Does the shape of the field-of-view influence the magnitude of artefacts from high-density materials in cone-beam computed tomography?

Objective: To compare cylindrical and convex triangular field-of-views (FOVs) concerning the magnitude of artefacts from high-density materials in cone-beam CT (CBCT).

Methods and materials: Cylinders of amalgam, chromium-cobalt, titanium, and zirconia were individually placed in the anterior and posterior regions of a polymethylmethacrylate phantom and scanned using cylindrical and convex triangular FOVs of the Veraview X800 CBCT device. Using the Image J software, 15 square regions of interest (ROIs) were placed in the axial reconstruction around the middle level of the cylinder and at distances of 0.5, 1.0, and 1.5 cm from the centre of the cylinder. Mean grey value and standard deviation of each ROI were averaged for each distance and subtracted from the values of a control ROI to calculate the magnitude of the artefacts by the grey value mean difference (GVMD) and grey value standard deviation (GVSD). Multiway analysis of variance with Tukey post-hoc test with a significance level of 5% evaluated the effect of the shape of the FOV, position inside the FOV, high-density material, and the distance of the artefact from the material.

Results: The convex triangular FOV increased the GVSD for all materials in the anterior and posterior regions at 0.5 cm compared to the cylindrical FOV (p < 0.0001). The convex triangular FOV showed greater GVMD for chromium-cobalt and zirconium in the anterior region and all materials in the posterior region at all distances (p < 0.0001).

Conclusion: The FOV shape influences the magnitude of artefacts from high-density materials. The convex triangular FOV showed greater artefact magnitude with variability among the high-density materials, region in the FOV, and distance from the material.