TISSUE INHOMOGENEITY CORRECTION IN ULTRASOUND IMAGING

• US 20040006272A1
• Filed: 07/08/2002
• Published: 01/08/2004
• Est. Priority Date: 07/08/2002
• Status: Active Grant

• Current Assignee: InSightec Ltd.
• Original Assignee: Insightec-Image-Guided Treatment Limited
• Inventors: Vitek, Shuki, Vortman, Kobi
• Granted Patent: US 6,705,994 B2
• Time in Patent Office: Days
• US Class Current: 600/443
• CPC Class Codes: A61B 8/0816 using echo-encephalography
• CPC Class Codes: A61B 8/14 Echo-tomography
• CPC Class Codes: A61B 8/5276 due to motion
• CPC Class Codes: G01S 15/8915 using a transducer array
• CPC Class Codes: G01S 15/8927 using simultaneously or sequentially two or more subarrays or subapertures
• CPC Class Codes: G01S 15/8952 using discrete, multiple frequencies
• CPC Class Codes: G01S 7/52049 using correction of medium-induced phase aberration

Abstract

A method of imaging a site of interest in a body using an ultrasound probe comprising a plurality of ultrasound transducer elements comprises obtaining an ultrasound image of a pass zone between the ultrasound probe and the site of interest. The image includes the site of interest and a plurality of tissue regions in a pass zone between the site of interest and the ultrasound probe. Boundaries of a selected tissue region in the pass zone are determined from the image. Focusing delay times are then computed for each ultrasound transducer element based in part on the speed of sound in the selected tissue region other than an average speed of sound in body tissue, and the boundaries of the selected tissue region. Preferably, a speed about the speed of sound in the selected tissue region is used and more preferably the speed of sound in the selected tissue region is used. Refraction may be considered, as well. Ultrasound imaging of the site of interest is then conducted employing the computed delay times. Fat and bone tissue regions are typically selected if present. Other tissue regions may be selected, as well. The boundaries of the tissue region or regions may be determined by segmentation. Tissue inhomogeneity is thereby compensated for, improving image contrast resolution. Ultrasound imaging systems and software are also disclosed. A new ultrasound probe comprising high and low frequency transducer elements is also disclosed.

Claims

1. A method of imaging a site of interest in a body using an ultrasound probe, the ultrasound probe comprising a plurality of ultrasound transducer elements, the method comprising:

obtaining an ultrasound image of a pass zone of the body between the site of interest and the ultrasound probe, the image including the site of interest and a plurality of tissue regions in the pass zone;

determining, from the image, boundaries of a selected tissue region in the pass zone;

computing respective focusing delay times for each transducer element associated with an ultrasound beam passing through the selected tissue region, the computed focusing delay times computed based, at least in part, on a speed of sound in, and the determined boundaries of, the selected tissue region, wherein the speed of sound is a speed other than an average speed of sound in body tissue; and

conducting an ultrasound imaging scan of the pass zone employing the computed focusing delay times.

2. The method of claim 1, wherein the computed focusing delay times are computed transmission delays, the method comprising:

computing a respective computed transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, each computed transmission delay computed such that ultrasound beams transmitted by respective transducer elements will constructively interfere at a selected focal point.

3. The method of claim 2, comprising computing the respective computed transmission delays, at least in part, by conducting a ray calculation between the focal point and each transducer element transmitting an ultrasound beam through the selected tissue region, to determine a respective distance traveled by each ultrasound beam through the selected tissue region, based on the determined boundaries.

4. The method of claim 3, further comprising:

determining a respective initial transmission delay for each transducer element of the plurality based, at least in part, on an average speed of sound in body tissue for each one of the plurality of tissue regions in the pass zone; and

conducting an initial ultrasound imaging scan of the site of interest employing the initial transmission delays to obtain the ultrasound image of the site of interest;

wherein computing the respective computed transmission delays comprises determining a respective adjustment to the initial transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, the adjustments based, at least in part, on a phase shift for each ultrasound beam, the phase shift due to passage through the selected tissue region.

5. The method of claim 3, wherein conducting the ray calculation comprises determining refraction of ultrasound beams passing through the selected tissue region at a boundary of the selected tissue region.

6. The method of claim 1, wherein the computed focusing delay times are computed reception delays, the method comprising:

computing respective computed reception delays for each transducer element receiving an ultrasound beam passing through the selected tissue region, the respective computed reception delays computed such that ultrasound beams reflected from reflecting bodies in the pass zone are in phase after detection.

7. The method of claim 6, comprising computing the computed reception delays, at least in part, by conducting a ray calculation between a reflecting body in the pass zone and each transducer element receiving a respective ultrasound beam traveling through the selected tissue region from the reflecting body, to determine a respective distance traveled by the ultrasound beam between the reflecting body and each transducer element.

