B lines

B lines indicate the presence of an interstitial process. B lines (arrows) develop at the visceral pleural surface, so their presence indicates that the lung is fully inflated at the site of probe placement on the chest wall, so there is no pneumothorax at that examination site. Likewise, the identification of consolidated lung rules out pneumothorax at the site of probe placement on the chest wall, as air within a pneumothorax space blocks all transmission of ultrasound.