B-lines on lung ultrasound. Phased array probe (1-5 MHz) with probe marker facing cephalad placed in an intercostal space. B lines (denoted by arrows), are well-defined comet-tail, vertical hyperechoic artifacts arising from the pleural line that obliterate normal A-lines, and descend to the bottom of the screen. Multiple B-lines in an interspace indicates an interstitial syndrome, where there are increased air-fluid interfaces creating this artifact.