Chest ultrasound is particularly useful in trauma, complementing radiographic findings or guiding diagnosis within seconds at the patient's bedside. In lung ultrasound, findings result from multiple pleural line artifacts. Consequently, if a pulmonary abnormality does not reach the pleural line, it remains undetectable due to the acoustic impedance mismatch between air and soft tissue.

The pleural line generates the bat sign, a consistent landmark visible in all circumstances. This sign refers to the characteristic appearance of the pleural line (representing the parietal pleura) along with the adjacent ribs. A normal lung surface is characterized by lung sliding (a to-and-fro movement) and horizontal repetitions of the pleural line, known as A-lines (A-profile).

In contrast, a B-line is a vertical comet-tail artifact caused by vertical reverberation that moves in sync with lung sliding. B-lines occur when ultrasound beams interact with both air and water and are considered significant if three or more appear in a single image between two ribs, as seen in interlobular septal edema.