Artifacts Flashcards
what is an artifact
anything that does not correctly display the structures of functions that are imaged
what are the 4 things artifacts can be related to
malfunctioning equipment
defective recording device
improper operation of equipment
acoustic properties of tissues and propagation of sound waves
4 assumptions about how sound propagates in tissue that can create artifacts
all tissues have same acoustic velocity (1540 m/s)
the sound beam always travels in a straight line
echo strength indicates organ echogenicity only
the distance to each reflector equals the round trip time
artifacts can be in the 4 following categories
not real
missing
improper location
improper brightness shape or size
ultimately artifacts belong to 2 groups
the propagation group
the attenuation group
axial resolution and artifacts
objects less tan 1/2 SPL in the axis of the beam are demonstrated as a single echo
lateral resoltuion has an artifact called
point spreading
point spreading
reflectors appear smeared across the screen in areas where the beam is wide
point spreading can be accenuated with increased ____ or ___
gain or TGC
how to correct for point spreading
lower overall gain or TGC and scan in the near zone with a properly adjusted focus
point spreading AKA
image broadening
point spreading is a beam ____ artifact
width
point spreading happens when an echo is ____ than the width of the beam
smaller
point spreading helpful or hurtful
hurtful especially in anechoic structures (simple cysts looks complex)
slice thickness referred to as ____
volume averaging
how to help slice thickness artifact
repositioning the probe so that the narrowest portion of the Z axis is at the desired location
slice thickness is same as lat resolution but __
in the Z axis
acosutic speckle is the result of several off axis reflections from ______ in the parenchyma
scatter reflection
cause of acoustic speckle
constructive and destructive interference occurs and creates heterogeneous brightness
what helps acoustic speckle
persistence is the controls that average out the frames to help homogenize the tissue brightness
acoustic speckle helpful/hurtful
hurtful
when do you not use persistance
echo/ob as we don’t want to average out motion
rverberation is the reflection of sound between the ____ and a _____
transducer
strong interface
reverberation is often seen _____ or ____
near the probe surface
in fluid filled structures