Ultrasound Physics

Ultrasound Artifacts

Lateral Resolution Artifact    Lateral Resolution (LR)    - Ability to separate two reflectors as two reflectors perpendicular to beam    - LR (mm) = Beam diameter (mm); narrow beams provide better resolution    - LR is best at beams focal zone or the end of the Near Field    - Also known as L.A.T.A. (Lateral, Angular, Transverse and Azimuthal)    - Factors affecting LR: width of the beam, distance from the transducer, frequency, side and grating lobe levels.      LATERAL RESOLUTION ARTIFACTS    Failure to resolve two reflectors perpendicular to the sound beam    Category: Resolution Artifact    · Pulse width artifact    · LR = Beam Diameter    · LR is best at focus    · LR changes when depth changes    · Lateral resolution usually degrades with depth. Near the probe, there is significantly better resolution than at greater depths    · Prevention:    o ↑f = Narrow Beam    o Smaller crystal = Narrow Beam    Closed arrow: beamwidth is about 2mm,    Open arrow: beamwidth is about 10 mm,    Hence, the structures appear “smeared out” as the depth increases (and anything beyond 2mm).    Cause:    It creates one reflection on the image from two closely spaced reflectors if the beam’s width used is wider than the space between two reflectors.    What assumption:    Reflections arise only from structures positioned in the beam’s main axis.    Description of Artifact:    Unresolved; it means it displays a small reflector a wide line rather than a narrow dot.    How to prevent:    Use transducers with higher frequency which provides narrower beams. Best at beams focus or the end of the Near Zone (Figure 1).    Hindrance, Helpful or Both- explain:    Hindrance, because there would be important anatomic information that are missing.

Lateral Resolution Artifact

Lateral Resolution (LR)

- Ability to separate two reflectors as two reflectors perpendicular to beam

- LR (mm) = Beam diameter (mm); narrow beams provide better resolution

- LR is best at beams focal zone or the end of the Near Field

- Also known as L.A.T.A. (Lateral, Angular, Transverse and Azimuthal)

- Factors affecting LR: width of the beam, distance from the transducer, frequency, side and grating lobe levels.

LATERAL RESOLUTION ARTIFACTS

Failure to resolve two reflectors perpendicular to the sound beam

Category: Resolution Artifact

· Pulse width artifact

· LR = Beam Diameter

· LR is best at focus

· LR changes when depth changes

· Lateral resolution usually degrades with depth. Near the probe, there is significantly better resolution than at greater depths

· Prevention:

o ↑f = Narrow Beam

o Smaller crystal = Narrow Beam

Closed arrow: beamwidth is about 2mm,

Open arrow: beamwidth is about 10 mm,

Hence, the structures appear “smeared out” as the depth increases (and anything beyond 2mm).

Cause:

It creates one reflection on the image from two closely spaced reflectors if the beam’s width used is wider than the space between two reflectors.

What assumption:

Reflections arise only from structures positioned in the beam’s main axis.

Description of Artifact:

Unresolved; it means it displays a small reflector a wide line rather than a narrow dot.

How to prevent:

Use transducers with higher frequency which provides narrower beams. Best at beams focus or the end of the Near Zone (Figure 1).

Hindrance, Helpful or Both- explain:

Hindrance, because there would be important anatomic information that are missing.

Lateral Resolution Artifact

Lateral Resolution Artifact

Lateral resolution, or the ability to discern between two points in the lateral plane, is dependent upon:FrequencyAperture (Beam Width)BandwidthSide/grating lobesFigure 4.12 Lateral Resolution    As the frequency is increased, the wavelength is decreased. A small wavelength will discern two points more easily than a larger wavelength. The aperture, or beam width, of the transducer also affects lateral resolution. Like wavelength, a narrower beam can discern two points better than a wide beam. After the beam's focal point has been reached, the beam starts to diverge. The divergence of the beam increases the beam's width such that deeper structures will be blurrier and exhibit linear artifacts (they appear wider than their actual width). At great depths the reflected signal may be as wide as the beam. Beam width is the most important factor in lateral resolution. Bandwidth, much like beam width, affects lateral resolution. Side lobes and grating lobes will display structures that are truly not along the beams path as if they were along the beams path. Side lobes and grating lobes decrease the lateral resolution.

