Role of Metabolic Nuclear Imaging in Follow-up of Malignant Liver Tumors after Radio- Frequency Ablation Compared to Radiological Imaging

The role of FDG in imaging HCC is impacted negatively by low glucose-transporter-1 and high glucose-6-phosphatase expression within HCC cells causing reduced FDG uptake. it is likely that FDG-PET have an expanded capacity to identify higher grade HCCs than low grade. Also, the detection of HCC is further limited by the physiologically elevated background FDG uptake seen in normal liver parenchyma. Most patients receive chemotherapy either before or after RFA treatment and it has been suggested that chemotherapy within a month before PET imaging can decrease the sensitivity of PET for detecting tumors, through a lowering of the FDG uptake. This could make diagnosing a local site progression more challenging.In addition, the spatial resolution of FDG-PET implies that lesions smaller than approximately 7 mm may produce a false negative result due to partial volume effects. There is now a growing interest in the use of the combined functional and anatomic information provided by FDG PET/CT over morphologic imaging alone for early assessment of the efficacy and effects of locally ablative procedures such as RFA and distinguishing residual or recurrent neoplasm from post-ablation changes. Early post-ablation imaging of the liver with contrast-enhanced MR, CT, and US demonstrates a rim of increased enhancement compared with normal liver tissue in the hyperemic zone surrounding the central non-enhancing area of necrosis. The rim of increased enhancement may mask residual viable tumor in the early post-ablation period.