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Purpose: The aim of this study was to compare combined gadolinium-ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA)-enhanced and diffusion-weighted (DW) MRI with IV contrast-enhanced 18F-FDG PET/CT to detect and assess the viability of colorectal liver metastases (CLMs) after neoadjuvant chemotherapy (NAC).

Patients and Methods: After NAC, 45 patients with CLMs were prospectively enrolled and underwent combined Gd-EOB-DTPA-enhanced and DW-MRI and contrast-enhanced 18F-FDG PET/CT. Forty patients subsequently underwent surgery based on intraoperative ultrasound, which served as the reference standard for the presence of CLMs. The number of metastases detected by each technique was then compared. In 69 resected metastases, the SUVmean and SUVmax, mean and maximum target-to-background ratio (TBR), total lesion glycolysis, metabolic tumor volume, and mean and minimum apparent diffusion coefficient (ADC) were examined to identify correlations with the corresponding tumor viability (TV) determined from histological specimens.

Results: Intraoperative ultrasound revealed 153 CLMs, 122 of which were resected. The detection rate of MRI and contrast-enhanced 18F-FDG PET/CT were similar (P = 0.61). The SUVmax and minimum ADC were negatively correlated (r = -0.34, P = 0.005) on preoperative imaging after NAC. However, TV was significantly correlated with the maximum TBR (r = 0.33, P = 0.006) and mean TBR (r = 0.37, P = 0.002), but not with the minimum ADC (r = -0.02, P = 0.9) or mean ADC (r = 0.01, P = 0.9).

Conclusions: Combined Gd-EOB-DTPA-enhanced and DW-MRI and contrast-enhanced 18F-FDG PET/CT allow confident detection of CLMs, but only 18F-FDG PET metrics are associated with TV after NAC.

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