Lateral resolution, or the ability to discern between two points in the lateral plane, is dependent upon:FrequencyAperture (Beam Width)BandwidthSide/grating lobesFigure 4.12 Lateral Resolution

As the frequency is increased, the wavelength is decreased. A small wavelength will discern two points more easily than a larger wavelength. The aperture, or beam width, of the transducer also affects lateral resolution. Like wavelength, a narrower beam can discern two points better than a wide beam. After the beam's focal point has been reached, the beam starts to diverge. The divergence of the beam increases the beam's width such that deeper structures will be blurrier and exhibit linear artifacts (they appear wider than their actual width). At great depths the reflected signal may be as wide as the beam. Beam width is the most important factor in lateral resolution. Bandwidth, much like beam width, affects lateral resolution. Side lobes and grating lobes will display structures that are truly not along the beams path as if they were along the beams path. Side lobes and grating lobes decrease the lateral resolution.

Ultrasound Artifacts    Axial Resolution Artifact    Axial Resolution    - Ability to separate two reflectors as two reflectors accurately along the beam axis. A shorter wavelength (higher frequency) can differentiate two structures more easily than a longer wavelength. If the two structures are greater than one wavelength's width apart then the two structures will be displayed as two distinct structures. If the structures are less than one wavelength's width apart then the two structures will be displayed as one structure.    - Also known as L.A.R.D. (Longitudinal, Axial, Range or Radial, Depth)    - Associated with:    a. Shorter spatial pulse length    b. Shorter pulse duration    c. Higher frequencies    d. Fewer cycle per pulse    e. Lower numerical values     *the pulse did not miss any of the reflectors    Artifact name: Axial Resolution Artifact    This artifact occurs when reflectors are parallel to the beam’s main axis create one reflection on the image from two closely spaced reflectors.    *the pulse missed to hit the #2 reflector     Cause:    Creates one reflection on the image from two closely spaced reflectors if structures are closer than ½ the spatial pulse length.     What assumption:    Reflections arise only from structures positioned in the beam’s main axis.    Description of Artifact:    Unresolved; it means two reflectors are shown one bigger reflector on the monitor.     How to prevent:    Use transducers with high frequency and short distinct pulses.     Hindrance, Helpful or Both- explain:    Hindrance, because there would be important anatomic information that are missing.

Ultrasound Artifacts

Axial Resolution Artifact

Axial Resolution

- Ability to separate two reflectors as two reflectors accurately along the beam axis. A shorter wavelength (higher frequency) can differentiate two structures more easily than a longer wavelength. If the two structures are greater than one wavelength's width apart then the two structures will be displayed as two distinct structures. If the structures are less than one wavelength's width apart then the two structures will be displayed as one structure.

- Also known as L.A.R.D. (Longitudinal, Axial, Range or Radial, Depth)

- Associated with:

a. Shorter spatial pulse length

b. Shorter pulse duration

c. Higher frequencies

d. Fewer cycle per pulse

e. Lower numerical values


*the pulse did not miss any of the reflectors

Artifact name: Axial Resolution Artifact

This artifact occurs when reflectors are parallel to the beam’s main axis create one reflection on the image from two closely spaced reflectors.

*the pulse missed to hit the #2 reflector


Cause:

Creates one reflection on the image from two closely spaced reflectors if structures are closer than ½ the spatial pulse length.


What assumption:

Reflections arise only from structures positioned in the beam’s main axis.

Description of Artifact:

Unresolved; it means two reflectors are shown one bigger reflector on the monitor.


How to prevent:

Use transducers with high frequency and short distinct pulses.


Hindrance, Helpful or Both- explain:

Hindrance, because there would be important anatomic information that are missing.

