Metallic materials in the exomass impair cone beam CT voxel values

To assess the influence of artefacts arising from metallic materials in the exomass on cone beam CT (CBCT) voxel values.

CBCT scans were taken of a phantom composed of 16 tubes filled with a homogeneous hyperdense solution and metallic materials of different compositions (titanium, cobalt-chromium and amalgam) and numbers (one, two and three). The phantom was centred in a 5 × 5 cm field of view such that the metallic materials were located in the exomass, using three CBCT units. Voxel values were obtained from the 16 homogeneous areas and averaged. Also, standard deviation was calculated to measure voxel value variability. Analysis of variance in a factorial scheme with additional treatment 3 × 3 + 3 (material × number + control) was performed, followed by Tukey's test for multiple comparisons, and Dunnett's test for comparisons with the control groups, at a level of significance of 5%.

Metallic material in the exomass significantly reduced the mean voxel value in the CS9300 and Picasso Trio units, and increased voxel value variability in all CBCT units. Amalgam was the material that induced significantly greater reduction of the mean voxel value in the CS9300 and Picasso Trio units, and significantly greater increase in the NewTom Giano. Voxel value variability was significantly greater for amalgam in all conditions. The presence of one cylinder induced significantly less pronounced effects on the mean voxel value and voxel value variability.

Artefacts arising from metallic materials in the exomass have a negative influence on CBCT voxel values.