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. 2025 Feb 1;54(2):140-148.
doi: 10.1093/dmfr/twae053.

Gray values and noise behavior of cone-beam computed tomography machines-an in vitro study

Nicolly Oliveira-Santos  1   2 , Hugo Gaêta-Araujo  3 , Rubens Spin-Neto  4 , Dorothea Dagassan-Berndt  5 , Michael M Bornstein  6 , Matheus L Oliveira  7 , Francisco Haiter-Neto  7 , Deborah Q Freitas  7 , Ralf Schulze  1   2
Affiliations

Gray values and noise behavior of cone-beam computed tomography machines-an in vitro study

Nicolly Oliveira-Santos et al. Dentomaxillofac Radiol. .

Abstract

Objectives: To systematically evaluate the mean gray values (MGVs) and noise provided by bone and soft tissue equivalent materials and air imaged with varied acquisition parameters in 9 cone-beam computed tomography (CBCT) machines.

Methods: The DIN6868-161 phantom, composed of bone and soft tissue equivalent material and air gap, was scanned in 9 CBCT machines. Tube current (mA) and tube voltage (kV), field of view (FOV) size, and rotation angle were varied over the possible range. The effect of the acquisition parameters on the MGV and contrast-to-noise indicator (CNI) was analyzed by Kruskal Wallis and Dunn-Bonferroni tests for each machine independently (α = 0.05).

Results: Tube current did not influence MGV in most machines. Viso G7 and Veraview X800 presented a decrease in the MGV for increasing kV. For ProMax 3D Max and X1, the kV did not affect the MGV. For the majority of machines, MGV decreased with increasing FOV height. In general, the rotation angle did not affect the MGV. In addition, CNI was lower with lower radiation and large FOV and did not change from 80 kV in all machines.

Conclusions: The MGV and noise provided by the tested phantom vary largely among machines. The MGV is mainly influenced by the FOV size, especially for bone equivalent radiodensity. For most machines, when the acquisition parameters affect the MGV, the MGV decrease with the increase in the acquisition parameters.

Keywords: CBCT; cone-beam computed tomography; gray values; imaging; phantoms.

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Conflict of interest statement

None declared.

Figures

Figure 1.
Figure 1.
CBCT axial image of the phantom scanned in the Viso G7 machine, with 5 mA, 120 kV, and medium FOV size. Region of interest selected on the soft tissue equivalent (1), bone equivalent (2), and air (3).
Figure 2.
Figure 2.
Boxplot indicating the mean gray value distribution according to the CBCT machine and structure.
Figure 3.
Figure 3.
Boxplot indicating the mean gray value distribution according to the tube current (mA). Different symbols mean statistical difference (p ≤ 0.02).
Figure 4.
Figure 4.
Boxplot indicating the mean gray value distribution according to the tube voltage (kV). Different symbols mean statistical difference (p ≤ 0.02).
Figure 5.
Figure 5.
Boxplot indicating the mean gray value distribution according to the field of view (FOV) size (S = Small, M = Medium, MΔ = Medium convex triangular field of view, L = Large). Different symbols mean statistical difference (p ≤ 0.05).
Figure 6.
Figure 6.
Boxplot indicating the mean gray value distribution according to the rotation angle. Different symbols mean statistical difference (p = 0.00).
Figure 7.
Figure 7.
Boxplot of the CNI of each CBCT machine according to the parameters evaluated. Different symbols mean statistical difference (p < 0.05).
See this image and copyright information in PMC

References

    1. Pauwels R, Jacobs R, Singer SR, Mupparapu M.. CBCT-based bone quality assessment: are Hounsfield units applicable? Dentomaxillofac Radiol. 2015;44(1):20140238. https://academic.oup.com/dmfr/article/7282105 - PMC - PubMed
    1. Reeves T, Mah P, McDavid W.. Deriving Hounsfield units using grey levels in cone beam CT: a clinical application. Dentomaxillofac Radiol. 2012;41(6):500-508. https://academic.oup.com/dmfr/article/41/6/500-508/7265139 - PMC - PubMed
    1. Pauwels R, Stamatakis H, Bosmans H, et al.; SEDENTEXCT Project Consortium. Quantification of metal artifacts on cone beam computed tomography images. Clin Oral Implants Res [Internet]. 2013;24Suppl A100(A100):94-99. https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0501.2011.02382.x - DOI - PubMed
    1. Cascante-Sequeira D, Fontenele RC, Martins LAC, et al.Does the shape of the field-of-view influence the magnitude of artefacts from high-density materials in cone-beam computed tomography? Dentomaxillofac Radiol. 2023;52(7):20230147. https://academic.oup.com/dmfr/article/doi/10.1259/dmfr.20230147/7497212 - DOI - PMC - PubMed
    1. Gaêta-Araujo H, Nascimento EHL, Fontenele RC, Mancini AXM, Freitas DQ, Oliveira-Santos C.. Magnitude of beam-hardening artifacts produced by gutta-percha and metal posts on cone-beam computed tomography with varying tube current. Imaging Sci Dent. 2020;50(1):1-7. https://isdent.org/DOIx.php?id=10.5624/isd.2020.50.1.1 - PMC - PubMed

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