Atlas-Based Segmentation of Temporal Bone Anatomy

Abstract

Purpose: To develop a time-efficient automated segmentation approach that could identify critical structures in the temporal bone for visual enhancement and use in surgical simulation software.

Methods: An atlas-based segmentation approach was developed to segment the cochlea, ossicles, semicircular canals (SCCs), and facial nerve in normal temporal bone CT images. This approach was tested in images of 26 cadaver bones (13 left, 13 right). The results of the automated segmentation were compared to manual segmentation visually and using DICE metric, average Hausdorff distance, and volume similarity.

Results: The DICE metrics were greater than 0.8 for the cochlea, malleus, incus, and the SCCs combined. It was slightly lower for the facial nerve. The average Hausdorff distance was less than one voxel for all structures, and the volume similarity was 0.86 or greater for all structures except the stapes.

Conclusions: The atlas-based approach with rigid body registration of the otic capsule was successful in segmenting critical structures of temporal bone anatomy for use in surgical simulation software.

Keywords: Atlas-based segmentation; Image registration; Surgical simulation; Temporal bone anatomy.

Fig. 1

a Result of first rigid body registration using whole bone. The yellow circle indicates the otic capsule and the ROI used for the second rigid body registration, b Result of second rigid body registration using ROI indicated in a. Red indicates reference image and green indicates the moving image

Fig. 2

Average image of the six spatially aligned bones used to build the atlas for segmentation. This image illustrates how the structures are spatially conserved in and around the otic capsule which makes an atlas-based approach suitable for segmentation

Fig. 3

Segmentation flowchart (cochlea, malleus, incus, lateral SCC, posterior SCC, superior SCC, vestibule)

Fig. 4

2D example of a manual and b automated segmentation (red-cochlea, green-malleus, blue-incus, aqua-stapes, orange-vestibule, yellow-facial nerve)

Fig. 5

3D rendering of structures obtained from a manual and b automated segmentation

Fig. 6

Example of use of segmented facial nerve (red) in simulation of mastoidectomy. The yellow arrow points to the segmented facial nerve canal as seen through bone after it has been drilled out using the simulator