Imaging Sci Dent.  2018 Jun;48(2):111-119. 10.5624/isd.2018.48.2.111.

Linear accuracy of cone-beam computed tomography and a 3-dimensional facial scanning system: An anthropomorphic phantom study

• Oh SH
• Kang JH
• Seo YK
• Lee SR
• Choi HY
• Choi YS
• Hwang EH

• KMID: 2413922
• DOI: http://doi.org/10.5624/isd.2018.48.2.111

Abstract

PURPOSE
This study was conducted to evaluate the accuracy of linear measurements of 3-dimensional (3D) images generated by cone-beam computed tomography (CBCT) and facial scanning systems, and to assess the effect of scanning parameters, such as CBCT exposure settings, on image quality.
MATERIALS AND METHODS
CBCT and facial scanning images of an anthropomorphic phantom showing 13 soft-tissue anatomical landmarks were used in the study. The distances between the anatomical landmarks on the phantom were measured to obtain a reference for evaluating the accuracy of the 3D facial soft-tissue images. The distances between the 3D image landmarks were measured using a 3D distance measurement tool. The effect of scanning parameters on CBCT image quality was evaluated by visually comparing images acquired under different exposure conditions, but at a constant threshold.
RESULTS
Comparison of the repeated direct phantom and image-based measurements revealed good reproducibility. There were no significant differences between the direct phantom and image-based measurements of the CBCT surface volume-rendered images. Five of the 15 measurements of the 3D facial scans were found to be significantly different from their corresponding direct phantom measurements (P < .05). The quality of the CBCT surface volume-rendered images acquired at a constant threshold varied across different exposure conditions.
CONCLUSION
These results proved that existing 3D imaging techniques were satisfactorily accurate for clinical applications, and that optimizing the variables that affected image quality, such as the exposure parameters, was critical for image acquisition.

Keyword

Imaging, Three-Dimensional; Dimensional Measurement Accuracy; Anthropometry; Cone-beam computed tomography

MeSH Terms

Anthropometry
Cone-Beam Computed Tomography*
Dimensional Measurement Accuracy
Imaging, Three-Dimensional

Figure

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  Fig. 1 Thirteen soft-tissue anatomic landmarks labeled on the anthropomorphic phantom, as described by Farkas.13

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  Fig. 2 Three-dimensional facial scan images were obtained using the 3D Neo optical scanning system. Three images were taken at 3 different horizontal angles (frontal, rotated 45° to the left, and rotated 45° to the right), merged, and automatically converted into a single 3-dimensional facial image.

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  Fig. 3 The image-based measurements were performed using multiple 3-dimensional (3D) analysis software programs. A. The linear measurements of the cone-beam computed tomography surface volume-rendered images were made using the 3D ruler tool in the OnDemand™ software program. B. For 3D facial scan images, the line length tool in the Morpheus Dental Solution® program was used to obtain measurements.

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  Fig. 4 Comparison of the means of different linear measurements on the phantom and on 3-dimensional images generated by cone-beam computed tomography (CBCT) and facial scanning.

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  Fig. 5 A visual comparison of cone-beam computed tomography surface volume-rendered images obtained with a constant threshold value of — 600 Hounsfield units at different tube voltages. A. 70 kVp. B. 75 kVp. C. 80 kVp. D. 85 kVp. The noise level decreased with increased tube voltage in D, in contrast to A.

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  Fig. 6 A visual comparison of cone-beam computed tomography surface volume-rendered images obtained with a constant threshold value of — 600 Hounsfield units at different tube currents. A. 3 mA. B. 6 mA. C. 10 mA. The noise level decreased with increased tube current in C, in contrast to A.

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