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Abstract:

Aims To evaluate metal artefacts on two CBCT devices: the Accuitomo® 3D (J. Morita Corp., Japan) and the i-CAT® (ISI, USA). Materials & Methods In a first in vitro study, an artificial tooth restored with an amalgam filling was placed in a human mandible. It was scanned using two protocols on the Accuitomo® 3D (4 and 6 mA, exposure time 18 s) and three protocols on the i-CAT® (mA 5.5, exposure time (pulsed scan) 1.75, 3.5 and 7 s). The acquired image datasets were evaluated by five experienced observers using a 4-step protocol. The general image quality and the influence of the artefact on the visibility of the two adjacent teeth was assessed first. Next, predefined window and level settings were evaluated. Also, area measurements were performed on the white streaks in two orthogonal directions in the axial plane, and on the black areas surrounding the amalgam. A final evaluation was performed on volume renderings of i-CAT® datasets, using scans of the mandible without the amalgam as a reference. In a second in vitro study, a human cadaver bone with three titanium implants was scanned using the same protocols. Using the same observers, artefacts were evaluated qualitatively. For the Accuitomo® sets, the implants were evaluated separately, to verify the influence of the position of the artefact in the field of view. Results Accuitomo® sets scored best on general image quality and influence of the amalgam artefact on neighbouring teeth. However, i-CAT® sets allowed for a wider intensity window (resulting in a less defined artefact), while the Accuitomo® showed too much contrast loss compared to smaller windows. Area measurements showed a considerable difference between the two devices, although the different appearance of the streaks compromised a comparison based on quantitative measurements alone. Finally, the amalgam artefact resulted in a lower quality of the volume rendering in the region of the artefact. In the second study on titanium artefacts, i-CAT® sets scored best, although the different nature of the artefacts was even more clear. Surprisingly, black artefacts surrounding the implants on i-CAT® sets (influencing an evaluation of implant osseointegration) did not seem to affect the scores as much as the white streaks surrounding the implants on Accuitomo® sets. Also, the artefacts were not extensive enough to show a difference between a central or peripheral positioning. For nearly all evaluations, no significant difference was found between acquisition protocols within one device. For these studies, an increase in mAs (leading to a higher radiation dose) did not coincide with any benefit in image quality. Conclusions These studies show that the large range of acquisition parameters in dental CBCT devices complicates their evaluation. This is especially clear for the two evaluated devices. Differences in voltage, current and beam type lead to different degrees of beam hardening and scatter when scanning metal objects. The influence of the resulting artefact on diagnostics can be highly observerand case-dependent. This requires a more extensive study, with an additional emphasis on artefact reduction during reconstruction and post-processing.