Ultrasound Artifacts and Acoustic Enhancement

Study Notes

Artifacts are unwanted marks in a radiograph
They obscure important anatomical details, potentially leading to misdiagnosis or the need for repeat imaging.
Artifacts are part of an ultrasound image that does not represent or directly correlate to the actual anatomic structures being evaluated.
An additional, missing or distorted image that does not conform to the real image of the part being examined.
Artifacts are commonly encountered, and familiarity is necessary to avoid false diagnoses.
In some cases, specific artifacts can even offer valuable diagnostic information, for instance, some may be indicative of certain pathologies.

Acoustic enhancement (also called posterior enhancement or enhanced through transmission) refers to the increased echoes deep to structures that transmit sound exceptionally well.
This is characteristic of fluid-filled structures such as cysts, the urinary bladder, and the gallbladder, as the fluid attenuates sound less (low-attenuating objects) than surrounding tissue.

Acoustic shadowing (posterior acoustic shadowing) is characterized by the apparent lack of signal deep to an imaged tissue interface.
This is due to all of the transmitted sound wave being reflected back to the transducer or absorbed by the tissue.
It commonly occurs when an area of interest contains a high Z/solid tissue (e.g., calcified gallstone or bone) or at an interface with high acoustic impedance mismatch (e.g., soft tissue/air).
Diagnostic significance: Limits examination of body regions behind gas or bone; useful in diagnosing stones, calcifications, or foreign bodies.

Edge shadowing occurs at the edges of rounded tissue structures due to the reflection and refraction of the beam within the structure.
These interactions result in an edge shadow, which are often seen in the internal carotid artery.

Clean and dirty shadowing are common phenomena in ultrasound imaging.
Clean shadowing is produced by sound-absorbing materials (e.g., stones), whereas dirty shadowing is produced by sound-reflecting materials (e.g., abdominal gas).

Reverberation artifacts result from two or more strong reflecting surfaces.
The ultrasound beam reflects back and forth between the reflectors, creating a reverberation.
The transducer interprets the returning sound waves as deeper structures.

A type of reverberation artifact; this results in a short train of reverberations from an echogenic focus with strong parallel reflectors (e.g., cholesterol crystals in adenomyomatosis).
With comet tail artifact, the space between the parallel reflectors is less than half the pulse length, causing echoes to be displayed as triangular lines with decreased amplitude.
Possible causes include: small renal or ureteric calculi; small common bile duct stones; adenomyomatosis of the gallbladder; pancreatic calcifications; testicular microlithiasis; thyroid colloid nodules; foreign bodies; surgical clips; catheter tips; debris/glass/metal.

This appears as a solid streak or series of parallel bands (ladder-like) radiating from abdominal gas collections.
The artifact is associated with gas bubbles.
The trapped fluid resonates.
Returning signal consists of one or more discrete frequencies.
A "beat" between these creates the ring down appearance.
There is no reverberation.

Side lobe artifacts occur when side lobes reflect sound from a strong reflector outside the central beam.
This shows as echoes originating from within the central beam.
Side lobe artifacts are caused by low-energy side lobes of the main ultrasound beam.
The side lobe beam returns to the receiver and is assigned to a false location as a main beam

A mirror image artifact occurs when a highly reflective surface (e.g., diaphragm) deflects the primary ultrasound beam.
The beam encounters another structure and reflects back to the reflective surface.
This creates a false echo on the opposite side of the reflective surface.

This artifact is caused by the refraction of the beam due to structures in the body such as areas like the rectus abdominis muscle on the anterior abdominal wall.
The edges of the muscle act like a lens causing the beam to be refracted.
The returned echoes give the appearance of multiple structures in the image.

Speed displacement artifact, also known as propagation velocity artifact.
It is a gray-scale finding like a discontinuity and displacement of an echo deeper than its true position.
Depth determination is based on the principle that an average propagation velocity of sound in human tissue is 1540 m/s.
If the tissue speed is much higher or lower than this value, the resulting distance calculation is false.

Twinkling artifact is seen with color Doppler ultrasound.
It appears as a signal with alternating colors behind a reflective object (e.g., calculus).
It often gives the appearance of turbulent blood flow and is more sensitive for detecting small stones than acoustic shadowing

Incorrect equipment control settings can lead to artifacts.
Excessively high gain can amplify inherent electronic noise, while too low a gain setting can result in a loss of crucial diagnostic information.