Ultrasound Artifact

ULTRASOUND ARTIFACT

Artifact is a structure in an image which is not direct similar with the actual anatomy of the tissue being scanned

Artifact assumes different forms including

• Structures in the image that are not actually present
• Objects that should be represented but are missing from the image
• Structures which are misregistered on the image
• MULTIPLE ECHO ARTIFACTS
• Reverberation
• Comet tail
• Ring down
• Mirror image
• Air artifact
• VELOCITY ERROR ARTIFACT
• Edge shadowing
• ATTENUATION ARTIFACT
• Acoustic shadowing enhencement

TYPES OF ARTIFACTS

• ULTRASOUND BEAM ARTIFACT
• Side lobes
• Grating lobes
• Beam width artifacts

Slice thickness artifact

REVERBERATION

This is the production of false echoes due to repeated reflections between two interface with a high acoustic impedance mismatch The echo from the interface is received by the transducer and displayed on the image The reverberation echoes will be equally spaced because the time for each additional echoes is multiple of the time of return of the first echo

This artifact will be seen at the skin-transducer interface and behind the bowel gas

RECTIFICATION

• Increase the amount of gel used

Reduce the gain

ACOUSTIC SHADOWING

This appears as an area of low amplitude echoes behind an area of strongly attenuating tissue.

It is caused by severe attenuation of a beam at an interface, resulting in very little sound being transmitted beyond The attenuation can be due to either absorption or reflection of the sound waves, or a combination of the two Acoustic shadowing will occur at interfaces with large acoustic mismatch such as soft tissue and gas and soft tissue and bone

ACOUSTIC ENHANCEMENT

This artifact appears as localized area of increased echo amplitude behind an area of low attenuation Acoustic Enhancement can to differentiate fluid filled structures from solid , hypoechoic masses.

Can commonly be seen distal to fluid filled structures such as the Urinary bladder, Gallbladder or a Cyst

EDGE SHADOWING

A combination of refraction and reflection occurring at the edge of rounded structures will results in edge shadowing artifacts It arises due to refraction of beam caused by both curvature of rounded edges and difference in speed of two materials When the ultrasound beam reaches the rounded edge of the structure reflection will occur with an angle of incidence equal to angle of reflection The combination of reflection and refraction of the beam sat the edges of a rounded structure results in a thin strip of tissue behind the edge not being inso nated and causes a shadow

It occurs at edges of rounded structures such as Gallbladder and Cyst

BEAM WIDTH ARTIFACT

When the ultrasound beam is produced from the transducer its width starts to narrow as it approaches the focal zone.

the structure outside the width of the main ultrasound beam if highly reflective will generate echoes that are assumed to originate within the main ultrasound beam It maybe recognized within echo free zones or anechoic structures such as Gallbladder and Blood vessels Correct positioning of the focal zone will help to reduce this artifact

SLICE THICKNESS ARTIFACT

This artifact is similar to the beam width artifact but occurs due to thickness of the beam which is transverse This artifact is caused by assuming that the ultrasound beam is thin like a sheet of paper but in reality it is not thin hence it is three dimensional Therefore structures above and below the beam can be mapped into the main ultrasound beam.

This artifact can be found in anechoic structures such as Gallbladder, Urinary Bladder, Cyst and Blood vessels

RING-DOWN ARTIFACT

• This is the type of reverberation artifact

It occurs as a line or series of parallel bands extended posterior to a gas correction As a sound wave encounters gas bubbles the sound waves excites the gas bubbles causing them to vibrate The vibrations creates a continuous sound wave directed backward the transducer It occurs in the posterior collections of gas, such as Portal Venous gas, Gas in abscesses and Bowels

COMET-TAIL ARTIFACT

This is the form of reverberation artifact As the sound wave bounces between the transducer and the strong reflector resulting in multiple lines of artifact Thus, the sequential echoes are closely spaced that individual signals are not perceivable in the image It occurs in calcifications, biopsy clip and surgical clip PREVENTION; by decreasing the TGC in the near field as well as changing the beam angle

DUPLICATE ARTIFACT

• This artifact is caused by refraction of the beam

It occurs in areas such as rectus abdominis muscle on the anterior abdominal wall In transverse plane, the edges of the muscle acts as a lens and the ultrasound beam to be refracted and this causes a single structure to interrogated by two separate refracted beam The two sets of echoes will therefore be returned and this will cause display of two structures in the image

MIRROR ARTIFACT

They arise due to specular reflection of the beam sat a large smooth interface An area close to a specular reflector will be emerged twice, once by the original ultrasound beam and once by the beam after it has reflect off the specular reflector It is commonly seen when scanning the liver, the diaphragm acts as a specular reflector

SIDE LOBE ARTIFACTS

The energy within the ultrasound beam exists as several sidelobes radiating at a number of angles from a central lobe Echoes are generated by these lobes in addition to the main lobe but all the returning echoes are assumed by the transducer to have arisen from the central axis of the main lobe Sidelobe echoes will therefore be misregistered in the display This artifact occurs in the urinary bladder and within a cyst

GROUP 5 MEMBERS

BARAKA LUSINDE

STEVEN ROBERT

LOISI KAMATA

OLGA EXAUD

BARAKA MANJALE

DAMA ALLY

ULTRASOUND ARTIFACT

Artifact is a structure in an image which is not direct similar with the actual tissue being scanned

Artifact assumes different forms including

• Structures in the image that are not actually present
• Objects that should be represented but are missing from the image
• Structures which are misregistered on the image

TYPES OF ARTIFACTS

• ULTRASOUND BEAM ARTIFACT
• Side lobes
• Grating lobes
• Beam width artifacts
• Slice thickness artifact
• MULTIPLE ECHO ARTIFACTS
• Reverberation
• Comet tail
• Ring down
• Mirror image
• Air artifact
• VELOCITY ERROR ARTIFACT
• Edge shadowing
• ATTENUATION ARTIFACT

Acoustic shadowing enhencement