8. The method of claim 7, comprising:

computing respective initial reception delays for each transducer element of the plurality based, at least in part, on an average speed of sound in body tissue for each one of the plurality of tissue regions in the pass zone; and

conducting an initial ultrasound imaging scan of the site of interest employing the initial transmission delays to obtain the ultrasound image of the site of interest;

wherein computing the respective computed reception delays comprises determining a respective adjustment to the initial reception delays for each transducer element receiving an ultrasound beam passing through the selected tissue region, the adjustments based, at least in part, on a phase shift for each ultrasound beam, the phase shift due to passage through the selected tissue region.

9. The method of claim 7, wherein conducting the ray calculation comprises determining refraction of ultrasound beams passing through the selected tissue region at a boundary of the selected tissue region.

10. The method of claim 1, wherein computing the respective computed focusing delay times comprises:

determining a respective propagation time between each transducer element and respective points in the pass zone based, at least in part, on a speed of sound that is about the speed of sound in the selected tissue region and a respective distance traveled by an ultrasound beam through the selected tissue region, based on the determined boundaries.

11. The method of claim 1, further comprising computing the respective computed focusing delay times based, at least in part, on refraction of each ultrasound beam passing through the selected tissue region at the boundaries of the selected tissue region.

12. The method of claim 11, comprising computing the respective computed focusing delay times to only correct for displacement of a focal point.

13. The method of claim 11, comprising computing the respective computed focusing delay times to only correct for defocusing at a focal point.

14. The method of claim 1, further comprising:

computing respective initial delay times for each transducer element of the plurality based, at least in part, on an average speed of sound in body tissue for each one of the plurality of tissue regions in the pass zone; and

obtaining the ultrasound image of the pass zone by conducting an initial ultrasound imaging scan of the site of interest employing the initial focusing delay times.

15. The method of claim 1, wherein the selected tissue region is a region of fat tissue.

19. The method of claim 1, wherein the selected tissue region is from the group consisting of fat tissue, muscle tissue, organ tissue and bone tissue.

20. The method of claim 1, wherein the boundaries of the selected tissue region are determined from the image by segmenting the selected tissue region from adjacent tissue regions.

21. The method of claim 1, comprising:

obtaining a plurality of ultrasound images of the pass zone, each image comprising a different sectional plane through the site of interest;

determining, from each image, the boundaries of the selected tissue region; and

determining a three dimensional boundary of the selected tissue region, based on the determined boundaries from each image.

22. The method of claim 1, wherein the ultrasound image is obtained by conducting an initial ultrasound imaging scan, wherein at least one imaging parameter used in the first ultrasound imaging scan is different than an imaging parameter used in the ultrasound imaging scan employing the computed focusing delay times.

23. The method of claim 22, wherein the imaging parameter is from a group consisting of transmission frequency, transmission pulse shape and transmission burst length.

24. The method of claim 1, wherein:

the ultrasound image is obtained by conducting a three dimensional ultrasound imaging scan; and

the determined boundaries of the selected tissue region are three dimensional.

25. The method of claim 1, further comprising:

obtaining a second ultrasound image of the pass zone based on the ultrasound imaging scan;

determining, from the second ultrasound image, second boundaries of the selected tissue region;

computing second respective focusing delay times for each transducer element associated with an ultrasound beam passing through the selected tissue region, the second focusing delay times computed based, at least in part, on the speed of sound in, and the determined second boundaries of, the selected tissue region; and

conducting a second ultrasound imaging scan of the pass zone, employing the second computed focusing delay times.

26. The method of claim 1, wherein the speed of sound other than the average speed of sound is a speed of sound in the tissue type of the selected tissue region.

16. The method of claim 16, further comprising computing the respective computed focusing delay times based, at least in part, on a uniform speed of sound through non-selected soft tissue regions.

17. The method of claim 16, wherein the uniform speed of sound is about a speed of sound in muscle tissue.

18. The method of claim 17, further comprising:

determining, from the image, boundaries of an additional selected tissue region in the pass zone;

wherein the respective focusing delay times are computed based, at least in part, on a speed of about a speed of sound in the additional selected tissue region and on the determined boundaries of the additional selected tissue region.

