Reducing metal artifacts between implants in cone-beam CT by adjusting angular position of the subject

Objectives To reduce inter-implant metal artifacts in cone-beam CT (CBCT) imaging by adjusting angular position of the subject relative to the source-detector plane. Materials and methods Two dental implants were placed in a block made of homogeneous dental impression material. Using a custom-made apparatus, the specimen was scanned with a CBCT machine at seven different angles (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees) along three different spatial axes, yielding 21 experimental groups. Thirteen volumes of interest (VOI) including inter- and peri-implant areas were selected from each axial reconstruction perpendicular to the implants. Gray values (GVs) of each pixel within these VOIs were measured. Mean differences in GV (Delta GV) between the VOIs and control area were calculated and expressed as a percentage. These Delta GVs from different spatial angle were compared and analyzed by Welch's analysis of variance (ANOVA) and linear regression using SPSS 25.0 software. Results As alpha angle increased, the Delta GV of the inter-implant area increased from - 62.02% to near-zero while the standard deviation decreased. Welch's ANOVA and linear regression analysis revealed Delta GV increased significantly with alpha angle (p < 0.001,R-2 = 0.406). VOIs on the extension line of two implants showed similar results. After adjusting the beta and gamma angles, there was no significant change in Delta GV. Conclusions Increasing the alpha angle can reduce metal artifacts in the inter-implant area in CBCT images.