A new technique for airway measurement that simultaneously estimates airway tilt angle, caliber, and wall thickness is presented. An idealized (circular cross-section) airway model is parameterized by airway caliber, wall thickness, and tilt angle. Using a 2D CT slice and the full-width-half-max principle we form an estimate of the inner and outer airway wall locations. We then fit ellipses to the inner and outer airway walls using a direct least squares fit and use the major and minor axes of the ellipses to estimate the tilt angle. The airway model is then initialized with tilt angle and size estimates and convolved with the 3D scanner PSF to generate a predicted image. We compare predicted versus actual images to determine the goodness-of-fit. The initial airway parameters are refined using a multi-dimensional, unconstrained, non-linear minimization routine (Nelder-Mead). When optimization converges, airway model parameters estimate the airway inner and outer radii, and tilt angle. Results using a plexiglass phantom show that tilt angle could be estimated to within plus or minus 5 degrees, the inner radius to within about one half of a pixel, and the outer radius to within one pixel.
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