Comparative computation of orbital volume from axial and coronal CT using three-dimensional image analysis.

Purpose: Volume measurements calculated from axial and coronal CT scans were compared to determine which method more accurately determines orbital volume.

Methods: Thirty facial CT scans were used to measure 30 normal orbits using an image analysis program (Dextroscope, Singapore). The 3-dimensional volumes determined from axial scans and coronal scans were analyzed. The coronal scan volume measurements were further subdivided based on anterior limit criteria (termed C1 and C2). Three novel cephalometric angular measurements of the anterior orbital aperture were calculated and used to analyze the volumetric methodologies described above.

Results: The calculated orbital volume was greatest on axial scan, 25.6 +/- 2.4 ml, followed by volume based on coronal calculations with C1 delimitation (23.8 +/- 2.9 ml) and C2 delimitation (16.6 +/- 2.2 ml). We measured 3 novel orbital aperture angles on sagittal 3-dimensional reconstruction images, anterovertical, posterovertical, and horizontal orbital aperture angles that are related to the volume measurement underestimation.

Conclusion: The orbital volume from coronal scans is underestimated compared with that from the axial scans, and the criterion for anterior limit of measurement can affect volume determination. Three novel cephalometric angle measurements may account for inaccuracies in orbital volume measurements.