Ultrasound Physics    Axial Resolution

Ultrasound Physics

Axial Resolution

Axial Resolution Artifact

Axial Resolution Artifact

Ultrasound Physics    Slice Thickness Artifact    Occurs when the beam elevational dimension is greater than the reflector size.    - Imaging in 2D but there are 3 dimensions to a sound beam.    · 3rddimension is slice thickness.    - The beam has a measurable thickness that varies with depth.    - Echoes originate not only from the center of the beam, but ASLO from off center.    - When the slice is thick reflectors above and below the assumed thin plane create reflections that appear incorrectly in the image.    Resolution Artifact; propagating Artifact    · AKA Partial Volume, Elevational Resolution Artifact and Section Thickness Artifact    · Assumption: Imaging plane is extremely thin    · The elevational plane is not thin, neither uniform    · Beam width perpendicular to the scan plane causes section thickness artifact    · Thinner elevational plane = better elevational resolution = less artifacts    Elevational plane Debris at the base of the bladder    · Hindrance: can appear as sludge or debris    · It is the filling in of cystic structures with echoes    · Prevention:    o Tissue harmonics imaging (has thinner sound beam)    o 1.5 (T) – thinner in elevational plane

Ultrasound Physics

Slice Thickness Artifact

Occurs when the beam elevational dimension is greater than the reflector size.

- Imaging in 2D but there are 3 dimensions to a sound beam.

· 3rddimension is slice thickness.

- The beam has a measurable thickness that varies with depth.

- Echoes originate not only from the center of the beam, but ASLO from off center.

- When the slice is thick reflectors above and below the assumed thin plane create reflections that appear incorrectly in the image.

Resolution Artifact; propagating Artifact

· AKA Partial Volume, Elevational Resolution Artifact and Section Thickness Artifact

· Assumption: Imaging plane is extremely thin

· The elevational plane is not thin, neither uniform

· Beam width perpendicular to the scan plane causes section thickness artifact

· Thinner elevational plane = better elevational resolution = less artifacts

Elevational plane Debris at the base of the bladder

· Hindrance: can appear as sludge or debris

· It is the filling in of cystic structures with echoes

· Prevention:

o Tissue harmonics imaging (has thinner sound beam)

o 1.5 (T) – thinner in elevational plane

Ultrasound Physics    Slice Thickness Artifact

Ultrasound Physics

Slice Thickness Artifact

CONTRAST RESOLUTION ARTIFACT      Occurs when grays scale range (dynamic range) is narrow (less shades of gray) and can’t distinguish between two echoes of slightly different amplitudes or intensities      · Contrast resolution is determined by number of bits per pixel in the image memory (gives image quality)    · ↑number of bits per pixel = more shades of grey = better contrast resolution    · Adjust Dynamic Range to increase gray scale and improve contrast resolution        · Types of contrast resolution artifacts:    o Noise    o Specle

CONTRAST RESOLUTION ARTIFACT

Occurs when grays scale range (dynamic range) is narrow (less shades of gray) and can’t distinguish between two echoes of slightly different amplitudes or intensities

· Contrast resolution is determined by number of bits per pixel in the image memory (gives image quality)

· ↑number of bits per pixel = more shades of grey = better contrast resolution

· Adjust Dynamic Range to increase gray scale and improve contrast resolution

· Types of contrast resolution artifacts:

o Noise

o Specle

Ultrasound Physics    Contrast Resolution

Ultrasound Physics

Contrast Resolution

Contrast Resolution      Is the ability of a gray-scale display to distinguish between echoes of slightly different intensities.      Contrast resolution depends on the number of bits per pixel in the image memory.      Increasing the number of bits per pixel (more gray shades) improves contrast resolution      ULS pulses DO NOT have a constant amplitude      Overlapping occurs      Better Contrast Resolution = Better Detail Resolution      Electronics & displays can degrade      An image with many shades of gray has better contrast resolution      An image with less shades of gray degrades contrast resolution      It is your final production; what you are looking at the display screen

Contrast Resolution

Is the ability of a gray-scale display to distinguish between echoes of slightly different intensities.

Contrast resolution depends on the number of bits per pixel in the image memory.

Increasing the number of bits per pixel (more gray shades) improves contrast resolution

