Figure 5.17. Slice‐thickness artifact at the AFAST CC view. (A) and (B) are the same images within the same cine loop that have been extracted to show how much gain settings affect the image. In (A) is a slice‐thickness artifact that is circled in (C). In (B) the gain is turned down, eliminating the artifact (true sediment would persist in gravity‐dependent regions). Color flow Doppler is another technique used to look for flow (mass versus thrombus versus sediment versus artifact). (C) and (D) are labeled images of (A) and (B) respectively. Note how the loop of small intestine outside the lumen of the urinary bladder could mimic a bladder stone (cystic calculi) with a hyperechoic line (reflective air) and clean shadowing through the far‐field. Note also that the screen provides a lot of information including a depth of 10 cm, an abdominal preset (Abv) in the upper right. Note, there is uniquely no focus cursor on machines from this manufacturer (SonoSite). Arrows indicate the body wall in the CC pouch. SI, small intestine; UB, urinary bladder.

      Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Image Interpretation

       Lacking Awareness of Most Common Locations for Artifacts

In Chapter 3, Table 3.1 lists the common ultrasound artifacts and the most common locations and examples for each. Briefly, we will list here some strategies to create better awareness of these artifacts, especially during the Global FAST approach. This leads to another major point…

      Saving images is important not only for archiving patient information but for learning by reviewing studies and being able to compare to other modalities, future studies, and clinical course and outcome. For learning artifacts and how your machine interprets them, you can go through studies playing the “artifact game.” For example, look at the AFAST views for mirror image artifact at the DH view on the pleural cavity side of the diaphragm, the CC view and the other side of the abdominal wall, and TFAST echo views for mirror image artifact on the far side of the pericardium. This can also be done with other artifacts in their most common locations, such as edge shadowing off the curved surface of the stomach wall, renal cortex, urinary bladder, etc.

       Mirror Image

      This most commonly occurs at the diaphragm but the most problematic is the mirroring of the gallbladder into the thorax, especially when it’s a partial mirror image. In this case, the gallbladder can mimic pleural and pericardial effusion to the hasty sonographer.

      Other places for mirror image, where generally a strong air–soft tissue interface exists, are on the far side of the heart when aerated lung is in direct opposition to the pericardium, and the urinary bladder against the colon or thin body wall. See Chapter 3 for more explanation and examples.

       Side‐lobe, Slice‐thickness

      This artifact occurs where there is a curve within a fluid‐filled structure and is especially associated with the urinary bladder and gallbladder mimicking sediment and a mass. To differentiate artifact from sediment, consider where the gravity‐dependent region is within the lumen of these structures. If “sediment” appears in nongravity‐dependent regions, you should consider the possibility of artifact. Other techniques to differentiate artifact from true pathology include eliminating the artifact by turning down the gain and ballottement or changing the patient’s position. Finally, some hasty sonographers will misinterpret an artifact for a mass. Simply place color flow Doppler on the suspect region for differentiation because a mass generally has pulsatile blood flow and an artifact (and thrombus) does not. See Chapter 3 for more explanation and examples.

       Edge Shadowing

      The edge shadowing artifact is created when the ultrasound beam strikes a curved surface, creating a dark shadow that extends from that curved surface through the far‐field. Edge shadowing most commonly occurs at the curved surfaces of stomach wall, renal cortex, gallbladder and urinary bladder and can be mistaken for free fluid along the stomach wall and renal cortex or defects in the wall of the gallbladder and urinary bladder, the latter especially when ascites is present on the AFAST CC view. See Chapter 3 for more explanation and examples.

Pearls, Pitfalls, and The Final Say

      The paradigm change of POCUS and FAST rests on expediting the learning process and we hope that this chapter will help accelerate your learning process by highlighting factors in a different way from other chapters in this textbook. The material in the chapter is based on training more than 1000 veterinarians in these techniques over the past 15 years as well as leading in clinical studies.

References