27. A method of imaging a site of interest in a body using an ultrasound probe, the ultrasound probe comprising a plurality of ultrasound transducer elements, the method comprising:

conducting a first ultrasound imaging scan of a pass zone of the body between the site of interest and the ultrasound probe with the ultrasound probe, wherein the pass zone comprises a plurality of tissue regions and the first ultrasound imaging scan employs initial transmission delays and initial reception delays for each transducer element, the initial transmission and reception delays being based, at least in part, on an average speed of sound in body tissue for each one of the tissue regions in the pass zone;

obtaining an ultrasound image of the pass zone from the first ultrasound imaging scan, the image including the site of interest and the plurality of tissue regions in the pass zone;

segmenting a selected tissue region from surrounding tissue regions in the image;

computing a respective adjusted transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, each adjusted transmission delay computed based, at least in part, on a speed about a speed of sound in, and the segmented boundaries of, the selected tissue region, such that ultrasound beams transmitted by the plurality of transducer elements will constructively interfere at a selected focal point proximate the site of interest;

computing respective adjusted reception delays for each transducer element receiving an ultrasound beam passing though the selected tissue region, the adjusted reception delays being computed based, at least in part, on a speed about a speed of sound in, and the segmented boundaries of, the selected tissue region, such that ultrasound beams reflected from reflecting bodies in the pass zone are in phase after detection; and

conducting a second ultrasound imaging scan of the site of interest employing the adjusted transmission delays and the adjusted reception delays.

28. The method of claim 27, wherein the selected tissue region is at least one of a fat tissue region and a bone tissue region.

29. The method of claim 28, further comprising computing the respective focusing delay times based, at least in part, on refraction of ultrasound beams passing through the selected tissue region at the boundaries of the selected tissue region.

30. The method of claim 28, further comprising:

obtaining a second ultrasound image of the pass zone based on the second ultrasound imaging scan;

determining, from the second ultrasound image, second boundaries of the selected tissue region;

computing a second respective focusing delay time for each transducer element associated with an ultrasound beam passing through the selected tissue region, the second focusing delay times computed based, at least in part, on the speed of sound in, and the determined second boundaries of, the selected tissue region; and

conducting a second ultrasound imaging scan of the pass zone, employing the second focusing delay times.

31. The method of claim 27, wherein:

the selected tissue region is a fat tissue region; and

the plurality of tissue regions comprises other soft tissue regions including a muscle tissue region;

the method further comprising;

computing the respective adjusted transmission delays and the respective adjusted reception delays based, at least in part, on a speed about an actual speed of sound in muscle tissue for the other soft tissue regions.

32. The method of claim 27, wherein the speed of sound in the selected tissue region is about a speed of sound in the selected tissue region.

33. An ultrasound imaging system comprising:

an ultrasound imaging probe comprising a plurality of transducer elements;

wherein the system is configured to;

determine, from ultrasound imaging data obtained of a pass zone between a site of interest in a body and the ultrasound probe, boundaries of a selected one of a plurality of tissue regions in the pass zone; and

compute a respective focusing delay time for each transducer element associated with an ultrasound beam passing through the selected tissue region during imaging, the delay times computed based, at least in part, on a speed of sound in, and the determined boundaries of, the selected tissue regions, wherein the speed of sound is other than an average speed of sound in body tissue.

34. The system of claim 33, further comprising:

a beam former coupled to the ultrasound probe to provide driving signals to the transducer elements and to receive ultrasound signals detected by the transducer elements;

at least one processor coupled to the beam former to receive detected ultrasound signals and process the received signals for display; and

a controller coupled to the beam former to compute the respective focusing delay times and to provide the delay times to the beam former.

35. The system of claim 33, wherein the respective focusing delay times are transmission delays, the system configured to compute:

a respective transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, each transmission delay computed such that ultrasound beams transmitted by respective transducer elements will constructively interfere at a selected focal point.

36. The system of claim 33, wherein the respective focusing delay times are reception delays, the system configured to:

compute respective reception delays for each transducer element receiving an ultrasound signal passing through the selected tissue region, the respective reception delays being computed such that ultrasound beams reflected from reflecting bodies in the pass zone are in phase after detection.

37. The system of claim 33, configured to determine the boundaries of the selected tissue region by segmenting the selected tissue region from adjacent tissue regions.

38. The system of claim 33, further configured to:

obtain ultrasound imaging data of a plurality of sectional planes through the site of interest;

determine, from the imaging data, the boundaries of the selected tissue region, and

determine a three dimensional boundary of the selected tissue region based on the determined boundaries from each image.

39. The system of claim 33, configured to determine, from three dimensional ultrasound imaging data, a three dimensional boundary of the selected tissue region in the pass zone.

40. The system of claim 33, further comprising computing the respective focusing delay times based, at least in part, on refraction of ultrasound beams passing through the selected tissue regions at the boundaries of the selected tissue region.

41. The system of claim 33, wherein the ultrasound probe comprises low frequency transducer elements and high frequency transducer elements.

