Page 53 - Advanced concepts in orbital wall fractures

Data collection
Orbital Volume
Digital imaging and communications in medicine (DICOM) data of the
CT scans were imported in iPlan 3.0.5 software (Brainlab, Feldkirchen,
Germany). The software presents the data in multiplanar views and a three-dimensional (3D) reconstruction by volume rendering. To calculate
the orbital volume, the previously validated semi-automatic method
described by Jansen et al. was used20. The built-in auto-segmentation C tool offers the possibility of segmenting the left and right orbital volumes 3 (Fig. 1). From this auto-segmentation of the orbital volumes, bone and
air density masks were subtracted. Subsequently, the stereolithographic (STL) files of the volumes were imported in Maxilim 2.3.0 (Medicim NV, Mechelen, Belgium). The anterior orbital plane was used to remove excess anterior volume in all orbits. Landmark points were placed along the edge of the orbital rim every 0.5 to 1.0 cm. Then, the points were connected and the centre of gravity of these landmarks was calculated. The surface that was created in this way was used as the anterior plane (Fig. 2). The anterior plane was validated in a previous study20. The final orbital volume was measured in Maxilim.
Orbital Contour
In addition to differences in orbital volumes, the orbit contours were compared. For every patient, the DICOM files and STL model of the left orbital volume were mirrored. The original and mirrored CT scans and the STL files of the right and mirrored left orbital volumes were imported in Maxilim 2.3.0. The reconstructed mirrored skull was matched to the original skull with the use of voxel-based matching of the cranial base. This matching method, which superimposes the two DICOM sets based on the Hounsfield units of the voxels, has proved to be accurate and valid in several studies21,22. In addition, the mirrored left orbital volume was projected over the right orbital volume to create a distance map (Fig. 3). The distance maps were created for the orbital floor and medial wall and illustrate the 3D contour difference between the left and right orbital cavities23.
Virtual mirroring
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