Theoretical investigation for functional Small Airway Disease in inspiratory and expiratory CT data

Abstract

An image processing method for detecting gas-trapping by small airway obstruction (termed functional small airway disease; fSAD) has been proposed by non-rigid image registration technique between inspiratory and expiratory 3D-CT data set(Nat. Med, 2012). The fSAD is defined as a voxel with HU values of -950 or more on inspiratory CT and less than -856 on expiratory CT. Although this definition presumes that expiratory voxels are accurately registered to corresponding inspiratory voxels, there have been no statements regarding registration accuracy in any published papers. We generated virtual inspiratory and expiratory 3D-CT data sets in computer, where emphysema voxels were randomly distributed in the lung parenchyma with fractal size distribution, and found that even a tiny mis-registration generated plenty of false fSAD voxels. We concluded that the proposed method for fSAD was not valid.