Comparison of the expression of the volumetric alteration artifact in cylindrical and triangular fields of view in two cone-beam computed tomography devices

The effect of voxel and field of view size on the volumetric alteration artifact of high-density materials with 2 cone beam computed tomography devices

OBJECTIVE

We investigated the influence of voxel and field of view (FOV) sizes on expression of the volumetric alteration artifact (VAA) of 5 high-density materials in 2 cone beam computed tomography (CBCT) devices.

STUDY DESIGN

Cylinders of amalgam, cobalt-chromium, gutta-percha, titanium, and zirconium were individually positioned in a polymethyl methacrylate phantom. OP300 Maxio and ProMax 3D Classic CBCT devices were used to acquire images with varying voxel and FOV sizes, totaling 585 scans. Two evaluators segmented the high-density cylinder images to obtain the tomographic volumes. The difference between the tomographic and physical volume of each cylinder (i.e., volumetric alteration) was calculated. Statistical analysis was conducted with multiway ANOVA and the Tukey post hoc test (α = 5%). Evaluator reliability was measured with the intraclass correlation coefficient (ICC).

RESULTS

All studied parameters and nearly all interactions influenced the VAA (P < .05). The post hoc test demonstrated less volumetric alteration for the smallest voxel sizes, 61 × 78 mm FOV, and gutta-percha for OP300, and for the smallest voxel sizes, 80 × 80 mm FOV, and gutta-percha and titanium for ProMax 3D (P < .05). The ICC demonstrated perfect reliability (1.00).

CONCLUSIONS

Voxel and FOV sizes influenced VAA expression. Using smaller voxel sizes, the 61 × 78 mm FOV for OP300 and the 80 × 80 mm FOV for ProMax 3D, and materials with lower density and lower atomic number reduced VAA expression.

High-density objects in exomass affect the volume of high-density objects inside the field of view

OBJECTIVES

To evaluate the effect of the presence and the number of high-density objects in the exomass on the volume of a high-density object in cone-beam CT (CBCT).

METHODS

Cylinders of cobalt-chromium (Co-Cr), titanium (Ti), and zirconium (Zi) were inserted into a polymethylmethacrylate phantom in five different combinations of number and position: 1-no cylinder; 2-one cylinder in a posterior region; 3-one cylinder in an anterior region; 4-two cylinders in posterior regions; and 5-three cylinders in anterior and posterior regions. The phantom underwent CBCT scanning using OP300 and X800 systems, with the afore mentioned cylinders of the same composition placed in the exomass and an additional high-density cylinder placed in the centre of the field of view (FOV), corresponding to the left-anterior region. The tomographic volume of the cylinder inside the FOV was measured using semi-automatic segmentation. The volumetric alteration (VA) between the segmented and physical volumes, in percentage, was compared among the experimental groups using repeated measures ANOVA and Tukey post-hoc (α = 5%).

RESULTS

The factors material, combination, and their interaction affected the volume or both CBCT systems. In OP300, more cylinders in the exomass reduced the VA, mainly for Co-Cr. In X800, more cylinders in the exomass tended to increase the VA inside the FOV, except for Zi.

CONCLUSIONS

In general, the presence of high-density objects in the exomass influences the VA of the object inside the FOV, although this oscillates according to object composition, number and position in the exomass, and CBCT system.

Convex triangular vs. cylindrical field of view: how does the shape of the FOV affect radiation dose?

OBJECTIVE

To compare the dosimetry between convex triangular fields of view (FOV) and similar dimension cylindrical FOVs of two cone-beam computed tomography (CBCT) models.

METHODS

Optically stimulated luminescence dosimeters (OSLDs) were placed in fiducial anatomical locations in an anthropomorphic phantom representing an adult head male for dosimetry scans. Convex triangular FOVs (100 × 80 mm/maxilla-mandible; 100 × 50 mm mandible; 100 × 50 mm/maxilla) from Veraviewepocs 3D R100 (J. Morita, Kyoto, Japan) (R100) and Veraview® X800 (J. Morita, Kyoto, Japan) (X800) and cylindrical FOVs from R100 and X800 (80 × 80 mm/maxilla-mandible; 80 × 50 mm/mandible; 80 × 50 mm/maxilla) were obtained, resulting in 12 different scan protocols. Equivalent doses for each relevant organ/tissue and the effective dose for each protocol were calculated. Mean effective doses were compared by the two-way analysis of variance (ANOVA) with Tukey's post hoc test to evaluate the effect of the FOV and device (α = 0.05).

RESULTS

The effective doses ranged between 69 and 324 μSv for the convex triangular FOVs and 76 and 332 μSv for the cylindrical FOVs. Convex triangular FOVs from the R100 device had effective doses 2.3 to 15.3% lower than their corresponding cylindrical FOVs with similar height (p < 0.05), and that difference ranged between 8.8 and 11.8% for the X800 device (p < 0.05).

CONCLUSION

Convex triangular fields of view delivered slightly lower effective doses than the cylindrical fields of view of similar dimensions in the R100 and X800 CBCT devices.

CLINICAL RELEVANCE

Understanding the influence of the image geometry formation in effective dose allows optimization to reduce patient dose.

Does cone-beam CT convex triangular field of view influence the image shape distortion of high-density materials?

OBJECTIVES

To assess the distortion of high-density materials using two CBCT devices presenting convex triangular and cylindrical fields of view (FOVs).

METHODS AND MATERIALS

Four high-density cylinders were individually placed in a polymethylmethacrylate phantom. 192 CBCT scans were acquired using the convex triangular and cylindrical FOVs of Veraviewepocs® R100 (R100) and Veraview® X800 (X800) devices. Using HorosTM's software, two oral radiologists determined the cylinders' horizontal and vertical dimensional alterations. Nine oral radiologists subjectively identified each cylinder's axial shape distortion. Statistical analysis comprised Multiway ANOVA (α = 5%), and the Kruskal-Wallis test.

RESULTS

The distortion in the axial plane was greater in the convex triangular FOVs for both devices in almost all the materials (p < 0.05). The evaluators subjectively identified a shape distortion in both FOVs for R100 device (p < 0.001), while no distortion was identified for X800 device (p = 0.620). A vertical magnification of all materials was observed in both FOVs for both devices (p < 0.05). No differences among vertical regions (p = 0.988) nor FOVs (p = 0.544) were found for the R100 device, while all materials showed higher magnification in all regions in the cylindrical FOV (p < 0.001) of the X800 device.

CONCLUSIONS

The convex triangular FOV influenced the axial distortion of the high-density materials in both devices. A vertical magnification was observed in both FOVs of both devices, but it was greater in the cylindrical FOV of the X800 device.

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.