B-line(s) is a lung artefact generated by an increased density of the underlying lung tissue. An example is when subpleural interlobular septae become edematous in cardiogenic pulmonary edema.
A B-line is a hyperechoic, laser-like, vertical, reverberation artefact originating from the pleural line.
B-lines are continuous from the pleural line to the bottom edge of the screen and do not fade in intensity.
Few narrow B-lines can be seen in healthy persons, while multiple and wide B-lines suggest pathology.
B-lines are used in emergency lung ultrasound to confirm or exclude the presence of pneumothorax and/or interstitial syndrome (i.e. pulmonary edema).