Functional imaging of hepatocellular carcinoma using diffusion-weighted MRI and 18F-FDG PET/CT in patients on waiting-list for liver transplantation

Background: To compare the apparent diffusion coefficient (ADC) on diffusion-weighted imaging (DWI) with the standardized uptake values (SUV) measured by F-18-FDG-PET/CT in naive hepatocellular carcinoma (HCC) nodules, and to determine whether these markers are associated with tumours at high-risk of aggressiveness. Methods: From 2007 to 2010, all patients with HCC on the waiting list for liver transplantation and who underwent both FDG-PET/CT and 1.5-T DWI-MRI (b values: 0, 200, 400, and 800 s/mm(2)) were included in this institutional review board-approved retrospective study. Tumour size, tumour ADC, tumour-to-liver ADC ratio (ADC(T/L)), maximal tumour SUV and tumour-to-liver SUV ratio (SUVT/L) were measured and compared to serum alpha-fetoprotein (AFP) levels, tumour size and differentiation grade on explanted specimens. Results: A total of 37 HCC nodules in 28 patients were available for correlation between MRI and PET/CT, 7 of which (in 7 patients) showed a SUVT/L > 1.15. We did not find any correlation between tumour ADC or ADC(T/L) and tumour SUV or SUVT/L. To note, SUVT/L was positively correlated with AFP levels (R = 0.95, P <= 0.0001), while ADC(T/L) was not (P = 0.73). Twenty-four patients (with 32 nodules) underwent liver transplantation. In this subgroup, an increased SUVT/L ratio was associated with larger tumours (average size, 32 +/- 14 mm; range, 18-60 mm; P < 0.0001) and with poor differentiation on pathology (grades 3 and 4; P = 0.04), while ADC(T/L) was neither associated with tumour size or differentiation grade. Conclusions: ADC and SUV measures in HCC nodules are not correlated. SUVT/L ratio correlates with AFP levels, tumour size and poor differentiation, and should probably be integrated as a co-variable in a predictive outcome model of patients on the waiting-list for liver transplantation.