Investigation of tumor assessment between two PET systems using various indices: comparison between PET/CT and PET/MRI systems.

This study aimed to determine the comparability of tumor-uptake indices of F-FDG in positron emission tomography/computed tomography (PET/CT) and positron emission tomography/magnetic resonance imaging (PET/MRI). 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) PET/CT and PET/MRI were performed on 55 patients with confirmed primary malignancies. PET/CT preceded PET/MRI in all examinations. Accumulation of F-FDG in lesions and normal organs (brain, liver) was measured. Maximum and peak standardized uptake values (SUVs; SUV and SUV, respectively), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) with margin thresholds of SUV of 50% (MTV; TLG, respectively) were measured as indices for comparison of measurements in tumors. Comparative indices with tumor SUV and liver ratio (TLR), brain ratio (TBR) were calculated. These indices were compared between PET/CT and PET/MRI examinations. The data measured using PET/CT and PET/MRI showed significant correlations for all tumor indices. The correlation was strongest for SUV (r = 0.933), followed by TBR (r = 0.929); and the index ratio of (PET/CT)/(PET/MRI) data was close to 1.0 for TLR (1.00 ± 0.22) and TBR (1.01 ± 0.21), followed by MTV (0.82 ± 0.33) and TLG (1.18 ± 0.45). The values of all indices showed strong correlations between PET/CT and PET/MRI examinations. Among them, TLR, TBR, MTV, and TLG showed a close value and may be useful for comparison of tumor evaluation between two PET systems.