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Do hardware artefacts influence the performance of head and neck PET scans in patients with oral cavity squamous cell cancer?

¹ Division of Nuclear Medicine, University Hospital Zurich, Switzerland; ² Department of Cranio-Maxillo-Facial Surgery, University Hospital Zurich, Switzerland

*Correspondence to: GW Goerres, Division of Nuclear Medicine, University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland; Email: gerhard.goerres{at}usz.ch

Received 15 October 2003; accepted 8 December 2003

Objective: The purpose of this study was to evaluate the influence of ⁶⁸Ge-based and CT-based attenuation correction as well as two standard image reconstruction algorithms on the appearance of artefacts due to dental hardware. Additionally, the intensity of such artefacts was compared with ¹⁸F-fluorodeoxyglucose (FDG) uptake in patients with known oral cavity squamous cell cancer.

Methods: Thirty-two metallic and non-metallic objects used for dentistry/dental surgery were scanned in a water-bath filled with FDG on a combined PET/CT scanner. Images were reconstructed with either CT-based or ⁶⁸Ge-based transmission data and by using iterative reconstruction or filtered backprojection. The intensity of artefacts was assessed visually using a subjective scale from 0 (no artefact visible) to 4 (very strong artefact), and by quantitative measurements. In a second study, images of 30 patients with known squamous cell cancer and dental hardware were retrospectively analysed by two observers, again using a visual assessment grading system. Wilcoxon signed rank test was used for statistical comparisons.

Results: Eighteen of 32 objects caused artefacts, which were visible with both attenuation correction methods. CT-based attenuation correction was visually more intense than ⁶⁸Ge-based attenuation correction (P<0.0001), and the measured ¹⁸F concentration was also higher (P=0.0002). No difference was found between the reconstruction algorithms. In 28 of 30 patients the primary tumour was visible. FDG uptake in the primary tumour was significantly higher than measured ¹⁸F concentration in artefacts (P<0.0001).

Conclusion: Attenuation correction of PET images generates artefacts adjacent to dental hardware that mimic FDG uptake. In this series, the primary lesion was discriminated from artefacts.

Keywords: PET; CT; attenuation correction; artefact; dental

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