The native frequency of B-lines artifacts may provide a quantitative measure of the state of the lung

B-lines are ultrasound-imaging artifacts, which correlate with several lung-pathologies. However, their understanding and characterization is still largely incomplete. To further study B-lines, ten lung-phantoms were designed. A layer of microbubbles was trapped in tissue-mimicking gel. To simulate the alveolar size reduction typical of various pathologies, 166 and 80-micrometer bubbles were used for phantom-type 1 and phantom-type 2, respectively. A normal alveolar diameter is around 280 micrometer. A LA332 linear-array connected to the ULA-OP platform was used for imaging. Standard ultrasound imaging at 4.5 MHz was performed. Next, a multi-frequency approach was used: images were sequentially generated using orthogonal sub-bands centered at different frequencies (3, 4, 5, and 6MHz). Results show that B-lines appear predominantly with the phantom-type 2, suggesting a link between increased artifact formation and the reduction of the alveolar size. Moreover, the multifrequency approach revealed that the B-lines have a native frequency: B-lines appeared with significantly stronger amplitude in one of the 4 images, and spectral-analysis confirmed B-lines to be centered at specific frequencies. These results can find relevant clinical application since, if confirmed by in-vivo studies, the native frequency of B-lines could serve as a quantitative-measure of the state of the lung.