Month: July 2022

Side lobe artifact occurs when the beam of an off-axis side lobe encounters a structure and returns this off-axis object as coming from the main beam. This creates a duplicate structure on the screen but in a different area.

In the example below, it seems like there is a moving structure in the left atrium, but it is actually a side lobe artifact resulting from the mitral valve leaflet. This is important because oftentimes these side lobe artifacts may be mistaken for clots or foreign bodies. It is always a good habit to get multiple views to confirm that what you are seeing is artifact versus pathology.

Previously, the ring down artifact was thought to be a type of comet tail artifact, since both have bright “echogenic” lines arising from a specific location. However, the ring down artifact has a distinct feature compared to the comet tail artifact in that the echos do NOT dissipate as the depth of the image is increased. These echogenic vertical lines will go all the way to the bottom of the screen, regardless of depth. This has become known as the “ring down artifact” and is most commonly seen as “B-lines” in lung ultrasound, signifying interstitial edema.

The theory for the ring down artifact is that when fluid is trapped in a tetrahedron of air bubbles, the ultrasound waves reflect infinitely and result in an infinitely long vertical echogenic line.

Comet tail artifact is a form of reverberation artifact. In comet tail artifact the two reflective surfaces are closely spaced together (such as the bevel of a metallic needle). The reflective surfaces are so close that it is difficult to distinguish between each reflected echo.

Comet tail artifact is different from ring down artifact (described next) because the comet tail artifact dissipates with depth and has a triangular and tapered shape. See the image below of a comet tail artifact arising from a needle tip.

In the presence of highly reflective surfaces, echoes may reflect back and forth between the reflective surface and the ultrasound probe. This can cause the ultrasound screen to record and display multiple echoes on the screen. This ultrasound artifact is known as Reverberation Artifact.

Let’s use the highly reflective pleural line as an example below. The ultrasound waves that return after a single reflection represents the actual pleural line (white arrows/line in the figure below). All of the subsequent echoes (blue, green, and red arrows/lines) will take longer to return the probe and the ultrasound will interpret those as increased equidistantly spaced linear reflections. These other lines are also known as “A-lines” and are a form of reverberation artifact in normal lung.

Edge artifact on ultrasound occurs because of refraction. Ultrasound waves are deflected from their original path when they encounter curved and smooth-walled structures. This will result in a shadow-like line that comes off of the edge of these structures. The most common times you will see this are: vessel walls, gallbladder, cystic structures, testicle, aorta.

This is the opposite of the acoustic shadowing artifact and occurs when ultrasound waves pass through a structure with significantly low attenuation such as blood or fluid-filled structures.

The most common situation you will see posterior acoustic enhancement: bladder, gallbladder, cysts, vessels, ocular ultrasound.

The mirror image artifact on ultrasound occurs when ultrasound waves encounter a highly reflective surface that is adjacent to air.

The most common instance of this is the pleural-diaphragm interface causing the appearance of “liver” or “spleen” inside the lung. You can also see mirror image artifact when you are performing cardiac ultrasound as the ultrasound waves, approach the pleural-pericardium interface. These are normal findings.

Ultrasound artifacts are frequently encountered and can be a source of confusion for interpreting providers. Ultrasound artifacts can be understood with a basic understanding of the ultrasound physics we just discussed pertaining to reflection, refraction, and attenuation.

The ability to recognize and fix correctable ultrasound artifacts is important for getting quality ultrasound images and optimizing the care of your patients.

Here are the main ultrasound artifacts we will cover:

• Mirror Image Artifact
• Acoustic Shadowing Artifact
• Posterior Acoustic Enhancement
• Edge Shadowing Artifact
• Reverberation Artifact
• Comet Tail Artifact
• Ring Down Artifact
• Side Lobe Artifact