Michael Schmidt MSc, Abstract Co-Author: Nothing to Disclose

Eva Marjolein Van Rikxoort PhD, Presenter: Stock holder, Thirona BV Co-founder, Thirona BV

Jan-Martin Kuhnigk PhD, MS, Abstract Co-Author: Stockholder, MeVis Medical Solutions AG

Philip F. Judy PhD, Abstract Co-Author: Nothing to Disclose

Bram Van Ginneken PhD, Abstract Co-Author: Stockholder, Thirona BV Co-founder, Thirona BV Research Grant, MeVis Medical Solutions AG Research Grant, Canon Inc Research Grant, Toshiba Corporation Research Grant, Riverain Technologies, LLC

Accurate quantification of airway wall thickness in thoracic CT is a key technique for the extraction of imaging biomarkers in obstructive pulmonary disease. We present an intensity integration approach that allows measurements of airway wall thickness with an accuracy higher than the resolution of the CT data.

For most airways visible on CT, wall thickness is less than the resolution of the image data and partial volume effects hamper accurate measurement. By making appropriate assumptions about the density of air, airway wall and lung parenchyma, it is possible to fit a model to an array of line profiles perpendicular to the airway wall and thus measure the wall thickness precisely. This intensity integration approach was compared with two established methods: Full-Width-at-Half-Maximum (FWHM) and Phase Congruency (PC). We used the improved COPDGene phantom with 7 polycarbonate tubes with varying sizes (lumen diameter: 2.5/3/3/6/6/6/6 mm, wall thickness: 0.4/0.6/0.6/0.9/1.2/1.2/1.5 mm) and orientations (tubes 3 and 6 at 30° angle from scanner z-axis, all others in z-axis direction). The intensity integration and FWHM method were implemented by the authors, PC measurements were obtained using the open source software Airway Inspector. We measured each tube at five positions and calculated the average measurement. Accuracy of each method was determined by calculating the minimum, mean and maximum signed as well as mean unsigned measurement errors for each method. Additionally, linear regression was used to determine each method’s ability to detect changes in wall thickness regardless of constant measurement bias.

The smallest minimum/mean/maximum signed errors were obtained for intensity integration: -0.07/-0.01/0.05 mm versus 0.39/0.74/1.04 mm (FWHM) and -0.26/0.13/0.57 mm (PC). Intensity integration also gave the lowest mean absolute errors: 0.05 mm versus 0.74mm (FWHM) and 0.27mm (PC). Correlation was very high for intensity integration and FWHM (r=0.997 and r=0.972, both p<0.001) and only high for PC (r=0.746, p=0.054).

Intensity integration yielded the superior results in terms of overall error and measurement consistency. FWHM significantly overestimates thin walls but provides consistent measurements. PC is unreliable for measuring small airways.

Airway wall thickness measurements are best performed with an intensity integration quantification algorithm.

Schmidt, M, Van Rikxoort, E, Kuhnigk, J, Judy, P, Van Ginneken, B, Subvoxel Accurate Airway Wall Measurements Using an Intensity Integration Approach: Comparative Study Using the COPDGene Phantom.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14014670.html