Page 35 - Advanced concepts in orbital wall fractures

(Semi-)automatic segmentation methods
Three different segmentation methods were used to measure orbital volume using iPlan 3.0.5 after importing the DICOM files (Fig. 3):
1. Method A (automatic): automatic segmentation of the orbital C2 cavity by means of the built-in functionality in the software.
The automatic segmentation is established by atlas-based
segmentation. This method uses prior information of training
images to recognise the shape and grey levels of determined parts of the body to perform auto-segmentation25,26.
2. Method SA (semi-automatic): the automatic segmentation with subtraction of bone and air density masks. A bone mask (+400 HU or more) and air mask (−600 HU or less) were created and subtracted from the segmentation that was obtained by the automatic method.
3. Method SAA (semi-automatic with manual adjustments): the automatic method with subtraction of bone and air mask, followed by manual adjustment of large errors using the smart shaper tool and eraser (both built-in functionalities in the software). First, the position of the scan was altered so that the skull was in a true horizontal position. The window was set between −200 and +200 HU. The axial slices were quickly scanned for significant irregularities and mistakes in added voxels outside the bony orbit. Then the sagittal plane was used to delineate the inferior orbital fissure by following the inferior rectus muscle and to define the apical limit. Finally, the axial slices were scanned to make final adjustments.
Final volume calculations were performed in Maxilim. In Maxilim, the anterior planes previously used for the manual reconstructions (gold standard) were used to remove content outside the bony orbit of the (semi-)automatic methods in order to measure the volume and compare it to the gold standard.
Volume segmentation method
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