Table 1.
Lines that can be seen in lung ultrasound (LUS)
| Line | Characteristics |
|---|---|
| Pleural line | Strongly hyperechoic line made of parietal and visceral pleura, may not be distinguished from parietal pericardium at its level |
| Lung line | Line representing visceral pleura in case of pleural fluid |
| Shred/fractal line | Shredded line on border of consolidation and normal lung |
| A-lines (Figure 1A) | • Long horizontal lines • Usually strongly hyperechoic, fading vertically • Reverberations at regular intervals (approximately skin-pleural line distance) • First is A1, second A2, and so forth • If lines in similar length are visible between, they are named A’, A’’, etc. • Indicate presence of air |
| B-lines | Defined by 7 criteria (most B-lines meet all of them): • Ring down artifacts • Arise from pleural line • Usually strongly hyperechoic • Laser-like, well defined, narrow • Do not fade (usually reach end of the screen) • Erase A-lines • Move with lung sliding |
| Sub-B-lines | As B lines, but arise from lung line or from shred line |
| C-lines | Small consolidations |
| E-lines (Figure 6D) | • Mainly ring down artifacts, reverberations, refractions, and posterior acoustic shadowing • Arise from horizontal stripes of subcutaneous gas |
| F-lines (Figure 2A) | • Small • Punctiform/round/discoid/oblique • Weakly hyperechoic • Should not be confused with air bronchograms • Do not move with lung sliding |
| G-lines (Figures 6A, B) | • They resemble A-, B-, and Z-lines (G-A, G-B, G-Z-lines) • Arise from abdominal structures |
| H-lines (Figure 6C) |
• Horizontal lines • Mostly strongly hyperechoic reverberations • Arise from bare probe • Show directly adjacent air |
| I-lines (Figures 4A, B) | • Short (max. 2-3 cm) reverberations • Hyperechoic (less than pleural line), fading • Move with lung sliding • More often seen with high frequency probes |
| J-lines | • Small horizontal lines • Usually strongly hyperechoic • Components of a vertical B-line (sum to make one) |
| K-lines | • Electric interference artifacts • Arise anywhere on the screen |
| M-lines (Figure 4C) | • Horizontal artifacts • Interspersing weakly and strongly hyperechoic, fading vertically • Sometimes arising in rib’s acoustic shadow • Seem to be reverberations |
| N-lines | • As B-lines, but hypoechoic • Probably refraction artifacts |
| O-lines | • No lines (no artifacts visible, “black ultrasound lung”) • May be encountered both physiologically and in pneumothorax |
| P-/Pi-/π-lines (Figures 1C, D) | • In same place as A, A’ lines, but shorter • Usually strongly hyperechoic, fading vertically • Reverberations at regular intervals • Nearly forming a vertical artifact • If seen, usually in thin people |
| R-lines | As B-lines, but arise from pericardium (at lung interface) |
| S-lines | • Said to be generated by pacemakers • Characteristic propagation (sinuous) |
| T-lines (Figures 5A, B) | • Vertical artifacts on M-mode • Frequency of heart rate • M-mode equivalent of lung pulse |
| U-lines (Figures 6A, B) | • Shape of inverted U • Strongly hyperechoic • Arise from and represent gas within colonic haustra |
| W-lines (Figure 6D) |
Like E-lines, but multiple and chaotic (not aligned) |
| X-lines | Occurrence of “B-line” and A-line on same image (“B-lines” which do not erase A-lines) |
| Z-lines (Figure 2D) | • Vertical lines • Usually weakly hyperechoic • III-defined reverberations • Fade • Do not erase A-lines • Do not move with lung sliding |