Evaluation of the potential of automatic segmentation of the mandibular canal using cone-beam computed tomography.

We aimed to investigate the effectiveness of software for automatically tracing the mandibular canal on data from cone-beam computed tomography (CT). After the data had been collected from one dentate and one edentate fresh cadaver head, both a trained Active Shape Model (ASM) and an Active Appearance Model (AAM) were used to automatically segment the canals from the mandibular to the mental foramen. Semiautomatic segmentation was also evaluated by providing the models with manual annotations of the foramina. To find out if the tracings were in accordance with the actual anatomy, we compared the position of the automatic mandibular canal segmentations, as displayed on cross-sectional cone-beam CT views, with histological sections of exactly the same region. The significance of differences between results were analysed with the help of Fisher's exact test and Pearson's correlation coefficient. When tracings based on AAM and ASM were used, differences between cone-beam CT and histological measurements varied up to 3.45mm and 4.44mm, respectively. Manual marking of the mandibular and mental foramina did not improve the results, and there were no significant differences (p=0.097) among the methods. The accuracy of automatic segmentation of the mandibular canal by the AAM and ASM methods is inadequate for use in clinical practice.

Accuracy of assessing the mandibular canal on cone-beam computed tomography: a validation study.

PURPOSE: To establish the accuracy of cone-beam computed tomographic (CBCT) views in determining the position and diameter of the mandibular canal. MATERIALS AND METHODS: Two freshly frozen cadaver heads, 1 dentate and 1 edentate, were used to acquire CBCT scans. Measurements on cross-sectional CBCT images were compared with measurements on digitized histologic sections of the same regions in the mandibles. The Student t test was used for statistical analysis. RESULTS: Comparing CBCT with histologic measurements showed that the position of the mandibular canal differed up to 0.47 mm (standard deviation, 0.29 mm). Mandibular canal diameters were up to 22.8% smaller in the CBCT planes. For the dentate jaw, these differences were statistically significant. CONCLUSION: To be safe, when assessing the mandibular canal position on CBCT views, a 0.76-mm deviation should be taken into account. Because the diameter of the mandibular canal is displayed smaller, an enlargement by 0.74 mm is recommended.

Accuracy of bone surface size and cortical layer thickness measurements using cone beam computerized tomography.

OBJECTIVES: The purpose of this study was to determine the accuracy of Cone Beam Computerized Tomography (CBCT) reconstructions in displaying bone surface size and cortical layer thickness. MATERIALS AND METHODS: Two fresh frozen cadaver heads were scanned using a CBCT (i-CAT(™) 3D Imaging System; Imaging Sciences International Inc.). The mandibles were sectioned and digitalized for histological evaluation. Dimensions as measured on these sections were compared with CBCT measurements of the same region with the use of 3D image-based planning software (Procera System NobelGuide(™); Nobel Biocare). To allow optimal comparison between histological and CBCT sections, reference markers were placed into the mandibles. The Student t-test was utilized to analyze the data. Differences with P-values <0.05 were considered significant. RESULTS: The total height and width of the mandibular body, as measured on CBCT views, were larger compared with the histological values with a maximum difference of 0.33 mm (SD ± 0.34). Cortical thickness measurements were significantly thicker on CBCT sections (P < 0.006) with absolute differences ranging up to ±0.63 mm (SD ±0.28) and relative differences ranging up to 82.6%. CONCLUSION: CBCT images (i-CAT 3D Imaging System), viewed on the planning software Procera System NobelGuide, tend to overestimate the anatomical truth in assessing both bone height and width; especially cortical thicknesses are depicted thicker than in reality. When using CBCT images for presurgical assessment, one should be aware of this phenomenon of exaggeration of dimensions.