Standardized uptake values for [¹⁸F] FDG in normal organ tissues: Comparison of whole-body PET/CT and PET/MRI

Purpose: To compare maximum and mean standardized uptake values (SUVmax/mean) of normal organ tissues derived from [¹⁸F]-fluoro-desoxyglucose (FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) using MR attenuation correction (MRAC) (DIXON-based 4-segment μ-map) with [¹⁸F]-FDG positron emission tomography/computed tomography (PET/CT) using CT-based attenuation correction (CTAC). Methods and materials: In 25 oncologic patients (15 men, 10 women; age 57 ± 13 years) after routine whole-body FDG-PET/CT (60 min after injection of 290 ± 40 MBq [¹⁸F]-FDG) a whole-body PET/MRI was performed (Magnetom Biograph mMR™, Siemens Healthcare, Erlangen, Germany). Volumes of interest of 1.0 cm³ were drawn in 7 physiological organ sites in MRAC-PET and the corresponding CTAC-PET images manually. Spearman correlation coefficients were calculated to compare MRAC- and CTAC based SUV values; Wilcoxon-Matched-Pairs signed ranks test was performed to test for potential differences. Results: The mean delay between FDG-PET/CT and PET/MRI was 92 ± 18 min. Excellent correlations of SUV values were found for the heart muscle (SUVmax/mean: R = 0.97/0.97); reasonably good correlations were found for the liver (R = 0.65/0.72), bone marrow (R = 0.42/0.41) and the SUVmax of the psoas muscle (R = 0.41). For subcutaneous fat, the correlation coefficient was 0.66 for SUVmean (p < 0.05). Correlations between MRAC and CTAC were non-significant for SUVmean of the psoas muscle, SUVmax of subcutaneous fat, SUVmax and SUVmean of the lungs, SUVmax and SUVmean of the blood-pool. The median SUVmax and SUVmean in MRAC-PET were lower than the respective CTAC values in all organs (p < 0.05) but heart (SUVmax) and the bone marrow (SUVmean). Conclusion: In conclusion, in oncologic patients examined with PET/CT and PET/MRI SUVmax and SUVmean values generally correlate well in normal organ tissues, except the lung, subcutaneous fat and the blood pool. SUVmax and SUVmean derived from PET/MRI can be used reliably in clinical routine