Artifacts-Physics
Terms
undefined, object
copy deck
- simply an error in imaging
- artifact
- artifact tupes includes reflections that are:
-
not real
not seen on the image
not of correct shape or size
not in correct position
not of correct brightness - causes of artifacts
-
violation of assuptions
equipment malfunction
physics
operator error - six assumptions of imaging systems:
-
sound travels in a straight line
sound travels directly to a reflector and back
sound travels 1.54 m/s2
reflections arise only from struct. postions in the beams main axis
imaging plane is thin
strength of a refection is related to charateristic of tissue creating reflection - Reverbaration appear on the display as ____, ___ ____ ___caused by the bouncing of the sound wave between two reflectors positioned parallel to the beam
- multiple, equally spaced echoes
- characteristics of reverbaration
-
appears in multiples
appears as equally spaced
located parallel to sounds beams main axis
located at ever increasing depths - _____resembles a ladder
- reverberation
- comet tail artifact often described as reverbation with the spaces squeezed out appears as a ___ __ ____ directed downward.
- solid hyperechoic line
- Comet tail is also known as
- ring down artifact
- ____can arised from the resonance or vibration of small structures such as gas bubbles after having been bombarded by an US pulse
- comet tail artifact
- characteristics of comet tail
-
appears as a single long hyperechoic echo
located parallel to the sounds beam main axis - Shadowing appears a ___or ____region extending downward from a very strong attenuating medium. Shadows are the same color as the _____
- hypoechoic or anechoic ; background
- characteristic of shadow
-
hypo or anechoic
the result of too much attenuation
located beneath the structure with abnormally high att.
prevents visulization of true anatomy - shadowning is entirely _____ to the speed of sound in a medium
- unrelated
- an edge shadow artifact is a special form of shadowing that appears as a ___ ___ extending along the edge of a curved reflector
- hypoechoic region
- with ____ ___, the sound refracts, (tranmits with a bend) at the edge of a curved reflector
- edge shadow
- an edge shadow is also called
- shadowing by refraction
- characterics of edge shadow
- hypo or anechoic
- charac. of edge shadow
-
hypo or anderchoic
results when the beam spreads after striking a curved reflector
extends downward from the curved reflectors edge parallel to beam
prevents visulation - enhancement artifact appears as a ___region beneath tissues with abnormall low attenuation
- hyperechoic
- although the number of reflectors on the image is correct, some of them are overly bright with ____
- enhancement
- enhancement is opposite of
- shadowing
- _____is entirely unrelated to speed that travels in a medium
- enhancement
- characterics of enhancement
-
hyperechoic (appears same as foreground)
result of too little attenuation
located beneath structure with abnormally low attentuation - ____is a special form of enhancement in which a _______ of an image appears brighter than tissues at other depths
- side to side region
- focal enhancement is also called ____
- focal banding
- characterics of focal banding
-
hyperechoic side to side (appears the same as the foreground color)
result of increased intensity at the focus - ___is created when sound reflects off a strong reflector (mirror) and is redireced toward a second structure
- mirror image
- with ___ ___, the artifact is placed deeper than the real structure
- mirror image
- ____is a mirror image artifact that appears on a spectral doppler display
- crosstalk
- _____is created when a sound wave propagates through a medium at a speed other than that of soft tissue (1.54km/s)
- speed error artifact
- when the mediums speed is faster than that is soft tissue
-
sound travels faster than the US expects
pulses return from trip in body- fast!!!
go return time is too short
system assumes reflectors are close to transducer
reflectors are too shallow
distances are underestimaed - when the mediums speed is slower than soft tissue
-
sound travels slower than US expects
- prop. speed errors are also called
- range error artifacts
- characteritics of speed error
-
correct number of reflection
improper depth
appears as a step off - _____appear when sound energy is transmitted in a direction other than along the beams main axis
- lobe artifacts
- lobe artifact degrades
- lateral res
- characterics of lobe artifact
- a second copy of true reflector
- characteristic of lobe artifact
-
second copy of true reflector
artifact and true reflector are side by side - lobes created by a single crystal transducer such as a mechancial probe are called
- side lobes
- lobes created by array transducers are called
- grating lobes
- reducing lobe artifacts are by __ and ____
-
subdicing
apodization - ____occurs when a sound pulse changes dirction during transmission
- refraction artifact
- refraction occurs weh a sound wave ____
- strikes a boundary obliquely and the media on either side of te boundary have different prop. speeds
- refraction artifact degrades
- lateral res
- characterics of refraction
-
a second copy of the reflector
the copy is side by side, or at the same depth as the true reflector - In reality, the imaging plane is neither thin nor of uniform thickness. Therefore, reflections from struct. __and __ the assumed imaging plane may in the image
- above and below
- slice thickness artifact is related to the dimension of the _____
- beam perpendicular to the beam
- ____ ____is determined by the thickness of the imaging plane
- elevational res
- slice thickness artifact appears when the beam dimension is ___than the reflector size
- greater
- slice thickness artifact is reduced with what?
- thinner imaging planes, such as those created by 1.5 dimensional array transducers
- lateral res artifact occurs when a beam is what?
- wider than the distance between two reflectors that are located side by side or perp. to the beam. In this situation, two objects appear as one.
- _____artifact may display a small reflector as a wide line rather than a narrow dot
- lateral res
- when is lateral res least likely to occur?
- at the focus of the sound beam; where the beam diameter is smallest
- when is axial res created:
- when a long pulse strikes two closely spaced structures, where one is in front of the other, or parallel to the main axis of the US beam.
- axial res artifact creates?
- one reflection on the image from two closely spaced reflectors
- what minimized axial res?
- transducers that create short pulses( higher freq. tranxducers and less ringing)
- ____is created when sound pulses glance off a second struct. on the way to or fro the primary reflector. As a result the transmit path differs from return.
- multipath
- when a sound beam strikes a ____ or ____ reflector, some of the reflected sound may be directed away from the transducer.
- curved or oblique
- the ability to precisely position a moving structure is called
- temp. resolution
- _____is related to the overall detail in an image. determined by sound beams spacing or line density.
- spatial res artifact
- How does the systems display affect spatial res?
-
with analog- Spatial res is determined by number of TV scan lines per frame.
with digital- SPR is related to pixel density. - appears as small amp. echoes and results from many sources including electrical interference, signal processing, and spurious reflections
- noise
- noise is more likely to affect
- low level hypoechoic regions
- a form of noise from small amp. sound waves interfering with each other
- speckle
- speckle appears as
- tissue texture close to the transducer that does not directly correspond to true anatomic scatterers in tissue
- ____is a form of noise associated with Doppler
- clutter
- ___ ____is a high tech solution for reducing an images noise content.
- harmonic
- the goal of harmonic imaging
- is to selectively distinguish meaningful reflections from noise thereby improving the SNR
- anatomic reflectors absent on image: possible causes
-
shadowing
shadowing by refraction
lateral res
axial res - anatomic reflectors appear with abnormal brightness
-
enhancement(hyperechoic)
banding(hyperechoic)
shadowing(hypoechic)
shadowing by refraction(hypoechoic) - single anatomic reflector appearing multiple times on image---artifact positioned deeper than the true anatomy
-
comet tail
ring down
reverb
mirror image
- single anatomic ref. app. multiple times on image---artifact displaced to the side of true anatomy
-
refraction
side lobe
grating lobe - anatomic struct. appearing at incorrect depth.
- speed errors
- anatomic struct. app. in the incorrect imaging plane
- slice or section thickness
- anatomic struct. not corresponding to echoes on the image
-
acoustic speckle
multipath