Jack Allan, MD, PGY1
The Article: Hindi, A. Peterson, C. Barr, Richard. “Artifacts in diagnostic ultrasound.” Reports in Medical Imaging 2013: 6 29-48.
The Idea: Ultrasound is a rapidly evolving imaging modality that plays many roles in both diagnosis and procedural assistance in daily clinical practice. However, ultrasound imaging can be obstructed by different forms of imaging artifact. These artifacts may be avoidable, such as those caused by improper scanning technique. Other artifacts, however, are unavoidable as they are inherent to the physical limitations of ultrasound technology but may still be useful in diagnosis. By understanding the physics of ultrasound, propagation of sound through a variety of tissues, and by understanding the assumptions made in ultrasound it is possible to better understand the origin of different artifacts. In this way, it is possible to avoid artifacts caused by poor technique and utilize other artifacts that may provide valuable diagnostic information, thereby optimizing patient care.
The Review: The article provides a short review of many common sound artifacts produced in B mode, spectral and color Doppler, and elastography. Here I will outline three of the most commonly seen of these artifacts encountered during Emergency Bedside Ultrasound:
1. Reverberation: This is the production of multiple equidistant gray lines within a structure composed of two highly reflective surfaces, such as a cyst. Because sound waves will reverberate between the two reflective surfaces before returning to the transducer, this is misinterpreted as presence of a surface within the structure.
2. Shadowing: This artifact comes in multiple degrees: clean, partial, or dirty shadowing. It refers to the anechoic, hypoechoic, or low-level echoes occurring distal to an area where sound attenuation is occurring. For example, large calcifications or stones produce clean shadowing as the stones attenuate sound waves and produce an anechoic shadow. Gas collections, on the other hand, produce dirty shadows due to the highly reflective gas bubble interfaces.
3. Increased through-transmission (posterior enhancement): This artifact appears as a hyperechoic area distal to a fluid-filled structure as fluid attenuates sound much less. This is commonly seen in structures such as the filled urinary bladder or fluid filled cysts.
Takeaways: Ultrasound is a powerful imaging modality in the practice of Emergency Medicine and provides extremely useful diagnostic information as well as support during procedures. The artifacts encountered during ultrasound are often avoidable by improved scanning technique, but are also often inherent in the image production and therefore unavoidable. The three artifacts mention here, while unavoidable even with changes to scanning technique, are still very valuable in patient care. For example, a patient coming to the emergency department with suspicion for gallbladder pathology may have a difficult gallbladder to visualize and gallstones could be missed, however, by understanding the physics of shadowing artifact one can confidently recognize presence of gallstones by shadowing alone. As ultrasound continues to grow as an imaging technique and is utilized in new ways, it will be important for all users to have basic understanding of artifacts and how and when to avoid or utilize them.