Multimodal imaging correlation in adult soft tissue sarcomas: a head-to-head comparison of LAFOV FDG PET-CT with diffusion-weighted and dynamic contrast-enhanced MRI

Purpose This explorative head-to-head comparison investigated correlations between imaging biomarkers of malignancy in soft tissue sarcomas (STS) using Long-Axial-Field-of-View (LAFOV) FDG PET-CT versus diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MRI (DCE-MRI). Methods A retrospective FDG PET-CT database search (December 2021–November 2025) identified 22 STS patients with comparable MRI acquired within three months. Seven patients were excluded for absent MRI or non-specific FDG uptake, leaving 15 patients with 53 FDG-avid lesions. VOI-based SUV, ADC values, and contrast enhanced signal intensity were measured and analyzed via a Spearman rank correlation. Results Moderate inverse correlation existed between SUVmax and mean/minimal ADC values (ρ = -0.35 to -0.47, p < 0.05). Strong correlations were found between FDG uptake and arterial phase signal intensity (ρ = 0.57), with moderate correlations in venous phase (ρ = 0.45), but negligible correlation in equilibrium phase. Diffusion-restricted tumors demonstrated strong negative correlations between ADC and arterial enhancement (ρ = -0.5 to -0.81) with moderate correlations in the venous phase (ρ = -0.33 to -0.53) and no relevant correlation to the equilibrium phase. Conclusions This head-to-head comparison indicates that FDG PET-CT, DWI, and DCE-MRI parameters behave synergistically in STS characterization. Diffusion-restricted, FDG-avid tumors demonstrated a characteristic pattern: strongest arterial phase enhancement, decreasing correlation in venous phase, and negligible correlation in equilibrium phase. Complementary multimodal assessment combining these parameters may enhance diagnostic accuracy and guide treatment planning in STS. In particular, due to heterogeneity of STS, larger prospective studies are needed to confirm these observations.