Measurement of Orbital Volume from Different Slice Thickness Facial Computed Tomography Scans Using a Semi-automatic Program

Purpose: To compare the orbital volume calculated from various slice thickness facial computed tomography scans using a semi-automated computer program.M ethods: Axial and coronal scans of 2, 2.5, 3 mm slice thickness facial computed tomography scans were used to measure the orbital volume.The cross-sectional area was determined from each slice using a semi-automated computer program (MATLAB 2009a ® , MathWorks, Inc., Natick, MA, USA), and then the volume was calculated from serial reconstruction of the cross sections.Results: The measured value in the 2 mm images was 33.14 ± 2.37 cm 3 in the right orbit and 34.32 ± 2.60 cm 3 in the left orbit for the axial scans, and 35.54 ± 3.58 cm 3 in the right orbit and 34.96 ± 4.05 cm 3 in the left orbit for the coronal scans.In the 2.5 mm images, the values were 33.28 ± 3.35 cm 3 in the right orbit and 33.73 ± 4.10 cm 3 in the left orbit for the axial scans, and 35.24 ± 3.98 cm 3 in the right orbit and 35.10 ± 3.93 cm 3 in the left orbit for the coronal scans.In the 3 mm images, the values were 33.23 ± 2.70 cm 3 in the right orbit and 33.39 ± 2.69 cm 3 in the left orbit for the axial scans, and 33.20 ± 3.64 cm 3 in the right orbit and 32.95 ± 3.45 cm 3 in the left orbit for the coronal scans.In the 3 mm image, there was not a significant difference in the calculated volume between the axial and coronal scans (p3mm = 0.62).Conclusions: Because there is no difference in the results of the orbital volumetric measurements between three other slice thicknesses in the axial scan, using axial scan images with a computer program that semi-automatically calculates orbital volume is useful.In addition, the volume measured by thick slice images has more reproducibility than the volume measured by thin slice images.