ULS pulses DO NOT have a constant amplitude

Overlapping occurs

Better Contrast Resolution = Better Detail Resolution

Electronics & displays can degrade

An image with many shades of gray has better contrast resolution

An image with less shades of gray degrades contrast resolution

It is your final production; what you are looking at the display screen

Spatial Resolution Artifacts    Definition:    - Spatial resolution pertains to the overall detail produced in an image. Spatial resolution artifacts are created when one or more components of the display monitor fail to produce adequate image detail.    Factoring Components    - Spatial resolution artifacts can be created in a number of ways.    1. Pixel Density    2. Line Density    3. Number of horizontal lines in a display monitor.    Causes    - Low pixel density gives us fewer pixels per inch. This results in larger pixels.    - Larger pixels provide less detailed images.    - Low line density creates less detailed images.    - Monitors with less horizontal lines built in degrade spatial resolution.    Description of Artifact    Pixel Density    - Spatial Resolution artifacts, as they pertain to digital displays, are caused by the pixel density of the digital picture.    - Each pixel contains a shade of gray which contributes to the overall detail of the image.    - Low pixel density is equivalent to having fewer pixels per inch. This creates larger pixels which allows for a diminished spatial resolution.    - The opposite holds true for higher pixel density. The more pixels per inch, the smaller the pixel and the better the detail resulting in better spatial resolution.    Horizontal lines in a digital display    - Another cause for degraded spatial resolution is the amount of horizontal scan lines on a monitor.    - Digital scan converters process the received information and display it on a monitor in horizontal lines. The more horizontal lines the better the spatial resolution.    Line Density    - Line density of the sound beam can directly affect spatial resolution.    - High line density provides sound beams that are tightly packed and create better detail imaging.    - Low line density provides wider gaps between the beams causing decreased detail, resulting in decreased spatial resolution.      USA    - Images with low pixel density will appear blurry and have less detail.    - Images produced with less line density will have decreased detail.    Prevention    - Line Density can sometimes be controlled by the operator; but are more often controlled by the ultrasound system itself.    - Modern display units address the lines per image. They are now equipped with more lines per image that provide better spatial resolution.    - The pixel density cannot be changed, but the quality of the picture may be improved by using write magnification. This pre-processing technique allows the sonographer to choose a region of interest, (ROI), and magnify it. The ultrasound system then rescans that image. This allows for a greater number of pixels which improves spatial resolution.    Helpful or Hindrance    - Degraded spatial resolution is a hindrance to imaging because it affects the quality and detail of the imaging.

Spatial Resolution Artifacts

Definition:

- Spatial resolution pertains to the overall detail produced in an image. Spatial resolution artifacts are created when one or more components of the display monitor fail to produce adequate image detail.

Factoring Components

- Spatial resolution artifacts can be created in a number of ways.

1. Pixel Density

2. Line Density

3. Number of horizontal lines in a display monitor.

Causes

- Low pixel density gives us fewer pixels per inch. This results in larger pixels.

- Larger pixels provide less detailed images.

- Low line density creates less detailed images.

- Monitors with less horizontal lines built in degrade spatial resolution.

Description of Artifact

Pixel Density

- Spatial Resolution artifacts, as they pertain to digital displays, are caused by the pixel density of the digital picture.

- Each pixel contains a shade of gray which contributes to the overall detail of the image.

- Low pixel density is equivalent to having fewer pixels per inch. This creates larger pixels which allows for a diminished spatial resolution.

- The opposite holds true for higher pixel density. The more pixels per inch, the smaller the pixel and the better the detail resulting in better spatial resolution.

Horizontal lines in a digital display

- Another cause for degraded spatial resolution is the amount of horizontal scan lines on a monitor.

- Digital scan converters process the received information and display it on a monitor in horizontal lines. The more horizontal lines the better the spatial resolution.

Line Density

- Line density of the sound beam can directly affect spatial resolution.

- High line density provides sound beams that are tightly packed and create better detail imaging.

- Low line density provides wider gaps between the beams causing decreased detail, resulting in decreased spatial resolution.

USA

- Images with low pixel density will appear blurry and have less detail.

- Images produced with less line density will have decreased detail.

Prevention

- Line Density can sometimes be controlled by the operator; but are more often controlled by the ultrasound system itself.

- Modern display units address the lines per image. They are now equipped with more lines per image that provide better spatial resolution.

- The pixel density cannot be changed, but the quality of the picture may be improved by using write magnification. This pre-processing technique allows the sonographer to choose a region of interest, (ROI), and magnify it. The ultrasound system then rescans that image. This allows for a greater number of pixels which improves spatial resolution.

Helpful or Hindrance

- Degraded spatial resolution is a hindrance to imaging because it affects the quality and detail of the imaging.

