The effect of fasting on PET Imaging of Hepatocellular Carcinoma.

The clinical utility of positron emission tomography (PET) imaging for liver cancer applications is not clearly defined either for diagnosis or treatment assessment. Previous clinical studies demonstrated that fluorodeoxyglucose (FDG) did not show uptake in some hepatocellular carcinoma (HCC) while acetate showed uptake. Pre-imaging fasting is required for clinical PET imaging with FDG. No studies were done to confirm the effect of fasting on acetate uptake in HCC for PET imaging. We investigated this situation with a woodchuck model of viral infection-induced HCC. METHODS Four tumor-bearing and one control woodchucks were involved in this study. They were first imaged by PET in fed state followed by another imaging session one week later when they were fasted over-night. Some animals also had FDG-PET scan that was acquired later on the same day. After imaging studies, animals were sacrificed, and their liver excised for histology. Standardized Uptake Value (SUV) was calculated using a region of interest (ROI) placed on each tumor with focal uptake. RESULTS Acetate showed uptake in each HCC lesion when the animals were either fasted or fed with no significant difference in SUV values (p=0.177); some of the tumors were histologically confirmed as well-differentiated HCC while others were confirmed as moderately- or poorly-differentiated HCC; no focal uptake was found in the control animal. For the accompanying FDG scans, the uptake was detected only in animals that were fasted although the uptake pattern was different from that with acetate. CONCLUSION This study provided a hint that fasting or not has little impact on PET imaging of HCC with acetate. It also confirmed prior finding regarding tumor heterogeneity that led to different tracer uptake pattern in the same tumor. Human studies are needed to validate the findings from this pre-clinical investigation.