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ultrasoundartifacts-200113150706.pdf
- 1. ULTRASOUND ARTIFACTS MAAJID MOHIUD DIN MALIK LECTURER COPMS ADESH UNIVERSITY BATHINDA PUNJAB
- 2. What is anArtifact? Artifact is used to describe any part of an image that does not accurately represent the anatomic structures present within the subject being evaluated.
- 3. In ultrasonography (US),artifacts may cause structures to appear in an image that are not present anatomically or a structure that is present anatomically may be missing from the image. US artifacts may also show structures as present but incorrect in location, size, or brightness.
- 4. US is proneto numerous imaging artifacts, and these are commonly encountered in clinical practice. Artifacts have the potential to interfere with image interpretation. Ultrasound display equipment relies on physical assumptions to assign the location and intensity of each received echo.
- 5. TYPES OF ARTIFACTS Acousticenhancement Acoustic shadowing Anisotropy Beam width artifact Blooming artifact Comet tail artifact Electrical interference artifact Hardware-related artifacts
- 6. Mirror image artifact Multipathartifact Reverberation artifact Ring down artifact Side lobe artifact Speckle artifact Twinkling artifact
- 7. Acoustic enhancement Acoustic enhancement,also called posterior enhancement or enhanced through transmission, refers to the increased echoes deep to structures that transmit sound exceptionally well.
- 8. This is characteristicof fluid filled structures such as cysts, the urinary bladder and the gallbladder. The fluid only attenuates the sound less than the surrounding tissue. The time gain-compensation (TGC) overcompensates through the fluid-filled structure causing deeper tissues to be brighter. Simply it is seen as increased echogenicity (whiteness) posterior to cystic area. The presence of acoustic enhancement aids in the identification of cystic masses but some solid masses, especially lymphoma, may also show acoustic enhancement posteriorly.
- 9. ACOUSTIC SHADOWING Acoustic shadowingon an ultrasound image is characterized by a signal void behind structures that strongly absorb or reflect ultrasonic waves. This happens most frequently with solid structures, as sound conducts most rapidly in areas where molecules are closely packed, such as in bone or stones.
- 10. ANISOTROPY Anisotropy is anartifact encountered in ultrasound, notably in muscles and tendons during a musculoskeletal ultrasound. In musculoskeletal applications, the artifact may prompt an incorrect diagnosis of tendon tear.
- 11. When the ultrasoundbeam is incident on a fibrillar structure as a tendon or a ligament, the organized fibrils may reflect a majority of the insonating sound beam in a direction away from the transducer. When this occurs, the transducer does not receive the returning echo and assumes that the insonated area should be hypoechoic.
- 12. This anisotropic effectis dependent on the angle of the insonating beam. The maximum return echo occurs when the ultrasound beam is perpendicular to the tendon. Decreasing the insonating angle on a normal tendon will cause it to change from brightly hyperechoic (the actual echo from tightly bound tendon fibers) to darkly hypoechoic. If the angle is then increased, the tendon will again appear hyperechoic.
- 13. If the artifactcauses a normal tendon to appear hypoechoic, it may falsely lead to a diagnosis of tendinosis or tear. In some situations, anisotropy may be useful in diagnosis. If a tendon is surrounded by other brightly hyperechoic structures (e.g. fat), then altering the angle of the transducer will cause the tendon to become hypoechoic, differentiating it from the other structures.
- 14. Beamwidthartifact Ultrasound beam widthartifact occurs when a reflective object located beyond the widened ultrasound beam, after the focal zone, creates false detectable echoes that are displayed as overlapping the structure of interest.
- 15. To understandthis artifact, it is important to remember that the ultrasound beam is not uniform with depth, the main beam leaves the transducer with the same width as it, then narrows as it approaches the focal zone and widens again distal to this zone. Usually, it occurs when scanning an anechoic structure and some peripheral echoes are identified, i.e. Gas bubbles in the duodenum simulating small gallstones and peripheric echoes in the bladder. It is possible to avoid this artifact adjusting the focal zone to the depth level of interest and by placing the transducer at the center of the object being studied.
- 16. BLOOMING ARTIFACT Blooming orcolor bleed artifact occurs when the color signal indicating blood flow extends beyond its true boundaries, spreading into adjacent regions with no actual flow. This artifact mainly affects the portion of the image distal to the vessel and the transducers. It is somewhat similar to its MRI namesake as both phenomena denote something that seemingly appears larger than its true physical limits.
- 17. Blooming occurs becausethe spatial resolution of color Doppler is lower than greyscale ultrasound . It can be exaggerated by inappropriately high color gain. It is important to be aware of as it may obscure partial occlusions such as thrombi resulting in misdiagnosis . It can be avoided by lowering the color gain until the bleed of signal outside of the vessel disappears.
- 18. COMET-TAIL ARTIFACT The comet-tailartifact is a grey-scale ultrasound finding seen when small calcific / crystalline / highly reflective objects are interrogated and is believed to be a special form of reverberation artifact. It is similar to the color comet-tail artifact and is seen in similar situations, although is in general less sensitive than the latter.
