Optimizing Lung Ultrasound: The Effect of Depth, Gain and Focal Position on Sonographic B-Lines.

Ultrasonographic B-lines are artifacts present in alveolar-interstitial syndromes. We prospectively investigated optimal depth, gain, focal position and transducer type for B-line visualization and image quality. B-Lines were assessed at a single rib interspace with curvilinear and linear transducers. Video clips were acquired by changing parameters: depth (6, 12, 18 and 24 cm for curvilinear transducer, 4 and 8 cm for linear transducer), gain (10%, 50% and 90%) and focal position (at the pleural line or half the scanning depth). Clips were scored for B-lines and image quality. Five hundred sixteen clips were obtained and analyzed. The curvilinear transducer improved B-line visualization (63% vs. 37%, p < 0.0001), with higher image quality (3.52 ± 0.71 vs. 3.31 ± 0.86, p = 0.0047) compared with the linear transducer. B-Lines were better visualized at higher gains (curvilinear: gain of 50% vs. 10%, odds ratio = 7.04, 95% confidence interval: 4.03-12.3; gain of 90% vs. 10%, odds ratio = 9.48, 95% confidence interval: 5.28-17.0) and with the focal point at the pleural line (odds ratio = 1.64, 95% confidence interval: 1.02-2.63). Image quality was highest at 50% gain (p = 0.02) but decreased at 90% gain (p < 0.0001) and with the focal point at the pleural line (p < 0.0001). Image quality was highest at depths of 12-18 cm. B-Lines are best visualized using a curvilinear transducer with at least 50% gain and focal position at the pleural line. Gain less than 90% and image depth between 12 and 18 cm improve image quality.