Abstract
Purpose: To compare diffusion-weighted imaging (DWI) and 18F-FDG PET-CT for detection and volumetric assessment of colorectal cancer liver metastases, evaluating the optimal b-value for volumetric correlation with metabolic tumor volume (MTV).
Materials and Methods: This retrospective study included 50 patients with histopathologically confirmed colorectal adenocarcinoma and liver metastases who underwent both PET-CT and liver MRI (including DWI at b=50, 400, 800 s/mm²) within 30 days. Synthetic DWI images at b=1000, 1500, and 2000 s/mm² were generated. Two radiologists and one nuclear medicine physician independently assessed lesion detection and measured volumes. Interobserver agreement was evaluated using intraclass correlation coefficients (ICC). Volumetric correlation between MTV and DWI-derived volumes was assessed using Bland-Altman analysis and paired t-tests.
Results: PET-CT identified 151 FDG-avid liver lesions while DWI detected significantly more lesions at all b-values: 184 (b=800), 183 (b=1000), 176 (b=1500), and 171 (b=2000) (all p<0.001). DWI demonstrated superior detection of small lesions (<10 mm). Interobserver agreement was excellent for both PET-CT MTV (ICC=0.92, 95% CI: 0.87-0.95) and DWI volumes (ICC=0.88-0.91). DWI at b=1500 s/mm² showed optimal volumetric match with MTV (mean difference=0.17 cc, 95% limits of agreement: -2.8 to 3.1 cc, p=0.999), while b=800-1000 s/mm² overestimated volumes by 8-12% and b=2000 s/mm² underestimated by 3.5%.
Conclusion: DWI detects significantly more colorectal liver metastases than PET-CT, particularly lesions <10 mm. DWI at b=1500 s/mm² provides optimal volumetric correlation with PET-CT MTV, suggesting potential alternative surveillance imaging modality for colorectal cancer liver metastases.
Keywords
Diffusion-weighted imaging, Positron emission tomography, Colorectal neoplasms, Liver metastases, Magnetic resonance imaging