Feasibility studies of virtual laryngoscopy by CT and MRI - from data acquisition, image segmentation, to interactive visualization

Virtual endoscopy concept has been applied to study the larynx, as well as other hollow organs in recent years, assuming a clean lumen. In this work, we investigated the feasibility of virtual laryngoscopy by (1) studying cur rently available imaging protocols, (2) developing a suitable image segment ation method, and (3) constructing an efficient visualization system. By ut ilizing helical computed tomography (CT), the images for laryngeal volume c an be obtained during a breath hold with 0.3mm resolution. A fast pulse seq uence using 1.5T magnetic resonance (MR) imager can achieve 1mm resolution within few minutes. The gain in tissue contrast on MR images is at the cost of resolution, and motion artifacts must be considered during image segmen tation. A first-order Lagrange interpolation was applied to mitigate the re duced resolution, as well as partial volume effect and-noise on the MR imag es. An automatic segmentation algorithm was adapted to extract the wall vol ume of the larynx. The algorithm considers local voxel property and classif ies voxels based on the local property in the KL (Karhunen-Loeve) space. A visualization System was constructed for examining the mucosa and wall geom etry with anatomical references in three dimensions. It navigates inside th e lumen, as well as outside the larynx interactively with capability of ins pecting and zooming into the regions of interest. It can also cut the laryn x in any orientation to open the whole volume for viewing the entire inner surface. The procedure was tested on 2 volunteers and 2 patients. The segme ntation performed consistently for all the studies and showed to be relativ ely insensitive to mild respiratory motion artifacts in the MR images. Imag e processing was accomplished within a few minutes or. PC and low-end SGI p latforms. These studies demonstrated the feasibility of virtual laryngoscop y for diagnosis of laryngeal abnormalities.