Ultrasonic Nonlinear Imaging- Tissue Harmonic Imaging

1. Ultrasonic Nonlinear Imaging-Tissue Harmonic Imaging

2. Tissue Nonlinear Imaging • Imaging based on nonlinear propagation in tissue. • Motivation: • Performance of ultrasound has been sub-optimal on technically difficult bodies. • Most recent new developments have bigger impact on technically satisfactory bodies. • Poor image quality leads to uncertainty in diagnosis and costly repeat examinations.

3. Tissue Harmonic Imaging • Methods to improve image quality: • Different acoustic window. • Lower frequency. • Adaptive imaging. • Non-linear imaging (or harmonic imaging).

4. Finite Amplitude Distortion Sound Velocity and Density Change Phase velocity Nonlinearity Particle velocity

5. When Peak Pressure Is Very High Shock Wave

6. Non-linear Parameter B/A • B/A defines non-linearity of the medium. The larger the B/A, the higher the non-linear response.

7. B/A Parameters: Typical Values • Typical values: • Water:5.5+/-0.3. • Liver: 7.23. • Fat: 10.9. • Muscle: 7.5. • B/A imaging may be used for tissue characterization.

8. transducer transducer Nonlinear Propagation

9. Reduction of Imaging Artifacts

10. Reduction of Imaging Artifacts

11. Advantages of Tissue Harmonic Imaging • Low sidelobes. • Better spatial resolution compared to fundamental imaging at the original frequency. • Less affected by tissue inhomogeneities – better performance on technically difficult bodies.

12. Non-linear Propagation: Numerical Analysis (1) • The frequency domain solution to Burgers’ equation: where b=1+B/(2A).

13. Wave at distance z angular spectrum method Linear propagation to z+Dz frequency domain solution to Burgers’ equation Nonlinear propagation at z+Dz Non-linear Propagation

14. Non-linear Propagation: Numerical Analysis (2) • KZK equation: diffraction loss quadratic nonlinearity

15. Characteristics in Tissue

16. Non-Linear Propagation

17. Non-Linear Propagation

18. Non-Linear Propagation One way Two way

19. Non-Linear Propagation

20. Nonlinear Propagation with Tissue Inhomogeneities

21. Sidelobe Reduction in Inhomogeneous Tissue

22. Requisite Field Amplitude

23. Increasing Harmonic Generation by Multiple Transmit Focusing

24. Harmonic Generation and Multiple Transmit Focusing

25. Harmonic Generation and Multiple Transmit Focusing

26. Pulse Bandwidth and Spectral Leakage

27. Axial Resolution vs. Harmonic Separation

28. Harmonic Leakage and Image Quality Degradation

29. Harmonic Leakage and Pulse Types

30. Harmonic Leakage and Bandwidth

31. Harmonic Leakage and Tissue Inhomogeneities

32. Harmonic Leakage from System Nonlinearity

33. Harmonic Leakage and Pulse Inversion

34. Harmonic Leakage and Pulse Inversion

35. Motion Artifacts in Pulse Inversion Imaging

36. Axial Motion

37. Lateral Motion

38. Motion Artifacts

39. Motion Artifacts

40. Motion Compensation

41. Motion Compensation • It is relatively easy to compensate for axial motion, but how about lateral and elevational motion?

42. Higher Order Nonlinear Imaging (Higher Order  Higher Harmonic)

43. Amplitude-Encoded Pulse Sequence For a point target:

44. Amplitude-Encoded Pulse Sequence

45. Spectral Convolution

46. Phase-Encoded Pulse Sequence 2-pulse 3-pulse

47. More Clinical Examples

48. Clinical Examples (1)

49. Clinical Examples (2)

50. Clinical Examples (3)