1. Pegasus Lectures, Inc. COPYRIGHT 2006 Volume II Companion Presentation Frank R. Miele Pegasus Lectures, Inc. Ultrasound Physics & Instrumentation 4 th Edition

2. Pegasus Lectures, Inc. COPYRIGHT 2006 License Agreement This presentation is the sole property of Pegasus Lectures, Inc. No part of this presentation may be copied or used for any purpose other than as part of the partnership program as described in the license agreement. Materials within this presentation may not be used in any part or form outside of the partnership program. Failure to follow the license agreement is a violation of Federal Copyright Law. All Copyright Laws Apply.

3. Pegasus Lectures, Inc. COPYRIGHT 2006 Volume II Outline  Chapter 7: Doppler  Chapter 8: Artifacts  Level 2  Chapter 9: Bioeffects  Chapter 10: Contrast and Harmonics  Chapter 11: Quality Assurance  Chapter 12: Fluid Dynamics  Chapter 13: Hemodynamics

4. Pegasus Lectures, Inc. COPYRIGHT 2006 Chapter 8: Artifacts Artifacts are any perturbation of a signal which distorts a display from “truth”. Understanding the principles and mechanisms of artifacts is one of the most important aspects of learning to perform and interpret ultrasound.  There are times when artifacts are extremely useful for making a correct diagnosis. The utility of these artifacts exists only when there is an understanding of the physics which results in these artifacts.  There are other times when artifacts obscure the information necessary. In these cases, minimizing the artifacts is critical and can only be achieved by a thorough understanding of the physical mechanisms which produce these artifacts.

5. Pegasus Lectures, Inc. COPYRIGHT 2006 Detail Resolution Artifacts associated with limited detail resolution include an inability to correctly visualize dimensions or even the presence of structures laterally, axially, and/or elevationally.

6. Pegasus Lectures, Inc. COPYRIGHT 2006 Lateral and Axial Resolution Fig. 1: (Pg 595) Pin Group 1 demonstrates the limit in axial resolution. Notice that the red arrow indicates the closest axially spaced pins still easily distinguishable. Pin Group 2 demonstrates the limit in lateral resolution. The green arrow indicates the closest laterally spaced pins still distinguishable. Pin 3, indicated by the yellow arrow shows how much lateral distortion there is at greater depths, where the beam is diverging. Pin 3 has the same physical dimension as all of the pins located in the line of pins directly above.

7. Pegasus Lectures, Inc. COPYRIGHT 2006 “Noise” eliminated by harmonics Elevation Resolution Elevation is usually the “forgotten” dimension, since (unless using 3-D imaging) there is no way of directly visualizing the elevation plane which corresponds to the image slice thickness. Fig. 2 & 3: (Pg 596) “Noise” from “slice thickness”

8. Pegasus Lectures, Inc. COPYRIGHT 2006 Locational Artifacts As the name suggests, “locational” artifacts result in structures appearing in an incorrect positions within the image. There are many sources of locational artifacts such as: Refraction Reverberation Comet tail Ring Down Multipath Grating lobes (and side lobes) Speed Error Range Ambiguity Mirror Image

9. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 4: (Pg 597) Refraction Artifact Refraction was discussed in detail in Chapter 3. Refraction artifact results in a lateral displacement of the structure within the image. Refracting Interface Strong Reflector (real) Displayed Image (Artifact)

10. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 5: (Pg 597) Refraction Artifact

11. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 598) Refraction Artifact (Animation)

12. Pegasus Lectures, Inc. COPYRIGHT 2006 Reverberation results in spurious structures caused by sound which reverberates, or rings, between two or more surfaces.  Reverberation is more likely when there is a large acoustic impedance mismatch and relatively specular reflection  Reverberation is highly angularly dependent  Reverberation is usually worst when the sound is perpendicular to the specular reflecting interface.  Reverberation causes all structures and tissue between the reverberating structures to be replicated as well as the reverberating structure itself.  Reverberation is very common and often not identified by the person scanning or by the person interpreting the scan. Reverberation

13. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 7: (Pg 599) Reverberation Artifact (simple case)

14. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 7: (Pg 599) Reverberation Artifact (simple case) As displayed in the last slide, the simple mechanism for this reverberation artifact is reverberation with the transducer surface.

15. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 599) Reverberation Artifact (Animation) Reverberation from a 20 gauge needle during a biopsy of a superficial mass.

