Grey- Scale Artifacts Flashcards
What is Acoustic Shadow?
A posterior shadow artifact appearing as a hypo- to anechoic region extending deep to a highly attenuating structure (e.g., calcium-comprised structures).
What is Edge Shadow?
A hypo- to anechoic region refracting from the edges of a curved structure (e.g., fetal head, gallbladder) positioned parallel to the main axis of the acoustic beam.
What is Acoustic Enhancement?
Also called posterior enhancement or through-transmission. A hyperechoic region extending deep to a structure of low attenuation.
What is Focal Enhancement?
A horizontal region of increased echoes mimicking an incorrect time gain compensation (TGC) setting.
What is Refraction?
The bending of the sound beam as it transmits from one medium to another due to differences in propagation speed and an oblique angle of incidence.
What is Reverberation?
An artifact produced when an acoustic signal bounces between two intense reflectors parallel to the main axis of the acoustic beam, creating a ladder or Venetian blind appearance.
What is Slice Thickness?
Also called section-thickness or partial-volume artifact. Occurs when the width of the acoustic beam is greater than a fluid-filled reflector, causing filling in of cystic structures with low-level internal echoes.
What is Ring Down?
A compressed reverberation artifact appearing as hyperechoic lines extending downward, often from gaseous structures (e.g., bowel). It is less bright and often deeper than comet tail artifact.
What is Comet Tail?
A compressed reverberation artifact appearing as hyperechoic lines extending downward, often from crystalline or metallic structures (e.g., implants, gallbladder adenomyomatosis).
What are Side and Grating Lobes?
Off-axis lateral acoustic extensions from the primary acoustic beam, leading to artifact formation.
What is Anisotropy?
An artifact of varying echogenicity produced by strong specular reflectors, often occurring in musculoskeletal (MSK) imaging due to improper transducer alignment.
