In this study the changes in upper airway geometry and resistance between images, obtained in upright and supine position, will be evaluated. Therefore a Cone Beam Computed Tomography (CBCT) scan and a low dose Computed Tomography (CT) scan will be taken in a population of 20 subjects. The upright morphology will be obtained using CBCT scan while the supine upper airway geometry will be determined using a standard High Resolution Computed Tomography (HRCT) scanner.