16. Pegasus Lectures, Inc. COPYRIGHT 2006 In this case, the reverberation occurs between the surface of the transducer and the anterior surface of a structure. Reverberation: Simple Continued 123 1 cm 2 cm 3 cm Artifactual Real

17. Pegasus Lectures, Inc. COPYRIGHT 2006 Reverberation: Increasing Complexity In this case, there are multiple reverberation paths. Don’t believe everything you see! 1 cm 2 cm 3 cm 1 2 3 True structures 12 3

18. Pegasus Lectures, Inc. COPYRIGHT 2006 Reverberation In this image of a silicon breast implant, there are many examples of reverberation artifact. 123 123

19. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 8: (Pg 600) Reverberation (multiple specular reflectors) Subclavian artery with multiple reverberation paths Strong Reflecting Surfaces

20. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 9: (Pg 601) Reverberation with Color Reverberation causing false color vessel – often referred to as a “Mirror” artifact.

21. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 601 B) Reverberation (Animation) Note that the same reverberation path causes color and spectral artifacts as well as the 2-D artifact.

22. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 10: (Pg 602) Reverberation There are times when reverberation can appear very similar to a thrombus.

23. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 11: (Pg 602) Reverberation Artifactual pedunculated mass caused by reverberation artifact.

24. Pegasus Lectures, Inc. COPYRIGHT 2006 Reverberation (Ring Down) The sound is ringing between the boundary of the air sacs within the biliary tree causing a reverberation artifact often called “Ring Down”. Fig. 12: (Pg 603)

25. Pegasus Lectures, Inc. COPYRIGHT 2006 Ringdown This image from the animation CD is a transverse scan of a liver in a patient with a stent in the common bile duct. The stent has allowed air into the biliary system causing pneumobilia. The air is the cause of the obvious ring down artifact. (Pg 603 A)

26. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 604 A) Reverberation: Comet Tail (Animation) Comet tail (reverberation within a metallic structure or high impedance medium) in a prosthetic valve (St Jude).

27. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 604 B) Reverberation: Comet Tail Comet tail from a calcification in the prostate gland (from Animation CD).

28. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 604 C) Twinkle Artifact: Comet Tail “Twinkle” artifact is refers to the resulting color artifact equivalent to comet tail reverberation. “Twinkle” in this case is caused by a small stone in the distal ureter at the ureterovesical junction (from Animation CD).

29. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 604 D) Twinkle Artifact: Comet Tail In this case, the color “comet tail” is from the metal of a prosthetic aortic valve (from Animation CD).

30. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 14: (Pg 604) Multi-path Artifact Multi-path artifact results in a structure appearing deeper than reality because of the elongated path length.

31. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 15: (Pg 605) Grating Lobes Grating lobes (for multi-elements and side lobes for single elements) result in a lateral displacement of structures within an image. As the name suggest, there is energy in regions other than the main beam which cause reflections. (Grating lobes are weaker lobes of energy in direction other than main beam direction) Spurious second aortic valve root Beam Directivity

32. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 16: (Pg 606) Speed Error The system assumes a propagation speed of 1540 m/sec. When the propagation speed is different than 1540 m/sec, structures are drawn at incorrect depths.

33. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 17: (Pg 606) Speed Error Artifact Example This speed error case results from a needle entering into a cystic structure. The needle appears bent giving rise to the name “broken needle” or “bayonet” sign.

34. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 18: (Pg 607) Range Ambiguity Artifact As mentioned in Chapter 7, all pulsed wave modalities, including 2-D imaging, suffer from range ambiguity artifact. Recall that range ambiguity artifact is the result of reflected data from the previous acoustic transmit adding to the reflection of the current acoustic line. Notice in the figure that the dotted line represents the unwanted data returning from the previous transmit (in the depth region of 1 cm to 2 cm) that superimposes into the current line of data (in the depth region of 0 cm to 1 cm).

35. Pegasus Lectures, Inc. COPYRIGHT 2006 Range Ambiguity Every acoustic line of the image is “corrupted” by data from the previous transmit. Notice how the image at depth “0” is affected by the reflection from depth “x” of the previous line. Similarly, the image just slightly deeper than “0” is affected by the reflections from just slightly deeper than the depth of “x” from the previous line. This process continues until the depth of “x” is affected by the reflection from the previous line reflection from “2x”. 2x x 0

36. Pegasus Lectures, Inc. COPYRIGHT 2006 Mirroring Mirroring results in an artificial structure symmetric to the actual structure across the “mirroring structure”. Strong Reflector “Mirrored” Structure caused by reflection of beam 1 Real Structure drawn correctly by beam 2 1 2

37. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 19: (Pg 607) Mirror Artifact This mirror image of a calcification in the liver is produced by reflection from the diaphragm.

38. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 20: (Pg 608) Mirror Artifact This image shows a large mirror artifact of a multi-nodular goiter reflected across the trachea.

39. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 21: (Pg 608) Shadowing Artifact Shadowing is caused by excessive reflection, absorption, or refraction. This case is shadowing produced by excessive reflection from a gallstone.

40. Pegasus Lectures, Inc. COPYRIGHT 2006 Shadowing Artifact Example This image demonstrates shadowing caused by excessive reflection as well as the obvious “ring down” artifact caused by pneumobilia.

41. Pegasus Lectures, Inc. COPYRIGHT 2006 Shadowing Artifact Example In this image there are many artifacts, including shadowing caused by calcifications within a heterogeneous plaque.

42. Pegasus Lectures, Inc. COPYRIGHT 2006 “Edge” (refractive) Shadowing Edge shadowing is caused by excessive refraction and commonly occurs from the edges vessels, cystic structures, and bones.

43. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 22: (Pg 609) Refractive (edge) Shadowing The shadowing evident in this fetal skull image is caused by refraction, not reflection from the bone. Notice how the shadow only exists in regions where the incident angle is far away from 0 degrees (recall Snell’s law).

44. Pegasus Lectures, Inc. COPYRIGHT 2006 Calculating the Critical Angle Fig. 23: (Pg 609) The calculation shows that total internal reflection occurs at an angle of approximately 35 degrees. Recall that the transmitted angle equals 90 degrees for the critical incident angle.

45. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 609 A) Shadowing: Case 1 (from Animation CD) Shadowing caused by reflection and absorption from the spiny process above a normal vertebral artery.

46. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 609 B) Shadowing: Case 2 (from Animation CD) The same vertebral artery as last slide. Notice how the angle of the shadow is different for the 2D image than for the color image (since the color is steered separately from the 2D).

47. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 609 C) Shadowing: Case 3 (from Animation CD)

48. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 609 D) Shadowing: Case 4 (from Animation CD) Image of a right kidney with shadowing from 2 kidney stones.

49. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 609 E) Shadowing: Case 5 (from Animation CD) Image of a breast with a silicon implant. The combination of a shadow and reverberation produce what is sometimes referred to as a “dirty shadow”.

50. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 25: (Pg 610) Enhancement Enhancement from an anechoic cyst in the liver.

51. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 24: (Pg 610) Enhancement Artifact Enhancement is the reciprocal of shadowing. Enhancement is most common deeper than a fluid filled structure. In this case, enhancement is from the blood pool in the femoral artery.

52. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 610 A) Enhancement: Case 1 (from Animation CD) Image of a fatty breast cyst creating enhancement.

53. Pegasus Lectures, Inc. COPYRIGHT 2006 Enhancement: Case 2 (from Animation CD) Enhancement from the blood pool within a femoral vein. (Pg 610 B)

54. Pegasus Lectures, Inc. COPYRIGHT 2006 Doppler Artifacts There are many Doppler artifacts to consider such as:  Aliasing  Range Ambiguity  Spectral Mirroring  Spectral Broadening  Blossoming  Circuit Saturation  Refraction

55. Pegasus Lectures, Inc. COPYRIGHT 2006 Aliasing Aliasing results when the Nyquist criterion is violated. When the Doppler frequency shift is greater than one half of the PRF, the Doppler signal wraps around either the spectrum (spectral Doppler) or the color scale (Color Doppler). Note that in this case, even though there is a true alias, since the peak velocity falls within the spectral window, it is still possible to determine the true peak velocity. Fig. 26: (Pg 611)

56. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 27: (Pg 611) Aliasing Note that in this case, the aliasing is a true alias in that it is not possible to determine the actual peak velocity.

57. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 611 A) Aliasing: (from Animation CD) A: Aliased Flow B: Shift Baseline (still aliased) C: Increase Scales (no aliasing)

58. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 611 B) Aliasing (Animation)

59. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 611 C) Aliasing Animation

60. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 28: (Pg 612) Color Aliasing As discussed in Chapter 7, aliasing is more likely to occur within the center of a vessel, whenever there is a bend, branch, narrowing, etc., when the angle is closer to 0 or 180 degrees, when the scales are low, and the transmit frequency is high. How many reasons can you find for why there is aliasing in this image?

61. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 612 A) Color Aliasing Case 1: (from Animation CD)

62. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 612 B) Color Aliasing Case 2: (from Animation CD)

63. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 612 C) Color Aliasing Case 3: (from Animation CD)

64. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 612 D) Color Aliasing Case 4: (from Animation CD)

65. Pegasus Lectures, Inc. COPYRIGHT 2006 Range Ambiguity In Chapter 7, the concept of range ambiguity was discussed in detail. Recall that range ambiguity is the potential to detect signals from deeper depths as the echo from previous transmit events overlaps the echoes from the current transmit event. Not only do all pulsed wave modalities exhibit range ambiguity, its mechanism is so predictable, that the spectral Doppler modality of HPRF is created by intentionally manipulating the range ambiguity artifact.

66. Pegasus Lectures, Inc. COPYRIGHT 2006 Spectral Mirroring Spectral mirroring results in an artificial Doppler signal to be displayed in the opposite direction of the true flow. The following conditions exacerbate spectral mirroring:  excessive transmit  excessive receive gain  superficial Doppler with high frequency transducer  Insonification angle close to 90 degrees  poor electronic design (poor separation between I and Q channels)

67. Pegasus Lectures, Inc. COPYRIGHT 2006 Spectral Mirroring: Case 1 An obvious case of spectral mirroring. The flow below the baseline is purely artifactual. Fig. 29: (Pg 612)

68. Pegasus Lectures, Inc. COPYRIGHT 2006 Spectral Mirroring: Case 2 (from Animation CD) As the gain is reduced, the apparent spectral mirroring decreases. (Pg 613 A)

69. Pegasus Lectures, Inc. COPYRIGHT 2006 Spectral Mirroring: Case 3 (from Animation CD) Sometimes it is difficult to tell what is real and what is artifact. Look for symmetry of the highest amplitude signals (brightest) about the baseline. (Pg 613 B)

70. Pegasus Lectures, Inc. COPYRIGHT 2006 Mirroring or Reverse Flow? Is the reverse flow real or a spectral mirror? Answer: Real flow at bifurcation in transcranial Doppler

71. Pegasus Lectures, Inc. COPYRIGHT 2006 Mirroring or Reverse Flow? (from Animation CD) Is the reverse flow real or a spectral mirror? Answer: Mirroring (Pg 613 C)

72. Pegasus Lectures, Inc. COPYRIGHT 2006 Spectral Mirroring Caused By Angle When the insonification angle is close to 90 degrees, elements on one side of the steer line will see flow towards the transducer, whereas elements on the other side of the steer line will see flow away – resulting in a spectral mirror. Fig. 30: (Pg 613) < 90° “Forward Flow” > 90° “Reverse Flow”

73. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 32: (Pg 614) Spectral Spread (Broadening) Spectral spread causes overestimation of the peak velocity as well as the diminishment of a “spectral window”. Fig. 31: (Pg 613) 80° (cosine correction too large) 60° (cosine correction too small) 70° True Spectrum Peak too high Window Diminished

74. Pegasus Lectures, Inc. COPYRIGHT 2006 Minimizing Spectral Spread Spectral spread is exacerbated by:  large array transducers (linear arrays)  superficial gate location  large insonification angles (especially as the angle get larger than 60º)  excessive gain

75. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 33a & 33b: (Pg 614) Spectral Broadening As just mentioned, spectral Broadening is exacerbated by larger insonification angles. In this case, compare the spectrum at 55 ° with the spectrum at 70°. 55 ° 70 °

76. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 34 & 35: (Pg 615) Blossoming Artifact Blossoming results when the signal is overgained. Blossoming results in a higher than true peak velocity as well as the potential loss or decrease of the spectral window (when one exists) in PW Doppler. Appropriate Gain Blossoming Artifact

77. Pegasus Lectures, Inc. COPYRIGHT 2006 (Pg 615) Blossoming Artifact (from Animation CD)

78. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 36: (Pg 616) Wall Filter Saturation As discussed in Chapter 7, when the dynamic range is not adequately reduced by the wall filters, circuit saturation occurs as evidenced in this spectrum.

79. Pegasus Lectures, Inc. COPYRIGHT 2006 Fig. 37: (Pg 616) Refraction and Total Internal Reflection Refraction was discussed in detail in Chapter 3. Total internal reflection can result in a loss in spectral signal as indicated in the diagram below. Total Internal Reflection θ i = θ critical XDCR

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