USG Artifacts.........................................

Artifacts in gray scale ultrasound imaging.

1. Artifacts in USG

2. Artifacts Any part of an image that doesn’t actually represent the anatomic structures present within the subject being evaluated. In general ,USG artifacts may be: a. structures that appear in the display but anatomically not present. b. structures that don’t appear in the display but anatomically present.

3. Why do artifacts arise? We make following assumptions in USG imaging: Sound wave arise uniformly from the transducer. Echoes return back after a single reflection. Depth is simply the time taken for the round trip of the sound. Speed of sound waves in human soft tissue is constant at 1540m/sec. Echoes travel in straight path. Acoustic energy of USG beam in uniformly attenuated.

4. Artifacts arise from Inherent characteristics of the USG beam. Presence of multiple echoes. Errors in velocity. Errors in attenuation.

5. 1.Artifacts Associated with Ultrasound Beam Characteristics Two artifacts associated: Beam width artifacts Side lobe artifacts The ultrasound beam exits the transducer bowtie shape with additional off-axis low-energy beams, which are referred to as side lobes and grating lobes. A strong reflector located outside of the main ultrasound beam may generate echoes that are detectable by the transducer. These echoes will be falsely displayed as having originated from within the main beam.

6. Beam width artifacts The main ultrasound beam exits the transducer at approximately the same width as the transducer, then narrows as it approaches the focal zone and widens again distal to the focal zone Artifacts occurs if structure lie in the diverging width of the beam but out of the line of the transducer. Artifact will be the display of that very image combined with other image.

7. Beam width artifact C linically most commonly seen in urinary bladder.

8. Overcome by Adjusting focal length to level of interest Placing the transducer at the center of object of interest.

9. Side lobe artifacts Are multiple beams of low-amplitude ultrasound energy that project radially from the main beam axis. Produced by radial expansion of piezoelectric crystals. Mainly seen in linear array transducer

10. Side lobe artifacts When a strong reflectors present in the path of these low-energy, off-axis beams may create echoes detectable by the transducer. These echoes will be displayed as having originated from within the main beam in the side lobe artifact

11. Side lobe artifact

12. 2.Artifacts associated with multiple echoes System assumes echoes return after single reflection and the depth of the structures imaged is the time taken for round travel. Types: a. Reverberation artifact Comet tail artifact Ring down artifact b. Mirror image artifact

13. In the presence of two parallel highly reflective surfaces, the echoes generated from a primary beam may be repeatedly reflected back and forth before returning to the transducer. When this occurs, multiple echoes are recorded and displayed. The echo that returns to the transducer after a single reflection will be displayed in the proper location. The sequential echoes will take longer to return to the transducer, and the ultrasound processor will place the delayed echoes at equidistance Reverberation artifacts

14. Reverberation artifact Mainly two types Comet tail artifact Ring down artifact

15. Two reflective surfaces are very close. Echoes from these surfaces are very near and it is difficult for the system to perceive individual signals. Echoes that arrive late have reduced amplitude. Triangular tapered image is created and displayed. Comet tail artifact

16. Comet tail artifact Adenomyomatosis of GB Comet tail artifacts: Adenomyomatosis of gb Colloid nodules in thyroid Biliary hamartoma Pancreatic calcifications Small renal or ureteric calculi Testicular microlithiasis

17. Ring down artifact Arise when fluid is trapped centrally surrounded by bubbles of air. T he transmitted ultrasound energy causes resonant vibrations within fluid These vibrations create continuous sound wave transmitted back to transducer. Displayed as series of parallel bands extending posterior to the gas collection.

18. Ring down artifacts

19. Occurs when primary beam encounters highly reflective surface. Reflected beam encounter the back side of another structure and are reflected back to the reflective interface. Two mirror image structures equidistant from the reflective interface are seen. Diaphragm and pleural air interface is an example. Mirror image artifacts

20. Mirror image artifacts

21. 3. Artifacts associated with velocity errors Arise because velocity of sound wave differs in various parts of the body. The average velocity in human body of the sound waves considered as 1540m/s. Deviation from this causes these artifacts. Types: speed displacement artifact. refraction artifact.

