Automated Analysis of Crackles in Patients with Interstitial Pulmonary Fibrosis

Table 2

Aggregate crackle features	Definition
Number of crackles per breath (Cr/breath)	The total number of crackles per breath as detected by the computer
Number of crackles per breath per quadrant (top left, top right, bottom left, bottom right)	These 4 features count the total number of crackles observed in each quadrant of the chest. Together they add up to the total number of crackles per breath
Percentage differences between crackle quadrants (6 total)	Calculated from the 4 features described above, these features represent a comparison between quadrants. Each percentage is a pairwise comparison of all 6 possible combinations of quadrants
Maximum distances (𝑥,𝑦,𝑧)	Distances between crackles in 3-dimensional space. There are separate features for 𝑥, 𝑦, and 𝑧 planes. One feature also records a maximum distance across all 3 dimensions
Channel distances	These features are similar to those described above, except that they are defined based upon which channel microphone picked up the crackle. Distances are defined accordingly