SPI Edelman - Chapter 20: Image Characteristics & Artifacts

*__________ describes portions of an image that are brighter than surrounding tissues, or tissues that appear brighter than normal

hyperechoic

*__________ is background color (too few reflections on the scan)

shadowing

*__________ results from too much attenuation in structure above the shadow

shadowing

*__________ causes an absence of true anatomy on scan in the region of shadow

shadowing

*Edge shadow or Shadowing by Refraction is eliminated by __________

spatial compounding

*__________ is hyperechoic, foreground color (brighter echoes on the scan), beneath the structure with reduced attenuation

enhancement

*Ultrasound systems assume that sound travels __________ to a reflector and back to the transducer

directly

*With mirror image, the artifact will be located __________ than the true reflector

deeper

*Propagation speed errors appear as a __________

step-off, split or cut

*Sound travels __________ than 1,540 m/s in fat. Therefore, reflectors beneath fat may be placed too __________ on the display

slower

deep

*__________ artifact appears side-by-side with the true anatomic structure

refraction

*__________ occurs with oblique incidence and different speeds

refraction

*HINT: Refraction artifact degrades __________ resolution

lateral

*__________ occurs when reflections arise from off-axis sound

side lobes and grating lobes

*__________ transducers create side lobes

mechanical

*__________ transducers create grating lobes

array

*Grating lobes can be reduced or cured by dividing each element into even smaller, miniature pieces. This is called __________

subdicing

*Grating lobes are further reduced by exciting the subdued elements with different voltages. Subelements closer to the center of the sound beam are excited with higher voltages, while the outermost subelements, further away from the center of the beam, are excited with lower voltages. This is called __________, which reduces lobes

apodization

*Subdicing and Apodization fix __________ only!

grating lobes

*Lobe artifact degrade __________ resolution

lateral

*With __________ artifact, the assumption that reflections arise from the beam's main axis is violated

lobe

*Ultrasound beams have measurable thickness. However, we assume that the imaging plane is razor thin. __________ artifact occurs when the beam has a greater width than the reflector

slice thickness

*Slice thickness artifact is also called '__________'

elevational resolution

*With slice thickness artifact, the reflections produced by structures above or below the ideal imaging plane appear in the image. This may act to fill in hollow structures such as cysts. Fill-in of an anechoic structure is called __________ or __________

partial volume artifact

section thickness artifact

*__________ reflector located outside of the idealized imaging plane (above or below) appears on the image

true

__________ is cured with 1 1/2 dimensional array and annular array transducers, since they make thin slices

slice thickness

*HINT: Generally, linear array transducers have poor __________ resolution

elevational

*__________ is a grainy appearance not directly from reflections from tissues in the shallow part of the image

speckle

*__________ is created by interference effects of scattered sound, both constructive & destructive, from the many tissue reflectors (HINT: look for these words)

speckles

*__________ artifact is created by reflections from structure located deeper than the maximum imaging depth

range ambiguity

*__________ is cured by imaging deeper (lower the PRF) or coded excitation

range ambiguity

*Artifacts are created when the sound beam is __________ than the reflector

larger

*Small sound is __________

good

*__________ pulses are better

short

*__________ pulses create artifacts

long

*__________ pulses degrade axial resolution

long

*__________ beams are better

narrow

*__________ beams create artifacts

wide

*__________ beams degrade lateral resolution

wide

*__________ slices are better

thin

*__________ slices create artifacts

thick

*__________ slices degrade elevational resolution

thick