Utility of Quantitative and Semi-Quantitative SPECT/CT Metrics in Differentiating Mueller–Weiss Syndrome

<b>Background/Objectives:</b> Mueller-Weiss syndrome (MWS) is a rare condition characterized by spontaneous adult-onset osteonecrosis of the navicular bone. This study aimed to assess the diagnostic value of quantitative and semi-quantitative standardized uptake value (SUV) measurements on Tc-99m MDP SPECT/CT for differentiating MWS from other foot pathologies. <b>Methods:</b> We retrospectively reviewed 21 MWS patients who underwent SPECT/CT and compared them with 10 feet from 5 non-MWS patients as controls. MWS severity was staged using the Maceira classification. Volumes of interest (VOIs) were defined in the lateral navicular and distal tibia. SUV_max values were measured for the navicular bone (N), tibial metaphysis (Tm), and diaphysis (Td). Uptake ratios (N/Tm and N/Td) were calculated for semi-quantitative comparison. <b>Results:</b> MWS patients showed significantly higher SUV_max in the navicular compared with controls (9.2 vs. 1.5, <i>p</i> < 0.001). Both N/Tm and N/Td ratios were also significantly elevated (<i>p</i> < 0.001). SUV_max and uptake ratios positively correlated with Maceira stage and visual navicular uptake intensity. Diagnostic thresholds of N SUV_max > 3.77 (AUC = 0.93), N/Tm > 1.139 (AUC = 0.95), and N/Td > 0.93 (AUC = 0.93) effectively distinguished MWS from non-MWS cases. <b>Conclusions:</b> Quantitative and semi-quantitative SUV analysis on SPECT/CT offers a reliable tool for diagnosing MWS and evaluating disease severity. Semi-quantitative ratios, by normalizing metabolic variability, provide a practical and reproducible alternative to absolute SUV measurements for early detection and treatment planning in MWS.