Method for optimization of transmit and receive ultrasound pulses, particularly for ultrasonic imaging

• US 7,297,117 B2
• Filed: 05/24/2004
• Issued: 11/20/2007
• Est. Priority Date: 05/22/2003
• Status: Active Grant

• Current Assignee: Esaote SpA
• Original Assignee: Esaote SpA
• Inventors: Trucco, Andrea, Curletto, Simone
• Primary Examiner(s): Jaworski; Francis J.
• Application Number:
  US10/852,572
• Publication Number:
  US 20050033167A1
• Time in Patent Office: 1,275 Days
• Field of Search: 600443-447, 600455-458, 128/916, 73625-626, 736/02
• US Class Current: 600/443
• CPC Class Codes: G10K 11/34 using electrical steering of transducer arrays, e.g. beam steering constructional aspects B06B1/0607, B06B1/085

Abstract

A method for optimizing transmit and receive ultrasound imaging pulses generates transmit pulses from an array of transducers which are energized by excitation signals that are applied to each individual transducer of the array. Each of the excitation signals are individually weighted to optimize the transducers'"'"' contribution to a predetermined energy function. Such optimization may also be performed on the received pulses.

Claims

1. A method of ultrasonic imaging comprising the step of optimizing one or more ultrasonic pulses in conjunction with ultrasonic imaging, wherein transmit pulses are generated from ultrasonic pulse contributions of each of a plurality of electroacoustic transducers, said transducers being grouped in an array and being individually triggered by electric excitation signals, said excitation signal being applied to each individual transducer of said array having a predetermined delay with respect to the application of the excitation signal that is applied to the other transducers of said plurality of transducers, and wherein a weight is applied to the excitation signal for each transducer for adjusting the amplitude of said excitation signal, characterized in the following steps:

defining an optimal desired mechanical pressure profile for said transmit pulses relative to the penetration depth of said transmit pulses within the body or object being examined as a function of at least amplitude weighting parameters for said transducers'"'"' contributions to said transmit pulses, and of the delays of excitation for transmission of individual pulse contributions of transducers, aimed at focusing comprehensive pulses on a scan line or band and at a certain penetration depth within the body or object under examination;

defining an ideal beam pattern for said transmit pulses relative to the propagation time or penetration depth within the body or object under examination as a function of at least amplitude weighting parameters for said transducers'"'"' contributions to said transmit pulses, and of delays of excitation delays for transmission of individual pulse contributions of transducers aimed at focusing comprehensive pulses on a scan line or band and at a certain penetration depth within the body or object under examination;

defining an energy function which depends on the difference between said ideal pressure profile and the actual pressure profile and between said ideal beam pattern and the actual beam pattern;

determining the minimum of said energy function;

determining said weighting parameters and said delays which correspond to the minimum of the energy function and applying said weighting parameters and said delays to said excitation signals for exciting said transducers to generate said comprehensive pulses.

2. A method as claimed in claim 1, characterized in that a further optimization variable for said transducers'"'"' pulse contributions is provided that forms said comprehensive pulses, which variable is the waveform of the pulse contribution generated by each transducer, that may be equal to or different from one transducer to the other.

3. A method as claimed in claim 1, characterized in that said energy function has the following general form:

$E<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>}\right)={\int <br><br>}_z<br><br>{\left[{\mathrm{Pcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z\right)-\mathrm{Pdes}<br><br>\left(z\right)\right]}^2<br><br>d<br><br>z+{\int <br><br>}_x<br><br>\int <br><br>[{\mathrm{BPcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z,x\right)-{\mathrm{BPdes}\left(z,x\right]}^2<br><br><br><br>d<br><br>x<br><br>d<br><br>z$

where;

Pdes(z) is the function that describes the desired pressure profile at the different penetration depths along the propagation axis x of the ultrasonic pulse,

Pcal_i(W,τ

,ω

,z) is the function that describes the pressure profile as determined from the weight vector, the delay vector and the waveform vector at the ith iteration of the minimization rector and at different penetration depths along the ultrasonic pulse propagation axis z, relative to the weight vector W, the delay vector τ and

the waveforms of the pulse contributions generated by the transducers at ω

/;

BPdes(z,x) is the function that describes the desired beam pattern at the different penetration depths along the ultrasonic pulse propagation axis z relative to the weight vector W, the delay vector τ and

the waveforms off the pulse contributions generated by the transducers ω

/;

BPcal_i(W,τ

,ω

,z,x) is the function that describes the beam pattern as determined from the weight vector, the delay vector and the waveform vector at the ith iteration of the minimization vector and at the different penetration depths along the ultrasonic pulse propagation axis z, relative to the weight vector W, the delay vector τ and

the waveforms of the pulse contributions generated by the transducers ω

.

4. A method as claimed in claim 3, characterized in that said energy function is discretized and integrals are transformed into a summation by assuming a certain approximation error margin.