- 19. Small renal orureteric calculi Small common bile duct stones Adenomyomatosis of the gallbladder Pancreatic calcifications of chronic pancreatitis Testicular microlithiasis (sometimes) Thyroid colloid nodules Identification of foreign bodies Surgical clips Catheter tips Debris / glass / metal
- 20. Electrical interference artifact Electricalinterference artifact is an ultrasound artifact usually caused by the ultrasound machine being too close to the unshielded electrical equipment. The disturbance appears as arc-like moving bands in the ultrasound image.
- 21. While the presenceof electrical equipment (e.g. unshielded ventilators) near the ultrasound machine may cause this artifact because of external electronic signals, the artifact can also occur when the ultrasound probe malfunctions.
- 22. Mirror image artifact Mirrorimage artifact in sonography is seen when there is a highly reflective surface (e.g. diaphragm) in the path of the primary beam. The primary beam reflects from such a surface (e.g. diaphragm) but instead of directly being received by the transducer, it encounters another structure (e.g. a nodular lesion) in its path and is reflected back to the highly reflective surface (e.g. diaphragm). It then again reflects back towards the transducer.
- 23. The ultrasound machinemakes a false assumption that the returning echo has been reflected once and hence the delayed echoes are judged as if being returned from a deeper structure, thus giving a mirror artifact on the other side of the reflective surface. It is a friendly artifact that allows the sonographer to exclude pleural effusion by the reflection of the liver image through the diaphragm.
- 24. Examples: reflection of aliver lesion into the thorax (the commonest example) reflection of abdominal ascites mimicking pleural effusion duplication of gestational sac (either ghost twin or heterotopic pregnancy) duplication of the uterus To avoid this artifact, change the position and angle of scanning to change the angel of insonation of the primary ultrasound beam.
- 25. Multipathartifact A multipath artifactis an ultrasound beam artifact in which the primary beam reflects off anatomy at an angle, resulting in a portion of the beam returning to the transducer, whilst another portion takes a longer duration as it reflects a second structure. This phenomenon results in a propagation path error in which the transducer will interpret a structured to be deeper than it is.
- 26. REVERBERATION ARTIFACT Reverberation artifactoccurs when an ultrasound beam encounters two strong parallel reflectors. When the ultrasound beam reflects back and forth between the reflectors ("reverberates"), the ultrasound transducer interprets the sound waves returning as deeper structures since it took longer for the wave to return to the transducer.
- 27. Reverberation artifacts canbe improved by changing the angle of insonation so that reverberation between strong parallel reflectors cannot occur. Comet-tail artifact is a specific type of reverberation artifact. This results a short train of reverberations from an echogenic focus which has strong parallel reflectors within it (e.g. Cholesterol crystals in Adenomyomatosis).
- 28. Ring down artifact Ringdown artifact is a special type of resonance artifact. Its appearance is similar to the ladder-like reverberation of comet-tail artifact, but it is produced by a completely different mechanism.
- 29. The artifactis only associated with gas bubbles, and occurs when an ultrasound pulse encounters a "horn" or "bugle" shaped fluid collection that is trapped between an inverted tetrahedron of 4 bubbles (3 on top and 1 nestled deep to them) The trapped fluid resonates, emitting a continuous signal back to the transducer. Whereas the transducer pulse is broad spectrum, the returning signal consists of one or more discrete (resonant) frequencies. "Beats" between these frequencies produce the variable appearance of the ring down. There is no "reverberation" ( i.e. multiple reflectances). This artifact can be eliminated by angling the ultrasound probe.
- 30. SIDE LOBE ARTIFACT Sidelobe artifacts occur where side lobes reflect sound from strong reflector that is outside of the central beam, and where the echoes are displayed as if they originated from within the central beam.
- 31. Ultrasound transducer crystalsexpand and contract to produce primary ultrasound beams in the direction of the expansion and contraction. Secondary beams also occur because the crystals also expand and contract radially. These radial beams are called side lobe beams. Side lobe beams are low-intensity beams that surround the central beam. Side lobe artifacts are echogenic, linear or curvilinear artifacts. Strong reflectors include bowel gas adjacent to the gallbladder or urinary bladder.
- 32. SPECKLE ARTIFACT Speckle artifactmay be encountered in ultrasound. It is caused by the scattering of waves from the surface of small structures within a certain tissue. The artifact produces a textured appearance.
- 33. Twinkling artifact Twinkling artifactis the result of intrinsic machine noise seen with color Doppler ultrasound. It occurs as a focus of alternating colors on Doppler signal behind a reflective object (such as calculi), which gives the appearance of turbulent blood flow . It appears with or without an associated color comet-tail artifact .
- 34. Twinkling artifact ismore sensitive for detection of small stones (e.g. urolithiasis, cholelithiasis) than is acoustic shadowing. It is most pronounced when the reflecting surface is rough and highly dependent on machine setting: when the focal zone is located below a rough reflecting surface, the twinkling artifact becomes more obvious than when it is above it increased pulse repetition frequency facilitates better visualization of the artifact .
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