Quantitative Assessment of Diffusion-Weighted MR Imaging in Patients with Primary Rectal Cancer: Correlation with FDG-PET/CT

PURPOSE: The aim of the study was to assess correlations between parameters on diffusion-weighted imaging and 2-deoxy-2-[(18)F]fluoro-d-glucose–positron emission tomography/computed tomography (FDG-PET/CT) in rectal cancer. PROCEDURES: Thirty-three consecutive patients with pathologically confirmed rectal adenocarcinoma were included in this study. Apparent diffusion coefficient (ADC) maps were generated to calculate ADC(mean) (average ADC), ADC(min) (lowest ADC), tumor volume, and total diffusivity index (TDI). PET/CT exams were performed within 1 week of magnetic resonance imaging. Standardized uptake values (SUVs) were normalized to the injected FDG dose and body weight. SUV(max) (maximum SUV), SUV(mean) (average SUV), tumor volume, and total lesion glycolysis (TLG) were calculated using a 50% threshold. RESULTS: Significant negative correlations were found between ADC(min) and SUV(max) (r = −0.450, p = 0.009), and between ADC(mean) and SUV(mean) (r = −0.402, p = 0.020). A significant positive correlation was found between TDI and TLG (r = 0.634, p < 0.001). CONCLUSION: The significant negative correlations between ADC and SUV suggest an association between tumor cellularity and metabolic activity in primary rectal adenocarcinoma.