21 artifacts

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/S

4. Reflections arise only from structures positioned in the beams main axis

5. The imagine plane is very thin

6. 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)