from an estimate made of the contributions to the echo signal from linear scattering and noise. Echo signals which exceed the threshold level are segmented as nonlinear (microbubble-originating) signals and displayed as such, whereas signals not exceeding the threshold are suppressed in the image display.

Claims

1. An ultrasonic diagnostic imaging system which produces images from linear and nonlinear ultrasonic signal components comprising:

a transmitter which transmits a series of one or more differently modulated transmit pulses;

a receiver which receives echo signals in response to the transmit pulses;

a signal processor, responsive to the received echo signals, which calculates both linear and nonlinear echo signal components;

a segmentation processor, responsive to both the linear and nonlinear echo signal components, which acts to determine the predominant characteristic of an echo signal on the basis of the relative power of the linear and nonlinear signal components; and

a display processor, responsive to the segmentation processor, which displays an echo signal on the basis of the determined predominant characteristic.

2. The ultrasonic diagnostic imaging system of

claim 1

, wherein the transmitter is a pulse inversion or pulse inversion Doppler transmitter.

3. The ultrasonic diagnostic imaging system of

claim 1

, wherein the signal processor calculates both nonlinear and linear echo signal components using radio frequency filtering, Doppler frequency filtering, or a combination of radio frequency filtering and Doppler frequency filtering.

4. The ultrasonic diagnostic imaging system of

claim 1

, wherein the segmentation processor acts to compare the nonlinear component of the echo signal to an estimate of contributions to the nonlinear component due to linear and/or weakly nonlinear scattering and noise.

5. The ultrasonic diagnostic imaging system of

claim 2

, wherein the pulse inversion processor exhibits a first filter characteristic for preferentially passing nonlinear echo signal components relative to linear echo components, and a second filter characteristic for preferentially passing linear echo components relative to nonlinear echo signal components.

6. The ultrasonic diagnostic imaging system of

claim 5

, wherein the pulse inversion processor comprises a pulse inversion Doppler filter.

7. The ultrasonic diagnostic imaging system of

claim 1

, further comprising first and second signal power detectors, coupled to the pulse inversion processor, which act to estimate the power of the linear and nonlinear echo signal components.

8. The ultrasonic diagnostic imaging system of

claim 7

, wherein the segmentation processor is responsive to the linear and nonlinear signal power estimates produced by the signal power detectors.

9. The ultrasonic diagnostic imaging system of

claim 1

, further comprising a speckle reduction processor, responsive to received echo signals and having an output coupled to the segmentation processor, which acts to reduce the speckle artifact of received echo signals.

10. The ultrasonic diagnostic imaging system of

claim 1

wherein the desired signal is a nonlinear echo signal from microbubble contrast agents and the undesired signal is a combined echo signal from tissue and electronic noise.

11. The ultrasonic diagnostic imaging system of

claim 1

, wherein the desired signal is a nonlinear echo signal from tissue and the undesired signal is a combined electronic noise and linear echo signal from tissue.

12. The ultrasonic diagnostic imaging system of

claim 1

wherein the signal processor processes the received echoes with a combination of Doppler and radio frequency wall filters to produce separate signals representative of desired and undesired echo components respectively.

13. The ultrasonic diagnostic imaging system of

claim 1

wherein the signal processor processes the received echoes with Doppler wall filters or radio frequency wall filters to produce separate signals representative of desired and undesired echo components respectively.

14. The ultrasonic diagnostic imaging system of

claim 1

wherein the transmitter is a pulse inversion Doppler transmitter which transmits a sequence of two or more differentially modulated transmit pulses.

15. The ultrasonic diagnostic imaging system of

claim 1

wherein the segmentation processor determines the predominant characteristic of an echo signal on the basis of the comparison:

(Desired Signal Power)≧

ρ

(Undesired Signal Power)+(Constant).

16. The ultrasonic diagnostic imaging system of

claim 1

further comprising a compensation processor, responsive to the segmentation processor, which acts to correct the power of a desired signal according to the equation:

(Corrected Power of Desired Signal=(Uncorrected Power of Desired Signal)−

ρ

(Power of Undesired Signal)−

(Constant)

where ρ

is a scaling factor.