22. Speed displacement artifact Arise when the sound wave encounters two medium with different velocities for the wave. If the encountered structure has lesser velocity that the surrounding than the resultant display of the structure of interest will be farther than its actual anatomical position.

23. Speed displacement artifact

24. Refraction artifact Arise when sound travels in medium with two different velocities and sound wave changes its original course. Refraction isn't read by the system and the images are displayed in a single line. Occur in pelvic structures deep to the rectus muscles and fat. Structure may be wide and duplicated.

25. Refraction artifact

26. GHOSTING ARTIFACTS S een due to refraction Centrally, no refraction occurs and the true position (black circle) of the object is obtained. Transverse US image of the liver shows ghosting artifact of the aorta, which appears in duplicate (arrows) deep to the rectus abdominis musculature

27. EDGE shadowing Diagram shows edge shadowing (defocusing) at the edge of a cystic structure with a different speed of sound than that of the surrounding medium. Refraction is greatest at the edges, resulting in shadowing due to the decreased beam intensity to deeper tissue

28. 4. Artifacts associated with attenuation errors Different structures attenuate sound beam differently. W hen the ultra- sound beam encounters a strongly attenuating or highly reflective structure, the amplitude of the beam distal to this structure is diminished T he echoes returning from structures beyond the highly attenuating structure will also be diminished. I n clinical imaging, this phenomenon is recognized as a dark or hypoechoic band. Types: Distal acoustic shadowing Distal acoustic enhancement or increased through transmission

29. When an us beam encounter focal material that attenuates sound greater than the surrounding tissue, strength of the beam distal to this structure will be weak. Arise from solid structures like bone, stone. Also arise form air with dirty distal shadow. Distal acoustic shadowing

30. Distal acoustic shadowing

31. When an us beam encounter focal material that attenuates sound lesser than the surrounding tissue, strength of the beam distal to this structure will be strong. Arise from cystic structures. Distal acoustic enhancement

32. Distal acoustic enhancement

33. Clinical significance of attenuation artifacts Distal acoustic enhancement and distal acoustic shadowing can be used by radiologist to determine the composition of tissue to narrow down the differential

34. M i scellaneous artifacts ANISOTROPy Due to Electronic interference ( spiking artifacts) BAnDING artifacts B ayonet artifacts Artifacts related to probe

35. Anisotropy These artifacts arise in MSK imaging. When USG beam strikes fibrils of structures the reflected waves travel away from the transducers. Reflected echoes returning back to the transducer depends upon the angle of incident beam. Maximum echoes return if the angle of incidence is perpendicular. May lead to incorrect diagnosis of tendon tears and tendinosis.

36. Anisotropy

37. S piking artifacts If non-dedicated electrical outlet is used along with another piece of equipment turned on , spurious electronic signals are detected by the US system  bands of noise are displayed.

38. Banding artifacts B and of increased brightness is seen at the focal zone. I mproper focal zone setting or time gain compensation settings can create banding artifact Appearance:- B and of increased brightness.

39. B ayonet artifacts S een in ultrasound guided needle techniques Results in apparent bending of needle as it passes into tissue with different sound transmission speed.

40. Artifacts related to probe Dropout artifacts B and of reduced echogenecity with loss of continuity of the reverberation pattern is noted in t he scan field D ead piezo elements can results in dropout artifacts.

41. D e lamination D isrupted reverberation pattern without complete signal loss D ue to weak piezo-element or manufacturing defect

42. Conclusion Artifacts are commonly encountered in usg . Often they are unavoidable.when done with proper technique, some artifacts can be minimized. Ability to recognize potentially correctable artifacts a. improve image quality. b. optimal patient care. Artifacts may give clue to tissue composition

43. Reference Diagnostic ultrasound, rumac & levine 5 th editions. US artifacts, volume 29 , number 4, 2009 , RSNA

44. Thank you