ASSESSMENT OF CBCT IMAGE ARTIFACTS GENERATED BY IMPLANTS LOCATED IN THE EXOMASS

Abstract

Background Currently, use of a small cone beam computed tomography (CBCT) field of view (FOV) has increased for several diagnostic purposes. However, smaller FOVs cause an indirect increase of the exomass, defined as the area outside of the FOV but between the source of x-rays and the image receptor. Metallic objects in the exomass generate artifacts that result in inconsistent image reconstructions. Objective The aim of this study was to evaluate the effect of artifacts arising from implants in the exomass on CBCT images. Study design Using titanium, titanium–zirconium and zirconium implants, 4 × 5 cm and 8 × 5 cm FOV images were acquired with the Planmeca ProMax, with or without metal artifact reduction (MAR), at 80 and 90 kVp. On each axial image, 3 rectangular regions of interest (ROIs) of 3.6 × 12 mm were delineated and standardized for all images as: region 1: closest to the implant; region 2: in the middle; and region 3: furthest from the implant. The standard deviation was determined from the ROI histograms and considered to be the measure of artifact. Effects of FOV size, implant type, MAR, kVp, region, and their interactions were assessed. Results The zirconium implant produced the most artifacts, followed by the titanium–zirconium and titanium implants, especially in region 1. The 8 × 5 cm FOV created more artifact than the 4 × 5 cm FOV when an implant was present. However, FOV size did not influence the amount of artifact when a zirconium implant or no MAR was used; 90 kVp produced fewer artifacts than 80 kVp, and MAR decreased the artifact only in the 8 × 5 cm FOV, 90 kVp, and zirconium and titanium–zirconium implant settings. Conclusion Implants in the exomass generated noticeable artifacts. Consideration should be given to imaging parameters that reduce artifacts, especially in the presence of a zirconium implant. Currently, use of a small cone beam computed tomography (CBCT) field of view (FOV) has increased for several diagnostic purposes. However, smaller FOVs cause an indirect increase of the exomass, defined as the area outside of the FOV but between the source of x-rays and the image receptor. Metallic objects in the exomass generate artifacts that result in inconsistent image reconstructions. The aim of this study was to evaluate the effect of artifacts arising from implants in the exomass on CBCT images. Using titanium, titanium–zirconium and zirconium implants, 4 × 5 cm and 8 × 5 cm FOV images were acquired with the Planmeca ProMax, with or without metal artifact reduction (MAR), at 80 and 90 kVp. On each axial image, 3 rectangular regions of interest (ROIs) of 3.6 × 12 mm were delineated and standardized for all images as: region 1: closest to the implant; region 2: in the middle; and region 3: furthest from the implant. The standard deviation was determined from the ROI histograms and considered to be the measure of artifact. Effects of FOV size, implant type, MAR, kVp, region, and their interactions were assessed. The zirconium implant produced the most artifacts, followed by the titanium–zirconium and titanium implants, especially in region 1. The 8 × 5 cm FOV created more artifact than the 4 × 5 cm FOV when an implant was present. However, FOV size did not influence the amount of artifact when a zirconium implant or no MAR was used; 90 kVp produced fewer artifacts than 80 kVp, and MAR decreased the artifact only in the 8 × 5 cm FOV, 90 kVp, and zirconium and titanium–zirconium implant settings. Implants in the exomass generated noticeable artifacts. Consideration should be given to imaging parameters that reduce artifacts, especially in the presence of a zirconium implant.