5. A method as claimed in claim 4, characterized in that said two integrals of said energy function or the equivalent summations are multiplied by a weighting coefficient.

6. A method as claimed in claim 3, characterized in that said variable z may obviously change in a range of interest which spans the ultrasonic pulse focusing depth, or in a range in which the focusing depth is one of the upper or lower limits or is close to one of said limits whereas said variable x may be in a range that is equal to or larger than the whole extension of the transducer array along the x axis parallel to the transmit surface of said transducer array, or said range may be smaller than said extension of the transducer array along the x axis and of the same order of magnitude as a scan band corresponding to a few parallel and adjacent scan lines.

7. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include integration of the absolute values of differences, instead of the squared of the differences Pcal_i-Pdes and/or BPcal_i-Bpdes.

8. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include integration of the variables x and/or z upon limited intervals, to only consider one of said the main lobe or said side lobes.

9. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include the replacement of the desired pressure profile Pdes and/or the desired beam pattern BPdes with a constant.

10. A method as claimed in claim 9, wherein said constant may be null.

11. A method as claimed in claim 9, characterized in that said constant replaced in lieu of the desired profile pressure and/or the desired beam pattern BPdes corresponds to the average value of the desired pressure profile Pdes and/or the desired beam pattern BPdes over the integration interval being considered.

13. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include replacement of the integral operator with a different operator.

14. A method as claimed in claim 13, wherein said different operator is a nonlinear operator.

15. A method as claimed in claim 13, wherein said different operator is a mean operator.

16. A method as claimed in claim 13, wherein said different operator is a maximum value operator.

17. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include an integration carried out with respect to polar coordinate variables.

18. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include an intergration carried out with respect to arbitrary variables, thereby proving an optimization that may apply to any steering angle of said scan line.

19. A method as claimed in claim 3, characterized in that said energy function is modified in such a manner as to include one or more of integration of the absolute values of differences;

integration of the variables x and/or z upon limited intervals;

the replacement of the desired pressure profile Pdes and/or the desired beam pattern Bpdes with a constant, wherein said constant may be null or may correspond to the average value of the desired pressure profile Pdes and/or the desired beam pattern BPdes over the integration interval being considered;

integration of any excess values of what was actually obtained with respect to what was desired;

replacement of the integral operator with a different operator, wherein said different operator is a nonlinear operator or a mean operator or a maximum value operator;

an integration carried out with respect to polar coordinate variables;

or an integration carried out with respect to arbitrary variables.

20. A method as claimed in claim 19, characterized in that said energy function is modified in such a manner as to include, for beam pattern optimization, a function that sums the integral of the square differences between obtained BPcal and desired Bpdes in the region of the side lobe, and the integral of the excess values with respect to a maximum level in the side lobe region.

21. A method as claimed in claim 19, characterized in that said energy function is modified in such a manner as to include, for pressure profile optimization, a function that considers pressure variance along the z axis.

22. A method as claimed in claim 1, characterized in that, as transducer excitation delays, typical ultrasonic pulse focusing delays may be used, which are constant in the energy function.

23. A method as claimed in claim 1, characterized in that, for all transducers, identical waveforms of respective contributions to said comprehensive pulses are defined.

24. A method as claimed in claim 1, characterized in that the minimization of said energy function is executed by using a stochastic algorithm or an evolutionary algorithm.

25. A method as claimed in claim 24, characterized in that minimization is executed by using a genetic algorithm.

26. A method as claimed in claim 24, characterized in that minimization is executed by using an algorithm named Simulated Annealing.

27. A method as claimed in claim 24, characterized in that minimization is executed by using an algorithm named Tabu search.

28. A method as claimed in claim 1, characterized in that it provides a combined transmit and receive optimization wherein amplitude weights of the individual pulse transducers'"'"' contributions are determined for only minimizing the mechanical pressure part of the energy function, whereas, upon reception, amplitude weights are applied to the signals emitted from the transducers, which weights are determined by only minimizing the beam pattern part of the energy function.

29. A method as claimed in claim 1, characterized in that, during transmission, the transmit pulse is optimized by minimization of the following function:

$E<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>}\right)={\int <br><br>}_z<br><br>{\left[{\mathrm{Pcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z\right)-\mathrm{Pdes}<br><br>\left(z\right)\right]}^2<br><br>d<br><br>z$

whereas, upon reception, the receive pulse is optimized by minimizing the following function;

$E<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>}\right)={\underset{x}{\int <br><br>\int <br><br>}}^{}[B<br><br><br><br>P<br><br><br><br>{\mathrm{ca}<br><br>l}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z,x\right)-B<br><br><br><br>P<br><br><br><br>{\mathrm{des}\left(z,x\right]}^2<br><br>d<br><br>x<br><br>d<br><br>z$

30. A method as claimed in claim 29, characterized in that the delays and/or waveforms are defined as constant whereas the transmit and/or receive optimization include the calculation of amplitude weights for individual transducers'"'"' contributions to the comprehensive transmit pulse and/or for individual transducers'"'"' contributions to the receive signal.