Good Spatial Resolution vs. Poor Spatial Resolution    Ultrasound Physics

Good Spatial Resolution vs. Poor Spatial Resolution

Ultrasound Physics

Multipath Artifact    Ultrasound Physics

Multipath Artifact

Ultrasound Physics

Multipath Artifact    Ultrasound Physics

Multipath Artifact

Ultrasound Physics

Multipath Artifact    Ultrasound Physics    Multipath artifacts result from additional reflections of a portion of the beam on the path to or from a primary reflector. For example, the transmitted beam may encounter a primary reflector, reflect back but off axis, and then reflect off a second adjacent reflector along the path back to the transducer. This results in the object appearing to be slightly deeper than it actually is because of an increased path length.

Multipath Artifact

Ultrasound Physics

Multipath artifacts result from additional reflections of a portion of the beam on the path to or from a primary reflector. For example, the transmitted beam may encounter a primary reflector, reflect back but off axis, and then reflect off a second adjacent reflector along the path back to the transducer. This results in the object appearing to be slightly deeper than it actually is because of an increased path length.

Mirror Artifact    Ultrasound Physics    The depth at which each structure is displayed on a US image    is proportional to the amount of time it takes for a US beam    to return to the transducer from the time when it leaves the    transducer. Normally, this amount of time would be primarily    dependent upon the depth of a tissue from which the beam    reflects. This would result in an image with an anatomically    accurate depth. In mirror-image artifact, the return of sound    beams is delayed, and therefore the structures from which    these delayed beams are reflected are displayed at a greater    depth than their true anatomic depth. This delay occurs    in the presence of highly reflective interfaces, such as the    diaphragm/lung base interface on a right upper quadrant    scan. The diaphragm/lung base interface is highly reflec-    tive because gas reflects almost 100% of the sound that    hits it and is therefore the best acoustic mirror in the body.    A pulse from the main beam travels through the liver and is reflected    off the diaphragm. This reflected echo reaches the liver lesion    and reflects back to the diaphragm.14 From the diaphragm,    the echo finally reaches the transducer.    Because color Doppler scanning creates images with    marked contrast between vascular structures and soft tissues    (ie, color vs gray scale), mirror-image artifacts are particu-    larly common on color Doppler scans. As with gray-scale    imaging, color Doppler mirror images occur most frequently    around the lung. However, the increased contrast also allows    weaker acoustic interfaces, such as bone or even the back wall    of the carotid, to act as mirrors for color Doppler imaging.      Artifact due to: Propagation assumption.    Where it commonly occurs:    Diaphragm with liver lesions or the liver itself being duplicated, trachea.

Mirror Artifact

Ultrasound Physics

The depth at which each structure is displayed on a US image

is proportional to the amount of time it takes for a US beam

to return to the transducer from the time when it leaves the

transducer. Normally, this amount of time would be primarily

dependent upon the depth of a tissue from which the beam

reflects. This would result in an image with an anatomically

accurate depth. In mirror-image artifact, the return of sound

beams is delayed, and therefore the structures from which

these delayed beams are reflected are displayed at a greater

depth than their true anatomic depth. This delay occurs

in the presence of highly reflective interfaces, such as the

diaphragm/lung base interface on a right upper quadrant

scan. The diaphragm/lung base interface is highly reflec-

tive because gas reflects almost 100% of the sound that

hits it and is therefore the best acoustic mirror in the body.

A pulse from the main beam travels through the liver and is reflected

off the diaphragm. This reflected echo reaches the liver lesion

and reflects back to the diaphragm.14 From the diaphragm,

the echo finally reaches the transducer.

Because color Doppler scanning creates images with

marked contrast between vascular structures and soft tissues

(ie, color vs gray scale), mirror-image artifacts are particu-

larly common on color Doppler scans. As with gray-scale

imaging, color Doppler mirror images occur most frequently

around the lung. However, the increased contrast also allows

weaker acoustic interfaces, such as bone or even the back wall

of the carotid, to act as mirrors for color Doppler imaging.

Artifact due to: Propagation assumption.

Where it commonly occurs:

Diaphragm with liver lesions or the liver itself being duplicated, trachea.

