3.6. Pseudo B‐lines. The B‐line artifact begins at the lung's pleural surface and continues without loss of intensity through the far‐field of the image as a hyperechoic (bright white) streak that obliterates A‐lines. In real time, B‐lines must oscillate with the to‐and‐fro motion of inspiration and expiration. Examples and descriptions are found in Chapters 22 and 23. Here, however, are pseudo B‐lines. In (A), what appears to be a single B‐line is in fact tightly stacked A‐lines off the far side of a very small lung nodule. In (B) are multiple pseudo B‐lines off the gastric wall. In (C) the nodule is indicated with a solid black circle overlay, and the arrows are over the pseudo B‐line. In (D), the pseudo B‐lines are indicated by the arrows (←).
Source: Courtesy of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Artifacts of Multiple Echoes
Side‐Lobe Artifact: Multiple Echoes
We like to think of the ultrasound beam as extending from the probe in a very thin fan or rectangle, and this is exactly what the processor thinks it sees. In reality, there are smaller beams that travel laterally to the main beam. When one of these smaller side beams is of sufficient strength and bounces off a highly reflective surface, such as the wall of the urinary bladder, it will be interpreted as coming from the main beam and the processor will place the resulting image within the main beam image, often mimicking sediment. The resulting image is usually weaker in intensity than the main image. Often, the artifact can be altered by changing probes or lowering the focal point, or lowering the gain setting – all ultrasonographic manipulations that will not remove true pathology (i.e., bladder sediment, bladder stones, etc.) (Penninck 2002) (Figure 3.7).
Figure 3.7. Sediment versus side‐lobe and slice‐thickness artifact. (A) Sediment will be affected by gravity and lead to a flat surface, as seen with the sludge within this gallbladder's lumen. True sediment can be stirred up by repositioning the patient or through ballottement with the ultrasound probe, whereas artifacts mimicking sediment cannot. (B) Slice‐thickness and side‐lobe artifacts mimic sediment in the gallbladder shown here; however, the artifact will not be altered by moving the patient's position or by ballottement. (C) True sediment in a urinary bladder with ballottement gives a snow globe appearance. (D) In contrast, the slice‐thickness and side‐lobe artifacts mimicking sediment shown here will fail to ballot (will not "snow globe") or change position to the gravity‐dependent side of the urinary bladder when the patient is moved. Other helpful tricks that discriminate true sediment from artifact include lowering the gain and/or moving the focus cursor. Generally speaking, artifacts can be eliminated by these maneuvers, but true sediment cannot.
Source: Courtesy of Robert M. Fulton, DVM, Richmond, VA.
Slice‐Thickness Artifact: Multiple Echoes
Slice‐thickness artifact is somewhat like the side‐lobe artifact. In the gallbladder and urinary bladder in particular, this artifact mimics sludge or sediment. It occurs when part of the beam's thickness lies just outside a fluid‐filled structure. These artifacts typically appear within the lumen of these structures and are somewhat hyperechoic (bright) and curved. They can be differentiated from real sediment by several methods or clues. First, gravity‐dependent sediments have a flat surface whereas the artifact will be rounded. Second, by changing the position of the patient, the relative position of true sediment will change as gravity pulls it to the new lower point. Third, the sonographer can use the ultrasound probe to ballot the bladder and stir the sediment up a bit; the artifact will not yield a “snow globe” effect (sediment will) (Penninck 2002) (see Figure 3.7).
Pearls and Pitfalls, The Final Say
By gaining a basic understanding of ultrasound physics and the common ultrasound artifacts, the nonradiologist veterinarian or veterinary sonographer can more clearly interpret the ultrasound image (Table 3.1). Always keep in mind the basic assumptions used to generate the image when scanning or viewing the ultrasound image. Your interpretive and diagnostic skills, and hence your patient, will benefit greatly.
Knowing the basic assumptions used to generate the image leads to less misinterpretation of the ultrasound image.
Artifacts are one of the primary pitfalls of ultrasonographic imaging.
Table 3.1. Summary of common artifacts and examples.
| Name of artifact | Fluid‐associated | Air‐associated | Other | Common examples |
|---|---|---|---|---|
| Shadowing, clean | No | No | Bone/stone | Cystouroliths, ribs |
| Shadowing, dirty | No | Yes | Irregular/partial penetration into gas | Lung, stomach, colon, small intestine |
| Edge shadowing | No | No | Refraction off round structures | Stomach wall, gallbladder wall, urinary bladder wall |
| Acoustic enhancement | Yes | No | Decreased attenuation | Gallbladder, cysts, eye |
| Mirror image | No | Frequently | Reflection | Diaphragm/liverUrinary bladder/colon |
| Reverberation A‐lines | No | Yes | Typically used only in reference to lung ultrasound | Lung surface |
| Comet‐tail, ring‐down | No | No | Bone/stone/metal | Calculi, surgical clips, tissue mineralization |
| B‐lines, also called ultrasound lung rockets (ULRs) | Yes | Yes | Air–fluid interfaces | Lung |
| Pseudo B‐lines | Yes | Yes | Air–fluid interfaces (gastric luminal contents); strong soft tissue–air interfaces, i.e., lung nodules |
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