Artifacts Chapter 21

What is an ultrasound artifact?

Any error in image display that does not represent true anatomy.

What causes most ultrasound artifacts?

Incorrect assumptions made by the ultrasound system about sound behavior.

What is acoustic shadowing?

A signal void distal to a highly attenuating structure.

What structures commonly cause acoustic shadowing?

-Bone

-Calcifications

-Stones

-Gas

How does shadowing appear on the image?

Dark area with absence of echoes posterior to the structure.

What is posterior acoustic enhancement?

Increased echogenicity distal to a low-attenuating structure.

Which structures cause posterior enhancement?

-Fluid

-Cysts

-Bladder

-Gallbladder

Why does posterior enhancement occur?

Sound travels through fluid with less attenuation, producing stronger echoes distally.

What is reverberation artifact?

Multiple equally spaced echoes caused by sound bouncing between strong reflectors.

What is comet tail artifact?

A type of reverberation with closely spaced echoes that taper distally.

What structures commonly produce comet tail artifact?

-Cholesterol crystals

-Surgical clips

-Gas

What is ring-down artifact?

Continuous echogenic band caused by resonating gas bubbles.

Difference between comet tail and ring-down?

-Comet tail: solid reflectors

-Ring-down: gas bubbles

What is mirror image artifact?

Duplication of a structure on the opposite side of a strong reflector.

What structure most commonly causes mirror image?

The diaphragm.

Why does mirror image artifact occur?

Sound reflects off a strong interface and returns along an indirect path.

What is refraction artifact?

Bending of sound when it crosses tissues with different propagation speeds.

How does refraction artifact appear?

Lateral displacement or duplication of structures.

What is edge shadowing?

Shadowing at the edges of curved structures due to refraction and divergence.

What structures commonly show edge shadowing?

-Gallbladder

-Cysts

-Kidneys

What is speed error artifact?

Misplacement of structures due to incorrect assumed speed of sound.

What is the assumed speed of sound in soft tissue?

1540 m/s

What happens if sound travels faster than 1540 m/s?

Structures appear deeper than their true location.

What happens if sound travels slower than 1540 m/s?

Structures appear more superficial.

What is range ambiguity artifact?

Echoes are assigned to the wrong depth due to high PRF.

Where is range ambiguity most likely to occur?

With PW Doppler and deep structures.

What is side lobe artifact?

Echoes created by off-axis energy displayed in the main beam.

What causes side lobe artifact?

Secondary beams reflecting off strong reflectors.

How does side lobe artifact appear?

False internal echoes within cystic structures.

How can side lobe artifact be reduced?

-Lower gain

-Use harmonics

-Proper focal zone placement

What is grating lobe artifact?

A type of side lobe artifact caused by array transducer element spacing.

What is beam width artifact?

Structures within the beam width are displayed as being in the same plane.

Where is beam width artifact most common?

-At focal zone edges

-Near the transducer

How does beam width artifact appear?

Partial volume averaging or false echoes.

What is anisotropy?

Artifact where echogenicity changes based on angle of insonation.

Where is anisotropy most commonly seen?

-Tendons

-Ligaments

-Muscles

How can anisotropy be corrected?

By changing the transducer angle.

What is clutter artifact?

Low-level echoes in fluid caused by noise or motion.

How can clutter be reduced?

-Adjust wall filter

-Reduce gain

-Use harmonics

Fluid-filled structures should show which artifact?

Posterior acoustic enhancement.