Mirror Artifact    Ultrasound Physics

Mirror Artifact

Ultrasound Physics

Mirror Artifact    Ultrasound Physics

Mirror Artifact

Ultrasound Physics

Refraction Artifact    Ultrasound Physics    Doubling by refraction is different from other artifacts generating double images, such as mirroring of the ultrasound beam (eg, by prosthetic valves). Anatomic structures between the transducer and the heart such as the pleura, pericardium, or rib cartilage may induce refraction of the ultrasound beam resulting in doubling of cardiac structures. The resulting doubling of anatomic structures must not be misdiagnosed.

Refraction Artifact

Ultrasound Physics

Doubling by refraction is different from other artifacts generating double images, such as mirroring of the ultrasound beam (eg, by prosthetic valves). Anatomic structures between the transducer and the heart such as the pleura, pericardium, or rib cartilage may induce refraction of the ultrasound beam resulting in doubling of cardiac structures. The resulting doubling of anatomic structures must not be misdiagnosed.

Refraction Artifact    Ultrasound Physics    The bending of a beam at an interface of two media. You MUST have a change in propagation speed and speed and have an incident angle other than 0 degrees.

Refraction Artifact

Ultrasound Physics

The bending of a beam at an interface of two media. You MUST have a change in propagation speed and speed and have an incident angle other than 0 degrees.

Refraction Artifact    Ultrasound Physics    Refraction alters beam direction. Scanner places dot in wrong location along line of assumed beam direction can alter reflector shape.

Refraction Artifact

Ultrasound Physics

Refraction alters beam direction. Scanner places dot in wrong location along line of assumed beam direction can alter reflector shape.

Grating Lobe Artifact    Ultrasound Physics    Grating lobe artifact occurs in a similar manner to side lobe artifacts, in which far off-axis grating lobes result in an error in positioning the returning echoes. Compared with side lobes, grating lobes occur at more oblique angles (up to 90°) relative to the primary beam and have a different origin. They are produced as a result of a discontinuous transducer surface comprised of multiple individual elements regularly spaced across the aperture that cause constructive interference of the ultrasound beam between adjacent elements of the array.    Grating lobe artifacts and refraction artifacts have a great deal in common. In both these cases, the path of the ultrasound beam has not followed the intended, steered direction. They are both “locational” artifacts, which is to say their result within the ultrasound image is the structure’s displacement from its true location. Generally, the spurious structure will be laterally displaced. As such, without a clear visualization of a refracting surface within the image, differentiation between grating lobe artifact and refraction artifact is relatively challenging.

Grating Lobe Artifact

Ultrasound Physics

Grating lobe artifact occurs in a similar manner to side lobe artifacts, in which far off-axis grating lobes result in an error in positioning the returning echoes. Compared with side lobes, grating lobes occur at more oblique angles (up to 90°) relative to the primary beam and have a different origin. They are produced as a result of a discontinuous transducer surface comprised of multiple individual elements regularly spaced across the aperture that cause constructive interference of the ultrasound beam between adjacent elements of the array.

Grating lobe artifacts and refraction artifacts have a great deal in common. In both these cases, the path of the ultrasound beam has not followed the intended, steered direction. They are both “locational” artifacts, which is to say their result within the ultrasound image is the structure’s displacement from its true location. Generally, the spurious structure will be laterally displaced. As such, without a clear visualization of a refracting surface within the image, differentiation between grating lobe artifact and refraction artifact is relatively challenging.

Grating Lobe Artifact    Ultrasound Physics    When grating lobe artifacts occur, they are at higher amplitudes than side lobe artifacts and are closer in intensity to that of the primary beam

Grating Lobe Artifact

Ultrasound Physics

When grating lobe artifacts occur, they are at higher amplitudes than side lobe artifacts and are closer in intensity to that of the primary beam

Grating Lobe Artifact    Ultrasound Physics    These artifacts are dependent on the spacing between individual transducer elements and will not occur if the interelement spacing is less than one-half the wavelength. Therefore, their effect will depend on the particular transducer being used and the transducer frequency. Subdicing results in suppression of grating lobes.

Grating Lobe Artifact

Ultrasound Physics

These artifacts are dependent on the spacing between individual transducer elements and will not occur if the interelement spacing is less than one-half the wavelength. Therefore, their effect will depend on the particular transducer being used and the transducer frequency. Subdicing results in suppression of grating lobes.

