An error in imaging is called an
Artifact
Artifacts include reflections that are described as
Not real, not seen on image, incorrect shape or size, incorrect position, incorrect brightness
Artifacts arise from
Violation of assumptions, equipment malfunction, physics of ultrasound, operator error
Portions of an image that are brighter than surrounding tissues or tissues that appear brighter than normal
Hyperechoic
Portions of an image that are not as bright as surrounding tissues or tissues that appear less bright than normal
Hypoechoic
An extreme form of hypoechoic, meaning entirely without echoes
Anechoic
Describes structures with equal echo brightness
Isoechoic
Portion of tissue or an image that has similar echo characteristics throughout
Homogenous
Portion of tissue or an image that has differing echo characteristics throughout
Heterogenous
Six assumptions of imaging systems
1. Sound travels in a straight line 2. Sound travels directly to a reflector and back 3.sound travels in soft tissue at exactly 1540 m/S4. Reflections arise only from structures positioned in the beams main axis5. The imagine plane is very thin6. The strength of a reflection is related to the characteristics of the tissue creating a reflection
What should be considered when obvious artifacts remain visible even after corrective measures have been taken
Instrument malfunction
Appear on the display as multiple, equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam
Reverberation
Characteristics of reverberation
Appear in multiples, equally spaced, located parallel to sound beams axis, located at ever increasing depths
Which reflections of reverberation are real
The first 2
Reverberations resemble what
Ladder or venetian blind
Appears as a solid hyperechoic line directed downward
Comet tail
Comet tail artifact is also known as
Ring down artifact
Comet tail artifact is created when
Closely spaced reverberations merge
Characteristics of comet tail
Appear as a single long hyperechoic echo, located parallel to the sound beams axis
Which artifact can also be seen with air
Comet tail
Appears as a hyperechoic or anechoic region extending downward from a highly attenuating structire
Shadow
Shadows are the same color as the
Image background
Shadows appear when the attention is ___ in the tissue above the shadow than in the surrounding tissues
Higher
Characteristics of shadowing
Hypo or anechoic, too much attenuation, located beneath the structure with abnormally high attenuation, prevents visualization of true anatomy
Shadows may provide ___ that may help to characterize tissue
Diagnostic information
How is shadowing and speed of sound in a medium related
Entirely unrelated
A special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector
Edge shadowing
The decrease in ____ causes edge shadowing
Intensity
An edge shadowing is also called
Shadowing by refraction
Characteristics of edge shadowing
Hypo or anechoic, results when the beam spreads after striking a curved reflector, extends downward frm the curved reflectors edge parallel to beam, prevents visualization of true anatomy
Appears as a hyperechoic region beneath tissues with abnormally low attenuation
Enhancement
With enhancement, the number of reflectors on the image is correct but some of them are
Overly bright
What artifact is the opposite of shadowing
Enhancement
What is the relationship between enhancement and speed of sound that travels in a medium
Entirely unrelated
Characteristics of enhancement
Hyperechoic, too little attenuation, located beneath a structure with low attenuation
Special form of enhancement in which a side to side region of an image appears brighter than tissues at other depths
Focal enhancement
Focal enhancement is also called
Focal banding
Focal banding has the same appearance as an incorrect what
TGC setting
Focal banding is the most prominent at the ___
Focus
With focal banding an entire horizontal region of tissue appears
Hyperechoic
Characteristics of focal enhancement
Hyperechoic side to side region and results from increased intensity at the focus
This artifact is created when send reflects off a strong reflectors and is redirected toward a second structure, this redirection causes a replica or second copy of the structure to incorrectly appear on television image
Mirror image
With mirror image, the artifact is located ___ than the real structure
Deeper
Characteristics of mirror image
Second copy of true reflector, artifact appears deeper, mirror lies on a straight line, true reflector and artifact are equal distances
A mirror image artifact that appears on a spectral doppler display
Crosstalk
Artifact created when a sound wave propagates through a medium at a speed other than that of soft tissue
Speed error
With speed error the correct number of reflectors are displayed but they appear at incorrect ___
Depths
Speed errors appear as a step off as if they are __ or __
Split or cut
When the mediums speed is slower than in soft tissue: sound travels ___ than ultrasound system expects, pulses return from their trip ___, go return time is ___, distance is ___.
