UCLA

Objectives: Current analyses of 3D cone beam computed tomography (CBCT) images used in orthodontic diagnosis and treatment planning still rely upon 2D linear and angular measures, along with subjective visual evaluation, to assess complex facial disharmony and other dentofacial characteristics. The overall objective of this investigation is to overcome these limitations by developing and testing protocol for mapping the surface of the human skull in three dimensions using CBCT images. In collaboration with the Laboratory of Neuroimaging (LONI) at UCLA, the specific goals of this project are:

-To apply and modify advanced technology used in brain mapping research to accurately and efficiently map the skull surface in 3D

-To apply and modify existing mathematical functions to find the average of multiple skull surfaces

-And to develop protocol for superimposing a sample skull on the average skull model, yielding a color-coded map of surface deviation and dysmorphology

Methods: Active patient files in the UCLA Section of Orthodontics were reviewed for the presence of a NewTom ® 3G CBCT scan. The search resulted in 67 patient scans that met the inclusion criteria for the study. CBCT files in DICOM format were first uploaded into a Beta version of Dolphin Imaging ® 11.5 Software. The surface was then segmented using a triangular mesh approach, after which the file was exported to MeshLab ® for viewing and to remove undesired nodes. Topology of each skull was corrected using a principal axis star map and smoothing of the extrapolated regions. Shapes were mapped to a sphere using conformal and area preserving maps, and were then registered using a spherical patch mapping approach. Finally an average was created using 7-parameter procrustes alignment.

Results: Size-standardized and non-size standardized average skull models were successfully created for the 67 patient sample. Color-coded displacement maps were generated for a sample patient to demonstrate the potential clinical applicability of this protocol.

Conclusions: The results of this investigation suggest that it is possible to average multiple shapes of highly variable topology such as the human skull. The most immediate application of this research will be rapid and detailed diagnostic imaging analysis for orthodontic and surgical treatment planning, particularly in complex cases involving congenital facial anomalies, facial asymmetry, and trauma. There is also great potential for application to areas outside orthodontics such as anthropometrics and genomics.