The fractal complexity of the segmented airway tree was measured by the Airway Fractal Dimension (AFD) using the Minkowski-Bougliand box-counting dimension. 
Minkowski-Bougliand box-counting dimension
This study was supported by NIH K23 HL133438 (SPB) and the COPDGene study (NIH Grant Numbers R01 HL089897 and R01 HL089856). 
COPDGene study
ClinicalTrials.gov identifier: NCT00608764.



ClinicalTrials.gov identifier
This study was supported by NIH K23 HL133438 (SPB) and the COPDGene study (NIH Grant Numbers R01 HL089897 and R01 HL089856). 
NIH Grant Numbers R01 HL089897 and R01 HL089856