Side Lobe Artifact    Ultrasound Physics    Every transducer has a main-beam axis along which the    main beams are transmitted parallel to the long axis of the    transducer. In linear array transducers, multiple other low-    amplitude beams project radially at different angles away    from the main-beam axis. These are termed side lobes.    Side lobes occur relatively close to the primary beam, as    opposed to grating lobes that have the same origin, but    are farther removed from the central beam. Side-lobe and    grating lobe beams may be reflected back (from a strong    reflector) to the transducer and sometimes detected. The    transducer/machine cannot differentiate between reflected    beams returning from the main beam versus those return-    ing from off-axis lobes. It considers any detected beam as    originating from the main axis. Off-axis lobes are lower in    amplitude than the main axis beam, and therefore in order    to be detected by the transducer, they must be reflected by    a highly reflective (ie, highly echogenic) structure. Off-axis    lobe artifacts have the appearance of a hyperechoic object    within an anechoic or hypoechoic structure, such as the    urinary bladder or gallbladder lumen. Also, this artifact    may be seen with needle biopsy when the needle is a strong    reflector.11 Off-axis lobe artifacts can also be seen on color    and spectral Doppler imaging.

Side Lobe Artifact

Ultrasound Physics

Every transducer has a main-beam axis along which the

main beams are transmitted parallel to the long axis of the

transducer. In linear array transducers, multiple other low-

amplitude beams project radially at different angles away

from the main-beam axis. These are termed side lobes.

Side lobes occur relatively close to the primary beam, as

opposed to grating lobes that have the same origin, but

are farther removed from the central beam. Side-lobe and

grating lobe beams may be reflected back (from a strong

reflector) to the transducer and sometimes detected. The

transducer/machine cannot differentiate between reflected

beams returning from the main beam versus those return-

ing from off-axis lobes. It considers any detected beam as

originating from the main axis. Off-axis lobes are lower in

amplitude than the main axis beam, and therefore in order

to be detected by the transducer, they must be reflected by

a highly reflective (ie, highly echogenic) structure. Off-axis

lobe artifacts have the appearance of a hyperechoic object

within an anechoic or hypoechoic structure, such as the

urinary bladder or gallbladder lumen. Also, this artifact

may be seen with needle biopsy when the needle is a strong

reflector.11 Off-axis lobe artifacts can also be seen on color

and spectral Doppler imaging.

Side Lobe Artifact    Ultrasound Physics    The existence of lower pressure or weaker beams pointing off-axis that occur with single element transducers.

Side Lobe Artifact

Ultrasound Physics

The existence of lower pressure or weaker beams pointing off-axis that occur with single element transducers.

Side Lobe Artifact    Ultrasound Physics    Beams propagating from a single element transducer in directions different from primary beam. Reflections from objects here will be placed on main sound transmission line.

Side Lobe Artifact

Ultrasound Physics

Beams propagating from a single element transducer in directions different from primary beam. Reflections from objects here will be placed on main sound transmission line.

Focal Banding Artifact    Focal Enhancement    Ultrasound Physics    This is a special form of enhancement is which a side-to-side region of an image appears brighter than tissues at other depths    - Focal banding have the same appearance as an incorrect TGC setting    - Banding is most prominent at focus    - Beam width strongly focused may have intensity of focal zone increased (reflections maybe abnormally strong)

Focal Banding Artifact

Focal Enhancement

Ultrasound Physics

This is a special form of enhancement is which a side-to-side region of an image appears brighter than tissues at other depths

- Focal banding have the same appearance as an incorrect TGC setting

- Banding is most prominent at focus

- Beam width strongly focused may have intensity of focal zone increased (reflections maybe abnormally strong)

Focal Banding Artifact    Focal Enhancement    Ultrasound Physics    Bands appear horizontally across an image in the region of multiple focusing that degrade the image.    Corrected by removing multiple focuses.

Focal Banding Artifact

Focal Enhancement

Ultrasound Physics

Bands appear horizontally across an image in the region of multiple focusing that degrade the image.

Corrected by removing multiple focuses.

Focal Banding Artifact    Focal Enhancement    Ultrasound Physics    Side-to-side region of increased intensity at the focus of an image.    - Most notable with linear array transducers.    - Decrease the artifact by altering focal zone, increasing # of focal zones.

Focal Banding Artifact

Focal Enhancement

Ultrasound Physics

Side-to-side region of increased intensity at the focus of an image.