12. A method as claimed in claimed 3, characterized in that said energy function is modified in such manner as to include integration of any excess values of what was actually obtained with respect to what was desired.

31. A method of ultrasonic imaging comprising the step of optimizing one or more ultrasonic pulses in conjunction with ultrasonic imaging, wherein receive pulses are generated from ultrasonic pulse contributions of each of a plurality of electroacoustic transducers, said transducers being grouped in an array and being individually triggered by electric excitation signals, said excitation signal being applied to each individual transducer of said array having a predetermined delay with respect to the application of the excitation signal that is applied to the other transducers of said plurality of transducers, and wherein a weight is applied to the excitation signal for each transducer for adjusting the amplitude of said excitation signal, characterized in the following steps:

defining an optimal desired mechanical pressure profile for said receive pulses relative to the penetration depth of said receive pulses within the body or object being examined as a function of at least amplitude weighting parameters for said transducers'"'"' contributions to said receive pulses, and of the delays of excitation for reception of individual pulse contributions of transducers, aimed at focusing comprehensive pulses on a scan line or band and at a certain penetration depth within the body or object under examination;

defining an ideal beam pattern for said receive pulses relative to the propagation time or penetration depth within the body or object under examination as a function of at least amplitude weighting parameters for said transducers'"'"' contributions to said receive pulses, and of delays of excitation delays for reception of individual pulse contributions of transducers aimed at focusing comprehensive pulses on a scan line or band and at a certain penetration depth within the body or object under examination;

defining an energy function which depends on the difference between said ideal pressure profile and the actual pressure profile and between said ideal beam pattern and the actual beam pattern;

determining the minimum of said energy function;

determining said weighting parameters and said delays which correspond to the minimum of the energy function and applying said weighting parameters and said delays to said excitation signals for exciting said transducers to generate said comprehensive pulses.

32. A method as claimed in claim 31, characterized in that a further optimization variable for said transducers'"'"' pulse contributions is provided that forms said comprehensive pulses, which variable is the waveform of the pulse contribution generated by each transducer, that may be equal to or different from one transducer to the other.

33. A method as claimed in claim 31, characterized in that said energy function has the following general form:

$E<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>}\right)={\int <br><br>}_z<br><br>{\left[{\mathrm{Pcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z\right)-\mathrm{Pdes}<br><br>\left(z\right)\right]}^2<br><br>d<br><br>z+{\int <br><br>}_x<br><br>\int <br><br>[{\mathrm{BPcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z,x\right)-{\mathrm{BPdes}\left(z,x\right]}^2<br><br><br><br>d<br><br>x<br><br>d<br><br>z$

where

Pdes(z) is the function that describes the desired pressure profile at the different penetration depths along the propagcation axis x of the ultrasonic pulse,

Pcal_i(W,τ

,ω

,z) is the function that describes the pressure profile as determined from the weight vector, the delay vector and the waveform vector at the ith iteration of the minimization vector and at different penetration depths along the ultrasonic pulse propagation axis z, relative to the weight vector W, the delay vector τ and

the waveforms of the pulse contributions generated by the transducers ω

/;

BPdes(z,x) is the function that describes the desired beam pattern at the different penetration depths along the ultrasonic pulse propagation axis z, relative to the weight vector W, the delay vector τ and

the waveforms of the pulse contributions generated by the transducers ω

/;

BPcal_i(W,τ

,ω

,z,x) is the function that describes the beam pattern as determined from the weight vector, the delay vector and the waveform vector at the ith iteration of the minimization vector and at the different penetration depths along the ultrasonic pulse propagation axis z, relative to the weight vector W, the delay vector τ and

the waveforms of the pulse contributions generated by the transducers ω

.

34. A method as claimed in claim 33, characterized in that said energy function is discretized and integrals are transformed into a summation by assuming a certain approximation error margin.

35. A method as claimed in claim 34, characterized in that said two integrals of said energy function or the equivalent summations are multiplied by a weighting coefficient.

36. A method as claimed in claim 33, characterized in that said variable z may obviously change in a range of interest which spans the ultrasonic pulse focusing depth, or in a range in which the focusing depth is one of the upper or lower limits or is close to one of said limits whereas said variable x may be in a range that is equal to or larger than the whole extension of the transducer array along the x axis parallel to the transmit surface of said transducer array, or said range may be smaller than said extension of the transducer array along the x axis and of the same order of magnitude as a scan band corresponding to a few parallel and adjacent scan lines.

37. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include integration of the absolute values of differences, instead of the squared of the differences Pcal_i-Pdes and/or BPcal_i-Bpdes.

38. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include integration of the variables x and/or z upon limited intervals, to only consider one of said the main lobe or said side lobes.

39. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include the replacement of the desired pressure profile Pdes and/or the desired beam pattern BPdes with a constant.

40. A method as claimed in claim 39, wherein said constant may be null.

41. A method as claimed in claim 39, characterized in that said constant replaced in lieu of the desired profile pressure and/or the desired beam pattern BPdes corresponds to the average value of the desired pressure profile Pdes and/or the desired beam pattern BPdes over the integration interval being considered.

43. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include replacement of the integral operator with a different operator.

44. A method as claimed in claim 43, wherein said different operator is a nonlinear operator.

45. A method as claimed in claim 43, wherein said different operator is a mean operator.

46. A method as claimed in claim 43, wherein said different operator is a maximum value operator.

47. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include an integration carried out with respect to polar coordinate variables.

48. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include an integration carried out with respect to arbitrary variables, thereby proving an optimization that may apply to any steering angle of said scan line.

49. A method as claimed in claim 33, characterized in that said energy function is modified in such a manner as to include one or more of integration of the absolute values of differences;

integration of the variables x and/or z upon limited intervals;

the replacement of the desired pressure profile Pdes and/or the desired beam pattern BPdes with a constant, wherein said constant may be null or may correspond to the average value of the desired pressure profile Pdes and/or the desired beam pattern Bpdes over the integration interval being considered;

integration of any excess values of what was actually obtained with respect to what was desired;

replacement of the integral operator with a different operator, wherein said different operator is a nonlinear operator or a mean operator or a maximum value operator;

an integration carried out with respect to polar coordinate variables;

or an integration carried out with respect to arbitrary variables.

50. A method as claimed in claim 49, characterized in that said energy function is modified in such a manner as to include, for beam pattern optimization, a function that sums the integral of the square differences between obtained Bpcal and desired Bpdes in the region of the side lobe, and the integral of the excess values with respect to a maximum level in the side lobe region.

51. A method as claimed in claim 49, characterized in that said energy function is modified in such a manner as to include, for pressure profile optimization, a function that considers pressure variance along the z axis.

52. A method as claimed in claim 31, characterized in that, as transducer excitation delays, typical ultrasonic pulse focusing delays may be used, which are constant in the energy function.

53. A method as claimed in claim 31, characterized in that, for all transducers, identical waveforms of respective contributions to said comprehensive pulses are defined.

54. A method as claimed in claim 31, characterized in that the minimization of said energy function is executed by using a stochastic algorithm or an evolutionary algorithm.

55. A method as claimed in claim 54, characterized in that minimization is executed by using a genetic algorithm.

56. A method as claimed in claim 54, characterized in that minimization is executed by using an algorithm named Simulated Annealing.

57. A method as claimed in claim 54, characterized in that minimization is executed by using an algorithm, named Tabu search.

58. A method as claimed in claim 31, characterized in that it provides a combined transmit and receive optimization wherein amplitude weights of the individual pulse transducers'"'"' contributions are determined for only minimizing the mechanical pressure part of the energy function, whereas, upon reception, amplitude weights are applied to the signals emitted from the transducers, which weights are determined by only minimizing the beam pattern part of the energy function.

59. A method as claimed in claim 31, characterized in that receive optimization is performed by minimizing the following energy function:

$E<br><br>\left(W\right)={\int <br><br>}_x<br><br>{\left[{\mathrm{BPcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},z_0,x\right)-\mathrm{BPdes}<br><br>\left(z_0,z\right)\right]}^2<br><br>d<br><br>x$

the so-called dynamic focus technique being applied upon reception, to maintain the focus of contributions from different depths.

60. A method as claimed in claim 31, characterized in that receive optimization is performed by minimizing the following energy function:

$E<br><br>\left(W\right)={\int <br><br>}_u<br><br>{\left[{\mathrm{BPcal}}_i<br><br>\left(W,\mathrm{\tau <br><br>},\mathrm{\omega <br><br>},u\right)-\mathrm{BPdes}<br><br>\left(u\right)\right]}^2<br><br>d<br><br>u$

where;

BPdes(u) is the function that describes the desired beam pattern as a function of an arbitrary variable u, whose possible values are of −

2 to +2;

is the function that describes the beam pattern BPcal_i(W,τ

,ω

,z) that was calculated on the basis of the weight vector, the delay vector and the waveform vector, at the ith iteration of the minimization algorithm and as a function of said arbitrary variable u;

and where the arbitrary variable u is defined as;

u=sin(θ

)−

sin (θ

₀)

where θ

₀ is the steering direction; and

θ

is the arrival direction.

42. A method as claimed in claimed 33, characterized in that said energy function is modified in such manner as to include integration of any excess values of what was actually obtained with respect to what was desired.