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Table 2 Basic LUS artifacts: a comparative summary

From: Lung ultrasound—a primary survey of the acutely dyspneic patient

  A-lines Lung comets (l-lines) Z-lines B-lines
Artifact generation mechanism Repetition: Long-paths reflections between transducer and reflector. Reverberation: Short-paths reflections within tissue structures or materials. Ring-down: Bubble-tetrahedron mechanism.
Characteristics Short, repetitive equidistance horizontal lines. Fades with increasing depth. Weak vertical artifacts comprising of irregularly spaced horizontal lines. Artifacts are often of variable length and fades with increasing depth. This is the typical description of a comet-tail artifact. Strong narrow vertical artifact comprising of tightly spaced short horizontal lines. Artifact starts from point of origin to the end of the ultrasound screen. Does not fade with increasing depth. This is the typical description of a ring-down artifact.
Artifact generation mechanism in LUS Ultrasound encounters the pleural line (strong reflector). Created in the lung interstitial or in the? Interpleural layer. Originate from an extra-pulmonary location probably between the parietal pleural and the endothoracic fascia. Created by “thickened” lung interstitia and interlobular structures near lung surface parenchyma.
Additional characteristics in LUS Found within SLF. Weak vertical artifact readily found within SLF with high-frequency transducers. Similarity to B-lines: • l-lines arise from the pleural line. • Move with lung sliding/respiration. Unlike B-lines: • Short, often <2 cm. Found within SLF • Does not appear to be related to the pleural line. • Static: does not move with lung sliding or respiration. • Blend with other background artifacts. Found within SLF. B-lines arise from the pleural line. Move with lung sliding/respiration, like search lights. Dominant over other \background artifacts (e.g., A-lines, Z-lines).
Significance Signifies ultrasound interaction with a highly reflective surface. No diagnostic significance. Signifies that the pleural layers are in contact. Important in pneumothorax diagnosis. As they are commonly found in the normal lung. Cannot be used for diagnosis of lung interstitial diseases. No clinical significance. The uninitiated may mistake these for B-lines. When more than 3 per SLF, may signify an interstitial disease process. Important in LUS diagnosis.
Mimics in LUS Linear foreign body in subcutaneous area. • Pockets of air in the subcutaneous tissue may give rise to reverberation artifacts, crossing the pleura lines and into the SLF. These are also called E-Lines or “emphysema lines” [8]. • Foreign body in subcutaneous area. • Subcutaneous emphysema could generate this artifact, originating from the subcutaneous area, instead of the SLF. • Linear foreign body in subcutaneous area. Pockets of air in the subcutaneous tissue may give rise to ring-down artifacts, crossing the pleura lines and into the SLF. These are also called E-lines in Lichtenstein's publications [7, 8].
Other common names (better terms in italics) Reverberation artifact. Comet-tails, lung comets Comet-tails, lung comets Comet-tails, lung comets
  1. As could be seen from this matrix, many lung conditions share similar LUS signs. It is the knowledge of extent, combination, and distribution of the lung signs that will help achieve a more accurate diagnosis. Legends: bilateral—seen in both left and right lung; symmetrical—distribution pattern in left and right lungs are similar; patchy—uneven distribution within one lung where one part of the lung is involved while others spared; focal—localised to one area of the lung, one lobe or one lung; normal (for pleural line)—thin and smooth appearance; uneven—pleural line of varying thickness