[en] To evaluate the scanning parameters affecting the apparent sizes of endoluminal lesions of the tracheobronchial tree, as seen on virtual bronchoscopy (VB), and to determine the optimal CT parameters for demonstration the real sizes of endobronchial lesions. Spherical beads of 8mm- 10mm diameter were randomly placed in the airways of fixed pig lung. CT scans were obtained with collimation and pitch of 3mm/1, 3mm/1.5, and 5mm/1, respectively. Volumetric data were reconstructed with 1mm-, 1.5mm-, and 2mm-collimation for each parameter. VBs were reconstructed with shaded-surface technique and soft tissue algorithm. A 10mm-sized bead in the trachea and two 8mm-sized beads in the left main bronchus were selected and their longest diameters were measured on VB at varying thresholds from -800 to -200HU. When the measured diameters of beads on VB were recorded as the percentage of real sizes, they were 1) 78.9%, 77.5%, and 73.7% at collimations and pitches of 3mm/1, 3mm/1.5, and 5mm/1, respectively; 2) 77.9%, 76.9%, and 75.1% at 1mm, 1.5mm and 2mm reconstructions, respectively; 3) 86.2% / 83.4% / 80.4% / 77.0% / 74.8% / 70.2% / 64.5% at isosurface thresholds of -800/-700/-600/-500/-400/-300/-200HU, respectively; 4) 85.6%, 75.0%, 69.3% at 23mm, 17mm and 11mm luminal diameters of lesion location, respectively. Overall, the diameters of endobronchial lesions are underestimated on VB. As the isosurface threshold values, collimations, pitches and reconstruction interuals decrease in size, the measured diameters approach to real diameter of the beads. Beads in peripheral airways appear smaller than those in proximal airways