17. A method for segmenting linear and nonlinear ultrasonic echo signals comprising:

receiving a plurality of echo signals from a target in response to differently modulated transmit signals;

identifying the linear and nonlinear components of the echo signals by pulse inversion processing;

comparing the nonlinear component against a threshold which is a function of an estimate of the contributions to the nonlinear component due to linear and weakly nonlinear scattering and electronic noise; and

identifying at least one of echo signals which exceed the threshold as nonlinear in character and echo signals which do not exceed the threshold as linear in character.

18. The method of

claim 17

, wherein identifying further comprises determining an echo signal to have originated from a contrast agent or a combination of tissue and electronic noise.

19. The method of

claim 17

, wherein identifying comprises displaying an echo signal identified as nonlinear in a distinguishing manner in an ultrasonic image display.

20. The method of

claim 19

, wherein identifying comprises displaying an echo signal identified as nonlinear in a distinguishing color in an ultrasonic image display.

21. The method of

claim 17

, wherein identifying comprises displaying an echo signal identified as linear in a distinguishing manner in an ultrasonic image display.

22. The method of

claim 21

, wherein identifying comprises displaying an echo signal identified as linear in grayscale in an ultrasonic image display.

23. The method of

claim 17

, further comprising transmitting a plurality of axially aligned, differently modulated transmit signals to the target.

24. The method of

claim 17

, further comprising transmitting a plurality of laterally adjacent, differently modulated transmit signals to the target.

38. The method of

claim 17

, wherein identifying further comprises determining an echo signal to have originated from tissue harmonics or a combination of clutter artifacts and electronic noise.

25. A method for segmenting linear and nonlinear ultrasonic echo signals comprising:

receiving an echo signal which may contain linear and nonlinear signal components from a target in response to a transmit signal;

processing the echo signal to reduce speckle artifact;

identifying at least one of the linear and nonlinear components of the echo signal;

estimating the contributions to the echo signal due to linear and weakly nonlinear scattering and electronic noise; and

identifying the echo signal as originating from a predominately linear or nonlinear reflector on the basis of the estimate.

26. The method of

claim 25

, wherein identifying comprises filtering the echo signal by a first filter having a passband which passes predominantly linear signal components, and by a second filter having a passband which passes predominantly nonlinear signal components.

27. The method of

claim 26

, wherein identifying further comprises filtering the echo signal by a third filter having a passband which passes linear signal components, and by a fourth filter having a passband which passes nonlinear signal components;

wherein the echo signals received by the first and second filters have been differently processed than the echo signals received by the third and fourth filters; and

wherein processing the echo signal to reduce speckle artifact comprises combining signals produced by the filters.

28. The method of

claim 25

, wherein processing the echo signal to reduce speckle artifact comprises at least one of the processes of frequency compounding, spatial compounding, processing signals produced by different transmit or receive apertures, and kernel image processing.

29. The method of

claim 25

, further comprising transmitting, for each echo signal, a plurality of differently modulated transmit signals

30. The method of

claim 29

, wherein the transmit signals are differently modulated by at least one of phase, polarity, or amplitude.

31. A method for segmenting linear and nonlinear ultrasonic echo signals comprising:

receiving an echo signal which may contain linear signal components and nonlinear tissue harmonic signal components from a target in response to a transmit signal;

identifying at least one of the linear signal clutter and nonlinear tissue harmonic components of the echo signal;

estimating the contributions to the echo signal due to clutter and electronic noise; and

identifying tissue harmonic signals for display on the basis of the estimate.

32. The method of

claim 31

, wherein echo signals which are not identified as tissue harmonic signals are suppressed in the display.

33. The method of

claim 31

, further comprising transmitting, for each echo signal, a plurality of differently modulated transmit signals

34. The method of

claim 33

, wherein the transmit signals are differently modulated by at least one of phase, polarity, or amplitude.

35. A method for displaying nonlinear ultrasonic echo information comprising:

receiving an echo signal from a target which may contain linear and nonlinear signal components;

separating the predominantly linear and predominantly nonlinear components of the echo signal;

scaling the linear component to produce an estimate of the residual linear component of the nonlinear component; and

combining the nonlinear component and the scaled linear component to produce a display signal.

36. The method of

claim 35

, further comprising transmitting, for each echo signal, a plurality of differently modulated transmit signals

37. The method of

claim 36

wherein separating comprises separating the linear and nonlinear components by pulse inversion processing.