Ultrasound Imaging Artifacts

This will be explained below are many causes of the ultrasound picture is not good , among other errors in placing the probe , and more details see below :

Basic Principles imaging ultrasound

> Definition: In ultrasound, artifacts are acoustic images that do not correlate with an anatomical structure. They result from the fact that not all physical phenomena are taken into account in the imaging process.
> Significance: Artifacts can have varying significance in the interpretation of sonographic images. Some, such as slice-thickness artifact, can interfere with image interpretation whereas others, such as acoustic shadowing, are diagnostically useful.

Side-Lobe Artifact

>Definition: An object is improperly represented in the display as a result of echoes generated by side lobes that accompany the main beam.
> Description: A side-lobe artifact appears as a curved line in an anechoic structure.
> Significance: They may be mistaken for internal echoes in cystic organs (septa, sediment).
> Differentiation from a real object: The artifact is easily eliminated by angling the transducer or changing the scan plane.

Side-lobe artifact: Intestinal gas (I) is a strong reflector that is projected into the interior of the gallbladder (Gb). S = side-lobe artifact, T = transducer.

Side-lobe artifact: The arrows indicate a side-lobe artifact in a stonefree gallbladder (GB). The artifact is caused by gas in the adjacent duodenum (DUO)

Noise

Definition: Extremely fine echoes caused by voltage fluctuations in the imaging electronics.
> Description: Noise appears as multiple tiny echoes in the near portion of anechoic structures (“ground glass” appearance in cystic structures).
> Significance: The fine spurious echoes in cystic structures may be mistaken for sludge or gravel. Small cysts may even appear solid.
> Differentiation from a real object: Noise can be eliminated by lowering the gain setting and/or changing the focus.

The amplification of echoes from areas closer to the transducer causes multiple fine echoes to appear within cystic organs. T = transducer, N = noise.

Noise in a hepatic cyst (C). Multiple fine echoes appear in the anterior part of the cyst.

Acoustic Shadowing

> Definition: An absence of echoes behind structures that are strong reflectors or absorbers of ultrasound.
> Description: The shadow appears as an anechoic band posterior to a high-amplitude echo (from a strong reflector such as calcium, air, or bone).
> Significance Helpful in the diagnosis of stones and cysts (edge shadowing).
> Troublesome in abdominal ultrasound (bowel gas and rib shadows).
>  Acoustic shadows are cast not only by strong reflectors but also by connective tissue that is struck tangentially by the beam (ligamentum teres, connective tissue in the porta hepatis).
> Small stones will cast an acoustic shadow only if they are directly within the focal zone of the transducer.

Acoustic shadowing: A strong acoustic reflector (e.g.,a gallstone = G) casts an acoustic shadow (S) due to reflection and absorption. T = transducer

Typical acoustic shadow (S) associated with a gallstone.

Acoustic Enhancement

> Definition: A relative increase in echogenicity caused by a lack of sound attenuation.
> Description: Structures located behind cysts, abscesses, or necrotic metastases
appear more echogenic than adjacent tissues at the same depth.
>Significance:
* Helpful in the diagnosis of cysts and other anechoic structures.
* Troublesome in evaluating areas behind cysts and other liquid structures.

Acoustic enhancement: Because sound waves are less attenuated in fluid, the echoes behind a fluid-filled structure have greater amplitude.
T = transducer, C = cyst, AE = acoustic enhancement

Posterior acoustic enhancement. An area of increased echogenicity (arrows) appears behind the gallbladder (GB)

Slice-thickness Artifact

> Definition: Artifact occurring at curved interfaces between anechoic and hyperechoic structures, caused by the beam thickness.
> Description: Appears as fine echoes layered along the inner wall of a fluid-filled structure, causing the wall to appear thickened and indistinct.
> Significance: May be mistaken for debris, sludge, gravel, or clotted blood.

Slice-thickness artifact: The anterior and posterior cyst walls appear thickened and indistinct. B = beam-width artifact, T = transducer.

Beam-width artifact: Transverse scan through the bladder (B) shows partial thickening and lack of sharpness of the bladder wall, especially on the far side (arrow).

>> Differentiation from a real object

> Reposition the patient
> Improve the focus
> Change the scan plane

Mirror Image Artifact

> Definition: “Ghost images” may appear behind strong reflectors because the
reflection alters the path of the beam and doubles its transit time.
> Description: Liver tissue located below the strong reflector of the diaphragm is
projected to a supradiaphragmatic location in the basal lung zone (“pseudoecho”).
>Significance: Minimal, since awareness of the artifact should preclude errors of
interpretation.
>Differentiation from a real object: The normal parenchyma of the liver and spleen can mimic a pleural effusion, but doubts can be resolved by examining the patient in a sitting position and scanning from the posterior side.

Mirror image artifact: Schematic representation of sound waves in the liver (L) reflected from the diaphragm (D), giving rise to a “mirror-image” liver.
T = transducer, LS = supraphrenic “mirror-image”
liver.

Mirror image artifact: Right subcostal oblique scan demonstrates the liver (L), the diaphragm (D, or lung entry echo), a subphrenic hepatic hemangioma, and the reflected hemangioma imaged at a supraphrenic location (arrows).

Reverberations

> Definition: Linear artifacts caused by multiple reflections between two highly reflective interfaces. The computer of the ultrasound system interprets the time delays as increasing distance from the transducer.
>Description: Appear as a series of echogenic lines that are parallel to one another and to the transducer face and whose amplitudes diminish at greater depths
>Special forms

>>Comet-tail artifact
>>Ring-down artifact

Schematic representation of typical reverberations (R) occurring between strongly reflective interfaces (I). T = transducer.

Reverberations: Longitudinal scan of the uterus and bladder (B) with “superimposed” parallel lines caused by abdominal wall structures. Arrows = IUD.

Significance: Reverberations are consistently present in cystic organs but may also occur in solid structures. They are always troublesome and rarely helpful. They can be eliminated by changing the direction of the beam.

Edge Shadowing

> Definition: Lateral acoustic shadows caused by a tangential beam angle, scattering, refraction, attenuation, and extinction of the ultrasound beam at cyst walls
> Description: Narrow hypoechoic bands or shadows at the edges of cystic structures, often showing a divergent pattern.
> Significance: Edge shadowing is a useful criterion for diagnosing cysts.
> Differentiation from a real object:
*Edge shadows can mimic stones, especially in the gallbladder fundus and cystic duct.
*Double-check the finding in a second scan plane.

Edge shadowing: When sound waves encounter cyst walls at a tangential angle, they are scattered or refracted. T = transducer,
C = cyst,
CE = cystic edge shadows

Edge shadowing. The refraction and attenuation of sound at cyst margins produces a divergent or convergent pattern of acoustic shadowing. Sound attenuation by the echogenic walls of cystic structures is not the only cause of this artifact, which may also result from deviation of the beam due to scattering and refraction. This explains the divergent pattern of edge shadowing that may be seen.

Ultrasound Tags: artifact ultrasound