(PR144) The Effect of the Relative to the Field of View Position of a Metal Object on Beam Hardening : a Pilot Study

Objectives: To examine whether including a dense object adjacent to a target tooth in the field of view (FOV) or not affects the relative beam hardening generated in CBCT images.

Methods: First lower molar and second premolar “target” sockets (tooth placed in the socket or removed) in a dry human mandible were scanned at 80, 125 and 250micron voxel resolution on a J Morita Veraview X800 CBCT system with a Ti dental implant placed in the adjacent tooth socket and included or not in the FOV. Triplicate 180 and 360 degree- and respective control (no implant in adjacent socket) scans were done. DICOM images were imported into CTAn (Bruker-Skyscan) software for integration of intensity value distribution histograms from 3mm cylindrical regions of interest drawn inside the target empty sockets. Bright and dark streaks in target sockets were also evaluated as “Present”, “Prominent” and “Very Prominent” by a single evaluator.

Results: In an 80micron resolution the average total intensity above background values within the ROIs were 170-245% (360 -180degree- scans) higher with the implant outside than included in the FOV, indicating a much higher beam hardening effect when implant was not included. Respective differences were 30-50% lower in lower resolutions. In a similar way, bright and dark streaks generated with the teeth in place were evaluated as “Very Prominent” vs. “Prominent” in 30% of the cases (intra-operator agreement=0.8).

Conclusions: Avoiding inclusion of a dense object adjacent to the target tooth in the FOV rather accentuates than reduces beam hardening effects.