class 13 artifacts

first assumption (beam pattern assumption)

the beam is narrow/uniform in width/intensity

types of Beam Pattern Artifacts

Axial/lateral Resolution, Partial Vol, Speckle, 2nd Lobes and Focal Banding

Partial Volume / Slice Thickness (beam pattern artifact) is caused by

multiple tissue types within the beam

most likely affected by partial volume (beam pattern artifact)

cysts and the gall bladder

partial volume (beam pattern artifact)

Fills in hypoechogenic structures

scatter (beam pattern artifact)

interference pattern where the brightness doesnt relate to the tissues properties

Speckle pattern changes with

wavelength and acoustic beam pattern

types of secondary lobes

Side lobes and Grating lobes (linear array)

Focal Banding (beam pattern artifact)

alternating bright and dark bands and inc brightness at the focal zone

Attenuation Artifacts

shadowing and Enhancement

shadowing (Attenuation Artifacts)

dec reflection below a strong reflector/attenuating structure (sound waves are blocked)

Enhancement (Attenuation Artifacts)

inc reflection (brighter) in areas below a weak attenuating structure

in Enhancement artifact

Depth varying gain is overcompensated since attenuation is less than expected

Enhancement

shadowing

Propagation Artifact assumes that the

beam travels in a straight/direct path

Propagation Artifacts

Reverberations (multiple reflections) and Refraction (change in beam direction)

Propagation Artifacts types of Reverberations

Comet Tail, Ring Down and Mirror Image

Propagation Artifacts types of Refractions

duplication and Edge Shadow

reverberations can occur

between the object and xdcr or within objects

in reverberations (Propagation Artifact)

a single interface is displayed more than once

Comet Tail causes

Multiple reverberations between closely spaced surfaces

Ring-Down (reverberations)

Continuous emission of US from resonance (gas bubbles)

Refraction (Propagation Artifact)

a change in the speed of sound from one medium to the next causes the beam to bend causing the reflector to be in the wrong position

Edge Shadow (Refraction)

Shadowing at the edges of curved structures (defocuses the beam inc attenuation)

Edge Shadow usually affects

vessel walls, fetal skull or cysts

If c > 1540 m/s

structures look artificially shallow

If c < 1540 m/s

structures look artificially deep

Range Ambiguity dec

FR/image clarity

Range Ambiguity assumes

echoes come from the most recent pulse

Spectral Doppler Artifacts

Aliasing and Spectral Mirror

Spectral Mirror

pattern is mirrored above and below the baseline

partial volume

in speckle constructive interference creates

brighter spots and destructive creates darker spots creating a random pattern of light/dark spots

speckle (light/dark pattern)

reverberation

refraction is displayed as multiple

equally spaced horizontal lines (Spacing corresponds to the distance between the two reflecting surfaces)

ring down

comet tail

ring down

refraction (causes side by side duplication)

refraction