The effect of computed tomographic scanner parameters and 3-dimensional volume rendering techniques on the accuracy of linear, angular, and volumetric measurements of the mandible

Abstract

Objectives: This study investigates the effect of scanning parameters on the accuracy of measurements from three-dimensional (3D), multi-detector computed tomography (MDCT) mandible renderings. A broader range of acceptable parameters can increase the availability of computed tomographic (CT) studies for retrospective analysis.

Study design: Three human mandibles and a phantom object were scanned using 18 combinations of slice thickness, field of view (FOV), and reconstruction algorithm and 3 different threshold-based segmentations. Measurements of 3D computed tomography (3DCT) models and specimens were compared.

Results: Linear and angular measurements were accurate, irrespective of scanner parameters or rendering technique. Volume measurements were accurate with a slice thickness of 1.25 mm, but not 2.5 mm. Surface area measurements were consistently inflated.

Conclusions: Linear, angular, and volumetric measurements of mandible 3D MDCT models can be confidently obtained from a range of parameters and rendering techniques. Slice thickness is the primary factor affecting volume measurements. These findings should also apply to 3D rendering using cone-beam CT (CBCT).

Figure 1

Specimens scanned: Glass prism, Mand1-Child, Mand2-Adult, and Mand3-Adult. Mand2 is labeled to reflect anatomic landmarks listed in Table 1: 1) Gonion, 2) Condyle Lateral, 3) Condyle Superior, 4) Coronoid Process, 5) Mental Foramen, 6) Dental Border Posterior-on Lingual aspect, and 7) Gnathion. The mental symphysis and ramus are also labeled.

Figure 2

Landmark and measurement definitions displayed on the 3D-CT gradient-shaded rendered model of Mand3 in three views (2A) inferior (2B) posterior, and 2(C) left lateral. Landmarks are depicted as bordered circles and measurements as black lines.

Figure 3

Linear distance measurements of Mand1-Child from 3D-CT segmented mandible models separated by rendering technique and compared to reference standard values (horizontal solid lines). The measurements include: MD – mental depth, LR – left ramus depth, LML – left mandible length, CW – coronoid width, GW – gonion width, and LCW – lateral condyle width. Box plots show the mean and lower/upper quartiles of data with whiskers representing 5^th and 95^th percentiles. To conserve space and for clarity of this figure, only left-sided measurements are presented, since left- and right-sided results were similar.

Figure 4

3D-CT rendered model volumes separated by specimen and scan slice thickness as compared to anatomic reference standard values (horizontal lines). Volumetric measurements using thin CT slices are closer to reference standards than thicker 2.5 mm slices. Box plots show the mean and lower/upper quartiles of data with whiskers representing 5^th and 95^th percentiles.