Positron emission tomography (PET) attenuation correction artefacts in PET/CT and PET/MRI

Objective: To compare the effect of implanted medical materials on F-18-fludeoxyglucose (F-18-FDG) positron emission tomography (PET)/MRI using a Dixon-based segmentation method for MRI-based attenuation correction (MRAC), PET/CT and CT-based attenuation-corrected PET (PETCTAC). Methods: 12 patients (8 males and 4 females; age 58 +/- 11 years) with implanted medical materials prospectively underwent whole-body F-18-FDG PET/CT and PET/MRI. CT, MRI and MRAC maps as well as PETCTAC and PETMRAC images were reviewed for the presence of artefacts. Their morphology and effect on the estimation of the F-18-FDG uptake (no effect, underestimation, overestimation compared with non-corrected images) were compared. In PETMRAC images, a volume of interest was drawn in the area of the artefact and in a reference site (contralateral body part); the mean and maximum standardised uptake values (SUVmean; SUVmax) were measured. Results: Of 27 implanted materials (20 dental fillings, 3 injection ports, 3 hip prostheses and 1 sternal cerclage), 27 (100%) caused artefacts in CT, 19 (70%) in T-1 weighted MRI and 17 (63%) in MRAC maps. 20 (74%) caused a visual overestimation of the F-18-FDG uptake in PETCTAC, 2 (7%) caused an underestimation and 5 (19%) had no effect. In PETMRAC, 19 (70%) caused spherical extinctions and 8 (30%) had no effect. Mean values for SUVmean and SUVmax were significantly decreased in artefact-harbouring sites (p<0.001). Conclusion: Contrary to PET attenuation correction artefacts in PET/CT, which often show an overestimation of the F-18-FDG uptake, MRAC artefacts owing to implanted medical materials in most cases cause an underestimation. Advances in knowledge: Being aware of the morphology of artefacts owing to implanted medical materials avoids interpretation errors when reading PET/MRI.