Artifacts Flashcards
Slice thickness
Def: Beam width perpendicular to the scan plane. Displays anatomic structures (reflectors) in the incorrect imaging plane- can cause hollow structures to fill in. Charac: Causes anechoic structures to have low level echoes or false debris. Fix: Turn on Harmonics.
Speckle
Def: A grainy appearance, created by interference effects of scattered sound from many tissues. Charac: Weak scatters in tissue giving a granular appearance & obscures anatomy; Usually appears near the face of the transducer Fix: Harmonics; Reduce the gain
Reverberation
Def: Sound waves bounce between the two reflectors eventually returning to the transducer; Multiple evenly-spaced echoes; Only the first two are real; A single structure being displayed repeatedly at greater depths Charac: Repeated hyperechoic reflections; Equal increments of space between artifacts; “Ladder” Fix: Use alternative window; Change beam angle; Decrease TGC
Mirror Image
Def: a duplication of a true object incorrectly appears on the opposite side of a strong reflector Charac: Replica of true reflector; Artifact will appear deeper than true reflector; “Mirror” is in straight line between artifact and true reflector; Artifact and true reflector are equidistant from mirror Fix: Change angle; Adjust focal zone or TGC at level of high reflector causing mirroring; Scan from multiple windows; Use spatial compounding
Comet Tail
Def: Due to merging of two closely spaced reverberations; Similar to a reverberation without the spacing; Two closely placed strong reflectors parallel to beam axis. Charac: Solid hyperechoic line directed inferiorly; Appears posterior to actual structure; Parallel to beams axis Fix: Use an alternative window; Change beam angle; Decrease TGC
Refraction
Def: A change in the direction of sound when it crosses a boundary; The bending of a sound beam Charac: Misplaced Reflector Fix: Change angle, artifact shouldn’t be in same place
Grating Lobes
Def: Grating lobes are additional weaker beams emitted from an array transducer; Grating lobes duplicate structures laterally to the true ones. Charac: The artifact and the true reflector are located side by side at the same depth; Lobe artifact degrades lateral resolution. Fix: With apodization and subdicing
Side Lobes
Def: Lobes created by a single crystal transducer, such as a mechanical probe, are called side lobes; These lobes are weaker than the original beam strength. Charac: Second copy of a true reflector artifact appears side by side with the anatomic structure; DEGRADES LATERAL RESOLUTION Fix: Apodization and use of harmonic frequencies.
Speed Error
Def: When sound propagates through medium at a rate other than 1540m/s; Displays the correct number of reflectors at incorrect depths causing misplaced echoes on image Charac: Appears as a step-off; Displaces true reflections Fix: Currently cannot be prevented; Use alternate viewing window; Change beam angle
Range Ambiguity
Def: Occurs when a reflecting structure is located deeper than the imaging depth of the image.
A deep reflector that is received after the next pulse is emitted, will be perceived as being part of the second pulse. It will be assumed that it is from a shallow location, although it is not. Charac: Places structures much closer to the surface than it should be. Fix: Increase PRP/decrease PRF
Edge Shadow
Def: Special form of shadowing; Hypoechoic region extending down from the edge of a curved reflector due to a combination of refraction and reflection Charac: Hypoechoic or anechoic; Extends downward from the curved reflector’s edge, parallel to the beam; Prevents visualization of true anatomy Fix: Changing the angle
Focal Enhancement
Def: Special form of enhancement in which the side to side region of an image appears brighter (hyperechoic) than tissues at other depths; Occurs in the focal region of the transducer when using multiple focal zones. Charac: Structures at the focus appear brighter than those at other depths; An entire horizontal region ”band” of tissue appears hyperechoic Fix: Decrease the number of foci; Change the location of multiple foci
Shadowing
Def: The weakening of echoes distal to a strongly attenuating or reflecting structure; Or from the edges of a refracting structure Charac: Hypoechoic/Anechoic area (background color) parallel to sound beam; The result of too much attenuation; Located beneath a structure with abnormally high attenuation Fix: Image structure in several angles to avoid missing information
Enhancement
Def: The strengthening of echoes from reflections that lie behind a weakly attenuating structure; A hyperechoic region that extends beneath structures with abnormally low attenuation; Opposite of shadowing Charac: Hyperechoic; Located beneath a structure with too low attenuation Fix: Reduced with spatial compounding; Several directional approaches allow the beam to get around the attenuating structure
Multipath
Def: Appears when sound pulses glance off a second structure on the way to or from the primary reflector; The transmit path length differs from the return path length; Transducer receives reflections from structures that are not in the main axis of the beam due to different beam paths. Charac: “go & return” time is longer due to the indirect path the reflection takes, the echo will be positioned improperly on the image (usually deeper or misplaced) Fix: Change angle of the beam; Change depth