42. The system of claim 33, wherein the speed of sound other than the average speed of sound is about a speed of sound in the selected tissue region.

43. The system of claim 42, wherein the speed of sound other than the average speed of sound is the speed of sound in the selected tissue region.

44. The system of claim 33, wherein the selected tissue region is from the group consisting of fat tissue, muscle tissue and bone tissue.

45. Software residing on a machine readable medium for operating a system for imaging of a site of interest in a body using an ultrasound probe, the ultrasound probe comprising a plurality of transducer elements, the software comprising instructions for causing the system to:

determine, from ultrasound imaging data obtained of a pass zone between a site of interest in the body and the ultrasound probe, boundaries of a selected one of a plurality of tissue regions in the pass zone; and

compute a respective focusing delay time for each transducer element associated with an ultrasound beam passing through the selected tissue region during imaging, the focusing delay times computed based, at least in part, on a speed of sound in, and the determined boundaries of, the selected tissue region, wherein the speed of sound is other than an average speed of sound in body tissue.

46. The software of claim 45, wherein the focusing delay times are transmission delays, the software comprising instructions for causing the system to:

compute a respective transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, each transmission delay being computed such that ultrasound beams transmitted by respective transducer elements will constructively interfere at a selected focal point.

47. The software of claim 45, wherein the focusing delay times are reception delays, the computer program comprising instructions for causing the system to:

compute respective reception delays for transducer elements receiving ultrasound beams passing through the selected tissue region, the reception delays being computed such that ultrasound beams reflected from reflecting bodies in the pass zone will be in phase.

48. The software of claim 45, further comprising instructions to:

provide the respective computed focusing delay times to a beam former; and

conduct ultrasound imaging of the site of interest employing the computed adjusted delay times.

49. The software of claim 45, comprising instructions to determine the boundaries of the region by segmenting the tissue region from adjacent tissue regions.

50. The software of claim 45, comprising instructions to:

determine the boundaries of the selected tissue region from ultrasound imaging data of a plurality of sectional planes through the site of interest; and

determine a three dimensional boundary of the selected tissue region based on the determined boundaries.

51. The software of claim 45, comprising instructions to determine, from three dimensional ultrasound imaging data, a three dimensional boundary of the selected tissue region in the pass zone.

52. The software of claim 45, further comprising computing the respective focusing delay times based, at least in part, on refraction of ultrasound beams passing through the selected tissue region at the boundaries of the selected tissue region.

53. The software of claim 45, wherein the speed of sound other than the average speed of sound is about a speed of sound in the selected tissue region.

54. The software of claim 45, wherein the selected tissue region is from the group consisting of fat tissue, bone tissue and muscle tissue.

55. A method of computing focusing delay times for use in ultrasound imaging of a site of interest in a body using an ultrasound probe, the ultrasound probe comprising a plurality of ultrasound transducer elements, the method comprising:

determining, from ultrasound imaging data of a pass zone between a site of interest in the body and the ultrasound probe, boundaries of a selected one of a plurality of tissue regions in the pass zone; and

computing respective focusing delay times for each transducer element associated with an ultrasound beam passing through the selected tissue region during imaging, the respective delay times being computed based, at least in part, on a speed of sound in, and the determined boundaries of, the selected tissue region, wherein the speed of sound is other than an average speed of sound in body tissue.

56. The method of claim 55, wherein the focusing delays are transmission delays, the method comprising:

computing a respective transmission delay for each transducer element transmitting an ultrasound beam through the selected tissue region, the transmission delays computed such that ultrasound beams transmitted by respective transducer elements will constructively interfere at a focal point proximate the site of interest, wherein the speed of sound other than the average speed of sound is about a speed of sound in the selected tissue region; and

computing respective reception delays for each transducer element receiving an ultrasound beam passing through the selected tissue region, the reception delays computed such that ultrasound beams reflected from reflecting bodies in the pass zone are in phase, wherein the speed of sound other than the average speed of sound is about a speed of sound in the selected tissue region.

57. The method of claim 55, further comprising computing the respective focusing delay times based, at least in part, on refraction of ultrasound beams passing through the selected tissue regions at the boundaries of the selected tissue region.

58. An ultrasound probe comprising:

a body portion;

a plurality of low frequency transducer elements supported by the body portion; and

a plurality of high frequency transducer elements supported by the body portion.

59. The ultrasound probe of claim 58, wherein the low frequency transducer elements are supported in a first section of the body portion and the high frequency transducer elements are supported in the second and third sections of the body portion, the second and third sections being on opposite sides of the first section.

60. The ultrasound probe of claim 59, wherein the first, second and third sections are linearly positioned.