Three-Dimensional Reconstruction of the Bony Nasolacrimal Canal by Automated Segmentation of Computed Tomography Images

<div><p>Objective</p><p>To apply a fully automated method to quantify the 3D structure of the bony nasolacrimal canal (NLC) from CT scans whereby the size and main morphometric characteristics of the canal can be determined.</p><p>Design</p><p>Cross-sectional study.</p><p>Subjects</p><p>36 eyes of 18 healthy individuals.</p><p>Methods</p><p>Using software designed to detect the boundaries of the NLC on CT images, 36 NLC reconstructions were prepared. These reconstructions were then used to calculate NLC volume. The NLC axis in each case was determined according to a polygonal model and to 2^nd, 3^rd and 4^th degree polynomials. From these models, NLC sectional areas and length were determined. For each variable, descriptive statistics and normality tests (Kolmogorov-Smirnov and Shapiro-Wilk) were established.</p><p>Main Outcome Measures</p><p>Time for segmentation, NLC volume, axis, sectional areas and length.</p><p>Results</p><p>Mean processing time was around 30 seconds for segmenting each canal. All the variables generated were normally distributed. Measurements obtained using the four models polygonal, 2^nd, 3^rd and 4^th degree polynomial, respectively, were: mean canal length 14.74, 14.3, 14.80, and 15.03 mm; mean sectional area 15.15, 11.77, 11.43, and 11.56 mm²; minimum sectional area 8.69, 7.62, 7.40, and 7.19 mm²; and mean depth of minimum sectional area (craniocaudal) 7.85, 7.71, 8.19, and 8.08 mm.</p><p>Conclusion</p><p>The method proposed automatically reconstructs the NLC on CT scans. Using these reconstructions, morphometric measurements can be calculated from NLC axis estimates based on polygonal and 2^nd, 3^rd and 4^th polynomial models.</p></div

Descriptive data for the NLC sectional area measurements.

<p>Descriptive data for the NLC sectional area measurements.</p

Segmentation results for slice 57 of subject #27 showing above the masks obtained by automatic segmentation for left and right NLC and below the contours of the segmented left and right NLC superimposed to CT slice.

<p>Segmentation results for slice 57 of subject #27 showing above the masks obtained by automatic segmentation for left and right NLC and below the contours of the segmented left and right NLC superimposed to CT slice.</p

Polynomial models for the right NLCs of six subjects selected at random.

<p>Polynomial models for the right NLCs of six subjects selected at random.</p

Wall thickness inhomogeneity in the nasolacrimal canals.

<p>Wall thickness inhomogeneity in the nasolacrimal canals.</p

Surface and axis models of NLCs: oblique and overhead views (subject #17).

<p>Surface and axis models of NLCs: oblique and overhead views (subject #17).</p

Descriptive data for depth of minimum NLC sectional area.

<p>Descriptive data for depth of minimum NLC sectional area.</p

Descriptive data for NLC length measurements.

<p>Descriptive data for NLC length measurements.</p

Descriptive data for minimum NLC sectional area.

<p>Descriptive data for minimum NLC sectional area.</p

Depiction of the four methods to compute NLC length: axial, end-to-end, polygonal, polynomial.

<p>Depiction of the four methods to compute NLC length: axial, end-to-end, polygonal, polynomial.</p