TY - JOUR T1 - Count of B-lines: A Matter with Persistent Limitations JF - The Journal of Rheumatology JO - J Rheumatol SP - 158 LP - 159 DO - 10.3899/jrheum.190823 VL - 47 IS - 1 AU - CARLA MARIA IRENE QUARATO AU - VALERIA VERROTTI DI PIANELLA AU - MARCO SPERANDEO Y1 - 2020/01/01 UR - http://www.jrheum.org/content/47/1/158.1.abstract N2 - To the Editor:After reading the interesting review by Gutierrez, et al1, entitled “Ultrasound in the assessment of interstitial lung disease in systemic sclerosis. A systematic literature review by the OMERACT Ultrasound Group,” we must take issue with some of the statements published.The authors state that “B-lines consist of ‘comet tails’… generated by the reflection of the [lung] US beam from thickened subpleural interlobar septa.” Actually, the generation of ultrasound (US) artifacts mainly depends on the high difference in acoustic impedance that the US beam encounters when it crosses surfaces with a different density. US scanner machines are calibrated at a constant sound speed of about 1500 m/s, but propagation velocity in air is only 330 m/s (in the lung, slightly increased to 440 m/s owing to presence of parenchyma): for this reason more than 96% of the US beam is reflected at tissue–chest wall/air-lung interface, resulting … Address correspondence to Dr. C.M. Quarato, Ospedali Riuniti di Foggia, Department of Respiratory Disease, Viale degli Aviatori 1, Foggia 71100, Italy. E-mail: c.quarato{at}libero.i ER -