Slower, slow, long, overestimated
When the mediums speed is faster than that in soft tissue: sound travels ___, pulses return from their trip ___, go return time is ___, distance is ___.
Fast, fast, short, underestimated
Propagation speed errors are also called
Range error artifact
Characteristics of speed error
Correct numbers of reflectors, improper depth, appears as a step off
Artifact appears when sound energy is transmitted in a direction other than along the beams main axis
Lobe artifact
Lobe artifact degrades
Lateral resolution
Characteristics of lobe artifact
Second copy of true reflector, artifact and true reflector are located side by side at same depth
Lobes created by a single crystal transducer are called
Side lobes
Lobes created by array transducers are called
Grating lobes
Grating lobes artifact can be reduced by diving each pzt crystal into small pieces. This is called
Subdicing
Grating lobes can be further reduced by exciting the subdiced elements with different voltage, this is called
Apodization
Artifact created when a sound pulse changes direction during transmission
Refraction
Refraction occurs when a sound wave strikes a boundary ___ and the media on either side of the boundary have different ____
Obliquely, propagation speeds
Refraction artifact degrades
Lateral resolution
Characteristics of refraction
Second copy, copy is side by side or at same depth
Slice thickness is also called
Section thickness artifact or partial volume artifact
Slice thickness artifact is related to
The dimension of the beam that is perpendicular to the imaging plane
Determined by the thickness of the imaging plane
Elevational resolution
Slice thickness artifact is reduced with
Thinner imaging planes
Artifact occurs when a pair of side by side reflectors are closer than the width of the sound beam
Lateral resolution
Two objects appear as one reflection on the image with what artifact
Lateral resolution
Lateral resolution artifact may display a smsll reflector as what rather than a narrow dot?
A wide line
Lateral resolution artifact is also called
Point spread artifact
Artifact created when a long pulse strikes two closely spaces structures where one is in front of the other
Axial resolution
With axial resolution only one reflection will appear on the image if the structures are closer together than
One half the spatial pulse length
What can minimize axial resolution
Transducers that create short pulses (higher frequency transducers)
Created when sound pulses glance off a second structure on the way to or from the primary reflector
Multipath
As a result of multipath the transmit path ___ from the return path length
Differs
When a sound beam strikes a curved or oblique reflecter some of the reflected sound may be directed away from the transducer
Curved and oblique reflecters
Wirh curved abd oblique reflecters The amplitude of the reflection received by the transducer may be less than expected, reflecters are:
Absent, appear too weak, appear different
The ability to precisely locate a moving structure at all times Is called
Temporal resolution
Temporal resolution is best with
High frame rates
Poor temporal resolution cased by low frame rates results in
Less accurate positioning of moving reflectors
Spatial resolution is related to the overall ___ in an image
Detail
Spatial resolution artifact is determined by
Line density, axial resolution, lateral resolution
When image information is displayed on a monitor, spatial resolution is affected by the number of
Horizontal scan lines per frame
When the image information is in digital form, spatial resolution is related to
Pixel density
Spatial resolution improves with a large number of pixels in an image of fixed size, this is called
High pixel density
Spatial resolution artifact occurs when the pixel size is greater than the size of the ____
Reflector
Artifact occurs when a reflecting structure is located deeper than the imaging depth of the image
Range ambiguity artifact
Range ambiguity is eliminated by increasing the
PRP
Appears as small amplitude echoes and results from many sources including electrical interference, signal processing, and spurious reflections
Noise
Noise is more likely to affect ___ level hypoechoic regions
Low
Noise resulting from constructive and deconstructive interference of small sound wavelets
Acoustic speckle
With speckle the displayed image will contain
Fake detail (grainy tissue)
What is an effective tool to reduce speckle
Spatial compounding
Reduces an images noise content
Harmonic imaging
The goal of harmonic imaging is to
Selectively distinguish meaningful reflections from noise (increase the signal to noise ratio)