Head positioning in a cone beam computed tomography unit and the effect on accuracy of the three‐dimensional surface mode

Abstract

Head position during cone beam computed tomography (CBCT) examination can easily deviate from the ideal, which may affect the accuracy of the segmented three‐dimensional (3D) model. The aim of this study was to determine the effect of head positioning on the accuracy of the 3D model. A human dry skull was positioned at predetermined orientations in a CBCT scanner and scanned in multiple orientations and voxel sizes. The resulting 3D surface models were superimposed over those derived from the reproducible centered positioned skull with 0° inclination. Color mapping and analysis of the differences expressed by the root mean square error (RMSE) were performed. The RMSE for each orientation using the 0.3 mm voxel ranged from 0.31 to 0.87 mm for the whole maxillofacial region, from 0.44 to 0.91 mm in the maxilla, and from 0.31 to 0.72 mm in the mandible. For the 0.4 mm voxel, the RMSE ranged from 0.47 to 0.86 mm for the whole maxillofacial region, from 0.60 to 0.96 mm in the maxilla, and from 0.56 to 0.86 mm in the mandible. The maxilla showed a slightly higher deviation than the mandible in both voxel groups. It can be concluded that the head position affects the accuracy of the segmented 3D model, but the inaccuracy does not exceed clinically relevant levels.

Acta Plane—A New Reference for Virtual Orientation of Cone Beam Computed Tomography Scans: A Pilot Study

“…In a similar study with a dry skull and variation of the position of the head, Sabban et al suggested that the head position might significantly influence linear measurements in CBCT scans, especially vertical and horizontal measurements as a result of extension and flexion head movements [22]. Another study in dry skulls showed that different head positions and orientations affected 3D model segmentation, but these differences were not clinically relevant [23]. In studies with dry skulls, the images are, however, not similar to clinical images as soft tissue is absent; it might be that clinical images would have more significant differences.…”

“…Different orientations of CBCT images might influence the operator's ability to identify landmarks and perform measurements, affecting the vertical measurements [22]. The orientation of the scan also affects 3D model segmentation [23]. Therefore, it is essential to virtually orient the CBCT images in order to improve the reliability in landmark detection, measurements, and segmentation.…”

Reorientation methodology for reproducible head posture in serial cone beam computed tomography images

“…However, the study designs are either arbitrary with fiducial markers or based on dry skull models 5,15,16 . Although lately different methods for head orientation in 3D space have been proposed, they have either been focused on 3D facial scans or based on high-resolution medical CT images 4,[17][18][19][20] .…”

A Posterior-Anterior Cephalometric Study of Skull Symmetry in Patients With Neurofibromatosis Type 1

“…The use of scanned X-rays from exposed film and their digital processing does not cause any changes in the skeletal reference points on cephalograms that limit their diagnostic evaluation (54). However, any scientific analysis of X-rays requires information on the measurement accuracy of the study (55)(56)(57)(58). Identifying landmarks is a critical step in cephalometric analysis and is prone to error.…”

“…However, the problem of measurement accuracy and error analysis must be considered in every study, regardless of the radiological imaging technology (64). For example, positioning errors may occur both with X-ray techniques that are based on threedimensional recording of the object (55,56,58); this is wellknown in standard cephalometry (64). Nevertheless, twodimensional cephalometry is still a standard tool in orthodontic and maxillofacial surgery treatment planning, for which the skull assessment in the lateral cephalogram is essential (63).…”