- Most notable with linear array transducers.

- Decrease the artifact by altering focal zone, increasing # of focal zones.

Beam Width Artifact    Slice Thickness Artifact    Elevation Resolution Artifact    Ultrasound Physics    Beam width artifact refers to the lateral blurring of a point target that occurs as echoes from the same target are insonated at adjacent beam positions. Similarly, if two adjacent point targets are separated by a distance less than the beam width, they will appear as one. The beam width decreases as the wavelength decreases; thus the beam width is narrower with higher-frequency transducers. Focusing is a process used to further improve the beam width so that it is narrowest at the focal zone. When electronic focusing is used, a defocusing effect can occur from imaging tissues that have a different speed of sound from what is assumed (usually 1540 m/sec), in a process called phase aberration. This results in a wider beam width and a degradation of lateral resolution.

Beam Width Artifact

Slice Thickness Artifact

Elevation Resolution Artifact

Ultrasound Physics

Beam width artifact refers to the lateral blurring of a point target that occurs as echoes from the same target are insonated at adjacent beam positions. Similarly, if two adjacent point targets are separated by a distance less than the beam width, they will appear as one. The beam width decreases as the wavelength decreases; thus the beam width is narrower with higher-frequency transducers. Focusing is a process used to further improve the beam width so that it is narrowest at the focal zone. When electronic focusing is used, a defocusing effect can occur from imaging tissues that have a different speed of sound from what is assumed (usually 1540 m/sec), in a process called phase aberration. This results in a wider beam width and a degradation of lateral resolution.

Beam Width Artifact    Slice Thickness Artifact    Elevation Resolution Artifact    Ultrasound Physics    The thickness of the main US beam as it exits the transducer    is equal to the thickness of the transducer array. The finite    beam width creates a partial-volume artifact related to slice    or section thickness. When the beam includes both a cystic    structure and a solid structure, the scan line consists of echoes    from both the cystic and solid structure. The accumulation    of scan lines of this nature produces filling in of the cystic    structure. As the beam propagates away from the transducer,    it narrows gradually until it reaches the focal zone. It then    gradually widens again. Structures that are proximal to and distal from the focal zone are more prone to artifacts resulting    from volume averaging between adjacent objects that both    fall within the thickness of the beam. In other words, the    thicker the image slice, the more likely that two different    adjacent objects will fall within that image slice. This artifact    can be minimized by placing the focal zone at the level of    the tissue/structure of interest.

Beam Width Artifact

Slice Thickness Artifact

Elevation Resolution Artifact

Ultrasound Physics

The thickness of the main US beam as it exits the transducer

is equal to the thickness of the transducer array. The finite

beam width creates a partial-volume artifact related to slice

or section thickness. When the beam includes both a cystic

structure and a solid structure, the scan line consists of echoes

from both the cystic and solid structure. The accumulation

of scan lines of this nature produces filling in of the cystic

structure. As the beam propagates away from the transducer,

it narrows gradually until it reaches the focal zone. It then

gradually widens again. Structures that are proximal to and distal from the focal zone are more prone to artifacts resulting

from volume averaging between adjacent objects that both

fall within the thickness of the beam. In other words, the

thicker the image slice, the more likely that two different

adjacent objects will fall within that image slice. This artifact

can be minimized by placing the focal zone at the level of

the tissue/structure of interest.

Beam Width Artifact    Slice Thickness Artifact    Elevation Resolution Artifact    Ultrasound Physics    the focal distance, the beam width and section thickness narrow; thus the lateral and elevational resolutions are at their highest. In contrast, although axial resolution is frequency dependent, it is independent of depth.    "Noise" in an image due to not being able to show slice thickness on a 2D image.

Beam Width Artifact

Slice Thickness Artifact

Elevation Resolution Artifact

Ultrasound Physics

the focal distance, the beam width and section thickness narrow; thus the lateral and elevational resolutions are at their highest. In contrast, although axial resolution is frequency dependent, it is independent of depth.

"Noise" in an image due to not being able to show slice thickness on a 2D image.

Beam Width Artifact    Slice Thickness Artifact    Elevation Resolution Artifact    Ultrasound Physics

Beam Width Artifact

Slice Thickness Artifact

Elevation Resolution Artifact

Ultrasound Physics