Ultrasound artifacts are simply an error in imaging. The artifact is a false image of the anatomy. It could be something that appears that is not really there anatomically. Or it could be an image that appears that hides the real anatomy. It could be an image that is not properly visualized thus creating a false image of the real anatomy.
Some artifacts can be the result of improper scanning technique and some are the result of the basic physical properties of the ultrasound beam, the spread and penetration of sound waves through tissue and the image processing by the ultrasound machine itself.
Some artifacts are diagnostic themselves despite it being an error in the propagation or image processing of the ultrasound wave (comet tails, ring down or posterior acoustic shadowing).
A good understanding of the physics of ultrasound would be ideal but that is not what this blog is about. It is about utilizing some elementary understanding of what the ultrasonic waves create when passing through different tissues in the body and what and how those waves are processed and reflected as images on the screen of your machine.
ABSORPTION, REFLECTION, SCATTERING AND REFRACTION:
Some sound waves are absorbed by the material (tissue) it meets, some are reflected, some scattered and others refracted.
Once an ultrasound wave is generated and travels through tissue, the probe switches from the “sending out” mode to the “listening” mode and waits for the returning ultrasound echoes. It is said that 99% of the time the probe is in the “listening” mode and this is occurring several million times per second. The returning echoes are created into an image on the ultrasound monitor.
There are a number of artifacts that the ultra-sonographer will likely encounter that could be problematic in image interpretation and some that will be utilized as being helpful when trying to understand an image.
SHADOWING
A highly attenuating or reflective structure(s) cause posterior shadowing behind the structure(s).
A weaker signal (shadow) returns from behind a strong reflector (air) or sound absorbing structures like gallstones, kidney stones or bone.
REVERBERATION
Ultrasound waves reflect back multiple times after hitting a highly reflective surfaces. Appear as multiple duplicated images of these surfaces. Multiple white lines. Also called “A-lines”
POSTERIOR ACOUSTIC ENHANCEMENT
When an ultrasound wave travels through a structure with low resistance (think fluid filled) the tissue at the far side of the structure appears brighter than the tissue beside it.
MIRROR ARTIFACT
Occurs when there is a highly reflective surface (think diaphragm). The ultrasonic waves pass through this surface and then are reflected back to that surface producing a mirror image of the structure that is nearest to the probe…on the far side of that reflective surface. Most often occurs in the RUQ where you will see a mirror image of the liver on the far side of the diaphragm.
COMET TAIL ARTIFACT
Similar to reverberation artifact this occurs when there are two highly reflective surfaces (viceral parietal plural interface). The sound waves pass through these two highly reflective surfaces and bounce back and forth producing a ladder like or venetian blind like echo return. Each subsequent reflection is weaker than the prior ones.
Comet tails, “search lights” or “B-lines” are present when there is an increase fluid or consolidation in lung fields during the ultrasound lung exam. Useful in the exam in that if there are comet tails visible there cannot be a pneumothorax (air within the pleural space hinders the sound waves preventing the comet tails).
EDGE ARTIFACT
Occurs when ultrasonic wave encounter a fluid filled structure (gallbladder, cyst). A mismatch in the speed of the sound waves through the edges of a fluid filled structure exhibit narrow, hypoechoic shadow lines extending a distance from the lateral edges of that fluid filled structure.
Overall, some ultrasound artifacts may be avoidable with proper scanning techniques along with the knowledge that other artifacts are generated by the physical properties of the ultrasonic waves and the tissue through which those waves pass. Awareness that artifacts are present in every scan and familiarity with those artifacts will help the sonographer in determining real verses misrepresentations of anatomy and in diagnosing pathology.
References Cited
Abdulla, A. (2014, May 07). Ultrasound artifacts. Retrieved May 27, 2019, from https://www.slideshare.net/ansaripv/ultrasound-artifact
Artifacts – Steph’s ultrasound. (n.d.). Retrieved May 28, 2019, from https://sites.google.com/site/stephsultrasound/home/physics-fun/artifacts
Hayden, G. (2013). Emergency Ultrasonography. Retrieved May 26, 2019, from http://www.emergencyultrasoundteaching.com/galleries/image_galleries/physics_images/index.php
Morovati, P., & Bickle, I. (n.d.). Acoustic enhancement: Radiology Reference Article. Retrieved May 25, 2019, from https://radiopaedia.org/articles/acoustic-enhancement?lang=us
Sonoguide. (n.d.). Retrieved May 25, 2019, from https://www.acep.org/sonoguide/physics.html
Ultrasound Artifacts. (2019). Retrieved May 28, 2019, from https://www.examrefresh.com/ultrasound_artifacts/