Integrated PET/MR for Resting State Functional and Metabolic Imaging in Human Brain: What is Correlated and What is Impacted

Purpose We aimed to, for the first time, investigate the interplay of simultaneous functional MRI (fMRI) and FDG PET using a randomized self-control protocol on an integrated PET/MR. Materials and methods 24 healthy volunteers underwent PET/MR scan 30 to 40 minutes after the injection of FDG. A 22-minute brain scan was separated into MRI-off (without fMRI pulsing) and MRI-on modes (with fMRI pulsing) with each one lasting for 11 minutes. We calculated the voxel-wise fMRI metric (ReHo, ALFF, fALFF and DC), resting networks, relative standardized uptake value ratios (SUVr), Patlak Ki and regional cerebral metabolic rate of glucose (rCMRGlu) maps. Paired two-sample t-tests were applied to assess the statistical differences between SUVr, Ki, correlation coefficients of fMRI metrics and rCMRGlu between MRI-off and MRI-on mode, respectively. Results Voxel-wise whole brain SUVr in MRI-off mode and MRI-on mode revealed no statistical difference, while Ki was significantly elevated in the whole brain (P༜0.05) during fMRI scan. Task-based group ICA revealed that the most active network components derived from combined MRI-off and MRI-on static PET images were frontal pole, superior frontal gyrus, middle temporal gyrus and occipital pole. High correlation coefficients were found among the four-fMRI metrics with rCMRGlu in MRI-off and MRI-on mode (P༜0.05). The highest correlation coefficients between rCMRGlu and all fMRI metrics were found in the visual network (R, 0.523 ± 0.057) and default network (R, 0.461 ± 0.099). Conclusions Static PET quantitation SUVr as an indicator of the accumulative effect of FDG update post-injection does not exhibit immediate change between MRI-on and MRI-off modes. Dynamic PET quantitation Ki is instantly elevated during MRI-on mode due to the additional impact of MRI sequence on imaging subjects. Network connectivity analysis also demonstrated intermediate modulation of brain function in MRI-on mode as compared to MRI-off mode.