Comparison of Semi-Quantitative Parameters of ¹⁸F-FDG Digital PET/CT and Simultaneous PET/MRI in Lymphoma Patients

This study evaluated the comparative performance of standardized uptake value (SUV) measurements derived from positron emission tomography/magnetic resonance imaging (PET/MRI) and digital positron emission tomography/computed tomography (PET/CT) in lymphoma patients. A retrospective analysis was conducted to compare semi-quantitative measures and assess the correlation and concordance between the two imaging modalities.

A total of 106 lymphoma patients underwent both PET/CT and PET/MRI, either in the order of PET/CT followed by PET/MRI (PET/CT_first group, n = 51) or PET/MRI followed by PET/CT (PET/MRI_first group, n = 55). SUV measurements in lesions, liver, and mediastinal blood pool were compared between modalities.

SUV_max and SUV_mean were significantly lower in PET/MRI than PET/CT (P < 0.001), except SUV_mean for mediastinal blood pool in the PET/MRI_first group (P = 0.090). Correlation between modalities was very high for the lesions (ρ = 0.90-0.96). The Deauville five-point scale (D5PS) scores had good agreement between modalities (κ = 0.6566 for PET/CT_first and κ = 0.4846 for PET/MRI_first; P < 0.001), but the response categorization would have been different in 22/262 PET/CT_first group and 21/155 PET/MR_first group.

SUV measurements from PET/MRI demonstrated strong correlation and good agreement in D5PS classification compared to digital PET/CT. Nonetheless, variations in PET subsystem technologies across modalities may influence quantitative values, and such differences should be carefully considered when interpreting results.