Relationship between anatomical, functional, and metabolic parameters obtained from pelvic MRI and whole-body 18F-FDG PET/MRI and distant metastatic disease in primary rectal adenocarcinoma

PURPOSE: To evaluate the relationships between anatomical, functional, and metabolic parameters and distant metastasis in the primary staging of rectal adenocarcinoma. METHODS: Seventy-three patients with rectal adenocarcinoma, who underwent pelvic MRI and whole-body 18 F-FDG PET/MRI for staging, were included. Anatomical [T and N stages, extramural venous invasion (EMVI) and circumferential resection margin (CRM) statuses] and functional parameters [apparent diffusion coefficient (ADC) mean (mm²/sn × 10 -6 )] of primary tumor were recorded from pelvic MRI, and metabolic data (maximum standard uptake value (SUV max ), mean SUV (SUV mean ), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and total lesion quotient (TLQ) were recorded from 18 F-FDG PET/MRI. Quantitative parameters combining functional and metabolic data (SUV max /ADC mean , SUV mean /ADC mean , MTV/ADC mean , TLG/ADC mean , TLQ/ADCmean) were calculated. Distant metastases were recorded via 18 F-FDG PET/MRI. To detect lung nodules, supplementary 18 F-FDG PET/CT scans of the thorax were utilized. Relationship between these parameters and distant metastasis, and their ability to predict for distant metastatic disease, were statistically evaluated. RESULTS: In the univariate logistic regression analysis, the SUV max (1.04; 1.0-1.08; P = 0.031), TLG (1.0; 1.0-1.005; P = 0.044), TLG/ADC mean (8.12; 1.04-63.78; P = 0.046), and presence of EMVI (4.13; 1.31-12.98; P = 0.015) (OR; CI; P ) were found to predict distant metastasis. In multivariate regression analysis, SUV max (1.05; 1.0-1.1; P = 0.023) and the presence of EMVI (6.82; 1.64-28.48; P = 0.008) were identified as independent predictors for distant metastatic disease (OR; CI; P ). Significant associations were detected between distant lymph node metastasis and T stage and the presence of EMVI, whereas significant associations were detected between the size of distant lymph node metastases and the SUV max , SUV mean , SUV max /ADC mean , and SUV mean /ADC mean ( P < 0.05). Patients with lung and other organ metastases had significantly greater TLG and TLG/ADC mean values ( P < 0.05). CONCLUSION: 18 F-FDG PET/MRI allows obtaining anatomical, functional, and metabolic parameters related to the primary tumor in a single session and has the potential to predict information regarding tumor behavior, including distant metastatic spread.