Potential influence of Gadolinium contrast on image segmentation in MR-based attenuation correction with Dixon sequences in whole-body 18F-FDG PET/MR

To evaluate the influence of Gadolinium contrast agent on image segmentation in magnetic resonance (MR)-based attenuation correction (AC) with four-segment dual-echo time Dixon-sequences in whole-body [18F]-fluorodeoxyglucose positron emission tomography (PET)/MR imaging, and to analyze the consecutive effect on standardized uptake value (SUV). Hybrid imaging with an integrated PET/MR system was performed in 30 oncological patients. AC was based on MR imaging with a Dixon sequence with subsequent automated image segmentation. AC maps (A mu maps) were acquired and reconstructed prior to (A mu map(-gd)) and after (A mu map(+gd)) Gd-contrast agent application. For quantification purposes, the SUV of organs and tumors based on both A mu maps were compared. Tissue classification based on A mu map(-gd) was correct in 29/30 patients; based on A mu map(+gd), the brain was falsely classified as fat in 12/30 patients with significant underestimation of SUV. In all cancerous lesions, tissue segmentation was correct. All concordant A mu maps(-gd/+gd) resulted in no significant difference in SUV. In PET/MR, Gd-contrast agent potentially influences fat/water separation in Dixon-sequences of the head with above-average false tissue segmentation and an associated underestimation of SUV. Thus, MR-based AC should be acquired prior to Gd-contrast agent application. Additionally, integrating the MR-based AC maps into the reading-routine in PET/MR is recommended to avoid interpretation errors in cases where tissue segmentation fails.